JP2005109353A

JP2005109353A - Method for manufacturing light emitting diode

Info

Publication number: JP2005109353A
Application number: JP2003343641A
Authority: JP
Inventors: Kazuaki Sasaki; 和明佐々木; Takanao Kurahashi; 孝尚倉橋
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2003-10-01
Filing date: 2003-10-01
Publication date: 2005-04-21

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a light emitting diode capable of increasing efficiency in manufacture. <P>SOLUTION: An epitaxial wafer 101 and a p-GaP substrate 7 are introduced into a heat-treatment furnace 120 while the epitaxial wafer 101 is in contact with the p-GaP substrate 7. After that, phosphine and arsine are supplied into the heat-treatment furnace 120 and a heat treatment mechanism 122 is actuated for performing heat treatment at about 800°C for about one hour. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は発光ダイオードの製造方法に関する。 The present invention relates to a method for manufacturing a light emitting diode.

近年、発光ダイオード（ＬＥＤ）が屋内外の表示デバイスとして脚光を浴びている。発光ダイオードの高輝度化に伴い、ネオン管灯に代る媒体として屋外ディスプレイ市場での需要が急増している。 In recent years, light emitting diodes (LEDs) have been spotlighted as indoor and outdoor display devices. With the increase in brightness of light emitting diodes, demand in the outdoor display market is rapidly increasing as a medium replacing neon tube lamps.

可視域の高輝度発光ダイオードとしては、ＡｌＧａＩｎＰ系材料で構成された発光ダイオードが知られている。図５に、特許文献１（特許第３２３０６３８号公報）に記載された技術に基づく従来（以下、従来例という）のＡｌＧａＩｎＰ系発光ダイオード１００の構造を示す。 As a high-intensity light-emitting diode in the visible range, a light-emitting diode made of an AlGaInP-based material is known. FIG. 5 shows a structure of a conventional (hereinafter referred to as a conventional example) AlGaInP-based light-emitting diode 100 based on the technique described in Patent Document 1 (Japanese Patent No. 3230638).

上記発光ダイオード１００は、ｎ−ＡｌＧａＡｓコンタクト層２（厚さ３μｍ、Ｓｉドープ：５×１０¹⁷ｃｍ^-3）、ｎ−ＡｌＧａＩｎＰクラッド層３（厚さ１．０μｍ、Ｓｉドープ：５×１０¹⁷ｃｍ^-3）、ＡｌＧａＩｎＰ系の発光部の一例としての（Ａｌ_0.05Ｇａ_0.95）_0.5Ｉｎ_0.5Ｐ活性層４（厚さ０．６μｍ）、ｐ−ＡｌＧａＩｎＰクラッド層５（厚さ０．７μｍ、Ｚｎドープ：５×１０¹⁷ｃｍ^-3）、ｐ−ＧａＩｎＰ保護層６（厚さ０．１μｍ、Ｚｎドープ：１×１０¹⁸ｃｍ^-3）およびｐ−ＧａＰ基板７（厚さ３００μｍ、Ｚｎドープ：３×１０¹⁸ｃｍ^-3）を有している。また、上記ｐ−ＧａＰ基板７下に水玉状のｐ−電極１１を形成する一方、ｎ−ＡｌＧａＡｓコンタクト層２の中央部分上にｎ−電極１２を形成している。 The light emitting diode 100 includes an n-AlGaAs contact layer 2 (thickness 3 μm, Si-doped: 5 × 10 ¹⁷ cm ⁻³ ), an n-AlGaInP cladding layer 3 (thickness 1.0 μm, Si-doped: 5 × 10 ¹⁷ cm). ^-3 ), (Al _0.05 Ga _0.95 ) _0.5 In _0.5 P active layer 4 (thickness 0.6 μm), p-AlGaInP clad layer 5 (thickness 0.7 μm, Zn-doped as an example of an AlGaInP-based light emitting portion: 5 × 10 ¹⁷ cm ⁻³ ), p-GaInP protective layer 6 (thickness 0.1 μm, Zn doped: 1 × 10 ¹⁸ cm ⁻³ ) and p-GaP substrate 7 (thickness 300 μm, Zn doped: 3 × 10 ¹⁸ cm ⁻³ ). In addition, a polka dot p-electrode 11 is formed under the p-GaP substrate 7, while an n-electrode 12 is formed on the central portion of the n-AlGaAs contact layer 2.

上記発光ダイオード１００は図６（Ａ）〜図６（Ｅ）に示すように製造する。 The light emitting diode 100 is manufactured as shown in FIGS. 6 (A) to 6 (E).

まず、図６（Ａ）に示すように、ｎ−ＧａＡｓ基板１上に、ＭＯＣＶＤ（有機金属気相成長）法によりｎ−ＡｌＧａＡｓコンタクト層２（厚さ３μｍ、Ｓｉドープ：５×１０¹⁷ｃｍ^-3）、ｎ−ＡｌＧａＩｎＰクラッド層３（厚さ１．０μｍ、Ｓｉドープ：５×１０¹⁷ｃｍ^-3）、（Ａｌ_0.05Ｇａ_0.95）_0.5Ｉｎ_0.5Ｐ活性層４（厚さ０．６μｍ）、ｐ−ＡｌＧａＩｎＰクラッド層５（厚さ０．７μｍ、Ｚｎドープ：５×１０¹⁷ｃｍ^-3）、ｐ−ＧａＩｎＰ保護層６（厚さ０．１μｍ、Ｚｎドープ：１×１０¹⁸ｃｍ^-3）を順次成長させる。ここまで成長したものをエピウエハ１０１とする。 First, as shown in FIG. 6A, an n-AlGaAs contact layer 2 (thickness: 3 μm, Si-doped: 5 × 10 ¹⁷ cm ⁻ on an n-GaAs substrate 1 by MOCVD (metal organic chemical vapor deposition). ³ ), n-AlGaInP cladding layer 3 (thickness 1.0 μm, Si-doped: 5 × 10 ¹⁷ cm ⁻³ ), (Al _0.05 Ga _0.95 ) _0.5 In _0.5 P active layer 4 (thickness 0.6 μm), p -AlGaInP cladding layer 5 (thickness 0.7 μm, Zn doped: 5 × 10 ¹⁷ cm ⁻³ ), p-GaInP protective layer 6 (thickness 0.1 μm, Zn doped: 1 × 10 ¹⁸ cm ⁻³ ) sequentially Grow. The epitaxial wafer 101 is grown up to this point.

