JP6628581B2 - Manufacturing method of epitaxial silicon carbide single crystal wafer - Google Patents
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- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims description 76
- 229910010271 silicon carbide Inorganic materials 0.000 title claims description 76
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- 239000000758 substrate Substances 0.000 claims description 41
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 4
- 239000012159 carrier gas Substances 0.000 claims description 4
- 229910052710 silicon Inorganic materials 0.000 claims description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 3
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 239000010703 silicon Substances 0.000 claims description 3
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- 239000010408 film Substances 0.000 description 33
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 11
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Description
本発明は、エピタキシャル炭化珪素単結晶ウェハの製造方法に関するものである。 The present invention relates to a method for manufacturing an epitaxial silicon carbide single crystal wafer.
炭化珪素（以下、SiC）は、耐熱性及び機械的強度に優れ、物理的、化学的に安定なことから、耐環境性半導体材料として注目されている。また、近年、高周波高耐圧電子デバイス等の基板としてエピタキシャルSiC単結晶ウェハの需要が高まっている。 BACKGROUND ART Silicon carbide (hereinafter, SiC) has attracted attention as an environment-resistant semiconductor material because it has excellent heat resistance and mechanical strength, and is physically and chemically stable. In recent years, there has been an increasing demand for epitaxial SiC single-crystal wafers as substrates for high-frequency high-voltage electronic devices and the like.
エピタキシャルSiC単結晶ウェハ（以下、単にSiCウェハと言う場合がある）を用いて、電力デバイス、高周波デバイス等を作製する場合には、通常、SiC単結晶基板上に熱CVD法（熱化学蒸着法）と呼ばれる方法を用いてSiC薄膜をエピタキシャル成長させたり、イオン注入法により直接ドーパントを打ち込んだりするのが一般的であるが、後者の場合には、注入後に高温でのアニールが必要となるため、エピタキシャル成長による薄膜形成が多用されている。 When power devices, high-frequency devices, and the like are manufactured using an epitaxial SiC single crystal wafer (hereinafter sometimes simply referred to as a SiC wafer), a thermal CVD method (thermal chemical vapor deposition method) is usually performed on a SiC single crystal substrate. It is common to epitaxially grow a SiC thin film using a method called) or directly implant a dopant by ion implantation, but in the latter case, annealing at a high temperature after implantation is necessary, Thin film formation by epitaxial growth is frequently used.
エピタキシャルSiC単結晶膜（以下、単にエピタキシャル膜と言う場合がある）上にデバイスを形成する場合、設計通りのデバイスを安定して製造するためには、エピタキシャル膜の膜厚及びドーピング密度、なかでもドーピング密度のウェハ面内均一性が重要になる。特に近年、SiCウェハの大口径化が進むとともに、デバイスの面積も大きくなり、デバイス歩留まり向上のためには、ドーピング密度のウェハ面内均一性がより重要となっている。具体的には、現在の主流である4インチウェハ上のエピタキシャル膜のドーピング密度面内均一性は、標準偏差/平均値（σ/mean）で安定的に5〜10%にすることが必要である。 When a device is formed on an epitaxial SiC single crystal film (hereinafter sometimes simply referred to as an epitaxial film), in order to manufacture a device as designed stably, the thickness and doping density of the epitaxial film, especially The in-plane uniformity of the doping density becomes important. In particular, in recent years, as the diameter of SiC wafers has increased, the device area has also increased, and in order to improve the device yield, uniformity of the doping density within the wafer surface has become more important. Specifically, the dominance in-plane uniformity of the doping density of epitaxial films on 4-inch wafers, which is currently the mainstream, needs to be stably set at 5 to 10% by standard deviation / mean value (σ / mean). is there.
