JP2009033212A - METHOD FOR DETECTING CONCENTRATION OF Cu ON SILICON SUBSTRATE - Google Patents
METHOD FOR DETECTING CONCENTRATION OF Cu ON SILICON SUBSTRATE Download PDFInfo
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本発明は、高濃度ボロンドープシリコン基板に存在するＣｕの濃度を検出する方法に関する。更に詳しくは、３×１０18atoms/cm3以上のボロンを含むシリコン基板に存在する１０11atoms/cm2未満の低濃度Ｃｕを検出する方法に関するものである。 The present invention relates to a method for detecting the concentration of Cu present in a high-concentration boron-doped silicon substrate. More specifically, the present invention relates to a method for detecting low concentration Cu of less than 10 11 atoms / cm 2 present in a silicon substrate containing boron of 3 × 10 18 atoms / cm 3 or more.
シリコン基板の酸化、拡散プロセスで生じる汚染金属のうち、Ｃｕは非常に拡散速度が速く容易にシリコン基板内部に拡散する。この拡散したＣｕはデバイス特性（電気特性等）を劣化させる。このため、このＣｕを低減し、熱プロセスを管理することが重要となる。 Of the contaminating metals produced in the oxidation and diffusion processes of the silicon substrate, Cu has a very high diffusion rate and easily diffuses into the silicon substrate. This diffused Cu deteriorates device characteristics (electrical characteristics, etc.). For this reason, it is important to reduce this Cu and manage the thermal process.
この基板内部のＣｕの濃度測定には原子吸光分析（以下、ＡＡＳという。）、二次イオン質量分析（ＳＩＭＳ）を使った分析方法が主に用いられている。特に、ＡＡＳ法は高感度分析が可能である。このＡＡＳを用いる方法は、シリコン基板をフッ化水素酸（以下、ＨＦという。）と硝酸を含む混合液でシリコン基板を全溶解して分析する必要がある。しかし、これらの方法には以下の問題がある。即ち測定に非常に手間がかかり、測定前の前処理中に更に汚染が生じることがあった。また、いずれの方法も基板を破壊して行うため、その基板を再利用することはできなかった。 An analysis method using atomic absorption analysis (hereinafter referred to as AAS) and secondary ion mass spectrometry (SIMS) is mainly used for measuring the Cu concentration inside the substrate. In particular, the AAS method can perform highly sensitive analysis. In the method using AAS, it is necessary to analyze the silicon substrate by completely dissolving the silicon substrate with a mixed solution containing hydrofluoric acid (hereinafter referred to as HF) and nitric acid. However, these methods have the following problems. That is, the measurement is very time-consuming and further contamination may occur during the pretreatment before the measurement. In addition, since any method is performed by destroying the substrate, the substrate cannot be reused.
そこで本出願人は半導体基板の非破壊分析に関する方法として半導体基板内部のＣｕ濃度の検出方法を提案した（例えば、特許文献１参照。）。この方法はシリコン基板を６００℃以下の温度で加熱し、シリコン基板内部に存在するＣｕを拡散させて表裏面側に集め、表裏面をＡＡＳ、全反射蛍光Ｘ線分析（以下、ＴＸＲＦという。）等の方法で分析する方法である。この方法によれば、シリコン基板がＰタイプの場合、大気中で５００℃で１５分間の加熱を行うことで十分なＣｕの拡散が行われる。 Therefore, the present applicant has proposed a method for detecting the Cu concentration inside the semiconductor substrate as a method relating to nondestructive analysis of the semiconductor substrate (see, for example, Patent Document 1). In this method, a silicon substrate is heated at a temperature of 600 ° C. or less, Cu existing inside the silicon substrate is diffused and collected on the front and back surfaces, and the front and back surfaces are AAS and total reflection X-ray fluorescence analysis (hereinafter referred to as TXRF). It is a method of analyzing by such a method. According to this method, when the silicon substrate is a P type, sufficient Cu diffusion is performed by heating at 500 ° C. for 15 minutes in the atmosphere.