その後、図７に示すように、上記エピウエハ１０１をホルダ２１に搭載して熱処理炉２０内に導入する。この時、図６（Ｂ）に示すように、上記エピウエハ１０１のｐ−ＧａＩｎＰ保護層６上にはｐ−ＧａＰ基板７を配置し、更に、ｐ−ＧａＰ基板７上には重し８を配置する。これにより、上記ｐ−ＧａＰ基板７のホルダ２１側の表面がｐ−ＧａＩｎＰ保護層６に接触する一方、ｐ−ＧａＰ基板７においてホルダ２１とは反対側の表面が重し８に接触する。 Thereafter, as shown in FIG. 7, the epi-wafer 101 is mounted on the holder 21 and introduced into the heat treatment furnace 20. At this time, as shown in FIG. 6B, a p-GaP substrate 7 is disposed on the p-GaInP protective layer 6 of the epi-wafer 101, and a weight 8 is disposed on the p-GaP substrate 7. To do. Thereby, the surface of the p-GaP substrate 7 on the holder 21 side contacts the p-GaInP protective layer 6, while the surface of the p-GaP substrate 7 opposite to the holder 21 overlaps and contacts the 8.

次に、上記熱処理炉２０内に窒素または水素を供給しながら、加熱処理機構２２を作動させて、８００℃程度の高温で約１時間加熱処理を行う。 Next, while supplying nitrogen or hydrogen into the heat treatment furnace 20, the heat treatment mechanism 22 is operated to perform heat treatment at a high temperature of about 800 ° C. for about 1 hour.

次に、上記熱処理炉２０からウエハ１０１を取り出して、図６（Ｃ）に示すように、重し８を除去すると、ｐ−ＧａＰ基板７はｐ−ＧａＩｎＰ保護層６に貼り付いている。なお、上記ｐ−ＧａＰ基板７は発光ダイオード１００において電流拡散と光取り出し窓の層として機能する。 Next, when the wafer 101 is taken out from the heat treatment furnace 20 and the weight 8 is removed as shown in FIG. 6C, the p-GaP substrate 7 is adhered to the p-GaInP protective layer 6. The p-GaP substrate 7 functions as a current diffusion and light extraction window layer in the light emitting diode 100.

その後、図６（Ｄ）に示すように、上記ＧａＡｓ基板１をアンモニア系のエッチング液（例えば、アンモニア：過酸化水素＝１：２０）で除去する。 Thereafter, as shown in FIG. 6D, the GaAs substrate 1 is removed with an ammonia-based etching solution (for example, ammonia: hydrogen peroxide = 1: 20).

最後に、図６（Ｅ）に示すように、ｐ−電極１１をｐ−ＧａＰ基板７上に水玉状に形成し、更に、ｎ−電極１２をｎ−ＡｌＧａＡｓコンタクト層２の中央部分下に形成する。 Finally, as shown in FIG. 6E, the p-electrode 11 is formed in a polka dot shape on the p-GaP substrate 7 and the n-electrode 12 is formed below the central portion of the n-AlGaAs contact layer 2. To do.

このように形成した発光ダイオード１００は、ｐ−ＧａＰ基板７側を下にしてステムにマウントして２０ｍＡで通電した場合、発光波長６３０ｎｍで全光束は４ｍＷと、ｐ−ＧａＰ基板７を貼付けない場合に比べて約２倍の高輝度が得られる。これは厚さ３００μｍのｐ−ＧａＰ基板７が透明基板として作用し、チップ側面から効率的に発光が取り出されるからである。 When the light-emitting diode 100 formed in this way is mounted on a stem with the p-GaP substrate 7 side down and energized at 20 mA, the total luminous flux is 4 mW at a light emission wavelength of 630 nm, and the p-GaP substrate 7 is not attached. As compared with the above, about twice as high brightness can be obtained. This is because the p-GaP substrate 7 having a thickness of 300 μm acts as a transparent substrate, and light emission is efficiently extracted from the side surface of the chip.

ところが、上記従来例の発光ダイオードの製造方法では、熱処理炉２０による加熱処理によってｎ−ＧａＰ基板７およびＧａＡｓ基板１の表層（図６（Ｃ）において黒く塗りつぶしている部分）が金属色になってしまう。この金属色の表層があると、上記加熱処理後に行うＧａＡｓ基板１の除去が失敗するケースが多発する。つまり、上記加熱処理後においては、ＧａＡｓ基板１を上記アンモニア系エッチング液でエッチングするのが困難になる。そのため、上記ＧａＡｓ基板１の表面を研磨して、ＧａＡｓ基板１から金属色の表層を物理的に取り除かなければならなかった。 However, in the above-described conventional method for manufacturing a light-emitting diode, the surface layers of the n-GaP substrate 7 and the GaAs substrate 1 (the portions blacked out in FIG. 6C) are changed to a metallic color by the heat treatment in the heat treatment furnace 20. End up. When this metal-colored surface layer is present, there are many cases where removal of the GaAs substrate 1 performed after the heat treatment fails. That is, after the heat treatment, it becomes difficult to etch the GaAs substrate 1 with the ammonia-based etchant. For this reason, the surface of the GaAs substrate 1 must be polished to physically remove the metal-colored surface layer from the GaAs substrate 1.

また、上記ｐ−ＧａＰ基板７の表層についても、ｐ−電極１１が付き難くなったり、発光が遮られたりするなどの問題が生じるため、やはり研磨して除去する必要があった。 Further, the surface layer of the p-GaP substrate 7 also has a problem that it becomes difficult to attach the p-electrode 11 or the light emission is blocked.

したがって、上記従来例の発光ダイオードの製造方法では、金属色の表層を除去するための工程が必要になるから、製造効率が低下するという問題がある。
特許第３２３０６３８号公報 Therefore, the above-described conventional method for manufacturing a light emitting diode requires a process for removing the surface layer of the metal color, and thus has a problem that the manufacturing efficiency is lowered.
Japanese Patent No. 3230638

そこで、本発明の課題は、製造効率を高めることができる発光ダイオードの製造方法を提供することにある。 Accordingly, an object of the present invention is to provide a method for manufacturing a light-emitting diode capable of improving manufacturing efficiency.

