FIELD OF THE INVENTION

The invention relates to methods for treating substrates, in particular to methods for repairing or preventing stiction of high aspect ratio structures on semiconductor substrates. The invention also relates to methods and apparatus for carrying out such methods, in particular for delivering hydrogen halides in the context of surface treatments.

BACKGROUND

Substrate processing systems may be used to deposit film on a substrate such as a semiconductor wafer or to etch, clean and/or otherwise treat the surface of the substrate. In some processes, the substrates may be subjected to wet processing. In these processes, the substrate may be mounted on a rotary chuck. As the rotary chuck is rotated, fluid nozzles may be used to dispense fluid such as a liquid or gas, and/or heat may be applied to treat the substrate.

Some of the substrates include high aspect ratio (HAR) structures, such as nanopillars, trenches or vias. The HAR structures have a width (parallel to a surface of the substrate) that is significantly less than a height (perpendicular to a surface of the substrate) of the feature. HAR structures having an aspect ratio greater than 5:1 (trench depth : trench width) are fairly common. More advanced processes include HAR structures having even higher aspect ratios.

Pattern collapse occurs when one or more of the HAR structures collapse, move laterally relative to a surface of the substrate and/or directly contact adjacent HAR structures.

Pattern collapse is often encountered during drying after a wet clean process. In particular, capillary forces created by the surface tension of rinsing liquid drying between HAR structures causes the surfaces of adjacent structures to undergo stiction - that is, adhere together.

Several processes have been used to reduce pattern collapse when drying substrates. For example, the substrate can be dried using supercritical CO2. The supercritical CO2, which has a low surface tension, displaces the rinsing fluid and sublimates upon heating, avoiding the capillary action which can cause stiction. However, supercritical CO2 is relatively expensive and has implementation issues. The surface of the substrate can be modified with a layer to prevent stiction. However, surface modification is often expensive since it requires extra chemistries to be used. Surface modification also leads to material loss since the modified layer needs to be removed. The substrate can also be dried using isopropyl alcohol (I PA) that is delivered to the surface of the substrate at a temperature close to the boiling point of I PA. However, some aspect ratios cannot be dried using boiling I PA without pattern collapse.

In the present applicant’s earlier application WO 2019/083735, the inventors describe a method for treating HAR structures involving the use of gaseous hydrogen fluoride (HF). Specifically, the method involves (a) spin rinsing the surface of the substrate using a first rinsing liquid; (b) spinning off the first rinsing liquid from the surface of the substrate; and (c) directing a gas mixture containing HF onto the surface of the substrate after the first rinsing liquid is dispensed. The HF addresses stiction by helping to break, or prevent formation of, bridging oxide bonds between HAR structures.

However, there remains a need for improved apparatus and methods for treating substrates and, in particular, a need for improved apparatus and methods for preventing or repairing pattern collapse.

SUMMARY OF THE INVENTION

The method described in earlier application WO 2019/083735provides a particularly effective way of preventing and repairing pattern collapse of HAR structures. However, the present inventors have found that the method can lead to inhomogeneities across the surface of a substrate after treatment. Specifically, upon detailed inspection, it was discovered that inhomogeneous treatment can arise due to the formation and coalescence of HF droplets during gas delivery, which subsequently randomly deposit on the substrate surface. The random delivery of the droplets can cause random spots on the surface due to localised etching, which can have a severe impact on quality of the finished product. In extreme cases, the condensation can lead to formation of droplets on the nozzle used for delivery of the HF gas, and subsequent dripping from the nozzle onto the substrate.

Accordingly, the present inventors have developed apparatus and methods to address this issue. In particular, to address this issue, the present invention provides a method of treating a substrate, comprising:

- combining a vapourised solvent with a hydrogen halide to form a gas mixture;

- flowing the gas mixture through a gas mixture supply line; and

- dispensing the gas mixture onto the surface of the substrate;

wherein the gas mixture supply line is heated to limit condensation of the gas mixture during transit. Crucially, the use of heated supply lines limits, or even prevents, the delivery of unwanted liquid droplets (e.g. droplets comprising HF) onto the substrate surface by keeping the hydrogen halide in the gas phase. This is achieved by limiting condensation of the gas mixture and optionally re-vapourising any droplets that are formed.

The temperature to which the gas mixture supply line is heated will depend on the type of gas mixture used - in particular, the type of hydrogen halide, the partial pressure of hydrogen halide used, and the overall pressure. However, generally, the gas mixture supply line is heated to at least about 40°C, alternatively at least about 50°C, preferably at least about 60°C. The upper limit for the temperature is not particularly limited, but may be, for example, about 150°C, about 120°C or about 100°C. The stated temperatures correspond to the temperature of the inner surface of the gas mixture supply line. When the heater and gas mixture are in close proximity, the temperature of the heater may be the same as that of the inner surface of the gas mixture supply line.

Suitably, the substrate is a semiconductor substrate, for example, a silicon substrate such as a wafer (that is, a slice or sheet of (generally thin) material). For example, the substrate may be an integrated circuit. The substrate may be flat.

Suitably, the substrate is a patterned substrate. In other words, the substrate includes surface structures. The surface structures may comprise or consist of pillars. Additionally, or alternatively, the surface structures may comprise or consist of trenches. Additionally, or alternatively, the surface structures may comprise or consist of vias. Preferably, the method is applied to semiconductor substrates having high aspect ratio (HAR) structures, for example, substrates having one or more structures (optionally, all structures) having an aspect ratio of at least about 5:1 , at least about 8:1 , or at least about 10:1 (trench depth : trench width). In the present specification, the“aspect ratio” refers to the ratio of height to width. Advantageously, the method of the present invention is particularly effective at repairing and/or preventing stiction of surface structures, in particular, HAR structures.

