JP6424742B2 - Pretreatment method for impurity analysis of semiconductor silicon crystal, and impurity analysis method of semiconductor silicon crystal - Google Patents
Pretreatment method for impurity analysis of semiconductor silicon crystal, and impurity analysis method of semiconductor silicon crystal Download PDFInfo
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- 239000012535 impurity Substances 0.000 title claims description 47
- 238000004458 analytical method Methods 0.000 title claims description 26
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims description 20
- 239000013078 crystal Substances 0.000 title claims description 20
- 239000004065 semiconductor Substances 0.000 title claims description 20
- 229910052710 silicon Inorganic materials 0.000 title claims description 20
- 239000010703 silicon Substances 0.000 title claims description 20
- 238000002203 pretreatment Methods 0.000 title claims description 18
- 238000000354 decomposition reaction Methods 0.000 claims description 93
- 239000002253 acid Substances 0.000 claims description 55
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 16
- 238000000034 method Methods 0.000 claims description 16
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- 238000001095 inductively coupled plasma mass spectrometry Methods 0.000 claims description 13
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 12
- 229910017604 nitric acid Inorganic materials 0.000 claims description 12
- 238000001479 atomic absorption spectroscopy Methods 0.000 claims description 9
- 239000000523 sample Substances 0.000 description 84
- 239000007789 gas Substances 0.000 description 65
- 239000012071 phase Substances 0.000 description 52
- 238000004090 dissolution Methods 0.000 description 18
- 238000005259 measurement Methods 0.000 description 13
- 239000002184 metal Substances 0.000 description 13
- 239000000047 product Substances 0.000 description 12
- 238000006243 chemical reaction Methods 0.000 description 8
- 239000012488 sample solution Substances 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 6
- 239000007791 liquid phase Substances 0.000 description 5
- 239000011347 resin Substances 0.000 description 5
- 229920005989 resin Polymers 0.000 description 5
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 4
- 229910052731 fluorine Inorganic materials 0.000 description 4
- 239000011737 fluorine Substances 0.000 description 4
- -1 polytetrafluoroethylene Polymers 0.000 description 4
- 229910004298 SiO 2 Inorganic materials 0.000 description 3
- 239000012159 carrier gas Substances 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 3
- 230000008020 evaporation Effects 0.000 description 3
- 238000001704 evaporation Methods 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- ABTOQLMXBSRXSM-UHFFFAOYSA-N silicon tetrafluoride Chemical compound F[Si](F)(F)F ABTOQLMXBSRXSM-UHFFFAOYSA-N 0.000 description 3
- 239000004809 Teflon Substances 0.000 description 2
- 229920006362 Teflon® Polymers 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- NBVXSUQYWXRMNV-UHFFFAOYSA-N fluoromethane Chemical compound FC NBVXSUQYWXRMNV-UHFFFAOYSA-N 0.000 description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 description 2
- 238000007781 pre-processing Methods 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 230000005587 bubbling Effects 0.000 description 1
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- 239000003153 chemical reaction reagent Substances 0.000 description 1
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- 239000007792 gaseous phase Substances 0.000 description 1
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- 238000009616 inductively coupled plasma Methods 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
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Description
本発明は、半導体シリコン結晶の不純物分析のための前処理方法、及び半導体シリコン結晶の不純物分析方法に関する。 The present invention relates to a pretreatment method for impurity analysis of semiconductor silicon crystals, and an impurity analysis method of semiconductor silicon crystals.
半導体シリコン結晶の表層やバルク中の金属不純物を分析する手法として、半導体シリコン結晶から採取した試料（Ｓｉサンプル片）を全溶解させ、誘導結合プラズマ質量分析（ＩＣＰ−ＭＳ：Ｉｎｄｕｃｔｉｖｅｌｙ Ｃｏｕｐｌｅｄ Ｐｌａｓｍａ−Ｍａｓｓ Ｓｐｅｃｔｒｏｍｅｔｒｙ）や原子吸光分析（ＡＡＳ：Ａｔｏｍｉｃ Ａｂｓｏｒｐｔｉｏｎ Ｓｐｅｃｔｒｏｍｅｔｒｙ）で分析する方法（以下、「全溶解分析法」と呼ぶ）が広く行われている。 As a method of analyzing metal impurities in the surface layer and bulk of semiconductor silicon crystal, a sample (Si sample piece) taken from the semiconductor silicon crystal is completely dissolved, and inductively coupled plasma mass spectrometry (ICP-MS: Inductively Coupled Plasma-Mass Spectrometry) ) And atomic absorption spectrometry (AAS) (hereinafter referred to as "total dissolution analysis method") are widely used.
このような全溶解分析法において、ＩＣＰ−ＭＳやＡＡＳによる測定を精度よく行う（即ち、検出下限を低くする）ためには、ＩＣＰ−ＭＳ等の測定に使用する試料溶液において、測定の外乱となるＳｉ成分をできるだけ少なくするとともに、Ｓｉ成分の濃度に比べて被測定金属不純物の濃度をできるだけ高くすることが求められる。これは、ＩＣＰ−ＭＳ等の測定に使用する試料溶液中にフッ化ケイ素のようなＳｉ成分が多く含まれていると、被測定金属不純物の質量ピークの位置にＳｉの複合分子によるゴーストピークが現れたり、ノイズが発生したりして分析感度が大きく損なわれるためである。従って、上記のような全溶解分析法では、ＩＣＰ−ＭＳ等の測定を行う前に、Ｓｉサンプル片を全溶解させＳｉ成分を除去する前処理を行う。 In such a total dissolution analysis method, in order to accurately perform measurement by ICP-MS or AAS (that is, to lower the lower limit of detection), in the sample solution used for measurement such as ICP-MS, measurement disturbance and It is required to reduce the Si component as much as possible and to make the concentration of the metal impurity to be measured as high as possible compared to the concentration of the Si component. This is because if the sample solution used for measurement such as ICP-MS contains a large amount of Si component such as silicon fluoride, a ghost peak due to the Si complex molecule is located at the position of the mass peak of the metal impurity to be measured. This is because the analysis sensitivity is greatly impaired due to appearance or noise. Therefore, in the total dissolution analysis method as described above, before the measurement of ICP-MS or the like, pretreatment is performed to completely dissolve the Si sample piece and remove the Si component.
