JP2014216415A - Semiconductor substrate manufacturing method and silicon substrate - Google Patents
Semiconductor substrate manufacturing method and silicon substrate Download PDFInfo
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- 239000000758 substrate Substances 0.000 title claims abstract description 66
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 41
- 239000010703 silicon Substances 0.000 title claims abstract description 41
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 40
- 239000004065 semiconductor Substances 0.000 title claims abstract description 24
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 16
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 115
- 239000001301 oxygen Substances 0.000 claims abstract description 115
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 22
- 238000000034 method Methods 0.000 claims description 11
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- 238000001556 precipitation Methods 0.000 abstract description 36
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- -1 Boron ions Chemical class 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
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- XEMZLVDIUVCKGL-UHFFFAOYSA-N hydrogen peroxide;sulfuric acid Chemical compound OO.OS(O)(=O)=O XEMZLVDIUVCKGL-UHFFFAOYSA-N 0.000 description 1
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- 238000000206 photolithography Methods 0.000 description 1
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- 238000004886 process control Methods 0.000 description 1
- WQGWDDDVZFFDIG-UHFFFAOYSA-N pyrogallol Chemical compound OC1=CC=CC(O)=C1O WQGWDDDVZFFDIG-UHFFFAOYSA-N 0.000 description 1
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- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/32—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers using masks
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Abstract
Description
本発明は、半導体基板、特に固体撮像素子のようなシリコン基板特性に左右されやすいデバイス用途半導体基板及びその製造方法に関するものであり、金属不純物に対するゲッタリングと酸素析出そのものに起因するリークの低減とを両立させるための手法に関するものである。 The present invention relates to a semiconductor substrate, particularly a device-use semiconductor substrate that is easily affected by the characteristics of a silicon substrate such as a solid-state imaging device, and a method for manufacturing the same, and is intended to reduce gettering against metal impurities and leakage due to oxygen precipitation itself. It is related with the technique for making it compatible.
メモリ、ＣＣＤ等の固体撮像素子等の半導体装置の微細化、高性能化に伴い、それらの製品歩留まりを向上させるために、材料としてのシリコン基板にも高品質化が要求され、これに対応した各種シリコン基板が開発されている。
特に、固体撮像素子においては、シリコン基板の品質が大きく影響するため、この品質を改善するための様々な検討がなされてきた。例えば、製品特性に直接影響を与えると推測されるウェーハ表層部の品質の改善策として、１）不活性ガス又は水素を含む雰囲気中での高温処理、２）引き上げ条件の改善によりグローンイン（Ｇｒｏｗｎ−ｉｎ）欠陥の低減、３）エピタキシャル成長ウェーハ等がある。
As semiconductor devices such as solid-state imaging devices such as memories and CCDs are miniaturized and improved in performance, silicon substrates as materials are also required to have higher quality in order to improve their product yield. Various silicon substrates have been developed.
In particular, in a solid-state imaging device, the quality of a silicon substrate has a great influence, and thus various studies have been made to improve this quality. For example, as a measure for improving the quality of the wafer surface layer portion that is supposed to directly affect the product characteristics, 1) high-temperature treatment in an atmosphere containing an inert gas or hydrogen, 2) growth-in (Grown-in) in) reduction of defects, and 3) epitaxially grown wafers.
一方では、主にシリコン基板の製造工程中に起こる金属汚染が固体撮像素子をはじめとしたデバイスの特性に大きく影響することから、素子領域から金属汚染元素を取り除くゲッタリング手法が広く用いられている。このゲッタリングは、良く知られているように各種手法が検討・開発されている。この中で、ＣＺ基板に含まれる酸素をＳｉＯ２（酸素析出物）として基板中に析出させ、これに金属元素をゲッタリングさせる、いわゆるＩＧ（Ｉｎｔｒｉｎｓｉｃ Ｇｅｔｔｅｒｉｎｇ）手法が広く用いられている。 On the other hand, gettering techniques that remove metal contamination elements from the element region are widely used because metal contamination that occurs mainly during the manufacturing process of silicon substrates greatly affects the characteristics of devices such as solid-state imaging devices. . As for this gettering, various methods have been studied and developed as is well known. Among these, a so-called IG (Intrinsic Gettering) method is widely used, in which oxygen contained in a CZ substrate is precipitated in the substrate as SiO 2 (oxygen precipitates), and a metal element is gettered thereto.