しかしながら、ドーピング密度は、エピタキシャル膜を成長させる材料ガス中の珪素原子数に対する炭素原子数の比（C/Si比）をはじめ、成長温度や成長圧力等が複雑に関係して決まるため、σ/meanを安定的に上記の値にすることは難しい。更に近年では、厚いエピタキシャル膜の需要が増加したため、珪素系及び炭素系の材料ガスの流量を多くするとともに成長炉内圧力を下げることによって高速エピタキシャル成長が行われるようになっているが（例えば非特許文献1参照）、高速成長下において高いドーピング密度のウェハ面内均一性を達成することはより困難である。加えて、厚いエピタキシャル膜の場合、高耐圧デバイスに応用されることなどから、ドーピング密度は一般的に低い値が求められ、ドーピング密度の偏析をなくしてウェハ面内均一性を維持したり、ウェハ面内均一性を向上させるための技術開発は一層重要な課題となっている。 However, the doping density is determined by the complicated relationship between the growth temperature and the growth pressure, including the ratio of the number of carbon atoms to the number of silicon atoms in the material gas for growing the epitaxial film (C / Si ratio). It is difficult to stably set mean to the above value. Further, in recent years, since the demand for a thick epitaxial film has increased, high-speed epitaxial growth has been performed by increasing the flow rate of silicon-based and carbon-based material gases and lowering the pressure in a growth furnace (for example, Non-Patent Document 1). It is more difficult to achieve high doping density wafer in-plane uniformity under high-speed growth. In addition, in the case of a thick epitaxial film, the doping density is generally required to be low because the film is applied to a high withstand voltage device. Technology development for improving in-plane uniformity has become an even more important issue.
今後デバイスへの応用が期待されるSiCウェハであるが、高速エピタキシャル成長の場合や一般的な成長速度の場合も含めて、エピタキシャル膜のドーピング密度の面内均一性をσ/meanで安定的に5〜10%にすることは従来の技術では困難であり、面内均一性の劣ったSiCウェハも使用せざるを得ないことによるデバイス特性の劣化、歩留まりの低下等が問題となっている。 Although SiC wafers are expected to be applied to devices in the future, the in-plane uniformity of the doping density of the epitaxial film can be stably measured at σ / mean, including the case of high-speed epitaxial growth and general growth rates. It is difficult with conventional techniques to make it 10% or less, and there are problems such as deterioration of device characteristics and reduction of yield due to the necessity of using SiC wafers with in-plane uniformity.
本発明は、このような状況を鑑みてなされてものであり、ドーピング密度のウェハ面内均一性に優れた高品質エピタキシャル膜を有するSiCウェハの安定的な製造方法を提供するものである。 The present invention has been made in view of such circumstances, and provides a method for stably manufacturing a SiC wafer having a high-quality epitaxial film having excellent in-wafer uniformity of doping density.
本発明者らは、エピタキシャル成長時に成長炉内圧力と成長速度の積の値がある範囲内になるように調整することで、ドーピング密度のウェハ面内均一性に優れた高品質エピタキシャル膜を備えたSiCウェハが得られるようになることを見出し、完成したものである。 The present inventors provided a high-quality epitaxial film having excellent in-wafer uniformity of the doping density by adjusting the value of the product of the growth furnace pressure and the growth rate to be within a certain range during epitaxial growth. We have found that a SiC wafer can be obtained and completed it.
即ち、本発明は、
(1) エピタキシャル成長炉内の炭化珪素単結晶基板上に、炭素と珪素の原子数比（C/Si比）が1.0以上2.0以下である珪素系及び炭素系の材料ガスと、ドーピング用ガスと、キャリアガスとを流して、1550℃以上1700℃以下の成長温度で熱CVD法により炭化珪素をエピタキシャル成長させて、エピタキシャル炭化珪素単結晶ウェハを製造する方法において、前記エピタキシャル成長の成長条件をエピタキシャル成長時の成長炉内圧力P（kPa）と得られるエピタキシャル層の成長速度R（μｍ/hr.）との積が45以上100以下（45≦P×R≦100）の範囲となるように調整して、炭化珪素をエピタキシャル成長させることを特徴とするエピタキシャル炭化珪素単結晶ウェハの製造方法、
(2) 前記エピタキシャル層の成長速度Rは、材料ガスの流量調整により制御される(1)に記載のエピタキシャル炭化珪素単結晶ウェハの製造方法、
(3) 前記炭化珪素単結晶基板のオフ角度が4°以下である(1)又は(2)に記載のエピタキシャル炭化珪素ウェハの製造方法、
(4) 前記炭化珪素単結晶基板の直径が4インチ（100mm）以上である(1)〜(3)のいずれかに記載のエピタキシャル炭化珪素ウェハの製造方法、
である。
That is, the present invention
(1) On a silicon carbide single crystal substrate in an epitaxial growth furnace, a silicon-based and carbon-based material gas having an atomic ratio of carbon to silicon (C / Si ratio) of 1.0 or more and 2.0 or less, and a doping gas; A method of manufacturing a silicon carbide single crystal wafer by flowing a carrier gas and epitaxially growing silicon carbide by a thermal CVD method at a growth temperature of 1550 ° C. or more and 1700 ° C. or less, wherein the epitaxial growth conditions are the same as those in the epitaxial growth. The carbonization was performed by adjusting the product of the furnace pressure P (kPa) and the obtained epitaxial layer growth rate R (μm / hr.) In the range of 45 to 100 (45 ≦ P × R ≦ 100). A method for producing an epitaxial silicon carbide single crystal wafer, characterized by epitaxially growing silicon,
(2) The method of manufacturing an epitaxial silicon carbide single crystal wafer according to (1), wherein the growth rate R of the epitaxial layer is controlled by adjusting a flow rate of a material gas.
