TECHNICAL FIELD

The present disclosure relates to chemical mechanical polishing, and more particularly to a polishing pad conditioner.

BACKGROUND

An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over anon-planar surface and planarizing the filler layer. For certain applications, a conductive filler layer is planarized until the top surface of a patterned layer is exposed. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness is left over the non- planar surface. In addition, planarization of the substrate surface is usually required for photolithography .

Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid is typically supplied to the surface of the polishing pad.

The polishing system typically includes a conditioner system to condition the polishing pad. Conditioning of the polishing pad maintains the polishing surface in a consistent roughness to ensure uniform polishing conditions from wafer-to-wafer. A conventional conditioner system has a conditioner head which holds a conditioner disk with an abrasive lower surface, e.g., with diamond particles, that is placed into contact with the polishing pad.

SUMMARY

In one aspect, a polishing system including a platen to support a polishing pad, a carrier head to hold a substrate against the polishing pad, a source of dry ice particles, and a pad conditioner. The pad conditioner includes a compressor to generate a compressed gas stream, a mixer coupled to the source and the compressor to mix the dry ice particles with the compressed gas stream to form a stream of compressed gas with entrained dry ice particles, and a nozzle coupled to the mixer to direct the stream of compressed gas with entrained dry ice particles onto a polishing surface of the polishing pad at sufficient velocity to condition the polishing pad.

In another aspect, a method of conditioning a polishing pad includes mixing dry' ice particles with a stream of compressed air to form a stream of compressed gas with entrained dry ice particles, and directing the stream of compressed gas with entrained dryice particles through a nozzle onto a polishing surface of the polishing pad at sufficient velocity'- to condition the polishing pad.

Implementations may optionally include, but are not limited to, one or more of the foil owing ad vantages.

A cold condensed gas may be more effective in conditioning and/or cleaning than a diamond abrasive disk. For example, sublimation of the condensed gas may lift debris off the polishing pad and may provide increased cleanliness. As another example, impact of particles of the condensed gas on the pad may reach a desired roughness faster. An entire radial length of the polishing pad can be conditioned at once, reducing avoiding need for sweeping of the conditioning area and improving conditioning uniformity. Pad conditioning and/or cleaning time can be reduced, thus improving system duty cycle. The need for a replaceable conditioning disk that wears out is avoided, reducing polishing system down-time for maintenance for conditioning disk replacement. Accumulation of dried abrasive particles on a conditioning disk can be avoided, which may improve polishing quality by reducing scratches and defects. Productivity of the polishing system can be improved because less time is devoted to the pad conditioner cleaning process.

The details of one or more implementations are set forth in the accompanying drawings and the description below; Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims,

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a polishing system that includes a pad conditioner system.

FIG. 2 is a schematic top view' of the polishing system.

FIG. 3 is a schematic diagram of a conditioning system.

Like reference numbers and designations in the various drawings indicate like elements. DETAILED DESCRIPTION

During chemical mechanical polishing, the surface of the polishing pad can become smoother due to friction and compression, and polishing debris can be pressed into the polishing pad. The polishing system typically includes a conditioner system that has a conditioner head and a conditioner disk with an abrasive lower surface to condition the polishing pad and maintain the polishing pad at a consistent roughness from substrate- to-substrate and to remove polishing debris. However, the conditioning disk itself wears out and needs to be replaced periodically. This required shutting down the polishing system for maintenance. Moreover, abrasive slurry can splash and stick to the conditioning disk. A build-up of dried or coagulated polishing liquid on the polishing pad over time has multiple deleterious effects. For example, the larger particulates can be dislodged and return to the polishing surface, thus creating the danger of scratching and defects, A significant amount of non-productive time is required to clean the conditioner head and conditioner disk to prevent build-up of the dried polishing liquid.

An alternative technique for conditioning is to direct a jet of cold condensed gas, e.g., dry ice particles (i.e., solid CO2), at onto the polishing pad. If jetted at sufficiently high speed, the impact of the particles can abrade the polishing surface and loosen debris. Moreover, sublimation of the particles generates a gas that can carry away the debris.

