JP2011054691A - Method of evaluating surface or surface layer of semiconductor wafer - Google Patents
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- 239000004065 semiconductor Substances 0.000 title claims abstract description 65
- 239000002344 surface layer Substances 0.000 title claims abstract description 39
- 238000000034 method Methods 0.000 title claims abstract description 35
- 230000007547 defect Effects 0.000 claims abstract description 53
- 238000011109 contamination Methods 0.000 claims abstract description 25
- 239000000969 carrier Substances 0.000 claims abstract description 23
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical group [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 41
- 229910052710 silicon Inorganic materials 0.000 claims description 41
- 239000010703 silicon Substances 0.000 claims description 41
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 31
- 238000005424 photoluminescence Methods 0.000 claims description 26
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- 230000001443 photoexcitation Effects 0.000 claims description 7
- 238000004140 cleaning Methods 0.000 claims description 5
- 238000011156 evaluation Methods 0.000 abstract description 17
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- 238000007796 conventional method Methods 0.000 abstract description 6
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 229910052814 silicon oxide Inorganic materials 0.000 description 4
- 230000002411 adverse Effects 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
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- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 2
- 238000004020 luminiscence type Methods 0.000 description 2
- 229910021421 monocrystalline silicon Inorganic materials 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 2
- 229910021642 ultra pure water Inorganic materials 0.000 description 2
- 239000012498 ultrapure water Substances 0.000 description 2
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 1
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 1
- 239000003929 acidic solution Substances 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 238000000861 blow drying Methods 0.000 description 1
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- CPBQJMYROZQQJC-UHFFFAOYSA-N helium neon Chemical compound [He].[Ne] CPBQJMYROZQQJC-UHFFFAOYSA-N 0.000 description 1
- 239000008214 highly purified water Substances 0.000 description 1
- 229910000040 hydrogen fluoride Inorganic materials 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 230000001678 irradiating effect Effects 0.000 description 1
- 229910052743 krypton Inorganic materials 0.000 description 1
- DNNSSWSSYDEUBZ-UHFFFAOYSA-N krypton atom Chemical compound [Kr] DNNSSWSSYDEUBZ-UHFFFAOYSA-N 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
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- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
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- 239000010937 tungsten Substances 0.000 description 1
- 238000009279 wet oxidation reaction Methods 0.000 description 1
- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 1
Abstract
Description
この発明は、半導体ウェーハの表面または表層評価方法、詳しくは半導体ウェーハの表面または表層に存在する欠陥および汚染を光励起分光法により評価可能な半導体ウェーハの表面または表層評価方法に関する。 The present invention relates to a method for evaluating the surface or surface layer of a semiconductor wafer, and more particularly to a method for evaluating the surface or surface layer of a semiconductor wafer capable of evaluating defects and contamination existing on the surface or surface layer of a semiconductor wafer by photoexcitation spectroscopy.
シリコンウェーハの表面または表層の欠陥および汚染を評価する技術として、光励起分光法の一種であるフォトルミネセンス（Ｐｈｏｔｏｌｕｍｉｎｅｓｃｅｎｃｅ）法が知られている。この方法は、バンドギャップ（禁制帯）より高エネルギの光をシリコンウェーハに照射し、励起された電子・正孔対（過剰キャリア）が再結合する際に放出された光（ルミネセンス）を計測し、シリコンウェーハの表面または表層に存在する欠陥および不純物を検出し、評価するものである。
従来、シリコンウェーハの表面において、微小な領域でのフォトルミネセンスの発光強度分布を得ることで、電気的に活性な欠陥や局所的な汚染を検出し、それを評価する方法は知られていた（例えば、特許文献１）。
As a technique for evaluating defects and contamination on the surface or surface layer of a silicon wafer, a photoluminescence method, which is a kind of photoexcitation spectroscopy, is known. This method irradiates a silicon wafer with light of energy higher than the band gap (forbidden band) and measures the light (luminescence) emitted when the excited electron-hole pairs (excess carriers) recombine. Then, defects and impurities existing on the surface or surface layer of the silicon wafer are detected and evaluated.
Conventionally, a method for detecting and evaluating electrically active defects and local contamination by obtaining a photoluminescence emission intensity distribution in a minute area on the surface of a silicon wafer has been known. (For example, patent document 1).
