JP3639073B2 - Defect observation method for silicon wafer - Google Patents

Description

前記数式１において、Ｐ_H2は雰囲気中での水素分圧、ｋはBoltzmann 定数、Ｔは熱力学温度である。シリコン結晶中に入っている水素原子は、シリコン表面層と埋め込み酸化物層との界面付近で、酸化物と化学反応を行うが、この反応が最も生じ易い場所（選択的にエッチングされる場所）はおそらく微小欠陥の付近であると考えられる。
【００１３】
さて、前記反応における生成物の一つは水であるが、シリコン中での水の存在確率は小さく、その拡散速度は不明である。しかし、生成された水は埋め込み酸化物中やシリコン層との界面で拡散可能であり、微小欠陥の付近で凝集状態になることが判った。
【００１４】
そこで、本発明者達は、水素原子の選択的エッチングと、生成物の水の凝集との両方を積極的に利用して微小欠陥を拡大することによって、微小欠陥を直接的に観察できることを見出したのである。観察装置としては、通常の微分光学顕微鏡やＸ線トポグラフ等を用いることができる。
【００１５】
本発明の評価方法は、シリコンウエーハを洗浄し、その後、水素分圧１０ｍｍＨ₂Ｏ〜３０ａｔｍの雰囲気中、８００℃〜１３００℃で１分間以上アニール処理し、しかる後に、微小欠陥を観察することを特徴としている。
【００１６】
水素分圧を１０ｍｍＨ₂Ｏ以上３０ａｔｍ以下とした理由を述べる。水素分圧が１０ｍｍＨ₂Ｏ未満の場合には、前記数式１からも分かるようにシリコン格子間における水素濃度も低くなり、埋め込み酸化物との反応速度が遅くなるからである。また、水素分圧を３０ａｔｍ以下としたのは、３０ａｔｍを超える水素分圧を実現するためには大掛かりな熱処理装置を必要としコスト高となるからである。
【００１７】
処理温度を８００℃〜１３００℃とした理由を述べる。処理温度が８００℃未満の場合には、水素とシリコン酸化物との反応が生じ難いからである。また、処理温度が１３００℃を超える場合には、石英炉芯管の寿命が短くなり、その結果コスト高となるからである。
【００１８】
以下、本発明の実施例１を説明する。
【００１９】
先ず、６インチのシリコンウエーハに対して酸素イオンを１．８×１０¹⁸ｃｍ^-2の密度で注入し、さらに酸化雰囲気で１３５０℃６時間のアニール処理を行い、その後、表面の酸化膜を除去してＳＩＭＯＸウエーハを得た。この試料の埋め込み酸化物層の厚さは３６０ｎｍ、その上層にあるシリコン表層の厚さは１８０ｎｍであった。
【００２０】
実施例１では、このＳＩＭＯＸウエーハを標準的に洗浄した後で、水素１００％、１気圧の雰囲気中で１２００℃２時間の熱処理を行った。
【００２１】
他方、前記水素処理を行わない以外は実施例１のウエーハと全く同じウエーハを準備し、比較例１とした。
【００２２】
そして、実施例１及び比較例１のウエーハを、微分干渉顕微鏡で観察した。
【００２３】
図１は、実施例１のウエーハの粒子構造を示す顕微鏡写真である。この写真から明らかなように、実施例１のウエーハには欠陥が観察された。この欠陥の密度を微分干渉顕微鏡で計数したところ、１〜２個／ｃｍ²であった。
【００２４】
これに対して、比較例１のウエーハでは、微分干渉顕微鏡で欠陥が観察されなかった。ここで注意すべきは、比較例１のウエーハにおいても、実施例１と同密度の微細な欠陥が存在していたはずであるが、微分干渉顕微鏡ではこれを観察できなかった点である。すなわち、実施例１では、微細な欠陥をある程度成長させることによって、これが観察可能になったのである。
【００２５】
さらに、実施例１及び比較例１のウエーハの欠陥を、Ｘ線トポグラフによって観察した。
【００２６】
その結果、実施例１のウエーハの欠陥の密度は、十数個／ｃｍ²であった。従って、実施例１のウエーハには、微分顕微鏡で観察できなかった欠陥が存在していたことが分かる。観察できなかった欠陥は、水素処理で成長したにも拘らず表面シリコン層を貫通しなかったものと考えられる。
【００２７】
一方、比較例１のウエーハをＸ線トポグラフによって観察したが、やはり欠陥は観察されなかった。
【００２８】
このように、本発明方法によれば、従来は事実上検出困難であったシリコンウエーハの欠陥を検出することが可能となる。
【００２９】
【発明の効果】
本発明方法によれば、特にＳＩＭＯＸウエーハの欠陥を視覚的に観察することが可能である。従って、デバイス工程を施しデバイス欠陥として事後的にウエーハ欠陥を知る前に、予めＳＩＭＯＸウエーハの品質を評価し、欠陥の有無を知ることができる。
【００３０】
なお、本発明は前述の実施例に限定されない。例えば、本発明方法は、Ｓｉ／ＳｉＯ₂／Ｓｉ構造の接着ウエーハについても適用可能である。
【図面の簡単な説明】
【図１】 本発明の実施例のシリコンウエーハの粒子構造を示す電子顕微鏡写真。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a defect observation method for a silicon wafer, and more particularly to a defect observation method for a silicon wafer that is optimal for quality evaluation of a SIMOX (Separation by Implanted Oxygen) wafer.
[0002]
[Prior art]
A SIMOX (Separation by Implanted Oxygen) wafer is used for manufacturing, for example, ULSI.