Although the use of dry ice has been proposed for use in temperature control of the surface of the polishing pad, the operating regime to perform a conditioning process should be fairly different, e.g., higher velocity and larger particulate size. In short, use of dry ice for temperature control does not inherently result in a conditioning operation.

FIG. 1 show's a polishing system 20 operable to polish a substrate 10. The polishing system 20 includes a rotatable platen 24, on which a polishing pad 30 is situated. The platen 24 is operable to rotate (see arrow A in FIG. 2) about an axis 25. For example, a motor 22 can turn a drive shaft 28 to rotate the platen 24. The polishing pad 30 can be a two-layer polishing pad with an outer polishing layer 34 having a polishing surface 36 and a softer backing layer 32.

The polishing system 20 includes a supply port 64, e.g., at the end of a slurry supply arm 62, to dispense a polishing liquid 60, such as an abrasive slurry, onto the polishing pad 30.

The polishing system 20 includes a carrier head 70 operable to hold the substrate 10 against the polishing pad 30. The carrier head 70 can include a flexible membrane 80 having a substrate mounting surface to contact the back side of the substrate 10, and a plurality of pressurizable chambers 82 to apply different pressures to different zones, e.g., different radial zones, on the substrate 10, The carrier head 70 is suspended from a support structure 72, for example, a carousel or track, and is connected by a carrier drive shaft 74 to a carrier head rotation motor 76 so that the carrier head can rotate about an axis 71. In addition, the carrier head 70 can oscillate laterally across the polishing pad 30, e.g., by moving in a radial slot in the carousel 72 as driven by an actuator, by rotation of the carousel as driven by a motor, or movement back and forth along the track as driven by an actuator. In operation, the platen 24 is rotated about its central axis 25, and the carrier head 70 is rotated about its central axis 71 and translated laterally across the top surface of the polishing pad 30.

Referring to FIG. 2, in some implementations, the polishing system 20 includes a temperature control system 40 to control the temperature of the polishing pad 30 and/or slurry' 38 on the polishing pad. 'The temperature control system 40 can provide a cooling system and/or a heating system. The temperature control system 40 can operate bydelivering a temperature-controlled medium, e.g., a liquid, vapor or spray, from a source 48 onto the polishing surface 36 of the polishing pad 30 (or onto a polishing liquid that is already present on the polishing pad).

An example temperature control system 40 includes an arm 42 that extends over the platen 24 and polishing pad 30 from an edge of the polishing pad to or at least near (e.g., within 5% of the total radius of the polishing pad) the center of polishing pad 30. The arm 42 can be supported by- a base 44, and the base 44 can be supported on the same frame 40 as the platen 24. The base 44 can include one or more an actuators, e.g., a linear actuator to raise or lower the arm 42, and/or a rotational actuator to swing the arm 42 laterally over the platen 24. The arm 42 is positioned to avoid colliding with other hardware components such as the polishing head 70 and the slurry- dispensing arm 62.

The arm 42 can include or support one or more apertures 46, e.g., nozzles, through which the temperature control medium is sprayed onto the polishing pad. Although FIG. 2 illustrates a single arm, there could be multiple arms, e.g., one arm dedicated for heating and one arm dedicated for cooling.

For cooling, the cooling medium can be a gas, e.g., air, or a liquid, e.g., water. The medium can be at room temperature or chilled below room temperature, e.g., at 5-15° C. In some implementations, the cooling system uses a spray of air and liquid, e.g., an aerosolized spray of liquid, e.g., water. In particular, the cooling sy stem can have nozzles that generate an aerosolized spray of water that is chilled below room temperature. In some implementations, solid material can be mixed with the gas and/or liquid. The solid material can be a chilled material, e.g., ice, or a material that absorbs heat, e.g., by chemical reaction, when dissolved in water.

