JP2007061961A - Manufacturing method of lapping plate and mechanical lapping method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lapping plate, reducing the load of CMP and shortening the machining time of CMP, in a lapping plate in the pre-process of CMP. <P>SOLUTION: An SiC monocrystal substrate is mechanically lapped using a lapping plate formed with a predetermined flatness manufactured by a facing process of cutting the surface of the lapping plate made of material quality having a predetermined hardness and generating two kinds of grooves by machining, a shaving process of shaving with a circular-arc shaving tool, and a process of charging the lapping plate after the shaving process using a charging ring. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a lapping platen used for mechanical polishing of a SiC single crystal substrate and a mechanical polishing method using the lapping platen.

  Power devices with low electrical energy loss and high performance directly contribute to a significant reduction in power consumption, and are used in many fields. Currently, a power device using a silicon substrate is used. However, due to material characteristics of silicon, there is a limit to further improving the performance of the power device by performing fine processing on silicon. In particular, since silicon cannot be used under conditions such as high temperatures, materials that replace silicon have become necessary.

  For example, SiC (silicon carbide) is an alternative material for silicon, but the forbidden band width of SiC is three times that of silicon, so that 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 SiC has excellent characteristics as described above, the SiC substrate is attracting attention as a semiconductor substrate for power devices that replaces the silicon substrate.

By the way, in order to use a SiC substrate as a power device, it is necessary to polish the surface. In the final polishing process, a polishing method using a suspension containing SiO ₂ (colloidal silica), which is a polishing method that does not leave a work-affected layer, is commonly used at present. (For example, refer to Patent Document 1).
JP 7-288243 A

  The first purpose of CMP polishing is to completely remove the work-affected layer in the previous step, and the second is to finish the surface to an average surface roughness of Ra = 0.2 nm. In order to achieve this, several tens of hours of processing time are required. The present invention has been made in view of the above, and by improving the lapping platen and lapping conditions of the mechanical lapping process, which is a pre-process of CMP, the burden of CMP is reduced and the CMP processing time is shortened. With the goal.

  In order to solve the above-mentioned conventional problems, the lapping platen manufacturing method of the present invention is a lapping platen manufacturing method used for mechanical polishing of compound semiconductors, in which the lapping platen made of a material having a predetermined hardness is rotated. However, the surface of the lapping platen is cut flat and the two types of grooves are machined and generated, and the arc-shaped shaving jig having a predetermined radius is rotated at a rotation speed lower than the rotation speed of the lapping platen. A shaving process for shaving, and a charging process by rotating the lapping platen after the shaving process at a rotation speed lower than that of the lapping platen using a charging ring. The board is formed with a predetermined flatness.

  The mechanical lapping method of the present invention is a mechanochemical lapping method for polishing a compound semiconductor workpiece by two-step lapping with different processing conditions, and the first lapping of the two-step lapping is diamond coating The second fine wrapping is characterized by polishing with fixed coating particles charged on the lapping platen.

  According to the lapping plate manufacturing method and the mechanical lapping method of the present invention, the polishing time required for several tens of hours in the final CMP polishing step of a compound semiconductor substrate having a high hardness such as SiC is reduced to the lapping platen of the previous step. It becomes possible to shorten to several hours by improvement by improving accuracy.

  Embodiments of a lapping surface plate manufacturing method and a mechanical lapping method according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of a polishing apparatus used in the single-sided lapping method used in the present invention. The single-sided wrapping apparatus used was a general desktop type. The lapping platen 1 was mounted on a lapping device and rotated counterclockwise. The SiC single crystal substrate 2 as the workpiece was fixed to the disk jig 3 with temporary bonding wax and rotated counterclockwise by the forced drive device 4. As the surface of the wrapping plate 1, a surface finished by facing, shaving and charging described later is used. As the slurry, diamond slurry was used, and an appropriate amount was dropped onto the lapping platen by the dispenser 5. Lapping is a processing method for transferring the shape of a polisher (here, lapping platen) to a workpiece.

