JP6817545B2 - Carbon measurement method in silicon - Google Patents
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- 229910052710 silicon Inorganic materials 0.000 title claims description 101
- 239000010703 silicon Substances 0.000 title claims description 101
- 229910052799 carbon Inorganic materials 0.000 title claims description 86
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims description 85
- 238000000691 measurement method Methods 0.000 title claims description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 97
- 239000013078 crystal Substances 0.000 claims description 65
- 238000000034 method Methods 0.000 claims description 61
- 238000001773 deep-level transient spectroscopy Methods 0.000 claims description 34
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 30
- 238000009835 boiling Methods 0.000 claims description 28
- 239000012535 impurity Substances 0.000 claims description 21
- 238000005259 measurement Methods 0.000 claims description 19
- 229910052739 hydrogen Inorganic materials 0.000 claims description 15
- 239000001257 hydrogen Substances 0.000 claims description 14
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 12
- 230000008569 process Effects 0.000 claims description 3
- 102100031920 Dihydrolipoyllysine-residue succinyltransferase component of 2-oxoglutarate dehydrogenase complex, mitochondrial Human genes 0.000 claims 3
- 101000992065 Homo sapiens Dihydrolipoyllysine-residue succinyltransferase component of 2-oxoglutarate dehydrogenase complex, mitochondrial Proteins 0.000 claims 3
- 235000012431 wafers Nutrition 0.000 description 16
- 239000002344 surface layer Substances 0.000 description 15
- 238000010306 acid treatment Methods 0.000 description 10
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- 230000035945 sensitivity Effects 0.000 description 6
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 description 5
- 238000001004 secondary ion mass spectrometry Methods 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 238000011088 calibration curve Methods 0.000 description 4
- 238000005530 etching Methods 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 3
- 150000003376 silicon Chemical class 0.000 description 3
- 239000000758 substrate Substances 0.000 description 3
- 230000001052 transient effect Effects 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 2
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- 238000002474 experimental method Methods 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000005498 polishing Methods 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 238000000862 absorption spectrum Methods 0.000 description 1
- 230000003213 activating effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 238000003486 chemical etching Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000000326 densiometry Methods 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
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Description
本発明はシリコン中の炭素測定方法に関する。 The present invention relates to a method for measuring carbon in silicon.
半導体集積回路等のデバイスの高密度化、高集積化に伴い、デバイス動作の安定化が頓に望まれてきている。特にリーク電流や酸化膜耐圧等の特性値改善は重要な課題である。しかし、不純物が集積回路基板であるシリコンウェーハ中に混入すると、その後作製したデバイスの安定動作は望めないことになる。例えば、半導体集積回路の製造工程において、ウェーハ中の炭素は、１×１０１５ａｔоｍｓ／ｃｍ３以下の濃度であっても、デバイス特性に悪影響を及ぼすことが広く知られている。 With the increasing density and high integration of devices such as semiconductor integrated circuits, stabilization of device operation has been desperately desired. In particular, improving characteristic values such as leakage current and oxide film withstand voltage is an important issue. However, if impurities are mixed into the silicon wafer, which is an integrated circuit board, stable operation of the device manufactured thereafter cannot be expected. For example, in the manufacturing process of semiconductor integrated circuits, it is widely known that carbon in a wafer adversely affects device characteristics even at a concentration of 1 × 10 15 atоms / cm 3 or less.
したがって、ウェーハ中の炭素を低く抑えるために、正確な濃度測定技術が必要とされている。通常、この目的で炭素濃度測定はフーリエ変換赤外分光法（Ｆｏｕｒｉｅｒ Ｔｒａｎｓｆｏｒｍ ＩｎｆｒａＲｅｄ Ｓｐｅｃｔｒｏｓｃｏｐｙ、ＦＴ−ＩＲ法）で測定される。この方法は、シリコンウェーハの赤外線吸収スペクトルから格子間炭素濃度を間接的に求める手法であり、簡便に測定できるため広く用いられている。 Therefore, in order to keep the carbon in the wafer low, an accurate concentration measurement technique is required. Usually, for this purpose, carbon concentration measurement is performed by Fourier Transform Infrared Spectroscopy (FT-IR method). This method is a method for indirectly obtaining the interstitial carbon concentration from the infrared absorption spectrum of a silicon wafer, and is widely used because it can be easily measured.
しかし、ＦＴ−ＩＲ法による炭素濃度測定において、１０１４ａｔоｍｓ／ｃｍ３台の濃度を精度良く測定することは極めて困難であるのが実情である。また、他の測定手法として挙げられるＳＩＭＳ（Ｓｅｃｏｎｄａｒｙ Ｉｏｎ Ｍａｓｓ Ｓｐｅｃｔｒｏｓｃｏｐｙ、二次イオン質量分析法）も同様である。 However, in the carbon concentration measurement by the FT-IR method, it is extremely difficult to accurately measure the concentration of 10 14 atоms / cm 3 units. The same applies to SIMS (Secondary Ion Mass Spectroscopy, secondary ion mass spectrometry), which is mentioned as another measurement method.