一方、近年シリコン基板の洗浄を含むクリーン化技術が向上し、シリコン基板を汚染する金属の濃度は１０11atoms／ｃｍ2程度に低下してきている。
しかし、上述した特許文献１に示された方法で、使用されるＰタイプシリコン基板は、ボロンが１０15atoms/cm3程度の濃度しか含まれていない、高濃度のボロンドープシリコン基板ではなかった。そのため、ボロンが３×１０18atoms/cm3以上の濃度を含むＰ+シリコン基板やＰ++シリコン基板のような、基板内部にボロンが高濃度にドープしたシリコン基板において、基板内部に存在するＣｕが１０11atoms/cm2未満の低濃度である場合、基板内部に存在するＣｕは、ボロンと電子静力学効果（electro statics effect）を生じて、Ｃｕは基板表裏面側への拡散が十分に行われず、基板に含まれるＣｕ濃度の評価を行う上で分析精度に劣る問題があった。 However, the P-type silicon substrate used in the method disclosed in Patent Document 1 described above is not a high-concentration boron-doped silicon substrate in which boron is contained only at a concentration of about 10 15 atoms / cm 3 . . Therefore, a silicon substrate in which boron is highly doped inside the substrate, such as a P + silicon substrate or a P ++ silicon substrate having a concentration of 3 × 10 18 atoms / cm 3 or more, exists inside the substrate. When Cu has a low concentration of less than 10 11 atoms / cm 2 , Cu present in the substrate causes boron and an electro static effect, and Cu is sufficiently diffused to the front and back sides of the substrate. However, there is a problem that the analysis accuracy is inferior in evaluating the Cu concentration contained in the substrate.
本発明の目的は、シリコン基板を全溶解することなくＣｕを簡便かつ定量的に評価できるシリコン基板のＣｕ濃度検出方法を提供することにある。 An object of the present invention is to provide a method for detecting the Cu concentration of a silicon substrate, which can easily and quantitatively evaluate Cu without completely dissolving the silicon substrate.
本発明の別の目的は、工程汚染の把握を行うシリコン基板のＣｕ濃度検出方法を提供することにある。 Another object of the present invention is to provide a method for detecting the Cu concentration of a silicon substrate for grasping process contamination.
請求項１に係る発明は、シリコン基板を６００℃以下の温度で加熱して基板に存在するＣｕ濃度を検出する方法の改良である。その特徴ある構成は、基板はボロンを３×１０18atoms/cm3以上の濃度で含み、基板は４分割され、この分割された基板を３００℃以上３５０℃未満の温度で１時間〜１２時間加熱し、加熱した基板の表裏面に存在するＣｕを定量分析するところにある。 The invention according to claim 1 is an improvement of a method for detecting a Cu concentration present in a substrate by heating the silicon substrate at a temperature of 600 ° C. or lower. Its characteristic configuration is substrate comprises at 3 × 10 18 atoms / cm 3 or more concentrations of boron, the substrate is divided into four, 1 hour in divided temperature 350 below ° C. 300 ° C. or more substrates of this ~ 12 Heating is performed for a time, and Cu existing on the front and back surfaces of the heated substrate is quantitatively analyzed.
この検出方法における定量分析はＡＡＳ、誘導結合プラズマ質量分析（以下、ＩＣＰ−ＭＳという。）又はＴＸＲＦにより行われることが好ましい。 The quantitative analysis in this detection method is preferably performed by AAS, inductively coupled plasma mass spectrometry (hereinafter referred to as ICP-MS) or TXRF.
多くのボロンが存在する基板内部ではボロンはマイナス電位、Ｃｕはプラス電位をそれぞれ有する。そのため電子静力学効果（electro statics effect）により基板内部のＣｕは拡散し難い状況となる。本発明ではボロンを３×１０18atoms/cm3以上の濃度で含む基板に上記範囲内の条件で加熱を施すことにより、Ｃｕを表裏面側への拡散量を向上させることができる。従って、この表裏面側に拡散したＣｕをＡＡＳ、ＩＣＰ−ＭＳ又はＴＸＲＦにより定量分析することでシリコン基板を全溶解することなくＣｕを簡便にかつ定量的に評価することができる。 Boron has a negative potential and Cu has a positive potential inside the substrate where many boron are present. Therefore, Cu inside the substrate is difficult to diffuse due to an electro static effect. In the present invention, the amount of diffusion of Cu to the front and back sides can be improved by heating a substrate containing boron at a concentration of 3 × 10 18 atoms / cm 3 or more under the conditions within the above range. Therefore, Cu can be easily and quantitatively evaluated without completely dissolving the silicon substrate by quantitatively analyzing the Cu diffused on the front and back sides by AAS, ICP-MS or TXRF.