  Specifically, while the diamond slurry rolls between the wrapping surface plate and the workpiece, the wrapping surface side is less affected because diamond is embedded as fixed abrasive grains by charging described later, The workpiece side is made of a material that is softer than diamond, so the surface protrusions are slowly scraped under the influence of the rolling diamond while tracing the shape of the lapping surface plate, and finally the lapping surface plate and the work surface. Things get closer to the same shape. That is, the surface shape of the lapping surface plate is transferred to the workpiece side. Therefore, the processing accuracy of the workpiece depends on the accuracy of the lapping platen, and the key is how to finish the lapping platen.

  In the present invention, the material of the wrapping surface plate is selected so that the work-affected layer and the flatness can be optimized. Further, in order to optimize the accuracy of the wrapping surface plate, shaving and further charging processing are performed after facing. Was given. The target was achieved by mechanical lapping using this lapping surface plate under appropriate machining conditions.

Hereinafter, (1) the material of the lapping surface plate, (2) facing, (3) shaving, (4) charging, and (5) lapping conditions will be described in detail step by step.
(1) Material of lapping surface plate First, regarding the material of the lapping surface plate, a tin plate having a purity of 99% was used in the examples of the present invention. Table 1 compares the materials of the lapping surface plate.

表中左側の材料ほど硬度が高く、この中では銅が最も硬い。また、右側の材料ほど硬度が低く、ポリウレタン製のパッドが最も軟らかい。比較項目の加工変質層は、被加工物に与える加工変質層の深さで、◎、○、△、×の順に深くなっていく。平坦性は、被加工物の平坦度で、◎、○、△、×の順に悪くなっていく。表１から加工変質層と平坦度は、ラッピング定盤の硬さと密接な関係があり、トレードオフの関係にあることがわかる。一般的には、平坦度のことは軽視されがちであるので、加工変質層が非常に少なく、フェーシング等の面倒な処理がまったく必要ない研磨パッドが使用されているが、本発明においては、ＣＭＰの加工時間を大きく左右しているのは、加工変質層よりも平坦度であると考え、加工変質層を最小限に抑えることが可能で、しかも平坦度を保ちやすい錫製プレートを選択し、さらに後で詳細に説明するフェーシング、チャージング等の処理を施すことで、さらなる平坦度の向上を達成した。
（２）フェーシング工程
次に、図２を用いてラッピング定盤のフェーシング工程について詳細に説明する。フェーシングとは、ラッピング定盤の表面を平坦度１μｍ程度に切削加工し、砥粒の保持等を目的とした溝や、ラッピング時に発生する切りくずを排出するための溝を加工する工法のことである。本発明においては、図２に示すような一般的なフェーシング装置を使用した。ラッピング定盤１は、スピンドルモータ（図中記載なし）により回転可能でエアー軸受け（図中記載なし）によって支えられた回転テーブル６上にセットされ、回転テーブル６とともに回転しながら、フェーシングアーム７の先端にセットされたダイヤモンドバイト８により、ラッピング定盤１の中心から外周に向かって切削加工される。ラッピング定盤の回転速度に対して、ダイヤモンドバイト８の移動速度が充分遅い場合、ラッピング定盤の表面は溝の無いフラット面に加工され、逆に、ラッピング定盤の回転速度に対して、ダイヤモンドバイト８の移動速度が速い場合、その速度差によって違ったピッチの溝が形成される。