例えば、非特許文献１には、酸素析出と素子の不良率について記載されている。これによると、酸素析出が多いほど素子不良が低減される。すなわちゲッタリング効果が高くなっていく。そのため、高酸素濃度の基板を使用したりするなどして、十分な量の酸素析出が行われるようにしている。このように、酸素析出物により金属元素をゲッタリングすることで素子領域の金属を低減し、例えばＰＮ接合部のリーク電流を低減させたりすることが可能になる。 For example, Non-Patent Document 1 describes oxygen precipitation and device defect rate. According to this, device defects are reduced as the amount of oxygen precipitation increases. That is, the gettering effect increases. Therefore, a sufficient amount of oxygen is deposited by using a substrate having a high oxygen concentration. Thus, gettering of the metal element by the oxygen precipitates can reduce the metal in the element region, for example, reduce the leakage current of the PN junction.
さらにＧｒｏｗｎ−ｉｎ欠陥がリーク電流に影響することが知られている。例えば、特許文献１には、多面体の結晶欠陥において、多面体の頂点からひげ状欠陥を伸ばすことでリーク不良領域を減少できることが記載されている。しかし、Ｇｒｏｗｎ−ｉｎ欠陥の大きさは小さく、また基本的にシリコンのみが構成元素であるため、酸素や金属のような異物が共存する析出物がリーク電流へ与える影響に比べて、Ｇｒｏｗｎ−ｉｎ欠陥がリーク電流へ与える影響は小さいと考えられる。 Further, it is known that a Grown-in defect affects a leakage current. For example, Patent Document 1 describes that in a polyhedron crystal defect, a leak defect region can be reduced by extending a whisker-like defect from the apex of the polyhedron. However, since the size of the grown-in defect is small, and basically only silicon is a constituent element, the grown-in defect is compared with the influence of precipitates coexisting with foreign matters such as oxygen and metal on the leakage current. It is considered that the influence of the defect on the leakage current is small.
また、非特許文献２には、リーク源として、酸素析出とシリコンの界面準位の存在が説明されている。 Non-Patent Document 2 describes the existence of an interface state between oxygen precipitation and silicon as a leak source.
酸素析出物そのものはリーク源となり、例えば図７に示すように、析出量ΔＯｉを多くすると酸素析出物そのものからのリーク電流が大きくなり、例えばウェーハ面内で同心円状のリークムラが発生することがある。このような現象は、例えば固体撮像素子の場合、もちろんデバイス構造により影響の大小はあるが、ウェーハ面内で暗電流差を生じることになり、不良の大きな原因の１つと考えられる。 The oxygen precipitate itself becomes a leak source. For example, as shown in FIG. 7, when the precipitation amount ΔOi is increased, the leak current from the oxygen precipitate itself increases, and for example, concentric leak unevenness may occur in the wafer surface. . Such a phenomenon, for example, in the case of a solid-state image sensor, of course, has a large or small influence depending on the device structure, but a dark current difference occurs in the wafer surface, which is considered to be one of the major causes of defects.
本発明者はこの事象を確認するために、以下のような実験を行った。
まず、酸素濃度１５ｐｐｍａのシリコンウェーハに、エピタキシャル層を１０μｍ成長させたエピタキシャルウェーハを２枚準備し、１枚のウェーハに低温、中温、高温の３段階の熱処理を組み合わせて酸素析出物を形成した。この酸素析出物を形成したウェーハと、酸素析出物を形成しないウェーハのそれぞれにＰＮ接合構造を形成し、リーク電流の面内分布を調べた。
In order to confirm this phenomenon, the present inventor conducted the following experiment.
First, two epitaxial wafers having an epitaxial layer grown by 10 μm were prepared on a silicon wafer having an oxygen concentration of 15 ppma, and oxygen precipitates were formed by combining three wafers of low temperature, medium temperature, and high temperature on one wafer. A PN junction structure was formed on each of the wafer on which the oxygen precipitate was formed and the wafer on which the oxygen precipitate was not formed, and the in-plane distribution of the leakage current was examined.
ここで、低温熱処理を５００℃、４時間の条件で、中温熱処理を８００℃、４時間の条件で、高温熱処理を１０００℃、８時間の条件でそれぞれ実施した。酸素析出物の析出量ΔＯｉは０．３ｐｐｍａであった。図４にリーク電流の面内分布の結果を示す。図４に示すように、析出熱処理なしの場合にはリークムラが見られないのに比べ、析出熱処理ありの場合には、析出量が０．３ｐｐｍａ程度であっても縞状のリークムラが観察された。 Here, low temperature heat treatment was performed under conditions of 500 ° C. for 4 hours, intermediate temperature heat treatment was performed under conditions of 800 ° C. for 4 hours, and high temperature heat treatment was performed under conditions of 1000 ° C. for 8 hours. The amount of precipitated oxygen ΔOi was 0.3 ppma. FIG. 4 shows the result of in-plane distribution of leakage current. As shown in FIG. 4, stripe-like leak unevenness was observed even when the precipitation amount was about 0.3 ppma in the case of the precipitation heat treatment, compared to the case where no leak unevenness was observed in the case of no precipitation heat treatment. .