(3) The method for manufacturing an epitaxial silicon carbide wafer according to (1) or (2), wherein the off angle of the silicon carbide single crystal substrate is 4 ° or less.
(4) The method for producing an epitaxial silicon carbide wafer according to any one of (1) to (3), wherein the diameter of the silicon carbide single crystal substrate is 4 inches (100 mm) or more.
It is.
本発明によれば、SiC単結晶基板上にエピタキシャル膜を形成したSiCウェハにおいて、高速エピタキシャル成長の場合も含めて、ドーピング密度のSiCウェハの面内均一性に優れた高品質SiCウェハを提供することが可能である。 According to the present invention, it is possible to provide a high-quality SiC wafer having excellent in-plane uniformity of a SiC wafer having a doping density, including a case of high-speed epitaxial growth, in an SiC wafer having an epitaxial film formed on a SiC single crystal substrate. Is possible.
また、本発明の製造方法は、CVD法であるため、装置構成が簡単で制御性にも優れ、再現性、安定性の高いエピタキシャル膜が得られる。 Further, since the manufacturing method of the present invention is a CVD method, an epitaxial film having a simple apparatus configuration, excellent controllability, and high reproducibility and stability can be obtained.
更に、本発明で得られたSiCウェハを用いたデバイスは、ドーピング密度のウェハ面内均一性に優れた高品質エピタキシャル膜上に形成されるため、その特性及び歩留りが向上する。 Furthermore, since the device using the SiC wafer obtained by the present invention is formed on a high-quality epitaxial film having excellent in-plane uniformity of the doping density on the wafer, its characteristics and yield are improved.
本発明は、熱CVDによりSiC単結晶基板上にSiC薄膜をエピタキシャル成長させる際の成長炉内圧力と成長速度との積の値がある範囲内になるように調整することで、ドーピング密度のウェハ面内均一性に優れた高品質エピタキシャル膜を備えたSiCウェハが得られるようになることを見出し、完成したものである。通常、エピタキシャル成長の成長速度を上げたい時は材料ガスの濃度を高めるが、気相中での核形成が生じやすくなり、エピタキシャル膜の品質を劣化させるため、同時に成長圧力を下げている。すなわち、成長炉内の圧力を下げる時は、SiC薄膜の高速成長を行う時である。ここで、本発明者らは、試験的に成長炉内の圧力を下げても材料ガスの濃度を変えずに、通常成長速度でエピタキシャル成長を行った。このように成長したエピタキシャル膜と、成長圧力を下げて材料ガスの濃度を高めた高速成長のエピタキシャル膜とのドーピング密度の面内分布を比較評価した。その結果、以下に示すように、成長炉内圧力と成長速度との積がドーピング密度の面内均一性に関連することを見出した。なお、成長速度は成長時間と成長後のエピタキシャル膜厚を測定することによって算出したものであり、上記核形成が発生するまでは材料ガスの濃度（流量）に比例する（つまり、核形成が起きるとSiドロップレットが生じ、原料のSiがそこで消費されてしまい、成長に寄与しなくなるため成長速度は低下する）。 The present invention adjusts the product of the pressure in the growth furnace and the growth rate when epitaxially growing a SiC thin film on a SiC single crystal substrate by thermal CVD so that the value is within a certain range. They have found that it is possible to obtain a SiC wafer provided with a high-quality epitaxial film having excellent internal uniformity, and have completed it. Usually, when it is desired to increase the growth rate of the epitaxial growth, the concentration of the material gas is increased. However, the nucleation in the gas phase is easily caused and the quality of the epitaxial film is deteriorated. That is, the time when the pressure in the growth furnace is reduced is when the SiC thin film is grown at a high speed. Here, the present inventors performed epitaxial growth at a normal growth rate without changing the material gas concentration even if the pressure inside the growth furnace was experimentally lowered. The in-plane distribution of the doping density of the epitaxial film grown in this manner and the high-speed epitaxial film in which the concentration of the material gas was increased by lowering the growth pressure were compared and evaluated. As a result, they have found that the product of the growth furnace pressure and the growth rate is related to the in-plane uniformity of the doping density, as described below. The growth rate is calculated by measuring the growth time and the epitaxial film thickness after the growth, and is proportional to the concentration (flow rate) of the material gas until the nucleation occurs (that is, nucleation occurs). And Si droplets are generated, and the raw material Si is consumed there, and does not contribute to the growth, so that the growth rate is reduced).
