JP2007283411A - Outline machining method for conductive ingot - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 27
- 238000003754 machining Methods 0.000 title abstract description 14
- 239000007788 liquid Substances 0.000 claims abstract description 5
- 239000013078 crystal Substances 0.000 claims description 50
- 238000003672 processing method Methods 0.000 claims description 24
- 229910001369 Brass Inorganic materials 0.000 claims description 13
- 239000010951 brass Substances 0.000 claims description 13
- 239000012530 fluid Substances 0.000 claims description 13
- 239000000463 material Substances 0.000 abstract description 8
- 238000010891 electric arc Methods 0.000 abstract description 4
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 39
- 229910010271 silicon carbide Inorganic materials 0.000 description 38
- 235000012431 wafers Nutrition 0.000 description 22
- 239000012535 impurity Substances 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 239000008367 deionised water Substances 0.000 description 6
- 229910021641 deionized water Inorganic materials 0.000 description 6
- 230000002093 peripheral effect Effects 0.000 description 6
- 239000000758 substrate Substances 0.000 description 5
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 238000005498 polishing Methods 0.000 description 3
- 239000004065 semiconductor Substances 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000005229 chemical vapour deposition Methods 0.000 description 2
- 231100000989 no adverse effect Toxicity 0.000 description 2
- 238000007517 polishing process Methods 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 238000000859 sublimation Methods 0.000 description 2
- 230000008022 sublimation Effects 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 239000006061 abrasive grain Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- -1 and the like Substances 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000002484 cyclic voltammetry Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000002019 doping agent Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 229910021642 ultra pure water Inorganic materials 0.000 description 1
- 239000012498 ultrapure water Substances 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
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Abstract
Description
本発明は、導電性インゴット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型の炭化珪素単結晶インゴットの外形加工方法に関するものである。 The present invention relates to an outer shape processing method for a conductive ingot, and more particularly to an outer shape processing method for a high-quality, large-sized silicon carbide single crystal ingot that is a base material of 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, 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 producing 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 chemical vapor deposition (CVD). 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 and the like 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 with 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。その場合、外周表面の加工変質層は、ウェハにスライスした後、べべリングによって除去することで対応できる。しかしながら、クラックが入ったインゴットはウェハ化しても最早商品価値は無く、無駄になってしまう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単結晶インゴットの外形加工を施すと、機械加工が故の力学的作用により、単結晶インゴットに悪影響を及ぼす。 As described above, when the outer shape of the SiC single crystal ingot is applied by the conventional mechanical grinding, the single crystal ingot is adversely affected by the mechanical action due to the machining.
本発明は、上記事情に鑑みてなされたものであり、機械的な研削加工に起因して発生する加工変質層を抑え、外形加工中にインゴットにクラックが入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 that suppresses a work-affected layer caused by mechanical grinding and can avoid cracks in the ingot during the outer shape processing. To do.
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。 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.
そこで、本発明者らは、SiC単結晶インゴットの外形加工について鋭意比較検討・観察・解析を行った結果、ワイヤー放電加工機によって外形加工が可能であることを見出し、従来の結晶成長プロセス後にワイヤー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、ワイヤー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。 Therefore, the present inventors have conducted extensive comparison examination, observation and analysis on the outer shape processing of the SiC single crystal ingot, and as a result, found that the outer shape processing is possible with a wire electric discharge machine, and after the conventional crystal growth process, the wire is processed. The outer shape was processed by an electric discharge machine, and then the validity of wire 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) 導電性インゴットを、比抵抗２．５MΩ・cm以上の誘電体の加工液に浸け、あるいは、加工液をかけながら、ワイヤー放電加工機によって外形加工することを特徴とする導電性インゴットの外形加工方法、
That is, the present invention
(1) The conductive ingot is soaked in a dielectric machining fluid having a specific resistance of 2.5 MΩ · cm or more, or is subjected to outer shape machining by a wire electric discharge machine while applying the machining fluid. Outline processing method,
(2) 前記インゴットのキャリア濃度が１×１０17cm-3以上である(1)記載の導電性インゴットの外形加工方法、
(3) 前記インゴットのキャリア濃度が４×１０17cm-3以上である(2)記載の導電性インゴットの外形加工方法、
(2) The outer shape processing method of the conductive ingot according to (1), wherein the carrier concentration of the ingot is 1 × 10 17 cm −3 or more,
(3) The outer shape processing method of the conductive ingot according to (2), wherein the carrier concentration of the ingot is 4 × 10 17 cm −3 or more,
(4) 前記インゴットがSiC単結晶である(1)記載の導電性インゴットの外形加工方法、
(5) 前記誘電体加工液の比抵抗が５MΩ・cm以上である(1)記載の導電性インゴットの外形加工方法、
(4) The outer shape processing method of the conductive ingot according to (1), wherein the ingot is a SiC single crystal,
(5) The outer shape processing method of the conductive ingot according to (1), wherein a specific resistance of the dielectric processing liquid is 5 MΩ · cm or more,
(6) 前記インゴットの外周とワイヤーとの相対移動速度が１〜１０mm/分である(1)記載の導電性インゴットの外形加工方法、
(7) 前記ワイヤーが、太さ０．０８〜０．５mmのワイヤーである(1)記載の導電性インゴットの外形加工方法、
(6) The outer shape processing method of the conductive ingot according to (1), wherein a relative movement speed between the outer periphery of the ingot and the wire is 1 to 10 mm / min,
(7) The outer shape processing method of the conductive ingot according to (1), wherein the wire is a wire having a thickness of 0.08 to 0.5 mm.
