JP2000354948A - Substrate polishing method and substrate polishing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend longevity of an abrasive cloth, reduce cost and carry out high quality polishing for a long period of time. SOLUTION: An abrasive cloth cleaning device 13 is set above a polishing surface plate 2. The abrasive cloth cleaning device 13 is furnished with an abrasive cloth cleaning mechanism 9, a dry ice particle spouting mechanism 14 and an oscillating mechanism 15. Loading removal of an abrasive cloth 3 is carried out by the dry ice particle spouting mechanism 14 furnished on the abrasive cloth cleaning device 13. As dry ice particles are spouted to the abrasive cloth 3, foreign matter causing loading is hit out to a surface of the abrasive cloth 3. As dry ice works on the abrasive cloth 3 as gas when it sublimates, the abrasive cloth 3 is rarely given mechanical damage. Consequently, as it is possible to extensively reduce consumption of the abrasive cloth in comparison with a conventional method, it is possible to realize increase of longevity of the abrasive cloth 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing method and a substrate polishing apparatus for performing chemical mechanical polishing (CMP) for flattening a surface on which elements are formed on a semiconductor substrate, a liquid crystal substrate or the like. It is about.

[0002]

2. Description of the Related Art In recent years, the density of a semiconductor manufacturing process has been increased,
Various microfabrication techniques have been researched and developed with miniaturization. Among them, chemical mechanical polishing (Chemical Mechanical polishing)
Polishing, CMP) is an indispensable technology for flattening the interlayer insulating film of the multilayer wiring structure, forming contact plugs, isolating buried elements, and forming buried wiring in miniaturized and high-density semiconductor devices. ing.

In the CMP method, a semiconductor substrate is polished by supplying an abrasive containing abrasive grains such as silica between a polishing cloth (pad) and the semiconductor substrate. This polishing cloth has an average roughness of 1.0 to 1.5 μm before polishing (excluding air bubbles), and the polishing cloth has bubbles of several tens μm in size on its surface. There are many (pores). The irregularities on the surface and the bubbles play a role not only in friction but also in holding abrasive grains in the abrasive.

As the polishing of the semiconductor substrate progresses, the surface roughness of the polishing cloth gradually decreases. For example, about 3 semiconductor substrates
After polishing for a minute, a smooth portion having an average roughness of 0.05 to 0.5 μm starts to be formed on the polishing cloth surface. It is recognized that the adhering ability capable of retaining the abrasive grains is reduced. Further, it is recognized that the pores are clogged by the abrasive and the polishing debris, and the ability to retain the abrasive at the pores is reduced. As a result, the polishing rate decreases. Therefore, in order to suppress a decrease in the polishing rate by returning the surface roughness of the polishing cloth to the same state as the initial state before the polishing, the dressing of the polishing cloth surface using a dresser (dressing) has conventionally been generally performed. It has been done.

FIG. 4 is a sectional view of a conventional substrate polishing apparatus. Reference numeral 2 denotes a rotatable polishing plate made of a rigid body having a flat surface. On the polishing platen 2, an elastic polishing cloth 3 is adhered. A carrier 4 for holding a semiconductor substrate 7 is arranged above the polishing platen 2. The carrier 4 is connected to a rotating shaft 5. The polishing platen 2 is connected to the rotating shaft 1. The carrier 4 is configured such that the semiconductor substrate 7 can be pressed against the polishing pad 3 at a predetermined pressure during polishing.

[0006] In the substrate polishing apparatus, the semiconductor substrate 7 is held by the carrier 4, and after the semiconductor substrate 7 is placed on the polishing cloth 3, a downward pressing force is applied to the rotating shaft 5. In this state, an abrasive containing abrasive grains is applied to the polishing pad 3.
The polishing platen 2 and the carrier 4 are rotated in the same direction while being dropped on the polishing table. As a result, the polishing surface of the semiconductor substrate 7 comes into sliding contact with the polishing cloth 3, and the unevenness on the surface of the semiconductor substrate 7 is gradually flattened.