請求項３に係る発明は、請求項１に係る発明であって、加熱したシリコン基板の表裏面に存在するＣｕを回収液により溶解して回収し、回収した回収液をＡＡＳ又はＴＸＲＦにより定量分析するシリコン基板のＣｕ濃度検出方法である。 The invention according to claim 3 is the invention according to claim 1, wherein Cu present on the front and back surfaces of the heated silicon substrate is dissolved and recovered by a recovery liquid, and the recovered recovery liquid is quantitatively analyzed by AAS or TXRF. This is a method for detecting the Cu concentration of a silicon substrate.
上記方法を用いることにより、表裏面側にＣｕを集め、表裏面を溶解して回収した回収液を測定するのでシリコン基板を全溶解することなく簡易に測定できる。 By using the above method, Cu is collected on the front and back sides, and the recovered liquid collected by dissolving the front and back sides is measured, so that the silicon substrate can be easily measured without completely dissolving it.
請求項４に係る発明は、請求項３に係る発明であって、回収液がＨＦ溶液、ＨＦ及び過酸化水素を含む混合溶液、塩酸溶液、塩酸及び過酸化水素を含む混合溶液、塩酸及びＨＦを含む混合溶液、ＳＣ−１溶液又は硫酸及び過酸化水素を含む混合溶液であるシリコン基板のＣｕ濃度検出方法である。 The invention according to claim 4 is the invention according to claim 3, wherein the recovered liquid is an HF solution, a mixed solution containing HF and hydrogen peroxide, a hydrochloric acid solution, a mixed solution containing hydrochloric acid and hydrogen peroxide, hydrochloric acid and HF. This is a method for detecting the Cu concentration of a silicon substrate, which is a mixed solution containing NO, an SC-1 solution, or a mixed solution containing sulfuric acid and hydrogen peroxide .
以上述べたように、本発明はシリコン基板を６００℃以下の温度で加熱して基板に存在するＣｕ濃度を検出する方法の改良であり、その特徴ある構成は、基板はボロンを３×１０18atoms/cm3以上の濃度で含み、基板を３００℃以上３５０℃未満の温度で１時間〜１２時間加熱し、加熱した基板の表裏面に存在するＣｕを定量分析するため、シリコン基板を全溶解することなくＣｕを簡便かつ迅速に評価できる。従って、工程汚染の把握も容易に行うことができる。 As described above, the present invention is an improvement of a method for detecting a Cu concentration present in a substrate by heating the silicon substrate at a temperature of 600 ° C. or lower. The characteristic configuration is that the substrate is made of 3 × 10 18 boron. The silicon substrate is completely dissolved in order to quantitatively analyze Cu present on the front and back surfaces of the heated substrate, which is contained at a concentration of atoms / cm 3 or higher, heated at a temperature of 300 ° C. or higher and lower than 350 ° C. for 1 to 12 hours. Cu can be evaluated easily and quickly without the need to do so. Therefore, it is possible to easily grasp the process contamination.
また、加熱したシリコン基板の表裏面に存在するＣｕを回収液により溶解して回収し、回収した回収液を原子吸光分析法又は全反射Ｘ線蛍光分析法により定量分析することによってもＣｕ濃度を簡便かつ定量的に評価できる。 Also, Cu concentration on the front and back surfaces of the heated silicon substrate can be recovered by dissolving it with a recovery liquid, and the recovered recovery liquid can be quantitatively analyzed by atomic absorption spectrometry or total reflection X-ray fluorescence analysis. Easy and quantitative evaluation.