Ｓｉサンプル片を全溶解させる方法としては、液相分解と気相分解が挙げられる。液相分解では、Ｓｉサンプル片をフッ化水素酸及び硝酸からなる混酸（ＨＦ・ＨＮＯ３混酸）に浸漬して溶解させるが、例えば５ｇのＳｉサンプル片を全溶解する場合、少なくとも１００ｍＬ程度の混酸が必要になる。市販されている超高純度試薬の保証純度は各金属不純物元素について１０ｐｐｔｗ以下であるが、これを使用してＳｉサンプル片を全溶解させた溶液を蒸発乾固後に１ｍＬの硝酸で再抽出すると、混酸が予め含有していた金属不純物は１ｐｐｂｗに濃縮される。この金属不純物量は５ｇのＳｉサンプル片に含有される被測定金属不純物量を超えてしまう。このように、液相分解では分解に使用する混酸由来の金属不純物が試料の分析に影響を与えてしまうという問題がある。また、Ｓｉサンプル片を液相分解によって全溶解させた場合には、溶解したＳｉ成分が混酸中に全量残留してしまうという問題もある。 Methods for completely dissolving the Si sample pieces include liquid phase decomposition and gas phase decomposition. In liquid phase decomposition, the Si sample piece is immersed and dissolved in a mixed acid (HF · HNO 3 mixed acid) consisting of hydrofluoric acid and nitric acid, but for example, when 5 g of the Si sample piece is totally dissolved, the mixed acid of at least about 100 mL Is required. The guaranteed purity of commercially available ultra-high purity reagents is 10 pptw or less for each metal impurity element, but using this solution to completely dissolve a sample of Si sample after evaporation to dryness and reextraction with 1 mL of nitric acid, The metal impurities previously contained in the mixed acid are concentrated to 1 ppbw. The amount of metal impurities exceeds the amount of metal impurities to be measured contained in the 5 g Si sample piece. As described above, in liquid phase decomposition, there is a problem that metal impurities derived from a mixed acid used for decomposition affect analysis of a sample. In addition, when the Si sample pieces are completely dissolved by liquid phase decomposition, there is also a problem that all the dissolved Si components remain in the mixed acid.
一方、気相分解では、ＨＦ・ＨＮＯ３混酸のガスによってＳｉサンプル片を溶解させる。より具体的には、閉塞容器内に、サンプルカップに入ったＳｉサンプル片と、ＨＦ・ＨＮＯ３混酸を入れた後、これを高温チャンバー内で１００℃程度に加熱することで混酸蒸気を発生させ、この混酸蒸気でＳｉサンプル片を溶解させる。あるいは、キャリアガスをＨＦ・ＨＮＯ３混酸にバブリングさせて得られたガスを閉塞容器内に導入し、Ｓｉサンプル片を溶解させる方法（特許文献１）や、キャリアガスにＨＦガスを混合したガスとキャリアガスにＨＮＯ３ガスを混合したガスを閉塞容器内に導入し、Ｓｉサンプル片を溶解させる方法（特許文献２）なども知られている。 On the other hand, in the gas phase decomposition, the Si sample piece is dissolved by the gas of HF · HNO 3 mixed acid. More specifically, after putting the Si sample piece in the sample cup and the HF / HNO 3 mixed acid in the closed vessel, the mixed acid vapor is generated by heating this to about 100 ° C. in a high temperature chamber Dissolve the Si sample piece with this mixed acid vapor. Alternatively, a gas obtained by bubbling a carrier gas into a mixed solution of HF and HNO 3 is introduced into the closed vessel and the Si sample piece is dissolved (Patent Document 1), or a gas obtained by mixing the carrier gas with HF gas A method is also known in which a gas in which HNO 3 gas is mixed with a carrier gas is introduced into a closed container to dissolve Si sample pieces (Patent Document 2).
気相分解では、Ｓｉが揮発性のＳｉＦ４（四フッ化ケイ素）に分解されるため、気相分解や後工程の蒸発乾固の過程でＳｉ成分を系外へ効率良く除去することができる。また、気相分解では混酸蒸気中の金属不純物量が少ないため、液相分解に比べて混酸由来の金属不純物による外乱を抑えることができるというメリットもある。 In the gas phase decomposition, Si is decomposed into volatile SiF 4 (silicon tetrafluoride), so the Si component can be efficiently removed out of the system in the process of gas phase decomposition and evaporation to dryness in the subsequent steps. . In addition, since the amount of metal impurities in the mixed acid vapor is small in gas phase decomposition, there is also an advantage that disturbance due to metal impurities derived from the mixed acid can be suppressed as compared with liquid phase decomposition.
しかしながら、気相分解は分解反応に時間がかかるため、単位時間あたりに処理できる試料の量が少なく、被測定金属不純物の濃度を高める（多量の試料を処理する）には長時間を要するという問題がある。 However, since the decomposition reaction takes time for decomposition reaction, the amount of sample that can be processed per unit time is small, and the concentration of the metal impurity to be measured is increased (processing a large amount of samples) takes a long time. There is.
本発明は、上記問題を解決するためになされたものであり、半導体シリコン結晶の不純物分析のための前処理において、より短時間でより多量の試料を気相分解によって全溶解させることができる前処理方法を提供することを目的とする。 The present invention has been made to solve the above problems, and in the pretreatment for impurity analysis of semiconductor silicon crystals, it is possible to completely dissolve a larger amount of sample in a shorter time in a shorter time. The purpose is to provide a treatment method.