FIG. 5 is a sectional view of a conventional substrate polishing apparatus equipped with a dresser 16. A dresser 16 for “sharpening” the surface of the polishing pad 3 is provided above the polishing platen 2.
Is provided. Diamond particles are electrodeposited in the contact area of the dresser 16 with the polishing pad 3. This dresser 16 is, as described above,
The surface roughness of the polishing pad 3 is provided for the purpose of regenerating the surface roughness of the polishing pad 3 because the surface roughness decreases as the polishing proceeds.

During polishing, the dresser 16 is separated from the polishing platen 2 and is located above the polishing platen 2 or the polishing platen 2.
Waiting in a different place than above. After the polishing, the dresser 16 is placed on the polishing pad 3 and brought into contact with the polishing pad 3, and then the polishing pad 3 is dressed, so that a decrease in the polishing rate is suppressed.

[0009]

The surface of the generally used polishing pad 3 is provided with holes having a diameter of 1 to 2 mm or lattice-like (or concentric) grooves having a width of several mm. ing. These are the holding of the abrasive on the polishing cloth 3, the polishing cloth 3
The purpose of the present invention is to improve the diffusibility of the polishing agent throughout, prevent sticking of the wafer, and the like.

However, in the conventional substrate polishing apparatus, when dressing is performed by a dresser 16 on which diamond particles are electrodeposited after polishing in order to regenerate the polishing cloth 3, the surface of the polishing cloth 3 is about several μm per dressing. Will be shaved. Therefore, when the number of times of dressing increases, the depth of holes or lattice-shaped (or concentric) grooves on the surface of the polishing pad 3 is greatly reduced, so that holding of the polishing pad on the polishing pad 3 and diffusion of the polishing pad are hindered. You. As a result, the polishing characteristics are deteriorated and a transfer error occurs due to wafer suction. Therefore, the used polishing pad 3 is replaced with a new polishing pad 3. That is, there is a problem that the life of the polishing pad 3 is short. At present, the polishing cloth 3 generally used reaches the end of its life after about 150 to 200 dressings. Such a life of the polishing pad 3 not only increases the manufacturing cost of the semiconductor product by the CMP process, but also causes a reduction in the operation rate due to frequent replacement of the polishing pad 3.

When the number of times of dressing is increased, abrasion and falling off of the diamond particles occur.
The polishing cloth 3 cannot be sufficiently cut. For this reason, the polishing rate by the polishing cloth 3 decreases. The life of the dresser 16 is when the polishing rate does not return to the original value even after the dressing.

Further, the diamond particles electrodeposited on the dresser 16 are not uniform in shape and particle diameter, and the protrusion amount varies. Therefore, the characteristics of the polishing pad 3 also vary due to differences in the shape and particle size of the diamond particles on the dresser 16.

Further, the drop of diamond particles due to the dressing causes micro-scratch on the semiconductor substrate 7, thereby lowering the yield.
Further, there is a problem of high cost due to the use of diamond particles.

The present invention has been made in view of the above-mentioned circumstances, and its main purpose is to extend the life of the polishing pad 3. Furthermore, the present invention provides a low-cost, high-quality polishing pad. The present invention provides a substrate polishing method and a substrate polishing apparatus that can be used for a long period of time.

[0015]

According to the present invention, there is provided a method for polishing a substrate, comprising the steps of: (a) performing chemical mechanical polishing with a polishing cloth;
A step (b) of removing clogging of the polishing cloth by spraying sublimable particles onto the polishing cloth.

In the substrate polishing method of the present invention, particles having the property of sublimation are ejected, and when the particles collide with the polishing pad, the polishing is performed by utilizing the expansion of the volume when the particles instantaneously sublime. Efficiently removes abrasive particles, polishing debris, and the like that cause clogging of the cloth. Therefore, these particles act on the polishing pad as a gas after sublimation, so that the surface of the polishing pad is not cut and there is almost no mechanical damage to the polishing pad. That is, the polishing cloth is hardly consumed. Therefore, a longer life of the polishing cloth can be realized.

