Chemical Mechanical Polishing Systems Including Brushes and Related Methods

The present invention relates to the field of microelectronics and more particularly to chemical-mechanical polishing systems and methods for microelectronic substrates.

As the critical dimensions of integrated circuit patterns decrease with increasing integration densities, the resolution and depth of focus achieved during photolithography steps becomes more critical. Accordingly, highly planar semiconductor wafers are required. Planarization techniques have thus been developed to provide highly planar surfaces for semiconductor wafers. In particular, chemical-mechanical polishing systems and methods have been developed which provide simultaneous and efficient planarization for multiple wafers.

FIGS. 1 and 2 illustrate a conventional chemical-mechanical polishing (CMP) system. In particular, FIG. 1 is a plan view illustrating a conventional chemical-mechanical polishing system. FIG. 2A is a cross-sectional view taken along sections lines 2a--2a of FIG. 1, and FIG. 2B is a cross-sectional view taken along section lines 2b--2b of FIG. 1. As shown in FIG. 1, a polishing portion A is used to polish the surface of semiconductor substrates, and a cleaning portion B is used to clean the surfaces of the semiconductor substrates after polishing.

The polishing portion A of the system includes a first platen 10a having a flat end portion, a first platen rotating shaft 11a for rotating the first platen 10a, and a polishing pad 20a fixed on the end portion of the first platen 10a. The polishing portion also includes a conditioner 50 for cutting back a surface of the polishing pad 20 to expose a new surface thereof, a conditioning head 60 having an end portion fixed to the conditioner 50, and a conditioning head arm 61 for transferring the conditioning head 60. In addition, the clamp 40 has an end portion for fixing the semiconductor substrate 30 thereto, and a clamp arm 41 for transferring the clamp 40. Furthermore, the polishing pad 20a has fine grooves on its surface so that a polishing slurry can be provided to the center portions of the semiconductor substrate 30 even though maintained in tight contact with the polishing pad 20a.

The cleaning portion B includes a second platen 10b having a first end portion, a second platen rotating shift 11b for rotating the second platen 10b, and an auxiliary pad 20b fixed to the end portion of the second platen 10b. As shown, the clamp 40 to which the semiconductor substrate 30 is attached can be transferred from the polishing portion A to the cleaning portion B using the clamp arm 41.

The operation of the chemical-mechanical polishing system discussed above will now be explained with reference to FIGS. 1 and 2A-2B. The surface of the semiconductor substrate 30 is first polished by rotating the semiconductor substrate 30 in tight contact with the polishing pad 20a while a slurry is being deposited on the polishing pad 20a. The semiconductor substrate 30 is then moved away from the polishing pad 20a using the clamp 40 and the clamp arm 41. The surface of the polishing pad 20a is then cut back to expose a new surface thereof by rotating the conditioner 50 in tight contact with the polishing pad 20a. This operation is referred to as pad conditioning. The pad conditioning operation is used to reduce abrasion of the surface of the polishing pad 20a thereby maintaining the speed at which the semiconductor substrates 30 can be polished.

Stated in other words, the purpose for the pad conditioning operation is to expose a new polishing pad surface by cutting back the abraded surface of the polishing pad 20a. It may be difficult, however, to completely remove polishing particle lumps which may be formed by the agglutination of particles during the polishing step. Moreover, polishing particles from the slurry may also be difficult to remove. In particular, it may be very difficult to remove polished particle lumps and slurry particles jammed into grooves formed on the surface of the polishing pad 20a.

Accordingly, particle lumps remaining on the polishing pad 20a may produce scratches on the surfaces of semiconductor substrates polished thereon. In particular, polishing particle lumps may roughen the surface of semiconductor substrates 30 polished thereon thereby decreasing the reliability of the chemical-mechanical polishing operation. This result may occur because portions of the semiconductor substrate 30 exposed to the polished particle lumps may be more rapidly polished than portions not exposed to the lumps.