本願発明者らが加熱処理後のｎ−ＧａＡｓ基板１およびｐ−ＧａＰ基板７の表面に生じた金属色の部分の組成を調べたところ、その部分においてＧａが多く観測された。これは、加熱処理中にｎ−ＧａＡｓ基板１およびｐ−ＧａＰ基板７の表面からＡｓやＰが蒸発して、ｎ−ＧａＡｓ基板１およびｐ−ＧａＰ基板７の表面に金属Ｇａが残ったためと考えられる。この考えに基いて、本発明者らは以降の発明を創作するに至った。 When the inventors of the present application examined the composition of the metal-colored portions generated on the surfaces of the n-GaAs substrate 1 and the p-GaP substrate 7 after the heat treatment, a large amount of Ga was observed in those portions. This is considered because As and P evaporated from the surfaces of the n-GaAs substrate 1 and the p-GaP substrate 7 during the heat treatment, and metal Ga remained on the surfaces of the n-GaAs substrate 1 and the p-GaP substrate 7. It is done. Based on this idea, the present inventors have created the following inventions.

第１の発明の発光ダイオードの製造方法は、ＧａＡｓ基板とこのＧａＡｓ基板上に形成されたＡｌＧａＩｎＰ系の発光部とを有するエピウエハ上にＧａＰ基板を載せた後、所定温度の加熱処理を行って、上記ＧａＰ基板を上記エピウエハに貼り付ける発光ダイオードの製造方法において、上記加熱処理はＡｓおよびＰを含む雰囲気中で行うことを特徴としている。 According to a first aspect of the present invention, there is provided a method of manufacturing a light emitting diode, comprising: placing a GaP substrate on an epi wafer having a GaAs substrate and an AlGaInP-based light emitting portion formed on the GaAs substrate; In the method for manufacturing a light-emitting diode in which the GaP substrate is attached to the epi-wafer, the heat treatment is performed in an atmosphere containing As and P.

上記構成の発光ダイオードの製造方法によれば、上記エピウエハ上にＧａＰ基板を載せた後、ＡｓおよびＰを含む雰囲気中で所定温度の加熱処理を行うことによって、ＧａＡｓ基板からＡｓが脱離するのが抑制され、かつ、ＧａＰ基板からＰが脱離するのが抑制される。その結果、上記ＧａＡｓ基板およびＧａＰ基板の表面が金属色にならないので、ＧａＡｓ基板およびＧａＰ基板の表面を研磨しなくてもよい。したがって、上記ＧａＡｓ基板およびＧａＰ基板の表面を研磨する工程を省いて、製造効率を高めることができる。 According to the method for manufacturing a light-emitting diode having the above-described structure, after a GaP substrate is placed on the epi-wafer, As is desorbed from the GaAs substrate by performing a heat treatment at a predetermined temperature in an atmosphere containing As and P. And P is desorbed from the GaP substrate. As a result, the surfaces of the GaAs substrate and the GaP substrate do not have a metallic color, so that the surfaces of the GaAs substrate and the GaP substrate need not be polished. Therefore, the manufacturing efficiency can be improved by omitting the step of polishing the surfaces of the GaAs substrate and the GaP substrate.

また、上記ＧａＡｓ基板およびＧａＰ基板の表面が金属色にならないので、加熱処理後、ＧａＡｓ基板の除去するためのエッチングや、ＧａＰ基板に対する電極の形成が容易になる。つまり、上記加熱処理後のプロセスを容易に行うことができる。 In addition, since the surfaces of the GaAs substrate and the GaP substrate do not have a metallic color, etching for removing the GaAs substrate and formation of electrodes on the GaP substrate are facilitated after the heat treatment. That is, the process after the heat treatment can be easily performed.

また、第２の発明の発光ダイオードの製造方法は、ＧａＡｓ基板とこのＧａＡｓ基板上に形成されたＡｌＧａＩｎＰ系の発光部とを有するエピウエハ上にＧａＰ基板を載せた後、所定温度の加熱処理を行って、上記ＧａＰ基板を上記エピウエハに貼り付ける発光ダイオードの製造方法において、上記加熱処理は、Ａｓを含む第１の脱離防止部材を上記ＧａＡｓ基板に接触または近接させ、かつ、Ｐを含む第２の脱離防止部材を上記ＧａＰ基板に接触または近接させて行うことを特徴としている。 According to a second aspect of the present invention, there is provided a method for manufacturing a light emitting diode, comprising: placing a GaP substrate on an epitaxial wafer having a GaAs substrate and an AlGaInP light emitting portion formed on the GaAs substrate; In the method of manufacturing a light-emitting diode in which the GaP substrate is attached to the epi-wafer, the heat treatment is performed by bringing the first detachment preventing member containing As into contact with or in proximity to the GaAs substrate and the second containing P. The detachment preventing member is brought into contact with or close to the GaP substrate.

上記構成の発光ダイオードの製造方法によれば、上記Ａｓを含む第１の脱離防止部材をＧａＡｓ基板に接触または近接させ、かつ、Ｐを含む第２の脱離防止部材をＧａＰ基板に接触または近接させて所定温度の加熱処理を行うことによって、ＧａＡｓ基板からＡｓが脱離するのが抑制され、かつ、ＧａＰ基板からＰが脱離するのが抑制される。その結果、上記ＧａＡｓ基板およびＧａＰ基板の表面が金属色にならないので、ＧａＡｓ基板およびＧａＰ基板の表面を研磨しなくてもよい。したがって、上記ＧａＡｓ基板およびＧａＰ基板の表面を研磨する工程を省いて、製造効率を高めることができる。 According to the method for manufacturing a light emitting diode having the above configuration, the first detachment preventing member containing As is brought into contact with or close to the GaAs substrate, and the second detachment preventing member containing P is brought into contact with the GaP substrate. By performing the heat treatment at a predetermined temperature in the vicinity, As is desorbed from the GaAs substrate, and P is desorbed from the GaP substrate. As a result, the surfaces of the GaAs substrate and the GaP substrate do not have a metallic color, so that the surfaces of the GaAs substrate and the GaP substrate need not be polished. Therefore, the manufacturing efficiency can be improved by omitting the step of polishing the surfaces of the GaAs substrate and the GaP substrate.

一実施形態の発光ダイオードの製造方法は、上記第１の発明の発光ダイオードの製造方法において、上記雰囲気はＴＢＰとＴＢＡｓとの少なくとも一方を含む。 In one embodiment of the method for manufacturing a light-emitting diode, the atmosphere includes at least one of TBP and TBAs.