The width of the one or more surface structures may be, for example, 100 nm or less, 80 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, or 20 nm or less. The pitch between features may be, for example, 200 nm or less, 150 nm or less, 100 nm or less, 80 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, or 30 nm or less. The height may be, for example, 100 nm or more, 200 nm or more, 300 nm or more, 400 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, or 1000 nm or more. For substrates incorporating an array of (optionally identical) surface structures, the pitch between structures (that is, the centre-to-centre distance between the structures) may be 500 nm or less, 400 nm or less, 300 nm or less 200 nm or less, 100 nm or less, 50 nm or less, 40 nm or less, or 30 nm or less. The structures’ pitch expressed as percentage of the structures’ height may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less. The structures’ pitch expressed as percentage of the structures’ width may be, for example, less than 500%, less than 400%, less than 300%, or less than 200%, or less 150%.

The hydrogen halide used is preferably hydrogen fluoride (HF) or hydrogen chloride (HCI), most preferably HF. HF is particularly effective at preventing or repairing pattern collapse due to its high reactivity. However, it is also the most prone to forming droplets due to its relatively high boiling point (19.5°C for pure HF at atmospheric pressure) arising due to interaction between the highly electronegative HF molecules, and due to its propensity to form higher boiling range mixtures with other hydrogen bond forming compounds (e.g. water, alcohols). Such mixtures with hydrogen bond forming compounds, which occur for all hydrogen halides to some extent, can have significantly higher boiling points than the pure hydrogen halide. Thus, the present inventors have found particularly good results using HF when the gas mixture supply line is heated to at least 40°C, particular for an HF/alcohol mixture such as HF mixed with isopropyl alcohol (I PA).

The relative and absolute amount of hydrogen halide and vapourised solvent will depend on the particular application for which the gas mixture is being used.

Suitably, the gas mixture includes the hydrogen halide (preferably HF) in an amount of at least 0.1% by volume, at least 0.5% by volume or at least 1% by volume. The upper limit for the amount of hydrogen halide in the gas mixture may be, for example, 10% by volume, or 5% by volume. For example, the amount of hydrogen halide may be in a range of from 0.5% to 5% by volume.

The vapourised solvent may be water or, preferably, an alcohol. For example, the alcohol may be methanol or I PA, preferably I PA. Advantageously, I PA is available in high purity grades, and does not undergo significant condensation at the temperatures set out above. Advantageously, when used in the context of a method for surface drying, the I PA displaces rinsing liquid from the surface and subsequently evaporates to give a moisture-free surface.

The solvent may be vapourised by a heated liquid ampoule, bubbler, or other vapouriser. Suitably, the gas mixture includes the vapourised solvent in an amount of at least 0.1 % by volume, at least 0.5% by volume or at least 1% by volume. The upper limit for the amount of vapourised solvent in the gas mixture may be, for example, 10% by volume, 5% by volume, or 2.5% by volume. For example, the amount of vapourised solvent may be in a range of from 0.5% to 2.5% by volume.

Preferably, the gas mixture includes a carrier gas. The carrier gas is preferably an inert gas, preferably nitrogen (N2) for reasons of cost, availability and lack of reactivity.

The combined amount of hydrogen halide, vapourised solvent and carrier gas may account for at least 95% by volume, at least 98% by volume, at least 99% by volume, at least 99.5% by volume of the total gas mixture. Optionally, the gas mixture consists of hydrogen halide, vapourised solvent and carrier gas.

Preferably, the gas mixture includes 0.5 to 5% by volume hydrogen halide (preferably HF), 0.5 to 2.5% by volume vapourised solvent (preferably I PA), with the remainder being carrier gas (preferably nitrogen). Advantageously, this mixture is able to repair or prevent pattern collapse without leading to excessive etching of the substrate’s surface.

Generally, the gas mixture is essentially free of oxidizing agents. For example, the gas mixture may have no more than 0.5% by volume, or no more than 0.1% by volume of oxidizing agents. For example, the total amount of oxygen, ozone, hydrogen peroxide, nitric acid, and sulfuric acid in the gas mixture may be no more than 0.5% by volume, or no more than 0.1 % by volume, or the gas mixture may be free of such compounds.

Preferably, the method is carried out using a gas delivery system having:

a hydrogen halide (HH) supply line;

a vapourised solvent (VS) supply line; and

a carrier gas (CG) supply line

wherein the supply lines are combined to form an HH/VS/CG mixture supply line, and wherein the HH/VS/CG mixture supply line is heated to limit condensation of the gas mixture during transit.

The method may comprise, for example;

(i) vapourising solvent and combining with carrier gas to form a VS/CG mixture supply line (for example, by combining the VS and CG supply lines); (ii) combining the VS/CG mixture supply line with the HH supply line to form an HH/VS/CG mixture supply line;

(iii) optionally, diluting the HH/VS/CG mixture supply line with further carrier gas, preferably pre-heated carrier gas (for example, heated to the same temperature as the HH/VS/CG mixture); and

(iv) dispensing the HH/VS/CG mixture from the HH/VS/CG mixture supply line.

Preferably, any or all of the HH supply line, VS supply line, CG supply line are also heated. Preferably, the CG supply line is heated. Preferably, the VS/CG mixture supply line is heated. In particularly preferred methods, both the HH supply line and VS/CG mixture supply line are heated. Heating the individual supply lines further helps to limit

condensation. In particular, heating the individual components of the gas mixture before they are combined helps to prevent condensation at the point at which the components are mixed.