上記課題を達成するために、本発明では、半導体シリコン結晶中の不純物を分析する際の前処理において、閉塞容器内に、前記半導体シリコン結晶から採取した試料と、フッ化水素酸及び硝酸からなる混酸を入れた後、前記混酸を加熱することで混酸蒸気を発生させて前記試料全体を気相分解する方法であって、
前記閉塞容器として圧力調整バルブが設けられたものを用い、前記閉塞容器内部の圧力が絶対圧で０．２０ＭＰａ以上０．４０ＭＰａ以下となるように、前記閉塞容器内部で発生した揮発性分解生成物及び混酸蒸気を前記圧力調整バルブから漏洩させながら気相分解を行う半導体シリコン結晶の不純物分析のための前処理方法を提供する。
In order to achieve the above object, in the present invention, in the pretreatment for analyzing the impurities in the semiconductor silicon crystal, the sample is collected from the semiconductor silicon crystal in the closed container, and is made of hydrofluoric acid and nitric acid. A mixed acid is added, and then the mixed acid is heated to generate a mixed acid vapor, thereby vapor phase decomposing the whole sample.
A volatile decomposition product generated inside the closed container such that the pressure inside the closed container is 0.20 MPa or more and 0.40 MPa or less in absolute pressure, using a pressure control valve as the closed container. And a pretreatment method for impurity analysis of semiconductor silicon crystals in which vapor phase decomposition is performed while leaking mixed acid vapor from the pressure control valve.
このような前処理方法であれば、より短時間でより多量の試料を気相分解によって全溶解させることができるため、試料の単位量あたりの前処理に要する時間を短縮し、また単位時間あたりに処理する試料の量を増やすことができる。 With such a pretreatment method, a larger amount of sample can be completely dissolved by gas phase decomposition in a shorter time, so that the time required for pretreatment of the sample per unit amount is shortened, and also per unit time The amount of sample to be processed can be increased.
また、本発明では、上記の前処理方法で前処理した試料を、誘導結合プラズマ質量分析又は原子吸光分析によって分析する半導体シリコン結晶の不純物分析方法を提供する。 Further, the present invention provides a method for analyzing impurities of semiconductor silicon crystals in which a sample pretreated by the above pretreatment method is analyzed by inductively coupled plasma mass spectrometry or atomic absorption spectrometry.
このような不純物分析方法であれば、より短時間でより多量の試料の前処理を行うことができるため、効率良く不純物の分析を行うことができ、また試料の量を従来よりも増やしてＳｉ成分の濃度に比べて不純物の濃度を高めることで、不純物の測定精度を高めることもできる。 With such an impurity analysis method, it is possible to carry out pretreatment of a larger amount of samples in a shorter time, so that analysis of impurities can be performed efficiently, and the amount of samples can be increased more than in the prior art to make Si The measurement accuracy of impurities can also be enhanced by increasing the concentration of impurities as compared to the concentration of components.
以上のように、本発明の前処理方法であれば、より短時間でより多量の試料を気相分解によって全溶解させることができるため、前処理に要する時間を大幅に短縮して不純物分析の作業効率を改善することができ、また試料の量を従来よりも増やしてＳｉ成分の濃度に比べて不純物の濃度を高めることで、不純物の測定精度を高めることもできる。 As described above, according to the pretreatment method of the present invention, a larger amount of sample can be completely dissolved by gas phase decomposition in a shorter time, so the time required for pretreatment can be greatly shortened and impurity analysis The working efficiency can be improved, and the measurement accuracy of impurities can also be enhanced by increasing the concentration of the impurities as compared to the concentration of the Si component by increasing the amount of the sample than in the past.
上述のように、半導体シリコン結晶の不純物分析のための前処理において、より短時間でより多量の試料を気相分解によって全溶解させることができる前処理方法の開発が求められていた。 As described above, in the pretreatment for impurity analysis of semiconductor silicon crystals, there has been a demand for development of a pretreatment method capable of totally dissolving a larger amount of samples by gas phase decomposition in a shorter time.
従来の前処理に使用される気相分解装置は、図４に示されるような容器本体１０１ａ、内蓋１０１ｂ、及び外蓋１０１ｃからなる閉塞容器１０１と、高温チャンバー１０２を備えたものである。このような閉塞容器１０１を使用して気相分解を行う際には、サンプルカップ１０３に入れたＳｉサンプル片１０４と、フッ化水素酸及び硝酸からなる混酸１０５を入れた後、閉塞容器１０１を高温チャンバー１０２内に設置して、混酸１０５を１００℃程度に加熱することで混酸蒸気を発生させ、Ｓｉサンプル片１０４を溶解させる。
The conventional vapor phase decomposition apparatus used for pretreatment includes a closed
このような従来の気相分解装置を用いた気相分解では、例えば容積１００ｍＬの閉塞容器と、５０ｗｔ％ＨＦ・発煙ＨＮＯ３混酸を使用し、１００℃で１６時間気相分解を行っても、約１．４ｇのＳｉサンプル片を分解するのが限界であった。 In the vapor phase decomposition using such a conventional vapor phase decomposition apparatus, the vapor phase decomposition is carried out at 100 ° C. for 16 hours using, for example, a closed vessel with a volume of 100 mL and a 50 wt% HF-fuming HNO 3 mixed acid The limit was to disassemble about 1.4 g of Si sample pieces.