上記実施形態の発光ダイオードの製造方法によれば、上記雰囲気がＴＢＰとＴＢＡｓとの少なくとも一方を含むことによって、雰囲気中に水素が生じるので、この水素で金属色の原因となる元素を除去することができる。 According to the method for manufacturing a light emitting diode of the above embodiment, since the atmosphere contains at least one of TBP and TBAs, hydrogen is generated in the atmosphere. Therefore, the element that causes the metal color is removed with the hydrogen. Can do.

一実施形態の発光ダイオードの製造方法は、上記第２の発明の発光ダイオードの製造方法において、上記第１の脱離防止部材はＧａＡｓ結晶ウエハであり、上記第２の脱離防止部材はＧａＰ結晶ウエハである。 The light emitting diode manufacturing method of one embodiment is the light emitting diode manufacturing method according to the second invention, wherein the first desorption preventing member is a GaAs crystal wafer, and the second desorption preventing member is a GaP crystal. It is a wafer.

上記実施形態の発光ダイオードの製造方法によれば、上記第１の脱離防止部材はＧａＡｓ結晶ウエハであるから、第１の脱離防止部材の調達が容易である。 According to the light emitting diode manufacturing method of the above embodiment, since the first detachment preventing member is a GaAs crystal wafer, the first detachment preventing member can be easily procured.

また、上記第２の脱離防止部材はＧａＰ結晶ウエハであるから、第２の脱離防止部材の調達が容易である。 Further, since the second desorption preventing member is a GaP crystal wafer, the second desorption preventing member can be easily procured.

第１の発明の発光ダイオードの製造方法は、エピウエハ上にＧａＰ基板を載せた後、ＡｓおよびＰを含む雰囲気中で所定温度の加熱処理を行うことによって、ＧａＡｓ基板からＡｓが脱離するのが抑制され、かつ、ＧａＰ基板からＰが脱離するのが抑制されるので、ＧａＡｓ基板およびＧａＰ基板の表面が金属色にならない。つまり、上記ＧａＡｓ基板およびＧａＰ基板の表面において、ＡｓおよびＰの抜けが抑制されて、Ｇａの発生が抑えられる。したがって、上記ＧａＡｓ基板およびＧａＰ基板の表面を研磨する工程を省いて、製造効率を高めることができる。 In the method of manufacturing a light emitting diode according to the first aspect of the invention, after a GaP substrate is placed on an epi-wafer, heat treatment at a predetermined temperature is performed in an atmosphere containing As and P, whereby As is desorbed from the GaAs substrate. Since it is suppressed and P is desorbed from the GaP substrate, the surfaces of the GaAs substrate and the GaP substrate do not become metallic. That is, on the surfaces of the GaAs substrate and the GaP substrate, the escape of As and P is suppressed, and the generation of Ga is suppressed. Therefore, the manufacturing efficiency can be improved by omitting the step of polishing the surfaces of the GaAs substrate and the GaP substrate.

第２の発明の発光ダイオードの製造方法は、Ａｓを含む第１の脱離防止部材をＧａＡｓ基板に接触または近接させ、かつ、Ｐを含む第２の脱離防止部材をＧａＰ基板に接触または近接させて所定温度の加熱処理を行うことによって、ＧａＡｓ基板からＡｓが脱離するのが抑制され、かつ、ＧａＰ基板からＰが脱離するのが抑制されるので、ＧａＡｓ基板およびＧａＰ基板の表面が金属色にならない。つまり、上記ＧａＡｓ基板およびＧａＰ基板の表面において、ＡｓおよびＰの抜けが抑制されて、Ｇａの発生が抑えられる。したがって、上記ＧａＡｓ基板およびＧａＰ基板の表面を研磨する工程を省いて、製造効率を高めることができる。 In the method for manufacturing a light emitting diode according to the second aspect of the invention, the first detachment preventing member containing As is brought into contact with or in proximity to the GaAs substrate, and the second detachment preventing member containing P is brought into contact with or in proximity to the GaP substrate. By performing the heat treatment at a predetermined temperature, As is desorbed from the GaAs substrate and P is desorbed from the GaP substrate, the surfaces of the GaAs substrate and the GaP substrate are reduced. Does not turn metallic. That is, on the surfaces of the GaAs substrate and the GaP substrate, the escape of As and P is suppressed, and the generation of Ga is suppressed. Therefore, the manufacturing efficiency can be improved by omitting the step of polishing the surfaces of the GaAs substrate and the GaP substrate.

以下、本発明の発光ダイオードの製造方法を図示の実施の形態により詳細に説明する。 Hereinafter, the manufacturing method of the light emitting diode of this invention is demonstrated in detail by embodiment of illustration.

Embodiment 1

実施の形態１に係る発光ダイオードの製造方法を説明する。実施の形態１の製造方法で得る発光ダイオードの構造は、図５の従来例の発光ダイオード１００の構造と同一である。 A method for manufacturing the light-emitting diode according to Embodiment 1 will be described. The structure of the light emitting diode obtained by the manufacturing method of the first embodiment is the same as the structure of the light emitting diode 100 of the conventional example of FIG.

実施の形態１では、図６(Ａ)に示すエピウエハ１０１を形成した後、図１に示すように、エピウエハ１０１をホルダ１２１に搭載して熱処理炉１２０内に導入する。この時、上記エピウエハ１０１のｐ−ＧａＩｎＰ保護層６上にｐ−ＧａＰ基板７を載せて、ｐ−ＧａＩｎＰ保護層６とｐ−ＧａＰ基板７とを接触させる。更に、ｐ−ＧａＰ基板７上に重し８を載せて、ｐ−ＧａＰ基板７と重し８とを接触させる。 In the first embodiment, after the epi-wafer 101 shown in FIG. 6A is formed, the epi-wafer 101 is mounted on the holder 121 and introduced into the heat treatment furnace 120 as shown in FIG. At this time, the p-GaP substrate 7 is placed on the p-GaInP protective layer 6 of the epi-wafer 101 and the p-GaInP protective layer 6 and the p-GaP substrate 7 are brought into contact with each other. Further, a weight 8 is placed on the p-GaP substrate 7, and the p-GaP substrate 7 and the weight 8 are brought into contact with each other.

