JP7616103B2 - Semiconductor substrate evaluation method - Google Patents
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- 239000000758 substrate Substances 0.000 title claims description 113
- 239000004065 semiconductor Substances 0.000 title claims description 97
- 238000011156 evaluation Methods 0.000 title description 13
- 238000004140 cleaning Methods 0.000 claims description 53
- 238000007254 oxidation reaction Methods 0.000 claims description 43
- 230000001698 pyrogenic effect Effects 0.000 claims description 43
- 230000003647 oxidation Effects 0.000 claims description 38
- 238000000034 method Methods 0.000 claims description 30
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 23
- 229910052710 silicon Inorganic materials 0.000 claims description 23
- 239000010703 silicon Substances 0.000 claims description 23
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- 229910052814 silicon oxide Inorganic materials 0.000 claims description 5
- 230000003746 surface roughness Effects 0.000 claims description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 230000001590 oxidative effect Effects 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- 238000009792 diffusion process Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 230000005856 abnormality Effects 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 239000012895 dilution Substances 0.000 description 2
- 238000010790 dilution Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 230000005587 bubbling Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 238000009279 wet oxidation reaction Methods 0.000 description 1
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Description
本発明は、半導体基板の評価方法に関する。 The present invention relates to a method for evaluating a semiconductor substrate.
半導体集積回路素子の多層化、薄型化に伴って、素子を構成する各種膜についてより一層の薄膜化が要求されている。このような極薄のシリコン酸化膜を面内であるいは基板間で均一にかつ再現性良く形成するためには、半導体基板に予め形成される自然酸化膜の影響を無視することは不可能となっている（特許文献１）。なお、本明細書においては、半導体基板を洗浄することで形成される酸化膜（化学酸化膜と呼ばれることもある）も、自然酸化膜に含まれるものとする。 As semiconductor integrated circuit elements become more multi-layered and thinner, there is a demand for the various films that make up the elements to be even thinner. In order to form such extremely thin silicon oxide films uniformly and reproducibly within a surface or between substrates, it is impossible to ignore the influence of the natural oxide film that is formed in advance on the semiconductor substrate (Patent Document 1). In this specification, the oxide film (sometimes called a chemical oxide film) that is formed by cleaning the semiconductor substrate is also included in the natural oxide film.
本発明者らの調査・研究では、例えば、半導体基板の洗浄方法が異なった場合、その後の熱酸化膜の膜厚に違いがあることが分かっている（特許文献２，３）。例えば、ＳＣ１洗浄温度については、洗浄に使用する温度帯によっては、５℃変化しただけでも、大きな影響があることがわかっている。さらに熱酸化後の酸化膜の違いが発生することにより、半導体集積回路素子の特性のバラツキや歩留まりの低下などの問題が懸念されている。 The inventors' research and studies have revealed that, for example, when the cleaning method for semiconductor substrates is different, the thickness of the thermal oxide film formed afterwards differs (Patent Documents 2 and 3). For example, it is known that even a change of just 5°C in the SC1 cleaning temperature can have a significant impact, depending on the temperature range used for cleaning. Furthermore, there are concerns that differences in the oxide film after thermal oxidation can lead to problems such as variations in the characteristics of semiconductor integrated circuit elements and reduced yields.
しかしながら、この膜厚の違いは、必ずしも熱酸化前の自然酸化膜厚の膜厚によらないことも分かっているが、膜厚変動が小さいために、外乱によるばらつきなのか、実際の表面の影響（例えば洗浄条件の変動）なのかを切り分けるために多大の労力を必要としているのが実情である。熱酸化膜の膜厚へ影響する半導体基板の表面状態を精度高く評価する手法が求められる。 However, it is known that this difference in film thickness does not necessarily depend on the thickness of the native oxide film before thermal oxidation. However, because the variation in film thickness is small, the reality is that it requires a great deal of effort to distinguish whether the variation is due to external disturbances or the influence of the actual surface (for example, fluctuations in cleaning conditions). A method is needed to accurately evaluate the surface condition of the semiconductor substrate that affects the thickness of the thermal oxide film.
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、熱酸化膜の膜厚へ影響する半導体基板の表面品質を精度高く評価する半導体基板の評価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 aims to provide a method for evaluating semiconductor substrates that can accurately evaluate the surface quality of the semiconductor substrate, which affects the thickness of the thermal oxide film.