しかしながら、評価されるシリコンウェーハにあっては、その表面に自然酸化膜（ＳｉＯ２）が形成されている場合がある。そのため、従来、フォトルミネセンス法によるシリコンウェーハの表面の評価は、自然酸化膜を通して測定された過剰キャリアの濃度分布(フォトルミネセンスの発光強度分布)に基づくもので、信頼性に乏しいものであった。
すなわち、自然酸化膜にはシリコンの表面準位が局在しており、この表面準位が過剰キャリアの濃度分布の測定精度に悪影響をおよぼす。そのため、従来法では、濃度分布の測定視野内での無欠陥領域の発光強度と、欠陥領域の発光強度との差は小さく、濃度分布のコントラストが明瞭でなかった。その結果、濃度分布から得られた電気的に活性な欠陥の検出結果および局所的な汚染の検出結果も信頼性が低かった。
However, in a silicon wafer to be evaluated, a natural oxide film (SiO 2 ) may be formed on the surface thereof. For this reason, conventionally, the evaluation of the surface of a silicon wafer by the photoluminescence method is based on the concentration distribution of excess carriers (photoluminescence emission intensity distribution) measured through a natural oxide film, and the reliability is poor. It was.
That is, the surface level of silicon is localized in the natural oxide film, and this surface level adversely affects the measurement accuracy of the excess carrier concentration distribution. Therefore, in the conventional method, the difference between the emission intensity of the defect-free region and the emission intensity of the defect region within the concentration distribution measurement field is small, and the contrast of the concentration distribution is not clear. As a result, the detection result of the electrically active defect obtained from the concentration distribution and the detection result of the local contamination were also unreliable.
そこで、発明者は、鋭意研究の結果、上述したフォトルミネセンス法によりシリコンウェーハの表面における欠陥や汚染の評価を実施する直前に、シリコンウェーハの表面に対して、例えばフッ酸などによるＨＦ処理を施せば、上述の問題は解消されることを知見し、この発明を完成させた。
この発明は、半導体ウェーハの表面または表層の欠陥および汚染を高感度に測定し、評価結果の信頼性を高めることができる半導体ウェーハの表面または表層評価方法を提供することを目的としている。
Therefore, as a result of earnest research, the inventor performed HF treatment with, for example, hydrofluoric acid on the surface of the silicon wafer immediately before the evaluation of defects and contamination on the surface of the silicon wafer by the above-described photoluminescence method. It has been found that the above-mentioned problems can be solved by applying it, and the present invention has been completed.
An object of the present invention is to provide a method for evaluating a surface or surface layer of a semiconductor wafer that can measure defects and contamination on the surface or surface layer of a semiconductor wafer with high sensitivity and can improve the reliability of evaluation results.
請求項１に記載の発明は、半導体ウェーハの表層に光励起により過剰キャリアを発生させ、前記半導体ウェーハの表面の微小な領域内における前記過剰キャリアの濃度分布を測定し、前記半導体ウェーハの表面または表層の電気的に活性な欠陥、局所的な汚染を評価する半導体ウェーハの表面または表層評価法であって、前記半導体ウェーハの表面に形成された自然酸化膜を含む酸化膜を除去し、その後、前記半導体ウェーハの表面に新たに自然酸化膜が形成されるまでの間に、前記電気的に活性な欠陥、局所的な汚染の評価を行う半導体ウェーハの表面または表層評価法である。 According to the first aspect of the present invention, excess carriers are generated by photoexcitation on the surface layer of a semiconductor wafer, the concentration distribution of the excess carriers in a minute region on the surface of the semiconductor wafer is measured, and the surface or surface layer of the semiconductor wafer is measured. A method for evaluating the surface or surface layer of a semiconductor wafer for evaluating electrically active defects and local contamination, wherein an oxide film including a natural oxide film formed on the surface of the semiconductor wafer is removed, and thereafter This is a method for evaluating the surface or surface layer of a semiconductor wafer, in which the electrically active defects and local contamination are evaluated before a natural oxide film is newly formed on the surface of the semiconductor wafer.
請求項１に記載の発明によれば、半導体ウェーハの表面または表層の領域において、過剰キャリアの濃度分布を測定する直前に、半導体ウェーハの表面に存在する自然酸化膜を含む酸化膜（熱酸化膜など）を、例えばＨＦ処理により除去する。
一般に、結晶中に欠陥または汚染が存在すれば、それらに対応した電子準位がバンドギャップ中に形成される。これらの電子準位がバンドギャップ中に存在すれば、励起された過剰キャリアがこの電子準位を介して再結合する。そのため、相対的に、バンド間での直接再結合によるバンド端発光の割合が低下する。これにより、欠陥または汚染が存在した場合には、これらが存在しない場合に比べて、バンド端発光強度が下がることになる。
According to the first aspect of the present invention, an oxide film (thermal oxide film) including a natural oxide film existing on the surface of the semiconductor wafer immediately before measuring the concentration distribution of excess carriers in the surface or surface layer region of the semiconductor wafer. Etc.) are removed by, for example, HF treatment.