The material on the left side of the table has a higher hardness, and copper is the hardest of these. Further, the material on the right side has a lower hardness, and the polyurethane pad is the softest. The work-affected layer of the comparison item is the depth of the work-affected layer given to the workpiece, and becomes deeper in the order of ◎, ◯, Δ, ×. The flatness is the flatness of the workpiece, and becomes worse in the order of ◎, ○, Δ, ×. From Table 1, it can be seen that the work-affected layer and the flatness are closely related to the hardness of the lapping platen and have a trade-off relationship. In general, since flatness tends to be neglected, a polishing pad is used that has very few work-affected layers and does not require any troublesome treatment such as facing. However, in the present invention, CMP is used. The processing time is greatly affected by the flatness of the work-affected layer, and a tin plate that can minimize the work-affected layer and keep the flatness is selected. Furthermore, the flatness was further improved by performing processing such as facing and charging described in detail later.
(2) Facing process Next, the facing process of the lapping surface plate will be described in detail with reference to FIG. Facing is a method of cutting the surface of a lapping surface plate to a flatness of about 1 μm and machining grooves intended to hold abrasive grains and grooves for discharging chips generated during lapping. is there. In the present invention, a general facing device as shown in FIG. 2 is used. The lapping platen 1 is set on a rotary table 6 that can be rotated by a spindle motor (not shown in the drawing) and supported by an air bearing (not shown in the drawing). Cutting is performed from the center of the lapping surface plate 1 toward the outer periphery by the diamond cutting tool 8 set at the tip. When the moving speed of the diamond tool 8 is sufficiently slow relative to the rotational speed of the lapping surface plate, the surface of the lapping surface plate is processed into a flat surface without a groove. When the moving speed of the cutting tool 8 is high, grooves having different pitches are formed depending on the speed difference.

  The groove shape that can be formed by using a facing device is spiral and concentric, and the effect is considered to be the same, but due to the processing principle of the facing device, it takes a longer time to form a concentric circle than a spiral. The spiral was selected to have Actually, two types of grooves are formed, and the first groove has a spiral shape, and the second groove is deeper than the first groove with a predetermined pitch interval between the spiral grooves. Concentric grooves are formed.

  Specifically, as described above, in the facing, the diamond tool 8 is brought into contact with the vicinity of the center of the lapping platen while the lapping platen is rotated at a constant speed, and is moved in the outer peripheral direction of the lapping platen at a constant speed. The groove depth is determined by the contact depth between the diamond bit 8 and the lapping surface plate, and the groove pitch is determined by the relationship between the number of rotations of the polishing surface plate and the moving speed of the diamond bit 8. Of course, the groove has a continuous spiral shape from the center to the outer periphery.

  Also, when forming concentric grooves, rotate the wrapping platen once with the diamond bite in contact with the wrapping platen to form the first groove, and then according to the groove pitch. The second groove is formed by further rotating the lapping platen while the diamond bit 8 is moved by a certain distance, which is much more time-consuming than the former. In addition, as an apparatus capable of forming grooves, a typical milling machine can be used as a processing machine, and a grid-like groove can be formed. However, a fine groove such as the first groove in this embodiment can be used. Formation is considered difficult due to the limit of miniaturization of the end mill, which is a processing tool.

  FIG. 3A is a view of the lapping surface plate 1 according to the present invention as viewed from above. The groove formed by facing is formed as an image spreading spirally from the center of the lapping platen toward the outside. FIG. 3B is a detailed view of the groove shape of the lapping surface plate 1 according to the present invention. In FIG. 3B, the difference between the maximum portion and the minimum portion in the groove peak portion is the flatness of the lapping platen, and the flatness of the facing is about 1 μm. The grooves 9 were produced for the purpose of discharging unnecessary abrasive grains, and the pitch was 1.8 mm and the depth was 1.5 mm. The grooves 6 were produced for the purpose of holding the abrasive grains, and the pitch was 0.3 mm and the depth was 0.75 mm. The groove shape is not limited to this specification, but it is known that when the groove 9 is not present or too shallow, clogging occurs and the processing rate is drastically reduced. Moreover, it can be said that it is necessary to optimize the groove | channel 10 with the kind and particle size of an abrasive grain.

