JP7652092B2 - Semiconductor substrate evaluation method - Google Patents
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- JP7652092B2 JP7652092B2 JP2022007511A JP2022007511A JP7652092B2 JP 7652092 B2 JP7652092 B2 JP 7652092B2 JP 2022007511 A JP2022007511 A JP 2022007511A JP 2022007511 A JP2022007511 A JP 2022007511A JP 7652092 B2 JP7652092 B2 JP 7652092B2
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- 239000000758 substrate Substances 0.000 title claims description 103
- 239000004065 semiconductor Substances 0.000 title claims description 87
- 238000011156 evaluation Methods 0.000 title description 14
- 238000004140 cleaning Methods 0.000 claims description 34
- 238000000034 method Methods 0.000 claims description 29
- 230000001698 pyrogenic effect Effects 0.000 claims description 25
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 19
- 229910052710 silicon Inorganic materials 0.000 claims description 19
- 239000010703 silicon Substances 0.000 claims description 19
- 230000001590 oxidative effect Effects 0.000 claims description 10
- 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
- 238000007254 oxidation reaction Methods 0.000 description 40
- 230000003647 oxidation Effects 0.000 description 31
- 230000000694 effects Effects 0.000 description 8
- 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
- 239000000243 solution Substances 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 4
- 238000009792 diffusion process Methods 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 3
- 238000011160 research 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
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 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
- 230000035945 sensitivity Effects 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の違い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。そしてこの膜厚の違いは、必ずしも熱酸化前の自然酸化膜厚によらないことも分かっている（特許文献２，３）。 The inventors' research has revealed that, for example, when the cleaning method for semiconductor substrates is different, there is a difference in the thickness of the thermally oxidized film after the thermal oxidation. Furthermore, there are concerns that differences in the oxide film after thermal oxidation may lead to problems such as variations in the characteristics of semiconductor integrated circuit elements and reduced yields. It has also been found that this difference in film thickness does not necessarily depend on the thickness of the natural oxide film before thermal oxidation (Patent Documents 2 and 3).
しかしながら、この熱酸化膜の膜厚差は非常に小さく、外乱によるばらつきなのか、基板の表面品質によるものなのかどうかの判断のためには、熱酸化膜の膜厚差をより大きくして、違いをより明確化する手法が求められる。 However, this difference in thickness of the thermal oxide film is very small, and in order to determine whether the variation is due to external disturbances or to the surface quality of the substrate, a method is required to increase the difference in thickness of the thermal oxide film and make the difference clearer.
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 semiconductor substrates based on differences in the thickness of thermal oxide films.
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、半導体基板の表面に形成された自然酸化膜を除去することなく、前記半導体基板をパイロジェニック酸化して前記半導体基板の表面にパイロジェニック酸化膜を形成し、前記パイロジェニック酸化膜の膜厚に基づいて、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 a semiconductor substrate, which comprises pyrogenically oxidizing the semiconductor substrate to form a pyrogenic oxide film on the surface of the semiconductor substrate without removing a natural oxide film formed on the surface of the semiconductor substrate, and evaluating the surface quality of the semiconductor substrate based on 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、熱酸化膜の膜厚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。 This method for evaluating semiconductor substrates can provide a method for evaluating the surface quality of semiconductor substrates with high accuracy based on differences in the thickness of the thermal oxide film.
このとき、前記パイロジェニック酸化膜の膜厚を、１～１０ｎｍとすることができる。 In this case, the thickness of the pyrogenic oxide film can be set to 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、前記表面品質を、前記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、前記表面品質を、前記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、前記半導体基板をシリコン基板、前記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 pyrogenic oxide film can be a silicon oxide film.
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、熱酸化膜の膜厚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 differences in the thickness of the thermal 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が求められていた。 As mentioned above, there was a need for a method of evaluating semiconductor substrates that could accurately evaluate the surface quality of semiconductor substrates based on differences in the thickness of thermal oxide films.
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、半導体基板の表面に形成された自然酸化膜を除去することなく、前記半導体基板をパイロジェニック酸化して前記半導体基板の表面にパイロジェニック酸化膜を形成し、前記パイロジェニック酸化膜の膜厚に基づいて、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 extensive research into the above-mentioned problem, the inventors discovered that the surface quality of a semiconductor substrate can be evaluated with high accuracy by a method for evaluating a semiconductor substrate, which comprises pyrogenically oxidizing the semiconductor substrate to form a pyrogenic oxide film on the surface of the semiconductor substrate without removing a native oxide film formed on the surface of the semiconductor substrate, and evaluating the surface quality of the semiconductor substrate based on the thickness of the pyrogenic oxide film, and thus completed 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).
本発明者らがさらに検討を行い、熱酸化方法、特にドライ酸化とパイロ酸化を比較したところ、パイロジェニック酸化で形成される酸化膜の膜厚が、特に半導体基板の洗浄条件の影響をより強く受けることが分かった。これは上述の通り、薄い酸化膜では酸化種の拡散以外に酸化膜／半導体界面の影響を強く受けるためである。 The inventors conducted further research and compared thermal oxidation methods, particularly dry oxidation and pyrogenic oxidation, and found that the thickness of the oxide film formed by pyrogenic oxidation is more strongly affected by the cleaning conditions of the semiconductor substrate. This is because, as mentioned above, thin oxide films are strongly affected by the oxide film/semiconductor interface in addition to the diffusion of oxidizing species.
