Method for Dressing Polishing Pad, Method for Polishing Silicon Wafer, Method for Producing Silicon Wafer, and Device for Polishing Silicon Wafer

This disclosure relates to a method for dressing a polishing pad, a method for polishing a silicon wafer, a method for producing a silicon wafer, and a device for polishing a silicon wafer.

In the manufacture of silicon wafers, which are a typical example of semiconductor device substrates, a double-side polishing process, in which front and back side surfaces of a silicon wafer are polished, and a single-side polishing process, in which one of front and back side surfaces of a silicon wafer is polished, are generally employed to obtain more precise wafer flatness quality and surface roughness quality.

In the double-side polishing process, a silicon wafer is held on a carrier plate, the carrier plate is sandwiched between a pair of rotating plates consisting of an upper plate and a lower plate to which polishing pads are attached, the rotating plates and the carrier plate are rotated relative to each other while a polishing fluid is supplied, and thus the front and back surfaces of the silicon wafer is polished simultaneously.

On the other hand, in the single-side polishing process, a silicon wafer is placed on a rotating plate to which a polishing pad is attached, the silicon wafer is pressed by a polishing head while the rotating plate and the polishing head rotate relative to each other with a supply of polishing fluid, and thus one of the front and back surfaces of the silicon wafer is polished.

When the above double-side or single-side polishing processes are performed repeatedly, abrasive grains and polishing debris contained in the polishing solution adhere to the polishing pad attached to the rotating plate, degrading the performance of the polishing pad and causing problems such as reduced polishing speed and unevenness in polishing. Therefore, a dressing process is periodically applied to the polishing pads to restore their performance.

For example, Patent Document 1 describes an art for regenerating a polishing pad by pressing a diamond dresser with diamond particles electrodeposited on its lower surface against the polishing pad and sliding the diamond dresser thereon to roughen the polishing pad, and then pressing a brush dresser with brushes on its lower surface against the polishing pad and sliding the brush dresser thereon to effectively remove foreign matter clogged in the recesses on the polishing surface of the polishing pad, even when the polishing pad has a recess.

In the art described in PTL 1, the dressing surface of the dresser is flat. When dressing a polishing pad using a dresser with a flat dressing surface, the accuracy of the dresser installation and the angle at which the dresser is pressurized cause differences in pressing force, at the inner and outer edges of the rotating plate, in the radial direction of the rotating plate, resulting in variation in the removal allowance in the radial direction of the rotating plate. Also, when the surface of the rotating plate is curved like a bowl or inverted bowl, the edge of the dresser is pressed more strongly against the polishing pad at the inner and outer edges of the rotating plate, which also causes variations in the removal allowance in the radial direction of the rotating plate.

In view of the above problem, it is an object of the present disclosure to propose a method for dressing a polishing pad that enables more even dressing of the polishing pad, even when the surface of the rotating plate is curved.

[1] A method for dressing a polishing pad performing dressing of the polishing pad by pressing a grindstone of a pad dresser having the grindstone attached thereto against the polishing pad attached to a polishing plate and sliding the grindstone thereon, wherein

[2] The method for dressing a polishing pad as described in [1], wherein changing the radius of curvature R1 of the dressing surface of the grindstone to be smaller than a radius of curvature R2 of a surface of the polishing pad, and then performing dressing of the polishing pad.

[3] The method for dressing a polishing pad as described in [1] or [2],wherein using a pad dresser in which the grindstone has a plurality of dressing surfaces with different radius of curvatures, and the radius of curvature R2 of the dressing surface that slides on the polishing pad can be changed by rotating the grindstone.

[4] The method for dressing a polishing pad as described in [1] or [2],wherein using a pad dresser in which a base material of the grindstone is made of an alloy capable of flexing, and the radius of curvature Rof the dressing surface can be changed by pressing the grindstone from an opposite side of the dressing surface.

[5] The method for dressing a polishing pad as described in [4], wherein using a pad dresser in which the grindstone is attached to the pad dresser via a retainer, two ends of the base material of the grindstone are coupled to the retainer, and the radius of curvature R1 of the dressing surface can be changed by pressing a portion of the grindstone on an opposite side of the dressing surface with a pressing member.

