JP2007109776A - Polishing method and polishing apparatus of silicon carbide crystal substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of performing polishing processing on a silicon carbide crystal substrate at a high speed while keeping processing scratches shallow and the surface stable. <P>SOLUTION: In this polishing method of the silicon carbide crystal substrate 2; an abrasive powder with diamond abrasive grains as a man component is dropped on a turning polishing plate 1, and then the silicon carbide crystal substrate 2 as a material to be polished is pressed against the turning polishing plate 1 with a predetermined pressure to be polished. The silicon carbide crystal substrate 2 has a surface roughness Rz larger than 1 μm but not exceeding 50 μm. By blending boron carbide abrasive grains whose grain diameter is smaller than the average grain diameter of the diamond abrasive grains, as a second abrasive powder at a predetermined weight ratio which is determined by the average grain diameter of the diamond abrasive grains; the silicon carbide crystal substrate is polished with the depth of the polishing scratches kept smaller than 0.6 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polishing method and a polishing apparatus for a silicon carbide crystal substrate, and more particularly to a technique for polishing a silicon carbide crystal substrate using a composite abrasive.

  Power devices that handle electrical energy with low loss are expected to be widely used and further developed in the future because they can greatly reduce power consumption. Current power devices are fabricated from silicon substrates, but there are limits to further performance enhancement due to the inherent characteristics of silicon. In particular, since silicon cannot be used at high temperatures, materials that replace silicon have become necessary.

  For this reason, in recent years, silicon carbide (SiC) has attracted attention. Since the forbidden band width of silicon carbide is three times the forbidden band width of silicon, it can be used under higher temperature conditions than silicon. In addition, since the breakdown electric field is about 10 times that of silicon, the size can be reduced. Furthermore, the thermal conductivity is about three times that of silicon, and there is an advantage that it is excellent in heat dissipation and is easily cooled. Since silicon carbide has excellent characteristics as described above, the silicon carbide crystal substrate is very promising as a power device substrate instead of a silicon substrate.

By the way, in order to produce a power device from a silicon carbide crystal substrate, it is necessary to finally polish the surface as smoothly as possible. At present, a silicon carbide ingot refined by crystal growth is first sliced with a wire saw, blade saw, etc., and then ground to remove irregularities present on the substrate, rough polishing using a hard polishing surface plate, soft polishing pad Processing is carried out through a precision (mirror surface) polishing process using. Of these, precision polishing is the most important process, and as a known method, as disclosed in Patent Document 1, composite diamond abrasive grains composed of a plurality of diamonds having an average particle diameter, single grain diameter diamond abrasive grains, and SiO ₂ (colloidal). A polishing method using a suspension containing silica) is currently generally used. In addition, rough polishing, which is a pretreatment process for the final processed surface, is an important process as well as precision polishing. If the state after rough polishing is good, such as the absence of deep scratches, the processing time of the final process can be shortened.
International Publication No. 98/022978 Pamphlet

However, since the technique of Patent Document 1 uses diamond as the abrasive grains, the time required for polishing (processing rate) is short, but damage to the workpiece is large. That is, during polishing, the silicon carbide crystal is greatly damaged, and the silicon carbide crystal is easily damaged by aggregates formed from the diamond abrasive grains. When the processing flaw is deep, there is a problem that the processing time in precision polishing performed using a colloidal silica or the like which is a subsequent process becomes very long.
The present invention solves the above-mentioned conventional problems, and is characterized in that a good pre-processed surface of a silicon carbide crystal substrate is obtained which suppresses damage to the silicon carbide crystal and has no deep processing flaws. .

In order to solve the above-mentioned conventional problems, the polishing method for a silicon carbide crystal substrate according to the present invention is a method in which an abrasive slurry containing diamond abrasive grains as a main component is dripped onto a rotating polishing plate. In a method for polishing a silicon carbide crystal substrate in which a silicon carbide crystal substrate, which is a material to be polished, is pressed against the polishing platen with a predetermined pressure and polished, the silicon carbide after surface processing to a surface roughness Rz = 50 μm or less in advance A silicon carbide boron crystal grain smaller than the average grain diameter of the diamond abrasive grains is used as a second abrasive, and is mixed at a predetermined weight ratio according to the average grain diameter of the diamond abrasive grains. The crystal substrate is polished to have a processing flaw depth smaller than a predetermined value.
Further, the present invention drops an abrasive slurry containing diamond abrasive grains as a main component in water to a rotating polishing platen to rotate the silicon carbide crystal substrate as a polishing material to the polishing platen. In a method for polishing a silicon carbide crystal substrate, which is pressed at a predetermined pressure and sequentially performs a plurality of polishing steps using abrasives having different average particle diameters of the diamond abrasive grains, boron carbide smaller than the average particle diameter of the diamond abrasive grains Abrasive grains are used as the second abrasive, and the mixing ratio of boron carbide is determined according to the average particle diameter of the diamond abrasive grains used in each polishing step. The maximum grain size is 60%, and the average grain size of the diamond abrasive grains used in the first polishing process is 30 μm. In the polishing process that is sequentially performed, the average grain diameter of the diamond abrasive grains should be reduced. It is obtained by the butterfly.

  Further, the polishing apparatus for a silicon carbide crystal substrate of the present invention drops a polishing liquid onto a polishing surface plate that rotates an abrasive slurry in which a polishing agent mainly containing diamond abrasive grains is contained in water. In a silicon carbide crystal substrate polishing apparatus that polishes a silicon carbide crystal substrate by pressing it against the polishing surface plate with a predetermined pressure, the silicon carbide crystal substrate that has been surface processed to a surface roughness Rz = 50 μm or less is pasted in advance. A bonding jig, a weight for applying a predetermined surface pressure to press the silicon carbide crystal substrate against the polishing surface plate through the bonding jig, and boron carbide having a predetermined weight ratio to the diamond abrasive grains of the main abrasive A storage tank for storing a polishing liquid containing mixed abrasive grains mixed with water, and a stirrer installed at the bottom of the storage tank for stirring the polishing liquid in the storage tank; And rotating the attaching jig to which the silicon carbide crystal substrate is attached, and agitating the polishing liquid using the stirring bar and polishing while dropping on the polishing surface plate. .

