JP5151059B2 - Outline processing method of silicon carbide single crystal wafer - Google Patents
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Description
本発明は、導電性ウェハの外形加工方法に関し、特に、青色発光ダイオードや電子デバイス等の基板ウェハの母材となる良質で大口径の炭化珪素単結晶ウェハの外形加工方法に関するものである。 The present invention relates to a method for processing an outer shape of a conductive wafer, and more particularly to a method for processing an outer shape of a high-quality, large-diameter silicon carbide single crystal wafer that is a base material for a substrate wafer such as a blue light emitting diode or an electronic device.
炭化珪素(SiC)は、耐熱性及び機械的強度に優れ、放射線に強い等の物理的、化学的性質から耐環境性半導体材料として注目されている。また、近年、青色から紫外にかけての短波長光デバイス、高周波高耐圧電子デバイス等の基板ウェハとして、SiC単結晶ウェハの需要が高まっている。しかしながら、大面積を有する高品質のSiC単結晶を、工業的規模で安定に供給し得る結晶成長技術は、未だ確立されていない。それ故、SiCは、上述のような多くの利点及び可能性を有する半導体材料にも拘らず、その実用化が阻まれていた。 Silicon carbide (SiC) has attracted attention as an environmentally resistant semiconductor material because of its physical and chemical properties such as excellent heat resistance and mechanical strength, and resistance to radiation. In recent years, the demand for SiC single crystal wafers is increasing as a substrate wafer for short wavelength optical devices from blue to ultraviolet, high frequency high voltage electronic devices, and the like. However, a crystal growth technique that can stably supply a high-quality SiC single crystal having a large area on an industrial scale has not yet been established. Therefore, practical use of SiC has been hindered despite the semiconductor materials having many advantages and possibilities as described above.
従来、研究室程度の規模では、例えば、昇華再結晶法(レーリー法)でSiC単結晶を成長させ、半導体素子の作製が可能なサイズのSiC単結晶を得ていた。しかしながら、この方法では、得られた単結晶の面積が小さく、その寸法及び形状を高精度に制御することは困難である。また、SiCが有する結晶多形及び不純物キャリア濃度の制御も容易ではない。また、化学気相成長法(CVD法)を用いて、珪素(Si)等の異種基板上にヘテロエピタキシャル成長させることにより、立方晶のSiC単結晶を成長させることも行われている。この方法では、大面積の単結晶は得られるが、基板との格子不整合が約２０%もあること等により、多くの欠陥(〜107cm-2)を含むSiC単結晶しか成長させることができず、高品質のSiC単結晶を得ることは容易でない。 Conventionally, on a laboratory scale scale, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain a SiC single crystal of a size capable of manufacturing a semiconductor element. However, with this method, the area of the obtained single crystal is small, and it is difficult to control its size and shape with high accuracy. Also, it is not easy to control the crystal polymorphism and impurity carrier concentration of SiC. In addition, a cubic SiC single crystal is grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using a chemical vapor deposition method (CVD method). In this method, a large-area single crystal can be obtained, but only a SiC single crystal containing many defects (˜10 7 cm −2 ) can be grown due to a lattice mismatch of about 20% with the substrate. It is not easy to obtain a high-quality SiC single crystal.
これらの問題点を解決するために、SiC単結晶[0001]ウェハを種結晶として用いて、昇華再結晶を行う改良型のレーリー法が提案されている(非特許文献１)。この方法では、種結晶を用いているため、結晶の核形成過程が制御でき、また、不活性ガスにより雰囲気圧力を１００Pa〜１５kPa程度に制御することにより、結晶の成長速度等を再現性良くコントロールできる。現在、口径２インチ(50mm)〜４インチ(100mm)のSiC単結晶インゴットは成長できるようになり、ウェハに加工されて、種々のデバイス作製に供されるようになって来た。 In order to solve these problems, an improved Rayleigh method for performing sublimation recrystallization using a SiC single crystal [0001] wafer as a seed crystal has been proposed (Non-patent Document 1). In this method, since the seed crystal is used, the nucleation process of the crystal can be controlled, and by controlling the atmospheric pressure to about 100 Pa to 15 kPa with an inert gas, the crystal growth rate can be controlled with good reproducibility. it can. At present, SiC single crystal ingots having a diameter of 2 inches (50 mm) to 4 inches (100 mm) can be grown, processed into wafers, and used for various devices.