本発明者らは、自然酸化膜が存在する半導体基板を、半導体基板の表面品質の違いに影響される熱酸化膜の膜厚の差がより大きくなるような半導体基板の熱処理方法で酸化、すなわち、自然酸化膜の膜質の影響を反映しやすいパイロジェニック酸化することで、半導体基板の表面品質を精度高く評価できることに想到した。そして、本発明者らは、半導体基板の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ジェニック酸化して半導体基板の表面にパイロジェニック酸化膜を形成し、パイロジェニック酸化膜の膜厚に基づけば、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を見出した。 The inventors have come up with the idea that the surface quality of a semiconductor substrate can be evaluated with high accuracy by oxidizing a semiconductor substrate having a native oxide film using a heat treatment method for the semiconductor substrate that increases the difference in thickness of the thermal oxide film, which is affected by differences in the surface quality of the semiconductor substrate, i.e., by pyrogenic oxidation that is likely to reflect the influence of the film quality of the native oxide film. The inventors have then discovered that it is possible to form a pyrogenic oxide film on the surface of a semiconductor substrate by pyrogenic oxidation without removing the native oxide film formed on the surface of the semiconductor substrate, and to evaluate the surface quality of the semiconductor substrate with high accuracy based on the thickness of the pyrogenic oxide film.
例えば、基準となるパイロジェニック酸化膜の膜厚を設定しておき、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, by setting a standard pyrogenic oxide film thickness and comparing it with this standard value, it is possible to grasp changes in the surface quality of the semiconductor substrate.
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、パイロジェニック酸化による膜厚の変化は、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、熱酸化膜の膜厚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 quality of the semiconductor substrate. As will be shown in the examples described later, the change in film thickness due to pyrogenic oxidation reflects the change in the cleaning conditions of the semiconductor substrate with high sensitivity. 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 progress of the thickness of the thermal oxide film, it is possible to detect changes in cleaning conditions and the occurrence of abnormalities.
なお、パイロジェニック酸化膜の膜厚は、半導体集積回路素子の薄膜化への影響を考慮して、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。 The thickness of the pyrogenic oxide film is preferably 1 to 10 nm, taking into consideration the effect on thinning of semiconductor integrated circuit elements. The semiconductor substrate evaluation method according to the present invention can more accurately evaluate the surface quality of semiconductor substrates, especially when the film thickness is in this thin 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、パイロジェニック酸化による酸化膜の膜厚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 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 final cleaning of the semiconductor substrate has a strong influence on the thickness of the oxide film formed by pyrogenic oxidation, so that 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より強く反映するパイロジェニック酸化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 defined as 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 pyrogenic oxidation, which more 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、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 pyrogenic oxide film is a silicon oxide film. The semiconductor substrate evaluation method according to the present invention is particularly effective in evaluating silicon substrates.
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）のシリコン基板を準備した。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で洗浄後に、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。
(Example)
A boron-doped silicon substrate with a diameter of 300 mm and a normal resistivity (about 10 Ωcm) was prepared. In order to eliminate the influence of a natural oxide film formed on the silicon substrate surface and to initialize it, the substrate was cleaned with 0.5% HF, and then cleaned with SC1 (NH 4 OH concentration: 3%) at cleaning solution temperatures of 40, 45, 50, 60, and 70° C.
この後、これらのシリコン基板を熱酸化としてパイロ酸化（７００℃、Ｎ２希釈、酸化時間：２３分）し、熱酸化膜を形成した。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、ＳＣ１洗浄温度が熱酸化膜厚に与える影響を評価した。その結果、図１（面内５点の平均と最大（ＭＡＸ）と最小（ＭＩＮ）のプロット）に示すように、ＳＣ１洗浄温度が高くなるほど熱酸化膜厚が厚くなることがわかった。 After this, these silicon substrates were thermally oxidized by pyro-oxidation (700°C, N2 dilution, oxidation time: 23 minutes) to form a thermal oxide film. The thermal oxide film thickness after thermal oxidation was measured at five points on the substrate surface using a spectroscopic ellipsometer to evaluate the effect of the SC1 cleaning temperature on the thermal oxide film thickness. As a result, as shown in Figure 1 (plot of the average of the five points on the substrate surface and the maximum (MAX) and minimum (MIN)), it was found that the higher the SC1 cleaning temperature, the thicker the thermal oxide film became.
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パイロ酸化を行った場合、パイロ酸化膜の膜厚は品質の違いを感度高く反映できるため、パイロ酸化膜の膜厚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。 The SC1 cleaning temperature is believed to affect 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, when pyro-oxidation is performed without removing the natural oxide film, the thickness of the pyro-oxide film can sensitively reflect differences in quality. 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 thickness of the pyro-oxide film.