以下、本発明を具体的に説明する。
先ず、SiC単結晶基板上へのエピタキシャル成長について述べる。本発明で好適にエピタキシャル成長に用いる装置は、横型のCVD装置である。CVD法は、装置構成が簡単であり、ガスのon/offで成長を制御できるため、エピタキシャル膜の制御性、再現性に優れた成長方法である。
Hereinafter, the present invention will be described specifically.
First, the epitaxial growth on the SiC single crystal substrate will be described. The apparatus preferably used for epitaxial growth in the present invention is a horizontal CVD apparatus. The CVD method is a growth method that is excellent in controllability and reproducibility of the epitaxial film because the apparatus configuration is simple and the growth can be controlled by turning on / off the gas.
図１には、従来のエピタキシャル膜成長を行う際の典型的な成長シーケンスの一例を、ガスの導入タイミングと併せて示している。先ず、成長炉にSiC単結晶基板をセットし、成長炉内を真空排気した後、水素ガスを導入して圧力を5k〜20kPaに調整する。その後、圧力を一定に保ちながら水素ガス流量と成長炉の温度を上げ、エピタキシャル成長温度である1550〜1700℃に達した後、毎分100〜200Lの水素ガス中でSiC単結晶基板の表面のエッチングを行う（10分程度）。エッチング終了後、材料ガスであるSiH4及びC3H8と、ドーピングガスであるN2を導入してエピタキシャル成長を開始する。SiH4流量は毎分100〜150cm3、C3H8流量は毎分50〜70cm3であり（材料ガス中のSi原子数に対するC原子数の比（C/Si比）は1〜2程度）、エピタキシャル成長速度は毎時〜10μmである。N2の流量は必要とされるドーピング密度によって決まるが、一般には1分間あたり10〜50cm3であり、ドーピング密度の値は1E15cm-3〜1E16cm-3である。一定時間エピタキシャル成長し、所望の膜厚が得られた時点でSiH4とC3H8の導入を止め、水素ガスのみ流した状態で温度を下げる。温度が常温まで下がった後、水素ガスの導入を止め、成長室内を真空排気し、不活性ガスを成長室に導入して、成長室を大気圧に戻してから、エピタキシャルSiCウェハを取り出す。 FIG. 1 shows an example of a typical growth sequence when a conventional epitaxial film is grown, together with gas introduction timing. First, a SiC single crystal substrate is set in a growth furnace, and after evacuation of the inside of the growth furnace, hydrogen gas is introduced to adjust the pressure to 5 kPa to 20 kPa. Thereafter, while maintaining the pressure constant, the hydrogen gas flow rate and the temperature of the growth furnace were increased, and after reaching the epitaxial growth temperature of 1550 to 1700 ° C., the surface of the SiC single crystal substrate was etched in hydrogen gas at 100 to 200 L / min. (About 10 minutes). After the etching is completed, SiH 4 and C 3 H 8 as material gases and N 2 as a doping gas are introduced to start epitaxial growth. The flow rate of SiH 4 is 100 to 150 cm 3 per minute, and the flow rate of C 3 H 8 is 50 to 70 cm 3 per minute (the ratio of the number of C atoms to the number of Si atoms in the material gas (C / Si ratio) is about 1 to 2) ), The epitaxial growth rate is 〜10 μm per hour. The flow rate of N 2 is determined by the doping density required, but generally a 10 to 50 cm 3 per minute, the value of the doping density of 1E15cm -3 ~1E16cm -3. Epitaxial growth is performed for a certain period of time, and when a desired film thickness is obtained, introduction of SiH 4 and C 3 H 8 is stopped, and the temperature is lowered with only hydrogen gas flowing. After the temperature has dropped to room temperature, the introduction of hydrogen gas is stopped, the growth chamber is evacuated, an inert gas is introduced into the growth chamber, and the growth chamber is returned to atmospheric pressure, and then the epitaxial SiC wafer is taken out.
