JP2006121111A - Mechanochemical polishing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mechanochemical polishing method and a mechanochemical polishing apparatus capable of efficiently polishing a hard material such as SiC even with a low processing pressure. <P>SOLUTION: A polishing cloth 2 is stuck on a polishing platen 1. A wafer holding table 3 is arranged above the polishing platen 1, and a SiC wafer 4 is held on the wafer holding table 3. A liquid discharging machine 5 is installed above the polishing platen 1, and chemical liquid (obtained by dispersing chrome oxide abrasive grains in hydrogen peroxide water) 6 is dropped on the polishing cloth 2 from the liquid discharging machine 5. A surface of the SiC wafer 4 to be polished is pressed against the polishing cloth 2 stuck on the polishing platen 1 with a predetermined processing pressure. The wafer holding table 3 and the polishing platen 1 are then rotated to perform a polishing while dropping the chemical liquid 6 on the polishing cloth 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to mechanochemical polishing, and more particularly to a polishing technique using chromium (III) oxide, that is, Cr ₂ O ₃ as abrasive grains.

  A power semiconductor element formed on silicon carbide (hereinafter referred to as SiC) having a physical property value larger than that of silicon (hereinafter referred to as Si) can realize performance superior to that of a Si power semiconductor element. Specifically, it can function as a semiconductor up to a high temperature by a wide energy gap (about 3 times that of Si), can have a high breakdown voltage by a high breakdown voltage (10 times), and has a high thermal conductivity (about 3). 2), the heat dissipation is excellent and the current can be further increased. Specifically, as shown in FIG. 22, for example, a SiC wafer for forming an element is a wafer in which a low impurity concentration SiC layer 101 is formed on a single crystal SiC substrate 100 having a high impurity concentration by epitaxial growth. The A device (for example, VDMOS) 103 of a type that allows current to flow in the vertical direction is formed in the low concentration layer 101. In the field of optical devices, GaN has been studied as a material capable of emitting light of a short wavelength. However, SiC has a smaller lattice mismatch with GaN than sapphire, and thus a SiC wafer forms a GaN thin film. It is also attracting attention as a base substrate.

  For SiC wafers, bulk single crystal SiC, which is grown by recrystallization from SiC powder by sublimation, is cut into a wafer shape, and then the surface (cut surface) is mirror-finished. An SiC layer or a GaN layer is epitaxially grown on this surface. In order to obtain an epitaxial layer with good crystallinity, it is required that the surface be defect-free and smooth at the atomic level.

  In general, mirror finishing of SiC is performed by polishing and smoothing the surface with diamond abrasive grains. This is a mechanical surface processing method in which the surface is cut using abrasive grains (diamond) that is harder than SiC (material to be polished). Here, the smaller the abrasive grain size is, the smoother the surface is (the surface roughness is improved), but it is not possible to suppress the occurrence of defects (working-affected layer) due to processing. Therefore, there has been a problem that a process for removing the work-affected layer such as dry etching after polishing or growing an oxide film by thermal oxidation and then wet etching with hydrofluoric acid must be performed as a post-polishing process.

  Diamond abrasive grains are expensive, and the smaller the particle size, the more expensive. Furthermore, if large abrasive grains are mixed in fine abrasive grains, the surface roughness will not improve, or scratches may occur and deep defects may occur locally. High-quality diamond abrasive grains must be used, and the abrasive grains are expensive in this respect as well. In addition, process management (control of abrasive grain size) becomes difficult. Thus, there was a problem in polishing using diamond abrasive grains.

  If polishing using a material whose hardness is lower than that of the material to be polished, the processing surface can be processed with less damage, but mechanical processing in which the abrasive particle directly cuts the material to be polished cannot be performed. If a polishing method in which mechanically brittle reaction products (oxides, compounds, etc.) are formed on the surface of the material to be polished and then peeled off with soft abrasive grains, so-called mechanochemical polishing (chemical mechanical polishing; MCP) can be achieved. Good. However, since SiC is a chemically stable material, it is difficult to form a reaction product.

  As a mechanochemical polishing method of SiC, a method of polishing SiC using chromium oxide as abrasive grains has been reported (Non-patent Document 1). According to this, it has been reported that polishing (MCP) without residual distortion and scratches can be realized by dry polishing SiC on a disk (fixed abrasive grains) in which chromium oxide abrasive grains are hardened with resin.

  Further, Patent Document 1 proposes a method for improving the surface flatness of SiC by using a chromium oxide powder of loose abrasive grains and a polishing surface plate having a micro Vickers hardness of 1000 to 2000. Yes. These methods are polishing methods in which a reaction layer generated by a direct solid phase reaction between the material to be polished and the abrasive grains is removed by the frictional action of the abrasive grains due to a mechanochemical phenomenon at the contact point between the material to be polished and the abrasive grains.