その点、ＤＬＴＳ（Ｄｅｅｐ Ｌｅｖｅｌ Ｔｒａｎｓｉｅｎｔ Ｓｐｅｃｔｒｏｓｃｏｐｙ）法は、１０１３ａｔоｍｓ／ｃｍ３台の濃度を測定できる可能性を持つ手法である。なお、ＤＬＴＳ法とは、測定対象に形成したショットキー接合部又はｐｎ接合部に逆バイアス電圧を印加した状態で正方向にパルス電圧を加え、このときにその接合部に生じる空乏層の静電容量変化の温度依存性から深い不純物準位に関する情報を得る方法である。このＤＬＴＳ法の測定結果は、例えばＤＬＴＳ信号強度と測定温度のグラフで示される。グラフ上に形成されたピークが、ある深い不純物準位の存在を示す。また、そのピークの温度から大まかに深い不純物準位のエネルギーが判明し、そのピークの高さが理論的に深い不純物準位の密度を示す。 In that respect, the DLTS (Deep Level Transient Spectroscopy) method is a method that has the potential to measure the concentration of 3 units of 10 13 atоms / cm. In the DLTS method, a pulse voltage is applied in the positive direction while a reverse bias voltage is applied to the Schottky junction or pn junction formed on the measurement target, and the capacitance of the depletion layer generated at the junction at this time is electrostatic. This is a method of obtaining information on deep impurity levels from the temperature dependence of capacitance change. The measurement result of this DLTS method is shown by, for example, a graph of DLTS signal intensity and measurement temperature. The peaks formed on the graph indicate the presence of some deep impurity levels. In addition, the energy of the deep impurity level is roughly determined from the temperature of the peak, and the height of the peak indicates the density of the deep impurity level theoretically.
ここで、例えば、非特許文献１に示される方法では、シリコン結晶中に存在する炭素関連準位Ｅ１、Ｅ２、Ｅ３がＨ−Ｃ、Ｈ−Ｃ−Ｏ複合体により形成される深い不純物準位であり、特に、Ｅ３の準位は、Ｈ−Ｃに起因する準位のため、酸素に影響を受けないとされている。 Here, for example, in the method shown in Non-Patent Document 1, the carbon-related levels E1, E2, and E3 existing in the silicon crystal are deep impurity levels formed by the HC and HCO composites. In particular, the level of E3 is said to be unaffected by oxygen because it is a level caused by HC.
とはいえ、このままでは１０１３ａｔоｍｓ／ｃｍ３台の炭素濃度を高感度に測定できるとまでは言えない。そこで、いくつかの工夫が提案されている。例えば、ＤＬＴＳ電極形成の前処理として行う湿式処理として、ＨＦとＨＮＯ３の混酸を用いることで、炭素関連準位が活性化され、高準位密度測定が可能になるという手法が知られている（非特許文献２参照）。 However, it cannot be said that the carbon concentration of 10 13 atоms / cm 3 units can be measured with high sensitivity as it is. Therefore, some ideas have been proposed. For example, as a wet process performed as a pretreatment for DLTS electrode formation, by using a mixed acid of HF and HNO 3, carbon-related level is activated, methods have been known that it is possible to Kojun'i densitometry (See Non-Patent Document 2).
他に、特許文献１では、炭素関連の不純物準位であるＥ１、Ｅ２、Ｅ３を合算することが有効であることを示している。 In addition, Patent Document 1 shows that it is effective to add up the carbon-related impurity levels E1, E2, and E3.
非特許文献２の手法により、炭素関連準位を高感度に測定可能になるが、この手法には問題点がある。つまり、ＨＦとＨＮＯ３による処理は、いわゆるエッチングであり、シリコンの表層部分が失われてしまうことである。したがって、表層近傍に存在する炭素準位密度測定にこの手法を適用する訳にはいかない。 The method of Non-Patent Document 2 makes it possible to measure carbon-related levels with high sensitivity, but this method has problems. That is, the treatment by HF and HNO 3 is so-called etching, and the surface layer portion of silicon is lost. Therefore, this method cannot be applied to the measurement of carbon level density existing near the surface layer.