本発明者らは、気相分解を行う際の閉塞容器内部の圧力と試料の溶解量に着目した。まず、上記のような従来の閉塞容器を使用して気相分解を行う際に、閉塞容器内に圧力センサを挿入して、気相分解中の閉塞容器内部の圧力変化を測定した。その結果、閉塞容器内部の圧力は絶対圧で約０．３ＭＰａをピークとして周期的に上昇・下降を繰り返していることが分かった。即ち、従来の閉塞容器１０１では、閉塞容器内部の圧力によって容器本体１０１ａと外蓋１０１ｃの間に間隙ができて、閉塞容器内部の気体が周期的に閉塞容器の外へ漏洩（リーク）しており、これによって気相分解反応が断続的に継続していることが分かった。
The present inventors paid attention to the pressure inside the closed container at the time of performing gas phase decomposition and the amount of dissolution of the sample. First, when performing the gas phase decomposition using the conventional closed container as described above, a pressure sensor was inserted into the closed container to measure the pressure change inside the closed container during the gas phase decomposition. As a result, it was found that the pressure inside the closed vessel was cyclically rising and falling with a peak of about 0.3 MPa in absolute pressure. That is, in the conventional closed
本発明者らは、上記の結果から、まず、閉塞容器内部の圧力を更に高めれば、混酸蒸気の濃度を上げて気相分解を促進できると予想した。従来の閉塞容器１０１は、容器本体１０１ａの外面と外蓋１０１ｃの内面にネジを切って密閉構造としているが、フッ素樹脂製（特に、ポリテトラフルオロエチレン、即ちテフロン（登録商標）製）であるために、閉塞容器内部の圧力が高まると容器本体１０１ａと外蓋１０１ｃの間に間隙ができリークが発生すると考え、ステンレス製の容器本体とステンレス製の外蓋に細目のネジを切った完全密閉型の閉塞容器を製作してＳｉサンプル片の気相分解を行ったところ、逆に気相分解反応が進まず、多くのＳｉサンプル片が未溶解のまま残留した。このことから、閉塞容器内部の圧力を高めるだけでは気相分解を促進できないことが判明した。
From the above results, the present inventors first predicted that if the pressure inside the closed vessel is further increased, the concentration of the mixed acid vapor can be increased to promote the vapor phase decomposition. In the conventional closed
本発明者らは、ここで気相分解過程で起こっている反応に着目した。ＨＦ・ＨＮＯ３混酸によるＳｉの気相分解過程の素反応式には諸説があるが、下記に一例を示す。
・Ｓｉ＋２ＨＮＯ３→ＳｉＯ２＋ＮＯ２＋ＮＯ＋Ｈ２Ｏ （１）
・ＳｉＯ２＋４ＨＦ→ＳｉＦ４＋２Ｈ２Ｏ （２）
・ＳｉＯ２＋６ＨＦ→Ｈ２ＳｉＦ６＋２Ｈ２Ｏ （３）
・Ｈ２ＳｉＦ６→ＳｉＦ４＋２ＨＦ （４）
つまり、反応系全体では以下の反応が起こっていると考えられる。
・Ｓｉ＋２ＨＮＯ３＋４ＨＦ→ＳｉＦ４＋ＮＯ２＋ＮＯ＋３Ｈ２Ｏ （５）
The present inventors focused attention on the reaction occurring in the gas phase decomposition process here. Although there are various theories in the elementary reaction process of the gas phase decomposition process of Si by HF · HNO 3 mixed acid, an example is shown below.
Si + 2HNO 3 → SiO 2 + NO 2 + NO + H 2 O (1)
· SiO 2 + 4HF → SiF 4 + 2H 2 O (2)
· SiO 2 + 6HF → H 2 SiF 6 + 2H 2 O (3)
H 2 SiF 6 → SiF 4 + 2HF (4)
In other words, the following reaction is considered to occur in the whole reaction system.
-Si + 2HNO 3 + 4HF → SiF 4 + NO 2 + NO + 3H 2 O (5)
気相分解では、このように、Ｓｉが揮発性のＳｉＦ４（四フッ化ケイ素）に分解される。従って、閉塞容器内で反応が進むにつれて閉塞容器内の分解生成物の濃度が高くなり、Ｓｉの気相分解反応が起こりにくくなると考えられる。つまり、閉塞容器内部の気体が周期的に閉塞容器の外へ漏洩すると、閉塞容器内部の圧力は低下するものの、揮発性が高い分解生成物であるＳｉＦ４ガスが反応の系外へ排出されて、Ｓｉの気相分解反応が促進されると考えられる。 In gas phase decomposition, Si is thus decomposed into volatile SiF 4 (silicon tetrafluoride). Therefore, as the reaction proceeds in the closed vessel, the concentration of decomposition products in the closed vessel increases, and it is considered that the gas phase decomposition reaction of Si is less likely to occur. That is, when the gas inside the closed container periodically leaks out of the closed container, the pressure inside the closed container decreases, but SiF 4 gas, which is a highly volatile decomposition product, is discharged out of the reaction system. It is believed that the gas phase decomposition reaction of Si is promoted.
より多量のＳｉサンプル片を気相分解するために従来の閉塞容器をそのまま大型化しても、容器本体と外蓋の間に偶然にできた間隙から内部の気体が安定してリークする保証はない。そこで、本発明者らは、閉塞容器に圧力調整バルブを設置し、閉塞容器内部の圧力を所定の範囲内に保ち、かつ閉塞容器内部で発生した揮発性分解生成物及び混酸蒸気を意図的に漏洩させながら気相分解を行うことで、従来よりも効率良く気相分解を行えることを見出し、本発明を完成させた。 There is no guarantee that the internal gas will stably leak from the gap created accidentally between the container body and the outer lid even if the conventional closed container is upsized as it is in order to vapor-degrade a larger amount of Si sample pieces . Therefore, the present inventors install a pressure control valve in the closed container, keep the pressure inside the closed container within a predetermined range, and intentionally use volatile decomposition products and mixed acid vapor generated inside the closed container. The inventors have found that gas phase decomposition can be performed more efficiently than in the past by performing gas phase decomposition while leaking, and the present invention has been completed.
即ち、本発明は、半導体シリコン結晶中の不純物を分析する際の前処理において、閉塞容器内に、前記半導体シリコン結晶から採取した試料と、フッ化水素酸及び硝酸からなる混酸を入れた後、前記混酸を加熱することで混酸蒸気を発生させて前記試料全体を気相分解する方法であって、
前記閉塞容器として圧力調整バルブが設けられたものを用い、前記閉塞容器内部の圧力が絶対圧で０．２０ＭＰａ以上０．４０ＭＰａ以下となるように、前記閉塞容器内部で発生した揮発性分解生成物及び混酸蒸気を前記圧力調整バルブから漏洩させながら気相分解を行う半導体シリコン結晶の不純物分析のための前処理方法である。
That is, according to the present invention, in the pretreatment for analyzing the impurities in the semiconductor silicon crystal, the mixed sample of hydrofluoric acid and nitric acid is placed in the closed container after the sample collected from the semiconductor silicon crystal, A method of generating mixed acid vapor by heating the mixed acid, and vapor phase decomposing the entire sample,
A volatile decomposition product generated inside the closed container such that the pressure inside the closed container is 0.20 MPa or more and 0.40 MPa or less in absolute pressure, using a pressure control valve as the closed container. And a pretreatment method for impurity analysis of semiconductor silicon crystals in which vapor phase decomposition is performed while leaking mixed acid vapor from the pressure control valve.