[6] The method for dressing a polishing pad as described in [4], wherein using a pad dresser in which the grindstone is attached to the pad dresser via a retainer that has a different coefficient of thermal expansion than the base material of the grindstone, and the radius of curvature Rof the dressing surface can be changed by changing temperature of the retainer.

[7] A method for polishing a silicon wafer, wherein comprising polishing a silicon wafer using a polishing pad that has been dressed using the method for dressing a polishing pad according to above [1] or [2].

[8] A method for producing a silicon wafer, wherein comprising polishing a silicon wafer obtained by performing wafer processing treatment on a single crystal silicon ingot grown by a predetermined method, using the method for polishing a silicon wafer according to above [7].

[9] A device for polishing a silicon wafer comprising a polishing plate; a polishing pad attached to the polishing plate; and a pad dresser having a grindstone attached thereto, and dresses the polishing pad, wherein

[10] A device for polishing a silicon wafer as described in above [9],wherein the grindstone has a plurality of dressing surfaces with different radius of curvatures, so that the device is configured to allow the radius of curvature R1 of the dressing surface that slides on the polishing pad to be changed by rotating the grindstone.

[11] A device for polishing silicon wafer as described in above [10], wherein a base material of the grindstone is made of an alloy capable of flexing, so that the device is configured to allow the radius of curvature Rof the dressing surface to be changed by pressing the grindstone from an opposite side of the dressing surface.

[12] A device for polishing silicon wafer as described in above [11], wherein the grindstone is attached to the pad dresser via a retainer and two ends of the base material of the grindstone are coupled to the retainer, so that the device is configured to allow the radius of curvature R1 of the dressing surface to be changed by pressing a portion of the grindstone on an opposite side of the dressing surface with a pressing member.

[13] A device for polishing a silicon wafer as described in claim [11], wherein the grindstone is attached to the pad dresser via a retainer that has a different coefficient of thermal expansion than the base material of the grindstone, so that the device is configured to allow the radius of curvature R1 of the dressing surface to be changed by changing temperature of the retainer.

Even if the surface of the rotating plate is curved, the polishing pad can be dressed more evenly.

Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. The method for dressing a polishing pad according to this disclosure is a method for dressing a polishing pad performing dressing of the polishing pad by pressing a grindstone of a pad dresser having the grindstone attached thereto against the polishing pad attached to a polishing plate and sliding the grindstone thereon. Here, this method is characterized in using a pad dresser which is configured to allow a radius of curvature R1, in the radial direction of the polishing plate, of a dressing surface of the grindstone that slides on the polishing pad to be changed.

As mentioned above, when dressing a polishing pad using a dresser with a flat dressing surface as in the art described in PTL 1, the accuracy of the dresser installation and the angle at which the dresser is pressurized cause differences in pressing force, at the inner and outer edges of the rotating plate, in the radial direction thereof, resulting in variation in the removal allowance in the radial direction of the rotating plate. Also, when the surface of the rotating plate is curved like a bowl or inverted bowl, the edge of the dresser is pressed more strongly against the polishing pad at the inner and outer edges of the rotating plate, which also causes variations in the removal allowance in the radial direction of the rotating plate.

We have thoroughly studied ways to dress a polishing pad more evenly when the surface of the rotating plate is curved. As a result, we conceived the idea of using a pad dresser which is configured to allow the radius of curvature, in the radial direction of the polishing plate, of the dressing surface of the grindstone that slides on the polishing pad (hereinafter, simply referred to as “radius of curvature of dressing surface”) R1 to be changed. We then found that by using such a pad dresser, it is possible to dress a polishing pad with a constant pressing pressure by changing the radius of curvature of the dressing surface to match the curvature of the rotating plate.

are respectively a perspective view and a top view of a drawing for explaining a method for dressing a polishing pad according to the present disclosure.illustrates the case of dressing a polishing padattached to the surface of a lower polishing plate of a double-side polishing device. As illustrated in, a pad dresserhas an armand a grindstoneattached to the arm, and the grindstoneis fixed to an end portionof the armvia a retainer. The grindstonecomprises a base materialand abrasive grains (not illustrated) adhered to the surface of the base materialThe abrasive grains are adhered to at least a dressing surfaceof the grindstone.