また、炭素関連準位を高感度に測定する手法として、特許文献１に示す方法を他手法と併用するにしても、非特許文献２に示すＨＦとＨＮＯ３の混酸を用いる限り、必ず表層近傍が失われるため、シリコン表層近傍の炭素濃度を評価する手法としては成立せず、シリコン表層やエピタキシャル層中の炭素濃度を評価するための方法としてはＤＬＴＳ法は有効とはいえなかった。 Further, even if the method shown in Patent Document 1 is used in combination with other methods as a method for measuring carbon-related levels with high sensitivity, as long as the mixed acid of HF and HNO 3 shown in Non-Patent Document 2 is used, the vicinity of the surface layer is always present. Therefore, the DLTS method was not established as a method for evaluating the carbon concentration in the vicinity of the silicon surface layer, and the DLTS method was not effective as a method for evaluating the carbon concentration in the silicon surface layer and the epitaxial layer.
本発明はこのような問題点に鑑みてなされたもので、シリコン表層を失うことなく、シリコン中の炭素関連準位を簡便に安定して測定するのに有効な測定手法を提供することを課題とする。 The present invention has been made in view of such problems, and it is an object of the present invention to provide an effective measurement method for easily and stably measuring carbon-related levels in silicon without losing the silicon surface layer. And.
上記課題を解決するため、本発明のシリコン中の炭素測定方法は、シリコンを６０〜１００℃の水で煮沸後、そのシリコンに含まれる炭素関連の不純物準位をＤＬＴＳ法により測定することを特徴とする。 In order to solve the above problems, the carbon measuring method in silicon of the present invention is characterized by boiling silicon in water at 60 to 100 ° C. and then measuring the carbon-related impurity levels contained in the silicon by the DLTS method. And.
本発明によれば、シリコン表層を失うことなく、シリコン中の炭素関連準位を簡便に安定して測定できる。また、ＤＬＴＳ電極形成の前処理を行わない手法に比べて、高感度に炭素関連準位を測定でき、より微量な炭素の存在を知ることができる。 According to the present invention, carbon-related levels in silicon can be easily and stably measured without losing the silicon surface layer. In addition, the carbon-related level can be measured with high sensitivity as compared with the method without pretreatment for DLTS electrode formation, and the presence of a trace amount of carbon can be known.
以下、実施の形態について述べる。ＤＬＴＳ法は通常、ショットキー接合を形成する金属電極を測定試料表面に形成し、裏面にはオーミック接合を持つ金属電極を形成し、その２つの電極間に逆バイアスを印加した状態で正方向にパルス電圧を加えることで生じた空乏層静電容量の変化（過渡的応答）の温度依存性を取得すると、不純物が形成するエネルギー準位に応じた温度で静電容量変化がピークを形成する。そのピーク位置の静電容量変化から不純物準位密度を算出することができる。具体的に、ｎ型シリコンウェーハにおいて、表面に形成するショットキー電極にはＡｕが用いられることが多く、裏面に形成するオーミック電極にはＧａが用いられることが多い。いずれの電極も酸化膜の存在しない清浄なシリコン面に形成することが望ましく、その清浄面を得るためにＨＦによる表面酸化膜除去が行われる。 Hereinafter, embodiments will be described. In the DLTS method, a metal electrode forming a Schottky junction is usually formed on the front surface of the measurement sample, a metal electrode having an ohmic junction is formed on the back surface, and a reverse bias is applied between the two electrodes in the forward direction. When the temperature dependence of the change (transient response) of the depletion layer capacitance caused by applying the pulse voltage is acquired, the capacitance change peaks at the temperature corresponding to the energy level formed by the impurities. The impurity level density can be calculated from the change in capacitance at the peak position. Specifically, in an n-type silicon wafer, Au is often used for the Schottky electrode formed on the front surface, and Ga is often used for the ohmic electrode formed on the back surface. It is desirable that both electrodes are formed on a clean silicon surface in which no oxide film is present, and the surface oxide film is removed by HF in order to obtain the clean surface.
非特許文献２に示すような従来法におけるＨＦとＨＮＯ３の混酸による前処理の意味は、前記混酸によるエッチング反応中において、シリコンウェーハ中に深く水素が導入され、その水素と炭素の相互作用による準位の活性化と考えられている。 The meaning of pretreatment with a mixed acid of HF and HNO 3 in the conventional method as shown in Non-Patent Document 2 is that hydrogen is deeply introduced into the silicon wafer during the etching reaction by the mixed acid, and the interaction between the hydrogen and carbon is used. It is considered to be the activation of the level.
しかし、前記混酸によるエッチング反応では、表層近傍を失ってしまうため、別の手法で、シリコンウェーハの表層近傍を失うことなく、ウェーハバルクに水素を導入する処理法を発見できれば、目的を達成できることに本発明者らは想到した。そこで、表面を除去しない前処理法としていくつもの実験を繰り返したところ、水による煮沸で炭素関連準位が活性化されることがわかった。 However, in the etching reaction using the mixed acid, the vicinity of the surface layer is lost. Therefore, if a treatment method for introducing hydrogen into the wafer bulk can be found by another method without losing the vicinity of the surface layer of the silicon wafer, the object can be achieved. The inventors have come up with the idea. Therefore, when a number of experiments were repeated as a pretreatment method that did not remove the surface, it was found that the carbon-related levels were activated by boiling with water.