このように、ゲッタリングの観点からは酸素析出物が多いと好ましいが、酸素析出物が多すぎるとリーク源となってしまう可能性がある。そのため、酸素析出物からのリークを出来るだけ軽減する必要がある。 Thus, from the viewpoint of gettering, it is preferable that there are many oxygen precipitates. However, if there are too many oxygen precipitates, there is a possibility of becoming a leak source. Therefore, it is necessary to reduce leakage from oxygen precipitates as much as possible.
酸素析出物がリーク電流に与える影響について、例えば特許文献２に、表面から５μｍ以内にある酸素析出物の対角線長さとリーク電流の関係や、リーク電流を測定しなくても酸素析出のサイズと密度を測定することで、リーク電流の大きさを見積もることが可能であることが記載されている。特許文献２には、析出物の形状についても議論されているが八面体のほうが若干リークが高いがほとんど同じレベルである。しかし、実際に酸素析出物は表面付近よりもバルクに多数存在しており、空乏層に含まれるよりも空乏層外からの拡散電流としての寄与の方が大きいと思われる。さらに微視的なリークの問題に対して、図４に示すような析出ムラに起因するリーク電流分布が縞状に存在する問題や、ゲッタリングとの両立という観点からの議論も十分ではない。 Regarding the influence of oxygen precipitates on leakage current, for example, Patent Document 2 discloses the relationship between the diagonal length of oxygen precipitates within 5 μm from the surface and the leakage current, and the size and density of oxygen precipitation without measuring the leakage current. It is described that it is possible to estimate the magnitude of the leakage current by measuring. Patent Document 2 discusses the shape of the precipitate, but the octahedron has a slightly higher leak, but is almost at the same level. However, there are actually a large number of oxygen precipitates in the bulk rather than near the surface, and it seems that the contribution as diffusion current from the outside of the depletion layer is greater than that contained in the depletion layer. Further, with respect to the problem of microscopic leakage, there is not enough discussion from the viewpoint of the problem that the leakage current distribution due to the deposition unevenness as shown in FIG.
本発明は前述のような問題に鑑みてなされたもので、ＣＣＤ、ＣＭＯＳセンサをはじめとした高歩留まりが要求される半導体装置に使用されるシリコン基板において、ゲッタリングを維持しつつ酸素析出物によるリーク電流を低減するという相反する特性を有した半導体基板の製造方法及びシリコン基板を提供することを目的とする。 The present invention has been made in view of the above-described problems. In a silicon substrate used for a semiconductor device that requires a high yield, such as a CCD and a CMOS sensor, the present invention is based on oxygen precipitates while maintaining gettering. It is an object of the present invention to provide a method for manufacturing a semiconductor substrate and a silicon substrate having conflicting characteristics of reducing leakage current.
上記目的を達成するために、本発明によれば、シリコン基板を準備する工程と、該シリコン基板に熱処理を施して酸素析出物を形成する工程を有する半導体基板の製造方法であって、前記酸素析出物を形成する工程において、前記シリコン基板に酸素析出核形成、酸素析出核成長、及び酸素析出物形成の３段階の熱処理を行い、前記酸素析出物形成の熱処理の温度を１１００℃以上とすることによって、前記形成する酸素析出物の形状を八面体状又は球状にすることを特徴とする半導体基板の製造方法が提供される。 In order to achieve the above object, according to the present invention, there is provided a method of manufacturing a semiconductor substrate, comprising: a step of preparing a silicon substrate; and a step of heat-treating the silicon substrate to form an oxygen precipitate. In the step of forming a precipitate, the silicon substrate is subjected to a three-step heat treatment of oxygen precipitate nucleation, oxygen precipitate nucleation growth, and oxygen precipitate formation, and the temperature of the heat treatment for forming the oxygen precipitate is set to 1100 ° C. or higher. Thus, there is provided a method for manufacturing a semiconductor substrate, characterized in that the shape of the oxygen precipitate formed is octahedral or spherical.