ウェハに加工するに際しては、成長したインゴットを所望の直径、即ち２インチ(50mm)〜４インチ(100mm)で目的に合致する口径の円筒形に加工した後、ウェハにスライスして更に表面を研磨する工程を踏む。その外形加工に際しては、従来、例えば、特許文献１に記載されているように、研削砥石を使って外周研削するのが一般的である。
When processing into a wafer, the grown ingot is processed into a cylindrical shape having a desired diameter, that is, 2 inches (50 mm) to 4 inches (100 mm), and then sliced into a wafer to further polish the surface. Steps to do. In the outer shape processing, conventionally, as described in, for example,
しかるに、SiC単結晶に代表される硬脆性材料では、機械研削の際に力学的な加工歪が入って外周表面に加工変質層が残る、あるいは、インゴットにクラックが入ることがある。外周加工を施さなくても、インゴットをウェハにスライスして、後工程に供することは可能であり、実際、研究段階の小規模生産では、外周加工を行わない例は多々あった。しかしながら、工業的規模でウェハを用いるためには、研磨工程でのチッピングを避けるためにも、デバイスを作成する工程で大量処理するためにウェハは同一形状であることが望ましいためにも、結果として、ウェハの外形加工が必須である。 However, in a hard and brittle material typified by SiC single crystal, mechanical processing strain occurs during mechanical grinding and a work-affected layer remains on the outer peripheral surface, or cracks may occur in the ingot. It is possible to slice an ingot into a wafer and use it in a subsequent process without performing peripheral processing. In fact, in small-scale production at the research stage, there were many examples in which peripheral processing was not performed. However, in order to use a wafer on an industrial scale, as a result, it is desirable to avoid chipping in the polishing process, and because it is desirable that the wafer has the same shape for mass processing in the process of creating a device. The outer shape processing of the wafer is essential.
しかしながら、特許文献１に記載されているように、研削砥石を使ってSiC単結晶ウェハの外形加工をすると、周辺からクラックが入ったり、ウェハが割れたりする。したがって、従来の研削加工技術では、SiC単結晶ウェハの外形加工が非常に困難であると言う課題があった。
上記したように、従来の機械的な研削加工でSiC単結晶ウェハの外形加工を施すと、機械加工が故の力学的作用により、SiC単結晶ウェハに悪影響を及ぼす。 As described above, when a SiC single crystal wafer is contoured by conventional mechanical grinding, it adversely affects the SiC single crystal wafer due to mechanical action due to mechanical processing.
本発明は、上記事情に鑑みてなされたものであり、SiC単結晶ウェハの外形加工中にウェハにクラックが入ったり、割れたりすることを回避できる外形加工法を提供するものである。 The present invention has been made in view of the above circumstances, and provides an outer shape processing method capable of avoiding cracking or cracking of a wafer during outer shape processing of a SiC single crystal wafer.
SiC単結晶インゴットは、結晶成長プロセスで不純物元素あるいはその化合物を混合することにより、様々な抵抗率のものを得ることができる。特に、パワーデバイス、発光デバイスの基板として用いられるウェハを得るためには、抵抗率の低い、即ち、キャリア濃度の高いインゴットが好まれる。インゴットをウェハにスライスした後で外形加工する場合、ウェハに機械的ダメージを与えない方法について鋭意比較検討・観察・解析を行った結果、本発明者らは、放電加工機によってウェハ外形加工が可能であることを見出した。ウェハにスライスした後に放電加工機で外形加工し、その後、従来のべべリング、研磨プロセスを通しても問題なく、放電加工の妥当性を確認し、本発明を完成させるに至った。 SiC single crystal ingots can be obtained in various resistivities by mixing impurity elements or their compounds in the crystal growth process. In particular, in order to obtain a wafer used as a substrate for a power device or a light emitting device, an ingot having a low resistivity, that is, a high carrier concentration is preferred. When slicing an ingot into a wafer and then processing the outer shape, the inventors have made extensive comparison studies, observations, and analyzes on methods that do not cause mechanical damage to the wafer. I found out. After slicing into a wafer, the outer shape was processed by an electric discharge machine, and then the validity of electric discharge machining was confirmed without problems even through conventional beveling and polishing processes, and the present invention was completed.