図１にその確認実験結果を示す。３つの炭素関連準位を低準位側からＥ１、Ｅ２、Ｅ３とする。そのうち、酸素の影響を受けないＥ３準位に関し、１）湿式処理を行わない場合、２）ＨＦとＨＮＯ３の混酸処理、３）水煮沸、の３つの場合において、湿式処理を行わない場合の準位密度を１として、各前処理後に得られた相対準位密度をＥ１〜Ｅ３の３つについて示す。図１の縦軸では、相対準位密度を活性化率（Ａｃｔｉｖａｔｉｏｎ Ｅｆｆｉｃｉｅｎｃｙ）として示している。図１の左図に混酸処理を行った場合の活性化率を示し、右図に水煮沸処理を行った場合の活性化率を示している。図１に示すように、最も活性化率の高い処理法は２）のＨＦとＨＮＯ３の混酸処理である。しかし、３）の水煮沸の場合、２）には及ばないまでも、湿式処理を行わない場合よりも活性化されていることがわかる。３）の手法の最大の利点は、ウェーハ表層近傍のシリコン層を失わないことであり、いかに活性化率の高い混酸処理ではあっても、表層近傍の炭素濃度を測定する目的からは、測定不可能という判断になるため、この水煮沸処理は大変有効な手法と考えられる。 FIG. 1 shows the results of the confirmation experiment. Let the three carbon-related levels be E1, E2, and E3 from the low level side. Of these, regarding the E3 level that is not affected by oxygen, in the three cases of 1) no wet treatment, 2) mixed acid treatment of HF and HNO 3 , and 3) boiling in water, no wet treatment is performed. The relative level densities obtained after each pretreatment are shown for three of E1 to E3, where 1 is the level density. The vertical axis of FIG. 1 shows the relative level density as the activation efficiency. The left figure of FIG. 1 shows the activation rate when the mixed acid treatment is performed, and the right figure shows the activation rate when the water boiling treatment is performed. As shown in FIG. 1, the treatment method having the highest activation rate is the mixed acid treatment of HF and HNO 3 in 2). However, in the case of boiling in water in 3), it can be seen that the activation is higher than in the case of not performing the wet treatment, if not as good as 2). The greatest advantage of the method 3) is that the silicon layer near the surface layer of the wafer is not lost, and even if the mixed acid treatment has a high activation rate, it cannot be measured for the purpose of measuring the carbon concentration near the surface layer. Since it is judged that it is possible, this boiling treatment is considered to be a very effective method.
一方、水煮沸処理は、混酸処理と比べて、活性化率がやや低いことも事実であるため、先に示した特許文献１の手法や、本出願人に係る特願２０１６−２４２９００号に示す手法、具体的にはＤＬＴＳ測定の前処理としてシリコン結晶に逆方向電圧を印加して熱処理する逆バイアスアニール処理を行う手法を併用し、感度を上げることが有効と考えられる。 On the other hand, since it is a fact that the water boiling treatment has a slightly lower activation rate than the mixed acid treatment, it is shown in the method of Patent Document 1 shown above and Japanese Patent Application No. 2016-242900 relating to the present applicant. It is considered effective to increase the sensitivity by using a method, specifically, a method of performing reverse bias annealing treatment in which a reverse voltage is applied to the silicon crystal to heat-treat it as a pretreatment for DLTS measurement.
以下、本実施形態に係るシリコン中の炭素濃度の測定方法の詳細を説明する。先ず、炭素濃度が異なる複数の第１シリコン結晶を準備する。具体的には、例えば、ＦＺ法で引き上げたｎ型シリコン結晶インゴットを所定の厚さに切り出し、切り出したウェーハに粗研磨、エッチング及び研磨などを施して表面に鏡面加工がされた基板（ポリッシュドウェーハ）を準備する。なお、この基板は、例えばトランジスタ、ダイオード等の電子デバイスの形成用として作製された基板とすることができる。次に、基板からシリコン結晶を切り出して第１シリコン結晶を作製する。第１シリコン結晶の炭素濃度は、ＦＴ−ＩＲ法やＳＩＭＳにて測定可能な範囲（例えば、１×１０１５〜１×１０１６ａｔоｍｓ／ｃｍ３）に調整するとよい。なお、第１シリコン結晶は、ＣＺ法（チョクラルスキー法）で形成されたとしても良いし、ＦＺ法（フローティングゾーン法）で形成されたとしても良いが、後述の第２シリコン結晶の結晶育成法と同じとする。また、第１シリコン結晶の炭素濃度は、ＳＩＭＳ、ＦＴ−ＩＲ法など、ＤＬＴＳ法以外の手法により予め測定、つまり既知としておく。 Hereinafter, the details of the method for measuring the carbon concentration in silicon according to this embodiment will be described. First, a plurality of first silicon crystals having different carbon concentrations are prepared. Specifically, for example, an n-type silicon crystal ingot pulled up by the FZ method is cut out to a predetermined thickness, and the cut out wafer is subjected to rough polishing, etching, polishing, etc., and the surface is mirror-finished (polished). Wafer) is prepared. The substrate can be a substrate manufactured for forming electronic devices such as transistors and diodes. Next, a silicon crystal is cut out from the substrate to prepare a first silicon crystal. The carbon concentration of the first silicon crystal may be adjusted within a range that can be measured by the FT-IR method or SIMS (for example, 1 × 10 15 to 1 × 10 16 atоms / cm 3 ). The first silicon crystal may be formed by the CZ method (Czochralski method) or by the FZ method (floating zone method), but the crystal growth of the second silicon crystal described later may be used. Same as the law. Further, the carbon concentration of the first silicon crystal is measured in advance by a method other than the DLTS method such as SIMS and FT-IR method, that is, known.