本発明は、シリコン基板を６００℃以下の温度で加熱して基板に存在するＣｕ濃度を検出する方法の改良である。その特徴ある構成は、基板はボロンを３×１０18atoms/cm3以上の濃度で含み、この基板を３００℃以上３５０℃未満の温度で１時間〜１２時間加熱し、加熱した基板の表裏面に存在するＣｕを定量分析するところにある。 The present invention is an improvement of a method for detecting a Cu concentration present in a substrate by heating the silicon substrate at a temperature of 600 ° C. or lower. The characteristic structure is that the substrate contains boron at a concentration of 3 × 10 18 atoms / cm 3 or more, and the substrate is heated at a temperature of 300 ° C. or more and less than 350 ° C. for 1 to 12 hours, and the front and back surfaces of the heated substrate It is in the place where quantitative analysis of Cu which exists in is.
多くのボロンが存在する基板内部ではボロンはマイナス電位、Ｃｕはプラス電位をそれぞれ有する状態で存在する。そのためボロンとＣｕによる電子静力学効果が働き、Ｃｕは拡散し難い状況となる。従って、高濃度のボロンが含まれる基板において、１０11atoms/cm2未満の低濃度のＣｕが汚染している場合、従来の条件で加熱を施したとしても、Ｃｕは十分な拡散が得られなかった。本発明ではボロンを３×１０18atoms/cm3以上の濃度で含む基板に上記加熱条件で加熱を施すことにより、汚染しているＣｕが低濃度であっても、Ｃｕを表裏面側への拡散量を向上させることができる。 Inside the substrate in which many boron exists, boron exists in a state having a negative potential and Cu has a positive potential. Therefore, the electrostatic effect of boron and Cu works, and Cu is difficult to diffuse. Therefore, if a substrate containing a high concentration of boron is contaminated with a low concentration of Cu of less than 10 11 atoms / cm 2 , Cu can be sufficiently diffused even when heated under conventional conditions. There wasn't. In the present invention, a substrate containing boron at a concentration of 3 × 10 18 atoms / cm 3 or more is heated under the above heating conditions, so that even if the contaminated Cu is at a low concentration, Cu is transferred to the front and back sides. The amount of diffusion can be improved.
本発明の第１の実施の形態について説明する。 A first embodiment of the present invention will be described.
バルク内部にボロンを３×１０18atoms/cm3以上の濃度で含み、Ｃｕ汚染の生じたシリコン基板であるシリコンウェーハで表面に酸化膜を有する場合、先ず、所定のＨＦ水溶液で洗浄してこの表面酸化膜（ＳｉＯ2）を除去する。具体的には２０〜５０重量％のＨＦ水溶液中にシリコン基板を約１０分間浸漬する。次いで、図１に示すように、このシリコン基板１０を清浄な別のシリコン基板１１の上に載せる。この清浄なシリコン基板１１は、ホットプレート１２（表面はセラミックス製）上に載せられている。清浄なシリコン基板１１には被測定物であるシリコン基板１０よりも径の大きいシリコン基板が選択される。次に、シリコン基板１０をその下表面（裏面）から大気中で３００℃以上３５０℃未満の温度で１時間〜１２時間加熱する。シリコン基板内部に３×１０18atoms/cm3以上の高濃度でボロンが含まれている場合、３００℃未満、１時間未満であるとボロンとＣｕによる電子静力学効果の影響からＣｕが十分に拡散されず、３５０℃を越えるとＣｕの固溶度が高くなり検出し難くなる。加熱時間が１２時間を越えてもそれ以上の成果は得られない。この加熱はシリコン基板を汚染しないクリーンルーム等の環境下で行うことが好ましい。特に、シリコン基板に汚染したＣｕ濃度が１０11atoms/cm2未満の場合、３００℃以上３５０℃未満で１２時間程度加熱することが好ましい。Ｃｕ濃度が１０11atoms/cm2〜１０12atoms/cm2の場合、３００℃以上３５０℃未満で１〜１２時間加熱することが好ましい。Ｃｕ濃度が１０12atoms/cm2を越える濃度の場合、３００℃以上３５０℃未満で１時間程度加熱することが好ましい。 