JP4061418B2 - Silicon substrate and manufacturing method thereof - Google Patents

Description

【００３５】
低温プロセスにおける重金属ゲッタリング能の比較
上記ゲッタリング能の比較を低温熱処理後に行い、同様の評価を行い比較した。低温プロセス： ６００℃×５ｈｒｓ．＋９００℃×３２ｈｒｓ．＋８００℃×５ｈｒｓ．
表２から明らかなように低温プロセスにおいても、この発明によるゲッタリング法が他の方法に比べて優れていることが示された。
【００３６】
【表２】

【００３７】
この発明における基板のボロン濃度の違いに対するゲッタリング能の安定性を調べたところ、表３に示すごとく、ボロン濃度が異なる基板を用いてもゲッタリング能に変化がないことが示された。
【００３８】
【表３】

【００３９】
また、この発明の試料をＳＩＭＳ分析したところ、図３Ａに示すごとく不整合転位が形成されている界面および高濃度ボロン層に重金属が選択的にゲッタリングされていることがわかった。この結果より本発明における不整合転位および高濃度ボロン層のゲッタリング効果が示された。
【００４０】
先の熱処理プロセスを通した後のゲッタリング能の熱的安定性を従来法と比較した結果を図４Ａ、図５Ａに示す。
【００４１】
パーティクルの発生量を純水中でのパーティクル転写により調べた。この方法はウェーハ裏面の鏡面加工した別の清浄表面をもつウェーハと向かい合わせて洗浄槽に入れ、裏面から発生するパーティクルを清浄な上面に転写させ、転写させたウェーハ表面の０．１２μｍ以上の大きさのパーティクルを面検器で評価することによって裏面からのパーティクル発生量を見積もる方法である。結果を表４に示す。
【００４２】
【表４】

【００４３】
実施例２
以下の実施例に用いた本発明の基板およびエピタキシャル層の構造は次の通りである。
１）外観： ８インチφ、（６７５±５）μｍ^t、両面鏡面基板
２）面方位： （１００）±０．５°
３）抵抗率： ３〜５Ω・ｃｍ（ボロン濃度：２．８〜４．５×１０¹⁵ａｔｏｍｓ／ｃｍ³）
４）第一層 ・抵抗率：０．００１〜０．００３Ω・ｃｍ（ボロン濃度：３．５〜１３×１０¹⁹ａｔｏｍｓ／ｃｍ³）
・膜厚：５μｍ^t
５）中間層 ・抵抗率：０．０１〜０．０２Ω・ｃｍ（ボロン濃度：３．５〜９×１０¹⁸ａｔｏｍｓ／ｃｍ³）
・膜厚：３μｍ^t
６）第二層 ・抵抗率：〜１０Ω・ｃｍ（ボロン濃度：〜ｌ．５×１０¹⁵ａｔｏｍｓ／ｃｍ³）
・膜厚：３μｍ^t
第一層、中間層、第二層はＳｉＨＣｌ₃を原料ガスとした熱ＣＶＤ法（化学気相成長法）により形成した。
【００４４】
重金属ゲッタリング能の比較
本発明と従来ゲッタリング法との比較を示す。それぞれのゲッタリングシンクを形成したエピ基板に〜１０¹²ａｔｏｍｓ／ｃｍ²のＦｅ、Ｎｉ、Ｃｒ、Ｃｕの混合汚染を施し、高温プロセスで熱処理した後、酸化膜耐圧の良品率（ｙｉｅｌｄ）およびＣ−ｔ法によるキャリア寿命を調べた。それぞれのプロセスを以下に示す。
高温プロセス： １１９０℃×６ｈｒｓ．＋６００℃×４ｈｒｓ．＋１０００℃×４ｈｒｓ．
酸化膜耐圧良品率の測定： 酸化膜厚１５０Å、印加電圧 １１ＭＶ／ｃｍ
表５から明らかなようにこの発明によるゲッタリング法が他の方法に比べて優れていることが示された。
【００４５】
【表５】