Although optional, step (iii) can be useful to obtain accurate dilution of the HH and VS to a desired partial pressure when used in conjunction with earlier dilution step (i).

The optional and preferred temperatures discussed above in relation to heating of the gas mixture of vapourised solvent and hydrogen halide also apply in respect of the other supply lines mentioned above. Specifically, any or all of the heated supply lines may be heated to at least about 40°C, alternatively at least about 50°C, preferably at least about 60°C. The upper limit for the temperature is not particularly limited, but may be, for example, about 150°C, about 120°C or about 100°C.

The method of the present invention may be used to repair structure collapse of a patterned semiconductor substrate, for example a method for repairing structure collapse of a patterned semiconductor substrate having HAR structures (as defined above).

Optionally, the gas mixture is used as part of a method for drying a patterned semiconductor substrate, for example a method for drying a patterned semiconductor substrate having HAR structures (as defined above). Advantageously, the vapourised solvent is used to dry the substrate, whilst the hydrogen halide helps to prevent structure collapse (in particular, the adhesion of adjacent surface structures). Preferably, such a method involves:

a) rinsing (preferably, spin rinsing) the surface of the substrate using a rinsing liquid (for example, water or an alcohol such as I PA); b) optionally, removing at least a portion of the rinsing liquid from the surface of the substrate (for example, by spinning off the liquid); and then

c) treating the surface of the substrate with a gas mixture of vapourised solvent and hydrogen halide as set out above, using a heated gas mixture supply line.

In such repair and drying methods, the conditions may be adjusted so that the hydrogen halide (preferably HF) is sufficient to help“unstick” or prevent sticking of, adjacent structures on the substrate surface, without causing excessive etching. Accordingly, conditions may be chosen to limit the etch rate. For example, preferably the gas mixture supply line supplying vapourised solvent and hydrogen halide is heated to a temperature in the range of 40°C to less than 100°C, to prevent excessively high temperatures which might otherwise cause unwanted levels of etching (since the reactivity of the hydrogen halide increases with increasing temperature). Similarly, the partial pressure of the hydrogen halide may be chosen so as to limit excessive etching.

Optionally, the time between step (c) and its preceding step (step (a) or step (b)) is no more than 60 seconds, for example, no more than 40 seconds, no more than 30 seconds, no more than 20 seconds, or no more than 10 seconds. Advantageously, having a short time before delivery of the gas mixture helps to achieve efficient drying whilst minimising the number of collapsed structures.

Optionally, step (c) at least partially overlaps with step (a) and/or step (b). In other words, the gas mixture is delivered at the same time as delivery of the rinsing liquid and/or the provisional drying step (b). Again, it has been found that this approach achieves efficient drying whilst helping to minimise the number of collapsed structures.

The rinsing step (a) above may be preceded by a chemical treatment step, such as an etching step. For example, the method may involve

delivering an etching liquid to the surface of the substrate;

rinsing the substrate surface with water (for example, deionised water);

rinsing the substrate surface with I PA to displace water;

optionally, removing at least a portion of the I PA from the substrate surface; and treating the surface of the substrate with a gas mixture of vapourised solvent and hydrogen halide as set out above, using a heated gas mixture supply line.

In the methods of the invention, the gas mixture may be dispensed from a dispensing outlet, for example, a nozzle or showerhead. Suitably, the outlet is positioned in close proximity to the substrate during dispensing of the gas mixture onto the substrate surface. This allows the gas mixture to efficiently impinge onto the substrate’s surface. The distance between the outlet and the substrate surface during dispensing of the gas mixture may be, for example, 2 to 20 mm, 2 to 15 mm, 2 to 10 mm or 2 to 5 mm. Preferably, the dispensing outlet is moved (e.g. scanned) across the surface of the substrate during delivery of the gas mixture of vapourised solvent and hydrogen halide. For example, the dispensing outlet may be provided on a movable arm, such as a rotatable arm which scans across the substrate surface. This helps to ensure an even level of treatment across the surface of the substrate.

Heating of the supply lines may be carried out using any suitable means. For example, the heating may be carried out using one or more heaters extending along the gas supply line. The heater(s) may be, for example, electric heaters (trace heaters, e.g. resistive heaters) such as heater bars, heater cables, heater bands, heater mats, heater coils or heater tape, which are placed on, or in close proximity, to the gas delivery tubes through which the gas is delivered. The temperature of the heaters is set so as to heat the gas transiting the gas supply line(s) to the desired temperature.

The heaters may extend along the majority of the length of the specified gas supply lines (for example the supply lines designated HH, VS, CG, VS/CG, HH/VS/CG designated above).

For example, the heater may extend along at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or along all of the specified gas supply line. For the

HH/VS/CG mixture supply line, the length calculation above generally does not include the dispensing outlet (e.g. nozzle) from which the gas is emitted (which dispensing outlet generally constitutes a separate part). Advantageously, heating the majority of the length of the supply line helps to achieve efficient and consistent heating of the relevant gases.

Optionally, the substrate itself may be heated whilst the gas mixture is dispensed. For example, the substrate may be heated to a temperature in the range of from 20°C to 400°C, such as between 50°C to 150°C.