(8) 前記ワイヤーを１〜１０m/分で繰り出す(1)記載の導電性インゴットの外形加工方法、
(9) 前記インゴットとワイヤーの間に１０〜１００Aの電流を流す(1)記載の導電性インゴットの外形加工方法、
(8) The outer shape processing method of the conductive ingot according to (1), wherein the wire is drawn out at 1 to 10 m / min.
(9) A method for externally processing a conductive ingot according to (1), wherein a current of 10 to 100 A is passed between the ingot and the wire,
(10) 前記ワイヤーが黄銅ワイヤーである(1)、(6)〜(9)のいずれかに記載の導電性インゴットの外形加工方法、
である。
(10) The wire is a brass wire (1), the outer shape processing method of the conductive ingot according to any one of (6) to (9),
It is.
本発明の外形加工方法によれば、加工後のインゴット側面の加工変質層を抑制することができ、ましてや、インゴットにクラックが入ってインゴットそのものを無駄にすることを皆無にできる。 According to the outer shape processing method of the present invention, it is possible to suppress the work-affected layer on the side surface of the ingot after processing, and furthermore, it is possible to eliminate the ingot itself from being wasted due to cracks in the ingot.
また、SiC単結晶インゴットでは、ワイヤー放電加工によって、外形加工した跡は黒く焼け焦げたような表面になるが、ウェハ状にスライスした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。 Further, in the SiC single crystal ingot, the trace of the outer shape processed by wire electric discharge machining becomes a black burnt surface, but the black-colored portion can be easily removed by the beveling process after slicing into a wafer shape. Therefore, there is no adverse effect on the processes after the outer shape processing.
また、SiC単結晶に関して説明を加えると、その機械的性質として、たいへん硬く、脆いと言う特徴がある。したがって、特許文献１に示すような従来の機械的加工法では、SiC単結晶インゴットに歪、クラック等の大変悪い影響を与えることが多かった。したがって、SiC単結晶インゴットの中でも充分導電性を有する材料については、機械的ダメージを与えない本発明が最適な加工法である。
In addition, when explaining the SiC single crystal, its mechanical properties are characterized by being very hard and brittle. Therefore, in the conventional mechanical processing method as shown in
本発明で加工の対象となる単結晶インゴットは、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ための必須条件である。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単結晶インゴット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 essential that the single crystal ingot 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 electrical conductivity, the easier the electricity flows, which is suitable as the object of the present invention. However, when compared with the carrier concentration of a single crystal ingot that expresses specific electrical conductivity, the carrier concentration is 1 × 10 17 cm −3 or more. When it is, 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 . As the upper limit of the carrier concentration, the dopant is limited by the solid solution limit,
It is about 2 × 10 19 cm -3 at most. 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.