The polishing method using this solid-phase reaction is a method proposed in Patent Document 2. In Non-Patent Document 1 and Patent Document 1 described above, the material to be polished is SiC and the abrasive grains are chromium oxide in combination. It is a thing.
M. Kikuchi, Y. Takahashi, T Suga, S Suzuki, and Y Bando, "Mechanochemical Polishing of Silicon Carbide Single Crystal with Chromium (III) Oxide Abrasive", J. Am. Ceram. Soc., 75 [1] (1992) 189 Japanese Patent Laid-Open No. 7-80770 Japanese Examined Patent Publication No. 56-23746

However, in order to cause a solid-phase reaction, it is presumed that it is important to bring them into contact at an extremely high pressure at the contact point between the material to be polished and the abrasive grains. In the non-patent document 1, the processing pressure is 0.34 MPa (3.5 kgf / cm ² ), and in Patent document 1, the experiment is performed at 900 kgf / cm ² . When a high processing pressure is required, a very high pressure is applied to the polishing surface plate when polishing a large-diameter wafer. Further, when a plurality of wafers are simultaneously polished on the same polishing surface plate, a higher pressure is applied. Therefore, there has been a problem that the polishing apparatus requires a high rigidity that has not been conventionally available.

  In addition, the processing pressure is applied not only to the wafer surface, which is the contact point with the abrasive grains, but also to the entire SiC wafer, causing crystal distortion and defects, the progression of existing defects, and even non-uniform force. In such a case, there arises a problem that the wafer breaks. However, there is a problem that a solid phase reaction does not occur at a low processing pressure, and even if a reaction occurs, the rate, that is, the polishing rate becomes slow and the polishing time becomes long.

  The present invention has been made based on such a background, and an object thereof is to provide a mechanochemical polishing apparatus capable of efficiently polishing a hard material such as SiC even at a low processing pressure.

  According to the mechanochemical polishing apparatus of the present invention, when a semiconductor wafer as a material to be polished is polished using chromium (III) oxide powder as abrasive grains, an oxidizing agent is present on the polishing surface. This oxidizing agent promotes the polishing efficiency.

  This is presumed to be due to the following reason. Regarding the action of the chromium oxide abrasive grains, the chromium oxide abrasive grains originally function as a catalyst for forming oxides on the surface of the semiconductor (for example, SiC), but the semiconductor (for example, SiC) and the oxide are disposed on the polished surface. It is considered that the reaction efficiency is increased by increasing the oxygen to be reacted, and hence the polishing efficiency is promoted.

  In this way, a hard material such as SiC can be efficiently polished even at a low processing pressure. Here, as the oxidizing agent, an oxidizing chemical solution (for example, hydrogen peroxide solution) is used as described in claim 1, or a solid powder having an oxidizing action (as described in claim 2). For example, it is possible to use at least one of manganese dioxide powder and dimanganese trioxide powder. In the first or second aspect of the invention, an oxidizing chemical solution (hydrogen peroxide solution) or a solid powder having an oxidizing action (manganese dioxide) is disposed on a polishing cloth disposed on the surface of a member that moves relative to the semiconductor wafer. At least one of the above powder and manganese trioxide powder) is supplied, and polishing is performed while pressing the semiconductor wafer against the polishing cloth at a predetermined processing pressure.

  Furthermore, as described in claim 3, a heating means for heating at least the polishing surface is provided, or a liquid in which a solid powder having a catalytic action of a chemical reaction other than chromium oxide powder is dispersed as described in claim 4. A liquid injector is provided for supplying the polishing surface to the polishing surface, or a solid powder having a catalytic action of a chemical reaction other than the chromium oxide powder is disposed on the member that moves relative to the semiconductor wafer as described in claim 5. Then, it becomes preferable. Here, as described in claim 6, it is preferable to provide a light source for irradiating light to the solid powder having a catalytic action of a chemical reaction.

  As described in claim 7, a polishing cloth is disposed on a surface of a member that moves relative to the semiconductor wafer, and the semiconductor wafer is pressed against the polishing cloth to be polished, so that the semiconductor wafer has scratches, cracks, and the like. It can be polished without damaging it.

  As described in claim 8, when a structure in which holes or voids that are continuous in the direction perpendicular to the surface are used as the polishing cloth, permeability from the surface of the polishing cloth in the depth direction is improved. Ease of discharge of semiconductor wafer fragments and the like makes it possible to form a good polished surface free from scratches, cracks and crystal distortion.

Here, as described in claim 9, a structure made of at least one of synthetic fiber, glass fiber, natural fiber, synthetic resin, and natural resin may be used as the polishing cloth.
In particular, as described in claim 10, a polyurethane material is used as a suede type abrasive cloth having a vertical foam structure, or as described in claim 11, the resin is impregnated with a fiber by impregnating the resin in a fiber entangled body. The nonwoven fabric-type abrasive cloth that functions as a binder or the resin layer itself has a continuous foam structure, or the fiber entangled body is impregnated with a resin to impregnate the resin with the fiber. A nonwoven fabric type fabric that works as a binder or the resin layer itself has a continuous foam structure is used as a base layer, and a suede type fabric with a vertical foam structure is bonded to this with a polyurethane material 2 A layered abrasive cloth is suitable.

  As described in claim 13, by using a structure in which independent holes or bubbles are formed on the surface and inside as the polishing cloth, the polishing cloth is hard and has the ability to retain abrasive grains and chemicals on the surface. The surface of the semiconductor wafer with unevenness can be flattened and smoothed in a short time. In addition, the work-affected layer generated in the pre-polishing process (grinding process, lapping process, etc.) can be removed in a short time.