  According to the present invention, the abrasive material is changed at high speed by changing the abrasive grain from conventionally used single-grain or multiple-grain diamond to abrasive grains composed of boron carbide and diamond. Polishing with reduced damage to the silicon carbide crystal surface can be performed.

  The present invention is used when roughly polishing a silicon carbide crystal substrate. Here, in the present invention, the rough polishing is defined as that the surface roughness Rz of the silicon carbide crystal substrate is more than 1 μm and not more than 50 μm and is made 1 μm or less after polishing.

  Here, the “surface roughness Rz” is a value defined by JIS standard B0601, and is defined as the sum of the maximum value of the peak height of the contour curve and the maximum value of the valley depth in the reference length.

  As a polishing liquid that is an abrasive slurry, a polishing liquid containing polishing abrasive grains made of diamond and polishing abrasive grains made of boron carbide is used. It is preferable to use diamond having an average particle diameter of 30 μm or less and boron carbide having an average particle diameter of 3 μm or less. More specifically, since the present invention assumes several processing steps using two types of abrasive grains in rough polishing, for example, on an SiC substrate with Rz = 50 μm that needs to be processed faster. On the other hand, a polishing liquid is used in which abrasive grains made of diamond having an average particle diameter of 30 μm are mixed with abrasive grains made of boron carbide having an average particle diameter of 0.5 μm and 50 wt% with respect to the abrasive grains made of diamond. For SiC substrates near Rz = 1 μm, which requires sufficient processing accuracy to be used in the subsequent precision polishing step, polishing abrasives composed of diamond with an abrasive particle composed of diamond having an average particle size of 15 μm. It is preferable to use a polishing liquid in which abrasive grains made of boron carbide having an average particle diameter of 0.5 μm and 10 wt% with respect to the grains are mixed. The diamond particles and boron carbide particles are both amorphous.

  Here, the average particle diameter is measured by a natural centrifugal sedimentation method, and the measuring apparatus measures the product name “CAPA-300” manufactured by Horiba, Ltd. The sample liquid containing about 1% by weight of the abrasive grain component is centrifuged in the measuring apparatus, and the average particle diameter is measured by the speed of the precipitated abrasive grain component.

  The polishing slurry, which is this abrasive slurry, is, for example, a dispersion of diamond in the proportion of 0.1% by weight or more and 1% by weight or less as abrasive grains in pure water, and the abrasive grains made of boron carbide are made of diamond. Although affected by the grain size of the abrasive grains, those dispersed at a ratio of 5 wt% to 60 wt% of the abrasive grains made of diamond can be preferably used.

  Here, pure water is ion-exchanged water. A solvent component of a general oily slurry using a hydrocarbon-based liquid may be used instead of pure water.

  In the method of the present invention, a storage tank, which is a polishing container in which a polishing liquid is placed, is disposed on a polishing surface plate for polishing a silicon carbide crystal substrate so that polishing abrasive grains in the polishing liquid inside the polishing container (tank) do not precipitate. It is preferable to perform polishing while dripping the polishing liquid onto the polishing surface plate while stirring the polishing liquid by rotating the stirring bar (10) installed at the lower part in the storage tank (15). In this way, since a polishing liquid having a uniform composition can be supplied to the surface of the silicon carbide crystal substrate, the polishing surface can be made uniform.

  In the polishing step of the present invention, it is preferable to include a plurality of polishing steps in which the average particle size of the polishing abrasive grains is different. If it does in this way, polish can be advanced in steps.

  In the above polishing step, the average particle size of the abrasive grains made of diamond used in the first polishing step is larger than the average particle size of the abrasive particles made of diamond used in the last polishing step, and the polishing step proceeds. Accordingly, it is preferable to gradually reduce the average particle size. If it does in this way, it can advance to precision polishing in steps from rough polishing.

  Furthermore, it is preferable that the average particle diameter of the abrasive grains made of diamond used in the silicon carbide crystal polishing method of the present invention is 30 μm or less. The average grain size of the abrasive grains made of boron carbide used in the silicon carbide crystal polishing method of the present invention is preferably 3 μm or less.

  Here, the average grain size of the abrasive grains composed of diamond and boron carbide used in the present invention varies depending on the combination and concentration, but the processing characteristics for the silicon carbide crystal substrate vary. Assuming that the diameter is about 0.5 μm and this is the minimum particle size of abrasive grains made of boron carbide, the average grain size of abrasive grains made of diamond used in the present invention is preferably 10 μm or more and 30 μm or less. I can say that. This is because when the average grain size of the abrasive grains made of diamond is 30 μm or more, the surface condition after processing deteriorates, and the abrasive grain components in the polishing liquid are aggregated and precipitation is likely to occur. It can no longer be obtained. On the other hand, when the average particle size is 10 μm or less, the effect of mixing abrasive grains made of boron carbide is weakened, that is, even if mixed, the processing flaw depth and processing rate are not improved. Table 1 describes the case where the diamond particle size is up to 30 μm, but if it exceeds 30 μm, precipitation increases and becomes impractical.