このような製造方法であれば、形成する酸素析出物の析出量を低減することなく、その表面積を低減できるので、必要なゲッタリング能力を維持しつつ酸素析出物によるリーク電流を低減できる。 With such a manufacturing method, the surface area can be reduced without reducing the amount of oxygen precipitates to be formed, so that leakage current due to oxygen precipitates can be reduced while maintaining the required gettering ability.
このとき、前記シリコン基板を準備する工程において、前記準備するシリコン基板に窒素をドープし、窒素濃度を４．９×１０１３ａｔｏｍｓ／ｃｍ３以下にすることによって、前記酸素析出物の形状を球状にすることが好ましい。
このようにすれば、酸素析出物の形状を球状にすることができ、酸素析出物の析出量に対する表面積をより低減できる。これにより、リーク電流をより効果的に低減できる。
At this time, in the step of preparing the silicon substrate, the silicon substrate to be prepared is doped with nitrogen, and the nitrogen concentration is reduced to 4.9 × 10 13 atoms / cm 3 or less, so that the shape of the oxygen precipitate is spherical. It is preferable to make it.
In this way, the shape of the oxygen precipitate can be made spherical, and the surface area relative to the amount of oxygen precipitate deposited can be further reduced. Thereby, leakage current can be reduced more effectively.
また、本発明によれば、酸素析出物を含有するシリコン基板であって、前記酸素析出物の形状が球状であることを特徴とするシリコン基板が提供される。
このようなものであれば、酸素析出物の析出量に対する表面積が最大限低減されたものであるので、必要なゲッタリング能力を維持しつつ酸素析出物によるリーク電流をより効果的に低減可能なものとなる。
In addition, according to the present invention, there is provided a silicon substrate containing an oxygen precipitate, wherein the oxygen precipitate has a spherical shape.
In such a case, since the surface area with respect to the amount of oxygen precipitates is reduced to the maximum, leakage current due to oxygen precipitates can be more effectively reduced while maintaining the necessary gettering ability. It will be a thing.
本発明では、シリコン基板に酸素析出核形成、酸素析出核成長、及び酸素析出物形成の３段階の熱処理を行い、酸素析出物形成の熱処理の温度を１１００℃以上とすることによって、形成する酸素析出物の形状を八面体状又は球状にするので、ゲッタリングを維持しつつ酸素析出物によるリーク電流を低減可能な半導体基板を製造できる。 In the present invention, a three-stage heat treatment of oxygen precipitation nucleation, oxygen precipitation nucleation growth, and oxygen precipitate formation is performed on the silicon substrate, and the temperature of the heat treatment for oxygen precipitate formation is set to 1100 ° C. or higher to form oxygen. Since the shape of the precipitate is octahedral or spherical, it is possible to manufacture a semiconductor substrate capable of reducing leakage current due to oxygen precipitates while maintaining gettering.
以下、本発明について実施の形態を説明するが、本発明はこれに限定されるものではない。
上記したように、従来より、高歩留まりが要求される半導体装置に使用されるシリコン基板に対し、ゲッタリングを維持しつつ酸素析出物によるリーク電流を低減するという相反する課題がある。
Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.
As described above, conventionally, there is a conflicting problem of reducing leakage current due to oxygen precipitates while maintaining gettering for a silicon substrate used in a semiconductor device that requires a high yield.
そこで、本発明者はこの課題を解決するために鋭意検討を重ねた。その結果、酸素析出物によるリーク電流は酸素析出物の表面を起源とし、その大きさは表面積に依存することを見出した。そして、リーク電流を低減するためには、酸素析出物の表面積を小さくすれば良く、そのためには酸素析出物形成の熱処理の温度を１１００℃以上として酸素析出物の形状を八面体又は球状にすれば良いことを見出し、本発明を完成させた。 Therefore, the present inventor has intensively studied to solve this problem. As a result, it was found that the leakage current due to the oxygen precipitate originated from the surface of the oxygen precipitate, and its magnitude depends on the surface area. In order to reduce the leakage current, the surface area of the oxygen precipitate may be reduced. For this purpose, the temperature of the heat treatment for forming the oxygen precipitate is set to 1100 ° C. or higher, and the shape of the oxygen precipitate is made octahedral or spherical. As a result, the present invention was completed.
以下、本発明の半導体基板の製造方法について、図１を参照して説明する。
まず、シリコン基板を準備する（図１の（Ａ））。このシリコン基板として、例えばＣＺ法により引き上げた、不純物として酸素を含有するシリコン単結晶から得られるシリコンウェーハや、シリコンエピタキシャルウェーハを準備することができる。
The semiconductor substrate manufacturing method of the present invention will be described below with reference to FIG.
