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Title:
METHOD AND APPARATUS FOR INDIRECTLY COOLING THIN COMPONENTS
Document Type and Number:
WIPO Patent Application WO/2009/053334
Kind Code:
A2
Abstract:
A method for cooling at least one thin component (2) and an apparatus (1) especially therefor, in which the thin component (2) is guided across a heat sink (3), while a coolant flows through said heat sink (3). Said method for cooling the at least one thin component (2) and said apparatus (1) especially therefor advantageously make it possible for thin components (2), such as, for example, semiconductor wafers, to be cooled gently and uniformly. In particular, the method according to the invention is distinguished by good controllability and uniform cooling of said at least one thin component (2).

Inventors:
KUTZ, Thomas (Tippheideweg 11, Brüggen-Born, 41379, DE)
LAUX, Peter (Trierer Str. 35, Lutzerath, 56826, DE)
HUMBERG, Eugen (Buschhagenweg 39b, Oldenburg, 26133, DE)
Application Number:
EP2008/064139
Publication Date:
April 30, 2009
Filing Date:
October 20, 2008
Export Citation:
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Assignee:
L'AIR LIQUIDE SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE (75 quai d'Orsay, Paris, Paris, F-75007, FR)
AIR LIQUIDE DEUTSCHLAND GMBH (Hans-Günther-Sohl-Strasse 5, Düsseldorf, 40235, DE)
KUTZ, Thomas (Tippheideweg 11, Brüggen-Born, 41379, DE)
LAUX, Peter (Trierer Str. 35, Lutzerath, 56826, DE)
HUMBERG, Eugen (Buschhagenweg 39b, Oldenburg, 26133, DE)
International Classes:
A23G7/00; H01L21/00; H01L31/18; H05K13/00
Foreign References:
GB2355511A2001-04-25
US5421723A1995-06-06
US5660047A1997-08-26
DE10022159A12001-11-29
US5373893A1994-12-20
Attorney, Agent or Firm:
MELLUL-BENDELAC, Sylvie (L'air Liquide S.A, DPI7, quai d'Orsay Paris Cedex 07, F-75321, FR)
Download PDF:
Claims:

Patent Claims

1. Method for cooling at least one thin component

(2) , in which the component (2) is guided across a heat sink (3), characterized in that a coolant (7) flows through the heat sink (3) .

2. Method according to Claim 1, in which the temperature to which the component (2) is cooled is controlled by varying at least one of the following parameters: a) the temperature of the heat sink (3) , and b) the speed at which the component (2) is guided across the heat sink (3) .

3. Method according to Claim 1 or 2, in which the at least one component (2) is guided across the heat sink by a conveying means (4) .

4. Method according to one of the preceding claims, in which a phase transition of the coolant (7, 8) takes place in the heat sink (3) .

5. Method according to one of the preceding claims, in which at least one of the following substances is used as the coolant: a) gaseous nitrogen (8) ; b) liquid nitrogen (7) ; c) solid carbon dioxide; and d) liquid carbon dioxide.

6. Method according to one of the preceding claims, in which the quantity of coolant (7) flowing to the heat sink (3) is controlled by means of physical parameters of the coolant (7) as it leaves the heat sink (3) .

7. Method according to Claim 6, in which the physical parameters comprise at least one of the following

vari able s : i) the temperature; ii) the pressure; and iii) the volumetric flow.

8. Method according to one of the preceding claims, in which the component (2) comprises at least one of the following components:

A) a semiconductor component; and B) a foodstuff.

9. Method according to one of the preceding claims, in which the coolant (7, 8), after flowing through the heat sink (3) , flows around the at least one component (2) .

10. Apparatus (1) for cooling at least one thin component (2), in particular according to the method according to one of the preceding claims, comprising:

- a heat sink (3) through which a coolant (7, 8) can flow;

- a conveying means by means of which the at least one component (2) can be guided across the heat sink (3) in such a manner that the component (2) is cooled.

11. Apparatus (1) according to Claim 10, in which the heat sink (3) comprises at least one flow path (13) for the coolant.