本発明は、上記目的を達成するためになされたものであり、半導体基板の評価方法であって、評価対象の半導体基板として同一の表面品質水準を有する複数の半導体基板を準備し、前記複数の半導体基板を同一の洗浄条件で洗浄し、前記複数の半導体基板から、前記洗浄により形成された自然酸化膜の除去を行うことなくドライ酸化してドライ酸化膜を形成した半導体基板と、前記洗浄により形成された自然酸化膜の除去を行うことなくパイロジェニック酸化してパイロジェニック酸化膜を形成した半導体基板とを個別に作製し、前記ドライ酸化膜の膜厚と前記パイロジェニック酸化膜の膜厚の比に基づいて、前記半導体基板の表面品質の評価を行うことを特徴とする半導体基板の評価方法を提供する。 The present invention has been made to achieve the above-mentioned object, and provides a method for evaluating semiconductor substrates, which comprises preparing a plurality of semiconductor substrates having the same surface quality level as semiconductor substrates to be evaluated, cleaning the plurality of semiconductor substrates under the same cleaning conditions, and separately preparing from the plurality of semiconductor substrates a semiconductor substrate on which a dry oxide film is formed by dry oxidation without removing the native oxide film formed by the cleaning, and a semiconductor substrate on which a pyrogenic oxide film is formed by pyrogenic oxidation without removing the native oxide film formed by the cleaning, and evaluating the surface quality of the semiconductor substrates based on the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film.
このような半導体基板の評価方法によれば、ドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比に基づいて半導体基板の表面品質を精度高く評価する半導体基板の評価方法を提供することができる。 This method for evaluating semiconductor substrates can provide a method for evaluating the surface quality of a semiconductor substrate with high accuracy based on the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film.
このとき、ドライ酸化膜及びパイロジェニック酸化膜の膜厚を、０．１～１０ｎｍとすることができる。 At this time, the film thickness of the dry oxide film and pyrogenic oxide film can be set to 0.1 to 10 nm.
このように膜厚が薄い範囲の場合に、特に、半導体基板の表面品質の評価をより精度高く行うことができる。 In this way, when the film thickness is in the thin range, it is possible to evaluate the surface quality of the semiconductor substrate with greater accuracy.
このとき、表面品質を、半導体基板の最終洗浄で形成された自然酸化膜の膜質及び／又は厚さとすることができる。また、表面品質を、半導体基板の表面粗さとすることができる。 In this case, the surface quality can be the film quality and/or thickness of the native oxide film formed in the final cleaning of the semiconductor substrate. The surface quality can also be the surface roughness of the semiconductor substrate.
本発明に係る半導体基板の評価方法は、特にこのような半導体基板の表面品質の評価に好適である。 The semiconductor substrate evaluation method according to the present invention is particularly suitable for evaluating the surface quality of such semiconductor substrates.
このとき、半導体基板をシリコン基板、ドライ酸化膜及びパイロジェニック酸化膜をシリコン酸化膜とすることができる。 In this case, the semiconductor substrate can be a silicon substrate, and the dry oxide film and pyrogenic oxide film can be silicon oxide films.
本発明に係る半導体基板の評価方法は、特にシリコン基板に形成されるシリコン酸化膜に対して好適である。 The semiconductor substrate evaluation method according to the present invention is particularly suitable for silicon oxide films formed on silicon substrates.
以上のように、本発明の半導体基板の評価方法によれば、ドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比の違いから半導体基板の表面品質を精度高く評価する半導体基板の評価方法を提供することができる。また、熱酸化膜厚に影響する半導体基板製造に係る工程条件を明確にすることが可能になる。 As described above, the semiconductor substrate evaluation method of the present invention can provide a semiconductor substrate evaluation method that accurately evaluates the surface quality of a semiconductor substrate based on the difference in the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film. It also makes it possible to clarify the process conditions related to semiconductor substrate manufacturing that affect the thickness of the thermal oxide film.
以下、本発明を詳細に説明するが、本発明はこれらに限定されるものではない。 The present invention is described in detail below, but is not limited to these.
上述のように、熱酸化膜の膜厚へ影響する半導体基板の表面品質を精度高く評価する半導体基板の評価方法が求められていた。 As mentioned above, there was a need for a method for evaluating semiconductor substrates that could accurately evaluate the surface quality of the semiconductor substrate, which affects the thickness of the thermal oxide film.