【００４６】
低温プロセスにおける重金属ゲッタリング能の比較を、実施例１と同様に行った結果を表２に示す。
【００４７】
また、この発明の試料をＳＩＭＳ分析したところ、図３Ｂに示すごとく不整合転位が形成されている界面および高濃度ボロン層に重金属が選択的にゲッタリングされていることがわかった。この結果より本発明における不整合転位の発生による重金属ゲッタリングおよび高濃度ボロン層のゲッタリング効果が示された。
【００４８】
先の熱処理プロセスを通した後のゲッタリング能の熱的安定性を従来法と比較した結果を図４Ｂ、図５Ｂに示す。
【００４９】
パーティクルの発生量を実施例１と同様に純水中でのパーティクル転写により調べた。結果を表４に示す。
【００５０】
実施例３
以下の実施例に用いた本発明の基板およびエピタキシャル層の構造は次の通りである。
１）外観： ８インチφ、（６７５±５）μｍ^t、両面鏡面基板
２）面方位： （１００）±０．５°
３）抵抗率： ４〜６Ω・ｃｍ（ボロン濃度：２．３〜３．５×１０¹⁵ａｔｏｍｓ／ｃｍ³）
４）第一層 ・抵抗率：０．００１〜０．００３Ω・ｃｍ（ボロン濃度：３．５〜１３×１０¹⁹ａｔｏｍｓ／ｃｍ³）
・膜厚：５μｍ^t
５）中間層 ・抵抗率：０．０１〜０．０２Ω・ｃｍ（ボロン濃度：３．５〜９×１０¹⁸ａｔｏｍｓ／ｃｍ³）
・膜厚：３μｍ^t
６）第二層 ・抵抗率：〜１０Ω・ｃｍ（ボロン濃度：〜ｌ．５×１０¹⁵ａｔｏｍｓ／ｃｍ³）
・膜厚：３μｍ^t
第一層はイオン注入法、中間層と第二層はＳｉＨＣｌ₃を原料ガスとした成長温度１１５０℃の熱ＣＶＤ法（化学気相成長法）により形成した。
【００５１】
第一層のイオン注入法は、まず、ＢＦｅ²⁺イオンを加速電圧１１０ｋｅＶでドープ量５×１０¹⁵／ｃｍ³を注入し、これをＲＴＰ（Ｒａｐｉｄ Ｔｈｅｒｍａｌ Ｐｒｏｃｅｓｓ）により、１０００℃、６０秒間熱処理した。このときのボロン濃度の深さ方向分布を図６に示す。ボロン濃度は第一層表面で１０²⁰ａｔｏｍｓ／ｃｍ³で深さ１μｍでほぼエピタキシャル用基板と同レベルであった。また、このとき基板とイオン注入により形成した第一層の界面には不整合転位は観察されなかった（Ｐｌａｎ ｖｉｅｗ ＴＥＭ観察）。従って、界面にはボロン濃度差による応力場のみが形成されていると考えられる。
【００５２】
本発明と従来ゲッタリング法との重金属ゲッタリング能の比較を示す。それぞれのゲッタリングシンクを形成したエピ基板に〜１０¹²ａｔｏｍｓ／ｃｍ²のＦｅ、Ｎｉ、Ｃｒ、Ｃｕの混合汚染を施し、高温プロセスで熱処理した後、酸化膜耐圧の良品率（ｙｉｅｌｄ）およびＣ−ｔ法によるキャリア寿命を調べた。それぞれのプロセスを以下に示す。
高温プロセス： １１５０℃×６ｈｒｓ．＋６００℃×４ｈｒｓ．＋９５０℃×４ｈｒｓ．
酸化膜耐圧良品率の測定： 酸化膜厚２００Å、印加電圧 １１ＭＶ／ｃｍ
表６から明らかなようにこの発明によるゲッタリング法が他の方法に比べて優れていることが示された。
【００５３】
【表６】

【００５４】
以下の低温プロセスにおける重金属ゲッタリング能の比較を低温熱処理後に行い、実施例と同様の評価を行い比較した。
低温プロセス： ６００℃×４ｈｒｓ．＋８５０℃×３ｈｒｓ．＋６８０℃×６ｈｒｓ．
表７から明らかなように低温プロセスにおいても、この発明によるゲッタリング法が他の方法に比べて優れていることが示された。
【００５５】
【表７】