  In this case, it can be said that the average particle diameter of the abrasive grains made of boron carbide is preferably 0.5 μm or more and 3 μm or less. However, the abrasive grains made of boron carbide may be classified here, and the average grain size of the abrasive grains made of boron carbide may be 0.3 μm or 0.1 μm. In practice, an average particle size of 0.1 μm or more is practical. Further, in this case, it can be estimated that good processing results can be obtained even if the average grain size of abrasive grains made of diamond is 10 μm or less.

  Furthermore, the number of rotations of the polishing platen used in the method of the present invention is preferably 5 rpm or more and 40 rpm or less, and the dropping rate of the polishing liquid onto the polishing platen is preferably 5 cc / min or more. In this way, efficient polishing can be performed. The conditions here are conditions for preventing the polishing platen from drying, and there are no lower limit of rotation speed and no upper limit of dropping speed. Practically, the number of revolutions is preferably 5 rpm or more, and in terms of dropping speed, there is no upper limit in practical use because the polishing surface plate may be immersed in the polishing liquid.

  Further, the polishing liquid used in the method of the present invention preferably uses pure water as a solvent, and the ratio of abrasive grains made of diamond to the polishing liquid is preferably 0.1 wt% or more and 1 wt% or less. This is because diamond is an extremely hard material, and even if abrasive grains made of diamond are mixed at a ratio of 1% by weight or more with respect to the polishing liquid, the processing amount is saturated. On the other hand, when the weight percent of the abrasive grains made of diamond is small, the processing efficiency deteriorates. At this time, the abrasive grains made of boron carbide are affected by the grain size of the abrasive grains made of diamond, but may be mixed in a proportion of 5 wt% to 60 wt% with respect to the abrasive grains made of diamond. preferable. When the proportion of abrasive grains made of boron carbide in the polishing liquid is 5% by weight or less, it becomes the same processing state as when polishing alone with abrasive grains made of diamond, improving the processing rate, carbonizing Each effect of suppressing damage to the silicon crystal substrate surface does not appear. On the other hand, when the proportion of abrasive grains made of boron carbide in the polishing liquid is 60% by weight or more, the effect of improving the sliding of diamond, which is the effect of mixing abrasive grains made of boron carbide, is almost lost. Think about it. That is, when the mixing amount increases, the number of boron carbide particles increases too much and the effect of increasing the momentum given to the diamond abrasive grains becomes weak. Since boron carbide has a smaller particle size than diamond, the number of particles increases as the mixing ratio increases, and it is thought that the movement of the diamond abrasive grains deteriorates due to collision and adhesion with the diamond abrasive grains on the polishing surface plate. . As a result, the effects of improving the processing rate and suppressing damage to the silicon carbide crystal substrate surface are deteriorated. Except for the case where the diamond abrasive grain size is 20 μm, boron carbide 1500 (average grain size 0.5 μm) and diamond abrasive grain size 30 μm, the mixing rate is remarkably reduced particularly when boron carbide is mixed by 60% by weight or more.

  Furthermore, it is preferable that the entire upper surface of the polishing platen in the polishing step of the present invention is always covered with the polishing liquid. This is because the dry polishing surface plate and the wet polishing surface plate have different frictional resistances at the contact portions of the abrasive grains, the polishing surface plate, and the silicon carbide crystal substrate. This is because it causes a large processing flaw on the surface of the silicon crystal substrate.

Further, in the polishing step of the present invention, when a polishing surface plate made of cast iron is used, a surface pressure of 50 gf / cm ² or more and 200 gf / cm ² or less is applied when the thickness of the silicon carbide crystal substrate is about 0.5 mm. It is preferable to perform polishing. This is because a practical processing rate cannot be obtained at a surface pressure of less than 50 gf / cm ² , and conversely, a silicon carbide crystal substrate may be damaged at a surface pressure exceeding 200 gf / cm ² .

  According to the present invention, polishing abrasive grains are made by mixing diamond and boron carbide from diamond that has been used conventionally, thereby reducing damage to the silicon carbide crystal to be polished and the surface of the polishing platen. And the surface can be polished precisely.

  An example of the method for polishing a silicon carbide crystal substrate of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following Example.

  1A is a plan view of a polishing apparatus according to an embodiment of the present invention, FIG. 1B is a side view thereof, and FIG. 1C is an assembly of a weight and a work guide in FIG. 1B. An enlarged view of the portion of the body 12, FIG. 1 (D) is an assembly view of FIG. 1 (C). As shown in FIGS. 1A to 1D, a bonding jig 3 in which a silicon carbide crystal substrate 2 is bonded to a polishing surface plate 1 and an appropriate amount of weight 4 for applying pressure are placed.

  Then, the work guide 5 is attached to the outside of the silicon carbide crystal substrate 2, the bonding jig 3, and the weight 4, and the polishing surface plate 1 is rotated in the direction of arrow P, so that the silicon carbide crystal substrate 2 is supported by the arm 6. The affixing jig 3, the weight 4, and the work guide 5 rotate on the polishing surface plate 1 in the direction of arrow Q. Then, a tubing pump 8 (for example, a cassette tubing pump SMP-21 manufactured by Tokyo Science Instruments Co., Ltd.) is used from a storage tank 15 for storing a polishing liquid 7 containing abrasive grains made of diamond and boron carbide through a silicon tube 9. Then, the polishing process proceeds by periodically dropping on the polishing platen 1. Here, the polishing liquid 7 is, for example, a stirrer 10 containing a commercially available magnet is placed in a container of the polishing liquid 7 and stirred by a commercially available stirrer 11 from the lower part of the container. Abrasive grains made of boron carbide are prevented from precipitating. Here, as the stirrer 10 and the stirrer 11, for example, a magnetic stirrer and a stirrer manufactured by Tokyo Science Instruments Co., Ltd. may be used.