以下、図面を参照しながら本発明について詳細に説明するが、本発明はこれらに限定されるものではない。 Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.
本発明の前処理方法では、閉塞容器内部の圧力が絶対圧で０．２０ＭＰａ以上０．４０ＭＰａ以下となるように、閉塞容器内部で発生した揮発性分解生成物及び混酸蒸気を漏洩させるため、閉塞容器として圧力調整バルブが設けられたものを用いる。図１は、本発明の前処理方法に使用される気相分解装置の一例を示す概略図である。 In the pretreatment method of the present invention, since the volatile decomposition product and mixed acid vapor generated inside the closed container are leaked so that the pressure inside the closed container becomes 0.20 MPa or more and 0.40 MPa or less in absolute pressure, A container provided with a pressure control valve is used. FIG. 1 is a schematic view showing an example of a vapor phase decomposition apparatus used in the pretreatment method of the present invention.
図１の気相分解装置は、容器本体１ａ、内蓋１ｂ、外蓋１ｃ、及び圧力調整バルブ１ｄからなる閉塞容器１と、高温チャンバー２を備えたものである。このような閉塞容器１を使用して気相分解を行う際には、サンプルカップ３に入れたＳｉサンプル片４と、フッ化水素酸及び硝酸からなる混酸５を入れた後、閉塞容器１を高温チャンバー２内に設置して、混酸５を１００℃程度に加熱することで混酸蒸気を発生させ、Ｓｉサンプル片４を溶解させる。その際、閉塞容器１内部の圧力が絶対圧で０．２０ＭＰａ以上０．４０ＭＰａ以下となるように、閉塞容器１内部で発生した揮発性分解生成物及び混酸蒸気を圧力調整バルブ１ｄから漏洩させる。
The gas phase decomposition apparatus shown in FIG. 1 comprises a
なお、閉塞容器及びサンプルカップとしては、特に限定されないが、従来と同様に、フッ素樹脂製のものを好適に使用することができる。また、圧力調整バルブとしては、特に限定されないが、フッ素樹脂製のものを好適に使用することができる。フッ素樹脂としては、ポリテトラフルオロエチレンが特に好適である。また、圧力調整バルブを設ける位置は、特に限定されないが、例えば、図１のように、閉塞容器１の内蓋１ｂと外蓋１ｃを貫通するように設けることができる。また、高温チャンバーとしては、排気機能のあるものを用いるのが好ましい。
The closed container and the sample cup are not particularly limited, but, as in the prior art, those made of fluorocarbon resin can be suitably used. Further, the pressure control valve is not particularly limited, but one made of a fluorine resin can be suitably used. As the fluorine resin, polytetrafluoroethylene is particularly preferable. Further, the position at which the pressure control valve is provided is not particularly limited. For example, as shown in FIG. 1, the pressure control valve can be provided so as to penetrate the inner lid 1 b and the outer lid 1 c of the
本発明の前処理方法では、気相分解に使用する混酸蒸気は、閉塞容器内に入れたフッ化水素酸及び硝酸からなる混酸を１００℃前後に加熱することで発生させる。このような方法で発生させた混酸蒸気であれば、上記の特許文献１や特許文献２に記載の方法で得られる混酸成分（フッ化水素酸及び硝酸）を含むガスよりも混酸成分の濃度の高いものとなるため、Ｓｉサンプル片全体を効率的に分解することができる。
In the pretreatment method of the present invention, the mixed acid vapor used for gas phase decomposition is generated by heating the mixed acid consisting of hydrofluoric acid and nitric acid placed in the closed vessel to around 100 ° C. In the case of mixed acid vapor generated by such a method, the mixed acid component concentration is higher than that of the gas containing mixed acid components (hydrofluoric acid and nitric acid) obtained by the methods described in
また、本発明では、気相分解中の閉塞容器内部の圧力を絶対圧で０．２０ＭＰａ以上０．４０ＭＰａ以下に保つ。閉塞容器内部の圧力とＳｉサンプル片の溶解量の相関を調べたところ、図３に示される相関が得られた。なお、図３のグラフでは、閉塞容器内部の圧力が絶対圧で０．１０ＭＰａのときのＳｉサンプル片の溶解量を１として溶解量を相対値で示している。図３に示されるように、閉塞容器内部の圧力が増すとＳｉサンプル片の溶解量は増加するが、溶解量が急激に増加しているのは圧力が０．２０ＭＰａ以上からである。このことから、気相分解中の閉塞容器内部の圧力を絶対圧で０．２０ＭＰａ未満とすると、Ｓｉサンプル片気相分解効率が大幅に低下する恐れがある。一方、閉塞容器内部の圧力が０．４０ＭＰａを超えると、フッ素樹脂製の閉塞容器の実用的な強度限界を超え、閉塞容器が破損するなどの問題が発生する恐れがある。 Further, in the present invention, the pressure inside the closed vessel during the gas phase decomposition is maintained at 0.20 MPa or more and 0.40 MPa or less in absolute pressure. When the correlation between the pressure inside the closed vessel and the dissolution amount of the Si sample piece was examined, the correlation shown in FIG. 3 was obtained. In the graph of FIG. 3, the amount of dissolution of the Si sample piece when the pressure inside the closed container is 0.10 MPa in absolute pressure is 1 and the amount of dissolution is shown as a relative value. As shown in FIG. 3, the dissolution amount of the Si sample piece increases as the pressure inside the closed container increases, but the dissolution amount increases rapidly because the pressure is 0.20 MPa or more. From this, when the pressure inside the closed vessel during the gas phase decomposition is made less than 0.20 MPa in absolute pressure, there is a possibility that the efficiency of the gas phase decomposition of the Si sample piece is significantly reduced. On the other hand, if the pressure inside the closed container exceeds 0.40 MPa, the practical strength limit of the closed container made of fluorocarbon resin may be exceeded, and problems such as breakage of the closed container may occur.