The various gases are delivered via gas delivery tubes. Preferably, the gases (in particular HF and the HF-containing gas mixtures) are supplied using plastic tubing, for example a fluorine-based tubing such as perfluoroalkoxy polymer (PFA) tubing. Commonly, HF is delivered using stainless steel components. However, the combination of HF with some solvents (including I PA) is corrosive to stainless steel, which limits the lifetime of the equipment and can lead to deposition of unwanted metal contaminants on the substrate. Therefore, in the present invention it is preferred that the gas mixture of hydrogen halide and vapourised solvent is supplied using plastic tubing. A downside of using plastic tubing, however, is that the tubing is generally not completely gas tight for HF. Thus, although the plastic tubing itself is not damaged by HF, the environment around the tube can be degraded by leaking HF. In particular, in the present invention, leaking HF can potentially damage the heater(s) used to heat the gas mixture supply line.

In view of this issue, the present inventors have developed a system which limits the impact of leaking HF. In particular, the present inventors have found that delivering the gas mixture of HF and vapourised solvent through a gas delivery tube (preferably made of PFA), and flowing a purge gas (preferably an inert gas, most preferably nitrogen) over the outer surface of the tube to purge any HF leaking through the walls of the tube, limits or avoids difficulties associated with leaking HF. This method can be implemented by positioning the gas delivery tube (e.g. a PFA tube) within a conduit (a pipe), flowing the gas through the tube, and flowing the purge gas through the conduit over the outer surface of the tube. The present inventors refer to this method as“double-containment”. The conduit is generally a further tube having a bigger diameter than the gas mixture delivery tube.

This double-containment approach in itself represents a useful addition to the art, and therefore a further aspect of the invention provides a method for transporting hydrogen halide (e.g. HF), comprising flowing hydrogen halide through a gas delivery tube (preferably made from plastic, for example PFA), and flowing a further gas over the outer surface of the gas delivery tube to purge any hydrogen halide leaking through the walls of the gas delivery tube. As above, this is preferably achieved by positioning the gas delivery tube within a conduit, establishing a flow of hydrogen halide through the gas delivery tube, and flowing a further gas (preferably an inert gas, most preferably nitrogen) through the conduit over the outer surface of the gas delivery tube.

The purge gas may be heated. For example, the purge gas may be heated by the same heater used to heat the gas mixture of vapourised solvent and hydrogen halide. In such embodiments, the purge gas itself may be used to heat additional parts of the gas delivery system. Preferably, the heated purge gas is used to heat the dispensing outlet from which said gas mixture is delivered, as described in greater detail below.

In a further aspect, the present invention provides a system suitable for carrying out the methods set out above. At its most general, the invention provides a gas delivery system, comprising a supply line connected to a source of a gas mixture comprising hydrogen halide and vapourised solvent, and heating means for heating said supply line in use. In particular, the present invention provides a gas delivery system, comprising:

a hydrogen halide (HH) supply line connected to a source of HH;

a vapourised solvent (VS) supply line connected to a source of solvent; and a carrier gas (CG) supply line connected to a source of carrier gas;

wherein:

the VS supply line and CG supply line combine (i.e. are connected) to form a VS/CG mixture supply line;

the VS/CG mixture supply line and HH supply line combine (i.e. are connected) to form an HH/VS/CG mixture supply line;

the HH/VS/CG mixture supply line includes a dispensing outlet for dispensing said HH/VS/CG mixture onto a substrate; and

the system includes a heater to heat the H H/VS/CG mixture supply line in use.

Preferably, the system also includes one or more heaters to heat the HH supply line and/or VS/CG mixture supply line in use.

Preferably, heater(s) extend along the majority of the length of the HH/VS/CG mixture supply line (as discussed above in relation to the method).

Optionally, the dispensing outlet comprises a housing which encases nozzle tubing extending to a nozzle outlet, wherein the nozzle tubing and nozzle outlet are for dispensing the HH/VS/CG mixture onto a substrate.

In such embodiments, the heater for heating the HH/VS/CG mixture supply line may extend into said housing, so as to further limit the possibility of liquid droplet formation.

Preferably, the dispensing outlet includes a gas mixture control valve, to control the flow of the HH/VS/CG mixture to the nozzle outlet. Preferably, the gas mixture control valve is switchable between an open and closed position. It is preferred that the distance between the gas mixture control valve and the nozzle orifice is no more than 20 cm, preferably no more than 15 cm, most preferably no more than 10 cm, as measured along the gas flowpath. Advantageously, ensuring a relatively short distance between the gas mixture control valve and the nozzle orifice minimises the time lag between opening the valve and gas being delivered from the nozzle orifice. In addition, it minimises the volume of gas between the gas mixture control valve and the nozzle orifice, which reduces the potential for

contaminants to build up in that volume when the valve is closed. On the other hand, if the distance between the gas mixture control valve and nozzle orifice is too small then this can disrupt the flow of gas through the nozzle, by creating turbulence. Accordingly, it is preferred that said distance is at least 2 cm, more preferably at least 3 cm, more preferably at least 4 cm, and most preferably at least 5 cm. Preferred ranges for the distance between the gas mixture control valve and nozzle orifice are 2 to 20 cm, more preferably 5 to 10 cm.

Preferably, the dispensing outlet also includes a flush line controlled by a flush line control valve. The flush line provides a means of diverting flow of the HH/VS/CG mixture to an exhaust, instead of delivering it to the substrate. The flush line control valve is preferably switchable between an open and closed position.

The gas mixture control valve and flush line control valve are preferably gas-operated (e.g. air-operated) valves. Advantageously, this avoids the need for external moving parts (that is, moving parts not housed within the valve) or metal parts associated with the valve, which might otherwise generate debris which could contaminate and/or damage equipment and the substrate.