In general, if there are defects or contamination in the crystal, electron levels corresponding to them are formed in the band gap. If these electronic levels are present in the band gap, the excited excess carriers are recombined through the electronic levels. For this reason, the ratio of band edge emission due to direct recombination between bands is relatively reduced. As a result, when there is a defect or contamination, the band edge emission intensity is lower than when there is no defect or contamination.
酸化膜、特に自然酸化膜には、例えばシリコンの表面の表面準位が局在しており、この表面準位（熱酸化膜の場合には、酸化膜とシリコンとの界面準位）が過剰キャリアの濃度分布の測定精度に悪影響をおよぼす。そのため、例えばＨＦ処理によりシリコンウェーハの表面を水素終端状態とすれば、表面準位の影響を低下させることができる。
その後、半導体ウェーハの表面に新たに自然酸化膜が形成されるまでの間に、光励起により半導体ウェーハの表面近傍に過剰キャリアを発生させ、半導体ウェーハの表面または表層の微小な領域内での過剰キャリアの濃度分布を測定する。その結果、半導体ウェーハの表面または表層での電気的に活性な欠陥、局所的な汚染を評価することができる。
For example, the surface level of the silicon surface is localized in the oxide film, particularly the natural oxide film, and this surface level (in the case of a thermal oxide film, the interface level between the oxide film and silicon) is excessive. This adversely affects the measurement accuracy of the carrier concentration distribution. Therefore, for example, if the surface of the silicon wafer is brought into a hydrogen-terminated state by HF treatment, the influence of the surface level can be reduced.
After that, until a natural oxide film is newly formed on the surface of the semiconductor wafer, excess carriers are generated near the surface of the semiconductor wafer by photoexcitation, and excess carriers on the surface of the semiconductor wafer or in a minute region of the surface layer are generated. Measure the concentration distribution. As a result, it is possible to evaluate electrically active defects and local contamination on the surface or surface layer of the semiconductor wafer.
このように、過剰キャリアの濃度分布の測定前に、半導体ウェーハの表面から自然酸化膜を含む酸化膜を除去するので、濃度分布の測定視野内における無欠陥領域上と欠陥領域上での発光強度の差が増大する。その結果、電気的に活性な欠陥や局所的な汚染を、自然酸化膜を含む酸化膜を除去しない従来法に比べて、明瞭なコントラストで高感度に検出し、よって高い信頼性のもとで、その評価を行うことができる。 In this way, the oxide film including the natural oxide film is removed from the surface of the semiconductor wafer before measuring the concentration distribution of excess carriers, so the emission intensity on the defect-free area and on the defect area within the concentration distribution measurement field. The difference between is increased. As a result, it is possible to detect electrically active defects and local contamination with clear contrast and high sensitivity compared to conventional methods that do not remove the oxide film including the natural oxide film. That can be evaluated.
半導体ウェーハとしては、例えば単結晶シリコンウェーハ、多結晶シリコンウェーハ、ガリウム砒素ウェーハなどを採用することができる。
半導体ウェーハの口径としては、例えば２００ｍｍ、３００ｍｍ、４５０ｍｍが挙げられる。
欠陥、汚染を評価可能な領域は、半導体ウェーハの表面または半導体ウェーハの表層である。
ここでいう「半導体ウェーハの表層」とは、半導体ウェーハの表面から１μｍ程度の深さ領域をいう。
光励起を伴って、半導体ウェーハの表面または表層の欠陥、汚染を評価する方法としては、光励起分光法を採用することができる。具体的には、フォトルミネセンス法などを採用することができる。
As the semiconductor wafer, for example, a single crystal silicon wafer, a polycrystalline silicon wafer, a gallium arsenide wafer, or the like can be employed.
Examples of the diameter of the semiconductor wafer include 200 mm, 300 mm, and 450 mm.
The region where defects and contamination can be evaluated is the surface of the semiconductor wafer or the surface layer of the semiconductor wafer.
Here, the “surface layer of the semiconductor wafer” refers to a region having a depth of about 1 μm from the surface of the semiconductor wafer.
Photoexcitation spectroscopy can be adopted as a method for evaluating defects and contamination on the surface or surface layer of a semiconductor wafer with photoexcitation. Specifically, a photoluminescence method or the like can be employed.
酸化膜としては、例えば、自然酸化膜が挙げられる。その他、半導体ウェーハを熱酸化炉での酸化性ガス雰囲気での加熱を伴うドライ酸化で得られたドライ酸化膜、塩酸などの酸性溶液に接触させるウエット酸化で得られたウエット酸化膜、および、自然酸化膜が挙げられる。半導体ウェーハがシリコンウェーハの場合、自然酸化膜を含む酸化膜はシリコン酸化膜となる。
自然酸化膜の場合の厚さは、０．２〜１ｎｍである。
自然酸化膜を含む酸化膜の除去方法としては、例えば、フッ酸などによるＨＦ処理を採用することができる。フッ酸には、フッ酸水蒸気が含まれる。
An example of the oxide film is a natural oxide film. In addition, a dry oxide film obtained by dry oxidation with heating in an oxidizing gas atmosphere in a thermal oxidation furnace, a wet oxide film obtained by wet oxidation in contact with an acidic solution such as hydrochloric acid, and natural An oxide film is mentioned. When the semiconductor wafer is a silicon wafer, the oxide film including the natural oxide film is a silicon oxide film.