Further, in the substrate polishing method of the present invention,
Injection of particles having the property of sublimation, in order to regenerate the polishing cloth, unlike the conventional method in which the same diamond particles are repeatedly used, it is possible to suppress the polishing rate from decreasing as the number of times of regenerating the polishing cloth increases. . Therefore, in the substrate polishing method of the present invention, high-efficiency polishing can be performed for a long period of time.Furthermore, in the substrate polishing method of the present invention, unlike the conventional method, since diamond particles are not used, there is no micro scratch. Along with high quality polishing, cost reduction can be realized.

The method for polishing a substrate of the present invention may further comprise, after the step (b), a step (c) of spraying a liquid onto the polishing cloth to wash the polishing cloth.

In the substrate polishing method of the present invention, the particles having the property of sublimation are preferably dry ice particles.

In the substrate polishing method of the present invention, the liquid is preferably pure water.

[0021] The substrate polishing apparatus of the present invention includes a polishing cloth for performing chemical mechanical polishing and means for jetting particles having a sublimation property onto the polishing cloth.

In the substrate polishing apparatus of the present invention, particles having the property of sublimation are jetted, and when the particles collide with the polishing pad, the particles are instantaneously sublimated by utilizing the expansion of the volume. Efficiently removes abrasive particles, polishing debris, and the like that cause clogging of the cloth. Therefore, these particles act on the polishing pad as a gas after sublimation, so that the surface of the polishing pad is not cut and there is almost no mechanical damage to the polishing pad. That is, the polishing cloth is hardly consumed. Therefore, a longer life of the polishing cloth can be realized.

In the substrate polishing apparatus of the present invention,
Injection of particles having the property of sublimation, in order to regenerate the polishing cloth, unlike the conventional method in which the same diamond particles are repeatedly used, it is possible to suppress the polishing rate from decreasing as the number of times of regenerating the polishing cloth increases. . Therefore, in the substrate polishing apparatus of the present invention, high-efficiency polishing can be performed for a long time.Furthermore, in the substrate polishing apparatus of the present invention, unlike the conventional method, since diamond particles are not used, there is no micro-scratch. Along with high quality polishing, cost reduction can be realized.

[0024] In the substrate polishing apparatus of the present invention, a means for jetting a liquid to the polishing cloth may be further provided.

In the substrate polishing apparatus of the present invention, the particles having the property of sublimation are preferably dry ice particles.

In the substrate polishing apparatus of the present invention, the liquid is preferably pure water.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A substrate polishing apparatus according to the present embodiment includes a polishing section for polishing a substrate and a polishing cloth cleaning apparatus 1.
3 is provided.

FIG. 1 is a sectional view of a polishing section for polishing a substrate according to the present embodiment. The polishing section mainly includes a polishing platen 2 and a carrier 4 installed above the polishing platen 2.
Consists of A rotating shaft 1 is attached to a lower portion of the polishing platen 2. A polishing cloth 3 is adhered on the polishing platen 2. On the other hand, a rotating shaft 5 is mounted on the upper part of the carrier 4. Further, a rotating mechanism 10 and a pressing mechanism 11 are attached to the rotating shaft 5. A part of the rotating shaft 5, the rotating mechanism 10 and the pressing mechanism 11 are incorporated in the carrier holding unit 6.