When a silicon wafer, which is a silicon substrate containing Cu in a bulk and contains boron at a concentration of 3 × 10 18 atoms / cm 3 or more and having an oxide film on the surface, is first cleaned with a predetermined aqueous HF solution. The surface oxide film (SiO 2 ) is removed. Specifically, the silicon substrate is immersed in a 20 to 50% by weight HF aqueous solution for about 10 minutes. Next, as shown in FIG. 1, this silicon substrate 10 is placed on another clean silicon substrate 11. This clean silicon substrate 11 is placed on a hot plate 12 (the surface is made of ceramics). As the clean silicon substrate 11, a silicon substrate having a diameter larger than that of the silicon substrate 10 that is the object to be measured is selected. Next, the silicon substrate 10 is heated from the lower surface (back surface) in the atmosphere at a temperature of 300 ° C. or higher and lower than 350 ° C. for 1 hour to 12 hours. When boron is contained at a high concentration of 3 × 10 18 atoms / cm 3 or more in the silicon substrate, Cu is sufficiently sufficient when the temperature is less than 300 ° C. and less than 1 hour due to the influence of the electrostatic effect of boron and Cu. If it is not diffused and the temperature exceeds 350 ° C., the solid solubility of Cu increases and it is difficult to detect. No further results can be obtained even if the heating time exceeds 12 hours. This heating is preferably performed in an environment such as a clean room that does not contaminate the silicon substrate. In particular, when the concentration of Cu contaminating the silicon substrate is less than 10 11 atoms / cm 2, it is preferable to heat at 300 ° C. or more and less than 350 ° C. for about 12 hours. When the Cu concentration is 10 11 atoms / cm 2 to 10 12 atoms / cm 2 , it is preferable to heat at 300 ° C. or higher and lower than 350 ° C. for 1 to 12 hours. When the Cu concentration exceeds 10 12 atoms / cm 2 , it is preferable to heat at 300 ° C. or higher and lower than 350 ° C. for about 1 hour.
シリコン基板を加熱処理すると加熱媒体であるホットプレートの非接触側の上表面に８０％以上のＣｕが集まる。一方、ホットプレートの接触側の下表面（裏面）には２０％未満のＣｕが集まる。加熱を施した後、シリコン基板１０表裏面を直接ＴＸＲＦにより定量分析することにより、全溶解することなくＣｕを簡便にかつ定量的に評価することができる。 When the silicon substrate is heat-treated, 80% or more of Cu collects on the upper surface of the non-contact side of the hot plate as a heating medium. On the other hand, less than 20% of Cu collects on the lower surface (back surface) of the contact side of the hot plate. After heating, the front and back surfaces of the silicon substrate 10 are quantitatively analyzed directly by TXRF, whereby Cu can be simply and quantitatively evaluated without being completely dissolved.
本発明の第２の実施の形態を図２に基づいて説明する。図２において、図１と同一符号は同一構成要素を示す。この実施の形態では、次の点が第１の実施の形態と相違する。即ち、加熱を施したシリコン基板１０の表裏面に存在するＣｕを回収液１３により溶解して回収し、この回収した回収液１３をＡＡＳ又はＴＸＲＦにより定量分析する。上記以外の構成は第１の実施の形態と同様である。 A second embodiment of the present invention will be described with reference to FIG. 2, the same reference numerals as those in FIG. 1 denote the same components. In this embodiment, the following points are different from the first embodiment. That is, Cu present on the front and back surfaces of the heated silicon substrate 10 is dissolved and recovered by the recovery liquid 13, and the recovered recovery liquid 13 is quantitatively analyzed by AAS or TXRF. The configuration other than the above is the same as that of the first embodiment.