The thickness of the natural oxide film is 0.2 to 1 nm.
As a method for removing the oxide film including the natural oxide film, for example, HF treatment with hydrofluoric acid or the like can be employed. The hydrofluoric acid includes hydrofluoric acid water vapor.
「自然酸化膜を含む酸化膜を除去し、その後、新たに自然酸化膜が形成されるまでの間」とは、例えば、半導体ウェーハの表面から自然酸化膜を含む酸化膜を除去した直後をいう。その他、自然酸化膜を含む酸化膜が除去されてから１週間以内が好ましい。１週間を超えれば、半導体ウェーハの表面に自然酸化膜が形成され、その影響により半導体ウェーハの表面または表層に形成された欠陥および汚染を明瞭なコントラストで高感度に検出することができない。ただし、自然酸化膜を含む酸化膜の除去から長時間が経過しても、その評価時まで、半導体ウェーハの表面に自然酸化膜を含む酸化膜が存在しない状態で保管（例えば不活性ガス雰囲気中での保管）されていれば問題はない。 “Before removing the oxide film including the natural oxide film and then forming a new natural oxide film” means, for example, immediately after the oxide film including the natural oxide film is removed from the surface of the semiconductor wafer. . In addition, it is preferably within one week after the oxide film including the natural oxide film is removed. If it exceeds one week, a natural oxide film is formed on the surface of the semiconductor wafer, and defects and contamination formed on the surface or surface layer of the semiconductor wafer due to the influence cannot be detected with high sensitivity with a clear contrast. However, even after a long time has passed since the removal of the oxide film including the natural oxide film, the oxide film including the natural oxide film is not stored on the surface of the semiconductor wafer until the evaluation (for example, in an inert gas atmosphere). If it is stored in), there is no problem.
「過剰キャリアの濃度分布」は、例えば、半導体ウェーハの表面または表層において、励起光が照射される位置を変更しながら、ルミネセンスの測定を行うことで得られる。
ここでいう「電気的に活性な欠陥」としては、例えば、結晶欠陥を採用することができる。
ここでいう「局所的な汚染」としては、例えば、金属汚染を採用することができる。
評価されるのは、電気的に活性な欠陥と、局所的な汚染とのうち、少なくとも１つである。
The “excess carrier concentration distribution” can be obtained, for example, by measuring the luminescence while changing the position where the excitation light is irradiated on the surface or surface layer of the semiconductor wafer.
As the “electrically active defect” here, for example, a crystal defect can be adopted.
As the “local contamination” here, for example, metal contamination can be adopted.
At least one of electrically active defects and local contamination is evaluated.
請求項２に記載の発明は、前記過剰キャリアの濃度分布の測定法がフォトルミネセンス法である請求項１に記載の半導体ウェーハの表面または表層評価方法である。 According to a second aspect of the present invention, there is provided the semiconductor wafer surface or surface layer evaluation method according to the first aspect, wherein the method for measuring the concentration distribution of excess carriers is a photoluminescence method.
請求項２に記載の発明によれば、過剰キャリアの濃度分布の測定法に、フォトルミネセンス法を採用した場合には、空間分解能が高く、微小な欠陥を検出することができる。 According to the second aspect of the present invention, when the photoluminescence method is employed as the method for measuring the concentration distribution of excess carriers, the spatial resolution is high and minute defects can be detected.
フォトルミネセンスは、浅い準位の不純物に対して高感度に測定することができる。例えば、１×１０１１ａｔｏｍｓ／ｃｍ３程度の微量分析は、多くの不純物において実施することができる。
フォトルミネセンス法による過剰キャリアの濃度分布の測定条件は任意である。
また、フォトルミネセンス測定装置の装置構成も任意である。一般的には、励起光源、半導体ウェーハがセッティングされるクライオスタット、収束レンズ、分光器、光検出器を備えている。励起光源としては、各種のレーザ（アルゴンレーザ、ヘリウム・ネオンレーザ、クリプトンレーザなど）を採用することができる。その他の励起光源として、キセノンアークランプ、タングステンランプなどでもよい。
Photoluminescence can be measured with high sensitivity to shallow level impurities. For example, a microanalysis of about 1 × 10 11 atoms / cm 3 can be performed on many impurities.