12. Apparatus (1) according to either of Claims 10 and 11, in which the heat sink (3) is formed from a metal .

13. Apparatus (1) according to one of Claims 10 to 12, in which the conveying means comprises a conveyor belt (4) .

14. Apparatus (1) according to Claim 13, in which the conveyor belt (14) is formed from a material comprising at least one of the following materials : I) polyester;

II) metal; and

III) high-quality steel.

15. Apparatus (1) according to one of Claims 10 to 14, in which the conveying means has a thermal conductivity of at least 0.15 W/ (m K) .

16. Apparatus (1) according to one of Claims 10 to 15, in which at least one hood (9) is formed over the conveying means.

17. Apparatus (1) according to Claim 16, in which flow means are formed by means of which the coolant, after flowing through the heat sink (3) , can be directed into the hood (9) .

Description:

Method and apparatus for indirectly cooling thin components

The present invention relates to a method and to an apparatus for indirectly cooling thin components, such as, for example, semiconductor substrates, wafers or else thin foodstuffs, such as, for example, chocolate bars or the like.

Thin components of this type generally have to be cooled during production. EP 1 732 138 A2, for example, discloses a method for producing semiconductor components, in which the latter are cooled to a temperature of approximately -40 0 C by having a cold gas or a cold liquid, such as, for example, liquid nitrogen, flowing over them or a refrigerating spray sprayed over them. This method is disadvantageous insofar as it results in a locally inhomogeneous cooling capacity which may lead to stresses in the component on a scale of micrometres to millimetres. Furthermore, the cooling capacity in this case and therefore also the temperature achieved for the component which is to be cooled can only be controlled with difficulty.

The present invention is therefore based on the object of at least mitigating or overcoming the disadvantages known from the prior art and in particular of proposing a method and an apparatus for cooling thin components, in which good controllability of the cooling capacity and uniform cooling of the components can be achieved.

This object is achieved by a method and an apparatus with the features of the independent claims. The dependent claims are focused on advantageous developments of the invention.

The method according to the invention for cooling at least one thin component, in which the component is

guided across a heat sink, is distinguished in that a coolant flows through the heat sink.

Here, direct cooling by application of a coolant is therefore not exactly achieved according to the invention, but rather a coolant first of all flows through a heat sink and cools the latter as a result, whereupon said heat sink then indirectly cools the components which are to be cooled. In particular, the method according to the invention permits the thin components not to be brought directly into contact with liquid nitrogen.

A component is understood here as meaning shaped parts which can be formed from any desired material. In particular, a thin component is understood as meaning a component, the thickness of which lies below 5 mm, preferably below 2 mm, particularly preferably below

1 mm. In particular, a heat sink is understood as meaning a body made of metal and/or ceramic which has flow paths for the coolant. Said flow paths can be designed in the form of tubes. However, as an alternative or in addition, a porous heat sink in which the coolant flows through the pores of the heat sink is also possible.

The preferred use of the method according to the invention and of the apparatus according to the invention is for cooling printed circuit boards, semiconductor substrates and/or semiconductor components. In particular, silicon wafers, as are used, for example, in the production of solar cells, can be cooled advantageously with the method according to the invention and the apparatus according to the invention. Said printed circuit boards, semiconductor substrates, wafers and/or semiconductor components are sensitive to stresses which may arise in the event of non-uniform cooling in the components. The method according to the invention and the apparatus according to the invention

permit highly uniform and efficient cooling of said components such that corresponding stresses can only build up to a very small extent, if at all, in said components .

The effect achieved by guiding the coolant through the heat sink and by a corresponding configuration is that the heat sink has a substantially uniform temperature. This means in particular that the surface temperature of the heat sink fluctuates by at most ± 5 K. Uniform cooling of the components is thereby possible. Owing to the fact that the coolant is no longer applied directly to the component to be cooled, temperature gradients due, for example, to the local evaporation of drops of nitrogen on the surface of the component, as during the direct cooling, no longer occur either. Furthermore, the heat sink has a certain thermal inertia which makes good control action possible at a certain predetermined temperature .

According to an advantageous configuration of the method according to the invention, the temperature to which the component is cooled is controlled by varying at least one of the following parameters: a) the temperature of the heat sink, and b) the speed at which the component is guided across the heat sink.

This makes it possible to easily set a desired temperature to which the thin components are cooled.