For heating, the heating medium can be a gas, e.g., steam or heated air, or a liquid, e.g., heated water, or a combination of gas and liquid. The medium is above room temperature, e.g., at 40-120° C, e.g., at 90-110° C. The medium can be water, such as substantially pure de-ionized water, or water that that includes additives or chemicals. In some implementations, the temperature control system uses a spray of steam. The steam can includes additives or chemicals.

The polishing system 20 can also include a high pressure rinse system 50. ’The high pressure rinse system 50 includes a plurality of nozzles 54, e.g., three to twenty nozzles that direct a cleaning fluid, e.g., water, at high intensity onto the polishing pad 30 to wash the pad 30 and remove used slurry', polishing debris, etc.

As shown in FIG. 2, an example rinse system 50 includes an arm 52 that extends over the platen 24 and polishing pad 30 from an edge of the polishing pad to or at least near (e.g., within 5% of the total radius of the polishing pad) the center of polishing pad 30,

The arm 52 can be supported by a base 54, and the base 54 can be supported on the same frame 40 as the platen 24. The base 52 can include one or more an actuators, e.g., a linear actuator to raise or lower the arm 52, and/or a rotational actuator to swing the arm 52 laterally over the platen 24.

The arm 52 is positioned to avoid colliding with other hardware components such as the polishing head 70, slurry dispensing arm 62, and temperature control system 40. Along the direction of rotation of the platen 24, the arm of the high pressure rinse system 50 can be between the slurry' delivery arm 62 and the arm of the conditioner system.

In some implementations, the polishing system 20 includes a wiper blade or body 66 to eventy distribute the polishing liquid 38 across the polishing pad 30. Along the direction of rotation of the platen 24, the wiper blade 66 can be between the slurry' delivery' arm 62 and the carrier head 70.

The polishing system 20 can also include a high pressure rinse system 50. The high pressure rinse system 50 includes a plurality of nozzles 54, e.g., three to twenty nozzles that direct a cleaning fluid, e.g., water, at high intensity onto the polishing pad 30 to wash the pad 30 and remove used slurry, polishing debris, etc. Referring to FIGS. I and 2, the polishing system 20 includes a conditioning system 100 that uses a jet of cold condensed gas to condition the polishing surface 36 of the polishing pad 30. An example conditioning system 100 includes an arm 102 that extends over the platen 24 and polishing pad 30 from an edge of the polishing pad to or at least near (e.g., within 5% of the total radius of the polishing pad) the center of polishing pad 30.

The arm 102. can be supported by a base 104, and the base 104 can be supported on the same frame 40 as the platen 24. The base 104 can include one or more an actuators, e.g., a linear actuator to raise or lower the arm 102, and/or a rotational actuator to swing the arm 104 laterally over the platen 24,

The arm 104 is positioned to avoid colliding with other hardware components such as the rinse system 52, temperature control system 40, slurry dispensing arm 62, and polishing head 70. Along the direction of rotation of the platen 24, the arm 102 of the conditioning system 100 can be between the carrier head 70 and the arm of the 42 of the temperature control system (if present) or the slurry dispensing arm 62. Along the direction of rotation of the platen 24, the components can be arranged in the following order: the arm 102 of the conditioning system 100, the arm 52 of the rinse system 50 (optional), the arm 42 of the temperature control system 40 (optional), the slurry’ dispensing arm 62, the wiper blade 66 (optional), and the polishing head 70.

The conditioning system 100 is configured to direct cold condensed gas through one or more openings 106, e.g., in one or more nozzles 108, that are formed in or suspended from the arm 102. In particular, the conditioning system can have a plurality of openings 106. The nozzles 108 can be convergent-divergent nozzles, e.g., Venturi nozzles. Each nozzle 108 can provide exactly one opening 106, In operation, the arm 110 can be supported by a base 104 so that the nozzles 108 are separated from the polishing pad 30 by a gap 126. The gap 126 can be 1 to 10 cm.