本発明者らは、上記課題について鋭意検討を重ねた結果、半導体基板の評価方法であって、評価対象の半導体基板として同一の表面品質水準を有する複数の半導体基板を準備し、前記複数の半導体基板を同一の洗浄条件で洗浄し、前記複数の半導体基板から、前記洗浄により形成された自然酸化膜の除去を行うことなくドライ酸化してドライ酸化膜を形成した半導体基板と、前記洗浄により形成された自然酸化膜の除去を行うことなくパイロジェニック酸化してパイロジェニック酸化膜を形成した半導体基板とを個別に作製し、前記ドライ酸化膜の膜厚と前記パイロジェニック酸化膜の膜厚の比に基づいて、前記半導体基板の表面品質の評価を行うことを特徴とする半導体基板の評価方法により、半導体基板の表面品質を精度高く評価できることを見出し、本発明を完成した。 As a result of intensive research into the above-mentioned problem, the inventors have found that the surface quality of a semiconductor substrate can be evaluated with high accuracy by a method for evaluating a semiconductor substrate, which comprises preparing a plurality of semiconductor substrates having the same surface quality level as semiconductor substrates to be evaluated, cleaning the plurality of semiconductor substrates under the same cleaning conditions, separately preparing a semiconductor substrate having a dry oxide film formed by dry oxidation without removing the native oxide film formed by the cleaning, and a semiconductor substrate having a pyrogenic oxide film formed by pyrogenic oxidation without removing the native oxide film formed by the cleaning, and evaluating the surface quality of the semiconductor substrate based on the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film, thereby completing the present invention.
以下、図面を参照して説明する。 The following explanation will be given with reference to the drawings.
シリコン基板などの半導体基板上に薄い熱酸化膜を形成するためには、一般的には、半導体基板を石英チューブの外側にヒータやランプを備えた熱処理炉内に設置して、半導体基板を加熱した状態で酸素を炉内に導入して、半導体を酸化することで半導体酸化膜を作製する。このような手法により１０ｎｍ以下の薄い熱酸化膜を形成するためには、温度を９００℃以下に下げる、酸素の分圧を下げるなどの手段をとる。このように酸化種として酸素を用いる方法を一般的にドライ酸化と呼び、形成された酸化膜をドライ酸化膜などと呼称することもある。 To form a thin thermal oxide film on a semiconductor substrate such as a silicon substrate, the semiconductor substrate is generally placed in a heat treatment furnace equipped with a heater or lamp on the outside of a quartz tube, and oxygen is introduced into the furnace while the semiconductor substrate is heated to oxidize the semiconductor, producing a semiconductor oxide film. In order to form a thin thermal oxide film of 10 nm or less using this method, measures such as lowering the temperature to 900°C or lower and lowering the partial pressure of oxygen are taken. This method of using oxygen as the oxidizing species is generally called dry oxidation, and the oxide film formed is sometimes called a dry oxide film.
一方で、酸化種として水（加熱水蒸気）を用いるパイロジェニック酸化（パイロ酸化、ウエット酸化ということもある）と呼ばれる方法がある。このようなパイロジェニック酸化法で形成された酸化膜を、パイロジェニック酸化膜（パイロ酸化膜）と称することもある。加熱水蒸気の導入方法としては、水を酸素でバブリングして炉内に供給する方法や、酸素と水素を炉内に個別に導入し炉内で燃焼させて水を生成させる方法などがある。特に、清浄度や安定性、安全性を考慮して、近年ではガス導入部に予備燃焼室を備え、この予備燃焼室で予め酸素と水素を燃焼させて、熱処理炉内へ導入する方法が一般的である。このパイロ酸化処理の酸化速度はドライ酸化に比べて大きく、一般的には厚い酸化膜を形成するために用いられることが多い（非特許文献１）。 On the other hand, there is a method called pyrogenic oxidation (sometimes called pyro-oxidation or wet oxidation) that uses water (heated steam) as the oxidizing species. The oxide film formed by this pyrogenic oxidation method is sometimes called pyrogenic oxide film (pyro-oxidation film). Methods for introducing heated steam include bubbling water with oxygen and supplying it to the furnace, and separately introducing oxygen and hydrogen into the furnace and burning them in the furnace to generate water. In particular, in consideration of cleanliness, stability, and safety, a method has become common in recent years to provide a preliminary combustion chamber at the gas inlet, burn oxygen and hydrogen in advance in this preliminary combustion chamber, and introduce them into the heat treatment furnace. The oxidation rate of this pyro-oxidation process is faster than that of dry oxidation, and it is generally used to form thick oxide films (Non-Patent Document 1).