The measurement conditions of the concentration distribution of excess carriers by the photoluminescence method are arbitrary.
The device configuration of the photoluminescence measuring device is also arbitrary. Generally, an excitation light source, a cryostat on which a semiconductor wafer is set, a converging lens, a spectroscope, and a photodetector are provided. Various lasers (argon laser, helium-neon laser, krypton laser, etc.) can be employed as the excitation light source. As another excitation light source, a xenon arc lamp, a tungsten lamp, or the like may be used.
請求項３に記載の発明は、半導体ウェーハがシリコンウェーハで、前記自然酸化膜を含む酸化膜の除去が、フッ酸洗浄およびその後の純水リンスにより行われる請求項１または請求項２に記載の半導体ウェーハの表面または表層評価方法である。 According to a third aspect of the present invention, the semiconductor wafer is a silicon wafer, and the oxide film including the natural oxide film is removed by hydrofluoric acid cleaning and subsequent pure water rinsing. This is a method for evaluating the surface or surface layer of a semiconductor wafer.
請求項３に記載の発明によれば、表面に自然酸化膜を含む酸化膜が形成されたシリコンウェーハをフッ酸洗浄し、その後、純水リンスすることで自然酸化膜を含む酸化膜を除去することができる。
シリコンウェーハとしては、単結晶シリコンウェーハ、多結晶シリコンウェーハを採用することができる。
フッ酸中のフッ化水素の濃度は任意である。例えばＨＦ：Ｈ２Ｏ＝１〜２０：１００のものを採用することができる。
フッ酸洗浄（フッ酸によるエッチング）の時間は、自然酸化膜を含む酸化膜の厚さに応じて変更される。
According to the third aspect of the present invention, the silicon wafer having the oxide film including the natural oxide film formed on the surface thereof is cleaned with hydrofluoric acid, and then rinsed with pure water to remove the oxide film including the natural oxide film. be able to.
As the silicon wafer, a single crystal silicon wafer or a polycrystalline silicon wafer can be employed.
The concentration of hydrogen fluoride in hydrofluoric acid is arbitrary. For example HF: H 2 O = 1~20: can be employed 100 ones.
The time of hydrofluoric acid cleaning (etching with hydrofluoric acid) is changed according to the thickness of the oxide film including the natural oxide film.
純水とは、物理的または化学的な処理によって不純物を除去した純度の高い水をいう。具体的には、１〜１０ＭΩ・ｃｍまたは１．０〜０．１μＳ／ｃｍの水を採用することができる。また、純水に代えて、超純水を使用してもよい。超純水としては、水に含まれる不純物の量が、例えば０．０１μｇ／リットル以下のものを採用することができる。
純水によるリンス時間は、例えば浸漬法の場合で５分程度である。純水リンス後は、半導体ウェーハを例えばスピン乾燥、窒素ブローなどで乾燥させる。
Pure water refers to highly purified water from which impurities have been removed by physical or chemical treatment. Specifically, 1 to 10 MΩ · cm or 1.0 to 0.1 μS / cm of water can be employed. Further, ultrapure water may be used instead of pure water. As the ultrapure water, one having an impurity amount contained in water of, for example, 0.01 μg / liter or less can be employed.
The rinse time with pure water is, for example, about 5 minutes in the case of the immersion method. After rinsing with pure water, the semiconductor wafer is dried by, for example, spin drying or nitrogen blowing.
請求項１に記載の発明によれば、過剰キャリアの濃度分布の測定前に、半導体ウェーハの表面から自然酸化膜を含む酸化膜を除去するので、濃度分布の測定視野内における無欠陥領域上と欠陥領域上での発光強度の差が増大する。その結果、電気的に活性な欠陥および局所的な汚染を、自然酸化膜を含む酸化膜を除去しない従来法に比べて高感度に検出し、評価することができる。 According to the first aspect of the present invention, the oxide film including the natural oxide film is removed from the surface of the semiconductor wafer before the measurement of the concentration distribution of excess carriers. The difference in emission intensity on the defect area increases. As a result, electrically active defects and local contamination can be detected and evaluated with higher sensitivity than in the conventional method in which an oxide film including a natural oxide film is not removed.
請求項２に記載の発明によれば、過剰キャリアの濃度分布の測定法としてフォトルミネセンス法を採用したので、空間分解能が高く、微小な欠陥を検出することができる。 According to the second aspect of the present invention, since the photoluminescence method is employed as a method for measuring the concentration distribution of excess carriers, the spatial resolution is high and minute defects can be detected.