即ち、本発明は、
(1) キャリア濃度が１×１０17cm-3以上であるSiC単結晶ウェハを誘電体の加工液に浸け、あるいは、加工液をかけながら、放電加工機によって矩形に外形加工することを特徴とする炭化珪素単結晶ウェハの外形加工方法、
That is, the present invention
(1) The feature is that a SiC single crystal wafer having a carrier concentration of 1 × 10 17 cm −3 or more is immersed in a dielectric processing liquid, or is processed into a rectangular shape by an electric discharge machine while applying the processing liquid. A method for processing an outer shape of a silicon carbide single crystal wafer,
(2) 前記ウェハのキャリア濃度が４×１０17cm-3以上である(1)記載の炭化珪素単結晶ウェハの外形加工方法、 (2) The outer shape processing method for a silicon carbide single crystal wafer according to (1 ), wherein the carrier concentration of the wafer is 4 × 10 17 cm −3 or more,
(3) 前記誘電体の加工液の比抵抗が１MΩ・cm以上である(1)又は(2)に記載の炭化珪素単結晶ウェハの外形加工方法、 (3) The silicon carbide single crystal wafer outer shape processing method according to (1) or (2), wherein a specific resistance of the dielectric processing liquid is 1 MΩ · cm or more,
(4) 前記放電加工機が、ワイヤーを用いるワイヤー放電加工機である(1)〜(3)のいずれかに記載の炭化珪素単結晶ウェハの外形加工方法、 (4) The electric discharge machine is a wire electric discharge machine using a wire (1) to the outer shape processing method for a silicon carbide single crystal wafer according to any one of (3) ,
(5) 前記放電加工機が、固定電極を用いる形彫り放電加工機である(1) 〜(3)のいずれかに記載の炭化珪素単結晶ウェハの外形加工方法、 (5) The electric discharge machine is a die-sinking electric discharge machine using a fixed electrode (1) to (3) the outer shape processing method for a silicon carbide single crystal wafer according to any one of the above,
(6) 前記形彫り放電加工機で、前記固定電極の材質がグラファイトである(5)に記載の炭化珪素単結晶ウェハの外形加工方法、
(7) 前記形彫り放電加工機で、加工液に油を用いる(5)又は(6)に記載の炭化珪素単結晶ウェハの外形加工方法、である。
(6) In the die-sinking electric discharge machine, the material for the fixed electrode is graphite, and the method for externally processing the silicon carbide single crystal wafer according to (5) ,
(7) The outer shape machining method for a silicon carbide single crystal wafer according to (5) or (6), wherein oil is used as a machining fluid in the die-sinking electric discharge machine.
本発明の外形加工方法によれば、硬脆性材料であって従来においては非常に困難であったスライス後のSiC単結晶ウェハの外周を矩形に加工する外形加工を容易に実現することができ、所謂半導体ウェハで一般的に用いられるデバイス最終形状と同じ大きさ及び形状のSiC単結晶ウェハを再現性良く安定に生産することができる。 According to the outer shape processing method of the present invention, it is possible to easily realize the outer shape processing of the outer periphery of the SiC single crystal wafer after slicing, which is a hard and brittle material and is very difficult in the past, into a rectangle , A SiC single crystal wafer having the same size and shape as the final shape of a device generally used for so-called semiconductor wafers can be stably produced with good reproducibility.
また、放電加工によって外形加工したSiC単結晶ウェハでは、周囲が黒く焼け焦げたような様相を呈するが、外形加工後のべべリングプロセスによって、黒く変色した部分は容易に除去できる。したがって、外形加工以降のプロセスにも何ら悪影響を与えない。 In addition, the SiC single crystal wafer that has been externally processed by electrical discharge machining appears to be burnt and scorched black, but the black-colored portion can be easily removed by the beveling process after external processing. Therefore, there is no adverse effect on the processes after the outer shape processing.
本発明で加工の対象となるウェハは、導電性を有することが必須条件である。即ち、導電性が高く電気抵抗が小さいことが、本発明を適用できる為の必須条件である。導電性は高ければ高いほど電気が流れ易く、本発明の対象として適しているが、具体的な導電性を表すウェハのキャリア濃度で比較すると、キャリア濃度が１×１０17cm-3以上であると加工し易く、更に、４×１０17cm-3以上になると加工し易さは顕著になる。但し、これは、キャリア濃度が１×１０17cm-3未満では、本発明が全く適用できないことを意味する訳ではない。キャリア濃度の上限値としては、ドーパントが固溶限界で制限されるので、高々２×１０19cm-3程度である。ここで、ウエハに導電性を付与する方法としては、例えば、不純物窒素のドーピング、不純物アルミニウムのドーピング、不純物ホウ素のドーピング等の方法があり、また、そのキャリア濃度の測定方法としては、例えば、ホール測定、Ｃ-Ｖ測定等の方法がある。 It is an essential condition that the wafer to be processed in the present invention has conductivity. That is, high electrical conductivity and low electrical resistance are essential conditions for applying the present invention. The higher the conductivity, the easier the electricity flows, which is suitable as the object of the present invention. However, the carrier concentration is 1 × 10 17 cm −3 or more when compared with the carrier concentration of the wafer representing specific conductivity. It is easy to process, and when it becomes 4 × 10 17 cm −3 or more, the ease of processing becomes remarkable. However, this does not mean that the present invention cannot be applied at all when the carrier concentration is less than 1 × 10 17 cm −3 . The upper limit of the carrier concentration is at most about 2 × 10 19 cm −3 because the dopant is limited by the solid solution limit. Here, as a method for imparting conductivity to the wafer, for example, there are methods such as impurity nitrogen doping, impurity aluminum doping, impurity boron doping and the like, and a carrier concentration measuring method is, for example, hole There are methods such as measurement and CV measurement.