次に、上記熱処理炉１２０内にホスフィン（ＰＨ₃）とアルシン（ＡｓＨ₃）とを微量（５０ｃｃｍ程度）流しながら、加熱処理機構１２２を作動させて、８００℃程度の高温で約１時間加熱処理を行う。 Next, the heat treatment mechanism 122 is operated while a small amount (about 50 ccm) of phosphine (PH ₃ ) and arsine (AsH ₃ ) are allowed to flow into the heat treatment furnace 120, and heat treatment is performed at a high temperature of about 800 ° C. for about 1 hour. I do.

上記加熱処理後、熱処理炉１２０内からエピウエハ１０１とｐ−ＧａＰ基板７を取り出すと、ｎ−ＧａＡｓ基板１の表面もｐ−ＧａＰ基板７の表面もほぼ全面にわたって金属色は見られなかった。これは、上記熱処理炉１２０内に供給したホスフィン、アルシンによって、リン（Ｐ）と砒素（Ａｓ）との雰囲気ができて、ＧａＡｓ基板１から砒素が蒸発するのが抑えられ、かつ、ＧａＰ基板７からリンが蒸発するのが抑えられたためである。つまり、上記ＧａＡｓ基板１およびＧａＰ基板７の表面においてＧａが生じなかったためである。しかしながら、上記ｎ−ＧａＡｓ基板１およびｐ−ＧａＰ基板７においては、一部（面積で約２％の散在した領域）がわずかに金属色が見られたため、リン（Ｐ）と砒素（Ａｓ）の抜けがわずかではあるが生じたことが伺える。 After the heat treatment, when the epiwafer 101 and the p-GaP substrate 7 were taken out from the heat treatment furnace 120, neither the surface of the n-GaAs substrate 1 nor the surface of the p-GaP substrate 7 was found to have a metal color. This is because an atmosphere of phosphorus (P) and arsenic (As) is created by the phosphine and arsine supplied into the heat treatment furnace 120, and the evaporation of arsenic from the GaAs substrate 1 is suppressed, and the GaP substrate 7 This is because phosphorus was prevented from evaporating. That is, no Ga was generated on the surfaces of the GaAs substrate 1 and the GaP substrate 7. However, in the n-GaAs substrate 1 and the p-GaP substrate 7, since a part of the metal (a region where the area is scattered by about 2%) is slightly metallic, phosphorous (P) and arsenic (As) are formed. It can be said that the omission occurred slightly.

このように、上記ｎ−ＧａＡｓ基板１の表面のほぼ全面において金属色の部分が形成されないので、ｎ−ＧａＡｓ基板１の表面を研磨しなくても、ＧａＡｓ基板１をアンモニア系のエッチング液（例えば、アンモニア：過酸化水素＝１：２０）で容易に除去することができる。 As described above, since the metal-colored portion is not formed on almost the entire surface of the n-GaAs substrate 1, the GaAs substrate 1 can be treated with an ammonia-based etching solution (for example, without polishing the surface of the n-GaAs substrate 1). , Ammonia: hydrogen peroxide = 1: 20).

また、上記ｐ−ＧａＰ基板７の表面のほぼ全面においても金属色の部分が形成されないので、ｐ−ＧａＰ基板７の表面を研磨しなくても、ｐ−ＧａＰ基板７の表面にｐ−電極１１を容易に付けることができる。 Further, since a metal color portion is not formed on almost the entire surface of the p-GaP substrate 7, the p-electrode 11 is formed on the surface of the p-GaP substrate 7 without polishing the surface of the p-GaP substrate 7. Can be attached easily.

したがって、上記ｎ−ＧａＡｓ基板１およびｐ−ＧａＰ基板７の表面を研磨する工程を無くせるから、製造効率を上げることができる。 Therefore, since the process of polishing the surfaces of the n-GaAs substrate 1 and the p-GaP substrate 7 can be eliminated, the production efficiency can be increased.

Embodiment 2

実施の形態２に係る発光ダイオードの製造方法を説明する。 A method for manufacturing the light-emitting diode according to Embodiment 2 will be described.

実施の形態２では、図６(Ａ)に示すエピウエハ１０１を形成した後、図７に示す熱処理炉２０内に、エピウエハ１０１をホルダ２１に搭載して導入する。この時、図２（Ａ）に示すように、第１の脱離防止部材の一例としての台座９上にエピウエハ１０１を載せて、エピウエハ１０１のｎ−ＧａＡｓ基板１と台座９とを接触させる。また、上記エピウエハ１０１上にｐ−ＧａＰ基板７を載せて、エピウエハ１０１のｐ−ＧａＩｎＰ保護層６とｐ−ＧａＰ基板７とを接触させる。更に、上記ｐ−ＧａＰ基板７上に第２の脱離防止部材の一例としての重し１０８を載せて、ｐ−ＧａＰ基板７と重し１０８とを接触させる。 In the second embodiment, after the epitaxial wafer 101 shown in FIG. 6A is formed, the epitaxial wafer 101 is mounted on the holder 21 and introduced into the heat treatment furnace 20 shown in FIG. At this time, as shown in FIG. 2A, the epi-wafer 101 is placed on a pedestal 9 as an example of a first detachment preventing member, and the n-GaAs substrate 1 of the epi-wafer 101 and the pedestal 9 are brought into contact with each other. Further, the p-GaP substrate 7 is placed on the epi-wafer 101 and the p-GaInP protective layer 6 of the epi-wafer 101 and the p-GaP substrate 7 are brought into contact with each other. Further, a weight 108 as an example of a second detachment preventing member is placed on the p-GaP substrate 7, and the p-GaP substrate 7 and the weight 108 are brought into contact with each other.

上記重し１０８の下部内には複数のＧａＰの破片２３を収容している。そして、上記重し１０８の下面は、図２（Ｂ）に示すようなメッシュ状になっている。これにより、上記ＧａＰの破片２３はｐ−ＧａＰ基板７に空間的に近接している。 A plurality of GaP fragments 23 are accommodated in the lower portion of the weight 108. The lower surface of the weight 108 has a mesh shape as shown in FIG. Thereby, the GaP fragments 23 are spatially close to the p-GaP substrate 7.

一方、上記台座９の上部内にはＧａＡｓの破片２４を収容している。そして、上記台座９の上面は、図２（Ｃ）に示すようなメッシュ状になっている。これにより、上記ＧａＡｓの破片２４はｎ−ＧａＡｓ基板１に空間的に近接する。 On the other hand, GaAs fragments 24 are accommodated in the upper portion of the base 9. The upper surface of the pedestal 9 has a mesh shape as shown in FIG. As a result, the GaAs fragments 24 are spatially close to the n-GaAs substrate 1.