  At this time, the silicon carbide crystal substrate 2, the bonding jig 3, the weight 4, and the work guide 5 can be rotated without attaching a motor to the arm 6, but the motor is attached to the arm 6 and independently rotated. Is preferable because the silicon carbide crystal substrate 2, the bonding jig 3, the weight 4, and the work guide 5 rotate at a more stable rotational speed. Further, the rotation direction of the polishing surface plate 1 and the arm 6 at this time may be the same direction or the reverse direction. Further, a swing mechanism may be attached to the arm 6.

The material of the polishing surface plate 1 is not special, and may be one that is used for rough polishing with normal diamond abrasive grains such as cast iron. The surface pressure pressing the silicon carbide crystal substrate 2 to a polishing platen 1, when the thickness is the polishing platen 1 with 0.5mm of cast iron 50gf / cm ² ~200gf / cm ² of silicon carbide crystal substrate 2 is desirable. When the surface pressure is lower than 50 gf / cm ^{2, the} silicon carbide crystal substrate 2 cannot be processed practically. On the contrary, when the surface pressure is higher than 200 gf / cm ² , the silicon carbide crystal substrate 2 is likely to crack. Become. Similarly, when the polishing surface plate 1 is tin, it may be 50 gf / cm ^{2 to} 400 gf / cm ² . Since tin is soft compared to cast iron, even if a higher pressure is applied, the substrate is not easily damaged, and the surface pressure can be increased. The polishing surface plate may be made of a material containing chromium oxide, silicon nitride, copper, lead, pure iron, phenol resin, or the like.

  The number of rotations of the silicon carbide crystal substrate 2 provided by the polishing surface plate 1 and the arm 6 is the size of the polishing surface plate 1, the silicon carbide crystal substrate 2, the material of the polishing surface plate 1, the groove shape and the silicon carbide crystal substrate 2. Depending on the combination, the concentration of the polishing liquid 7, the temperature during processing, the humidity, and the shape of the polishing apparatus, the polishing surface plate 1 made of cast iron has a diameter of 200 mm, the silicon carbide crystal substrate 2 has a diameter of 5.08 cm (2 inches), and polishing. When 5 cc of liquid 7 is dropped per minute, the maximum is 40 rpm. When the other polishing processing conditions are the same, the processing efficiency deteriorates when the rotational speed is small, but damage to the surface of the silicon carbide crystal substrate 2 is small, so that it is particularly effective in the final stage of the present embodiment. . On the contrary, when the rotational speed is large, the polishing liquid 7 on the polishing surface plate 1 is likely to be scattered, and the polishing surface plate 1 is more easily dried. Drying of the polishing surface plate 1 must be avoided because it leads to the occurrence of agglomeration of abrasive grains on the polishing surface plate 1 and causes deep processing flaws.

  The number of revolutions of the polishing surface plate 1 and the silicon carbide crystal substrate 2 is normally decreased as the size of the polishing object corresponding to the polishing surface plate 1 and the silicon carbide crystal substrate 2 in the present embodiment increases. preferable. When the size of the polishing surface plate 1 and the material to be polished is large, the amount of the polishing liquid 7 required to keep the surface of the polishing surface plate 1 from being dried is larger than when the polishing surface plate 1 and the material to be polished are small. For this reason, the efficiency becomes worse unless machining is performed at a lower speed. Further, when the polishing surface plate 1 is large, the peripheral speed itself of the part that is actually processed increases, so that the processing efficiency is reduced even if the number of rotations is reduced as compared with the case where the size of the polishing surface plate 1 is small. Hateful. The same applies to the size of the silicon carbide crystal substrate 2. As described above, these actual processing conditions are the size of the polishing surface plate 1, the silicon carbide crystal substrate 2, the material of the polishing surface plate 1, the combination of the groove shape and the silicon carbide crystal substrate 2, the concentration of the polishing liquid 7, the time of processing The temperature, humidity, and shape of the polishing apparatus have a great influence. Further, the polishing surface plate 1 does not need to be circular, and it is not necessary to perform polishing while rotating, and may be linear motion or unsteady motion.

  During the polishing process, it is preferable to supply the polishing liquid 7 onto the polishing surface plate 1 while constantly stirring the polishing liquid 7. This is because in the polishing liquid 7, some precipitation occurs during a long polishing process. Further, for example, a dispersant such as ethylenediaminetetraacetic acid, which is an amine material, may be added to the polishing liquid 7 to enhance the dispersibility.

  It is effective to perform the polishing step a plurality of times while changing the average particle diameter of the abrasive grains made of diamond. This is the same as other general polishing processes, but the silicon carbide crystal substrate 2 before polishing has a rough surface, so that it is a polishing abrasive made of diamond contained in the polishing liquid 7 when first polishing. It is preferable to use a grain having a large average particle diameter, and gradually reduce the average grain diameter of the abrasive grains made of diamond as the polishing process proceeds. In general, if the surface pressure applied to the substrate to be polished is the same, the processing rate increases (the polishing time decreases) and the surface roughness after polishing increases as the average particle size of the abrasive grains increases. Conversely, the smaller the average grain size of the abrasive grains, the smaller the processing rate and the smaller the surface roughness after polishing.

  The composition of the polishing liquid 7 is composed of pure water and a polishing abrasive grain component composed of diamond and boron carbide, and the content of diamond in the pure water is preferably 0.1% by weight or more and 1% by weight or less. As for the content of abrasive grains made of diamond in pure water, diamond is inherently extremely harder than other materials (Knoop hardness is about 7000-9000 diamond, boron carbide about 2750, Even if silicon carbide is about 2500 (reference is quartz 820) and it is slightly contained (if it is not 0%), sufficient polishing can be performed. However, if the content is too high, the processing becomes saturated, the processing rate does not increase, and precipitation occurs depending on the size of the abrasive grains, and the abrasive grains composed of precipitated diamond aggregate. The apparent abrasive grain size increases, and the polishing surface plate 1 and the silicon carbide crystal substrate 2 are greatly damaged during polishing. Furthermore, since the concentration distribution is generated in the polishing liquid 7, it causes unevenness in processing quality. On the other hand, when the content of abrasive grains made of diamond in pure water is low, there arises a problem that processing does not proceed.