  Here, as described in claim 14, a structure made of synthetic resin or natural resin may be used as the polishing cloth. In particular, a foamed polyurethane type abrasive cloth having a closed foam structure is suitable as described in claim 15.

  17. A polishing cloth having a structure in which holes or voids continuous in a direction perpendicular to the surface are formed as an undercoat layer, and pores or bubbles independent of the surface and the interior thereof By using a two-layered polishing cloth bonded to the structure cloth on which the structure is formed, the structure on the surface layer side (the cloth in contact with the wafer) has excellent polishing speed and planarization efficiency, and the underlayer With this structure (base cloth), the followability to the undulation and warpage of the semiconductor wafer is improved, so that the wafer can be polished with high accuracy.

  In particular, as described in claim 17, as an abrasive cloth, the resin acts as a fiber binder by impregnating the resin in the fiber entangled body, or the resin layer itself has a continuous foam structure. A two-layer polishing cloth in which a non-woven cloth is used as a base layer and a polyurethane foam cloth having an independent foam structure is bonded thereto is suitable.

  According to the present invention, it is possible to provide a mechanochemical polishing apparatus capable of efficiently polishing a hard material such as SiC even at a low processing pressure.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, the schematic block diagram of the mechanochemical polishing apparatus in this Embodiment is shown.

  A polishing cloth 2 is affixed to the polishing surface plate 1. For the polishing cloth 2, foamed polyurethane, nonwoven fabric, felt, suede or the like is used. A wafer holding table 3 is disposed above the polishing surface plate 1 so that the SiC wafer 4 can be held on the wafer holding table 3. At the time of processing, the wafer holding table 3 is pressed toward the polishing cloth 2, and the surface to be polished in the SiC wafer 4 is pressed at a predetermined processing pressure.

Further, the wafer holding table 3 and the polishing surface plate 1 can rotate.
Further, a liquid injector (nozzle) 5 is installed above the polishing surface plate 1, and a chemical liquid 6 is dropped onto the polishing cloth 2 from the liquid injector 5. This chemical solution 6 is obtained by dispersing abrasive grains of chromium (III) oxide in hydrogen peroxide water (oxidizing chemical solution). That is, chromium oxide abrasive grains and an oxidizing chemical solution are mixed and used.

  As described above, when polishing is performed while pressing the single crystal SiC wafer (semiconductor wafer) 4 as the material to be polished against the polishing cloth 2 using the chromium (III) oxide powder as the abrasive grains, A mechanism is provided in which hydrogen peroxide solution, which is an oxidizing chemical solution, is dropped from the liquid injector 5 to supply the hydrogen peroxide solution to the polishing surface. Thereby, it can grind | polish in the state in which hydrogen peroxide water (oxidant) exists in a grinding | polishing surface.

When the wafer holding table 3 is swung with respect to the polishing surface plate 1, the processing accuracy in the wafer surface can be improved and the life of the polishing pad can be improved.
Next, a mechanochemical polishing method will be described.

  First, the SiC wafer 4 is held on the wafer holding table 3. Then, the surface to be polished is pressed against the polishing cloth 2 affixed to the polishing surface plate 1 with a predetermined processing pressure. Further, the wafer holding table 3 and the polishing surface plate 1 are rotated, and polishing is performed while dripping a chemical solution (hydrogen peroxide solution in which chromium oxide abrasive grains are dispersed) 6 onto the polishing cloth 2.

  When performing this polishing, a hydrogen peroxide solution (oxidant) is present on the polishing surface, and the polishing efficiency is promoted by this hydrogen peroxide solution. This is because the chromium oxide abrasive grains function as a catalyst for forming an oxide on the surface of SiC, and the hydrogen peroxide solution disposed on the polishing surface increases the oxygen that reacts with SiC, improving the reaction efficiency and improving the polishing efficiency. It is thought that promotion is planned. In this way, a hard material such as SiC can be efficiently polished even at a low processing pressure.

  Here, the minimum pressure that can be polished is the type of polishing cloth 2, the concentration and particle size of chromium oxide abrasive grains, the concentration and dropping amount of hydrogen peroxide, and the rotation of the wafer holding table 3 and the polishing surface plate 1. It depends on the number.

In the experiments of the present inventors, the surface roughness of 1.20 nm (centerline average roughness Ra) can be smoothed to 0.43 nm by polishing for 30 minutes even at a low processing pressure (0.34 kgf / cm ² ). It was. The polishing conditions at this time were a polishing liquid in which 0.5 μm (particle diameter) chromium oxide abrasive grains (concentration 10 wt%) were dispersed in a foamed polyurethane polishing cloth and hydrogen peroxide (concentration 10%). 5.0 ml / min), a wafer holding table rotation speed of 40 rpm, and a polishing platen rotation speed of 40 rpm.