次に、ＤＬＴＳ測定に先立ち、各第１シリコン結晶に対して６０〜１００℃の水中で煮沸処理を行う。このとき、水温度が６０℃未満では、シリコン結晶中への水素の導入効果が低いので、６０℃以上とするのが良い。また、処理時間が１０分未満ではシリコン結晶中への水素の導入効果（言い換えると、炭素関連準位の活性化の程度）が低いので、処理時間は１０分以上とするのが良い。また、処理時間が４時間を超えてもシリコン結晶中への水素の導入効果（言い換えると、炭素関連準位の活性化の程度）はそれほど向上しないので、処理時間は４時間以下とすることができる。つまり、水煮沸処理の時間は１０分〜４時間とすることができる。 Next, prior to DLTS measurement, each first silicon crystal is boiled in water at 60 to 100 ° C. At this time, if the water temperature is less than 60 ° C., the effect of introducing hydrogen into the silicon crystal is low, so it is preferable to set the water temperature to 60 ° C. or higher. Further, if the treatment time is less than 10 minutes, the effect of introducing hydrogen into the silicon crystal (in other words, the degree of activation of carbon-related levels) is low, so the treatment time is preferably 10 minutes or more. Further, even if the treatment time exceeds 4 hours, the effect of introducing hydrogen into the silicon crystal (in other words, the degree of activation of carbon-related levels) does not improve so much, so the treatment time may be set to 4 hours or less. it can. That is, the time for boiling in water can be 10 minutes to 4 hours.
次に、水煮沸処理を実施した後の各第１シリコン結晶に対してＤＬＴＳ法により炭素関連の不純物準位の密度を測定する。具体的には、炭素と水素とを少なくとも含んだ複合体の不純物準位の密度を測定する。炭素と水素とを少なくとも含んだ複合体の中でも特に炭素、水素以外の元素（酸素等）を含んでいない複合体（つまり、炭素、水素のみの複合体（Ｈ−Ｃ複合体））の準位密度を測定するのが好ましい。酸素等の他の元素の濃度の影響で、ＤＬＴＳ信号がばらついてしまうのを抑制するためである。第１シリコン結晶の導電型がｎ型の場合には、非特許文献１に示された炭素関連準位Ｅ１、Ｅ２、Ｅ３のうち、Ｈ−Ｃ複合体に起因した準位Ｅ３を測定するのが好ましい。なお、３つの不純物準位Ｅ１、Ｅ２、Ｅ３は、ＤＬＴＳ法でｎ型シリコン結晶を測定することにより検出される約０．１１〜０．１５ｅＶの範囲に形成される炭素関連の不純物準位であって、準位Ｅ１のエネルギーが０．１１ｅＶ、準位Ｅ２のエネルギーが０．１３ｅＶ、準位Ｅ３のエネルギーが０．１５ｅＶである。 Next, the density of carbon-related impurity levels is measured by the DLTS method for each first silicon crystal after the water boiling treatment. Specifically, the density of impurity levels of a complex containing at least carbon and hydrogen is measured. Among the complexes containing at least carbon and hydrogen, the level of the complex containing no elements other than carbon and hydrogen (oxygen, etc.) (that is, the complex containing only carbon and hydrogen (HC complex)). It is preferable to measure the density. This is to prevent the DLTS signal from fluctuating due to the influence of the concentration of other elements such as oxygen. When the conductive type of the first silicon crystal is n type, among the carbon-related levels E1, E2, and E3 shown in Non-Patent Document 1, the level E3 caused by the HC complex is measured. Is preferable. The three impurity levels E1, E2, and E3 are carbon-related impurity levels formed in the range of about 0.11 to 0.15 eV detected by measuring the n-type silicon crystal by the DLTS method. The energy level E1 is 0.11 eV, the energy level E2 is 0.13 eV, and the energy level E3 is 0.15 eV.