  Subsequently, the content ratio of abrasive grains made of boron carbide to abrasive grains made of diamond contained in pure water, which is an average grain of abrasive grains made of diamond to be mixed and abrasive grains made of boron carbide It is largely controlled by the diameter. Tables 1 and 2 show that F1000 (with an average particle diameter of about 5 μm and a particle diameter of 3 μm to 7 μm is 60 μm) made of diamond having four types of average particle diameters of 10 μm, 15 μm, 20 μm and 30 μm F1200 (mean particle size is about 2 μm and abrasive particles with a particle size of 3 μm or less is 60% or more), 1500 (average particle size is about 0.5 μm, 0. Abrasive grains having a particle diameter of 5 μm or less are said to contain 60% or more.) Three types of abrasive grains made of boron carbide having an average particle diameter are mixed at a plurality of mixing ratios, and the prepared polishing liquid 7 is used. Tables 1 and 2 show the processing flaw depth and processing rate when polishing is performed.

The processing conditions are as follows. The polishing surface plate 1 was cast iron, the rotation number of the polishing surface plate 1 was 40 rpm, the surface pressure was 150 gf / cm ² , and the supply amount of the polishing liquid 7 was 5 cc per minute. Here, the processing flaw depth in Table 1 was measured with a laser microscope VK8500 manufactured by Keyence Corporation. In the present invention, all the depths of the processing flaws were measured with the same laser microscope. The processing rates in Table 2 were calculated from the difference between the weights of the silicon carbide crystal substrate 2 before and after processing measured by an electronic balance. In Table 1, x indicates that the depth of the processing flaw is 1.0 μm or more, Δ indicates that the depth of the processing flaw is 0.6 μm or more and less than 1.0 μm, and ○ indicates that the depth of the processing flaw is less than 0.6 μm Indicates. In Table 2, △ is the same as the processing rate when boron carbide is not mixed (boron carbide mixing ratio 0%), × is the processing rate slower than 10%, and ○ is △ The processing rate was increased by 10% or more, and ◎ indicates that the processing rate was increased by 30% or more with respect to Δ.

ここで表１中では示していないが、表１において示したすべての炭化ボロンを含有した加工条件において加工傷深さは、炭化ボロンを含有しない条件と比べ同等か浅くなっていることが確認された。また表１には炭化ボロン砥粒の混合範囲は、記載していないが、表１の結果において加工傷深さが０．６μｍ未満となっている条件のダイヤモンドに対する炭化ボロン含有量±１０重量％の範囲で加工傷深さ及び加工レートにおいて、良好な結果が得られた。

Here, although not shown in Table 1, it was confirmed that the processing flaw depth was the same or shallower than the conditions not containing boron carbide in the processing conditions containing all boron carbide shown in Table 1. It was. In Table 1, although the mixing range of boron carbide abrasive grains is not described, the boron carbide content with respect to diamond under the condition that the processing flaw depth is less than 0.6 μm in the result of Table 1 is ± 10% by weight. Good results were obtained in the processing flaw depth and processing rate in the range of.

  However, when the average particle diameter of diamond was 15 μm and the average particle diameter of boron carbide was 0.5 μm, the boron carbide mixing ratio with respect to diamond was good at 5 wt% or more and 20 wt% or less. When the average particle diameter of diamond is 20 μm and the average particle diameter of boron carbide is 0.5 μm, the mixing ratio of boron carbide to diamond is 20% by weight to 40% by weight, the average particle diameter of diamond is 30 μm, When the average particle size was 0.5 μm, the mixing ratio of boron carbide to diamond was 40% by weight or more and 60% by weight or less, and good results were obtained.

  When the average particle diameter of diamond is 15 μm, the average particle diameter of boron carbide is 0.5 μm, and the boron carbide to diamond mixing ratio is 5 wt% or more and 20 wt% or less, the surface roughness Rz after polishing is 1 μm or less. It was confirmed that the target value for the rough polishing step of the silicon carbide crystal substrate in the present invention was achieved. The point in the present invention is that the depth of the processing flaw is shallow and the processing rate is fast, but more important is that the depth of the processing flaw is shallow, so Table 1 is important when searching for effective conditions in the present invention. . Normally, there are applications where the processing depth is shallow and the processing rate is slow, but there are no applications for conditions where the processing depth is deep and the processing rate is high, so diamond abrasive grains and boron carbide abrasive grains A method of polishing a silicon carbide crystal substrate using the composite abrasive grains is useful.

  From the results shown in Tables 1 and 2, it can be confirmed that the effect of reducing the processing flaw depth and improving the processing rate is high by mixing the abrasive grains made of small boron carbide with the abrasive grains made of large diamond. For example, when the average particle diameter of diamond is 10 μm, good results are not obtained, but it can be seen that better results are obtained as the average particle diameter of diamond is increased to 20 μm and 30 μm. Further, when the condition that the average particle diameter of diamond is 20 μm is seen, it can be seen that the smaller the average particle diameter of boron carbide is, the better results are obtained. In particular, a remarkable tendency can be seen in the processing rate.

  In Table 1, the case where the depth of the processing flaw is less than 0.6 μm is indicated by “◯”, and FIG. 2 shows the relationship between the processing time and the processing amount under the condition where the result of “◯” is obtained. In addition, FIG. 2 also shows the case of polishing abrasive grains (average particle diameter of 15 μm) consisting only of diamond abrasive grains, which is a conventional condition.