The polished semiconductor substrate 30 is then transferred from the polishing portion A to the cleaning portion B. The polish surface of the semiconductor substrate 30 is then cleaned by rotating the semiconductor substrate 30 in tight contact with the auxiliary pad 20b while depositing a cleaning solution onto the surface of the auxiliary pad 20b. Particles and polishing particle lumps, however, may stick to the semiconductor substrate 30 and may thus be transferred to the auxiliary pad 20b.

In addition to the cleaning operation discussed above, an auxiliary polishing operation can also be performed on the cleaning portion B of the chemical-mechanical polishing system. The auxiliary polishing operation can be used to remove scratches from the surface of the semiconductor substrate 30 formed during the polishing operation discussed above with reference to FIG. 2A. The auxiliary polishing operation is performed by depositing a slurry including polishing particles instead of the cleaning solution onto the auxiliary pad 20b. The auxiliary polishing operation is sometimes referred to as slurry buffing or touch up. Like the polishing operation, the auxiliary polishing operation may generate scratches on the surface of the semiconductor substrate 30 and roughen the surface of the semiconductor substrate 30.

Notwithstanding the methods and systems discussed above, there continues to exist a need in the art for improved chemical-mechanical polishing systems and methods.

It is therefore an object of the present invention to provide improved systems and methods for polishing semiconductor substrates.

This and other objects are provided according to the present invention by a chemical-mechanical polishing system including a polishing pad having a polishing surface for polishing the semiconductor substrate, and a polishing pad brush including a plurality of bristles attached to a support for cleaning the polishing surface of the polishing pad. In addition, a polishing pad brush arm is operatively coupled to the brush support for transferring the polishing pad brush to and from the polishing pad. Accordingly, particles generated during the polishing of the semiconductor substrate can be removed by the polishing pad brush. The chemical-mechanical polishing system can also include a conditioner for conditioning the polishing surface of the polishing pad, and a conditioner arm operatively coupled to the conditioner for transferring the conditioner to and from the polishing pad.

Preferably, each of the bristles comprises a synthetic resin, and each of the bristles has a diameter in the range of 10 .mu.m to 2,000 .mu.m.

Moreover, each of the bristles can have a diameter that decreases from a first end adjacent the support to a second end opposite the support. The reduced diameter increases the efficiency at which particles can be removed from grooves in the polishing pad.

Alternately, a chemical-mechanical polishing system can include a polishing station for polishing the semiconductor substrate and a cleaning station for cleaning the polished semiconductor substrate. The polishing station can include a polishing pad having a polishing surface for polishing the semiconductor substrate, a conditioner for conditioning the polishing surface of a polishing pad, and a conditioner arm operatively coupled to the conditioner for transferring the conditioner to the polishing pad. The cleaning station can include an auxiliary pad having a cleaning surface for cleaning the polished semiconductor substrate, an auxiliary pad brush including a plurality of bristles attached to an auxiliary pad brush, a support for cleaning the cleaning surface of the auxiliary pad, and an auxiliary pad brush arm operatively coupled to the auxiliary pad brush support for transferring the auxiliary pad brush to and from the cleaning pad.

According to an alternate aspect of the present invention, a method can include the steps of polishing surface of a semiconductor substrate by rotating the semiconductor substrate in contact with the surface of a polishing pad, and brushing a surface of the polishing pad with a polishing pad brush thereby removing particles from the surface of the polishing pad. Moreover, the polishing step can include providing a slurry of polishing particles on the polishing pad.

The methods and systems of the present invention thus increase the efficiency of the substrate polishing by removing particles from the polishing pad. In particular, these particles are removed by brushing the pad.

FIG. 1 is a plan view of a chemical-mechanical polishing (CMP) system according to the prior art.

FIG. 2A is a cross-sectional view taken along section line 2a--2a of FIG. 1.

FIG. 2B is a cross-sectional view taken along section line 2b--2b of FIG. 1.

FIG. 3 is a plan view of a chemical-mechanical polishing (CMP) system according to the present invention.

FIG. 4A is a cross-sectional view taken along section line 4a--4a of FIG. 3.

FIG. 4B is a cross-sectional view taken along section line 4b--4b of FIG. 3.