The various openings 106 can direct jets 122 of cold condensed gas onto different radial zones 12.4 on the polishing pad 30. Adjacent radial zones can overlap. Optionally, some of the openings 106 can be oriented so that a central axis (D) of the spray from that opening is at an oblique angle relative to the polishing surface 36. The jets can be directed from one or more of the openings 106 to have a horizontal component (D) in a direction opposite to the direction of motion (E) of polishing pad 30 in the region of impingement as caused by rotation of the platen 24. Although FIGS. 1 and 2 illustrate the openings 106 and nozzles 108 as spaced at even intervals, this is not required. The openings, e.g., the nozzles, could be distributed non-unifonnly either radially, or angularly, or both. For example, openings 106 could be clustered more densely toward the outer edge of the polishing pad 30 (to compensate for the greater area being covered at the outer radius). In addition, although FIGS. 1 and 2 illustrate nine openings, there could be a larger or smaller number of openings.

The jets 12.2 of cold condensed gas can include cold solid particles of condensed gas that are carried by a carrier gas. In particular, the cold solid particles can be dry ice particles, i.e., solid carbon dioxide. The carrier gas can be air, or a purified gas such as nitrogen.

Referring to FIG. 3, an example conditioning system 100 draws in air into a compressor 130. The compressed air is directed through a drier 132 to remove excess water from the air stream. The compressed dry air is then mixed with dry' ice in a mixer 134, e.g., the dry ice particles are entrained in the compressed air stream. The mixer 134 can include a feeder 136 to receive dry' ice pellets or slabs, and a shredder 138, e.g., a pair of bladed rollers, to shred the large dry ice pieces into smaller particles suitable for entrainment into the compressed air stream.

The particles can have an average diameter of 0.05 to 5 mm, e.g., 0.1 to 1 mm. In some implementations, have an average diameter of at least 0.05 mm, e.g., at least 0.1 mm, e.g., at least 0.2 mm, e.g., at least 0.3 mm, e.g., at least 0.5 mm, e.g., at least 1 mm. In some implementations, have an average diameter of at most 0.1 mm, e.g., at most 0.2 mm, e.g., at most 0.3 mm, e.g., at most 0.5 mm, e.g., at most 2 mm, e.g., at most 3 mm, e.g., at most 5 mm.

Optionally the compressed air stream with entrained dry' ice particles is directed through a strainer 140 to block dry' ice particles above a threshold size.

The compressed air stream with entrained dry ice particles passes through an opening 106 of a nozzle 108 to form ajet 122 of dry' ice particles 126 that, is directed onto the surface 36 of the polishing pad 30. For example, the compressed air stream with entrained dry' ice particles can pass through insulated conduit, e.g., provided by piping, tubing, etc., and a conduit 140 in the arm 102 to the nozzles 108. Although FIG. 3 illustrates a single nozzle, there can be multiple openings and multiple nozzles as shown in FIGS. 1 and 2.

As the compressed gas passes through the nozzle 108 or exits the opening 106, it can expand such that the dry ice particles are carried at high speed. The impact of the dry' ice particles on the polishing surface and the sublimation of the drv ice with can function to abrade the polishing pad 30 and/or to dislodge and cany away debris that is stuck on the polishing pad, thereby conditioning the polishing pad 30.

In some implementations, the dry ice particles impact the polishing surface at a velocity up to Mach 1.5. In some implementations, the dry ice particles impact the polishing surface at a velocity of at least 50 m/s, e.g., at least 100 m/s, e.g., at least 150 m/s, e.g., at least 200 m/s, e.g., at least 250 m/s, e.g., at least 300 m/s, e.g,. at least 343 m/s. In some implementations, the dry ice particles impact the polishing surface at a velocity of at most 100 m/s, e.g., at most 150 m/s, e.g., at most 200 m/s, e.g., at most 250 m/s, e.g., at most 300 m/s, e.g,. at most 343 m/s (Mach 1), e.g., at most Mach 1.25. In some implementations, the dry ice particles reach supersonic speeds, i.e., above 343 m/s, within or at the exit of the nozzle.

A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other embodiments are within the scope of the following claims.