第１の実施の形態と比較して、第２の実施の形態では、表裏面側にＣｕを集め、表裏面を溶解して回収した回収液を測定するのでシリコン基板を全溶解することなく簡易に測定できる。回収方法としては、ＤＥ法（one Drop Etching Method）が好適である。ＤＥ法はシリコン基板表面の端部に回収液を数滴滴下し、図２に示すように、この液滴を基板表面全体に行き渡らせて、相対向する端部に再び液滴の形態で集めることにより、基板表面を清浄化して金属不純物を回収する方法である。回収液にはＨＦ溶液、ＨＦ及び過酸化水素を含む混合溶液、塩酸溶液、塩酸及び過酸化水素を含む混合溶液、塩酸及びＨＦを含む混合溶液、ＳＣ−１溶液又は硫酸及び過酸化水素を含む混合溶液から選択される。 Compared to the first embodiment, in the second embodiment, Cu is collected on the front and back sides, and the recovered liquid is measured by dissolving the front and back sides. Can be measured. As the recovery method, the DE method (one Drop Etching Method) is suitable. In the DE method, a few drops of recovered liquid are dropped on the edge of the silicon substrate surface, and as shown in FIG. 2, the droplet is spread over the entire surface of the substrate and collected again in the form of a droplet at the opposite edge. In this way, the substrate surface is cleaned to recover metal impurities. The recovered liquid contains HF solution, mixed solution containing HF and hydrogen peroxide, hydrochloric acid solution, mixed solution containing hydrochloric acid and hydrogen peroxide, mixed solution containing hydrochloric acid and HF, SC-1 solution or sulfuric acid and hydrogen peroxide. Selected from a mixed solution.
なお、シリコン基板２０を４枚に分割し、分割した基板２０を加熱、定量分析してもよい。４分割することにより、ホットプレート上に４枚の基板を載せることができるので、例えば図３に示すように、４枚のシリコン基板２０，３０，４０，５０を用意して、これらの基板をそれぞれ４分割する。４分割した基板片２０ａ〜２０ｄ，３０ａ〜３０ｄ，４０ａ〜４０ｄ，５０ａ〜５０ｄのうち、各シリコン基板から各１枚ずつ基板片（図３中では２０ａ，３０ｂ，４０ｃ，５０ｄ）をホットプレート上に載せて加熱処理を施すことで、４枚のシリコン基板を同時に定量分析できるため、スループットを向上させることが可能となる。 The silicon substrate 20 may be divided into four pieces, and the divided substrate 20 may be heated and quantitatively analyzed. By dividing into four, four substrates can be placed on the hot plate. For example, as shown in FIG. 3, four silicon substrates 20, 30, 40, and 50 are prepared, and these substrates are mounted. Divide each into four. Of the four divided substrate pieces 20a to 20d, 30a to 30d, 40a to 40d, and 50a to 50d, one piece from each silicon substrate (20a, 30b, 40c, and 50d in FIG. 3) is placed on the hot plate. By performing the heat treatment on the substrate, the four silicon substrates can be quantitatively analyzed simultaneously, so that the throughput can be improved.
次に本発明の実施例を比較例とともに詳しく説明する。 Next, examples of the present invention will be described in detail together with comparative examples.
＜実施例１＞
シリコン基板にボロンを１×１０19atoms/cm3の濃度でドープしたＰ+シリコン基板を６枚用意した。このＰ+シリコン基板をスピンコーティング法により各所定濃度だけＣｕ汚染させた。汚染させた基板をＮ2雰囲気中９００℃、２時間の条件で熱処理を施して、バルク中のＣｕ濃度が２×１０11atoms/cm2、４×１０11atoms/cm2、５×１０11atoms/cm2、８×１０11atoms/cm2、１×１０12atoms/cm2及び３×１０12atoms/cm2の６種類のサンプル基板（Ａ基板〜Ｆ基板）を用意した。
<Example 1>
Six P + silicon substrates doped with boron at a concentration of 1 × 10 19 atoms / cm 3 were prepared on a silicon substrate. This P + silicon substrate was contaminated with Cu at each predetermined concentration by spin coating. The contaminated substrate was heat-treated in an N 2 atmosphere at 900 ° C. for 2 hours, and the Cu concentration in the bulk was 2 × 10 11 atoms / cm 2 , 4 × 10 11 atoms / cm 2 , 5 × 10 11. Six types of sample substrates (A substrate to F substrate) of atoms / cm 2 , 8 × 10 11 atoms / cm 2 , 1 × 10 12 atoms / cm 2 and 3 × 10 12 atoms / cm 2 were prepared.