このような前処理方法であれば、以下のような効果が期待できる。
（ｉ）閉塞容器内部の圧力を絶対圧で０．２０ＭＰａ以上０．４０ＭＰａ以下に保持することで、高い混酸蒸気の濃度によってＳｉの気相分解反応が促進される。
（ｉｉ）閉塞容器内部の気体（閉塞容器内部で発生した揮発性分解生成物及び混酸蒸気）がリークすることで、揮発性が高い分解生成物であるＳｉＦ４ガスが反応の系外へ多く排出され、Ｓｉの気相分解反応が促進される。即ち、上記反応式（５）において、反応生成物であるＳｉＦ４を系外へ除去することで、Ｓｉが分解する方向へ平衡が移動する。
（ｉｉｉ）ＨＦ・ＨＮＯ３混酸蒸気の一部も閉塞容器の外へリークするため、常に新鮮な（より純度の高い）混酸蒸気が提供されることで、Ｓｉの気相分解反応が促進される。
With such a pretreatment method, the following effects can be expected.
(I) By maintaining the pressure inside the closed vessel at an absolute pressure of 0.20 MPa or more and 0.40 MPa or less, the vapor phase decomposition reaction of Si is promoted by the concentration of the high mixed acid vapor.
(Ii) Leakage of the gas inside the closed vessel (volatile decomposition products and mixed acid vapor generated inside the closed vessel) causes a large amount of highly volatile decomposition product SiF 4 gas to be discharged to the outside of the reaction system And the gas phase decomposition reaction of Si is promoted. That is, in the above reaction formula (5), by removing the reaction product SiF 4 out of the system, the equilibrium moves in the direction in which Si decomposes.
(Iii) Since a part of the HF / HNO 3 mixed acid vapor also leaks out of the closed vessel, the fresh (higher purity) mixed acid vapor is always provided, thereby promoting the vapor phase decomposition reaction of Si. .
このように、本発明の前処理方法であれば、より短時間でより多量の試料を気相分解によって全溶解させることができる。つまり、試料の単位量あたりの前処理に要する時間を従来法に比べて短縮することができ、また単位時間あたりに処理する試料の量を従来法に比べて増やすことができる。 Thus, with the pretreatment method of the present invention, a larger amount of sample can be completely dissolved by gas phase decomposition in a shorter time. That is, the time required for pretreatment per unit amount of sample can be shortened as compared to the conventional method, and the amount of sample to be treated per unit time can be increased as compared to the conventional method.
また、本発明では、上記の本発明の前処理方法で前処理した試料を、誘導結合プラズマ質量分析（ＩＣＰ−ＭＳ）又は原子吸光分析（ＡＡＳ）によって分析する半導体シリコン結晶の不純物分析方法を提供する。 The present invention also provides a method for analyzing impurities of semiconductor silicon crystals in which a sample pretreated by the above pretreatment method of the present invention is analyzed by inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectrometry (AAS). Do.
なお、このような不純物分析方法では、上記のようにして前処理した試料から測定用の試料溶液を調製し、ＩＣＰ−ＭＳやＡＡＳ等で不純物の分析を行うが、前処理後のサンプルカップ内には、被測定金属不純物とともにＨ２ＳｉＦ６（ヘキサフルオロケイ酸）などのＳｉ分解残渣が残留する場合がある。そこで、更にサンプルカップを加熱（蒸発乾固）することで、サンプルカップ内に残ったＳｉ分解残渣を除去した後、残留物を硝酸によって再抽出して、測定用の試料溶液を調製し、ＩＣＰ−ＭＳやＡＡＳ等で不純物の分析を行うのが好ましい。 In such an impurity analysis method, a sample solution for measurement is prepared from the sample pretreated as described above, and analysis of impurities is performed by ICP-MS, AAS, etc. In some cases, Si decomposition residue such as H 2 SiF 6 (hexafluorosilicic acid) may remain together with the metal impurity to be measured. Therefore, the sample cup is further heated (evaporated to dryness) to remove the Si decomposition residue remaining in the sample cup, and then the residue is reextracted with nitric acid to prepare a sample solution for measurement, ICP It is preferable to analyze the impurities by MS, AAS or the like.
図２に本発明の不純物分析方法のフローの一例を示す。図２の不純物分析方法では、まず、上述の本発明の前処理方法で前処理を行う。この前処理では、半導体シリコン結晶から試料を採取し、サンプルカップに入れた試料とＨＦ・ＨＮＯ３混酸を、圧力調整バルブを設けた閉塞容器内に入れる。次に、混酸を１００℃程度に加熱し、閉塞容器内部の圧力が絶対圧で０．２０ＭＰａ以上０．４０ＭＰａ以下となるように、閉塞容器内部で発生した揮発性分解生成物及び混酸蒸気を圧力調整バルブから漏洩させながら試料を気相分解する。次に、前処理（気相分解）後のサンプルカップを閉塞容器内から取り出し、蒸発乾固を行う。蒸発乾固後、硝酸で残留物を再抽出し、測定用試料溶液を調製する。最後に、このようにして調製した測定用試料溶液を用いて、ＩＣＰ−ＭＳで不純物の分析を行う。 FIG. 2 shows an example of the flow of the impurity analysis method of the present invention. In the impurity analysis method of FIG. 2, first, pretreatment is performed by the above-described pretreatment method of the present invention. In this pretreatment, a sample is taken from a semiconductor silicon crystal, and the sample and HF / HNO 3 mixed acid placed in a sample cup are placed in a closed container provided with a pressure control valve. Next, the mixed acid is heated to about 100 ° C., and the pressure of the volatile decomposition product and mixed acid vapor generated inside the closed container is reduced so that the pressure inside the closed container becomes 0.20 MPa or more and 0.40 MPa or less in absolute pressure. Gas phase decomposition of the sample while leaking from the adjustment valve. Next, the sample cup after the pretreatment (gas phase decomposition) is taken out from the closed vessel and evaporated to dryness. After evaporation to dryness, the residue is re-extracted with nitric acid to prepare a sample solution for measurement. Finally, analysis of impurities by ICP-MS is performed using the sample solution for measurement thus prepared.