請求項３に記載の発明によれば、表面に自然酸化膜を含む酸化膜が形成された半導体ウェーハをフッ酸洗浄し、その後、純水リンスすることで自然酸化膜を含む酸化膜を除去することができる。 According to the third aspect of the present invention, a semiconductor wafer having an oxide film including a natural oxide film formed on its surface is cleaned with hydrofluoric acid, and then rinsed with pure water to remove the oxide film including the natural oxide film. be able to.
以下、この発明の実施例を具体的に説明する。ここでは、半導体ウェーハとしてシリコンウェーハを採用する。そのため、自然酸化膜はシリコン酸化膜（ＳｉＯ２膜）となる。 Examples of the present invention will be specifically described below. Here, a silicon wafer is employed as the semiconductor wafer. Therefore, the natural oxide film becomes a silicon oxide film (SiO 2 film).
以下、図１のフローシートに基づき、この発明の実施例１に係る半導体ウェーハの表面または表層評価方法を説明する。
シリコンウェーハは、ＣＺ法により引き上げられたシリコン単結晶を加工して得られた直径が３００ｍｍ、ボロンドープによる比抵抗が１．０Ω・ｃｍのもので、その露出面全域に厚さ１ｎｍ前後のシリコン酸化膜が形成されている。
次に、シリコンウェーハを洗浄槽に貯液されたフッ酸（２５℃）に１分間だけ浸漬し、自然酸化膜を除去（フッ酸洗浄）する。フッ酸中のＨＦ濃度は１％である。
A method for evaluating the surface or surface layer of a semiconductor wafer according to Example 1 of the present invention will be described below based on the flow sheet of FIG.
A silicon wafer has a diameter of 300 mm obtained by processing a silicon single crystal pulled by the CZ method and a specific resistance of 1.0 Ω · cm by boron doping, and a silicon oxide having a thickness of about 1 nm over the entire exposed surface. A film is formed.
Next, the silicon wafer is immersed in hydrofluoric acid (25 ° C.) stored in a cleaning tank for 1 minute to remove the natural oxide film (hydrofluoric acid cleaning). The HF concentration in hydrofluoric acid is 1%.
自然酸化膜の除去後、純水によりシリコンウェーハをリンスする。具体的には、シリコンウェーハをリンス槽に貯液された純水に５分間だけ浸漬する。
その後、純水リンス後のシリコンウェーハをスピン乾燥機の回転テーブルに固定し、所定の回転速度で所定時間だけスピン乾燥し、シリコンウェーハの表面に水滴が残らないようにする。スピン乾燥に代えて、窒素ブロー乾燥でもよい。
After removing the natural oxide film, the silicon wafer is rinsed with pure water. Specifically, the silicon wafer is immersed for 5 minutes in pure water stored in a rinse tank.
Thereafter, the silicon wafer after rinsing with pure water is fixed to a rotary table of a spin dryer and spin-dried at a predetermined rotational speed for a predetermined time so that no water droplets remain on the surface of the silicon wafer. Nitrogen blow drying may be used instead of spin drying.
次に、乾燥直後のシリコンウェーハをフォトルミネセンス測定装置に移送し、シリコンウェーハの表面の欠陥の評価を行う。
まず、図２を参照して、フォトルミネセンス測定装置を具体的に説明する。このフォトルミネセンス測定装置は、強励起顕微フォトルミネッセンス法に基づく欠陥検出装置である。具体的にはｎａｎｏｍｅｔｒｉｃｓ社製の商品名ＳｉＰＨＥＲを採用している。フォトルミネセンス測定装置１０は、シリコンウェーハ１１の表面にレーザ光を照射するレーザ光源１２，１３と、ハーフミラー１４，１５と、出力計１６と、表面散乱光用検出器１７と、オートフォーカス用検出器１８と、可動ミラー１９と、白色光源２０と、ＣＣＤカメラ２１と、顕微鏡対物レンズ２２と、長波パスフィルタ２３と、フォトルミネセンス光用検出器２４と、オートフォーカス用のミラー２５とを備えている。
Next, the silicon wafer immediately after drying is transferred to a photoluminescence measuring device, and defects on the surface of the silicon wafer are evaluated.
First, with reference to FIG. 2, a photoluminescence measuring apparatus will be specifically described. This photoluminescence measuring device is a defect detection device based on a strong excitation microscopic photoluminescence method. Specifically, trade name SiPHER manufactured by nanometrics is adopted. The photoluminescence measuring apparatus 10 includes laser light sources 12 and 13 for irradiating the surface of a silicon wafer 11 with laser light, half mirrors 14 and 15, an output meter 16, a surface scattered light detector 17, and an autofocusing device. A detector 18, a movable mirror 19, a white light source 20, a CCD camera 21, a microscope objective lens 22, a long wave path filter 23, a photoluminescence light detector 24, and an autofocus mirror 25. I have.