FIG. 5 is a flow chart including steps of a method for performing a chemical-mechanical polishing (CMP) operation according to the present invention.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

A chemical-mechanical polishing system according to the present invention will now be discussed with reference to FIGS. 3 and 4A-4B. This system includes a polishing portion C for polishing the surface of a semiconductor substrate, and a cleaning portion D for cleaning the surface of the semiconductor substrate.

The polishing portion C includes a first platen 110a having a flat end portion, a first platen rotating shaft 111a for rotating the first platen 110a. A conditioner 150 is provided for cutting back the surface of the polishing pad 120a to expose a new surface of the polishing pad 120a, a conditioning head 160 having an end portion fixed to the conditioner 150, and a conditioning head arm 161 for transferring the conditioning head 160. The clamp 140 has an end portion for fixing the semiconductor substrate 130 thereto, and a clamp arm 141 is provided for transferring the clamp 140. In addition, a polishing pad brush 170 is provided for cleaning the polishing pad 120a, and a polishing pad brush arm 171 is provided for transferring the polishing pad brush 170.

In particular, the conditioner 150 can be a strip of metal having diamond particles on a surface thereof which can make tight contact with the polishing pad 120a. Alternately, a brush can be used as the conditioner 150 to reduce damage to the surface of the polishing pad 120a depending on the composition of the polishing pad. When using a brush as the conditioner, the brush preferably has thick and stiff bristles to provide adequate conditioning of the polishing pad 120a.

Fine grooves can be formed on the surface of the polishing pad 120a so that a slurry can be provided to the center of the semiconductor substrate 130 even when tight contact is made between the surface of the polishing pad 120a and the surface of the semiconductor substrate 130.

The polishing pad brush includes bristles 173 formed from an elastic synthesized resin wherein each of the bristles has a diameter in the range of 10 .mu.m to 2,000 .mu.m. Each of the bristles 173 is attached at one end thereof to the support 175, and the support is connected to the polishing pad brush arm 170. In particular, the bristles can be attached to the support by inserting each of the bristles into the support. Preferably, the diameter of each bristle 173 decreases from the end portion inserted into the support 175 to the other end portion which makes contact with the polishing pad 120a. For example, each bristle 173 can have a cone shape thereby facilitating the removal of particles remaining in the grooves on the polishing pad 120a.

The cleaning portion D includes a second platen 110b having a flat end portion, a second platen rotating shaft 111b for rotating the second platen 110b, and an auxiliary pad 120b on the second platen 110b. As shown, the clamp 140 has an end portion to which the semiconductor substrate 130 can be fixed, and the clamp arm 141 on the substrate 130 can be transferred from the polishing portion C to the cleaning portion D. The auxiliary pad brush 180 is provided for cleaning the auxiliary pad 120b, and the auxiliary pad brush arm 181 is provided for transferring the auxiliary pad brush 180. The auxiliary pad brush 180 and the auxiliary pad brush arm 181 can thus be transferred to and from the cleaning portion D.

The auxiliary pad brush 180 includes bristles 183 formed from an elastic synthesized resin wherein each of the bristles has a diameter in the range of 10 .mu.m to 2,000 .mu.m. Each of the bristles 183 is attached at one end thereof to the support 185, and the support 185 is connected to the polishing pad brush arm 181. In particular, each of the bristles can be connected to the support by inserting one end of each of the bristles into the support. Preferably, the diameter of each bristle 183 decreases from the end inserted into the support 175 to the end which makes contact with the polishing pad 120b.

FIG. 5 is flow chart outlining steps of a chemical-mechanical polishing method using the system illustrated in FIGS. 3, 4A and 4B. In step 200, the surface of the semiconductor substrate 130 is polished by rotating the surface of the semiconductor substrate 130 while maintaining the surface of the semiconductor substrate in tight contact with the polishing pad 120a. In addition, a slurry is deposited onto the polishing pad 120a while rotating the semiconductor substrate 130. In addition, the platen 110a can be simultaneously rotated thereby increasing the polishing efficiency.