The purpose of the grooves 9 and 10 will be further described. If a polishing surface plate having no grooves is used, the abrasive grains are not held, so that the abrasive particles only slide between the workpiece and the polishing surface plate. It is clear that processing does not progress. Therefore, the groove 10 is necessary. Next, when only the groove 10 is produced and the groove 9 is not present, the abrasive grains are in contact with the entire polished surface of the workpiece, so as to obtain a necessary processing pressure (load ÷ workpiece area). Requires a considerable load. That is, since a processing pressure is applied to the entire portion where the groove 10 exists, a large weight is required to obtain a desired processing rate. Therefore, when processing is possible with a load within an appropriate range, a second groove having a certain depth such as the groove 9 is required.
(3) Shaving process Next, the shaving process will be described. As described above, the flatness of the processed surface of the lapping platen after facing is about 0.5 μm to 1.5 μm, depending on the accuracy of the facing device. (Difference between maximum and minimum peak in Fig. 3 (B))
When the lapping surface plate in this state is used, two problems occur. One is that, as mentioned earlier, lapping is a method of transferring the shape of a lapping platen to the work piece. Limits arise. Secondly, in the charging in which diamond abrasive grains are embedded in the surface of the lapping platen, 5 to 10 times the charging time required when shaving is applied, or even in the worst case, uniform charging cannot be performed. Problems occur.

  FIG. 4 is an explanatory diagram of the shaving method in the present invention. First, the lapping plate 1 is set on the single-sided lapping apparatus described with reference to FIG. 1, and the shaving jig 11 is set on the lapping surface plate 1. The shaving jig is adjusted to 500 g to 5000 g including its own weight depending on the processing state. The rotation speed of the lapping platen was 5 to 10 rpm, and the rotation speed of the shaving jig 11 was 1 to 5 rpm. The rotational speed of the shaving jig 11 must be smaller than the rotational speed of the wrapping surface plate. If the rotational speed of the wrapping surface plate is exceeded, a deep flaw is generated on the wrapping surface plate, making it unusable. By processing in this state for 5 to 30 minutes, the flatness of the lapping surface plate can be improved to 0.2 μm or less.

  FIG. 5 is an explanatory diagram of the shaving jig 11 according to the present invention. The material of the shaving jig 11 was alumina. In addition to alumina, it can be used if it is sufficiently harder than a lapping plate such as zirconia or carbide. The surface (lower surface) of the shaving jig 11 that is in contact with the lapping platen is a spherical surface of R100 m and has a cross-sectional shape as shown in FIG. By taking such a shape, only the inner peripheral end surface (the cutting edge in FIG. 5) of the lower surface of the shaving jig comes into contact with the lapping surface plate. In other words, it works as a cutting edge. Conversely, when minus R100 m is set, the outer peripheral end surface comes into contact with the lapping surface plate to form a cutting edge. If the lower surface is flat, no cutting edge is generated because the surface comes into contact with the lapping surface plate. That is, it is not shaved. When the outer side is a cutting edge, the cutting edge portion has an acute angle with respect to the lapping surface plate, so that the sharpness is improved. On the other hand, it is easy to make deep scratches on the lapping surface plate. On the other hand, when the inner periphery is a cutting edge, the cutting edge becomes obtuse with respect to the lapping surface plate, so that the sharpness is deteriorated. When the sharpness is good, it is easy to leave deep scratches on the lapping surface plate, so it is better to use the inner periphery with poor sharpness as the cutting edge. Further, the spherical R is not fixed to R100m, but if R is too small, it is easy to cause a processing flaw, and conversely if it is too large, it is hardly shaved.

  FIG. 6 is a diagram illustrating a cross-sectional shape of the lapping platen after the shaving process. It can be seen that the difference (flatness) between the maximum portion and the minimum portion in the peak portion of the groove is improved within 0.2 μm. Further, the peak portion of the mountain is cut away to form a flat portion for embedding (charging) the lapping abrasive grains. In the present invention, the width of the flat portion is adjusted to about 0.1 mm by adjusting the shaving time.