[0003]
The silicon layer on the surface of this SIMOX wafer is very thin. For this reason, even if normal etching is performed on the SIMOX wafer, the pits to be formed are considerably small. In addition, when the density is small, counting is not easy even if additional etching is performed.
[0004]
Conventionally, in order to detect defects near the interface between the silicon layer and the buried oxide layer, various analysis means have been tried by preparing a cross-sectional sample.
[0005]
[Problems to be solved by the invention]
However, near the interface between the two layers, the defect density is small and the size is small, so it is difficult to directly observe the defects.
[0006]
Thus, a reliable method for evaluating the quality of a wafer by knowing the presence or absence of defects in the vicinity of the interface between the surface silicon layer and the buried oxide layer in a SIMOX wafer has not been established so far.
[0007]
For this reason, there is no method other than knowing the quality of the SIMOX wafer as a device defect after the ULSI is formed, that is, as a defect of the finished product.
[0008]
In view of such problems of the prior art, the present invention provides a defect observation method for a silicon wafer that can accurately know the presence or absence of defects, particularly in the vicinity of the interface between the surface silicon layer and the buried oxide layer of the SIMOX wafer. The purpose is to do.
[0009]
[Means for Solving the Problems]
In the first invention of this application, after the silicon wafer is cleaned, defects contained in the silicon wafer are grown by annealing at 800 ° C. to 1300 ° C. for 1 minute or more in an atmosphere having a hydrogen partial pressure of 10 mmH ₂ O to 30 atm. The gist of the method for observing defects in a silicon wafer is characterized by observing defects in the silicon wafer later.
[0010]
【Example】
The defect observation method for a silicon wafer according to the present invention is a configuration in which defects can be directly observed by forcibly expanding defects by utilizing the interaction between hydrogen atoms contained in a silicon single crystal lattice and crystal defects. It has become. Details will be described below.
[0011]
In high-purity silicon crystals, hydrogen is mostly present in an atomic state, and the hydrogen atom concentration at a high temperature is represented by the following general formula.
[0012]
[Expression 1]