そして、上記熱処理炉２０内に窒素または水素を供給しながら、加熱処理機構２２を作動させて、８００℃程度の高温で約１時間加熱処理を行う。 Then, while supplying nitrogen or hydrogen into the heat treatment furnace 20, the heat treatment mechanism 22 is operated to perform heat treatment at a high temperature of about 800 ° C. for about 1 hour.

上記加熱処理後、熱処理炉２０内からエピウエハ１０１とｐ−ＧａＰ基板７を取り出すと、ｎ−ＧａＡｓ基板１の表面もｐ−ＧａＰ基板７の表面もほぼ全面にわたって金属色は見られなかった。これは、上記ＧａＡｓの破片２４によって、ｎ−ＧａＡｓ基板１の表面近傍に砒素（Ａｓ）の雰囲気ができて、ｎ−ＧａＡｓ基板１の表面からＡｓの蒸発が抑えられると共に、ＧａＰの破片２３によって、ｐ−ＧａＰ基板７の表面近傍にリン（Ｐ）の雰囲気ができて、ｐ−ＧａＰ基板７の表面からＰの蒸発が抑えられたためである。しかしながら、上記実施の形態１と同様に、ｎ−ＧａＡｓ基板１およびｐ−ＧａＰ基板７の表面の一部（全表面積に対して約２．５％の散在した領域）でわずかに金属色が見られたため、リンと砒素との抜けがわずかではあるが生じた。 After the heat treatment, when the epiwafer 101 and the p-GaP substrate 7 were taken out from the heat treatment furnace 20, neither the surface of the n-GaAs substrate 1 nor the surface of the p-GaP substrate 7 was found to have a metal color. This is because the GaAs fragments 24 create an arsenic (As) atmosphere in the vicinity of the surface of the n-GaAs substrate 1. As a result, the evaporation of As from the surface of the n-GaAs substrate 1 is suppressed and the GaP fragments 23. This is because an atmosphere of phosphorus (P) is formed in the vicinity of the surface of the p-GaP substrate 7 and evaporation of P is suppressed from the surface of the p-GaP substrate 7. However, as in the first embodiment, a slight metal color is observed on part of the surfaces of the n-GaAs substrate 1 and the p-GaP substrate 7 (a region in which about 2.5% of the total surface area is scattered). As a result, there was a slight loss of phosphorus and arsenic.

したがって、本実施の形態の発光ダイオードの製造方法は、上記実施の形態１と同様の効果を奏する。 Therefore, the method for manufacturing the light emitting diode according to the present embodiment has the same effects as those of the first embodiment.

Embodiment 3

実施の形態３の発光ダイオードの製造方法を説明する。 A method for manufacturing the light-emitting diode of Embodiment 3 will be described.

実施の形態３では、図６(Ａ)に示すエピウエハ１０１を形成した後、図３に示すように、エピウエハ１０１をホルダ２２１に搭載して熱処理炉２２０内に導入する。この時、上記エピウエハ１０１のｐ−ＧａＩｎＰ保護層６上にｐ−ＧａＰ基板７を載せて、ｐ−ＧａＩｎＰ保護層６とｐ−ＧａＰ基板７とを接触させている。更に、上記ｐ−ＧａＰ基板７上に重し８を載せて、ｐ−ＧａＰ基板７と重し８とを接触させている。 In the third embodiment, after the epitaxial wafer 101 shown in FIG. 6A is formed, the epitaxial wafer 101 is mounted on the holder 221 and introduced into the heat treatment furnace 220 as shown in FIG. At this time, the p-GaP substrate 7 is placed on the p-GaInP protective layer 6 of the epi-wafer 101 and the p-GaInP protective layer 6 and the p-GaP substrate 7 are brought into contact with each other. Further, a weight 8 is placed on the p-GaP substrate 7 to bring the p-GaP substrate 7 and the weight 8 into contact with each other.

そして、上記熱処理炉２２０内にターシャリブチルホスフィン（ＴＢＰ）とターシャリブチルアルシン（ＴＢＡｓ）とを供給しつつ、加熱処理機構２２２を作動させて、８００℃程度の高温で約１時間加熱処理を行う。なお、上記ターシャリブチルホスフィンはリン（Ｐ）を含む一方、ターシャリブチルアルシンは砒素（Ａｓ）を含んでいる。 Then, while supplying tertiary butylphosphine (TBP) and tertiary butylarsine (TBAs) into the heat treatment furnace 220, the heat treatment mechanism 222 is operated to perform heat treatment at a high temperature of about 800 ° C. for about 1 hour. Do. The tertiary butyl phosphine contains phosphorus (P), while the tertiary butyl arsine contains arsenic (As).

上記加熱処理後、熱処理炉２２０内からエピウエハ１０１とｐ−ＧａＰ基板７を取り出すと、ｎ−ＧａＡｓ基板１およびｐ−ＧａＰ基板７の全表面にわたって金属色は見られなかった。これは、上記熱処理炉２２０内に供給したターシャリブチルホスフィンおよびターシャリブチルアルシンによって、リンと砒素との雰囲気ができて、ＧａＡｓ基板１から砒素の蒸発が抑えられ、かつ、ＧａＰ基板７からリンの蒸発が抑えられたためである。つまり、上記ＧａＡｓ基板１およびＧａＰ基板７の表面においてＧａが生じなかったためである。 After the heat treatment, when the epiwafer 101 and the p-GaP substrate 7 were taken out from the heat treatment furnace 220, no metal color was observed over the entire surfaces of the n-GaAs substrate 1 and the p-GaP substrate 7. This is because the atmosphere of phosphorus and arsenic is created by the tertiary butyl phosphine and the tertiary butyl arsine supplied into the heat treatment furnace 220, the evaporation of arsenic from the GaAs substrate 1 is suppressed, and the phosphorous from the GaP substrate 7 is phosphorus. This is because the evaporation of was suppressed. That is, no Ga was generated on the surfaces of the GaAs substrate 1 and the GaP substrate 7.