また、この結果をもとにすれば、洗浄装置の日常管理を行うことが可能になる。すなわち、酸化膜厚が通常と違う厚さになった場合は、洗浄装置の温度管理に異常があることがわかる。本例はわかりやすいように薬液温度を振ったが、日常管理として酸化膜厚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できる。 Based on these results, it will be possible to perform daily management of the cleaning equipment. In other words, if the oxide film thickness becomes different from normal, it will be clear 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 oxide film thickness is determined and monitored as part of daily management, fluctuations in the cleaning conditions can be detected.
（比較例）
直径３００ｍｍ、ボロンドープの通常抵抗率（約１０Ωｃｍ）のシリコン基板を準備した。シリコン基板表面を初期化のために０．５％ＨＦで洗浄後に、洗浄液の温度を４０～７０℃としてＳＣ１洗浄（ＮＨ４ＯＨ濃度：３％）を行った。
Comparative Example
A boron-doped silicon substrate with a diameter of 300 mm and a normal resistivity (about 10 Ωcm) was prepared. The silicon substrate surface was washed with 0.5% HF for initialization, and then washed with SC1 (NH 4 OH concentration: 3%) at a cleaning solution temperature of 40 to 70° C.
この後、これらのシリコン基板を熱酸化としてドライ酸化（９００℃、Ｎ２希釈、酸化時間：２３分）し、熱酸化膜を形成した。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、ＳＣ１洗浄温度が熱酸化膜厚に与える影響を評価した。その結果、図１（面内５点の平均と最大（ＭＡＸ）と最小（ＭＩＮ）のプロット）に示すように、ＳＣ１洗浄温度が高くなるほど熱酸化膜厚が厚くなる傾向が見られたものの、実施例のパイロ酸化と比較してＳＣ１洗浄温度による熱酸化膜厚の差が小さいことがわかる。図１に示すように、比較例では、薬液温度による酸化膜厚の差があることはわかるが、酸化時の基板面内でのばらつきを考慮すると薬液温度の影響が小さくなりその差が不明確である。 After this, these silicon substrates were subjected to dry oxidation (900°C, N2 dilution, oxidation time: 23 minutes) as thermal oxidation to form a thermal oxide film. The thermal oxide film thickness after thermal oxidation was measured at five points on the substrate surface using a spectroscopic ellipsometer to evaluate the effect of the SC1 cleaning temperature on the thermal oxide film thickness. As a result, as shown in FIG. 1 (plot of the average of the five points on the substrate surface and the maximum (MAX) and minimum (MIN)), the thermal oxide film thickness tended to increase as the SC1 cleaning temperature increased, but the difference in the thermal oxide film thickness due to the SC1 cleaning temperature was smaller than that in the pyro-oxidation of the embodiment. As shown in FIG. 1, in the comparative example, it is clear that there is a difference in the oxide film thickness due to the chemical solution temperature, but when considering the variation in the substrate surface during oxidation, the effect of the chemical solution temperature becomes smaller and the difference is unclear.
このように、実施例のパイロ酸化に代えてドライ酸化を行った比較例の場合には、シリコン基板表面の品質の変化に対するドライ酸化膜厚の変化が小さく、シリコン基板表面の評価の精度が低いことがわかった。 As such, in the comparative example, where dry oxidation was performed instead of the pyro-oxidation used in the embodiment, the change in the dry oxide film thickness relative to the change in the quality of the silicon substrate surface was small, and it was found that the accuracy of the evaluation of the silicon substrate surface was low.
以上の通り、本発明の実施例によれば、パイロ酸化で形成した熱酸化膜（パイロ酸化膜）の膜厚が、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。パイロ酸化を行うと、半導体基板の品質を精度高く評価でき、洗浄条件の変化の影響をより精度高く評価できることがわかった。また、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 thickness of the thermal oxide film (pyro-oxide film) formed by pyro-oxidation accurately reflects the fluctuations in the SC1 cleaning conditions (temperature). It was found that pyro-oxidation allows the quality of the semiconductor substrate to be evaluated with high accuracy, and allows the effects of changes in the cleaning conditions to be evaluated with even higher accuracy. It was also found that it can be applied to the management of cleaning processes and cleaning machines. Furthermore, it is believed that it is 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 exhibits similar effects is included within the technical scope of the present invention.
Claims (4)
半導体基板の表面に形成された自然酸化膜を除去することなく、前記半導体基板をパイロジェニック酸化して前記半導体基板の表面にパイロジェニック酸化膜を形成し、前記パイロジェニック酸化膜の膜厚に基づいて、前記半導体基板の表面品質である表面粗さ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:
A method for evaluating a semiconductor substrate, comprising: pyrogenically oxidizing a semiconductor substrate to form a pyrogenic oxide film on the surface of the semiconductor substrate without removing a native oxide film formed on the surface of the semiconductor substrate; and evaluating the surface roughness, which is the surface quality of the semiconductor substrate, based on the film thickness of the pyrogenic oxide film.
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| JP2006203228A (en) | 2006-02-23 | 2006-08-03 | Renesas Technology Corp | Manufacturing method of semiconductor integrated circuit device |
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