ウェハを誘電体の加工液に浸漬、あるいは、加工液をかけながら、パルス電圧をかけながら、例えばワイヤー放電加工機のワイヤーをインゴットに近づけると、誘電体の加工液で保たれていたワイヤーとウェハの間で絶縁破壊が起こって、アーク放電が起こる。アーク放電の火花によりウェハ側表面が高温になって溶解し、溶解した材料は、同じく急激に高温になる加工液の熱膨張により、ワイヤーとウェハの間から除去される。その加工液の性質としては、より好ましい条件として、比抵抗が１MΩ・cm以上であることが望ましい。このような加工液としては、例えば、比抵抗１MΩ・cmから１×１０21MΩ・cmのケロシン油、比抵抗５MΩ・cmの脱イオン水、ppmオーダーの濃度で不純物を含む比抵抗１０MΩ・cm未満の純水、ppbオーダーの濃度で不純物を含む比抵抗１０〜１８．３MΩ・cmの超純水等を例示することができる。 For example, when the wire of a wire electric discharge machine is brought close to an ingot while a pulse voltage is applied while the wafer is immersed in a dielectric processing liquid or while applying the processing liquid, the wire and wafer that have been kept in the dielectric processing liquid Insulation breakdown occurs, and arc discharge occurs. The surface on the wafer side melts due to the arc discharge spark, and the melted material is removed from between the wire and the wafer by the thermal expansion of the working fluid that also becomes rapidly hot. As a property of the working fluid, as a more preferable condition, it is desirable that the specific resistance is 1 MΩ · cm or more. Examples of such processing fluid include kerosene oil having a specific resistance of 1 MΩ · cm to 1 × 10 21 MΩ · cm, deionized water having a specific resistance of 5 MΩ · cm, and a specific resistance of 10 MΩ · cm containing impurities at a concentration on the order of ppm. For example, ultrapure water having a specific resistance of 10 to 18.3 MΩ · cm containing impurities at a concentration of ppb order or less can be exemplified.
本発明のワイヤー放電加工法でウェハの外形加工をする際は、扱い易さやコスト等の観点から廉価で柔らかなワイヤーを用いる。この点で、ワイヤーの材質は黄銅、黄銅系合金、Ａｌ入り黄銅、亜鉛被覆合金等を例示でき、信頼性、費用対効果の観点から好ましくは黄銅であるのがよい。また、そのワイヤーが細過ぎると断線し易く、太過ぎると、コストアップに繋がる。そこで、太さ０．０８mm以上０．５mm以下、好ましくは０．１mm以上０．３mm以下のワイヤー用い、誘電体の加工液中に浸したもしくは加工液をかけながら、SiCウェハとワイヤーの間に電流を流してアーク放電させて、SiC結晶を分解・除去しながら、SiCウェハとワイヤーの位置関係を変えることにより、SiCウェハを所望の直径の円盤形状に加工できる。 When the outer shape of a wafer is processed by the wire electric discharge machining method of the present invention, an inexpensive and soft wire is used from the viewpoint of ease of handling and cost. In this respect, the material of the wire can be exemplified by brass, brass-based alloy, Al-containing brass, zinc-coated alloy, and the like, and brass is preferable from the viewpoint of reliability and cost effectiveness. Moreover, if the wire is too thin, it will be easy to disconnect, and if too thick, it will lead to a cost increase. Therefore, a wire having a thickness of 0.08 mm or more and 0.5 mm or less, preferably 0.1 mm or more and 0.3 mm or less, is used between the SiC wafer and the wire while being immersed in or immersed in a dielectric processing solution. By changing the positional relationship between the SiC wafer and the wire while applying an electric current to cause arc discharge to decompose and remove the SiC crystal, the SiC wafer can be processed into a disk shape having a desired diameter.
SiCウェハとワイヤーの間に流す電流は、小さ過ぎては効率的に加工できず、大き過ぎては電源が巨大化してコストアップに繋がる。そこで、１０A以上１００A以下、好ましくは２０A以上８０A以下の電流を流してSiC結晶を分解・除去する。放電の際、SiC結晶が分解・除去されるのみならず、ワイヤー自身も損耗するので、少しずつ新たなワイヤーを繰り出して、損耗によりワイヤーが断線しないようにして加工する。 If the current flowing between the SiC wafer and the wire is too small, it cannot be processed efficiently, and if it is too large, the power supply becomes enormous and the cost increases. Therefore, the SiC crystal is decomposed and removed by supplying a current of 10 A to 100 A, preferably 20 A to 80 A. At the time of discharge, not only the SiC crystal is decomposed and removed, but also the wire itself is worn, so a new wire is drawn out little by little and processed so that the wire is not broken by the wear.