  From this, it can be confirmed that the machining amount is dramatically increased at the machining rate when the machining flaw depth (0.6 μm or less) is considered under the condition (4) in FIG. For example, when cutting the silicon carbide crystal substrate 2 by 50 μm, it takes about 50 minutes under the conventional conditions (condition (1) in FIG. 2). However, the polishing abrasive grains made of diamond having an average particle diameter of 30 μm have a thickness of 0.5 μm. Under the condition (4) in which abrasive grains made of boron carbide having an average particle diameter are mixed, the time required for cutting the silicon carbide crystal substrate 2 by 50 μm is only about 15 minutes. Further, the depth of the processing flaw on the surface of the silicon carbide crystal substrate 2 at this time was 0.6 μm or more and less than 1.0 μm under the conventional condition (1), but decreased to less than 0.6 μm under the condition (4). Therefore, it is possible to greatly reduce the burden in the precision polishing process using colloidal silica or the like in the subsequent process.

  Of course, regarding the processing rate, even when only diamond abrasive grains not mixed with boron carbide abrasive grains are used, the processing rate is close to that when boron carbide abrasive grains having an average particle diameter corresponding to the average particle diameter of each diamond abrasive grains are mixed. However, when the composite abrasive is used, the processing rate considering the processing flaw depth is improved as compared with the case where the abrasive abrasive using only the diamond abrasive is used.

  The following can be said by summarizing the results of Tables 1 and 2. It can be confirmed that if the average grain size of the abrasive grains made of diamond is 10 μm or more and 30 μm or less, the processing flaw depth can be reduced. Here, when the average grain size of the abrasive grains made of diamond is 10 μm, the effect of suppressing the processing scratch depth is confirmed, but the practicality is low. On the other hand, if it exceeds 30 μm, it is not easy to disperse the abrasive grains in the polishing liquid 7 because the abrasive grains are too large, and precipitation and aggregation of the abrasive grains occur during the polishing process. Not right.

  If the average particle size of the abrasive grains made of boron carbide is 3 μm (F1200) or less, there is a condition that the depth of the processing flaw becomes shallow and the processing rate is also increased by 30% or more. The average particle size of boron is preferably 0.5 μm (1500) or less.

  Since the processing flaw is determined by the diamond abrasive grains, the smaller the average particle size, the shallower the processing flaw depth. However, the processing rate is better as the average grain size of the diamond abrasive grains is larger, and a processing example in which boron carbide abrasive grains are mixed is shown as a condition that the average grain diameter of the diamond abrasive grains is smaller and the processing rate is also better. From Table 1 and Table 2, the average particle diameter of the diamond abrasive grains is 15 μm, the average particle diameter of the boron carbide abrasive grains is 0.5 μm, and the mixing ratio is 5 to 15% by weight.

  When mixed abrasive grains with boron carbide are used, the results of Tables 1 and 2 show that when the average grain size of abrasive grains made of diamond is reduced, the surface roughness after processing of the silicon carbide crystal substrate is reduced. In many cases, Rz of 1 μm or less can be obtained. As conditions where the depth of processing flaws is shallow and the processing rate is high, the average grain size of abrasive grains made of diamond is 15 μm, the average grain size of abrasive grains made of boron carbide is 0.5 μm (1500), and boron carbide against diamond The mixing ratio of 10 wt% (5 wt% or more and 20 wt% or less) can be said to be most suitable as the final polishing condition in the rough polishing step in the present invention. Here, the abrasive grains made of diamond having an average grain size of 15 μm contain 50% or more of abrasive grains having a diameter of 12 μm to 16 μm.

  When abrasive grains made of boron carbide are mixed with abrasive grains made of diamond and used as polishing liquid 7, the reason is that the depth of machining flaws is reduced and the machining rate is improved. This is because diamond and boron carbide are improved. It can ask for the fluidity of each abrasive grain. Since it is difficult to confirm the fluidity of the polishing liquid 7 itself, the fluidity of the diamond and boron carbide abrasive grains was confirmed instead. As a method for confirming the fluidity of powder, there is a method called angle of repose measurement. The angle of repose varies greatly depending on the measurement environment and is not suitable for quantitative measurement, but it can be measured easily and is one of the basic data of powder flowability. As a method of measuring the angle of repose, the container is filled with powder, and the angle at which the slip occurs when the container is tilted is confirmed. That is, if slip occurs at a lower angle, the fluidity is high, and conversely, if slip occurs at a high angle, the fluidity is low. By measuring the angle of repose, it was confirmed that the abrasive grains made of boron carbide (repose angle: about 40 °) have higher fluidity than the abrasive grains made of diamond (repose angle: about 60 °), and made of diamond. Composite abrasive grains containing 10% boron carbide abrasive grains in the abrasive grains are intermediate repose angle values between the single abrasive grains composed of diamond and the single abrasive grains composed of boron carbide (the angle of repose). : About 50 °), and it was confirmed that the fluidity of the particles was increased by incorporating abrasive grains made of boron carbide into abrasive grains made of diamond.

  From the measurement result of the angle of repose, when the content of abrasive grains made of boron carbide with respect to abrasive grains made of diamond contained in pure water is low, fluidity does not increase, and conventional abrasive grains made of diamond alone Processing in a state equal to the processing in step 1 is performed, which causes deep scratches to be formed on the surface of the silicon carbide crystal substrate 2. On the other hand, when the content of abrasive grains made of boron carbide with respect to abrasive grains made of diamond contained in pure water is high, the polishing fluid 7 becomes too fluid and the abrasive grains made of diamond are more slippery. As a result, the processing on the surface of the silicon carbide crystal substrate 2 does not proceed, which causes a decrease in workability. In addition, the abrasive grain concentration is increased in part, and agglomeration of the abrasive grains occurs, which may cause sudden processing flaws.