【００５６】
また、この発明の試料をＳＩＭＳ分析したところ、図３Ｃに示すごとく応力場が形成されている界面および高濃度ボロン層である第一層に重金属が選択的にゲッタリングされていることがわかった。この結果より本発明における応力場および高濃度ボロン層のゲッタリング効果が示された。
【００５７】
【発明の効果】
この発明は、ドーパント濃度が大きく異なる層を積層した３層構造を持ったシリコンウェーハとなすことにより、ドーパント濃度が大きく異なる層の界面に不整合転位や応力場が形成され、これらにより重金属をゲッタリングでき、シリコン基板の特性（ＰタイプかＮタイプ、ドーパント濃度、酸素濃度など）に依存せず、熱的に安定で、パーティクル発生がなく、低コストで効率よく重金属をゲッタリングでき、エピタキシャル成長によりＤＺ層を形成しているので酸素析出が起こり難く、ＤＺ−ＩＧ処理工程を省略し、熱的に安定なＤＺ層でかつＤＺ層の厚さの制御が可能なＤＺ層が形成でき、ＤＺ層として高濃度ドープ層を用いているので、ラッチアップ対策としても非常に有効である。
【図面の簡単な説明】
【図１】この発明に関して参考とされるシリコン基板の２層構造を示す説明図である。
【図２】この発明によるシリコン基板の３層構造を示す説明図である。
【図３】Ａ，Ｂ，Ｃはこの発明またはこの発明の参考例となるシリコン基板のＳＩＭＳ分析プロファイスを示すグラフである。
【図４】Ａ，Ｂは高温プロセス回数とキャリア寿命との関係を示すグラフである。
【図５】Ａ，Ｂは高温プロセス回数とＤＺ層厚さとの関係を示すグラフである。
【図６】深さとボロン濃度との関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a semiconductor silicon substrate on which an epitaxial layer is formed, and in particular, using a silicon substrate having a dopant concentration of 1 × 10 ¹⁶ atoms / cm ³ or less, a dopant concentration by a vapor phase growth method or an ion implantation method. By stacking different layers, a heavy metal getter having a defect-free layer (DZ layer) that is easy to manufacture, has high heavy metal gettering capability, is thermally stable and easy to control its thickness, and generates misfit dislocations The present invention relates to a semiconductor silicon substrate having a ring and auto-doping suppression effect and a method for manufacturing the same.
[0002]
[Prior art]
Important characteristics required for silicon substrates include heavy metal contamination countermeasures and formation of oxygen precipitate free zones. Here, the prior art of these two characteristics will be described first. First, it is well known that the influence of heavy metal contamination is that the breakdown voltage of an oxide film is deteriorated, a deep impurity level is formed, the leakage current of a pn junction is increased, and a defect generation nucleus is formed. .
[0003]
As a conventional heavy metal gettering technique, an intrinsic gettering (IG) method such as gettering by a stress field formed by oxygen precipitates (BMD) or Fe—B pair formation by boron doping, Ixtrinic gettering (gettering due to stress field and dislocation formed by side damage (BSD), gettering due to stress field and grain boundary formed by polyback seal (PBS) (poly-Si film formation) The EG) method, and the extrinsic internal gettering method that performs gettering by misfit dislocations formed by inserting a Si (Ge) layer or a stress field have been put into practical use.
[0004]
BMD is effective in gettering heavy metals, but on the other hand, device characteristics, particularly trench capacitor capacitance, are changed in the device process, so that a surface region without BMD, that is, a DZ layer is required. In order to form the DZ layer, a so-called DZ-IG treatment is generally performed in which heat treatment is performed in oxygen, nitrogen, or a mixed atmosphere thereof.
[0005]
On the other hand, in a silicon epitaxial wafer, oxygen is hardly diffused in the epitaxial layer, BMD is not formed, and as a countermeasure for latch-up, it is possible to use a low resistance, that is, a high concentration dove substrate, to improve the degree of freedom in device design. It is known to be effective in preventing malfunction.
[0006]
[Problems to be solved by the invention]
The conventional gettering technology as a countermeasure against heavy metal contamination has the following problems. The BMD method is thermally unstable, and BMD formation greatly depends on the oxygen concentration and dopant concentration of the substrate, is difficult to control, requires a process for promoting precipitation, and increases the number of processes. The Fe-B pair formation method by boron doping cannot perform gettering other than Fe, and the gettering ability of a substrate having a low boron concentration such as P-Si or N-Si is lowered.
[0007]
The BSD method is thermally unstable, such as generation of particles from the strained part, low gettering ability in low-temperature processes, relaxation of the stress field and disappearance of dislocations due to heat treatment, and deterioration of gettering ability. There is a problem. The PBS method generates fewer particles than the BSD method, but has a low gettering capability in a low-temperature process, and heat-unstable problems such as poly-Si becoming a single crystal due to heat treatment, resulting in a decrease in gettering capability. There is.
[0008]
In addition, the method using the Si (Ge) layer has a problem that an increase in equipment cost due to the new gas line for introducing Ge and the addition of incidental facilities in the epitaxial growth cannot be avoided.
[0009]
The formation of the DZ layer not only increases the number of steps by the DZ-IG process, but there is a concern about thermal instability of the DZ layer, such as the possibility of oxygen diffusing and forming BMD after the heat treatment.
[0010]
In addition, in the case of a highly doped substrate for an epitaxial wafer, autodoping becomes prominent. When the boron concentration is high, BMD is difficult to be formed, and gettering ability is deteriorated.
[0011]
The present invention eliminates the above-described problems of the semiconductor silicon substrate, has a DZ layer that is easy to manufacture, has high gettering ability for heavy metals, is thermally stable, and can be easily controlled in thickness, and is caused by misfit dislocations. An object of the present invention is to provide a semiconductor silicon substrate having an effect of suppressing heavy metal gettering and autodoping, and a method of manufacturing the same.
[0012]
[Means for Solving the Problems]