According to an advantageous configuration of the method according to the invention, the at least one component is guided across the heat sink by a conveying means.

This may in particular be a conveyor belt. Said conveyor belt is preferably formed from at least one polymer, in particular polyester.

According to a further advantageous configuration, a phase transition of the coolant takes place in the heat sink .

In particular, this is an evaporation or sublimation process. By this means, a greater quantity of energy can be used for the cooling, for example the evaporation enthalpy or the sublimation enthalpy. The energy specifically employable for the cooling is therefore increased significantly in comparison to a pure heating process of the coolant.

According to a further advantageous configuration of the method according to the invention, at least one of the following substances is used as the coolant: a) gaseous nitrogen; b) liquid nitrogen; c) dry ice; and d) liquid carbon dioxide.

Gaseous nitrogen can preferably be used when it is available, for example from another process, in particular by means of the evaporation of liquid nitrogen in cold form. In the case of liquid nitrogen, the evaporation enthalpy can advantageously also be used for the cooling. In particular, it is advantageous to allow the liquid nitrogen to evaporate as it flows through the heat sink such that ultimately a mixture of liquid and gaseous nitrogen is used as the coolant. Dry ice, i.e. solid carbon dioxide, can be used in particular in the form of snow or pellets, if appropriate with a flow medium for flowing through the heat sink. In the case of dry ice, the sublimation enthalpy released during the sublimation can advantageously be used for the cooling. In the case of liquid carbon dioxide, both the released energy during the phase transition from liquid to solid and also subsequently during the phase transition from solid to gaseous can be used for the cooling.

In this case, the use of at least partially liquid nitrogen as the coolant is particularly preferred. An at least partial evaporation takes place in this case within the heat sink.

According to a further advantageous configuration of the method according to the invention, the quantity of coolant flowing to the heat sink is controlled by means of physical parameters of the coolant as it leaves the heat sink.

The physical parameters are understood in particular as meaning at least one of the following variables: i) the temperature; ii) the pressure; and iii) the volumetric flow.

It has been shown that, firstly, the monitoring of at least one of the physical parameters referred to can be carried out in a simple manner as the coolant leaves the heat sink, i.e. as it flows out of the heat sink.

Furthermore, a correlation with the corresponding desired temperature of the heat sink and therefore also with the cooling temperature to be achieved for the components can be achieved by said parameter, for example by means of calibration measurements.

In particular, the control with reference to the temperature of the coolant flowing out, preferably of the gaseous nitrogen flowing out, has turned out to be a control variable which can be measured in a simple manner and can easily be used. By monitoring at least one of the abovementioned parameters, the operating state of the heat sink can furthermore be monitored, since, for example, blockages in the flow paths of the coolant in the heat sink, which may occur possibly via the formation of ice, lead to changes in the temperature, the volumetric flow and/or the pressure of

the coolant as it leaves the heat sink. Thus, monitoring of one or in particular more of said parameters can lead to a monitoring of the operating state and to a possible switching of the process in the event of problems, effectively preventing breakdowns and damage to the heat sink.

According to a further advantageous configuration of the method according to the invention, the component comprises at least one of the following components:

A) a semiconductor component; and

B) a foodstuff.

The method according to the invention has proven advantageous in particular in the semiconductor industry, for the cooling of wafers, solar cells or other semiconductor substrates. The method according to the invention has also proven advantageous for the cooling of thin foodstuffs, such as, for example, chocolates, cakes, pralines or the like, which have to be produced at a raised temperature but stored at a lower temperature and/or at ambient temperature.

According to a further advantageous configuration of the method according to the invention, the coolant, after flowing through the heat sink, flows around the at least one component.

In particular when nitrogen is used as the coolant, said nitrogen preferably either being fed in in liquid form or being produced from the evaporation of liquid nitrogen, said coolant constitutes a dry gas which is in principle available for further use. Circulation around the components is preferred in this case, since a dry atmosphere can thereby be provided around the components. Many thin components are moisture-sensitive precisely during production. Moisture in the case of foodstuffs frequently leads to an unattractive appearance of the foodstuffs while wafers or

semiconductor substrates may even be damaged by moisture during the production process such that they are no longer functional. When it flows around the component, the coolant preferably has a temperature of -10 0 C or less.