(4) Charging Step Next, the charging step will be described. After the shaving is completed, the lapping platen is thoroughly wiped with IPA and waste, and the shaving jig 11 is replaced with the charging ring 12 shown in FIG. The charging ring 12 was made of alumina, and its cross-sectional shape was flat, and the end face was chamfered to invite diamond abrasive grains. The chamfer width was 1 mm.

  FIG. 8 is an image diagram when the diamond abrasive grains 13 a are charged on the lapping platen 1. The lapping platen 1 rotates in the direction of the arrow in the figure, and carries the diamond slurry 13 applied on the lapping platen 1 to the charging ring 12. The diamond abrasive grains 13 a contained in the diamond slurry 13 are attracted between the charging ring 12 and the lapping platen 1 by the invitation provided on the lower end surface of the charging ring 12. The induced diamond abrasive grains are embedded in the surface of a lapping surface plate made of tin, which is overwhelmingly softer than diamond or alumina. In other words, it will be charged. As more specific charging conditions, the lapping platen is rotated at 20 rpm and the charging ring 12 is rotated at 5 rpm while dropping diamond abrasive grains having an average particle size of 0.125 μm on the lapping platen at a rate of 1 cc per minute. I let you. The charging ring 12 was 5 kg including its own weight. Although depending on the state of shaving, diamond abrasive grains can be uniformly embedded in the entire surface of the lapping platen in 1 to 2 hours.

FIG. 9 is an image of the surface state of the lapping surface plate 1 after charging. Since the diamond abrasive grains 13a are uniformly embedded in the surface of the lapping platen 1 and are firmly held by the stress inside the lapping platen, they do not fall off during subsequent lapping.
(5) Wrapping method Next, the mechanical wrapping conditions of the present invention will be described. Table 2 is an example of the mechanical wrapping conditions in the present invention. In the present invention, the processing conditions are divided into two stages of lapping and fine lapping. In lapping, the processing-affected layer in the previous process is efficiently removed, and the surface condition is set to be finished with high precision in fine lapping. .

ラフラッピングプロセスにおいては、ラッピング定盤１の回転数を５０ｒｐｍ、ＳｉＣ単結晶基板２の回転数（ワーク回転数）を２５ｒｐｍとした。また、ラッピング定盤上に粒径０．１２５μｍのダイヤモンドスラリーを毎秒１滴の割合で滴下し、ＳｉＣ単結晶基板２に加える荷重は、２００ｇ/ｃｍ²とした。

In the lapping process, the rotation speed of the lapping platen 1 was set to 50 rpm, and the rotation speed (workpiece rotation speed) of the SiC single crystal substrate 2 was set to 25 rpm. A diamond slurry having a particle size of 0.125 μm was dropped on the lapping plate at a rate of 1 drop per second, and the load applied to the SiC single crystal substrate 2 was 200 g / cm ² .

  In this example, a diamond slurry having an average particle diameter of 0.125 μm was used. First, regarding the particle diameter, the finer the work, the smaller the work-affected layer can be made. Since the dependence on the accuracy of the lapping platen is high, no significant improvement is seen even if the particle size is further reduced. As for the type of abrasive grains, there are boron carbide and the like in addition to diamond, but it is predicted that the flatness tends to deteriorate because the sharpness is dull compared to diamond. The lapping process was performed for about 40 minutes, the surface roughness (Ra) after lapping was about Ra = 0.5 nm, and the work-affected layer was about 200 nm.

  Next, in the fine wrapping process, after the lapping, all loose abrasive grains on the lapping platen are wiped off with a waste cloth, followed by fine wrapping. In fine wrapping, oil is dropped instead of slurry, and processing is performed only with fixed abrasive grains embedded in the wrapping surface plate in a state where free abrasive grains are completely eliminated. In the fine wrapping process, the rotational speed of the lapping platen 1 was 10 rpm, and the rotational speed of the SiC single crystal substrate was 5 rpm. By processing for 10 to 20 minutes under these conditions, the surface roughness can be improved to about Ra 0.4 nm and the work-affected layer can be improved to about 100 nm. For comparison, when the same diamond slurry was used and the same lapping process was performed using a polyurethane polishing pad instead of the lapping plate of the present invention, Ra was 0.7 nm or more.