Firstly, the inventors do not depend on the above-mentioned problems related to heavy metal contamination, that is, the characteristics of the silicon substrate, such as P type or N type, dopant concentration, oxygen concentration, etc., and are thermally stable and generate particles. As a result of various studies on gettering methods that can capture heavy metals efficiently at low cost, mismatch dislocations and stress fields are formed at the interface by stacking layers and substrates with significantly different dopant concentrations on a silicon substrate. Thus, it has been found that these can getter heavy metals and achieve the above-mentioned object.
[0013]
In addition to the heavy metal contamination, the inventors have obtained the above-mentioned problems related to the DZ layer, that is, they do not depend on the characteristics of the silicon substrate, are thermally stable, do not generate particles, and efficiently get heavy metal at low cost. As a result of various investigations on the formation method of the DZ layer that can be ring-shaped and the DZ-IG treatment step is omitted, and is a thermally stable DZ layer and the thickness of the DZ layer can be easily controlled. By forming a laminated silicon wafer having a two-layer structure or a three-layer structure, misfit dislocations and stress fields are formed at the interface of layers with greatly different dopant concentrations, and these can getter heavy metals, and by epitaxial growth. Since the DZ layer is formed, oxygen precipitation is unlikely to occur, and a highly doped layer is used as the DZ layer. And knowledge to be effective in, and have completed the present invention.
[0014]
Furthermore, as a result of examining all combinations on the condition that three layers having different dopant concentrations are formed on a silicon substrate , the inventors have found that the simplest creation and heavy metal gettering due to generation of misfit dislocations and The following substrates are proposed as semiconductor substrates having an autodoping effect.
[0016]
The invention according to claim 1, in the silicon substrate dopant concentration 1 × 10 ¹⁶ atoms / cm ³ or less, on the silicon substrate, the first layer is the dopant concentration 1 × 10 ¹⁸ atoms / cm ³ or more , an intermediate epitaxial layer with a dopant concentration in the range of ^{1 × 10 16 ~1 × 10 18} atom / cm 3, a second epitaxial layer dopant concentration is below ^{1 × 10 16 atoms / cm 3} , were sequentially laminated It is a silicon substrate.
[0017]
According to the second aspect of the present invention, the first layer having a dopant concentration of 1 × 10 ¹⁸ atoms / cm ³ or more is ion-implanted on a silicon substrate having a dopant concentration of 1 × 10 ¹⁶ atoms / cm ³ or less. , A step of laminating an intermediate epitaxial layer having a dopant concentration in the range of 1 × 10 ¹⁶ to 1 × 10 ¹⁸ atoms / cm ³ on the first layer, and a dopant on the intermediate epitaxial layer Laminating a second epitaxial layer having a concentration of 1 × 10 ¹⁶ atoms / cm ³ or less.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In order to form misfit dislocations and stress fields at the interface for heavy metal gettering, there is a method using mixed crystals as represented by SiGe crystals (including thin films). Since this method uses only elements contained in a normal silicon substrate, there is an advantage that there is almost no deterioration of other characteristics or an increase in manufacturing equipment costs.
[0019]
In this invention, as the difference in dopant concentration is as large as possible, distortion increases and misalignment dislocations and stress fields are easily formed. As a result of examining the dopant concentration difference at the interface, silicon having any of the known characteristics is obtained. Even when a substrate is used, an interface formed by silicon having a dopant concentration of 1 × 10 ¹⁶ atoms / cm ³ or less and silicon having a dopant concentration of 1 × 10 ¹⁸ atoms / cm ³ or more is most effective. confirmed.
[0020]
In the present invention, one or more interfaces using the difference in dopant concentration may be formed in two or more multilayer films laminated on the silicon substrate. The type and characteristics of the silicon substrate, the required coating type, etc. The dopant concentration in the coating layer may be changed continuously or gradually if the dopant concentration in the coating layer is constant and a difference in the predetermined dopant concentration at the interface can be secured. Even if the film is formed, the gettering ability according to the present invention is exhibited similarly.
[0021]
In addition, as shown in the examples, the vapor phase growth method and the ion implantation method are used as the method for forming the gettering layer at the interface utilizing the difference in dopant concentration, so that the dopant concentration can be easily controlled. Has an effect of forming a steep interface. In addition, the inventors have confirmed that the same configuration and operational effects as described above can be obtained by the method of bonding the substrates.
[0022]
As an example, as shown in FIG. 1, the dopant concentration 1 × 10 ¹⁶ atoms / cm ³ or less on the silicon substrate 1 by vapor deposition or ion implantation, dopant concentration 1 × 10 ¹⁸ atoms / cm By forming the first layer 2 that is ³ or more, mismatched dislocations and strain fields are formed at the interface due to the difference in dopant concentration, and heavy metals are efficiently gettered to the dislocations and strain fields.
[0023]