この導電性インゴット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導電性インゴット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導電性インゴット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、ワイヤーと導電性インゴットの間から除去される。その加工液の性質としては、アーク放電を起こすために、比抵抗２．５MΩ・cm以上の誘電体の液体であることが必須であるが、より好ましい条件として５MΩ・cm以上１８．３MΩ・cm以下であることが望ましい。このような加工液として、例えば、比抵抗５MΩ・cmの脱イオン水を始めとして、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。 When this conductive ingot is immersed in a dielectric processing fluid, or when the wire of a wire electric discharge machine is brought close to the ingot while applying a pulse voltage while applying the processing fluid, the wire held in the dielectric processing fluid Dielectric breakdown occurs between the conductive ingots and arc discharge occurs. The surface of the conductive ingot is melted at a high temperature due to the arc discharge spark, and the melted material is removed from between the wire and the conductive ingot by the thermal expansion of the working fluid that also has a rapid temperature. In order to cause arc discharge, it is essential that the working fluid is a dielectric liquid having a specific resistance of 2.5 MΩ · cm or more, but more preferable conditions are 5 MΩ · cm or more and 18.3 MΩ · cm. The following is desirable. Examples of such a processing fluid include deionized water having a specific resistance of 5 MΩ · cm, pure water having a specific resistance of less than 10 MΩ · cm containing impurities at a concentration on the order of ppm, and a specific resistance containing impurities at a concentration on the order of ppb. Examples thereof include ultrapure water of 10 to 18.3 MΩ · cm.
本発明で実施するワイヤー放電加工では、扱い易さ、コスト等の観点から廉価なワイヤーを用いる。その点で、ワイヤーの材質としては、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、費用体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、誘電体の加工液に浸け、あるいは、加工液をかけながら、SiCインゴットとワイヤーの間に電流を流して放電させてSiC結晶を分解・除去しながら、SiCインゴットとワイヤーの位置関係を変えることにより、SiCインゴットを所望の直径の円筒形状に加工する。 In the wire electric discharge machining performed in the present invention, an inexpensive wire is used from the viewpoint of ease of handling, cost, and the like. In this respect, examples of the material of the wire include 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 it is 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, soaked in a dielectric processing fluid, or while being poured, between the SiC ingot and the wire. The SiC ingot is processed into a cylindrical shape with a desired diameter by changing the positional relationship between the SiC ingot and the wire while dissociating and removing the SiC crystal by discharging with an electric current.
SiCインゴット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 ingot 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、１m/分以上１０m/分以下、好ましくは２m/分以上８m/分以下の範囲が適切である。インゴットに対するワイヤーの位置を動かすことにより、所望の円筒形状にインゴットを加工するのだが、その速度が速過ぎるとワイヤーがインゴットにぶつかって断線を招き、遅過ぎると加工効率が落ちる。インゴットとワイヤーの相対移動速度は１mm/分以上１０mm/分以下、好ましくは２mm/分以上８mm/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。 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, so the range is from 1 m / min to 10 m / min, preferably from 2 m / min to 8 m / min. Is appropriate. By moving the position of the wire with respect to the ingot, the ingot is processed into a desired cylindrical shape. However, if the speed is too high, the wire hits the ingot, causing disconnection, and if it is too slow, the processing efficiency is reduced. The relative moving speed of the ingot and the wire is 1 mm / min to 10 mm / min, preferably 2 mm / min to 8 mm / min. 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.
円筒形状に加工されたインゴットは、その後、スライサーに依って、円盤状のウェハにスライス加工される。スライス直後のウェハは、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、ウェハ周辺部、即ち、円筒形状に加工した部分には、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。例え円筒形状に加工したインゴット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 ingot processed into a cylindrical shape is then sliced into a disk-shaped wafer by a slicer. Since the wafer immediately after slicing has an uneven surface and remains damaged, it is polished to a mirror surface. Prior to polishing, a chamfering process called beveling is applied to the peripheral part of the wafer, that is, the part processed into a cylindrical shape. This is an indispensable process for preventing chipping from the edge portion during the polishing process. Even if the ingot processed into a cylindrical shape has a large surface roughness or is burnt black, there is no problem because the surface is removed by this beveling process.
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、本発明を実施例で説明する。
図１は、本発明におけるワイヤーがインゴットに接する部分の拡大図を示す。成長したSiC単結晶インゴット１は、所望の直径より少し大きな円筒形をしている。その中心軸と並行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単結晶インゴット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単結晶インゴット１と黄銅ワイヤー２の間では放電現象が起こり、SiC単結晶インゴット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単結晶インゴット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。
Hereinafter, the present invention will be described with reference to examples.
FIG. 1 shows an enlarged view of a portion where a wire is in contact with an ingot in the present invention. The grown SiC
図２は、本方法によって外周加工を施したSiC単結晶インゴットの断面形状を示す。外形加工後のSiC単結晶インゴットはほぼ円筒形であるため、その断面形状はほぼ円形になるが、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単結晶インゴットの方位を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。 FIG. 2 shows a cross-sectional shape of a SiC single crystal ingot that has been subjected to peripheral processing by the present method. Since the SiC single crystal ingot after the outer shape processing is substantially cylindrical, its cross-sectional shape is almost circular, but there is a part that is not a circular arc but a straight line. 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 ingot 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 the [-1000] direction, or [1-210] direction or [1-100] direction from the [-1000] direction. Corresponds to the direction tilted several degrees.