This positive effect can be assisted in that the components are guided through a space permitting a certain positive pressure of the coolant in relation to the ambient pressure to be produced. The penetration of ambient air and therefore also of atmospheric moisture is thus effectively prevented. This can preferably be achieved by means of a shield, for example by means of a hood, over the conveying means or over the components to be cooled.

According to a further aspect of the present invention, an apparatus for cooling at least one thin component is proposed, comprising: - a heat sink through which a coolant can flow;

- a conveying means by means of which the at least one component can be guided across the heat sink in such a manner that the component is cooled.

The apparatus according to the invention preferably operates in accordance with the method according to the invention. In this case, the heat sink is preferably configured in such a manner that it does not permit any contact of the component with the coolant in the region of the cooling surface. The heat sink may comprise, for example, a substantially solid body made of metal and/or ceramic through which coolant can flow through corresponding flow paths. In this case, the flow paths can be directed, for example in the form of corresponding channels or tubes, or undirected, for example in the form of a plurality or multiplicity of pores .

A configuration of the apparatus is preferred in this

case in which the heat sink comprises at least one flow path for the coolant.

In principle, configurations of the apparatus from materials with a specific heat capacity of at least 300 J/ (kg K) (joules per kilogram and Kelvin), preferably of at least 350 J/ (kg K) , in particular of 800 J/ (kg K) and/or a thermal conductivity of at least 200 W/ (m K) (watt per m and Kelvin) , in particular of at least 350 W/ (m K), are possible and advantageous. This minimum size of the heat capacity has proven advantageous, since it permits a certain buffering of temperature fluctuations. The heat sink can thus advantageously act as a type of damping element by means of which a spatially inhomogeneous evaporation, for example of liquid nitrogen, can be further compensated for. Even more uniform cooling of the at least one component is thus achieved.

According to a further advantageous configuration of the apparatus according to the invention, the heat sink is formed from a metal.

Metallic bodies have a sufficiently large heat capacity, can easily be worked and have good properties with regard to durability and tightness of the flow paths for the coolant. In this case, a configuration comprising at least one of the following metals: a) aluminium; b) alloys of aluminium; c) high-quality steel; d) copper; and e) alloys of copper is particularly preferred.

According to a further advantageous configuration of the apparatus according to the invention, the heat sink is advantageously formed integrally with at least one embedded channel for the coolant.

Formation as an integral workpiece with at least one embedded channel for the coolant is advantageous in

particular if contact of the component to be cooled with the coolant is to be reliably prevented. In addition, this configuration has hardly any tightness problems .

According to a further advantageous configuration of the apparatus according to the invention, the conveying means comprises at least one conveyor belt.

A conveyor belt of this type can preferably encircle the heat sink as a whole and can be fed on one side with the components to be cooled such that the latter are conveyed across the heat sink. In the case of circulation on the opposite side, precooling of the conveyor belt can advantageously be achieved.

According to a further advantageous configuration of the apparatus according to the invention, the conveyor belt is formed from a material comprising at least one of the following materials:

I) polyester;

II) metal; and

III) high-quality steel.

According to a further advantageous configuration of the apparatus according to the invention, the conveying means is cold-resistant and/or abrasion-insensitive. In particular, the conveying means has a thermal conductivity of at least 0.15 W/ (m K) (watts per metre and Kelvin) .

Cold-resistant is understood here in particular as meaning that the conveying means can be operated without structural damage, such as, for example, embrittlement, in a temperature range of -196 to 150 0 C, preferably at -130 0 C to 100°C. The term abrasion- insensitive is understood in particular as meaning that, during the movement of the conveying means across the heat sink, material losses at the conveying means

due to mechanical friction do not occur.

According to a further advantageous configuration of the apparatus according to the invention, at least one hood is formed over the conveying means.

This hood makes it possible to produce a specifically controllable atmosphere in that region of the conveying means through which the components to be cooled pass. For example, a certain gas composition can thus be produced under the hood or else an atmosphere with as little atmospheric moisture as possible. Furthermore, for example, a dry, inert atmosphere can be produced. This can be brought about, for example, by essentially dry nitrogen, for example produced from the evaporation of liquid nitrogen, flowing through the region limited by the hood. A configuration is preferred in this case in which the hood makes it possible to maintain or to allow a positive pressure in comparison to the ambient pressure in its interior. This makes it possible to avoid gas, in particular air, from penetrating into the hood from the surroundings of the same.