次に、本発明における成長シーケンスの一例を図２で説明する。SiC単結晶基板をセットし、SiC単結晶基板の表面のエッチングを行うまでは、図１と同様である。エッチング終了後、成長炉内圧力がP(kPa)になるように調整し（図２では圧力を下げた場合を示している）、材料ガスであるSiH4とC3H8の流量についてエピタキシャル層の成長速度がR(μｍ/hr.)となるように調整して、下記式（１）
45≦P×R≦100 （１）
の関係を満たすようにする。図２に示されているように、SiH4とC3H8の流量調整（必要があればN2も）は、例えばこれらのガスを成長炉内部に流さずにベントラインに排出しながら行う。調整終了後、材料ガスとN2を成長炉内に導入してエピタキシャル成長を開始する。その後の手順は図１と同様である。
Next, an example of a growth sequence according to the present invention will be described with reference to FIG. It is the same as FIG. 1 until the SiC single crystal substrate is set and the surface of the SiC single crystal substrate is etched. After the etching was completed, the pressure in the growth furnace was adjusted to P (kPa) (FIG. 2 shows the case where the pressure was lowered), and the flow rates of the material gases SiH 4 and C 3 H 8 were increased. Is adjusted so that the growth rate of R becomes R (μm / hr.), And the following formula (1) is obtained.
45 ≦ P × R ≦ 100 (1)
To satisfy the relationship. As shown in FIG. 2, the flow rates of SiH 4 and C 3 H 8 (and N 2 if necessary) are adjusted, for example, by discharging these gases to the vent line without flowing them into the growth furnace. . After the adjustment, material gas and N 2 are introduced into the growth furnace to start epitaxial growth. Subsequent procedures are the same as in FIG.
上記式（１）を満たすようにして成長条件を調整するにあたり、成長炉内圧力Pについては、図１で示したような一般的なエピタキシャル成長で採用される5kPa以上20kPa以下の範囲で調整するのがよく、また、成長速度Rについては、5μm/hr.以上20μm/hr.以下の範囲で調整するのがよい。先の図２の例ではエッチング終了後に成長炉内の圧力を下げて、SiC単結晶基板に供給する材料ガスの流量を減らしているが、勿論、圧力Pを上げたりそのまま維持したり、或いは、材料ガスの流量を上げたりそのまま維持したりして（図2の例ではSiH4及びC3H8の流量を上記の範囲内で調整するのがよい）、式（１）を満たすようにすることもできる。また、成長速度Rを制御するにあたり、成長温度を調整するようにしてもよい。なお、珪素系の材料ガスや炭素系の材料ガスについては上記の例以外にも、例えば、炭素系材料ガスとして他の炭化水素ガスを用いたり、珪素系材料ガスとして他のシラン系ガスを用いることができる。また、ドーピング用ガスやキャリアガスについても同様に他の公知のものを用いることができる。 In adjusting the growth conditions so as to satisfy the above expression (1), the pressure P in the growth furnace is adjusted within the range of 5 kPa to 20 kPa employed in general epitaxial growth as shown in FIG. The growth rate R is preferably adjusted in the range of 5 μm / hr. To 20 μm / hr. In the example of FIG. 2 described above, the pressure in the growth furnace is reduced after the etching is completed to reduce the flow rate of the material gas supplied to the SiC single crystal substrate, but, of course, the pressure P may be increased or maintained, or The flow rate of the material gas is increased or maintained as it is (in the example of FIG. 2, the flow rates of SiH 4 and C 3 H 8 are preferably adjusted within the above range) to satisfy the expression (1). You can also. In controlling the growth rate R, the growth temperature may be adjusted. It should be noted that, in addition to the above examples, for example, a silicon-based material gas or a carbon-based material gas may use another hydrocarbon gas as the carbon-based material gas, or use another silane-based gas as the silicon-based material gas. be able to. Further, as the doping gas and the carrier gas, other known gases can also be used.