Accordingly, it is possible to getter heavy metals efficiently at low cost without being dependent on the characteristics of the silicon substrate such as P type or N type, dopant concentration, oxygen concentration, etc., and being thermally stable. In addition, since it is formed by a vapor deposition method or an ion implantation method, the film thickness and the dopant concentration can be easily controlled and a steep interface can be obtained.
[0024]
Next, as shown in FIG. 1, a second layer 3, that is, an epitaxial layer, having a dopant concentration of 1 × 10 ¹⁶ atoms / cm ³ or less is formed on the first layer 2 by vapor deposition or ion implantation. It has a two-layer structure. The first layer 2 is a DZ layer that also serves as a heavy metal gettering layer. When formed by the vapor phase growth method, the DZ-IG treatment step can be omitted. By the vapor phase growth method or ion implantation method. Makes it possible to control the thickness of the DZ layer. Furthermore, since the diffusion of oxygen into the epitaxial layer is almost negligible, BMD is not formed after the heat treatment and is thermally stable.
[0025]
Since the interface between the first layer 2 that is the DZ layer and the second layer 3 that is the epitaxial layer is close to the device region and is also a region where a trench capacitor is formed, the occurrence of misfit dislocations is prevented and stress is reduced. There is a need. As a countermeasure, it is necessary to increase the width of the transition layer at the interface, preferably 0.5 μm or more. Therefore, as long as an interface having a predetermined dopant concentration difference can be formed with a constant thickness, the film may be formed so that the dopant concentration in the layer changes continuously or gradually.
[0026]
In the present invention, as shown in FIG. 2, the three-layer structure has a dopant concentration of 1 × 10 ¹⁸ on a silicon substrate 1 having a dopant concentration of 1 × 10 ¹⁶ atoms / cm ³ or less by vapor deposition or ion implantation. atoms / cm ³ to form an in that the first layer 2 or more, the dopant concentration of the intermediate layer 4 are laminated in the same manner in the range of ^{1 × 10 16 ~1 × 10 18} atom / cm 3 thereon, further dopant concentration A second layer 3 having a thickness of 1 × 10 ¹⁶ atoms / cm ³ or less, that is, an epitaxial layer is formed to form a three-layer structure.
[0027]
With this three-layer structure, heavy metals can be efficiently gettered by mismatched dislocations and stress fields formed at the interface above or below the layer having a high dopant concentration, and the tensile stress of the inserted layer. As a result, since the dopant concentration of the inserted layer is high, Fe-B pairs are also efficiently generated, and the gettering ability of Fe is improved.
[0028]
The misfit dislocations at the interface and the high-concentration boron layer are thermally stable, and their gettering ability does not depend on the characteristics of the substrate. Further, since no PBS or BSD is formed on the back surface, there is an effect that no particles are generated. Furthermore, a secondary effect that the back surface can be mirror-finished simultaneously with the front surface, the processing cost can be reduced, and the processing accuracy (flatness, etc.) is improved also occurs. In addition, since the gettering sink position is close to the device formation region, heavy metal can be efficiently gettered even in a low temperature process where the diffusion rate of heavy metal is low.
[0029]
When the intermediate layer 4 serving as the DZ layer is formed by the vapor phase growth method, the DZ-IG treatment process can be omitted. When the vapor phase growth method or the ion implantation method is used, the thickness of the DZ layer can be controlled. . Furthermore, since the diffusion of oxygen into the epitaxial layer is almost negligible, BMD is not formed after the heat treatment and is thermally stable.
[0030]
In the present invention, since a silicon substrate having a dopant concentration of 1 × 10 ¹⁶ atoms / cm ³ or less is used, the autodoping level in the epitaxial layer is extremely low, and an effect of being almost negligible is produced.
[0031]
【Example】
Reference example 1
The structures of the substrate and epitaxial layer of the present invention used in the following reference examples and examples are as follows.
1) Appearance: 8 inches φ, (675 ± 5) μm ^t , double-sided mirror substrate 2) Plane orientation: (100) ± 0.5 °
3) Resistivity: 3-5 Ω · cm (Boron concentration: 2.8-4.5 × 10 ¹⁵ atoms / cm ³ )
4) First layer Resistivity: 0.001 to 0.003 Ω · cm (Boron concentration: 3.5 to 13 × 10 ¹⁹ atoms / cm ³ )
・ Film thickness: 5μm ^t
5) Second layer Resistivity: 10 Ω · cm (Boron concentration: ˜1.5 × 10 ¹⁵ atoms / cm ³ )
・ Film thickness: 3μm ^t
The first layer and the second layer were formed by a thermal CVD method (chemical vapor deposition method) using SiHCl ₃ as a source gas.
[0032]
Comparison of heavy metal gettering ability A comparison between the present invention and a conventional gettering method is shown. Each epitaxial substrate formed with each gettering ability is mixed with 10 ¹² atoms / cm ² of Fe, Ni, Cr, and Cu, heat treated by a high temperature process, and then the yield rate of the oxide film withstand voltage (yield) and C The carrier life by the -t method was examined. Each process is shown below.
High temperature process: 1150 ° C. × 5 hrs. + 700 ° C. × 6 hrs. + 1050 ° C. × 5 hrs.
Measurement of oxide film withstand voltage non-defective rate: oxide film thickness 200 mm, applied voltage 11 MV / cm
[0033]
As is apparent from Table 1, the gettering method according to the present invention is superior to the other methods. The BMD shown in the gettering performance specification is a value measured using an optical microscope after performing selective etching of 2 μm on one side using a Wright Etch solution.
[0034]
[Table 1]