レーザ光源１２，１３から照射されたレーザ光は、出力計１６により出力測定されながらハーフミラー１４，１５を経て、顕微鏡対物レンズ２２からシリコンウェーハ１１の表面に照射され、フォトルミネセンスが発生する。発生したフォトルミネセンスの一部は、ハーフミラー１５を透過し、長波パスフィルタ２３を経てフォトルミネセンス光用検出器２４により検出される。検出された光は、出力が増幅されて記録計に記録され、シリコンウェーハ１１の欠陥評価に用いられる。 The laser light emitted from the laser light sources 12 and 13 is irradiated to the surface of the silicon wafer 11 from the microscope objective lens 22 through the half mirrors 14 and 15 while being output and measured by the output meter 16, and photoluminescence is generated. Part of the generated photoluminescence passes through the half mirror 15 and is detected by the photoluminescence light detector 24 through the long wave pass filter 23. The detected light is amplified in output and recorded in a recorder, and used for defect evaluation of the silicon wafer 11.
シリコンウェーハ１１に自然酸化膜が存在する場合、シリコンの表面には表面準位が局在し、この表面準位が過剰キャリアの濃度分布の測定精度に悪影響をおよぼす。そこで、シリコンウェーハ１１をフッ酸洗浄し、シリコンウェーハ１１の表面を水素終端状態としたので、過剰キャリアの濃度分布の測定の際、表面準位の影響を抑えることができる。 When a natural oxide film is present on the silicon wafer 11, surface levels are localized on the surface of silicon, and this surface level adversely affects the measurement accuracy of the concentration distribution of excess carriers. Therefore, since the silicon wafer 11 is cleaned with hydrofluoric acid and the surface of the silicon wafer 11 is in a hydrogen-terminated state, the influence of the surface level can be suppressed when measuring the concentration distribution of excess carriers.
ここで、図３〜図５を参照し、実際に実施例１のフォトルミネセンス測定装置１０を用いて、同一のシリコンウェーハに対して、自然酸化膜の除去前と除去後における過剰キャリアの濃度（バンド端発光強度）の分布を比較した結果を報告する。
図３に示すように、自然酸化膜を除去する前は微小であった欠陥が、自然酸化膜の除去後は明瞭なコントラストで高感度に検出できた。これを、図５のグラフを用いて検出信号の強度差で表示すれば、自然酸化膜を除去する前の欠陥は、幅が１０ｎｍ程度、ウェーハ表面の平坦領域の検出信号を基準強度１．００とした場合、欠陥の信号強度が０．９９程度であった。これに対して、自然酸化膜除去後の欠陥は、幅が１０ｎｍ程度、欠陥の信号強度が０．９３程度と、欠陥の存在が明瞭となった。
Here, with reference to FIG. 3 to FIG. 5, the concentration of excess carriers before and after removal of the natural oxide film on the same silicon wafer using the photoluminescence measuring apparatus 10 of Example 1 actually. The result of comparing the distribution of (band edge emission intensity) is reported.
As shown in FIG. 3, the defects that were minute before the natural oxide film was removed could be detected with high sensitivity with clear contrast after the natural oxide film was removed. If this is represented by the difference in intensity of the detection signal using the graph of FIG. 5, the defect before removing the natural oxide film is about 10 nm in width, and the detection signal of the flat region on the wafer surface is the reference intensity 1.00. In this case, the signal strength of the defect was about 0.99. On the other hand, the defect after the natural oxide film was removed had a width of about 10 nm and the signal intensity of the defect was about 0.93.
また、図４に示すように、自然酸化膜を除去する前は無欠陥とされたウェーハ表面の別の部位について、シリコン酸化膜の除去後、新たに欠陥が検出された。このように、自然酸化膜を通して表面欠陥を評価する従来法に比べて、自然酸化膜を除去する実施例１の方法では、シリコンウェーハの表面の欠陥を高感度に検出することができ、その結果、欠陥の評価に高い信頼性が得られることが判った。 In addition, as shown in FIG. 4, a new defect was detected after removing the silicon oxide film at another portion of the wafer surface that was made defect-free before the natural oxide film was removed. Thus, compared to the conventional method of evaluating surface defects through a natural oxide film, the method of Example 1 that removes the natural oxide film can detect defects on the surface of the silicon wafer with high sensitivity. It was found that high reliability can be obtained in the evaluation of defects.