この半導体の酸化には、酸化種が酸化膜を拡散して酸化膜／半導体界面に到達する必要があり、酸化速度は酸化種の拡散によって律速されるために、酸化時間とともに（熱酸化膜厚の増加ととともに）遅くなっていく。しかしながら、酸化膜厚は酸化膜厚が薄い場合や酸化の初期のように酸化種の拡散の影響が小さい場合は、拡散の影響は小さく、酸化膜／半導体界面の反応（構造）にも依存する。 For this type of semiconductor oxidation, the oxidizing species must diffuse through the oxide film to reach the oxide film/semiconductor interface, and the oxidation rate is determined by the diffusion of the oxidizing species, so it slows down with oxidation time (as the thermal oxide film thickness increases). However, when the oxide film is thin or the effect of the diffusion of the oxidizing species is small, such as in the early stages of oxidation, the effect of diffusion is small, and the oxide film thickness also depends on the reaction (structure) at the oxide film/semiconductor interface.
このように、薄い酸化膜では半導体基板表面に形成されている自然酸化膜の影響も無視することはできず、自然酸化膜の膜厚や膜質が熱酸化膜の膜厚にも影響する。 As such, with thin oxide films, the influence of the natural oxide film formed on the surface of the semiconductor substrate cannot be ignored, and the thickness and quality of the natural oxide film also affect the thickness of the thermal oxide film.
本発明者らはこれまでに、例えば、半導体基板の洗浄条件（洗浄液の種類や組成等）の違いが、洗浄により半導体基板表面に形成される自然酸化膜の構成（膜質、膜厚等の品質）に影響を及ぼすことを解明してきた（特許文献２，３）。 The inventors have previously elucidated that, for example, differences in the cleaning conditions for semiconductor substrates (such as the type and composition of the cleaning solution) affect the structure (quality of the film, such as film quality and thickness) of the native oxide film formed on the surface of the semiconductor substrate by cleaning (Patent Documents 2 and 3).
本発明者らはさらに検討を行い、熱酸化方法、具体的にはドライ酸化とパイロジェニック酸化による酸化種の違いに着目して、酸化種が異なり、酸化機構が異なることを利用することに想到した。評価対象の半導体基板として同一の表面品質水準を有する複数の半導体基板を準備し、同一の洗浄条件で洗浄を行い同じ表面品質の半導体基板とする。これらの半導体基板に対し、洗浄により形成された自然酸化膜の除去を行うことなく、ドライ酸化とパイロジェニック酸化のそれぞれを個別に行い、ドライ酸化膜が形成された半導体基板と、パイロジェニック酸化膜が形成された半導体基板とを作製する。このようにして作製した半導体基板の熱酸化膜の膜厚測定を行って得られたドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比（以下、単に「酸化膜厚比」ということもある）に基づいて、半導体基板の表面品質の評価を行う。このとき、基準となる洗浄条件を決めて、洗浄条件を振った時の酸化膜厚の差分を求め、この差分を用いてドライ酸化とパイロジェニック酸化の比を取ることもできる。このようにすれば、半導体基板の表面品質の評価を精度高く行うことが可能となること、さらに、表面品質の差を評価することが可能になることを見出し、本発明を完成した。 The inventors further studied the thermal oxidation method, specifically, focusing on the difference in the oxidation species due to dry oxidation and pyrogenic oxidation, and came up with the idea of utilizing the difference in the oxidation species and the oxidation mechanism. A plurality of semiconductor substrates having the same surface quality level are prepared as semiconductor substrates to be evaluated, and are cleaned under the same cleaning conditions to obtain semiconductor substrates with the same surface quality. These semiconductor substrates are individually subjected to dry oxidation and pyrogenic oxidation without removing the natural oxide film formed by cleaning, and a semiconductor substrate with a dry oxide film and a semiconductor substrate with a pyrogenic oxide film are produced. The surface quality of the semiconductor substrate is evaluated based on the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film (hereinafter, sometimes simply referred to as the "oxide film thickness ratio") obtained by measuring the thickness of the thermal oxide film of the semiconductor substrate produced in this way. At this time, the standard cleaning conditions are determined, and the difference in the oxide film thickness when the cleaning conditions are changed is calculated, and the ratio of dry oxidation to pyrogenic oxidation can be obtained using this difference. It was discovered that this makes it possible to evaluate the surface quality of semiconductor substrates with high accuracy, and furthermore, to evaluate differences in surface quality, leading to the completion of the present invention.