[0035]
Comparison of heavy metal gettering ability in low temperature process The above gettering ability was compared after low temperature heat treatment, and the same evaluation was made and compared. Low temperature process: 600 ° C. × 5 hrs. + 900 ° C. × 32 hrs. + 800 ° C. × 5 hrs.
As is apparent from Table 2, the gettering method according to the present invention is superior to other methods even in a low temperature process.
[0036]
[Table 2]

[0037]
When the stability of the gettering ability with respect to the difference in boron concentration of the substrate in the present invention was examined, as shown in Table 3, it was shown that there was no change in the gettering ability even when substrates having different boron concentrations were used.
[0038]
[Table 3]

[0039]
When the sample of the present invention was analyzed by SIMS, it was found that heavy metal was selectively gettered at the interface where misfit dislocations were formed and the high-concentration boron layer as shown in FIG. 3A. The results show the misfit dislocations and the gettering effect of the high-concentration boron layer in the present invention.
[0040]
FIG. 4A and FIG. 5A show the results of comparing the thermal stability of the gettering ability after the previous heat treatment process with the conventional method.
[0041]
The amount of generated particles was examined by transferring particles in pure water. In this method, a wafer having another clean surface mirror-finished on the back surface of the wafer is placed in a cleaning tank, particles generated from the back surface are transferred to a clean upper surface, and the transferred wafer surface has a size of 0.12 μm or more. This is a method of estimating the amount of particles generated from the back surface by evaluating the particles with a surface detector. The results are shown in Table 4.
[0042]
[Table 4]