The slurry can be a mixture of particles, such as alumina or silica particles, deionized water, and a chemical to provide chemical polishing. The particles contribute to the mechanical polishing while the chemical contributes to the chemical polishing. In addition, KOH or NaOH can be added to the mixture to control the ph-level.

The semiconductor substrate 130 can then be removed from the polishing pad 120a. In step 220, the surface of the polishing pad 120a is cut back to expose a new surface thereof by rotating the conditioner 150 while maintaining the conditioner 150 in tight contact with the polishing pad 120a. Alternately, the conditioning step 220 can be performed simultaneously with the step of polishing the semiconductor substrate 130.

As previously discussed, the conditioning step is performed primarily to cut back the surface of the polishing pad 120a. It may be difficult, however, to remove polishing particle lumps formed by agglutination of particles generated during the polishing step. It may also be difficult to remove polishing particles from the polishing slurry. In particular, it may be extremely difficult to remove polishing particle lumps which may become jammed in grooves formed on the surface of the polishing pad 120a. Even if a brush is used as the conditioner 150, the same results may be obtained because the bristles of a brush used as a conditioner will be thick and stiff.

Accordingly, the surface of the polishing pad 120a is brushed with polishing pad brush 170 as shown in step 240. This brushing step removes particles and polishing particle lumps remaining on the polishing pad 120a after the conditioning step. The brushing step may be performed after the conditioning step. Alternately, the brushing step may be performed simultaneously with the conditioning step.

The brushing step is performed while maintaining the polishing pad brush 170 in tight contact with the polishing pad 120a. Preferably, the polishing pad brush 170 is transferred from the center of the polishing pad 120a to an edge thereof while maintaining tight contact between the polishing pad brush and polishing pad. The polishing pad brush 170 is preferably detached from the polishing pad 120a when the polishing pad brush is transferred from the edge of the polishing pad 120a to the center thereof. By performing the brushing step while moving the brush from the center to the edge of the polishing pad, the brushing efficiency can be increased. The brushing efficiency can be further increased by performing the brushing step while applying a cleaning solution onto the surface of the polishing pad 120a. The brushing efficiency can also be increased by rotating the polishing pad brush during the brushing operation. The brushing step reduces scratching and roughening of semiconductor substrates 130 polished on the polishing pad which has been brushed.

The polished semiconductor substrate 130 is then transferred from the polishing portion C to the cleaning portion D. The polished surface of the semiconductor substrate 130 is then cleaned by rotating the semiconductor substrate 130 while maintaining tight contact between the semiconductor substrate and the auxiliary pad 120b as shown in step 260. In addition, a cleaning solution can be deposited on the surface of the auxiliary pad 120b during the cleaning step. The platen 110b can also be simultaneously rotated to increase cleaning efficiency.

Particle lumps and polishing particles stuck to the surface of the semiconductor substrate 130 during the polishing step may be transferred to the auxiliary pad 120b. Scratches may thus be produced on the surface of the semiconductor substrate 130. Accordingly, auxiliary polishing may be performed in the cleaning portion D to remove scratches produced on the surface of the semiconductor substrate 130 to reduce surface roughness thereof. The auxiliary polishing may also be referred to as slurry buffing or touch up. The auxiliary polishing can be performed by supplying a slurry including polishing particles instead of the cleaning solution to the auxiliary pad 120b. Even though auxiliary polishing is performed, scratches may be generated on the surface of the semiconductor substrate 130. Accordingly, polishing particles and particle lumps remaining on the cleaning pad 120b are preferably removed by brushing the auxiliary pad 120b with the auxiliary pad brush 180 after the cleaning or auxiliary polishing steps. The cleaning efficiency can be increased by rotating the auxiliary pad brush 180. In addition, the second platen 110b and the auxiliary pad brush 180 can be rotated simultaneously. Furthermore, it is preferable to perform a brushing while a cleaning solution is deposited onto the auxiliary pad 120b.

As discussed above, the scratching and roughness of a semiconductor substrate 130 can be reduced by efficiently removing particles and polishing particle lumps from the polishing pad 120a and the auxiliary pad 120b with a brush.

In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.