It is particularly preferred that the gas delivery system includes both a gas mixture control valve and a flush line control valve, to control the delivery of the HH/VS/CG mixture to either the substrate or the flush line. In such embodiments, it is preferred that control of the gas mixture control valve and flush line control valve is linked, so that when one is open the other is closed. This ensures that a flowpath is always provided for the HH/VS/CG mixture, so as to avoid pressure build-up in the system. In such a system, it is preferred that the flush line control valve is open and the gas mixture control valve is closed in the system’s resting state. For example, the flush line control valve and gas mixture control valve may be gas- operated (e.g. air-operated valves) with the flush line control valve open in a resting state (a normally-open valve) and the gas mixture control valve closed in a resting state (a normally- closed valve), and flush line control valve closed and the gas mixture control valve open when gas is used to actuate the valves.

In particularly preferred embodiments, the dispensing outlet comprises a housing containing:

nozzle tubing extending to a nozzle outlet;

a gas mixture control valve as described above; and

a flush line controlled by a flush line control valve as described above.

When in use, it is preferred that the HH/VS/CG mixture is continuously supplied to the dispensing outlet, and controlled using the gas mixture control and flush line control valve. Providing a continuous supply of HH/VS/CG mixture helps to minimise variations in the supply which might otherwise have an impact on consistency of treatment.

Preferably, in accordance with the“double-containment” strategy discussed above, the HH/VS/CG mixture supply line is a gas delivery tube held within a conduit, wherein the conduit is connected to a purge gas supply line configured to allow a purge gas to flow through the conduit over the outer surface of the gas delivery tube, to purge any HH escaping through the walls of the tube in use. Advantageously, as stated above, the double containment approach allows the HH/VS/CG mixture to be supplied through plastic tubing, despite the fact such tubing can be porous to HH, because any HH leaking through the tubing can be safely removed by the purge gas. In view of this, said gas delivery tube may be plastic, for example perfluoroalkoxy alkane polymer.

In such embodiments, the system may include an enclosure housing at least a portion (optionally all) of the HH supply line and, optionally, at least a portion of one or more of the VS supply line, CG supply line, VS/CG mixture supply line and H H/VS/CG mixture supply line, and wherein said conduit opens into said enclosure. This enclosure is generally referred to as a“gas blending box”. Advantageously, this approach means that HH escaping from either the HH supply line or the HH/VS/CG mixture supply line is delivered to the enclosure, where it can be safely removed. This limits the number of exhaust ports through which any leaking HH must be removed, providing safety advantages. In addition, configuring the system so that leaking HH flows to a common enclosure (whether that leak originates from the HH supply line or HH/VS/CG mixture supply line) facilitates and simplifies detection of HH leaks. Accordingly, the system may comprise an HH detector for detecting HH in the enclosure. This detector may be positioned within the enclosure itself, or may be configured to detect HH from an exhaust port of the enclosure.

Optionally, one end of the conduit is capped or sealed. In such embodiments, the purge gas supply line may have an outlet proximate to the capped/sealed end of the conduit, such that, in use, purge gas exiting the purge gas supply line impinges on the capped/sealed end and is blown back down the conduit. Advantageously, this approach provides a particularly simple way for implementing the“double-containment” strategy. In particular, the purge gas can be introduced (via the purge gas supply line) and removed via the same end of the conduit. When the system incorporates the enclosure housing (at least in part) the HH supply line, the conduit may have a first end opening into the enclosure, a middle section extending along and around the gas delivery tube, and a second capped or sealed end (for example, an end sealed around the circumference of the gas delivery tube). Advantageously, this arrangement allows leaking hydrogen halide from the conduit to be delivered into and exhausted from the enclosure. In such embodiments, the purge gas supply line may extend from the enclosure through the conduit to said capped or sealed end. This provides a particularly simple and effective way of implementing the“double

containment” approach, allowing both purge gas delivery and purge gas removal via the enclosure. In particular, this approach does not require the conduit to incorporate a separate port to allow the introduction of the purge gas supply line, which can provide greater flexibility in terms of the type of material for the conduit (for example, it can allow the use of relatively thin, flexible material).

Preferably, in“double-containment” embodiments the heater for heating the H H/VS/CG mixture supply line is held within said conduit. This allows close proximity between the H H/VS/CG mixture supply line and the heater, and therefore facilitates efficient heat transfer. Furthermore, the ability to flow gas through the conduit helps to minimise damage to the heater which might otherwise occur due to HH leaking through the gas delivery tube.

Preferably, in“double-containment” embodiments, the dispensing outlet comprises said housing containing nozzle tubing (either a continuation of the gas delivery tube, or a separate piece of tubing) extending to a nozzle outlet (and preferably said gas mixture control valve and said flush line controlled by a flush line valve), wherein said conduit opens into the housing to allow purge gas to enter the housing. In other words, the interior of the housing of the dispensing outlet and the conduit are in fluid communication, allowing the purge gas to enter the housing. Advantageously, this arrangement can be used to heat the nozzle tubing and nozzle outlet, because purge gas heated by the H H/VS/CG mixture supply line heater can enter into the housing and heat the nozzle tubing and nozzle outlet. Heating the dispensing outlet using a heated gas allows each of the components of the dispensing outlet to be heated to the same temperature in a relatively straightforward manner, without the need to provide each of the dispensing outlet components (which can be small in size) with an electrical heating element. Suitably, in such embodiments the housing is sealed, so that purge gas entering the housing via the conduit must also exit via the same conduit. In such instances, the housing effectively“caps” the conduit, so that purge gas must travel back down the conduit.