First, a silicon substrate is prepared (FIG. 1A). As this silicon substrate, for example, a silicon wafer obtained from a silicon single crystal containing oxygen as an impurity, which is pulled up by the CZ method, or a silicon epitaxial wafer can be prepared.
次に、この準備したシリコン基板に熱処理を施して酸素析出物を形成する。この熱処理工程は、図１に示すように、酸素析出核形成、酸素析出核成長、及び酸素析出物形成の３段階の熱処理として組み合わせる。酸素析出核形成、酸素析出核成長、及び酸素析出物形成の各熱処理は、それぞれ低温、中温、高温熱処理とする。このようにすることで、低温で酸素析出核を形成し（図１の（Ｂ））、中温で形成された酸素析出核を消滅することなく成長させ（図１の（Ｃ））、高温で酸素析出物を確実に成長させることができる（図１の（Ｄ））。 Next, this prepared silicon substrate is subjected to heat treatment to form oxygen precipitates. As shown in FIG. 1, this heat treatment process is combined as a three-step heat treatment of oxygen precipitation nucleus formation, oxygen precipitation nucleus growth, and oxygen precipitate formation. The heat treatments for the formation of oxygen precipitate nuclei, the growth of oxygen precipitate nuclei, and the formation of oxygen precipitates are respectively a low temperature, medium temperature, and high temperature heat treatment. In this way, oxygen precipitation nuclei are formed at a low temperature ((B) in FIG. 1), and oxygen precipitation nuclei formed at a medium temperature are grown without disappearing ((C) in FIG. 1). Oxygen precipitates can be reliably grown ((D) in FIG. 1).
この酸素析出物形成の熱処理における熱処理温度を１１００℃以上とする。こうすることで、形成する酸素析出物の形状を八面体状又は球状にすることができる。酸素析出物の形状が八面体状又は球状であれば、例えば酸素析出物の形状が板状である場合に比べて、析出量は同じであっても表面積は小さくなる。従って、ゲッタリングを維持しつつ酸素析出物によるリーク電流を低減できる。 The heat treatment temperature in this heat treatment for forming oxygen precipitates is set to 1100 ° C. or higher. By doing so, the shape of the oxygen precipitate to be formed can be octahedral or spherical. If the shape of the oxygen precipitate is octahedral or spherical, for example, the surface area becomes smaller even if the amount of precipitation is the same as compared with the case where the shape of the oxygen precipitate is plate-like. Therefore, leakage current due to oxygen precipitates can be reduced while maintaining gettering.
また、酸素析出核形成の熱処理温度は５００℃程度、酸素析出核成長の熱処理温度は８００℃程度とすることが好ましい。このようにすれば、酸素析出核を確実に成長させることができる。 The heat treatment temperature for forming oxygen precipitation nuclei is preferably about 500 ° C., and the heat treatment temperature for growing oxygen precipitation nuclei is preferably about 800 ° C. In this way, oxygen precipitation nuclei can be reliably grown.
酸素析出物の形状を球状とすれば、析出量に対する表面積を最大限に低減できるので好ましい。酸素析出物の形状を球状にするためには、上記したシリコン基板を準備する工程において、準備するシリコン基板に窒素をドープすれば良い。このとき、窒素濃度を４．９×１０１３ａｔｏｍｓ／ｃｍ３以下にする。これよりも多くても形状変化には寄与しない。窒素濃度の下限は特に限定されないが、シリコン基板の作製時の窒素添加方法を考慮すると、おおよそ１×１０１３ａｔｏｍｓ／ｃｍ３程度が現実的であると考えられる。
尚、窒素添加の有無による析出熱処理の差はない。
It is preferable that the oxygen precipitates have a spherical shape because the surface area relative to the amount of precipitation can be reduced to the maximum. In order to make the shape of the oxygen precipitate spherical, in the step of preparing the silicon substrate described above, the prepared silicon substrate may be doped with nitrogen. At this time, the nitrogen concentration is set to 4.9 × 10 13 atoms / cm 3 or less. More than this does not contribute to the shape change. Although the lower limit of the nitrogen concentration is not particularly limited, it is considered that about 1 × 10 13 atoms / cm 3 is realistic considering the nitrogen addition method at the time of manufacturing the silicon substrate.
There is no difference in the precipitation heat treatment depending on whether or not nitrogen is added.
酸素析出物の形状を球状とした本発明のシリコン基板は、酸素析出物の析出量に対する表面積が最大限低減されたものであるので、必要なゲッタリング能力を維持しつつ酸素析出物によるリーク電流をより効果的に低減可能なものとなる。 Since the silicon substrate of the present invention in which the shape of the oxygen precipitate is spherical has a reduced surface area with respect to the amount of oxygen precipitate deposited, the leakage current caused by the oxygen precipitate while maintaining the required gettering ability. Can be reduced more effectively.