それぞれ用意したＡ基板〜Ｆ基板をそれぞれ清浄な基板を介してホットプレート上に載せ、３００℃で１時間加熱した。加熱した基板の表裏面をＴＸＲＦによりＣｕを定量分析した。 Each of the prepared A to F substrates was placed on a hot plate through a clean substrate and heated at 300 ° C. for 1 hour. Cu was quantitatively analyzed by TXRF on the front and back surfaces of the heated substrate.
＜実施例２＞
実施例１のＡ基板〜Ｆ基板と同様の基板をそれぞれ用意し、これらの基板を清浄な基板を介してホットプレート上に載せ、３００℃で１２時間加熱した。加熱した基板の表裏面をＡＡＳ、ＩＣＰ−ＭＳ、ＴＸＲＦによりＣｕを定量分析した。
<Example 2>
Substrates similar to the A to F substrates in Example 1 were prepared, and these substrates were placed on a hot plate through clean substrates and heated at 300 ° C. for 12 hours. Cu was quantitatively analyzed on the front and back surfaces of the heated substrate by AAS, ICP-MS, and TXRF.
＜比較例１＞
実施例１のＡ基板〜Ｆ基板と同様の基板を用意し、これらの基板を清浄な基板を介してホットプレート上に載せ、５００℃で１５分間加熱した。加熱した基板の表裏面をＡＡＳ、ＩＣＰ−ＭＳ、ＴＸＲＦによりＣｕを定量分析した。
<Comparative Example 1>
Substrates similar to the A to F substrates in Example 1 were prepared, and these substrates were placed on a hot plate through clean substrates and heated at 500 ° C. for 15 minutes. Cu was quantitatively analyzed on the front and back surfaces of the heated substrate by AAS, ICP-MS, and TXRF.
＜比較例２＞
先ず、実施例１のＡ基板〜Ｆ基板と同様の基板をそれぞれ用意した。次いで、ポリプロピレン（ＰＰ）製収容容器にＨＦと硝酸とＨ2ＳＯ4を含む分解液を入れ、ポリテトラフルオロエチレン製の支持台を収容容器の内部に置いた。支持台のテーブルは分解液の液面より高い位置にあり、このテーブルの上にＡ基板を載置した。収容容器にＰＰ製の蓋をして、室温下、反応容器を密閉に保った。約１２時間保持することにより、Ａ基板をそれぞれ分解昇華させた。分解残渣に塩酸と硝酸を混合した酸を滴下することにより、分解残渣を溶解し、溶解液を２００℃で３０分間加熱することにより、分解残渣を昇華させた。この残留物をＩＣＰ−ＭＳにより定量分析した。Ｂ基板〜Ｆ基板についても同様の方法を用いて分解昇華させ、ＩＣＰ−ＭＳにより定量分析した。
<Comparative Example 2>
First, substrates similar to the A to F substrates in Example 1 were prepared. Next, a decomposition solution containing HF, nitric acid, and H 2 SO 4 was placed in a polypropylene (PP) container, and a support made of polytetrafluoroethylene was placed inside the container. The table of the support base was at a position higher than the liquid level of the decomposition solution, and the A substrate was placed on this table. The container was covered with PP and the reaction vessel was kept sealed at room temperature. By holding for about 12 hours, each of the A substrates was decomposed and sublimated. The decomposition residue was dissolved by adding dropwise an acid mixture of hydrochloric acid and nitric acid to the decomposition residue, and the decomposition residue was sublimated by heating the solution at 200 ° C. for 30 minutes. This residue was quantitatively analyzed by ICP-MS. B substrate to F substrate were also decomposed and sublimated using the same method and quantitatively analyzed by ICP-MS.
＜比較評価１＞
実施例１〜２及び比較例１及び２のＡ基板〜Ｆ基板に存在するＣｕ検出濃度の測定結果を図４に示す。
<Comparison evaluation 1>
The measurement result of the Cu detection density | concentration which exists in Examples 1-2 and Comparative Example 1 and the A board | substrate-F board | substrate of FIG. 4 is shown in FIG.