In these embodiments, the outlet of the purge gas supply line preferably opens into or proximate to (for example, less than 5 cm from, less than 4 cm from, less than 3 cm from, less than 2 cm from, or less than 1 cm from) the housing of the dispensing outlet. In this way, the purge gas is delivered into the housing and can flow back through the conduit without encountering significant counter-flow. In contrast, if the outlet of the purge gas supply line opens a significant distance from the housing, the flow to and from the housing will be more complicated (less laminar) due to interference of gas returning from the housing with gas being delivered from the purge gas supply line. In such embodiments, the purge gas supply line preferably runs alongside the gas delivery tube within the conduit, and the same heater is used to heat both the gas delivery tube and the purge gas supply line in use. This not only simplifies construction of the apparatus, but also allows the purge gas to maintain the housing at, or around, the same temperature as the gas delivery tube as it transits through the conduit.

Preferably, the dispensing outlet is mounted on a movable arm, to allow the dispensing outlet to be moved/scanned across the surface of a substrate in use. For example, the gas delivery system may have a dispensing outlet comprising said housing containing nozzle tubing extending to a nozzle outlet (and preferably said gas mixture control valve and said flush line controlled by a flush line valve), wherein the dispensing outlet and its components mentioned above are mounted to a movable arm. In this way, the nozzle outlet can be scanned across the surface of the substrate without affecting relative arrangement of the nozzle outlet compared to other parts of the dispensing outlet.

Optionally, the HH/VS/CG mixture supply line and heater for heating the HH/VS/CG mixture supply line are surrounded by a heat-insulating material. This helps to ensure efficient heating of the gas mixture supply line.

In a particularly preferred embodiment, the gas delivery system, comprises:

a hydrogen halide (HH) supply line connected to a source of HH;

a vapourised solvent (VS) supply line connected to a source of solvent; and a carrier gas (CG) supply line connected to a source of carrier gas;

wherein:

the VS supply line and CG supply line combine to form a VS/CG mixture supply line;

the VS/CG mixture supply line and HH supply line combine to form an HH/VS/CG mixture supply line;

the HH/VS/CG mixture supply line includes a dispensing outlet for dispensing said HH/VS/CG mixture onto a substrate, the dispensing outlet comprising a housing containing: nozzle tubing extending to a nozzle outlet (and preferably a gas mixture control valve; and a flush line controlled by a flush line control valve); at least a portion (optionally all) of the HH supply line (and, optionally, at least a portion of one or more of the VS supply line, CG supply line, VS/CG mixture supply line and HH/VS/CG mixture supply line) is housed within an enclosure; the HH/VS/CG mixture supply line is a gas delivery tube held within a conduit, wherein the conduit is connected to a purge gas supply line configured to allow a purge gas to flow through the conduit over the outer surface of the gas delivery tube, to purge any HH escaping through the walls of the gas delivery tube in use, wherein said conduit opens into said enclosure and said housing of the dispensing outlet; and

the system includes a heater to heat the H H/VS/CG mixture supply line in use (preferably, wherein said heater for heating the HH/VS/CG mixture supply line is held within said conduit).

In view of the advantages of the“double-containment strategy” above, another aspect of the present invention provides a heatable gas dispenser comprising a gas delivery tube extending to a dispensing outlet, the dispensing outlet comprising a housing containing: nozzle tubing extending to a nozzle outlet (and preferably a gas mixture control valve; and a flush line controlled by a flush line control valve as described above), wherein the gas delivery tube is held within a conduit which opens into said housing, and wherein the conduit further contains: a heater for heating the gas delivery tube and a purge gas supply line configured to allow a purge gas to flow through the conduit over the outer surface of the gas delivery tube. As explained above, this dispenser allows heating of a gas transiting through the gas delivery tube and the dispensing outlet itself.

In a further aspect, the present invention provides treatment apparatus for treating a substrate according to the method of the present invention. The apparatus preferably comprises:

- a treatment chamber;

- a substrate holder in the treatment chamber;

- means for rotating the substrate holder; and

- a gas delivery system comprising a dispensing outlet, as described above.

Optionally, the treatment apparatus may further comprise a liquid delivery system, suitable for dispensing a liquid onto a substrate held on said substrate holder. Such apparatus allows liquid treatment steps, such as etching and rinsing, to be carried out on a substrate before and/or after (optionally before) the gas delivery system is used to dry or otherwise treat the substrate. When the treatment apparatus comprises a liquid delivery system, the apparatus preferably has a liquid disposal system, such as that described in the applicant’s patent EP 1 609 172.

Preferably, when in use, the dispensing outlet of the gas delivery system is positioned so that the orifice through which the HH/VS/CG mixture is supplied is 2 to 20 mm from the substrate’s surface, for example 2 to 15 mm, 2 to 10 mm or 2 to 5 mm.

The orifice of the dispensing outlet may be, for example, 4 to 22 mm from the upper surface of the substrate holder, such as 4 to 17 mm, 4 to 12 mm or 4 to 7 mm. The upper surface of the substrate holder is defined as the uppermost part of the substrate holder underneath the area provided for the substrate.

The substrate holder may be a rotatable platform with suitable substrate gripping means.