ワイヤーの繰り出し速度は、遅過ぎるとワイヤー供給が間に合わずにワイヤーが断線し、早過ぎるとコストアップに繋がるので、０．１m/分以上１０m/分以下、好ましくは０．２m/分以上８m/分以下の範囲が適切である。ウェハに対するワイヤーの位置を動かすことにより、所望の円盤形状にウェハを加工するのだが、その速度が速過ぎるとワイヤーがウェハにぶつかって断線を招き、遅過ぎると加工効率が落ちる。ウェハとワイヤーの相対移動速度は１０mm/分以上２００mm/分以下、好ましくは２０mm/分以上１６０mm/分以下が適切な範囲である。この場合、インゴットを固定してワイヤーを移動させても、ワイヤーを固定してインゴットを移動させても、更には、インゴットとワイヤーの双方を移動させても良く、適宜選択すれば良い。なお、外形加工後のウェハ周辺は黒く焼け焦げる。 If the wire feeding speed is too slow, the wire will not be delivered in time, and the wire will break, and if it is too fast, the cost will increase. Therefore, it will be 0.1 m / min to 10 m / min, preferably 0.2 m / min to 8 m / min. A range of minutes or less is appropriate. By moving the position of the wire with respect to the wafer, the wafer is processed into a desired disk shape. However, if the speed is too high, the wire hits the wafer and breaks, and if it is too slow, the processing efficiency decreases. The relative movement speed of the wafer and the wire is 10 mm / min or more and 200 mm / min or less, preferably 20 mm / min or more and 160 mm / min or less. In this case, the ingot may be fixed and the wire may be moved, the wire may be fixed and the ingot may be moved, or both the ingot and the wire may be moved, and may be appropriately selected. Note that the periphery of the wafer after the outer shape processing is burnt black.
スライサーでインゴットからスライスされた直後のウェハは、表面が凸凹で、ダメージが残っているので、鏡面に研磨する。研磨に先立って、ウェハの周辺部分には、べべリングと呼ぶ面取り加工を施す。これは、研磨加工中にエッジ部分からチッピングが起こるのを防ぐために必要不可欠な工程である。そのため、例え円盤形状に加工したウェハ側面の面粗さが大きかったり、黒く焦げていても、このべべリング工程によって表面が除去されるので、問題は無い。 The wafer immediately after being sliced from the ingot by the slicer has an uneven surface and remains damaged, so it is polished to a mirror surface. Prior to polishing, a chamfering process called beveling is applied to the peripheral portion of the wafer. This is an indispensable process for preventing chipping from the edge portion during the polishing process. Therefore, even if the surface roughness of the wafer processed into a disk shape is large or burnt black, the surface is removed by this beveling process, so there is no problem.
本発明では、ワイヤーを用いる代わりに、固定電極による形彫り放電加工機を用いて導電性ウェハの外形を加工することも行われる。形彫り放電加工の場合、その移動距離は、ワイヤーを用いる場合に比べて、１００分の１から１０００分の１に小さくできる。他方、形彫り放電加工では、ワイヤーのように太さ０．０８〜０．５mmまで細くしたのでは電極の剛性が保てないので、必然的に肉厚の厚い固定電極を用いる。その結果、加工中の電極の損耗を補うことは難しいが、電極の損耗に因るウェハの加工寸法誤差は小さく、誤差はその後に行うべべリングプロセスで容易に修正できる。この形彫り放電加工機を用いて外形加工する場合においても、加工液を用いるが、この際に用いられる加工液としては、例えば、比抵抗１MΩ・cmから１×１０21MΩ・cmのケロシン油、比抵抗５MΩ・cmの脱イオン水、ppmオーダーの濃度で不純物を含む比抵抗１０MΩ・cm未満の純水、ppbオーダーの濃度で不純物を含む比抵抗１０〜１８．３MΩ・cmの超純水等を例示することができ、好ましくは誘電体であるケロシン油などの油を用いる。 In the present invention, instead of using a wire, the outer shape of the conductive wafer is also processed using a sculpture electric discharge machine with a fixed electrode. In the case of die-sinking electric discharge machining, the moving distance can be reduced from 1/100 to 1/1000 compared to the case of using a wire. On the other hand, in die-sinking electric discharge machining, if the thickness is reduced to 0.08 to 0.5 mm as in a wire, the rigidity of the electrode cannot be maintained, so a thick fixed electrode is inevitably used. As a result, it is difficult to compensate for electrode wear during processing, but the wafer processing dimension error due to electrode wear is small, and the error can be easily corrected by a subsequent beveling process. In the case of external machining using this sculpture electric discharge machine, a machining fluid is used. For example, a kerosene oil having a specific resistance of 1 MΩ · cm to 1 × 10 21 MΩ · cm is used as the machining fluid. , Deionized water with a specific resistance of 5 MΩ · cm, pure water with a specific resistance of less than 10 MΩ · cm containing impurities in the order of ppm, ultrapure water with a specific resistance of 10 to 18.3 MΩ · cm containing impurities with a concentration of ppb An oil such as kerosene oil, which is preferably a dielectric, is preferably used.
べべリング工程の後、ウェハの表面は研磨されるが、砥粒の粒径、研磨装置の運転状態を適切に調整することにより、最終的に、ウェハの表面は鏡面状態にまで研磨される。 After the beveling step, the surface of the wafer is polished, but the surface of the wafer is finally polished to a mirror surface state by appropriately adjusting the grain size of the abrasive grains and the operating state of the polishing apparatus.