例えば、基準となる酸化膜厚比を設定しておき、この基準値と比較することで半導体基板の表面品質の変化を把握することができる。 For example, a reference oxide film thickness ratio can be set and changes in the surface quality of the semiconductor substrate can be identified by comparing with this reference value.
また、本発明に係る半導体基板の評価方法を用いれば、半導体基板の表面品質の評価に基づいて、洗浄工程など熱酸化前の工程の管理を行うことも可能となる。後述の実施例に示すように、酸化膜厚比の変化は、半導体基板の洗浄条件の変化をより感度高く反映する。このことを利用し、洗浄工程の評価を行うことも好ましい。例えば、通常の製品を処理する洗浄工程を定期的なモニタリングとして、酸化膜厚比の推移を把握することで、洗浄条件の変化や異常の発生などを検出することも可能となる。 In addition, by using the semiconductor substrate evaluation method according to the present invention, it is possible to manage processes before thermal oxidation, such as the cleaning process, based on the evaluation of the surface quality of the semiconductor substrate. As shown in the examples described later, changes in the oxide film thickness ratio more sensitively reflect changes in the cleaning conditions of the semiconductor substrate. It is also preferable to utilize this to evaluate the cleaning process. For example, by periodically monitoring the cleaning process for processing normal products and understanding the trends in the oxide film thickness ratio, it is possible to detect changes in cleaning conditions and the occurrence of abnormalities.
なお、ドライ酸化膜及びパイロジェニック酸化膜を形成する時の酸化処理における酸化膜厚の狙い値は、ドライ酸化及びパイロジェニック酸化で同程度の膜厚とすることが好ましく、膜厚の範囲としては０．１～１０ｎｍとすることが好ましい。本発明に係る半導体基板の評価方法は、このような膜厚範囲の場合に特に、半導体基板の表面品質の評価をより精度高く行うことができる。 The target oxide film thickness in the oxidation process for forming the dry oxide film and pyrogenic oxide film is preferably approximately the same for dry oxidation and pyrogenic oxidation, and the film thickness range is preferably 0.1 to 10 nm. The semiconductor substrate evaluation method according to the present invention can more accurately evaluate the surface quality of the semiconductor substrate, especially in the case of such a film thickness range.
表面品質を、半導体基板の最終洗浄で形成された自然酸化膜の膜質及び／又は厚さとすることができる。本発明に係る半導体基板の評価方法では、特に、半導体基板の最終洗浄で形成された自然酸化膜の膜質が、ドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比に強く影響を及ぼすため、より精度の高い評価を行うことができる。 The surface quality can be the quality and/or thickness of the native oxide film formed during the final cleaning of the semiconductor substrate. In the semiconductor substrate evaluation method according to the present invention, the quality of the native oxide film formed during the final cleaning of the semiconductor substrate has a strong influence on the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film, and therefore a more accurate evaluation can be performed.
また、表面品質を、半導体基板の表面粗さとすることもできる。半導体基板の洗浄条件は半導体基板の表面粗さにも影響を及ぼす。このため、酸化膜／半導体界面の影響を強く反映するドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比を用いる本発明に係る半導体基板の評価方法では、半導体基板の表面粗さを精度高く評価することも可能である。 Surface quality can also be the surface roughness of a semiconductor substrate. The cleaning conditions of a semiconductor substrate also affect the surface roughness of the semiconductor substrate. Therefore, the semiconductor substrate evaluation method of the present invention, which uses the ratio of the film thickness of the dry oxide film to the film thickness of the pyrogenic oxide film, which strongly reflects the influence of the oxide film/semiconductor interface, can also accurately evaluate the surface roughness of a semiconductor substrate.
半導体基板としてはシリコン基板が好ましい。この場合、ドライ酸化膜及びパイロジェニック酸化膜はシリコン酸化膜である。本発明に係る半導体基板の評価方法は、特にシリコン基板の評価において有効である。 The semiconductor substrate is preferably a silicon substrate. In this case, the dry oxide film and the pyrogenic oxide film are silicon oxide films. The semiconductor substrate evaluation method according to the present invention is particularly effective in evaluating silicon substrates.