The polishing platen 2 can rotate at a constant speed about the rotating shaft 1. The carrier 4 is a semiconductor substrate 7
Hold. The carrier 4 can be rotated at a constant speed around the rotating shaft 5 by a rotating mechanism 10 such as a motor. The carrier 4 can hold the semiconductor substrate 7 on its lower surface by a suction method or the like. Further, the carrier 4 is driven by a pressurizing mechanism 11 using a hydraulic or pneumatic cylinder as a driving source.
It is supported above the polishing platen 2 so as to be able to move up and down. When polishing is performed, pressure is applied from the back surface of the semiconductor substrate 7 to the polishing platen 2 via the carrier 4 holding the semiconductor substrate 7 so that the surface to be polished of the semiconductor substrate 7 is The polishing unit is configured so that it can be pressed. In the polishing section, the pressurizing mechanism 11 using pressurized air uniformly pressurizes the semiconductor substrate 7. Therefore, the pressurizing mechanism 11 using pressurized fluid (for example, Japanese Patent Application Laid-Open No. H8-339979). ) Should be provided.

FIG. 2 is a sectional view of the polishing cloth cleaning device 13. Above the polishing table 2, a polishing cloth cleaning device 13 is installed. The polishing cloth cleaning device 13 includes a polishing cloth cleaning mechanism 9,
A dry ice particle injection mechanism 14 and a swing mechanism 15 are provided. The polishing cloth cleaning mechanism 9 is connected to the pure water spray nozzle 8. Further, the dry ice particle injection mechanism 14 is connected to the dry ice injection nozzle 12.

After the polishing, the polishing pad 3 is clogged with abrasives and polishing debris, so that the polishing rate is lowered. To prevent this, above the polishing platen 2,
A polishing cloth cleaning device 13 for removing clogging of the polishing cloth 3 and cleaning the polishing cloth 3 is provided.

The removal of the clogging of the polishing pad 3 is performed by a dry ice particle spraying mechanism 14 provided in the polishing pad cleaning device 13. Dry ice particles are jetted onto the polishing pad 3 by high-pressure air from a dry ice jet nozzle 12 connected to the dry ice particle jetting mechanism 14.
At this time, the dry ice particles instantaneously become gas (CO ₂ gas) and blow off the clogging, so that the foreign matter causing the clogging is beaten to the surface of the polishing pad 3. The removal of foreign matter adhering to the surface of the polishing cloth 3
This is performed by the polishing cloth cleaning mechanism 9 provided in the polishing cloth cleaning device 13. Pure water is sprayed onto the surface of the polishing cloth 3 from a pure water spray nozzle 8 connected to the polishing cloth cleaning mechanism 9.
As a result, foreign matter is washed away from the polishing pad 3. The swing mechanism 15 can swing the pure water spray nozzle 8 and the dry ice spray nozzle 12 above the entire surface of the polishing pad 3.

Next, a method for removing the clogging of the polishing pad 3 after polishing the semiconductor substrate 7 using a polishing section for polishing will be described in detail.

After the semiconductor substrate 7 has been polished, the carrier 4 is transported from above the polishing platen 2 to the wafer unloading unit at another location by the carrier holding unit 6.

Next, while rotating the polishing platen 2, the dry ice spray nozzle 12 is simultaneously swung by the swinging mechanism 15 so as to move from above the center of the polishing pad 3 to above the peripheral portion of the polishing pad 3. . In this state, dry ice particles are jetted from the dry ice particle jet nozzle 12 to the polishing pad 3 by high-pressure air. In the present embodiment, the particle size of the dry ice particles used is 300 μm. This value is considerably larger than the pore size of the polishing pad 3 which is several tens μm, but it has been confirmed that the clogging can be completely removed. The injection conditions were an air pressure of 4.2 kg / cm ² and an injection time of 30 seconds.

When the dry ice particles are sprayed on the polishing pad 3, the dry ice particles accelerated by the high pressure air collide with the surface of the polishing pad 3. It is considered that the polishing cloth 3 is mechanically roughened by the collision, so that the roughness of the polishing cloth 3 is increased. The kinetic energy of the accelerated dry ice particles is converted into heat when the kinetic energy collides with the polishing pad 3. At this time, the volume expands because the dry ice particles are instantaneously vaporized into CO ₂ gas. It is considered that the clogged particles (abrasives, polishing debris, etc.) are beaten to the surface of the polishing pad 3 due to the expansion of the volume.