(実施例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５m/分及びウェハとの相対移動速度１．５mm/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、直線状に矢印方向に移動させる。インゴットは、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、インゴットは直径が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、２時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。即ち、脱イオン水に浸漬した状態のインゴットを放電加工したものである。加工後のインゴット外周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。図３は、本方法によって加工した後のSiC単結晶インゴット側面の実体顕微鏡像例である。
(Example 1)
In this example, the wire was processed in the direction of the arrow in FIG. 1 while moving a wire of φ0.18 mm at a feeding speed of 5 m / min and a relative movement speed of 1.5 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 described above. Then, the wire is moved in the direction of the arrow in a straight line instead of an arc. The ingot is made conductive by adding nitrogen during crystal growth, and its carrier concentration is about 1.2 × 10 17 cm −3 . The current was flowing at 50 A, and the ingot was dimensionally adjusted to a diameter of 3 inches (75 mm), and the outer shape processing was completed in 2 hours. This electric discharge machining was performed using deionized water having a specific resistance of 5 MΩ · cm as a machining fluid. That is, an ingot that has been immersed in deionized water is subjected to electric discharge machining. The outer surface of the ingot after processing had black burnt properties, and when it was magnified with a microscope, it had a rough surface. FIG. 3 is an example of a stereoscopic microscope image of the side surface of the SiC single crystal ingot after being processed by this method.
(実施例２)
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５m/分及びウェハとの相対移動速度６mm/分で移動させながら加工した。インゴットは、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、こちらのインゴット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、６mm/分の速度で外形加工した。インゴットは直径が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、３０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。本実施例では、インゴットを脱イオン水に浸漬する代わりに、インゴットとワイヤーの間に脱イオン水をかけながら行った。加工後の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。加工後のインゴット外周表面は、実施例１同様、黒く焼け焦げたような性状を持つ。
(Example 2)
In this example, the wire was processed while moving a 0.18 mm wire in the direction of the arrow in FIG. 1 at a feeding speed of 5 m / min and a relative moving speed of 6 mm / min with the wafer. The ingot 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 ingot had a lower electrical resistance, so it could be processed faster, and the outer shape was processed at a speed of 6 mm / min. The ingot was dimensionally adjusted so that the diameter was 3 inches (75 mm), and the contouring was completed in 30 minutes. This electric discharge machining was performed using deionized water having a specific resistance of 5 MΩ · cm as a machining fluid. In this example, instead of immersing the ingot in deionized water, it was performed while applying deionized water between the ingot and the wire. The surface after processing was black and burnt, and when it was magnified with a microscope, it had a rough surface. The outer surface of the ingot after processing has the property of being burnt black as in Example 1.
上記各実施例１及び２のインゴット共、本外形加工工程の後に、ウェハにスライスして、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インゴットにクラックが入ることも無かったため、インゴットを無駄にすることがなかったのは、言うまでもない。 In the ingots of Examples 1 and 2 described above, after this outer shape processing step, the wafer was sliced, beveled, and polished. In this process, the work-affected layer around the wafer was removed and turned black. The burnt surface properties had no adverse effect. It goes without saying that the ingot was not wasted because there was no crack in the ingot by this outer shape processing step.
本発明によって、導電性を有するSiC単結晶インゴットは、全く機械的なダメージを受けることなく外形加工ができ、その意味で歩留りは１００%である。他方、従来の研削砥石を使って外周研削する方法では、機械の動作条件を改善して歩留りは良くなりつつあるものの、現時点では１０%以下の歩留りである。 According to the present invention, the SiC single crystal ingot having conductivity can be processed without any mechanical damage, and in that sense, the yield is 100%. On the other hand, in the conventional method of peripheral grinding using a grinding wheel, the operating conditions of the machine are improved and the yield is improving, but at present, the yield is 10% or less.
１…インゴット
２…ワイヤー
1 ...
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| CN111497043A (en) * | 2020-03-05 | 2020-08-07 | 秦皇岛本征晶体科技有限公司 | Method for manufacturing magnesium fluoride wave plate element |
| CN114211208A (en) * | 2021-12-27 | 2022-03-22 | 安徽金寨将军磁业有限公司 | Processing method for arc surface of permanent magnetic ferrite magnetic shoe alloy die |
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