図４より明らかなように、本発明の加熱条件である３００℃以上３５０℃未満の温度で１時間〜１２時間の範囲外で加熱処理を施した比較例１では、Ｃｕ汚染させた濃度が十分に検出されていない。シリコン基板を全て昇華させてその残渣より定量分析した比較例２は、汚染させたＣｕ濃度を十分に検出することはできるが、分析時間がかかるために、スループットの面から不利である。これらに対して、実施例１及び２は、汚染させたＣｕ濃度の約７０％以上が検出できた。 As is clear from FIG. 4, in Comparative Example 1 where heat treatment was performed outside the range of 1 hour to 12 hours at a temperature of 300 ° C. or more and less than 350 ° C., which is the heating condition of the present invention, the concentration contaminated with Cu was sufficient. Not detected. In Comparative Example 2 in which the silicon substrate is all sublimated and quantitatively analyzed from the residue, the contaminated Cu concentration can be sufficiently detected, but the analysis time is required, which is disadvantageous in terms of throughput. On the other hand, in Examples 1 and 2, about 70% or more of the contaminated Cu concentration could be detected.
＜比較評価２＞
実施例１のＦ基板（３×１０12atoms/cm2）と同様にＣｕ汚染させた基板を２１枚用意した。これらの基板をそれぞれ清浄な基板を介してホットプレート上に載せ、所定の加熱温度で、所定の保持時間加熱した。加熱温度は２５０℃、３００℃、３５０℃、４００℃、４５０℃、５００℃及び５４０℃とし、各加熱温度ごとに加熱保持時間を５分間、１５分間及び６０分間と変化させた。これら上記条件のもとで熱処理を施した基板の表裏面をＴＸＲＦによりＣｕを定量分析した。これら２１枚の基板より検出されたＣｕ濃度の測定結果を図５に示す。
<Comparison evaluation 2>
As with the F substrate (3 × 10 12 atoms / cm 2 ) of Example 1, 21 substrates contaminated with Cu were prepared. Each of these substrates was placed on a hot plate through a clean substrate and heated at a predetermined heating temperature for a predetermined holding time. The heating temperature was 250 ° C., 300 ° C., 350 ° C., 400 ° C., 450 ° C., 500 ° C. and 540 ° C., and the heating and holding time was changed to 5 minutes, 15 minutes and 60 minutes for each heating temperature. Cu was quantitatively analyzed by TXRF on the front and back surfaces of the substrate that had been heat-treated under these conditions. The measurement results of the Cu concentration detected from these 21 substrates are shown in FIG.
図５より明らかなように、３×１０12atoms/cm2のようなＣｕ汚染濃度が高い場合、加熱温度が３００℃〜３５０℃の範囲内であれば６０分間の加熱保持で十分な検出濃度が得られることが判る。しかし、加熱保持時間が５分間、１５分間と短い場合、十分な検出濃度が得られていない。これは短時間の保持時間では、基板表面へのＣｕ拡散が十分に行われないためであると考えられる。 As is clear from FIG. 5, when the Cu contamination concentration is high, such as 3 × 10 12 atoms / cm 2 , if the heating temperature is in the range of 300 ° C. to 350 ° C., sufficient detection concentration can be achieved by holding for 60 minutes. It can be seen that However, when the heating and holding time is as short as 5 minutes and 15 minutes, a sufficient detection concentration is not obtained. This is considered to be because Cu diffusion to the substrate surface is not sufficiently performed with a short holding time.
Claims (4)
前記基板はボロンを３×１０18atoms/cm3以上の濃度で含み、
前記基板は４分割され、
前記分割された基板を３００℃以上３５０℃未満の温度で１時間〜１２時間加熱し、前記加熱した基板の表裏面に存在するＣｕを定量分析することを特徴とするシリコン基板のＣｕ濃度検出方法。 In a method for detecting a Cu concentration present in the substrate by heating the silicon substrate at a temperature of 600 ° C. or lower,
The substrate includes boron at a concentration of 3 × 10 18 atoms / cm 3 or more ,
The substrate is divided into four parts,
The divided substrate is heated at a temperature of 300 ° C. or higher and lower than 350 ° C. for 1 hour to 12 hours, and Cu present on the front and back surfaces of the heated substrate is quantitatively analyzed. .
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