Detailed experimental results will be described with reference to FIGS.
The experiment was performed as follows. Single-crystal SiC (6H—SiC) was used as a sample, and the (0001) Si surface of this SiC wafer was polished. There are three polishing conditions: (i) polishing while dropping hydrogen peroxide solution (oxidant) described in this embodiment, and (ii) dry polishing and (iii) wet polishing for comparison. . Specifically, for polishing while dropping the hydrogen peroxide solution of (i), a solution in which chromium oxide abrasive grains (10 wt%) are dispersed in hydrogen peroxide solution (concentration 10%) is dropped onto the polishing cloth. Polished. The dry polish (ii) was polished with a polishing cloth coated with chromium oxide abrasive grains. About the wet polish of (iii), the chromium oxide liquid which disperse | distributed the chromium oxide abrasive grain in water by 10 wt% was dripped at polishing cloth, and it grind | polished.

Polishing was evaluated by temporal changes in surface roughness. That is, the change in the surface roughness of each sample was examined.
Further, foamed polyurethane was used as the polishing cloth, and abrasive grains having a particle diameter of 0.5 μm were used as the chromium oxide. The processing pressure is 3.0 kgf / cm ² . The surface before polishing was a surface processed by grinding (# 8000), and there were irregularities (grinding marks) formed by grinding a diamond grindstone in a certain direction.

  In FIG. 2, the surface state after performing the above-mentioned dry polish for 10 minutes is shown. The surface roughness Ra at this time was 1.11 nm. Similarly, FIG. 3 shows the surface state after 20 minutes of dry polishing. The surface roughness Ra at this time was 0.80 nm. FIG. 4 shows the surface state after the above-described wet polishing is performed for 10 minutes. The surface roughness Ra at this time was 1.15 nm. Similarly, FIG. 5 shows the surface state after 20 minutes of wet polishing. The surface roughness Ra at this time was 0.92 nm. Further, FIG. 6 shows the surface state after polishing for 10 minutes while dropping the above-described hydrogen peroxide solution (oxidant). The surface roughness Ra at this time was 0.73 nm. Similarly, FIG. 7 shows a surface state after polishing for 20 minutes while dropping a hydrogen peroxide solution (oxidant). The surface roughness Ra at this time was 0.57 nm.

  A summary of the data thus obtained is shown in FIG. The horizontal axis in FIG. 8 represents the polishing time, and the vertical axis represents the surface roughness. From the graph showing the change in the surface roughness, it can be seen that the surface roughness is improved in a short polishing time under the condition (sample) in which the oxidizing agent is mixed. Further, at the stage of processing for 20 minutes, the grinding streaks disappeared only when the oxidizing agent was mixed. As described above, the effect of promoting the polishing was confirmed by mixing the oxidizing agent.

Furthermore, the same experiment was conducted with the processing pressure lowered (polishing was performed under the same conditions except for the processing pressure). Specifically, it was 3.0 kgf / cm ² until now, but it was reduced to 0.6 kgf / cm ² , and wet polishing (chromium oxide abrasive grains dispersed in water at 10 wt%) and oxidizer mixed polish (Chromium oxide abrasive grains were dispersed in hydrogen peroxide solution (10%) at 10 wt%). FIG. 9 shows the experimental results (change in surface roughness).

Comparing FIG. 9 with FIG. 8 described above, it can be seen that the difference in polishing efficiency becomes significant with and without hydrogen peroxide when the processing pressure is low between wet polishing and polishing with an oxidizing agent mixture. That is, for example, when compared with polishing for 40 minutes, Ra = 0.6 nm and a processing pressure of 0.6 kgf / cm ^{2 in} an experiment with a processing pressure of 3.0 kgf / cm ^{2 in} wet polishing (FIG. 8). In FIG. 9 (FIG. 9), Ra≈1.2 nm, whereas in the oxidizer-mixed polish, Ra≈0.6 nm in FIG. 8 and Ra≈0.6 nm in FIG. In the case of (dispersion), the polishing efficiency is greatly reduced when the processing pressure is lowered, but it is understood that the polishing efficiency is small for the polish mixed with hydrogen peroxide as an oxidizing agent.

Although the data is not shown, the experiment was carried out under a polishing condition of oxidant mixing with a lower processing pressure (0.34 kgf / cm ² ), but the surface roughness was Ra in 30 minutes of polishing time. Reduced from 1.20 nm to 0.43 nm.

From this, it can be seen that by mixing hydrogen peroxide as an oxidizing agent, the reduction in polishing efficiency is small even when the processing pressure is lowered.
From the above considerations and experimental results, when chromium oxide (Cr ₂ O ₃ ) is used as abrasive grains for polishing, mixing chromium oxide abrasive grains and an oxidizing agent facilitates efficiency at a low processing pressure. A SiC wafer can be polished well. More preferably, the processing pressure for polishing the wafer is 0.0098 to 0.294 MPa (0.1 to 3.0 kgf / cm ² ).

  If the amount of chromium oxide is the same, the smaller the abrasive particle size of chromium oxide is, the larger the surface area becomes, so that the polishing efficiency is improved and the surface roughness is also improved. Therefore, it is desirable that the abrasive grain size be 5 μm or less.

As an application example of this embodiment, it may be carried out as follows.
As shown in FIG. 10, the same effect can be obtained even when a hydrogen peroxide solution (chemical solution 10) is dropped and polished on the polishing cloth 2 coated with the chromium oxide abrasive grains 11.