  Boron carbide is one of the hardest materials except diamond and is chemically stable, so that the silicon carbide crystal substrate 2 can be stably polished without being deformed during the polishing process. Can do.

  That is, in the present invention, polishing the silicon carbide crystal substrate 2 using the polishing liquid 7 containing an appropriate amount of abrasive grains made of boron carbide in abrasive grains made of diamond contained in pure water is carbonization. The inclusion of the abrasive grains made of boron improves the fluidity of the abrasive grains made of diamond, and as a result, the momentum of the abrasive grains made of diamond and boron carbide increases, so that the silicon carbide crystal substrate 2 can be made faster. In addition, the slip of the abrasive grains made of diamond and boron carbide is improved, so that the abrasive grains made of diamond do not pierce the silicon carbide crystal substrate 2 deeply, and deep work scratches are less likely to occur. I can say that. As a result, the processing scratches in the rough polishing step become shallow, and it becomes possible to reduce the burden of precision polishing using colloidal silica or the like, which is a subsequent step.

  Hereinafter, the effect of the polishing method of the present invention will be described in detail with reference to an example in which the processing flaw depth was measured using the polishing apparatus of FIG. Shown in

表３のサンプル１においては、純水とそれぞれ粒径の異なるダイヤモンドからなる研磨砥粒と炭化ボロンからなる研磨砥粒を含む２種類の研磨液７を使用した。１つ目の研磨液７は純水中に０．２重量％で平均粒径３０μｍのダイヤモンドからなる研磨砥粒を含有させ、そのダイヤモンドに対して５０重量％の割合で平均粒径０．５μｍの炭化ボロンからなる研磨砥粒を含有したものである。２つ目の研磨液７は純水中に０．２重量％で平均粒径１５μｍのダイヤモンドからなる研磨砥粒を含有させ、そのダイヤモンドに対して１０重量％の割合で平均粒径０．５μｍの炭化ボロンからなる研磨砥粒を含有したものである。上記２つの研磨液７のうちダイヤモンドからなる研磨砥粒の平均粒径が３０μｍのものを第１工程、上記２つの研磨液７のうちダイヤモンドからなる研磨砥粒の平均粒径が１５μｍのものを第２工程として使用した。それぞれ研磨加工中には研磨砥粒の沈殿が生じないように研磨液７中を攪拌子１０により攪拌を行った。ダイヤモンドは有限会社エフアールティージャパン製のダイヤモンド砥粒を用い、炭化ボロンはＷａｃｋｅｒＣｅｒａｍｉｃｓ社製の炭化ボロン砥粒を使用した。

In Sample 1 of Table 3, two types of polishing liquids 7 containing polishing grains made of pure water and diamonds each having a different particle diameter and polishing grains made of boron carbide were used. The first polishing liquid 7 contains 0.2% by weight of abrasive grains made of diamond having an average particle diameter of 30 μm in pure water, and the average particle diameter of 0.5 μm at a ratio of 50% by weight to the diamond. It contains abrasive grains made of boron carbide. The second polishing liquid 7 contains abrasive grains made of diamond having an average particle diameter of 15 μm at 0.2 wt% in pure water, and an average particle diameter of 0.5 μm at a ratio of 10 wt% to the diamond. It contains abrasive grains made of boron carbide. Of the two polishing liquids 7, one having an average particle diameter of 30 μm of abrasive grains made of diamond is the first step, and one of the two polishing liquids 7 having an average particle diameter of polishing abrasive grains made of diamond of 15 μm. Used as the second step. In each of the polishing processes, the polishing liquid 7 was stirred with a stirrer 10 so as not to cause precipitation of polishing abrasive grains. The diamond used was diamond abrasive grains manufactured by FRT Japan Co., Ltd., and the boron carbide used was boron carbide abrasive grains manufactured by Wacker Ceramics.

  As the silicon carbide crystal substrate 2, a SiC single crystal substrate manufactured by CREE, INC having an initial surface roughness Rz (maximum height) = 50 μm and a 2-inch size was used. Rz was measured with a stylus type shape measuring instrument Surfcorder SE3500 manufactured by Kosaka Laboratory. Electron wax made by Nikka Seiko Co., Ltd. was used for attaching the silicon carbide crystal substrate 2 to the attaching jig 3.

The polishing surface plate 1 was cast iron in the first step and tin in the second step. 5 cc of the polishing liquid 7 is dropped on the polishing platen 1 per minute, the rotation speed of the polishing platen 1 and the arm 6 is set to 40 rpm in the same direction, and the weight 4 is applied to the silicon carbide crystal substrate 2 at a surface pressure of 150 gf / cm. A pressing force of ² was applied. The processing time was 10 minutes for the first step and 15 minutes for the second step, and after completion of the second step, the surface state of the silicon carbide crystal substrate 2 was Rz = 1 μm.

  In Comparative Example 1, a polishing liquid 7 containing diamond abrasive grains manufactured by FRT Japan Ltd. in pure water was used. As the abrasive grains made of diamond, those having an average particle diameter of 15 μm in the first step and those having an average particle size of 1 μm in the second step were used. Example 1 was the same as Example 1 except that the polishing liquid 7 used contained only abrasive grains of diamond. The processing time was 20 minutes for the first step and 30 minutes for the second step.

  Table 3 shows the processing rate and the processing flaw depth under the respective processing conditions among the polishing processing results of the first step, the second step, the first step of the comparative example 1, and the second step of Example 1. Show. The processing rate is a value obtained by measuring the weight of the silicon carbide crystal substrate 2 before and after polishing with an electronic balance and calculating the amount of processing removal calculated by assuming the specific gravity of the silicon carbide crystal substrate 2 to be 3.2. . The processing flaw depth is a value measured by the above-mentioned laser microscope.