なお、ドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比の計算は、パイロジェニック酸化膜厚／ドライ酸化膜厚、ドライ酸化膜厚／パイロジェニック酸化膜厚のどちらとしてもよい。 The ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film can be calculated as either pyrogenic oxide film thickness/dry oxide film thickness or dry oxide film thickness/pyrogenic oxide film thickness.
以下、実施例を挙げて本発明について具体的に説明するが、これは本発明を限定するものではない。 The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.
（実施例）
直径３００ｍｍ、ボロンドープの通常抵抗率（約１０Ωｃｍ）のシリコン基板を複数枚準備した。準備した複数枚のシリコン基板は、すべて同一の表面品質水準を有するものである。まず、シリコン基板表面に形成されている自然酸化膜の影響を排除し初期化するために０．５％ＨＦで洗浄（すべてのシリコン基板について共通）を行った。次に、洗浄液の温度を４０、４５、５０、６０、７０℃としてＳＣ１洗浄（ＮＨ４ＯＨ濃度：３％）を行った。１つの洗浄液温度水準について、複数枚のシリコン基板を洗浄処理した。
(Example)
A plurality of silicon substrates with a diameter of 300 mm and a normal resistivity (about 10 Ωcm) doped with boron were prepared. All of the prepared silicon substrates had the same surface quality level. First, they were cleaned with 0.5% HF (common to all silicon substrates) to eliminate the influence of the natural oxide film formed on the silicon substrate surface and to initialize it. Next, SC1 cleaning (NH 4 OH concentration: 3%) was performed with the cleaning solution temperature set to 40, 45, 50, 60, and 70° C. A plurality of silicon substrates were cleaned for one cleaning solution temperature level.
洗浄処理を行ったシリコン基板を用い、各洗浄液温度水準のシリコン基板について、表面に形成された自然酸化膜を除去することなく、パイロ酸化（７００℃、Ｎ２希釈、酸化時間：２３分）してパイロ酸化膜を形成したシリコン基板と、ドライ酸化（９００℃、Ｎ２希釈、酸化時間２３分）してドライ酸化膜を形成したシリコン基板を個別に作製した。熱酸化後の熱酸化膜厚を分光エリプソメータで基板中の面内５点を測定して膜厚の平均値を計算し、ＳＣ１洗浄温度が４０℃のときの酸化膜厚を基準として、各ＳＣ１洗浄温度における酸化膜厚の差分を取って、ドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の差分の比（パイロジェニック酸化膜厚／ドライ酸化膜厚）を求め、ＳＣ１洗浄温度がドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比に与える影響を調査した。その結果、図１に示すように、ＳＣ１洗浄温度によってドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比が変化することがわかった。 Using silicon substrates that had been cleaned, silicon substrates with pyro-oxidation (700°C, N2 dilution, oxidation time: 23 minutes) to form pyro-oxidation films and silicon substrates with dry oxidation (900°C, N2 dilution, oxidation time: 23 minutes) to form dry oxide films were individually prepared without removing the natural oxide film formed on the surface of the silicon substrates at each cleaning solution temperature level. The thermal oxide film thickness after thermal oxidation was measured at five points on the substrate surface with a spectroscopic ellipsometer to calculate the average film thickness, and the oxide film thickness at each SC1 cleaning temperature was taken as the standard with the oxide film thickness at 40°C, and the ratio of the difference between the dry oxide film thickness and the pyrogenic oxide film thickness (pyrogenic oxide film thickness/dry oxide film thickness) was obtained to investigate the effect of the SC1 cleaning temperature on the ratio between the dry oxide film thickness and the pyrogenic oxide film thickness. As a result, it was found that the ratio between the dry oxide film thickness and the pyrogenic oxide film thickness changes depending on the SC1 cleaning temperature, as shown in FIG. 1.