[0043]
Example 2
The structure of the substrate and epitaxial layer of the present invention used in the following examples is as follows.
1) Appearance: 8 inches φ, (675 ± 5) μm ^t , double-sided mirror substrate 2) Plane orientation: (100) ± 0.5 °
3) Resistivity: 3-5 Ω · cm (Boron concentration: 2.8-4.5 × 10 ¹⁵ atoms / cm ³ )
4) First layer Resistivity: 0.001 to 0.003 Ω · cm (Boron concentration: 3.5 to 13 × 10 ¹⁹ atoms / cm ³ )
・ Film thickness: 5μm ^t
5) Intermediate layer Resistivity: 0.01 to 0.02 Ω · cm (Boron concentration: 3.5 to 9 × 10 ¹⁸ atoms / cm ³ )
・ Film thickness: 3μm ^t
6) Second layer Resistivity: 10 Ω · cm (Boron concentration: ˜1.5 × 10 ¹⁵ atoms / cm ³ )
・ Film thickness: 3μm ^t
The first layer, the intermediate layer, and the second layer were formed by a thermal CVD method (chemical vapor deposition method) using SiHCl ₃ as a source gas.
[0044]
Comparison of heavy metal gettering ability A comparison between the present invention and a conventional gettering method is shown. The epitaxial substrate on which each gettering sink is formed is subjected to mixed contamination of Fe, Ni, Cr, Cu of 10 ¹² atoms / cm ² and heat-treated in a high-temperature process, and then the yield rate of the oxide film withstand voltage (yield) and C The carrier life by the -t method was examined. Each process is shown below.
High temperature process: 1190 ° C. × 6 hrs. + 600 ° C. × 4 hrs. + 1000 ° C. × 4 hrs.
Measurement of oxide film withstand voltage non-defective rate: oxide film thickness 150 mm, applied voltage 11 MV / cm
As is apparent from Table 5, it was shown that the gettering method according to the present invention is superior to other methods.
[0045]
[Table 5]

[0046]
Table 2 shows the results of comparison of heavy metal gettering ability in the low temperature process in the same manner as in Example 1.
[0047]
When the sample of the present invention was analyzed by SIMS, it was found that heavy metal was selectively gettered at the interface where the misfit dislocations were formed and the high-concentration boron layer as shown in FIG. 3B. From these results, the heavy metal gettering due to the occurrence of misfit dislocations in the present invention and the gettering effect of the high-concentration boron layer were shown.
[0048]
4B and 5B show the results obtained by comparing the thermal stability of the gettering ability after the previous heat treatment process with the conventional method.
[0049]
The amount of generated particles was examined by particle transfer in pure water as in Example 1. The results are shown in Table 4.
[0050]
Example 3
The structure of the substrate and epitaxial layer of the present invention used in the following examples is as follows.
1) Appearance: 8 inches φ, (675 ± 5) μm ^t , double-sided mirror substrate 2) Plane orientation: (100) ± 0.5 °
3) Resistivity: 4-6 Ω · cm (Boron concentration: 2.3-3.5 × 10 ¹⁵ atoms / cm ³ )
4) First layer Resistivity: 0.001 to 0.003 Ω · cm (Boron concentration: 3.5 to 13 × 10 ¹⁹ atoms / cm ³ )
・ Film thickness: 5μm ^t
5) Intermediate layer Resistivity: 0.01 to 0.02 Ω · cm (Boron concentration: 3.5 to 9 × 10 ¹⁸ atoms / cm ³ )
・ Film thickness: 3μm ^t
6) Second layer Resistivity: 10 Ω · cm (Boron concentration: ˜1.5 × 10 ¹⁵ atoms / cm ³ )
・ Film thickness: 3μm ^t
The first layer was formed by an ion implantation method, and the intermediate layer and the second layer were formed by a thermal CVD method (chemical vapor deposition method) at a growth temperature of 1150 ° C. using SiHCl ₃ as a source gas.
[0051]
In the first layer ion implantation method, first, BFe ²⁺ ions are implanted with an acceleration voltage of 110 keV and a doping amount of 5 × 10 ¹⁵ / cm ³ , and this is heat-treated by RTP (Rapid Thermal Process) at 1000 ° C. for 60 seconds. . FIG. 6 shows the boron concentration distribution in the depth direction at this time. The boron concentration was 10 ²⁰ atoms / cm ³ on the surface of the first layer and the depth was 1 μm, which was almost the same level as that of the epitaxial substrate. At this time, no misfit dislocation was observed at the interface between the substrate and the first layer formed by ion implantation (Plan view TEM observation). Therefore, it is considered that only the stress field due to the boron concentration difference is formed at the interface.
[0052]
A comparison of heavy metal gettering ability between the present invention and a conventional gettering method is shown. The epitaxial substrate on which each gettering sink is formed is subjected to mixed contamination of Fe, Ni, Cr, Cu of 10 ¹² atoms / cm ² and heat-treated in a high-temperature process, and then the yield rate of the oxide film withstand voltage (yield) and C The carrier life by the -t method was examined. Each process is shown below.
High temperature process: 1150 ° C. × 6 hrs. + 600 ° C. × 4 hrs. + 950 ° C. × 4 hrs.
Measurement of oxide film withstand voltage non-defective rate: oxide film thickness 200 mm, applied voltage 11 MV / cm
As is apparent from Table 6, the gettering method according to the present invention is superior to other methods.
[0053]
[Table 6]