本発明者は、リーク電流が酸素析出物の表面積に依存することを確認するために以下の実験を行った。
酸素濃度１５ｐｐｍａのＣＺ Ｐ型基板（ＣＺ基板）、及びエピタキシャル層を形成したｐ／p−ウェーハ（ＥＰウェーハ）をそれぞれ３枚づつ準備した。準備したＣＺ基板及びＥＰウェーハに５００℃の酸素析出核形成の熱処理及び８００℃の酸素析出核成長の熱処理を行った。その後、同じ析出量で形状が異なる酸素析出物を成長させるために熱処理温度を変更した。
The present inventor conducted the following experiment in order to confirm that the leakage current depends on the surface area of the oxygen precipitate.
Three CZP type substrates (CZ substrate) having an oxygen concentration of 15 ppma and three p / p-wafers (EP wafers) on which an epitaxial layer was formed were prepared. The prepared CZ substrate and EP wafer were subjected to heat treatment for forming oxygen precipitation nuclei at 500 ° C. and heat treatment for growing oxygen precipitation nuclei at 800 ° C. Thereafter, the heat treatment temperature was changed in order to grow oxygen precipitates having different shapes with the same precipitation amount.
具体的には、１枚のＣＺ基板及びＥＰウェーハに１０００℃の熱処理を実施して平板状の酸素析出物を成長させた。また、残りの２枚のＣＺ基板及びＥＰウェーハにそれぞれ１１００℃（八面体１）、１１５０℃（八面体２）の熱処理を実施して八面体状の酸素析出物を成長させた。
このようにして製造したＣＺ基板及びＥＰウェーハにＰＮ接合構造を形成し、リーク電流を測定した。その結果を図５に示す。図５に示すように、ＣＺ基板及びＥＰウェーハのリーク電流のレベルは異なる。この理由としては、ＣＺ基板では酸素析出物が表面近くまで存在するのに対して、ＥＰウェーハでは酸素析出物のないエピタキシャル層が存在することから、ＰＮ接合部と酸素析出物までの距離に差がある（ＥＰウェーハの方が遠い）ためである。
Specifically, a heat treatment at 1000 ° C. was performed on one CZ substrate and EP wafer to grow a flat oxygen precipitate. Further, the remaining two CZ substrates and EP wafers were heat-treated at 1100 ° C. (octahedron 1) and 1150 ° C. (octahedron 2), respectively, to grow octahedral oxygen precipitates.
A PN junction structure was formed on the thus produced CZ substrate and EP wafer, and the leakage current was measured. The result is shown in FIG. As shown in FIG. 5, the CZ substrate and the EP wafer have different leakage current levels. The reason for this is that the oxygen precipitates exist close to the surface in the CZ substrate, whereas the epitaxial layer without oxygen precipitates exists in the EP wafer, so there is a difference in the distance between the PN junction and the oxygen precipitates. (EP wafer is farther).
析出物の形状が平板状と八面体状ではリーク電流レベルに違いが見られ、その差は、ＣＺ基板とＥＰウェーハ共に、平板形状が八面体状の１．８倍程度のリーク電流となっている。また、ＣＺ基板及びＥＰウェーハでは、図６に示すようなリーク電流に温度依存性を有し、傾きが１．１ｅＶに相当する温度特性を持つことから、リーク電流は拡散電流が支配的である。 There is a difference in the leakage current level between the precipitate shape of the flat plate and the octahedron, and the difference between the CZ substrate and the EP wafer is a leakage current about 1.8 times that of the octahedron in the flat plate shape. Yes. Further, the CZ substrate and the EP wafer have temperature dependence on the leakage current as shown in FIG. 6 and have a temperature characteristic corresponding to a slope of 1.1 eV, so that the diffusion current is dominant in the leakage current. .
このような酸素析出物の形状によるリーク電流の違いは以下のように理解することができる。平板状及び八面体状それぞれの析出物の表面積を算出したところ、平板状のものが４５０００Å２、八面体状のものが１３３１６Å２で、その比は約３．４倍（平板／八面体）である。球状であると表面積は１１３０４６Å２であり、更に小さい。
一方のリーク電流の拡散成分は以下に示す式で表され、およそ表面積比（３．４倍）の平方根（１．８倍）に比例している。すなわち、酸素析出物によるリーク電流は酸素析出物の表面を起源とし、その大きさは表面積に依存することが明らかとなった。
The difference in leakage current depending on the shape of such oxygen precipitates can be understood as follows. When the surface areas of the precipitates of the flat plate and the octahedron were calculated, the flat plate was 45000 cm 2 and the octahedral plate was 13316 mm 2 , and the ratio was about 3.4 times (flat plate / octahedron). is there. When spherical, the surface area is 113046 2 , which is even smaller.