  As a result of CMP polishing of the SiC substrate created by the lapping process using the mechanical lapping surface plate in the present invention and the SiC substrate created by the lapping process using the above-described polyurethane polishing pad as a comparison, in mechanical lapping in the present invention The CMP polishing could be completed in about 6 hours, but in the comparative example, a processing time of about 20 hours was required.

  Compared with the conventional processing method, the mechanical lapping method of the compound semiconductor substrate according to the present invention can improve the productivity of the CMP polishing process, which is a bottleneck in productivity in the manufacture of semiconductors. It is very useful as a method.

Schematic of a polishing apparatus used for a lapping method in an embodiment of the present invention Schematic diagram of a fading device used in a facing process in an embodiment of the present invention The figure for demonstrating the lapping surface plate in the Example of this invention Schematic of the shaving apparatus used for the shaving process in the Example of this invention. The figure for demonstrating the shaving jig | tool used for the shaving process in the Example of this invention. The figure for demonstrating the lapping platen after the shaving in the Example of this invention The figure for demonstrating the charging ring used for the charging process in the Example of this invention. The figure for demonstrating the charging process in the Example of this invention typically The figure for demonstrating the lapping surface plate after charging in the Example of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lapping surface plate 2 SiC single crystal substrate 3 Disk jig | tool 4 Forced drive device 5 Dispenser 6 Turning table 7 Facing arm 8 Diamond bit 9 1st groove | channel 10 2nd groove | channel 11 Shaving jig | tool 12 Charging ring 13 Diamond slurry 13a Diamond abrasive

Claims (7)

In the method of manufacturing a lapping platen used for mechanical polishing of compound semiconductors,
A fading step of cutting and flattening the surface of the lapping platen while rotating the lapping platen made of a material having a predetermined hardness, and processing and generating two types of grooves;
A shaving step of shaving by rotating an arc-shaped shaving jig having a predetermined radius at a rotational speed lower than the rotational speed of the lapping platen;
And rotating the lapping platen after the shaving step using a charging ring at a rotation speed lower than the rotation number of the lapping platen, and charging the lapping platen to a predetermined flatness. A method for producing a lapping surface plate characterized by forming. 2. The fading process according to claim 1, wherein a spiral first groove and a concentric second groove deeper than the first groove are formed at a predetermined interval on the lapping platen. How to make a lapping surface plate. 3. The lapping surface plate according to claim 2, wherein the shaving step scrapes off a peak portion of the first groove formed on the lapping surface plate to make the lapping surface plate have a predetermined flatness. Production method. In the charging step, the diamond coating is charged on the flattened groove using a rotating charging ring having a predetermined weight while dropping the diamond coating on the shaved lapping surface plate ( 4. A method for manufacturing a lapping surface plate according to claim 3, wherein the wrapping surface plate is embedded. A lapping surface plate used in a mechanical lapping method, wherein the lapping surface plate is produced by the production method according to claim 4. A mechanochemical lapping method for polishing a compound semiconductor workpiece by two-stage lapping using different lapping conditions using the lapping platen according to claim 5, wherein the first lapping of the two-stage lapping is diamond A mechanical lapping method characterized in that a coating grain is dropped and polished mainly by a free coating grain of the dropping coating grain, and the second fine wrapping is polished by a fixed coating grain charged on the lapping platen. The mechanical speed according to claim 6, wherein a lapping platen rotation speed and a workpiece rotation speed at the time of the second fine lapping are smaller than a lapping platen rotation speed and a workpiece rotation speed at the time of the first lapping. Wrapping method.

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