The substrate may be held by the rotatable platform by, for example, a vacuum chuck (or grip), edge gripping chuck or Bernoulli chuck (or grip). The treatment chamber of the treatment apparatus of the invention may comprise an annular liquid collector surrounding the rotating platform and substrate, to collect liquid flowing from the surface of the substrate.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figures 1A-1C show a cross-sectional view of a substrate having HAR features, showing the development of stiction between the HAR features after a rinsing step, and the subsequent repair of that stiction using a method of the present invention;

Figures 2A and 2B shows treatment apparatus according to the present invention, for carrying out a rinsing process, and subsequently dispensing a gas mixture according to the method of the present invention;

Figure 3 shows the various gas delivery lines used in Figures 2A and 2B, including a heater for heating the HH/VS/CG mixture supply line;

Figure 4 is the same as Figure 3, but incorporates additional heaters for heating the VS/CG mixture supply line and HH supply line;

Figure 5 is the same as Figure 4, but with the HH/VS/CG mixture supplied through tubing which is itself held within a conduit, as per the“double-containment” approach described above;

Figure 6 is a lengthways cross-sectional view through the HH/VS/CG mixture supply line of Figure 5, showing the double-containment approach in greater detail; Figure 7 is a cross-sectional view across the HH/VS/CG mixture supply line shown in Figure 5, again showing the double-containment approach in greater detail;

Figure 8 shows an alternative embodiment of the“double-containment” approach.

DETAILED DESCRIPTION OF THE INVENTION

In Figure 1A, a substrate 1 is shown prior to wet processing and drying. Substrate 1 includes high aspect ratio (HAR) pillars 2a, 2b, 2c and 2d formed on an underlying layer 3. The features have an aspect ratio of ~ 5:1 (height to width). Figure 1 B shows the substrate 1 after wet processing and drying. The capillary action of liquid between pillars 2b and 2c during the drying process has led to structure collapse, with the pillars being forced into contact with one another. Once in contact, the pillars have stuck together, in this case through a combination of van der Waals force, and a bridging oxide bond between the structures. The type of bridging oxide bonds will depend on the type of material from which the pillars are formed, but may include for example silicon oxide (SiO _x ), silicon oxynitride (SiOxN _y ) and titanium oxide (TiO _x ). In Figure 1C, the structure has been treated with a gas mixture of HF, I PA and nitrogen according to the method of present invention, to break the bonding interaction between pillars 2b and 2c.

Figures 2A and 2B shows an example of apparatus 10 used to carry out the method of the present invention. The apparatus includes a chamber 51 housing a rotary chuck 12. A substrate 1 is attached to the surface of the rotary chuck 12 through a suitable mechanism, in this case through the use of gripping pins 13. Suitable examples of gripping pins are shown and described in the applicant’s earlier application US 2018/0047593. The surface 14 of the rotary chuck 12 is transparent, and a heater 15 is arranged under the surface 14.

In this case, the heater 15 includes a plurality of light emitting diodes (LEDs) arranged in one or more radial zones to allow radial heating of the substrate 1. The heater can be operated to provide a moving heat wave that moves from a central location of the substrate outwardly to a radially outer edge thereof as the rotary chuck 12 rotates. Suitable examples of a rotary chuck performing radial heating of a substrate are shown and described in US

2018/0047593.

The rotary chuck 12 is rotated by chuck rotating motor 16 via a drive shaft 17 as shown. In other examples, the motor 16 includes a rotor and stator and the rotor is driven magnetically without physical contact. Suitable examples are shown in the applicant’s earlier patent US 6,485,531. In a first step, a first rinsing liquid is delivered to the rotating substrate 1 by a liquid delivery arm 21 and a nozzle 22. A valve 24 selectively supplies the rinsing liquid from a liquid supply 20 to the arm 21. The arm 21 and nozzle 22 are scanned across the substrate 1 by arm motor 23, to ensure that all regions of the substrate are treated. Liquid spun off of the substrate 1 is collected by first liquid collector 54 circumferentially surrounding the chuck 12, from where it is removed via drain 57. Gas from the interior of the first liquid collector 54 (in particular, mist generated by spun liquid impacting the liquid collector) is removed by exhaust 56. Suitable examples of the liquid collecting apparatus are shown in the applicant’s earlier patent EP 1 609 172 B.

Next, chuck 12 is raised along its rotation axis within housing 51 to a second position by chuck raising motor 18. The rinsing procedure is then carried out with a second liquid, with liquid spun off into second liquid collector 55 and removed by a separate liquid drain and gas exhaust.

After rinsing is complete, the arm motor 23 rotates liquid delivery arm 21 away from the surface of the substrate 1 , into an inactive position, and the arm motor 33 rotates gas delivery arm 31 into position above the substrate. This is shown in greater detail in Figure 2B, in which liquid delivery arm 21 has been rotated into an inactive position, and gas delivery arm 31 has been rotated into a position above the substrate 1.

The substrate 1 is then treated with a gas mixture according to the method of the present invention. The gas delivery system (shown in greater detail in Figures 3-5) delivers a gaseous mixture of HF, I PA and nitrogen from gas supply 30 to nozzle 34 via control valve 32 and heated supply line. In this embodiment, the horizontal position of the nozzle 34 is adjusted by arm motor 33, so as to scan the nozzle across the surface of the rotating substrate 1 , generally from the centre outwards. The action of the motors and the various valves is coordinated by controller 40.

During processing, a fan 52 provides a continuous supply of air to the chamber 51. To avoid pressure build up in the chamber 51 , air inserted through the fan filter unit is exhausted through exhausts 56 and, to a lesser extent, through vent 53.