本実施の形態では、ＧａＡｓ基板１およびＧａＰ基板７の表面において金属色は全く見られなかった。これは、上記加熱処理の過程でｐ−ＧａＰ基板７とｎ−ＧａＡｓ基板１とからＰとＡｓとがわずかに抜け、ｐ−ＧａＰ基板７およびｎ−ＧａＡｓ基板１の表面にわずかにＧａが生じたとしても、ターシャリブチルホスフィン、ターシャリブチルアルシンの分解過程で生じた水素がＧａを蒸発させるエッチング機能を果たしたためである。 In the present embodiment, no metallic color was seen on the surfaces of the GaAs substrate 1 and the GaP substrate 7. This is because P and As are slightly removed from the p-GaP substrate 7 and the n-GaAs substrate 1 during the heat treatment, and a slight amount of Ga is generated on the surfaces of the p-GaP substrate 7 and the n-GaAs substrate 1. This is because hydrogen generated in the decomposition process of tertiary butylphosphine and tertiary butylarsine has performed an etching function for evaporating Ga.

したがって、本実施の形態の発光ダイオードの製造方法は、上記実施の形態１に比べて、製造効率をより高めることができる。 Therefore, the manufacturing method of the light emitting diode of the present embodiment can further increase the manufacturing efficiency as compared with the first embodiment.

また、本実施の形態の結果より、上記加熱処理の処理ガス（雰囲気ガス）はターシャリブチルホスフィン、ターシャリブチルアルシンが望ましいことが判る。 From the results of this embodiment, it can be seen that the processing gas (atmosphere gas) for the heat treatment is preferably tertiary butylphosphine or tertiary butylarsine.

上記実施の形態３は、上記熱処理炉２２０内にターシャリブチルホスフィンとターシャリブチルアルシンとを供給しながら所定の加熱処理を行ったが、熱処理炉２２０内にホスフィン（ＰＨ₃）とターシャリブチルアルシンとを供給しながら所定の加熱処理を行っても、あるいは、熱処理炉２２０内にターシャリブチルホスフィンとアルシン（ＡｓＨ₃）とを供給しながら所定の加熱処理を行っても、ＧａＡｓ基板１およびＧａＰ基板７の表面において金属色の発生を完全に無くすことができることを確認している。 In the third embodiment, predetermined heat treatment is performed while supplying tertiary butylphosphine and tertiary butylarsine into the heat treatment furnace 220, but phosphine (PH ₃ ) and tertiary butyl are contained in the heat treatment furnace 220. Even if a predetermined heat treatment is performed while supplying arsine, or a predetermined heat treatment is performed while supplying tertiarybutylphosphine and arsine (AsH ₃ ) in the heat treatment furnace 220, the GaAs substrate 1 and It has been confirmed that the generation of the metal color can be completely eliminated on the surface of the GaP substrate 7.

Embodiment 4

実施の形態４に係る発光ダイオードの製造方法を説明する。 A method for manufacturing the light-emitting diode according to Embodiment 4 will be described.

実施の形態４では、図６(Ａ)に示すエピウエハ１０１を形成した後、図７に示す熱処理炉２０内に、エピウエハ１０１をホルダ２１に搭載して導入する。この時、図４に示すように、第１の脱離防止部材の一例としてのＧａＡｓ結晶ウエハ３１上にエピウエハ１０１を載せて、エピウエハ１０１のＧａＡｓ基板１とＧａＡｓ結晶ウエハ３１とを接触される。また、上記エピウエハ１０１のｐ−ＧａＩｎＰ保護層６上にｐ−ＧａＰ基板７を載せて、ｐ−ＧａＩｎＰ保護層６とｐ−ＧａＰ基板７とを接触させる。更に、上記ｐ−ＧａＰ基板７上に第２の脱離防止部材の一例としてのＧａＰ結晶ウエハ３２を載せて、ＧａＰ基板７とＧａＰ結晶ウエハ３２とを接触させる。ただし、ＧａＡｓどうし、ＧａＰどうしで貼り付かないように、ＧａＡｓ結晶ウエハ３１とＧａＰ結晶ウエハ３２の接触面は粗面（図４では破線で図示）とする。 In the fourth embodiment, after the epitaxial wafer 101 shown in FIG. 6A is formed, the epitaxial wafer 101 is mounted on the holder 21 and introduced into the heat treatment furnace 20 shown in FIG. At this time, as shown in FIG. 4, the epi wafer 101 is placed on the GaAs crystal wafer 31 as an example of the first detachment preventing member, and the GaAs substrate 1 of the epi wafer 101 and the GaAs crystal wafer 31 are brought into contact with each other. Further, the p-GaP substrate 7 is placed on the p-GaInP protective layer 6 of the epi-wafer 101, and the p-GaInP protective layer 6 and the p-GaP substrate 7 are brought into contact with each other. Further, a GaP crystal wafer 32 as an example of a second detachment preventing member is placed on the p-GaP substrate 7, and the GaP substrate 7 and the GaP crystal wafer 32 are brought into contact with each other. However, the contact surface of the GaAs crystal wafer 31 and the GaP crystal wafer 32 is a rough surface (shown by a broken line in FIG. 4) so that the GaAs and GaP are not attached to each other.

上記加熱処理後、熱処理炉２０から取り出したｎ−ＧａＡｓ基板１およびｐ−ＧａＰ基板７の全表面にわたって金属色は見られなかった。ただし、上記ＧａＡｓ結晶ウエハ３１とＧａＰ結晶ウエハ３２の表面は金属色になっていた。これは、上記ＧａＡｓ結晶ウエハ３１とＧａＰ結晶ウエハ３２とによって、リン（Ｐ）と砒素（Ａｓ）との雰囲気ができて、ＧａＡｓ基板１から砒素の蒸発が抑えられ、かつ、ＧａＰ基板７からリンの蒸発が抑えられたためである。つまり、上記ｎ−ＧａＡｓ基板１およびｐ−ＧａＰ基板７の表面においてＧａが生じなかったためである。 After the heat treatment, no metal color was observed over the entire surface of the n-GaAs substrate 1 and the p-GaP substrate 7 taken out from the heat treatment furnace 20. However, the surfaces of the GaAs crystal wafer 31 and the GaP crystal wafer 32 were metallic. This is because the atmosphere of phosphorus (P) and arsenic (As) is created by the GaAs crystal wafer 31 and the GaP crystal wafer 32, and the evaporation of arsenic from the GaAs substrate 1 is suppressed, and the GaP substrate 7 This is because the evaporation of was suppressed. That is, no Ga was generated on the surfaces of the n-GaAs substrate 1 and the p-GaP substrate 7.