Next, while the polishing platen 2 is being rotated, the pure water jet nozzle 8 is simultaneously swung by the swinging mechanism 15 so as to move from above the central portion of the polishing pad 3 to above the peripheral portion of the polishing pad 3. Let it. In this state, pure water is injected from the pure water injection nozzle 8 to the polishing pad 3. As a result, foreign matter is washed away from the polishing pad 3.

After the cleaning of the polishing pad 3 is completed, the semiconductor substrate 7 to be polished next is loaded onto the carrier 4, and
The carrier 4 is transported by the carrier holding unit 6 above the polishing platen 2. Thereafter, the semiconductor substrate 7 is polished again. The step of removing the clogging described above may be performed at a fixed number of times of polishing in addition to each time of polishing, and can be determined according to the degree of clogging.

FIG. 3A is a scanning electron microscope photograph of the surface of the polishing pad 3 after the substrate is polished by the polishing section for polishing the substrate according to the present embodiment. FIG. 3B shows a conventional dresser 1 electrodeposited with diamond particles shown in FIG.
6 is a scanning electron micrograph of the surface of the polishing pad 3 after dressing by No. 6. FIG. 3C is a scanning electron micrograph of the surface of the polishing pad 3 after removal of the clogging of the polishing pad 3 and cleaning by the polishing pad cleaning apparatus 13 according to the present embodiment.

As shown in FIG. 3A, after polishing the substrate, the pores are closed in the polishing pad 3 due to clogging. On the surface of the polishing cloth 3, the average roughness is 0.0
A smooth surface of 5 to 0.5 μm is formed. When the next polishing was performed in this state, the polishing rate was reduced by about 10%. This is because the polishing agent does not sufficiently adhere to the polishing pad 3 due to clogging, and the polishing pad 3 does not hold the polishing agent.

As shown in FIG. 3B, after dressing with diamond particles, a large number of pores due to foaming are present on the surface of the polishing pad 3. The polishing cloth 3 after dressing has a surface roughness having an average roughness of 1.0 to 1.5 μm in a portion having no pore.

On the other hand, as shown in FIG. 3C, after the clogging is removed and washed according to the present embodiment, the clogging can be removed, so that the pores are opened on the surface of the polishing pad 3, and the pores are opened. The polishing pad 3 recovered to a surface roughness having an average roughness of about 1 μm even in a portion having no pore. This result is almost the same as the result of dressing using the conventional diamond particles shown in FIG. Moreover,
When the amount of consumption of the polishing pad 3 after the removal and washing of the clogging according to the present embodiment was evaluated, there was no consumption that could be clearly measured.

As described above, in the present embodiment, instead of dressing the polishing pad with a dresser on which diamond particles are electrodeposited, dry ice particles are ejected by high-pressure air and the dry ice particles collide with the polishing pad. At this time, the method is characterized in that the expansion of the volume when the dry ice particles instantaneously sublimate is used to efficiently remove abrasive particles, polishing debris, and the like that cause clogging of the polishing pad. Further, in the present embodiment, since the dry ice acts on the polishing pad 3 as a gas after sublimation, the surface of the polishing pad 3 is not cut, and the polishing pad 3 is hardly mechanically damaged. Absent. That is, the polishing cloth 3 is hardly consumed. Therefore, the consumption of the polishing pad 3 can be greatly reduced as compared with the conventional method, so that the life of the polishing pad 3 can be extended.

In this embodiment, since the polishing pad 3 is regenerated by spraying dry ice particles, unlike the conventional method in which the same diamond particles are repeatedly used, the number of times the polishing pad 3 is regenerated increases. The polishing rate can be prevented from being lowered. That is, according to the present embodiment, highly efficient polishing can be performed for a long period of time. Further, in the present embodiment, by using dry ice particles having a constant shape and particle size, it is possible to suppress occurrence of variation in the regeneration of the polishing pad 3.