ＤＬＴＳ測定では、第１シリコン結晶の表面及び裏面に対してＨＦによる表面酸化膜除去処理を実施した後、表面に例えばＡｕを蒸着してショットキー電極とするとともに、その裏面には例えばＧａを塗布してオーミック電極を作製する。そして、２つの電極間に逆バイアス（例えば−５Ｖ）を印加した状態で正方向にパルス電圧を加えることで生じる空乏層静電容量の過渡的変化を、所定温度範囲（例えば３０〜３００Ｋの範囲）で掃引しながら取得し、得られた過渡的変化の温度依存性から炭素関連の準位密度を測定する。 In DLTS measurement, the surface oxide film is removed by HF on the front and back surfaces of the first silicon crystal, and then Au is vapor-deposited on the front surface to form a Schottky electrode, and Ga is applied to the back surface. Then, the ohmic electrode is manufactured. Then, the transient change of the depletion layer capacitance caused by applying a pulse voltage in the positive direction while applying a reverse bias (for example, -5V) between the two electrodes is set in a predetermined temperature range (for example, 30 to 300K). ) Is obtained while sweeping, and the carbon-related level density is measured from the temperature dependence of the obtained transient change.
次に、各第１シリコン結晶から得られた炭素関連の準位密度と、各第１シリコン結晶の炭素濃度とに基づいて、炭素関連の準位密度と、シリコン中の炭素濃度との相関関係を示した検量線を導出する。なお、炭素関連の準位密度と、シリコン中の炭素濃度とがほぼ比例の関係となる場合には、第１シリコン結晶から得られた炭素関連の準位密度を、第１シリコン結晶の炭素濃度で除算することで、シリコン中の炭素が不純物準位を形成する割合である準位形成率を導出しても良い。この準位形成率も、炭素関連の準位密度とシリコン中の炭素濃度との相関関係を示した指標となる。 Next, the correlation between the carbon-related level density and the carbon concentration in silicon is based on the carbon-related level density obtained from each first silicon crystal and the carbon concentration of each first silicon crystal. Derivation of the calibration curve showing. When the carbon-related level density and the carbon concentration in silicon have a substantially proportional relationship, the carbon-related level density obtained from the first silicon crystal is used as the carbon concentration of the first silicon crystal. By dividing by, the level formation rate, which is the ratio of carbon in silicon forming the impurity level, may be derived. This level formation rate is also an index showing the correlation between the carbon-related level density and the carbon concentration in silicon.
次に、炭素濃度が未知の第２シリコン結晶を準備する。第２シリコン結晶の作製法は第１シリコン結晶と同様である。 Next, a second silicon crystal having an unknown carbon concentration is prepared. The method for producing the second silicon crystal is the same as that for the first silicon crystal.
この第２シリコン結晶に対して、第１シリコン結晶に対して実施したのと同様の水煮沸処理を実施する。このとき、水煮沸処理の温度及び時間は、第１シリコン結晶に対して実施した水煮沸処理の温度及び時間と同じとするのが良い。 The second silicon crystal is subjected to the same water boiling treatment as that performed for the first silicon crystal. At this time, the temperature and time of the water boiling treatment should be the same as the temperature and time of the water boiling treatment performed on the first silicon crystal.
次に、水煮沸処理を実施した後の第２シリコン結晶に対してＤＬＴＳ法により炭素関連の不純物準位の密度を測定する。このとき、先に導出した検量線又は準位形成率が、Ｈ−Ｃ複合体に起因した準位Ｅ３に基づいて得られた場合には、第２シリコン結晶に対しても準位Ｅ３の密度を測定する。つまり、検量線又は準位形成率を構成する不純物準位と同じ不純物準位を第２シリコン結晶から測定する。なお、第２シリコン結晶に対するＤＬＴＳ測定の手順は、第１シリコン結晶に対するＤＬＴＳ測定の手順と同じである。 Next, the density of carbon-related impurity levels is measured by the DLTS method on the second silicon crystal after the water boiling treatment. At this time, if the calibration curve or level formation rate derived earlier is obtained based on the level E3 caused by the HC complex, the density of the level E3 is also relative to the second silicon crystal. To measure. That is, the same impurity level as the impurity level constituting the calibration curve or the level formation rate is measured from the second silicon crystal. The DLTS measurement procedure for the second silicon crystal is the same as the DLTS measurement procedure for the first silicon crystal.
次に、第２シリコン結晶の炭素関連の準位密度と、第１シリコン結晶から得られた検量線又は準位形成率（シリコン中の炭素濃度と炭素関連の準位密度との相関関係）とに基づいて、第２シリコン結晶中の炭素濃度を求める。以上により、シリコン結晶中の炭素濃度をＤＬＴＳ法により求めることができる。 Next, the carbon-related level density of the second silicon crystal and the calibration curve or level formation rate (correlation between the carbon concentration in silicon and the carbon-related level density) obtained from the first silicon crystal. The carbon concentration in the second silicon crystal is determined based on. From the above, the carbon concentration in the silicon crystal can be determined by the DLTS method.