  Moreover, as shown in FIG. 11, you may grind | polishing the chemical | medical solution 20 which disperse | distributed the chromium oxide abrasive grain in the hydrogen peroxide solution with respect to the polishing cloth 2 which apply | coated the chromium oxide abrasive grain 21. FIG. In this case, the polishing efficiency is further improved because the number of abrasive grains in contact with the polishing surface increases.

  Moreover, not only a polishing cloth but a metal and a ceramic may be sufficient if a chromium oxide abrasive grain and an oxidizing agent can be hold | maintained. Specifically, examples of the metal include tin, lead, aluminum, stainless steel, and copper.

  Further, instead of the polishing cloth, as shown in FIG. 12, a wrapping film 30 in which chromium oxide particles 32 are uniformly coated on a polyester film base material 31 with a resin adhesive may be used. It may be a hard disk. Here, in the case of a fixed abrasive such as the wrapping film 30, unlike the free abrasive, the abrasive does not agglomerate, so that polishing with an abrasive having a uniform particle size is possible. Considering that the wrapping film 30 is likely to be clogged, it is also effective to spray the hydrogen peroxide solution (chemical solution) on the film 30 at a high pressure to remove the polishing debris and prevent clogging. Alternatively, as shown in FIG. 12, when the SiC wafer 35 is polished while applying the pressure to the wrapping film 30 and feeding the film 30 at a constant speed (in the tape polishing method), a liquid injector (nozzle) ) Polishing while dropping the hydrogen peroxide solution (chemical solution) 37 from 36 prevents clogging.

Further, as shown in FIG. 13, solid powder having a catalytic action of chemical reaction other than chromium oxide powder, specifically, titanium dioxide (TiO ₂ ) may be dispersed in a dropping solution and supplied to the polishing surface. (It may be dropped as the chemical solution 40). That is, TiO ₂ powder is mixed in hydrogen peroxide water, and this liquid (a liquid in which a solid powder having a catalytic action of a chemical reaction other than chromium oxide powder is dispersed) is supplied from the liquid injector 5 to the polishing surface. With regard to supplying the TiO ₂ powder to the polishing surface, this may be performed in the second and third embodiments described later. In addition to titanium dioxide (TiO ₂ ), cadmium sulfide (CdS), diindium trioxide (In ₂ O) are used as catalysts for promoting chemical reactions that form reaction products on the SiC surface other than chromium oxide powder. ₃ ), zirconia dioxide (ZrO ₂ ), dialuminum trioxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ) powder may be used.

Alternatively, a solid powder (TiO ₂ powder or the like) having a catalytic action other than chromium oxide powder is applied to the polishing cloth 2 (by disposing it on the side of the member that moves relative to the SiC wafer 4), and the polishing surface May be supplied.

Here, when such TiO ₂ powder or the like is used, a chemical reaction is performed using light sources 42, 43, and 44 as shown in FIG. The solid powder (such as TiO ₂ powder) having the catalytic action may be irradiated with light. Specifically, polishing may be performed while applying light to the polishing pad 2 using the light source 43, or polishing while applying light to the polishing surface of the SiC wafer 4 using the light sources 42 and 44.

  In this embodiment, it is preferable to carry out the polishing cloth in consideration of the following. That is, the polishing cloth 2 is arranged on the surface of the member (polishing surface plate 1) that moves relative to the SiC wafer 4, and the SiC wafer 4 is pressed and polished on the polishing cloth 2, thereby scratching the SiC wafer 4. The polishing can be performed without causing damage such as cracks. In this case, the following is taken into consideration.

In the above-described experiment, it was confirmed that the surface irregularities were efficiently flattened by using a polyurethane foam material for the polishing cloth.
However, depending on the polishing cloth, minute scratches and crystal distortion are likely to occur on the polished surface.

  Polyurethane foam is a hard polishing cloth that contains spherical foam holes. Since the foam holes are independent of each other, abrasive grains, chemicals, etc. on the polishing cloth do not penetrate into the polishing cloth. Therefore, it is difficult to eliminate a chip that has been chipped from the end of the object to be polished and dropped on the polishing cloth, and the chip tends to remain on the polishing cloth. The piece on the polishing cloth may scratch the polishing surface and cause scratches and crystal distortion.

Therefore, if you use a polishing cloth with holes or voids that are continuous in the direction perpendicular to the surface, it is permeable in the depth direction and soft, so it is effective in preventing scratches and crystal distortion. I found that there is. In other words, when a structure in which holes or voids that are continuous in the direction perpendicular to the surface are used as the polishing cloth, the penetration from the surface of the polishing cloth in the depth direction is improved, and semiconductor wafer fragments etc. are discharged. This facilitates formation of a good polished surface free from scratches, cracks and crystal distortion.
Here, as the polishing cloth, a structure made of at least one of synthetic fiber, glass fiber, natural fiber, synthetic resin, and natural resin may be used. More specifically,
(i). Suede type polishing cloth with polyurethane foam and vertical foam structure,
(ii). A nonwoven fabric-type abrasive cloth in which the resin acts as a fiber binder by impregnating the resin in the fiber entangled body, or the resin layer itself has a continuous foam structure,
(iii). By impregnating the resin in the fiber entanglement body, the resin works as a fiber binder, or the nonwoven fabric type cloth in which the resin layer itself has a continuous foam structure is used as a base layer. A two-layered polishing cloth in which a suede type cloth with a vertical foam structure is bonded,
Are particularly suitable.