以下に、本発明を参考例及び実施例に基いて説明する。
図１は、本発明の加工方法を説明するための参考例においてワイヤーがウェハに接する部分の拡大図を示す。スライスしたSiC単結晶ウェハ１は、所望の直径より少し大きな円盤形をしている。その円盤と垂直にワイヤー放電加工機の黄銅ワイヤー２を配置し、電流を流しながら、SiC単結晶ウェハ１に対して黄銅ワイヤー２を矢印の方向に移動させる。SiC単結晶ウェハ１と黄銅ワイヤー２の間では放電現象が起こり、SiC単結晶ウェハ１に機械的なダメージが入ることなく、黄銅ワイヤー２に接するSiC単結晶ウェハ１の表面が分解・除去される。放電現象によって黄銅ワイヤー２も損耗し、放置しておくと黄銅ワイヤー２が細くなって断線してしまうので、新しい黄銅ワイヤーを図１中の上方から常に供給し、古いワイヤーは図１中の下方へと排出される。
Below, this invention is demonstrated based on a reference example and an Example.
FIG. 1 is an enlarged view of a portion where a wire is in contact with a wafer in a reference example for explaining the processing method of the present invention. The sliced SiC
図２は、本方法の参考例によって外周が加工されたSiC単結晶ウェハの平面図を示す。この参考例においては、外形加工後のSiC単結晶ウェハは、ほぼ円盤形であるため、その平面図がほぼ円形になるが、一部円弧形状ではなく直線状になっている部分がある。これはオリエンテーションフラットと呼ばれる部分で結晶の方位を示す。即ち、外形加工の前に、SiC単結晶ウェハの方位をＸ線で計測しておき、図２中第１オリエンテーションフラットが[1-100]方向を示し、第２オリエンテーションフラットが[1-210]方向を示すように配置する。図と垂直な方向が、本工程の後に研磨加工した後のウェハ表面に該当し、[-1000]方向又は、[-1000]方向から、[1-210]方向若しくは[1-100]方向に数度傾いた方向に対応する。 Figure 2 shows a plan view of a SiC single crystal wafer outer periphery is machined by a reference example of the present method. In this reference example, SiC single crystal wafer after outline processing is almost disc-shaped, its plan view is substantially circular, there are portions which is straight rather than some arcuate shape. This indicates the orientation of the crystal in a portion called an orientation flat. That is, before processing the outer shape, the orientation of the SiC single crystal wafer is measured with X-rays. In FIG. 2, the first orientation flat indicates the [1-100] direction and the second orientation flat is [1-210]. Arrange to show direction. The direction perpendicular to the figure corresponds to the wafer surface after polishing after this step, and from the [-1000] direction or [-1000] direction to the [1-210] direction or [1-100] direction Corresponds to a direction tilted several degrees.
（参考例１）
本実施例では、図１中の矢印方向に、φ０．１８mmのワイヤーを繰り出し速度２m/分及びウェハとの相対移動速度１５mm/分で移動させながら加工した。直径が３インチ(75mm)になるように、即ち、ワイヤーは、概ね、直径に対応する円弧状に矢印方向に移動させるが、上記、第１オリエンテーションフラット、及び、第２オリエンテーションフラットに対応する箇所では、ワイヤーは、円弧状ではなく、直線状に移動させた。ウェハは、結晶成長中に窒素を添加することによって導電性を持たせたもので、そのキャリア濃度は凡そ１．２×１０17cm-3である。電流は５０A流しており、ウェハは直径が３インチ(75mm)になるように寸法調整をして外形加工しており、１２分間で外形加工は終了した。本放電加工は加工液として比抵抗５MΩ・cmの脱イオン水を用いて実施した。加工後の側表面は黒く焼け焦げたような性状を持ち、顕微鏡で拡大すると、梨地のザラザラな面になっていた。
( Reference Example 1 )
In this example, the wire was processed in the direction of the arrow in FIG. 1 while moving a 0.18 mm wire at a feeding speed of 2 m / min and a relative movement speed of 15 mm / min with the wafer. The diameter is 3 inches (75 mm), that is, the wire is moved in the direction of the arrow in the shape of an arc corresponding to the diameter, but the locations corresponding to the first orientation flat and the second orientation flat are described above. Then, the wire was moved not linearly but in a straight line. The wafer is made conductive by adding nitrogen during crystal growth, and its carrier concentration is about 1.2 × 10 17 cm −3 . The current flowed 50A, and the wafer was dimensioned so that the diameter was 3 inches (75 mm), and the contour processing was completed in 12 minutes. This electric discharge machining was performed using deionized water having a specific resistance of 5 MΩ · cm as a machining fluid. The side surface after processing had black burnt properties, and when it was magnified with a microscope, it had a rough surface.