The radius of curvature Rof the dressing surfaceof the grindstoneis configured to be changeable. By changing the radius of curvature Rof the dressing surfaceto match the curvature of the rotating plate, the polishing padcan be dressed with a constant pressing pressure to dress the polishing padmore evenly. The specific pad dresserthat can change the radius of curvature Rwill be described in detail later.

In the present disclosure, the “dressing surface of the grindstone” means the surface of the grindstonethat slides on the polishing padwhen dressing the polishing pad, and in, the dressing surfaceis the entire lower surface of the grindstone. In addition, the “radius of curvature of the dressing surface” means the radius Rof the arc when fitting an arc to the surface profile, in the radial direction of the polishing plate, for the dressing surfaceof the grindstonethat slides on the polishing pad, as illustrated in. The surface profile of the dressing surfacecan be measured using a commercially available non-contact shape measuring instrument. Also, fitting of arcs can be performed by the least-squares method or other methods.

As illustrated in, the pad dresserconfigured as described above is moved from one of the inner and outer edges of the lower plate to the other while rotating the lower plate, so that to dress the entire polishing pad.

In the present disclosure, it is preferable to change the radius of curvature Rof the dressing surfaceof the grindstoneto be smaller than a radius of curvature Rof a surface of the polishing pad, and then to perform dressing of the polishing pad. By making the radius of curvature Rof the dressing surfacesmaller than the radius of curvature Rof the surface of the polishing pad, dressing can be performed with a more constant pressing pressure and the polishing padcan be dressed more evenly. The radius of curvature Rof the dressing surfaceis preferably 10 mm or more. This ensures that the contact area between the grindstoneand the polishing padis sufficient to perform even and efficient dressing of the entire polishing pad.

The “radius of curvature of the polishing pad” means the radius Rof the arc when fitting an arc to the surface profile, in the radial direction of the polishing plate, for the surfaceof the polishing pad, as illustrated in. Here, the surface profile is the profile of the entire surface of the polishing padfrom one end (e.g., the inner edge) to the other end (e.g., the outer edge). The surface profile of the polishing padcan be measured using a commercially available non-contact shape measuring instrument as well as a dedicated surface profiler. Also, fitting of arcs can be performed by the least-squares method or other methods.

illustrates an example of a pad dresser that can be used in the present disclosure, configured to allow the radius of curvature of the dressing surface of the grindstone to be changed. The pad dresserillustrated inA has a grindstone, which has a base materialand abrasive grains (not illustrated) adhered to at least the dressing surface of the base materiala. The grindstonehas four dressing surfaces with different radius of curvatures:(radius of curvature: 50.0 mm),(radius of curvature: 100.0 mm),(radius of curvature: 250.0 mm), and(radius of curvature: 500.0 mm).

The grindstoneis connected to an armvia a rotating shaftand a cylinder, as illustrated in. The dresser is configured to allow the radius of curvature Rof the dressing surface to be changed by rotating the grindstonein the radial direction of the plate around the rotating shaft. The grindstoneand the rotating shaftcan be fixed by screwing, for example, as illustrated in.

For example, SUS with a DLC coated surface can be used as the base material of the grindstone. In addition, for example, diamond or ceramic abrasive grains can be used as the abrasive grains.

In the pad dresserhaving this configuration, the dressing surface of the grindstoneis appropriately selected according to the surface profile of the polishing plate to which the polishing padis attached. The cylinderthen slides the selected dressing surface (in, the dressing surface) onto the rotating polishing pad. This allows dressing of the polishing padwith a constant pressing pressure, thus dressing the polishing padmore evenly.

The pad dresserillustrated inhas four dressing surfacestobut may have two, three, or five or more dressing surfaces. In addition, the radius of curvature Rof the dressing surfacestois not limited to the above values, but can be set appropriately according to the surface profile of the polishing plate to which the polishing padis attached.