このように、本実施形態では、ＤＬＴＳ測定に先立って、シリコン結晶に対して水煮沸処理を実施するので、シリコン結晶の表層を失うことなく、シリコン結晶中に水素を導入できる。この導入により、シリコン結晶中の不純物準位のうち、炭素と水素を含んだ複合体の準位を活性化でき、ＤＬＴＳ測定により、この準位を高感度に測定できる。これにより、シリコン結晶中の微量炭素の存在を検知できる。このように、本実施形態では、シリコン結晶の表層を含めた形で結晶中の炭素関連の準位密度及び炭素濃度を簡便に安定して測定できる。これにより、シリコン結晶の表層近傍（例えばエピタキシャル層）の炭素を評価できる。 As described above, in the present embodiment, since the silicon crystal is subjected to the boiling treatment in water prior to the DLTS measurement, hydrogen can be introduced into the silicon crystal without losing the surface layer of the silicon crystal. By this introduction, among the impurity levels in the silicon crystal, the level of the complex containing carbon and hydrogen can be activated, and this level can be measured with high sensitivity by DLTS measurement. As a result, the presence of trace carbon in the silicon crystal can be detected. As described above, in the present embodiment, the carbon-related level density and the carbon concentration in the crystal can be easily and stably measured including the surface layer of the silicon crystal. This makes it possible to evaluate carbon in the vicinity of the surface layer of the silicon crystal (for example, the epitaxial layer).
以下、本発明の実施例及び比較例を挙げて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。 Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.
（比較例１）
ＦＺ法により、直径６インチ、方位＜１００＞、ｎ型、抵抗率が１０Ωｃｍで炭素を０．０３ｐｐｍａ程度含むシリコン結晶棒を引き上げた。このシリコン結晶棒を加工してシリコンウェーハとした。このシリコンウェーハを２群に分け、１群は何もせず、もう１群は、ＨＦとＨＮＯ３の混酸により表層をエッチングした。その後、ただちに２群のウェーハともＨＦによる酸化膜除去を施し、ショットキー電極とオーミック電極をそれぞれ表裏面に形成後、ＤＬＴＳ測定を行った。その結果、混酸処理を行った試料では、８×１０１０ｃｍ−３程度の炭素関連準位Ｅ３の密度が得られたのに対し、混酸処理を行わなかった試料では、２×１０１０ｃｍ−３程度の炭素関連準位Ｅ３の密度が得られ、混酸処理がＥ３準位活性化の効果をもつことがわかった。
(Comparative Example 1)
By the FZ method, a silicon crystal rod having a diameter of 6 inches, an orientation <100>, an n-type, a resistivity of 10 Ωcm, and containing about 0.03 ppma of carbon was pulled up. This silicon crystal rod was processed into a silicon wafer. Divide the silicon wafer into two groups, one group does nothing, the other group was etched surface by mixed acid of HF and HNO 3. Immediately after that, both groups of wafers were subjected to oxide film removal by HF, Schottky electrodes and ohmic electrodes were formed on the front and back surfaces, respectively, and then DLTS measurement was performed. As a result, the density of the carbon-related level E3 of about 8 × 10 10 cm -3 was obtained in the sample subjected to the mixed acid treatment, whereas the density of the carbon-related level E3 was obtained in the sample not subjected to the mixed acid treatment, whereas the sample not subjected to the mixed acid treatment was 2 × 10 10 cm −. A density of about 3 carbon-related level E3 was obtained, and it was found that the mixed acid treatment had the effect of activating the E3 level.
（実施例１）
ＦＺ法により、直径６インチ、方位＜１００＞、ｎ型、抵抗率が１０Ωｃｍで炭素を０．０３ｐｐｍａ程度含むシリコン結晶棒を引き上げた。このシリコン結晶棒を加工してシリコンウェーハとした。このシリコンウェーハに対し、９５℃の水中で３０分の煮沸処理を施した後、ＨＦによる酸化膜除去を施し、ショットキー電極とオーミック電極をそれぞれ表裏面に形成後、ＤＬＴＳ測定を行った。その結果、４×１０１０ｃｍ−３程度の炭素関連準位Ｅ３の密度が得られ、比較例１のＤＬＴＳ電極形成前に何ら処理を行わない場合の測定結果よりも、２倍程度のＥ３準位密度を得ることができ、表層における炭素存在の定性的判断を確実に行うことができた。
(Example 1)
By the FZ method, a silicon crystal rod having a diameter of 6 inches, an orientation <100>, an n-type, a resistivity of 10 Ωcm, and containing about 0.03 ppma of carbon was pulled up. This silicon crystal rod was processed into a silicon wafer. This silicon wafer was boiled in water at 95 ° C. for 30 minutes, then the oxide film was removed by HF, Schottky electrodes and ohmic electrodes were formed on the front and back surfaces, and then DLTS measurement was performed. As a result, a density of carbon-related level E3 of about 4 × 10 10 cm -3 was obtained, which was about twice as much as the measurement result when no treatment was performed before the DLTS electrode formation of Comparative Example 1. The position density could be obtained, and the qualitative judgment of the carbon presence in the surface layer could be surely performed.