（参考例２）
本実施例では、図１中矢印方向にφ０．１８mmのワイヤーを繰り出し速度２m/分及びウェハとの相対移動速度６０mm/分で移動させながら加工した。ウェハは、結晶成長中に窒素を添加することによって導電性を持たせたもので、そのキャリア濃度は凡そ４．５×１０17cm-3である。電流は実施例１と同じく５０Aであったが、こちらのウェハの方が電気抵抗が小さいために早く加工することができて、６０mm/分の速度で外形加工した。ウェハは直径が３インチ(75mm)になるように寸法調整をして外形加工しており、３分で外形加工は終了した。本放電加工は加工液として比抵抗５MΩ・cmの脱イオン水を用いて実施した。加工後の側表面は黒く焼け焦げたような性状を持ち、顕微鏡で拡大すると、梨地のザラザラな面になっていた。加工後の側表面は、実施例１同様、黒く焼け焦げたような性状を持つ。速度が速かったためか、側表面の粗さは実施例１よりも寧ろ大きくなっている。
( Reference Example 2 )
In this embodiment, a wire having a diameter of 0.18 mm was processed while moving at a feeding speed of 2 m / min and a relative movement speed of 60 mm / min with the wafer in the direction of the arrow in FIG. The wafer is made conductive by adding nitrogen during crystal growth, and its carrier concentration is about 4.5 × 10 17 cm −3 . The current was 50 A as in Example 1, but this wafer could be processed faster because of its lower electrical resistance, and the outer shape was processed at a speed of 60 mm / min. The wafer was dimensionally adjusted so that the diameter was 3 inches (75 mm), and the contour processing was completed in 3 minutes. This electric discharge machining was performed using deionized water having a specific resistance of 5 MΩ · cm as a machining fluid. The side surface after processing had black burnt properties, and when it was magnified with a microscope, it had a rough surface. The side surface after processing has the property of being burnt black as in Example 1. The roughness of the side surface is rather larger than that of Example 1 because the speed was high.
（実施例１）
本実施例では、実施例２同様、図１中矢印方向にφ０．１８mmのワイヤーを繰り出し速度２m/分及びウェハとの相対移動速度６０mm/分で移動させながら加工した。ウェハは、結晶成長中に窒素を添加することによって導電性を持たせたもので、そのキャリア濃度は凡そ４．５×１０17cm-3である。電流は参考例１と同じく５０Aであったが、こちらのウェハの方がその電気抵抗が小さいために早く加工することができて、６０mm/分の速度でその外周を矩形に外形加工することができた。参考例２との違いは、ウェハを５０mm角の正方形になるように寸法調整をして外形加工している点であり、４分で加工は終了した。本放電加工は加工液として比抵抗５MΩ・cmの脱イオン水を用いて実施した。加工後の側表面は黒く焼け焦げたような性状を持ち、顕微鏡で拡大すると、梨地のザラザラな面になっていた。加工後の正方形ウェハの平面図を図３に示す。図に示すように、正方形の一辺が[1-100]方向に、他の一辺が[1-210]方向に向くように、予めウェハの方位をX線で計測してから、外形加工した。
Example 1
In this example, as in Example 2, a wire having a diameter of 0.18 mm was processed in the direction of the arrow in FIG. 1 while moving at a feeding speed of 2 m / min and a relative movement speed of 60 mm / min with the wafer. The wafer is made conductive by adding nitrogen during crystal growth, and its carrier concentration is about 4.5 × 10 17 cm −3 . The current was 50A as in Reference Example 1, but this wafer can be processed faster because of its lower electrical resistance, and its outer periphery can be processed into a rectangle at a speed of 60 mm / min. did it. The difference from Reference Example 2 is that the wafer is dimensionally adjusted so as to be a 50 mm square, and the outer shape is processed, and the processing is completed in 4 minutes. This electric discharge machining was performed using deionized water having a specific resistance of 5 MΩ · cm as a machining fluid. The side surface after processing had black burnt properties, and when it was magnified with a microscope, it had a rough surface. A plan view of the square wafer after processing is shown in FIG. As shown in the figure, the wafer orientation was measured with X-rays in advance so that one side of the square was in the [1-100] direction and the other side was in the [1-210] direction, and then the outer shape was processed.