  As shown in Table 3, it can be seen that Sample 1 is improved in both the processing rate and the processing flaw depth as compared with the case of using the polishing liquid 7 consisting only of diamond of Comparative Example 1. Here, the polishing liquid 7 used in the second step of Sample 1 is the same as that shown in FIG. 2 (2), but the processing rate is different because the hardness of the polishing surface plate 1 is different. That is, since the surface plate used is slightly harder than the polishing surface plate used in (2) of FIG. 2, the processing rate is about half, but compared with Comparative Example 1, the processing rate is 10 times or more in the second step. There is an improvement.

  From Table 3, a processing rate of 180 μ / h was obtained at a processing scratch depth of 0.55 μm in the first step, and a processing rate of 35 μm / h was obtained at a processing scratch depth of 0.53 μm in the second step. Therefore, if the polishing process is performed under the conditions of the sample 1, the processing can be performed at a higher speed and without giving deep processing scratches to the silicon carbide crystal substrate 2 as compared with the conventional case, and the silicon carbide crystal with higher quality can be obtained. The substrate 2 can be obtained.

  According to the present invention, by mixing abrasive grains made of diamond with abrasive grains made of boron and using it as a polishing liquid, compared to polishing with ordinary abrasive grains made of diamond, It is possible to provide a silicon carbide crystal substrate that can prevent damage to the silicon carbide crystal substrate at high speed, and is useful as a method for polishing a silicon carbide crystal substrate.

Configuration diagram of polishing apparatus for silicon carbide crystal substrate of the present invention The figure for demonstrating the relationship between the processing time and the processing amount in the grinding | polishing method of a silicon carbide crystal substrate

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polishing surface plate 2 Silicon carbide crystal substrate 3 Sticking jig 4 Weight 5 Work guide 6 Arm 7 Polishing liquid 8 Tubing pump 9 Silicon tube 10 Stirrer 11 Stirrer 12 Assembly of weight and work guide 15 Storage tank

Claims (7)

An abrasive slurry containing diamond abrasive as a main component is dripped onto a rotating polishing surface plate, and a silicon carbide crystal substrate as a material to be polished is pressed against the polishing surface plate with a predetermined pressure. In the polishing method of the silicon carbide crystal substrate to be polished,
A silicon carbide crystal substrate after surface processing to a surface roughness Rz = 50 μm or less in advance,
Boron carbide abrasive grains smaller than the average grain diameter of the diamond abrasive grains are used as a second abrasive, and are mixed at a predetermined weight ratio according to the average grain diameter of the diamond abrasive grains. A method for polishing a silicon carbide crystal substrate, characterized by polishing the thickness less than a predetermined value. An abrasive slurry containing diamond abrasive as a main component is dripped onto a rotating polishing surface plate, and a silicon carbide crystal substrate as a material to be polished is pressed against the polishing surface plate with a predetermined pressure. In the method for polishing a silicon carbide crystal substrate in which a plurality of polishing steps are sequentially performed using abrasives having different average particle diameters of the diamond abrasive grains,
Boron carbide abrasive grains smaller than the average grain size of the diamond abrasive grains as the second abrasive,
The mixing ratio of the boron carbide is determined in accordance with the average particle diameter of the diamond abrasive grains used in each polishing step, and the maximum polishing ratio is 60% with respect to the abrasive of the diamond abrasive grains. A method for polishing a silicon carbide crystal substrate, characterized in that the average grain size of diamond abrasive grains used in the process is 30 μm, and the average grain diameter of the diamond abrasive grains is reduced in the sequential polishing process. The method for polishing a silicon carbide crystal substrate according to claim 2, wherein the boron carbide abrasive grains have an average particle diameter of about 0.5 μm. The final polishing step of the sequential polishing step performed by changing the average particle diameter of the diamond abrasive grains is such that the average particle diameter of the diamond abrasive grains is 15 μm and the weight mixing ratio of boron carbide abrasive grains is 5% to 20%. The method for polishing a silicon carbide crystal substrate according to claim 3. 2. The method for polishing a silicon carbide crystal substrate according to claim 1, wherein the predetermined pressure is 50 gf / cm ² to 400 gf / cm ² . A polishing liquid is dropped on a polishing surface plate rotating a polishing material slurry containing a polishing agent mainly containing diamond abrasive grains in water, and a silicon carbide crystal substrate as a material to be polished is applied to the polishing surface plate with a predetermined pressure. In the silicon carbide crystal substrate polishing apparatus pressed and polished with
An affixing jig for affixing a silicon carbide crystal substrate that has been surface-treated to a surface roughness Rz = 50 μm or less in advance;
A weight for applying a predetermined surface pressure to press the silicon carbide crystal substrate against the polishing surface plate via the attaching jig;
A storage tank for storing a polishing liquid containing water containing composite abrasive grains in which a predetermined weight ratio of boron carbide is mixed with diamond abrasive grains of a main abrasive;
A stirring bar installed at the bottom of the storage tank for stirring the polishing liquid in the storage tank;
With
A silicon carbide crystal substrate comprising: a silicon carbide crystal substrate, wherein the silicon carbide crystal substrate is polished while rotating a bonding jig on which the silicon carbide crystal substrate is bonded, stirring the polishing liquid using the stirrer, and dropping the polishing liquid on the polishing platen. Polishing equipment. The apparatus for polishing a silicon carbide crystal substrate according to claim 6, wherein the predetermined surface pressure is 50 gf / cm ² to 400 gf / cm ² .

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