次に、図６および図７を参照し、実施例１のフォトルミネセンス測定装置１０を使用し、シリコンウェーハの表面の欠陥に関して、実際に自然酸化膜の除去前から自然酸化膜の除去後、７７日間が経過するまでの過剰キャリアの濃度分布の経時変化を報告する。
図６の顕微鏡写真から明らかなように、評価試料となる自然酸化膜が形成されたシリコンウェーハの表面（ＨＦ処理前）には、幅１μｍ、長さ２μｍ程度の欠陥が存在した。
Next, referring to FIG. 6 and FIG. 7, using the photoluminescence measuring apparatus 10 of Example 1, with respect to defects on the surface of the silicon wafer, after actually removing the natural oxide film from before removing the natural oxide film, The change over time in the concentration distribution of excess carriers until 77 days elapse is reported.
As is apparent from the micrograph of FIG. 6, defects having a width of about 1 μm and a length of about 2 μm were present on the surface of the silicon wafer (before HF treatment) on which a natural oxide film serving as an evaluation sample was formed.
図７に示すように、この欠陥が、過剰キャリアの濃度分布図では直径２〜３μｍ程度の点として表れた。ＨＦ処理直後、この欠陥が直径１０μｍ程度まで拡大し、ＨＦ処理から３〜４日後はさらに２０μｍ程度まで拡大した。これが、ＨＦ処理から２６日後には１０μｍ程度まで縮小し、さらにＨＦ処理から７７日後には自然酸化膜を除去する前の直径２〜３μｍ程度まで戻った。これにより、ＨＦ処理から７７日後にはシリコンウェーハの表面に新たな自然酸化膜が形成されることが判明した。図７のデータから明らかなように、自然酸化膜を除去後、２６日以内であれば、従来法の場合に比べて、ウェーハ表面の欠陥を数倍に拡大して判定することができることが判った。特に、自然酸化膜の除去後１週間以内、さらに好ましくはＨＦ処理後３〜４日間は、この欠陥の拡大倍率を高めて、より高感度な欠陥評価を行えることが判明した。 As shown in FIG. 7, this defect appeared as a point having a diameter of about 2 to 3 μm in the concentration distribution diagram of excess carriers. Immediately after the HF treatment, this defect expanded to a diameter of about 10 μm, and further expanded to about 20 μm 3 to 4 days after the HF treatment. This decreased to about 10 μm 26 days after the HF treatment, and returned to about 2 to 3 μm in diameter before removing the natural oxide film 77 days after the HF treatment. This revealed that a new natural oxide film was formed on the surface of the silicon wafer 77 days after the HF treatment. As is apparent from the data in FIG. 7, it can be seen that within 26 days after removing the natural oxide film, the defect on the wafer surface can be determined several times larger than in the conventional method. It was. In particular, it has been found that within 1 week after removal of the natural oxide film, more preferably 3 to 4 days after the HF treatment, the defect magnification can be increased to perform highly sensitive defect evaluation.
この発明は、半導体ウェーハの表面または表層に存在する欠陥、汚染の評価に有用である。 The present invention is useful for evaluating defects and contamination existing on the surface or surface layer of a semiconductor wafer.
１０ フォトルミネセンス測定装置、
１１ シリコンウェーハ（半導体ウェーハ）。
10 Photoluminescence measuring device,
11 Silicon wafer (semiconductor wafer).
Claims (3)
前記半導体ウェーハの表面に形成された自然酸化膜を含む酸化膜を除去し、その後、前記半導体ウェーハの表面に新たに自然酸化膜が形成されるまでの間に、前記電気的に活性な欠陥、局所的な汚染の評価を行う半導体ウェーハの表面または表層評価法。 Excess carriers are generated in the surface layer of the semiconductor wafer by photoexcitation, the concentration distribution of the excess carriers in a minute region on the surface of the semiconductor wafer is measured, and electrically active defects on the surface or surface layer of the semiconductor wafer, local A method for evaluating the surface or surface layer of a semiconductor wafer for evaluating general contamination,
Removing the oxide film including the natural oxide film formed on the surface of the semiconductor wafer, and then forming a new natural oxide film on the surface of the semiconductor wafer, the electrically active defect, A method for evaluating the surface or surface layer of a semiconductor wafer to evaluate local contamination.
前記過剰キャリアの濃度分布の測定法がフォトルミネセンス法である請求項１に記載の半導体ウェーハの表面または表層評価方法。 The semiconductor wafer is a silicon wafer,
The method for evaluating the surface or surface layer of a semiconductor wafer according to claim 1, wherein the method for measuring the concentration distribution of excess carriers is a photoluminescence method.
前記自然酸化膜を含む酸化膜の除去が、フッ酸洗浄およびその後の純水リンスにより行われる請求項１または請求項２に記載の半導体ウェーハの表面または表層評価方法。 The semiconductor wafer is a silicon wafer,
The method for evaluating a surface or surface layer of a semiconductor wafer according to claim 1 or 2, wherein the removal of the oxide film including the natural oxide film is performed by hydrofluoric acid cleaning and subsequent pure water rinsing.
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