（実施例２）
本実施例では、実施例１同様、ウェハを５０mm角の正方形になるように寸法調整をしてその外周を矩形に外形加工した。実施例１との違いは、ワイヤーを用いずに、直方体のグラファイト固定電極を用いて加工した点である。ウェハは、結晶成長中に窒素を添加することによって導電性を持たせたもので、そのキャリア濃度は凡そ４．５×１０17cm-3である。電流は参考例１と同じく５０Aであったが、ワイヤーでなく固定電極を用いたため電流密度は小さくなったので、電極の移動速度は０．１mm/分にまで遅くした。図４に形彫り放電加工において固体電極がウェハに接する部分の拡大図を示す。図中固体電極を矢印の方向に０．１mm/分で移動して、ウェハの一辺を加工した。一辺の加工の後、丁度図４の矢印を中心にウェハを９０度回転して、第二辺を加工。更に同様の手続きにより、第三辺と第四辺を加工した。全加工の後、ウェハは実施例３同様５０mm角の正方形に加工された。加工時間は２０分を要しなかった。本放電加工は加工液としてケロシン油を用いて実施した。加工後の側表面は黒く焼け焦げたような性状を持ち、顕微鏡で拡大すると、梨地のザラザラな面になっていた。
(Example 2)
In this example, as in Example 1, the size of the wafer was adjusted so as to be a square of 50 mm square, and the outer periphery thereof was shaped into a rectangle . The difference from Example 1 is that it was processed using a rectangular parallelepiped graphite fixed electrode without using a wire. The wafer is made conductive by adding nitrogen during crystal growth, and its carrier concentration is about 4.5 × 10 17 cm −3 . The current was 50 A as in Reference Example 1, but the current density was reduced because a fixed electrode was used instead of a wire, so the moving speed of the electrode was reduced to 0.1 mm / min. FIG. 4 shows an enlarged view of a portion where the solid electrode is in contact with the wafer in the sculpture electric discharge machining. In the figure, the solid electrode was moved in the direction of the arrow at 0.1 mm / min to process one side of the wafer. After processing one side, the wafer is rotated 90 degrees just about the arrow in Fig. 4 to process the second side. Furthermore, the third side and the fourth side were processed by the same procedure. After all processing, the wafer was processed into a 50 mm square as in Example 3. Processing time did not require 20 minutes. This electric discharge machining was performed using kerosene oil as a machining fluid. The side surface after processing had black burnt properties, and when it was magnified with a microscope, it had a rough surface.
（実施例３）
本実施例では、実施例２で用いたグラファイト固定電極３の代わりに、図５に示す内側が５０mm角の正方形のグラファイト固定電極４を用いて、形彫り放電加工によりウェハの外形加工を行った。図５の固体電極の下にウェハを配置し、矢印の方向に固体電極４を移動して加工した。ウェハは、結晶成長中に窒素を添加することによって導電性を持たせたもので、そのキャリア濃度は凡そ４．５×１０17cm-3である。電流は実施例１と同じく５０Aであったが、電極が大きいために電流密度が小さくなったので、電極の移動速度は０．０２mm/分にまで遅くした。しかし、実施例２と違ってウェハの向きを９０度ずつ３回変える必要が無く、一括で四辺が加工できたので、加工時間は１５分と、実施例４より寧ろ短くなった。本放電加工は加工液としてケロシン油を用いて実施した。加工後の側表面は黒く焼け焦げたような性状を持ち、顕微鏡で拡大すると、梨地のザラザラな面になっていた
(Example 3 )
In this example, the outer shape of the wafer was processed by die-sinking electric discharge machining using the graphite fixed electrode 4 having a square inside of 50 mm shown in FIG. 5 instead of the graphite fixed electrode 3 used in Example 2 . . A wafer was placed under the solid electrode in FIG. 5, and the solid electrode 4 was moved in the direction of the arrow for processing. The wafer is made conductive by adding nitrogen during crystal growth, and its carrier concentration is about 4.5 × 10 17 cm −3 . The current was 50 A as in Example 1, but the current density was reduced due to the large electrode, so the moving speed of the electrode was slowed down to 0.02 mm / min. However, unlike Example 2, it was not necessary to change the orientation of the wafer three times by 90 degrees, and the four sides could be processed at once, so the processing time was 15 minutes, which was rather shorter than Example 4. This electric discharge machining was performed using kerosene oil as a machining fluid. The side surface after processing had black burnt properties, and when magnified with a microscope, it was a rough surface of pear texture
上記のように加工した参考例１及び２並びに実施例１〜３のウェハ全てにおいて、本外形加工工程の後に、べべリング、研磨加工を行ったが、その過程で、ウェハ周辺の加工変質層は除去されて、黒く焼け焦げた表面性状は全く悪影響を及ぼさなかった。本外形加工工程によってウェハにクラックが入ることも無かったため、ウェハを無駄にすることがなかったのは、言うまでもない。 In all of the wafers of Reference Examples 1 and 2 and Examples 1 to 3 processed as described above, beveling and polishing were performed after this outer shape processing step. The surface properties removed and burnt black had no adverse effect. Needless to say, the wafer was not wasted because the wafer was not cracked by this outer shape processing step.
他方、従来の研削加工でスライスしたSiC単結晶ウェハの外周を矩形に外形加工することを試みたが、研削砥石を押し付けた時にウェハに応力が発生したため、ウェハが破損して上手く加工できなかった。 On the other hand, we tried to make the outer periphery of the SiC single crystal wafer sliced by conventional grinding into a rectangular shape, but because the wafer was stressed when the grinding wheel was pressed, the wafer was damaged and could not be processed well .
１…ウェハ
２…ワイヤー
３…形彫り放電加工用の固定電極
４…一括加工用の形彫り放電加工用の固定電極
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