One diffusion component of the leakage current is expressed by the following formula, and is approximately proportional to the square root (1.8 times) of the surface area ratio (3.4 times). That is, it has been clarified that the leakage current due to the oxygen precipitate originates from the surface of the oxygen precipitate, and its magnitude depends on the surface area.
ｑ：電子電荷量
ｎｉ：真性キャリア濃度
ＮＡ：アクセプタ不純物濃度
Ｄｎ：電子の拡散係数
τｎ：Ｐ型半導体での電子寿命
σｎ：電子の捕獲断面積
Ｖｔ：キャリアの熱速度
Ｎｔ：欠陥（発生再結合）密度
以下、本発明の実施例及び比較例を示して本発明をより具体的に説明するが、本発明はこれらに限定されるものではない。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.
（実施例１）
本発明の半導体基板の製造方法に従って半導体基板を製造し、リーク電流を評価した。
まず、抵抗率１０Ω・ｃｍ、酸素濃度１５ｐｐｍａ、ボロンドープの直径２００ｍｍシリコンウェーハを２枚準備した（ＣＺウェーハ）。このうち１枚のウェーハに抵抗率１０Ω・ｃｍのエピタキシャル層を１０μｍ成長させた（ＥＰウェーハ）。これらのウェーハに５００℃、４時間の低温熱処理、８００℃、４時間の中温熱処理、１１５０℃、１００分の高温熱処理を施し、酸素析出物を形成した。
Example 1
A semiconductor substrate was manufactured according to the semiconductor substrate manufacturing method of the present invention, and leakage current was evaluated.
First, two silicon wafers having a resistivity of 10 Ω · cm, an oxygen concentration of 15 ppma, and a boron dope diameter of 200 mm were prepared (CZ wafer). Of these, an epitaxial layer having a resistivity of 10 Ω · cm was grown to 10 μm on one wafer (EP wafer). These wafers were subjected to low temperature heat treatment at 500 ° C. for 4 hours, intermediate temperature heat treatment at 800 ° C. for 4 hours, high temperature heat treatment at 1150 ° C. for 100 minutes to form oxygen precipitates.
酸素析出物を調査したところ、析出量は０．３ｐｐｍａ、表面積は１３３１６Å２、形状は八面体であった。後述の比較例と比較すると、低温熱処理条件が同じであるため、析出量も同じとなったが、高温熱処理条件が異なることから、実施例１では八面体状、比較例では平面状と異なる形状になった。そのため、表面積が比較例の４５０００Å２よりも実施例１の方が小さくなった。 When the oxygen precipitate was investigated, the amount of precipitation was 0.3 ppma, the surface area was 13316 cm 2 , and the shape was octahedral. Compared to the comparative example described later, since the low-temperature heat treatment conditions are the same, the amount of precipitation is also the same, but because the high-temperature heat treatment conditions are different, the shape is different from the octahedral shape in Example 1 and the planar shape in the comparative example. Became. For this reason, the surface area of Example 1 was smaller than that of Comparative Example 45000 2 .
これらのウェーハに、Ｐｙｒｏ雰囲気１０００℃、９０分の熱処理で厚さ２００ｎｍの酸化膜を形成した。この後、レジストを塗布し、フォトリソを行った。今回はネガレジストを選択した。マスクには各種面積の開口部を準備しておき、接合リークの面積依存が測定できるように工夫した。また同一面積で周辺長を変えたものも準備した。このレジスト付きウェーハをバッファードＨＦ溶液にてエッチングして酸化膜を除去し、硫酸過酸化水素混合液にてレジストを除去後、ＲＣＡ洗浄を実施した。 An oxide film having a thickness of 200 nm was formed on these wafers by heat treatment at 1000 ° C. for 90 minutes in a Pyro atmosphere. Thereafter, a resist was applied and photolithography was performed. This time I chose negative resist. The mask was prepared with openings of various areas so that the area dependence of junction leakage could be measured. In addition, the same area with different peripheral lengths was also prepared. This resist-coated wafer was etched with a buffered HF solution to remove the oxide film, and after removing the resist with a sulfuric acid hydrogen peroxide mixed solution, RCA cleaning was performed.