[0054]
Comparison of heavy metal gettering ability in the following low-temperature process was performed after low-temperature heat treatment, and the same evaluation as in the examples was performed for comparison.
Low temperature process: 600 ° C. × 4 hrs. + 850 ° C. × 3 hrs. + 680 ° C. × 6 hrs.
As is apparent from Table 7, the gettering method according to the present invention is superior to the other methods even in the low temperature process.
[0055]
[Table 7]

[0056]
Moreover, when the sample of this invention was analyzed by SIMS, it was found that heavy metal was selectively gettered at the interface where the stress field was formed and the first layer which is a high-concentration boron layer as shown in FIG. 3C. . From these results, the gettering effect of the stress field and the high-concentration boron layer in the present invention was shown.
[0057]
【The invention's effect】
In the present invention, by forming a silicon wafer having a three-layer structure in which layers having greatly different dopant concentrations are laminated , mismatched dislocations and stress fields are formed at the interfaces of the layers having greatly different dopant concentrations, and thereby heavy metals are gettered. It can ring, does not depend on the characteristics of the silicon substrate (P type or N type, dopant concentration, oxygen concentration, etc.), is thermally stable, does not generate particles, and can efficiently getter heavy metals at low cost. Since the DZ layer is formed, oxygen precipitation is unlikely to occur, the DZ-IG treatment step is omitted, a thermally stable DZ layer that can control the thickness of the DZ layer can be formed, and the DZ layer Since a highly doped layer is used, it is very effective as a latch-up countermeasure.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a two-layer structure of a silicon substrate which is a reference regarding to the present invention.
FIG. 2 is an explanatory view showing a three-layer structure of a silicon substrate according to the present invention.
FIGS. 3A and 3B are graphs showing SIMS analysis profiles of a silicon substrate according to the present invention or a reference example of the present invention . FIGS.
FIGS. 4A and 4B are graphs showing the relationship between the number of high-temperature processes and the carrier life.
FIGS. 5A and 5B are graphs showing the relationship between the number of high-temperature processes and the thickness of a DZ layer.
FIG. 6 is a graph showing the relationship between depth and boron concentration.

Claims (2)

1x10 dopant concentration ¹⁶ atoms / cm ^Three In the following silicon substrates:
  On this silicon substrate,
  1x10 dopant concentration ¹⁸ atoms / cm ^Three The first layer,
  1x10 dopant concentration ¹⁶ ~ 1x10 ¹⁸ atom / cm ^Three An intermediate epitaxial layer in the range of
  1x10 dopant concentration ¹⁶ atoms / cm ^Three A silicon substrate in which the following second epitaxial layers are sequentially laminated. 1x10 dopant concentration ¹⁶ atoms / cm ^Three On the following silicon substrate, the dopant concentration is 1 × 10 ¹⁸ atoms / cm ^Three Forming the first layer as described above by ion implantation;
  On this first layer, the dopant concentration is 1 × 10 ¹⁶ ~ 1x10 ¹⁸ atom / cm ^Three Laminating an intermediate epitaxial layer in the range of
  On this intermediate epitaxial layer, the dopant concentration is 1 × 10 ¹⁶ atoms / cm ^Three Laminating a second epitaxial layer which is the following, a method for producing a silicon substrate.

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