Figures 3 to 5 show gas delivery systems according to the present invention, which may be used as gas delivery system 30 in Figure 2. In Figure 3, isopropyl alcohol (I PA) and molecular nitrogen are supplied to vapouriser 102, to create a vapourised solvent. The vapourised solvent is then combined with HF, further diluted with molecular nitrogen (preferably, pre-heated), and then passed along gas delivery tubing heated by heater 103. Valves 104 and 105 are used to control the flow of the mixture of HF, I PA and nitrogen to nozzle 106 and an exhaust respectively. The nozzle is oriented downwardly, to supply gas to an underlying substrate (not shown). In this way, the flow of gas mixture can be continuously prepared and supplied and alternately delivered to the substrate or returned to an exhaust, as needed. This continuous flow ensures consistency in the gas supplied, and further helps to minimise the possibility of liquid droplets forming.

The valves 104 and 105 are air operated valves, so as to avoid the need for moving parts in proximity to the nozzles, which might otherwise generate debris which could contaminate and/or damage equipment and the substrate. Separate gas lines are provided to actuate the valves (not shown). The valves are linked so that when valve 104 is open, valve 105 is closed, and vice versa. In a resting state (without any air supplied to the valves), valve 105 is open and valve 104 is closed, so as to minimise the possibility of accidental gas supply from nozzle 106. In other words, the default position is for gas to exit via a flush line.

Valve 105 is positioned in close proximity to the opening of nozzle 104, generally between 2- 20 cm, so as to reduce the lag time between valve 105 opening and gas being delivered from nozzle 106, and to minimise the possibility of contamination by gas occupying the nozzle prior to gas delivery.

The valves 104 and 105 and nozzle 106 are provided as part of the gas delivery arm 31 shown in Figures 2A and 2B. This allows the nozzle 106 to be scanned across the surface of the substrate in use, without affecting the position of the valves relative to each other and to nozzle 106.

The gas delivery system 110 in Figure 4 is identical to that in Figure 3, but includes additional heaters 107 and 108. Heater 107 heats the I PA and nitrogen flow from the vapouriser until the point at which HF is introduced to the mixture. Heater 108 heats the HF until the point at which it is combined with the I PA and nitrogen mixture.

In Figure 5, the system of Figure 4 is further adapted to include a double-containment system 200 for delivering the HF/IPA/nitrogen mixture. In this system, shown in greater detail in Figures 6 and 7, the HA/IPA/nitrogen mixture is supplied through a perfluoroalkoxy alkane polymer (PFA) gas delivery tube 201 , heated by heater 203. The gas delivery tube 201 and heater 203 are enclosed within an outer tube 202 whose open ends are sealed to, and interconnect, a gas blending box 208 and nozzle housing 205. The outer tube 202 also accommodates a purge gas tube 204, which sits alongside the gas delivery tube 201 and heater 203 (as shown in Figure 7), and extends into the nozzle housing 205. The purge gas tube 204 is shown entering through the side of the outer tube 202, but it is equally possible (and, indeed beneficial) for the tube 204 to be introduced via the gas blending box 208. In this instance, the outer tube 202 is corrugated, to maintain flexibility and to facilitate insertion of the various components. The flexibility of the tubes is beneficial when the housing 205 with valves 213 and 214 and nozzle 212 moves with the gas delivery arm 31.

In use, the gas mixture of HF, I PA and nitrogen is flowed down gas delivery tube 201. At the same time, nitrogen purge gas is flowed through tube 204 whilst being heated by heater 203, before being ejected into nozzle housing 205. When ejected into nozzle housing 205, the heated nitrogen purge gas circulates within the housing (as shown in Figure 6) and transfers heat to the nozzle components (for example, the nozzle tubing, valves 213 and 214 and nozzle 212), thereby minimising formation of liquid droplets in the HF/IPA/nitrogen mixture ejected from nozzle 212. The nozzle housing 205 is sealed, which means that nitrogen purge gas must then transit back through outer tube 202 into gas blending box 208 (as indicated by arrow 209 in Figure 5), from where it is removed via exhaust 210. In this way, a flow of nitrogen is established over the outer surface of gas delivery tube 201 back into the gas blending box 208, to carry away any HF leaking through the walls of the gas delivery tube 201 and/or through the nozzle components. In this instance, the system incorporates an HF sensor 206, to detect the level of HF in the gas blending box 208. In this way, the sensor is able to detect leaking of HF through the gas delivery tubing used to supply the gas mixture, and any leakage of the HF supply line.

Although not illustrated in Figures 5-7, it is also possible for heater 203 to extend into nozzle housing 205 in order to provide additional heating.

Figure 8 shows an alternative embodiment of the double containment system 300, in which outer tube 302 has a closed end 303 sealed around gas delivery tube 301. In this embodiment, the nitrogen purge gas does not enter the nozzle apparatus, but is instead directed back down the outer tube 302 by closed end 303.

EXAMPLE

A repair process as set out in WO 2019/083735 was performed on a silicon substrate with nanopillars, corresponding to cylinders having a diameter of 30 nm, pitch of 90 nm, and height of 600 nm. The process of the present invention was found to repair 90% of collapsed structures, resulting in a collapse percentage of less than 10%. The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

Throughout this specification, including the claims which follow, unless the context requires otherwise, the word“comprise” and“include”, and variations such as“comprises”, “comprising”, and“including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

It must be noted that, as used in the specification and the appended claims, the singular forms“a,”“an,” and“the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from“about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent“about,” it will be understood that the particular value forms another embodiment. The term“about” in relation to a numerical value is optional and means for example +/- 10%.