本実施の形態では、上記実施の形態３と同じく、ＧａＡｓ基板１およびＧａＰ基板７の表面において金属色は全く見られなかった。これは、上記ｎ−ＧａＡｓ基板１の表面が別のＧａＡｓ結晶と空間的に密着することにより、ｎ−ＧａＡｓ基板１から砒素が蒸発せず、かつ、ｐ−ＧａＰ基板７の表面が別のＧａＰ結晶と空間的に密着することにより、ｐ−ＧａＰ基板７からリンが蒸発しなかったためと考えられる。 In the present embodiment, as in the third embodiment, no metal color was observed on the surfaces of the GaAs substrate 1 and the GaP substrate 7. This is because the surface of the n-GaAs substrate 1 is in close contact with another GaAs crystal so that arsenic is not evaporated from the n-GaAs substrate 1 and the surface of the p-GaP substrate 7 is separated from another GaP. It is considered that phosphorus did not evaporate from the p-GaP substrate 7 due to spatial contact with the crystal.

上記実施の形態１〜４において述べなかった工程は上記従来例と同様に行っている。 The steps not described in the first to fourth embodiments are performed in the same manner as in the conventional example.

上記実施の形態１〜４では、（Ａｌ_0.05Ｇａ_0.95）_0.5Ｉｎ_0.5Ｐ活性層４を有するエピウエハ１０１を用いたが、ＡｌＧａＩｎＰ系の発光部を有するエピウエハであれば本発明に用いることができる。 In the first to fourth embodiments, the epiwafer 101 having the (Al _0.05 Ga _0.95 ) _0.5 In _0.5 P active layer 4 is used. However, any epiwafer having an AlGaInP light emitting portion can be used in the present invention.

以上のように、本発明の発光ダイオードの製造方法は、透明基板型のＡｌＧａＩｎＰ系発光ダイオードの製造方法に最適である。 As described above, the method for producing a light emitting diode of the present invention is most suitable for a method for producing a transparent substrate type AlGaInP light emitting diode.

図１は本発明の実施の形態１の発光ダイオードの製造方法に用いる熱処理炉の概略構成図である。FIG. 1 is a schematic configuration diagram of a heat treatment furnace used in the method for manufacturing a light emitting diode according to Embodiment 1 of the present invention. 図２（Ａ）〜（Ｃ）は本発明の実施の形態２の発光ダイオードの製造方法を説明するための図である。2A to 2C are views for explaining a method for manufacturing the light emitting diode according to the second embodiment of the present invention. 図３は本発明の実施の形態３の発光ダイオードの製造方法に用いる熱処理炉の概略構成図である。FIG. 3 is a schematic configuration diagram of a heat treatment furnace used in the method for manufacturing a light emitting diode according to Embodiment 3 of the present invention. 図４は本発明の実施の形態４の発光ダイオードの製造方法を説明するための図である。FIG. 4 is a diagram for explaining a method of manufacturing the light emitting diode according to the fourth embodiment of the present invention. 図５は従来例および本発明の製造方法で作製する発光ダイオードの概略構造を示す図である。FIG. 5 is a diagram showing a schematic structure of a light emitting diode manufactured by a conventional example and the manufacturing method of the present invention. 図６（Ａ）〜（Ｅ）は従来例の発光ダイオードの製造方法を説明するための図である。6A to 6E are views for explaining a conventional method for manufacturing a light emitting diode. 図７は上記実施の形態２，４および上記従来例の発光ダイオードの製造方法に用いる熱処理炉の概略構成図である。FIG. 7 is a schematic configuration diagram of a heat treatment furnace used in the light emitting diode manufacturing methods of Embodiments 2 and 4 and the conventional example.

Explanation of symbols

１ｎ−ＧａＡｓ基板
２ｎ−ＡｌＧａＡｓコンタクト層
３ｎ−ＡｌＧａＩｎＰクラッド層
４活性層
５ｐ−ＡｌＧａＩｎＰクラッド層
６ｐ−ＧａＩｎＰ保護層
７ｐ−ＧａＰ基板
８，１０８重し
９台座
１１ｐ−電極
１２ｎ−電極
２１，１２１，２２１ホルダ
２２，１２２，２２２加熱処理機構
２３ＧａＰの破片
２４ＧａＡｓの破片
３１ＧａＡｓ結晶ウエハ
３２ＧａＰ結晶ウエハ
１００発光ダイオード
１０１エピウエハ DESCRIPTION OF SYMBOLS 1 n-GaAs substrate 2 n-AlGaAs contact layer 3 n-AlGaInP clad layer 4 Active layer 5 p-AlGaInP clad layer 6 p-GaInP protective layer 7 p-GaP substrate 8, 108 Weight 9 Base 11 P-electrode 12 n Electrode 21, 121, 221 Holder 22, 122, 222 Heat treatment mechanism 23 GaP fragment 24 GaAs fragment 31 GaAs crystal wafer 32 GaP crystal wafer 100 Light emitting diode 101 Epi wafer

Claims

A GaP substrate is mounted on an epitaxial wafer having a GaAs substrate and an AlGaInP-based light emitting portion formed on the GaAs substrate, and then a heat treatment at a predetermined temperature is performed to attach the GaP substrate to the epitaxial wafer. In the manufacturing method,
The method for manufacturing a light emitting diode, wherein the heat treatment is performed in an atmosphere containing As and P.

A GaP substrate is mounted on an epitaxial wafer having a GaAs substrate and an AlGaInP-based light emitting portion formed on the GaAs substrate, and then a heat treatment at a predetermined temperature is performed to attach the GaP substrate to the epitaxial wafer. In the manufacturing method,
The heat treatment is performed by bringing a first desorption preventing member containing As into contact with or in proximity to the GaAs substrate, and a second desorption preventing member containing P in contact with or in proximity to the GaP substrate. A method for producing a light emitting diode.

In the manufacturing method of the light emitting diode of Claim 1,
The method for manufacturing a light-emitting diode, wherein the atmosphere includes at least one of TBP and TBAs.

In the manufacturing method of the light emitting diode of Claim 2,
The method of manufacturing a light emitting diode, wherein the first detachment preventing member is a GaAs crystal wafer and the second detachment preventing member is a GaP crystal wafer.