洗浄後のウェーハに加速電圧５５ＫｅＶ、ドーズ量２×１０１２ａｔｏｍｓ／ｃｍ２でボロンをイオン注入し、１０００℃、窒素雰囲気下で回復アニール後、リンガラスを塗布拡散し、リンを表面より拡散することで、ＰＮ接合を形成し、逆方向バイアス印加時のリーク電流を測定した。
上記ＣＺウェーハのリーク電流の分布の結果を図２に示す。図２中の色が濃い方がリーク電流が高いことを示している。図２に示すように、後述する比較例の分布（図３）に比べて、実施例１のウェーハはリークが減少し、縞模様もかなり緩和されている。また、ＥＰウェーハに関しても同様の結果となった。
Boron ions are implanted into the cleaned wafer at an acceleration voltage of 55 KeV and a dose of 2 × 10 12 atoms / cm 2 , and after recovery annealing in a nitrogen atmosphere at 1000 ° C., phosphorus glass is applied and diffused, and phosphorus is diffused from the surface. Thus, a PN junction was formed, and the leakage current when reverse bias was applied was measured.
The result of the leakage current distribution of the CZ wafer is shown in FIG. A darker color in FIG. 2 indicates a higher leakage current. As shown in FIG. 2, compared with the distribution of the comparative example (FIG. 3) to be described later, the leak of the wafer of Example 1 is reduced and the stripe pattern is considerably relaxed. Similar results were obtained for EP wafers.
（実施例２）
窒素濃度が４．９×１０１３となるように窒素をドープしたシリコンウェーハを用い、球状の酸素析出物を形成した以外、実施例１と同様の条件で半導体基板を製造し、同様に評価した。
酸素析出物を調査したところ、析出量は０．３ｐｐｍａと実施例１と同じであったが、表面積が１１３０４Å２と実施例１よりも更に低減された。
ＣＺウェーハのリーク電流の分布の結果を図２に示す。図２に示すように、実施例１よりも更にリークが減少し、縞模様もより緩和されている。後述する比較例の結果と比べるとリークが大幅に低減されていることが分かった。ＥＰウェーハに関しても同様の結果となった。
(Example 2)
A semiconductor substrate was manufactured under the same conditions as in Example 1 except that a silicon wafer doped with nitrogen so that the nitrogen concentration was 4.9 × 10 13 was used, and a spherical oxygen precipitate was formed. .
When checking oxygen precipitates, although precipitation amount was the same as 0.3ppma as Example 1, it was further reduced than that of Example 1 surface area and 11304Å 2.
The result of the leakage current distribution of the CZ wafer is shown in FIG. As shown in FIG. 2, the leakage is further reduced as compared with the first embodiment, and the stripe pattern is more relaxed. It was found that the leakage was greatly reduced as compared with the results of comparative examples described later. Similar results were obtained for EP wafers.
（比較例）
高温熱処理の温度を１０００℃とした以外、実施例１と同様な条件で半導体基板を製造し、同様に評価した。
結果を図３に示す。図３に示すように、実施例１、実施例２と比べ、リークが増加してしまった。
(Comparative example)
A semiconductor substrate was manufactured under the same conditions as in Example 1 except that the temperature of the high-temperature heat treatment was 1000 ° C., and evaluated in the same manner.
The results are shown in FIG. As shown in FIG. 3, the leakage increased as compared with Example 1 and Example 2.
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 embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.
Claims (3)
前記酸素析出物を形成する工程において、前記シリコン基板に酸素析出核形成、酸素析出核成長、及び酸素析出物形成の３段階の熱処理を行い、前記酸素析出物形成の熱処理の温度を１１００℃以上とすることによって、前記形成する酸素析出物の形状を八面体状又は球状にすることを特徴とする半導体基板の製造方法。 A method for manufacturing a semiconductor substrate, comprising: preparing a silicon substrate; and performing heat treatment on the silicon substrate to form an oxygen precipitate,
In the step of forming the oxygen precipitate, the silicon substrate is subjected to a three-step heat treatment of forming an oxygen precipitate nucleus, growing an oxygen precipitate nucleus, and forming an oxygen precipitate, and the temperature of the heat treatment for forming the oxygen precipitate is 1100 ° C. or higher. Thus, the shape of the oxygen precipitate to be formed is octahedral or spherical.
前記酸素析出物の形状が球状であることを特徴とするシリコン基板。 A silicon substrate containing oxygen precipitates,
A silicon substrate characterized in that the oxygen precipitate has a spherical shape.
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