Moreover, verification by the following experiment was performed.
The cause of scratches and crystal distortion is that the pieces of the object to be polished are caused by water polishing (a method for cleaning the surface, not for processing the surface), in which pure water is dropped on the polishing cloth. When using an independent foam polyurethane as the polishing cloth, scratches and crystal distortion occur on the surface, but when using an abrasive cloth with continuous holes or voids formed in the direction perpendicular to the surface, scratches and crystal distortion occur. I figured out from not doing. Furthermore, on a suede type (Supreme RN-H Rodel Nitta Co., Ltd.) polishing cloth, while dropping a solution of chromium oxide abrasive grains (10 wt%) dispersed in hydrogen peroxide (concentration 10%) As a result of polishing experiments, it was confirmed that polishing without scratches or crystal distortion was possible. Specifically, the change in the surface state was evaluated by etching the polished surface polished with the polyurethane of the independent foam and the polished surface polished with the suede type with a potassium hydroxide (KOH) solution. As a result, it was found that the closed foam polyurethane had rough surfaces due to the presence of scratches and crystal distortion, but the suede type had no surface roughness, so there were no scratches or crystal distortions.

  Therefore, if emphasis is placed on the processing efficiency of polishing, the polyurethane foam type polishing cloth in which independent holes or voids are formed on the surface and inside should be made into a high-quality polishing surface free from scratches and crystal distortion. If importance is attached, a suede type polishing cloth in which holes or voids continuous in the direction perpendicular to the surface are formed may be used.

  Here, reference will be made to a polishing cloth with an emphasis on polishing efficiency. By using a structure in which pores or bubbles that are independent on the surface and inside are formed as the polishing cloth, the polishing cloth is hard and improves the retention of abrasive grains and chemicals on the surface. The surface can be flattened and smoothed in a short time. In addition, the work-affected layer generated in the pre-polishing process (grinding process, lapping process, etc.) can be removed in a short time. Here, as the polishing cloth, a structure made of synthetic resin or natural resin may be used. In particular, a foamed polyurethane type polishing cloth having a closed foam structure is suitable.

Alternatively, as a polishing cloth, a cloth of a structure in which holes or voids continuous in the direction perpendicular to the surface is formed as an underlayer, and a structure in which holes or bubbles independent of the surface and the inside are formed on the cloth. By using a polishing cloth with a two-layer structure that is bonded to the cloth, the structure on the surface layer side (the cloth in contact with the wafer) provides excellent polishing speed and flattening efficiency. ) Improves the followability to the undulation and warpage of the semiconductor wafer, so that the wafer can be polished with high accuracy. In particular, as an abrasive cloth, the resin works as a fiber binder by impregnating the resin in the fiber entangled body, or the cloth layer of the nonwoven fabric type in which the resin layer itself has a continuous foam structure, For this, a two-layered polishing cloth in which a foamed polyurethane type cloth having an independent foam structure is bonded is suitable.
(Second Embodiment)
Next, the second embodiment will be described focusing on the differences from the first embodiment.

In FIG. 14, the schematic block diagram of the mechanochemical polishing apparatus in this Embodiment is shown.
In this apparatus, the abrasive 50 applied on the polishing pad 2 is a mixture of chromium oxide and solid powder having an oxidizing action. That is, a solid powder having an oxidizing action as an oxidizing agent, specifically, manganese dioxide (MnO ₂ ) powder is used, and this powder is disposed on the polishing cloth 2 (on the side of the member that moves relative to the SiC wafer 4). This is a mechanism for supplying to the polishing surface.

As a polishing procedure, the SiC wafer 4 is polished in a state where chromium oxide abrasive grains and manganese dioxide (MnO ₂ ) powder are applied as abrasive grains 50 on the polishing cloth 2. Here, since manganese dioxide has an oxidizing action, it reacts with SiC to form an oxide on the SiC surface, but chromium oxide abrasive grains promote the oxidation reaction as a catalyst and remove the formed oxide. Functions as abrasive grains. This improves the polishing efficiency and enables polishing even at a low processing pressure.

As an application example of this embodiment, it may be carried out as follows.
As shown in FIG. 15, chromium oxide abrasive grains and manganese dioxide (MnO ₂ ) powder are applied as abrasive grains 50 onto the polishing cloth 2, and hydrogen peroxide solution (chemical liquid 52) is dropped from a liquid injector 51. May be. If it carries out like this, oxidation efficiency (polishing efficiency) can be improved. Further, in this case, MnO ₂ and hydrogen peroxide react to generate oxygen, thereby further improving efficiency. Here, as the chemical solution 52, a solution obtained by dispersing chromium oxide abrasive grains in hydrogen peroxide water may be used.

In FIG. 15, a chemical solution 52 in which a powder of manganese dioxide (MnO ₂ ) is dispersed in a dispersion medium (for example, water) may be used. In other words, solid powder (MnO ₂ ) having an oxidizing action may be supplied to the polishing surface by dispersing it in the dropping liquid.

In addition to manganese dioxide (MnO ₂ ) powder, as powder having oxidizing action, powder of dimanganese trioxide (Mn ₂ O ₃ ) or a mixture of MnO ₂ powder and Mn ₂ O ₃ powder is used. May be.