このような本発明の不純物分析方法であれば、より短時間でより多量の試料の前処理を行うことができるため、効率良く不純物の分析を行うことができ、また試料の量を従来よりも増やしてＳｉ成分の濃度に比べて不純物の濃度を高めることで、不純物の測定精度を高めることもできる。 According to such an impurity analysis method of the present invention, it is possible to carry out pretreatment of a larger amount of samples in a shorter time, so that analysis of impurities can be performed efficiently, and the amount of samples is larger than that of the prior art. The measurement accuracy of the impurities can also be enhanced by increasing the concentration of the impurities by increasing the concentration as compared to the concentration of the Si component.
以下、実施例及び比較例を用いて本発明を具体的に説明するが、本発明はこれらに限定されるものではない。 EXAMPLES The present invention will be specifically described below using Examples and Comparative Examples, but the present invention is not limited to these.
［実施例１］
図１に示される圧力調整バルブが設けられた閉塞容器１（容積：約１，５００ｍＬ）の底に、５０ｗｔ％ＨＦと発煙ＨＮＯ３からなる混酸５（５０ｗｔ％ＨＦ：発煙ＨＮＯ３＝１：１）を３６０ｍＬ入れた。次に、３個のテフロン（登録商標）製サンプルカップ３のそれぞれに約７ｇのＳｉサンプル片４を入れたものを閉塞容器１の中に載置した。次に、閉塞容器１を排気機能のある高温チャンバー（オーブン）２中で１００℃に加熱し、１６時間保持した。１６時間経過後にサンプルカップ３を取り出して計量し、気相分解前後の重量差を溶解量として求めた。なお、気相分解中の閉塞容器１内部の圧力は絶対圧で０．３０ＭＰａとした。結果を表１に示す。なお、分解前のＳｉ重量（ｇ）、分解後のＳｉ重量（ｇ）、溶解量（ｇ）の有効数字は小数点以下２桁とした。これは以降の表でも同様である。
Example 1
In the bottom of the closed vessel 1 (volume: about 1,500 mL) provided with the pressure control valve shown in FIG. 1, mixed acid 5 (50 wt% HF: fume HNO 3 = 1: 1) consisting of 50 wt% HF and fuming HNO 3 ) Was added. Next, each of three Teflon (registered trademark)
［実施例２］
５０ｗｔ％ＨＦ：発煙ＨＮＯ３＝１：１の混酸４４０ｍＬを使用する以外は実施例１と同様にして、合計約２１ｇ（約７ｇ×３）のＳｉサンプル片４の気相分解を行い、気相分解前後の重量差からＳｉサンプル片４の溶解量を求めた。結果を表２に示す。
Example 2
Gas phase decomposition of a total of about 21 g (about 7 g × 3) of the
［実施例３］
５０ｗｔ％ＨＦ：発煙ＨＮＯ３＝２：１の混酸４５０ｍＬを使用する以外は実施例１と同様にして、合計約２１ｇ（約７ｇ×３）のＳｉサンプル片４の気相分解を行い、気相分解前後の重量差からＳｉサンプル片４の溶解量を求めた。結果を表３に示す。
[Example 3]
Gas phase decomposition of a total of about 21 g (about 7 g × 3) of the
［実施例４］
気相分解中の閉塞容器１内部の圧力を絶対圧で０．２０ＭＰａとする以外は実施例１と同様にして、合計約２１ｇ（約７ｇ×３）のＳｉサンプル片４の気相分解を行い、気相分解前後の重量差からＳｉサンプル片４の溶解量を求めた。結果を表４に示す。
Example 4
The gas phase decomposition of a total of about 21 g (about 7 g × 3) of the
［実施例５］
気相分解中の閉塞容器１内部の圧力を絶対圧で０．４０ＭＰａとする以外は実施例１と同様にして、合計約２１ｇ（約７ｇ×３）のＳｉサンプル片４の気相分解を行ったところ各約７ｇのＳｉサンプル片は全て溶解してしまったため、改めて、合計約４８ｇ（約１６ｇ×３）のＳｉサンプル片４の気相分解を行い、気相分解前後の重量差からＳｉサンプル片４の溶解量を求めた。結果を表５に示す。
[Example 5]
A total of about 21 g (about 7 g × 3) of the
［比較例１］
気相分解中の閉塞容器１内部の圧力を絶対圧で０．１５ＭＰａとする以外は実施例１と同様にして、合計約２１ｇ（約７ｇ×３）のＳｉサンプル片４の気相分解を行い、気相分解前後の重量差からＳｉサンプル片４の溶解量を求めた。結果を表６に示す。
Comparative Example 1
A total of about 21 g (about 7 g × 3) of the
［比較例２］
図１に示される閉塞容器１の容器本体１ａ（容積：約１，５００ｍＬ）のみを用い、閉塞容器の内蓋１ｂ、外蓋１ｃ、及び圧力調整バルブ１ｄを用いずに、大気圧（絶対圧０．１ＭＰａ）に開放した状態で使用する以外は実施例１と同様にして、合計約２１ｇ（約７ｇ×３）のＳｉサンプル片４の気相分解を行い、気相分解前後の重量差からＳｉサンプル片１０４の溶解量を求めた。結果を表７に示す。
Comparative Example 2
Atmospheric pressure (absolute pressure) using only the container body 1a (volume: about 1,500 mL) of the
表１〜５に示されるように、圧力調整バルブが設けられた閉塞容器を用い、閉塞容器内部の圧力が絶対圧で０．２０ＭＰａ以上０．４０ＭＰａ以下となるように、閉塞容器内部で発生した揮発性分解生成物及び混酸蒸気を圧力調整バルブから漏洩させながら気相分解を行った実施例１〜５では、合計約８ｇのＳｉサンプル片を溶解させることができた。また、表１〜３に示されるように、いずれの混酸の比率においてもＳｉサンプル片の溶解量は合計約１８ｇであり、混酸の組成によらず安定した気相分解が行えることが分かった。 As shown in Tables 1 to 5, using a closed vessel provided with a pressure control valve, the pressure inside the closed vessel was generated within the closed vessel so that the absolute pressure would be 0.20 MPa or more and 0.40 MPa or less In Examples 1 to 5 in which gas phase decomposition was performed while leaking volatile decomposition products and mixed acid vapor from the pressure control valve, a total of about 8 g of Si sample pieces could be dissolved. In addition, as shown in Tables 1 to 3, it was found that the dissolution amount of the Si sample piece was about 18 g in total at any ratio of mixed acid, and stable gas phase decomposition could be performed regardless of the composition of mixed acid.