図３にはエピタキシャル成長時のP×Rに対するσ/meanで表したドーピング密度の面内均一性の関係を示す。図３から明らかなように、P×Rが大きくなるとσ/meanが小さくなり、すなわち面内均一性が向上していることが分かる。これは以下のように考えられる。なお、このドーピング密度の面内均一性の評価は、後述する実施例のとおりにして行った。 FIG. 3 shows the relationship between the in-plane uniformity of the doping density expressed by σ / mean with respect to P × R during epitaxial growth. As is clear from FIG. 3, it is found that as P × R increases, σ / mean decreases, that is, the in-plane uniformity improves. This is considered as follows. The evaluation of the in-plane uniformity of the doping density was performed as in Examples described later.
キャリアガス流量が一定の場合、成長圧力が小さいと成長炉内でのガス流速が増大するため、材料ガスおよびN2がSiC単結晶基板上に留まる時間が短くなる。エピタキシャル膜へのドーピングはN2が分解して生成された窒素原子がSiCのC位置を置換する事によって行われるが、これにはある程度の時間が必要であり、SiC単結晶基板上に留まる時間が短くなると、前記置換のために必要な反応が十分に行われないまま排気されることになり、結果としてSiCウェハ面内でのドーピングが不均一になると考えられる。 When the carrier gas flow rate is constant, if the growth pressure is small, the gas flow rate in the growth furnace increases, so that the time during which the material gas and N 2 stay on the SiC single crystal substrate is shortened. Although doping into the epitaxial film is the nitrogen atom to which N 2 is generated by decomposition is carried out by replacing the C position of SiC, this requires a certain amount of time, time spent in the SiC single crystal substrate It is considered that when the reaction time is short, the gas is exhausted without sufficiently performing the reaction necessary for the replacement, and as a result, the doping in the SiC wafer surface becomes non-uniform.
この時に材料ガスの流量を増やし、成長速度を上げると、窒素原子と反応するSiおよびC原子の数が増加するため、窒素原子がSiC単結晶基板上に留まる時間が短くても置換反応が確実に行われ、均一性が向上する。一方、成長圧力が上がるとガス流速が下がり、置換反応のための時間は十分にあると考えられるが、SiC単結晶基板の表面に到達する窒素原子および表面を動く窒素原子の動きが遅くなる。その状態で材料ガスの流量を増やして成長速度を上げると、窒素原子が置換サイトに到達する前に窒素原子を含まないSiCが成長する部分が多くできてしまい、ドーピング密度の均一性が悪化すると考えられる。すなわち、ドーピング密度の良好な面内均一性を得るためには、ガス流速が大きい（成長圧力が低い）時には成長速度を高く、ガス流速が小さい（成長圧力が高い）時には成長速度を低くする必要があり、上記の関係式（１）を満たせばσ/meanが10%以下になることを見出したのが本発明に繋がっている。 At this time, if the flow rate of the material gas is increased and the growth rate is increased, the number of Si and C atoms that react with the nitrogen atoms increases, so the substitution reaction is ensured even if the nitrogen atoms stay on the SiC single crystal substrate for a short time. And the uniformity is improved. On the other hand, when the growth pressure increases, the gas flow rate decreases, and it is considered that there is sufficient time for the substitution reaction. However, the movement of the nitrogen atoms reaching the surface of the SiC single crystal substrate and the movement of the nitrogen atoms moving on the surface become slow. If the growth rate is increased by increasing the flow rate of the material gas in that state, many portions of SiC that do not contain nitrogen atoms grow before the nitrogen atoms reach the substitution site, and the uniformity of the doping density deteriorates. Conceivable. That is, in order to obtain good in-plane uniformity of the doping density, it is necessary to increase the growth rate when the gas flow rate is high (low growth pressure) and to decrease the growth rate when the gas flow rate is low (high growth pressure). It has been found that if the above relational expression (1) is satisfied, σ / mean becomes 10% or less, which leads to the present invention.