As illustrated in, unlike the pad dresserabove, it is also possible to use a pad dresser in which a base material of the grindstone is made of an alloy capable of flexing and the radius of curvature Rof the dressing surface can be changed by pressing the grindstone from an opposite side of the dressing surface.

illustrates another example of a pad dresser that can be used in the present disclosure, configured to allow the radius of curvature of the dressing surface of the grindstone to be changed. In, only the configuration near the grindstone of the pad dresser is illustrated.

The pad dresser, illustrated in, has an arm(not illustrated) and a grindstone. The grindstoneis secured to a retainerby two fixtures, and the retaineris secured to an end portionof the arm(not illustrated). The pad dresseralso comprises a pressing member, and is configured to allow the radius of curvature Rof the dressing surfaceto be changed by pressing a portion of the grindstoneon an opposite side of the dressing surfacewith the pressing member.

The metal capable of flexing that composes the base materialof the grindstoneis not limited as long as it can be flexed by the pressing member, and SUS, titanium, aluminum, superelastic alloys, and the like can be used.

The pad dresserillustrated incan reduce the radius of curvature Rof the dressing surfaceby increasing the force of pressing the grindstoneby the pressing member, causing the grindstoneto deform as illustrated by the dotted line in. In this way, the radius of curvature Rof the dressing surfaceis changed to match the surface profile of the polishing plate, and by sliding the grindstoneon the rotating polishing pad, the polishing padis dressed with a constant pressing pressure to dress the polishing padmore evenly.

illustrates yet another example of a pad dresser that can be used in the present disclosure, configured to allow the radius of curvature of the dressing surface of the grindstone to be changed. In, only the configuration near the grindstone of the pad dresser is illustrated.

The pad dresser, illustrated in, comprises an arm(not illustrated) and a grindstone. The grindstoneis secured by a fixtureto a retainer, which has a different coefficient of thermal expansion than a base materialand is attached to an end portionof the arm(not illustrated) via the retainer. A channelthrough which the liquid W flows is provided inside the retainer.

A liquid W of a predetermined temperature, such as water, is introduced and circulated in the channelof the retainerconfigured in this way to change the temperature of the grindstoneand the retainer. Then, the difference in the thermal expansion coefficients between the two will deform the grindstone, thereby changing the radius of curvature Rof the dressing surfaceIn this way, the radius of curvature Rof the grindstoneis changed to match the surface profile of the polishing plate, and by sliding the grindstoneon the rotating polishing pad, the polishing padis dressed with a constant pressing pressure to dress the polishing padmore evenly.

Metals with different coefficients of thermal expansion can be used as materials for the base materialof the grindstoneand the retainer. For example, the base materialof the grindstonecan be made of SUS, titanium, aluminum, low thermal expansion alloy (Invar), etc. As for the retainer, it can be made of SUS, titanium, aluminum, etc. Specifically, the base materialof the grindstonecan be made of a low thermal expansion alloy (Invar) and the retainercan be made of SUS, but is not limited to this.

When making the coefficient of thermal expansion of the retainerlarger than that of the base materialof the grindstone, for example, cold water is distributed as the liquid W in a channelof the retainer. This allows the retainerto contract and change the radius of curvature Rof the dressing surfaceof the grindstone. On the other hand, when making the coefficient of thermal expansion of the retainersmaller than that of the base materialof the grindstone, for example, high-temperature water is distributed as the liquid W in the channelof the retainer. This allows the base materialof the grindstoneto expand and change the radius of curvature Rof the dressing surfaceof the grindstone.

illustrates still another example of a pad dresser that can be used in the present disclosure, configured to allow the radius of curvature of the dressing surface of the grindstone to be changed. In, only the configuration near the grindstone of the pad dresser is illustrated.

The pad dresser, illustrated in, comprises an arm(not illustrated) and a plurality of grindstones. Each grindstoneis fixed to the lower surface of a cylinder, and the top of the cylinderis fixed to a retainer. The retaineris then fixed to the end portionof the arm(not illustrated).

In the pad dresser, the entire lower surface of the plurality of grindstonesform a dressing surface, and the radius of curvature Rof the dressing surface can be changed by changing the degree of expansion and contraction of each cylinder. The radius of curvature Rof the dressing surface can be obtained by fitting the profile of the surface composed of the lower surfaces of all grindstoneswith a circular arc.