一方、表６に示されるように、圧力調整バルブが設けられた閉塞容器を用いた場合でも、閉塞容器内部の圧力を絶対圧で０．１５ＭＰａ（０．２０ＭＰａ未満）となるように、閉塞容器内部で発生した揮発性分解生成物及び混酸蒸気を圧力調整バルブから漏洩させながら気相分解を行った比較例１では、合計約６ｇのＳｉサンプル片しか溶解させることができなかった。また、表７に示されるように、閉塞容器を使用せず、大気圧開放状態（絶対圧０．１ＭＰａ）で気相分解を行った比較例２では、合計約５ｇのＳｉサンプル片しか溶解させることができなかった。なお、図４に示すように完全に容器を閉塞させた場合、実施例１〜５と同じような小さな容積では容器内の圧力が上昇して、上述のようにフッ素樹脂製の閉塞容器が破損する恐れがあり危険であるため、圧力調整バルブが設けられていない閉塞容器を使用した比較実験は行わなかった。 On the other hand, as shown in Table 6, even when using a closed container provided with a pressure control valve, the closed container is set to have an internal pressure of 0.15 MPa (less than 0.20 MPa) in absolute pressure. In Comparative Example 1 in which gas phase decomposition was performed while leaking internally generated volatile decomposition products and mixed acid vapor from the pressure control valve, only a total of about 6 g of Si sample pieces could be dissolved. In addition, as shown in Table 7, in Comparative Example 2 in which the gas phase decomposition was performed in the atmospheric pressure release state (0.1 MPa absolute pressure) without using the closed container, only a total of about 5 g of Si sample pieces is dissolved I could not. When the container is completely closed as shown in FIG. 4, the pressure in the container rises with a small volume as in the first to fifth embodiments, and the fluorine resin-made closed container is broken as described above. Because of the danger and danger of doing so, we did not conduct a comparative experiment using a closed vessel without a pressure control valve.
以上のように、本発明の前処理方法であれば、従来法の約１０倍のＳｉサンプル片を溶解させることができた。このことから、従来と同様に分解残渣を蒸発乾固後に１ｍＬの硝酸で再抽出すると、測定用試料溶液中の被測定金属不純物濃度を１０倍に高めることができ、これによって金属不純物の検出下限を従来の１／１０に改善することができることが示唆された。また、Ｓｉサンプル片の溶解量を従来と同程度にした場合には、前処理に要する時間を短縮することができるため、不純物分析の作業効率を改善することができることが示唆された。 As described above, according to the pretreatment method of the present invention, it was possible to dissolve about 10 times as many Si sample pieces as the conventional method. From this, when the decomposition residue is evaporated to dryness and then reextracted with 1 mL of nitric acid as in the prior art, the concentration of the metal impurity to be measured in the sample solution for measurement can be increased tenfold. It is suggested that it can be improved to 1/10 of the conventional one. In addition, when the dissolution amount of the Si sample piece is made comparable to that in the past, the time required for the pretreatment can be shortened, which suggests that the work efficiency of the impurity analysis can be improved.
なお、本発明は、上記実施形態に限定されるものではない。上記実施形態は例示であり、本発明の特許請求の範囲に記載された技術的思想と実質的に同一な構成を有し、同様な作用効果を奏するものは、いかなるものであっても本発明の技術的範囲に包含される。 The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has the substantially same constitution as the technical idea described in the claims of the present invention, and the same effects can be exhibited by any invention. It is included in the technical scope of
１…閉塞容器、 １ａ…容器本体、 １ｂ…内蓋、 １ｃ…外蓋、
１ｄ…圧力調整バルブ、 ２…高温チャンバー、 ３…サンプルカップ、
４…Ｓｉサンプル片、 ５…混酸。
1 ... closed container, 1a ... container body, 1b ... inner lid, 1c ... outer lid,
1d ... pressure adjustment valve, 2 ... high temperature chamber, 3 ... sample cup,
4 ... Si sample piece, 5 ... mixed acid.
Claims (2)
前記閉塞容器として圧力調整バルブが設けられたものを用い、前記閉塞容器内部の圧力が絶対圧で０．２０ＭＰａ以上０．４０ＭＰａ以下となるように、前記閉塞容器内部で発生した揮発性分解生成物及び混酸蒸気を前記圧力調整バルブから漏洩させながら気相分解を行うことを特徴とする半導体シリコン結晶の不純物分析のための前処理方法。 In the pretreatment for analyzing the impurities in the semiconductor silicon crystal, the mixed acid containing hydrofluoric acid and nitric acid is placed in the closed vessel, and then the mixed acid is heated. A method of generating mixed acid vapor with the
A volatile decomposition product generated inside the closed container such that the pressure inside the closed container is 0.20 MPa or more and 0.40 MPa or less in absolute pressure, using a pressure control valve as the closed container. And vapor phase decomposition is performed while leaking mixed acid vapor from the pressure control valve, and a pretreatment method for impurity analysis of semiconductor silicon crystal.
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