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、かつ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 example, and any object having substantially the same structure as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. Is included in the technical scope of.
例えば、上記実施例では、Ｈ−Ｃ複合体の準位Ｅ３の密度をＤＬＴＳ測定した例を示したが、Ｈ、Ｃを少なくとも含む準位Ｅ３以外の不純物準位（Ｈ−Ｃ−Ｏ複合体など）の密度をＤＬＴＳ測定して、その測定値に基づいてシリコン中の炭素濃度を評価しても良いし、特許文献１のように、Ｈ−Ｃ複合体、Ｈ−Ｃ−Ｏ複合体の準位Ｅ１、Ｅ２、Ｅ３の密度をＤＬＴＳ測定して、得られた密度の合計値に基づいて、シリコン中の炭素濃度を評価しても良い。 For example, in the above-mentioned example, the density of the level E3 of the HC complex was measured by DLTS, but the impurity level (H-CO complex) other than the level E3 containing at least H and C was shown. Etc.) may be measured by DLTS and the carbon concentration in silicon may be evaluated based on the measured value, or as in Patent Document 1, the HC complex and the HCO complex may be evaluated. The density of levels E1, E2, and E3 may be measured by DLTS, and the carbon concentration in silicon may be evaluated based on the total value of the obtained densities.
Claims (5)
前記水煮沸工程後、前記シリコン結晶に含まれる炭素と水素を少なくとも含んだ複合体の不純物準位の密度をＤＬＴＳ法により測定する測定工程と、
前記密度に基づいて前記シリコン結晶中の炭素濃度を得る取得工程と、
を備えることを特徴とするシリコン中の炭素測定方法。 A water boiling process in which silicon crystals are boiled in water at 60 to 100 ° C.
A measuring step of measuring after the water boiling step, the density of the impurity level including at least complex carbon and hydrogen contained in the silicon crystal by DLTS method,
The acquisition step of obtaining the carbon concentration in the silicon crystal based on the density, and
A method for measuring carbon in silicon, which comprises.
炭素濃度が既知の前記シリコン結晶である第１シリコン結晶を６０〜１００℃の水で煮沸する第１水煮沸工程と、 The first water boiling step of boiling the first silicon crystal, which is the silicon crystal having a known carbon concentration, in water at 60 to 100 ° C.
炭素濃度が未知の前記シリコン結晶である第２シリコン結晶を６０〜１００℃の水で煮沸する第２水煮沸工程とを備え、 It is provided with a second water boiling step of boiling the second silicon crystal, which is the silicon crystal having an unknown carbon concentration, in water at 60 to 100 ° C.
前記測定工程は、 The measurement step is
前記第１シリコン結晶に対して前記密度をＤＬＴＳ法により測定する第１測定工程と、 The first measuring step of measuring the density of the first silicon crystal by the DLTS method, and
前記第２シリコン結晶に対して前記密度をＤＬＴＳ法により測定する第２測定工程とを備え、 The second silicon crystal is provided with a second measuring step of measuring the density by the DLTS method.
前記取得工程は、 The acquisition process is
前記第１シリコン結晶から得られた前記密度と、前記第１シリコン結晶の炭素濃度とに基づいて、前記密度とシリコン中の炭素濃度との相関関係を取得する相関関係取得工程と、 A correlation acquisition step of acquiring a correlation between the density and the carbon concentration in silicon based on the density obtained from the first silicon crystal and the carbon concentration of the first silicon crystal.
前記第２シリコン結晶から得られた前記密度と、前記相関関係とに基づいて、前記第２シリコン結晶中の炭素濃度を得る濃度取得工程とを備えることを特徴とする請求項１に記載のシリコン中の炭素測定方法。 The silicon according to claim 1, further comprising a concentration acquisition step of obtaining a carbon concentration in the second silicon crystal based on the density obtained from the second silicon crystal and the correlation. Carbon measurement method inside.
前記測定工程では、エネルギーが０．１５ｅＶの準位の密度を測定することを特徴とする請求項１〜４のいずれか１項に記載のシリコン中の炭素測定方法。 The method for measuring carbon in silicon according to any one of claims 1 to 4, wherein in the measuring step, a density at a level having an energy of 0.15 eV is measured.
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