In this embodiment, unlike the conventional method, no diamond particles are used and no particles that damage the semiconductor substrate 7 are generated.
Micro scratches on the surface can be eliminated. Therefore, in the present embodiment, a decrease in yield due to micro scratches can be suppressed, and high-quality polishing can be performed. Furthermore, since diamond particles are not used, cost reduction can be realized.

The method according to the present embodiment also has an effect of appropriately reducing the roughness of a portion without clogging (a portion without pores) due to the mechanical polishing action by the collision of dry ice particles. Further, in the present embodiment, the injection time of the dry ice particles is set to 30 seconds, but clogging can be removed even if the time is further shortened. Although the air pressure is set to 4.2 kg / cm ² , it is preferable to set the air pressure lower than this value in order to reduce the mechanical polishing action.

In this embodiment, in the step of removing the clogging of the polishing pad 3, dry ice particles are sprayed. Instead of the dry ice particles, particles having a subliming property such as iodine and camphor are used. May be used.
Further, in the present embodiment, pure water is injected in the step of cleaning the polishing pad 3, but a liquid such as ammonia-added water may be used instead of pure water.

[0048]

In the substrate polishing method and the substrate polishing apparatus according to the present invention, the expansion of the volume when the particles instantaneously sublimate when the particles collide with the polishing pad by jetting the particles having the property of sublimation. Utilization of the polishing cloth effectively removes abrasive particles and polishing debris that cause clogging of the polishing cloth, thereby hardly causing mechanical damage to the polishing cloth, thereby realizing a longer life of the polishing cloth. be able to.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a polishing section for polishing a substrate according to an embodiment.

FIG. 2 is a sectional view of the polishing cloth cleaning apparatus.

FIG. 3 is a scanning electron micrograph of the surface of the polishing cloth after polishing the substrate by the polishing unit for polishing the substrate according to the present embodiment, and the surface of the polishing cloth after dressing using a conventional dresser electrodeposited with diamond particles. 1 and a scanning electron micrograph of the surface of the polishing pad after removal of clogging and cleaning of the polishing pad by the polishing pad cleaning apparatus according to the present embodiment.

FIG. 4 is a sectional view of a conventional substrate polishing apparatus.

FIG. 5 is a cross-sectional view of a conventional substrate polishing apparatus equipped with a dresser.

[Description of Signs] 1 Rotary shaft 2 Polishing platen 3 Polishing cloth 4 Carrier 5 Rotary shaft 6 Carrier holding unit 7 Semiconductor substrate 8 Pure water spray nozzle 9 Polishing cloth cleaning mechanism 10 Rotary mechanism 11 Pressurizing mechanism 12 Dry ice spray nozzle 13 Polishing cloth cleaning device 14 Dry ice particle injection mechanism 15 Swing mechanism 16 Dresser

Claims (8)

[Claims] A step of performing chemical mechanical polishing with a polishing cloth; and a step of removing clogging of the polishing cloth by jetting particles having a sublimation property onto the polishing cloth. A substrate polishing method comprising: 2. The substrate polishing method according to claim 1, further comprising a step (c) of washing the polishing cloth by spraying a liquid onto the polishing cloth after the step (b). 3. The substrate polishing method according to claim 1, wherein the sublimable particles are dry ice particles. 4. The substrate polishing method according to claim 1, wherein the liquid is pure water. 5. A substrate polishing apparatus comprising: a polishing cloth for performing chemical mechanical polishing; and means for jetting particles having a sublimation property onto the polishing cloth. 6. The substrate polishing apparatus according to claim 5, further comprising means for injecting a liquid onto said polishing cloth. 7. The substrate polishing apparatus according to claim 5, wherein the sublimable particles are dry ice particles. 8. The substrate polishing apparatus according to claim 5, wherein the liquid is pure water.