According to a further advantageous configuration of the apparatus according to the invention, flow means are formed by means of which the coolant, after flowing through the heat sink, can be directed into the hood.

In particular if liquid nitrogen or gaseous nitrogen from a different process is used as the cooling means, the design of the flow means can be used in an advantageous manner to provide as dry an atmosphere as possible within the hood. This dry atmosphere is important in particular if the components being cooled are wafers and/or semiconductor substrates.

The details and advantages disclosed for the apparatus according to the invention can be transferred to and used for the method according to the invention, and

vice-versa. The invention is explained in more detail below with reference to the attached figures without being limited to the details and exemplary embodiments shown there. The figures show, schematically:

Fig. 1: an apparatus according to the invention, and

Fig. 2: an example of a heat sink of an apparatus according to the invention.

Fig. 1 shows, schematically, an exemplary embodiment of an apparatus 1 according to the invention for cooling components 2. The component 2 here is thin and constitutes a wafer. The component 2 is guided across a heat sink 3. This guiding is undertaken by means of a conveying means designed as a conveyor belt 4. Said conveyor belt 4 is realized as an endless belt which is moved continuously around the heat sink 3 during operation .

According to the invention, liquid nitrogen flows as the coolant through the heat sink 3. In the process, the liquid nitrogen at least partially evaporates such that, in addition to the energy released by the heating of the nitrogen, the evaporation enthalpy of the nitrogen is also available for cooling the component 2. By this means, indirect cooling of the component 2 takes place starting from the heat sink 3 and through the conveyor belt 4. The heat sink 3 has a supply line 5 and a removal line 6. By means of the supply line 5, liquid nitrogen 7 flows through the heat sink 3 during operation. After evaporation, gaseous nitrogen 8 leaves the heat sink 3 through the removal line 6. Said nitrogen flows through a space which is delimited by two hoods 9 and through which the conveyor belt 4 with the components 2 also moves. Owing to its production by means of evaporation of the liquid nitrogen 7, the gaseous nitrogen 8 is virtually completely dry, i.e. contains virtually no water molecules. Said dry gaseous

nitrogen 8 then flows around the conveyor belt 4 and the components 2 to be cooled such that the latter are exposed to a defined dry atmosphere. This has a positive effect on the corresponding quality of the components 2, in particular if they are wafers.

Furthermore, control means 10 which are connected via a corresponding data line 11 to a measuring sensor (not shown) in the removal line 6 are formed. Via said measuring sensor (not shown) , in particular via a corresponding temperature measuring sensor, the temperature of the gaseous nitrogen 8 flowing through the removal line 6 is measured. With reference to said data, the control means 10 determines the deviation from a predetermined or predeterminable desired temperature which corresponds to the desired cooling temperature of the heat sink 3. The control means 10 controls a correspondingly designed valve 12 in accordance with a required increased or reduced inflow of liquid nitrogen 7 through the supply line 5.

Fig. 2 schematically shows a heat sink 3 of an apparatus 1 according to the invention in cross section. The heat sink 3 is designed integrally as a substantially solid component. It has at least one embedded channel 13. The channel cross section may be different, for example circular, elliptical, rectangular, triangular or square. Channels of differing size, differing cross sections and differing cross-sectional shapes may be formed in a single configuration of a heat sink 3.

The method according to the invention and the apparatus 1 according to the invention for cooling thin components advantageously enable thin components, such as, for example, wafers, to be cooled gently and uniformly. In particular, the method according to the invention is distinguished by good controllability and uniform cooling of the components 2 such that stresses

produced in the components by non-uniform cooling can be avoided.

List of reference numbers

1 Apparatus for cooling components

2 Component

3 Heat sink

4 Conveyor belt

5 Supply line

6 Removal line

7 Liquid nitrogen

8 Gaseous nitrogen

9 Hood

10 Control means

11 Data line

12 Valve

13 Channel