When a wrapping film (see FIG. 12) is used, a solid powder having an oxidizing action is applied on a film to which chromium oxide abrasive grains are fixed, or a solid powder having an oxidizing action is applied to chromium oxide abrasive grains. You may mix and adhere on a film. Examples of the solid powder having an oxidizing action used at this time include MnO ₂ , Mn ₂ O ₃ , BaCO ₃ , CaCO ₃ , SiO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , MgO, In ₂ O _{3 and the} like. Can do.
(Third embodiment)
Next, the third embodiment will be described with a focus on differences from the first embodiment.

In this embodiment, a gas containing at least oxygen, specifically, oxygen gas is used as the oxidizing agent.
As the configuration of the apparatus, as shown in FIG. 16, a closed container structure is employed in order to make the polishing surface in an oxidizing gas atmosphere. Specifically, the polishing surface plate 1, the polishing cloth 2, and the wafer holding table 3 are arranged in the oxygen atmosphere creation chamber 60. The inside of the chamber 60 is in an oxygen atmosphere, and oxygen gas is supplied to the polishing surface by performing polishing in this oxygen atmosphere.

  As a polishing procedure, after setting the SiC wafer 4 on the wafer holding table 3, the inside of the chamber 60 is brought into an oxygen atmosphere. Then, polishing is performed in an oxygen atmosphere. That is, the SiC wafer 4 is polished on the polishing cloth 2 coated with the chromium oxide abrasive grains 61. At this time, oxygen is supplied to the contact surface between the SiC wafer 4 and the polishing pad 2.

  As an apparatus instead of FIG. 16, as shown in FIG. 17, oxygen gas may be blown from a gas injector 70 toward a portion (polishing surface) to be polished to supply oxygen gas to the polishing surface. Specifically, oxygen gas is blown from the gas injector 70 for injecting oxygen gas onto the polishing cloth 2 (the portion on the upstream side of the SiC wafer 4 in the polishing cloth 2) immediately before contacting the SiC wafer 4.

  Further, as an apparatus instead of FIG. 16, an oxygen gas supply passage 80 is provided in the polishing surface plate 1 as shown in FIG. That is, the gas passage 80 for supplying the oxidizing gas to the polishing surface through a member that moves relative to the SiC wafer 4 is provided. Then, oxygen gas is blown out from the back surface side of the polishing cloth 2 (the member side that moves relative to the SiC wafer 4) through the passage 80 to a portion where polishing on the surface of the polishing cloth 2 is to be performed.

  More specifically, in the case of the configuration of FIG. 18 (when oxygen is supplied from the back surface of the polishing pad 2), in addition to providing the polishing platen 1 with a gas passage 80, the polishing pad 2 has a minute gas passage for passing gas. Select one with holes. For example, if the foamed part of the polyurethane foam polishing cloth is closed, holes that penetrate from the front to the back are already formed, and the nonwoven foam polishing cloth of the continuous foam can pass oxygen. It is.

Note that as a gas to be supplied, that is, a gas containing at least oxygen, other gas containing oxygen such as water vapor can be used in addition to the oxygen gas.
Further, as shown in FIG. 19, when a SiC wafer 35 is polished on a wrapping film 30 in which chromium oxide particles 32 are uniformly coated on a film base 31 with a resin adhesive, oxygen gas (in a broad sense) is supplied from a gas injector 70. If a gas containing oxygen is sprayed, clogging can be prevented.

  In addition, as shown in FIG. 20, in order to promote the reaction (in order to improve the polishing efficiency), the SiC wafer 4 may be polished while heating the SiC wafer 4. In FIG. Is used to heat the SiC wafer 4. Alternatively, as shown in FIG. 21, the SiC wafer 4 is partially protruded at the end of the polishing cloth 2 (polishing surface plate 1) and polished, and infrared light is applied to the protruding region 4a from the light source 95. You may make it heat. At this time, the table 3 (SiC wafer 4) is preferably swung.

In this way, heating means 90, 91, 95 for heating at least the polishing surface may be provided. This can also be performed in the first embodiment and the second embodiment described above.
Or, polishing efficiency can be improved by heating a polishing cloth in which chromium oxide abrasive grains and oxidant are held, metal, ceramic, a wrapping film coated with chromium oxide particles, or a disk in which chromium oxide abrasive grains are hardened with resin. May be improved (may be improved).