In Equation 1, P _H2 is the hydrogen partial pressure in the atmosphere, k is the Boltzmann constant, and T is the thermodynamic temperature. The hydrogen atoms contained in the silicon crystal undergo a chemical reaction with the oxide near the interface between the silicon surface layer and the buried oxide layer, but this reaction is most likely to occur (where it is selectively etched). Is probably near the microdefect.
[0013]
Now, one of the products in the reaction is water, but the probability of water in silicon is small and its diffusion rate is unknown. However, it was found that the generated water can be diffused in the buried oxide or at the interface with the silicon layer, and becomes agglomerated in the vicinity of minute defects.
[0014]
Accordingly, the present inventors have found that microdefects can be directly observed by enlarging microdefects by actively utilizing both selective etching of hydrogen atoms and product water aggregation. It was. As an observation apparatus, a normal differential optical microscope, an X-ray topograph, or the like can be used.
[0015]
According to the evaluation method of the present invention, a silicon wafer is cleaned, and then annealed at 800 ° C. to 1300 ° C. for 1 minute or more in an atmosphere with a hydrogen partial pressure of 10 mmH ₂ O to 30 atm , and then a minute defect is observed. It is characterized by.
[0016]
The reason why the hydrogen partial pressure is set to 10 mmH ₂ O to 30 atm will be described. This is because when the hydrogen partial pressure is less than 10 mmH ₂ O, the hydrogen concentration between the silicon lattices becomes low as can be seen from Equation 1, and the reaction rate with the buried oxide becomes slow. The reason why the hydrogen partial pressure is set to 30 atm or less is that, in order to realize a hydrogen partial pressure exceeding 30 atm , a large heat treatment apparatus is required and the cost is increased.
[0017]
The reason why the processing temperature is set to 800 ° C. to 1300 ° C. will be described. This is because when the treatment temperature is less than 800 ° C., the reaction between hydrogen and silicon oxide hardly occurs. Further, when the processing temperature exceeds 1300 ° C., the life of the quartz furnace core tube is shortened, resulting in high cost.
[0018]
Embodiment 1 of the present invention will be described below.
[0019]
First, oxygen ions are implanted into a 6-inch silicon wafer at a density of 1.8 × 10 ¹⁸ cm ⁻² , and further annealed in an oxidizing atmosphere at 1350 ° C. for 6 hours, and then the surface oxide film is removed. As a result, a SIMOX wafer was obtained. In this sample, the thickness of the buried oxide layer was 360 nm, and the thickness of the silicon surface layer thereabove was 180 nm.
[0020]
In Example 1, after this SIMOX wafer was cleaned as standard, heat treatment was performed at 1200 ° C. for 2 hours in an atmosphere of 100% hydrogen and 1 atm.
[0021]
On the other hand, a wafer exactly the same as that of Example 1 was prepared except that the hydrogen treatment was not performed, and Comparative Example 1 was obtained.
[0022]
The wafers of Example 1 and Comparative Example 1 were observed with a differential interference microscope.
[0023]
FIG. 1 is a photomicrograph showing the particle structure of the wafer of Example 1. As apparent from this photograph, defects were observed in the wafer of Example 1. The density of the defects was counted with a differential interference microscope and found to be 1 to 2 / cm ² .
[0024]
On the other hand, in the wafer of Comparative Example 1, no defect was observed with the differential interference microscope. It should be noted here that even in the wafer of Comparative Example 1, fine defects having the same density as in Example 1 should have existed, but this could not be observed with a differential interference microscope. That is, in Example 1, this became observable by growing a minute defect to some extent.
[0025]
Furthermore, the defects of the wafers of Example 1 and Comparative Example 1 were observed by X-ray topography.
[0026]
As a result, the density of defects in the wafer of Example 1 was 10 / cm ² . Therefore, it can be seen that the wafer of Example 1 had defects that could not be observed with the differential microscope. It is considered that the defects that could not be observed did not penetrate the surface silicon layer despite growing by hydrogen treatment.
[0027]
On the other hand, when the wafer of Comparative Example 1 was observed by X-ray topography, no defects were observed.
[0028]
As described above, according to the method of the present invention, it is possible to detect a defect of a silicon wafer that has been practically difficult to detect.
[0029]
【The invention's effect】
In particular, according to the method of the present invention, it is possible to visually observe defects in a SIMOX wafer. Therefore, before the device process is performed and the wafer defect is subsequently known as a device defect, the quality of the SIMOX wafer can be evaluated in advance to know the presence or absence of the defect.
[0030]
In addition, this invention is not limited to the above-mentioned Example. For example, the method of the present invention can be applied to a bonded wafer having a Si / SiO ₂ / Si structure.
[Brief description of the drawings]
FIG. 1 is an electron micrograph showing the particle structure of a silicon wafer according to an embodiment of the present invention.

Claims (4)

After the silicon wafer is cleaned, defects contained in the silicon wafer are grown by annealing at 800 ° C. to 1300 ° C. for 1 minute or more in an atmosphere having a hydrogen partial pressure of 10 mmH ₂ O to 30 atm , and then the silicon wafer has a defect. A method for observing defects in a silicon wafer, characterized in that   2. The method for observing defects in a silicon wafer according to claim 1, wherein the silicon wafer to be observed is a SIMOX (Separation by Implanted Oxygen) wafer having a buried oxide layer.   The silicon wafer defect observation method according to claim 1 or 2, wherein the annealed silicon wafer is observed with a differential interference microscope.   The silicon wafer defect observation method according to claim 1, wherein the annealed silicon wafer is observed by X-ray topography.

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