ＳＣ１洗浄温度は、シリコン基板表面の粗さと、シリコン基板表面に洗浄で形成された自然酸化膜の品質に影響を及ぼすと考えられる。本実施例で示されたように、自然酸化膜を除去せずにドライ酸化を行ったシリコン基板と、自然酸化膜を除去せずにパイロ酸化を行ったシリコン基板とから測定、計算できるドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比（本実施例ではパイロ酸化膜厚／ドライ酸化膜厚）は、シリコン基板の表面品質の違いを感度高く反映できるため、ドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比に基づいて評価を行うことで、半導体基板の表面品質（本実施例の場合は、シリコン基板表面の粗さと、シリコン基板表面に洗浄で形成された自然酸化膜の品質）の評価を精度高く行うことが可能であることがわかった。 It is believed that the SC1 cleaning temperature affects the roughness of the silicon substrate surface and the quality of the natural oxide film formed on the silicon substrate surface by cleaning. As shown in this example, the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film (pyro-oxide film thickness/dry oxide film thickness in this example), which can be measured and calculated from a silicon substrate that has been dry-oxidized without removing the natural oxide film and a silicon substrate that has been pyro-oxidized without removing the natural oxide film, can sensitively reflect the difference in the surface quality of the silicon substrate. Therefore, it was found that it is possible to accurately evaluate the surface quality of the semiconductor substrate (in this example, the roughness of the silicon substrate surface and the quality of the natural oxide film formed on the silicon substrate surface by cleaning) by performing an evaluation based on the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film.
また、この結果をもとにすれば、洗浄条件を推定したり洗浄装置の日常管理を行ったりすることも可能になる。例えば、ドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比が通常と違う比になった場合は、洗浄装置の温度管理に異常があると判断できる。本例はわかりやすいように薬液温度を振ったが、日常管理としてドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比を決めてモニタリングをしていけば、洗浄条件の変動を検知することも可能である。 Based on these results, it is also possible to estimate cleaning conditions and perform daily management of the cleaning equipment. For example, if the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film becomes different from normal, it can be determined that there is an abnormality in the temperature management of the cleaning equipment. In this example, the chemical solution temperature was varied for ease of understanding, but if the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film is determined and monitored as part of daily management, it is also possible to detect fluctuations in the cleaning conditions.
以上の通り、本発明の実施例によれば、ドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比が、ＳＣ１洗浄条件（温度）の変動を精度高く反映していることがわかった。ドライ酸化膜の膜厚とパイロジェニック酸化膜の膜厚の比を用いると、半導体基板の品質を精度高く評価できることがわかった。また、これを利用すれば、洗浄条件の変化の影響をより精度高く評価でき、洗浄工程や洗浄機の管理にも適用できることがわかった。さらに、従来の方法では測定、評価できなかった半導体基板の表面品質の変化を評価することも可能と考えられる。 As described above, according to the embodiment of the present invention, it was found that the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film accurately reflects the fluctuations in the SC1 cleaning conditions (temperature). It was found that the quality of the semiconductor substrate can be evaluated with high accuracy by using the ratio of the thickness of the dry oxide film to the thickness of the pyrogenic oxide film. It was also found that this can be used to more accurately evaluate the effects of changes in cleaning conditions, and can be applied to the management of cleaning processes and cleaning machines. Furthermore, it is believed that it will be possible to evaluate changes in the surface quality of semiconductor substrates that could not be measured or evaluated using conventional methods.
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-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and provides similar effects is included within the technical scope of the present invention.
Claims (5)
評価対象の半導体基板として同一の表面品質水準を有する複数の半導体基板を準備し、前記複数の半導体基板を同一の洗浄条件で洗浄し、前記複数の半導体基板から、前記洗浄により形成された自然酸化膜の除去を行うことなくドライ酸化してドライ酸化膜を形成した半導体基板と、前記洗浄により形成された自然酸化膜の除去を行うことなくパイロジェニック酸化してパイロジェニック酸化膜を形成した半導体基板とを個別に作製し、
前記ドライ酸化膜の膜厚と前記パイロジェニック酸化膜の膜厚の比に基づいて、前記半導体基板の表面品質の評価を行うことを特徴とする半導体基板の評価方法。 A method for evaluating a semiconductor substrate, comprising:
preparing a plurality of semiconductor substrates having the same surface quality level as semiconductor substrates to be evaluated, cleaning the plurality of semiconductor substrates under the same cleaning conditions, and individually preparing, from the plurality of semiconductor substrates, a semiconductor substrate on which a dry oxide film is formed by dry oxidation without removing a native oxide film formed by the cleaning, and a semiconductor substrate on which a pyrogenic oxide film is formed by pyrogenic oxidation without removing a native oxide film formed by the cleaning,
A method for evaluating a semiconductor substrate, comprising: evaluating a surface quality of the semiconductor substrate based on a ratio of a thickness of the dry oxide film to a thickness of the pyrogenic oxide film.
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