The schematic block diagram of the mechanochemical polishing apparatus in 1st Embodiment. The figure which shows the time change of the surface roughness of a grinding | polishing surface. The figure which shows the time change of the surface roughness of a grinding | polishing surface. The figure which shows the time change of the surface roughness of a grinding | polishing surface. The figure which shows the time change of the surface roughness of a grinding | polishing surface. The figure which shows the time change of the surface roughness of a grinding | polishing surface. The figure which shows the time change of the surface roughness of a grinding | polishing surface. The figure which shows the surface roughness with respect to grinding | polishing time. The figure which shows the surface roughness with respect to grinding | polishing time. The schematic block diagram of a mechanochemical polishing apparatus. The schematic block diagram of a mechanochemical polishing apparatus. The schematic block diagram of a mechanochemical polishing apparatus. The schematic block diagram of a mechanochemical polishing apparatus. The schematic block diagram of the mechanochemical polishing apparatus in 2nd Embodiment. The schematic block diagram of a mechanochemical polishing apparatus. The schematic block diagram of the mechanochemical polishing apparatus in 3rd Embodiment. The schematic block diagram of a mechanochemical polishing apparatus. The schematic block diagram of a mechanochemical polishing apparatus. The schematic block diagram of a mechanochemical polishing apparatus. The schematic block diagram of a mechanochemical polishing apparatus. The schematic block diagram of a mechanochemical polishing apparatus. FIG. 14 is a cross-sectional view of a semiconductor device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Polishing surface plate, 2 ... Polishing cloth, 3 ... Wafer holding table, 4 ... SiC wafer, 5 ... Liquid injector, 6 ... Chemical solution (hydrogen peroxide solution + chromium oxide abrasive grain), 11 ... Chrome oxide abrasive grain , 42, 43, 44 ... light source, 50 ... manganese dioxide abrasive grain, 51 ... liquid injector, 52 ... chemical solution, 60 ... chamber, 70 ... gas injector, 80 ... passage, 90, 91 ... heater, 95 ... light source.

Claims (17)

In a mechanochemical polishing apparatus that uses a chromium (III) oxide powder as abrasive grains and polishes a semiconductor wafer as a material to be polished,
A polishing cloth is arranged on the surface of a member that moves relative to the semiconductor wafer, and a liquid injector is provided on the polishing surface to supply hydrogen peroxide as an oxidizing chemical solution. The polishing surface is pressed at a predetermined pressure. A mechanochemical polishing apparatus for polishing while dropping hydrogen peroxide on the polishing cloth. In a mechanochemical polishing apparatus that uses a chromium (III) oxide powder as abrasive grains and polishes a semiconductor wafer as a material to be polished,
While arranging a polishing cloth on the surface of the member that moves relative to the semiconductor wafer, supplying at least one of manganese dioxide powder and manganese trioxide powder as a solid powder having an oxidizing action on the polishing cloth, A mechanochemical polishing apparatus for polishing a polishing surface while pressing the polishing surface against the polishing cloth with a predetermined pressure. The mechanochemical polishing apparatus according to claim 1 or 2, further comprising a heating means for heating at least the polishing surface. The liquid injector for supplying the liquid which disperse | distributed the solid powder which has a catalytic reaction of chemical reactions other than a chromium oxide powder to a grinding | polishing surface was provided. Mechanochemical polishing equipment. The mechanochemical polishing apparatus according to any one of claims 1 to 3, wherein a solid powder having a catalytic action of a chemical reaction other than the chromium oxide powder is disposed on a member that moves relative to the semiconductor wafer. 6. The mechanochemical polishing apparatus according to claim 4, further comprising a light source for irradiating light to the solid powder having a catalytic action of the chemical reaction. The mechanochemical polishing apparatus according to claim 1, wherein a polishing cloth is disposed on a surface of a member that moves relative to the semiconductor wafer. The mechanochemical polishing apparatus according to claim 7, wherein the polishing cloth is a structure in which holes or voids that are continuous in a direction perpendicular to the surface are formed. The mechanochemical polishing apparatus according to claim 8, wherein the polishing cloth is a structure made of at least one of synthetic fiber, glass fiber, natural fiber, synthetic resin, and natural resin. The mechanochemical polishing apparatus according to claim 9, wherein the polishing cloth is a polyurethane material and is a suede type polishing cloth having a vertical foam structure. The abrasive cloth is a nonwoven cloth type abrasive cloth in which the resin acts as a fiber binder by impregnating the resin in the fiber entangled body, or the resin layer itself has a continuous foam structure. The mechanochemical polishing apparatus according to claim 9. The abrasive cloth is made by impregnating a resin in a fiber entangled body so that the resin acts as a fiber binder, or a non-woven cloth type cloth in which the resin layer itself has a continuous foam structure. The mechanochemical polishing apparatus according to claim 9, wherein the polishing cloth is a two-layered polishing cloth in which a suede cloth having a vertical foam structure is bonded to a polyurethane material. 8. The mechanochemical polishing apparatus according to claim 7, wherein the polishing cloth is a structure in which independent holes or bubbles are formed on the surface and inside. The mechanochemical polishing apparatus according to claim 13, wherein the polishing cloth is a structure made of a synthetic resin or a natural resin. The mechanochemical polishing apparatus according to claim 14, wherein the polishing cloth is a polyurethane foam type polishing cloth having an independent foam structure. The polishing cloth has a structure cloth in which holes or voids are formed in a direction perpendicular to the surface as a base layer, and a structure cloth in which independent holes or bubbles are formed on the surface and inside. The mechanochemical polishing apparatus according to claim 7, wherein the polishing cloth is a two-layer polishing cloth bonded together. The abrasive cloth is made by impregnating a resin in a fiber entangled body so that the resin acts as a fiber binder, or a non-woven cloth type cloth in which the resin layer itself has a continuous foam structure. The mechanochemical polishing apparatus according to claim 16, wherein the polyurethane foam type cloth having an independent foam structure is a two-layer structure polishing cloth bonded together.

Images