図３から、P×Rが45(kPa・μｍ/hr.)以上であればドーピング密度のσ/meanを安定的に10％以下にできることが分かるが、上限について実験的に確認することは困難である。これは、PあるいはRを大きくすると、成長が不安定になり鏡面状のエピタキシャル膜が得られなくなるためであるが、現在一般的に利用されているRとPの最大値から考えて、P×Rは実質的に100(kPa・μｍ/hr.)以下であるのがよいと考えられる。先にも述べているが、成長炉内圧力Pの好ましい範囲は6kPa以上12kPa以下であり、成長速度Rに関しては7μm/hr.以上14μm/hr.以下である。また、エピタキシャル層を成長させる際の材料ガス中のC/Si比は、小さすぎると残留不純物密度が増加するためドーピング密度のウェハ面内均一性が劣化する。一方で、C/Si比が大きすぎるとキラー欠陥が多発し、これはデバイス特性とドーピング密度のウェハ面内均一性の両方に悪影響を与える。従って、C/Si比は1.0以上2.0以下、より好適には1.2以上1.8以下である。更に、エピタキシャル層を成長させる際の成長温度は、低すぎるとキラー欠陥が増え、高すぎるとこれもドーピング密度のウェハ面内均一性に悪影響を与えるエピタキシャル層表面荒れが生じるため、1550℃以上1700℃以下、より好適には1580℃以上1680℃以下である。なお、図３で示される傾向は、上記C/Si比や成長温度の範囲内では殆ど変化しない。 FIG. 3 shows that if P × R is 45 (kPa · μm / hr.) Or more, the doping density σ / mean can be stably reduced to 10% or less, but it is difficult to experimentally confirm the upper limit. It is. This is because if P or R is increased, the growth becomes unstable and a mirror-like epitaxial film cannot be obtained.However, considering the currently generally used maximum values of R and P, P × It is considered that R should be substantially 100 (kPa · μm / hr.) Or less. As described above, the preferable range of the pressure P in the growth furnace is 6 kPa to 12 kPa, and the growth rate R is 7 μm / hr. To 14 μm / hr. Further, if the C / Si ratio in the material gas when growing the epitaxial layer is too small, the residual impurity density increases, so that the in-plane uniformity of the doping density deteriorates. On the other hand, if the C / Si ratio is too large, many killer defects occur, which adversely affects both the device characteristics and the in-plane uniformity of the doping density. Therefore, the C / Si ratio is 1.0 or more and 2.0 or less, more preferably 1.2 or more and 1.8 or less. Furthermore, when the growth temperature when growing the epitaxial layer is too low, killer defects increase, and when it is too high, the epitaxial layer surface roughening also adversely affects the in-plane uniformity of the doping density. ° C or lower, more preferably 1580 ° C or higher and 1680 ° C or lower. Note that the tendency shown in FIG. 3 hardly changes within the range of the C / Si ratio and the growth temperature.
本発明は、SiCウェハにおけるエピタキシャル膜について、ドーピング密度の良好な面内均一性を安定的に得るためのものであるが、ここまでの説明から分かるように、ドーピングに寄与する窒素原子のSiC単結晶基板上での動きを成長圧力（ガス流速）というパラメータで制御しながら成長速度を設定することが１つのポイントとなっている。従って、本発明は、ガスの動きを制御すべき領域が広い程、その作用はより有効になり、SiC単結晶基板の口径が4インチ（100mm）以上でより重要になり、更には、現在製造報告が出されているいわゆる口径150mm基板や口径200mm基板のような大口径SiC単結晶基板において好適である。また、SiC単結晶基板の表面でのステップ密度が少なくなると、表面に吸着したガスは基板上の長い距離を動いて反応する必要が生じるため、同様に本発明の有効性は高まる。すなわち、(0001)面に対して＜11-20＞方向へ傾けた角度であるSiC単結晶基板のオフ角度が小さい程、その効果は大きい。しかし、オフ角度が小さすぎると成長そのものが困難となるため、SiC単結晶基板のオフ角については0.5°以上であるのがよく、また、その上限はSiC単結晶基板の現在の主流である4°以下が好ましい。 The present invention is intended to stably obtain good in-plane uniformity of doping density for an epitaxial film on a SiC wafer. As can be understood from the above description, the SiC single atom of nitrogen atoms contributing to doping is used. One point is to set the growth rate while controlling the movement on the crystal substrate with a parameter called growth pressure (gas flow rate). Therefore, the present invention is more effective when the region where the movement of gas is to be controlled is wider, the effect becomes more important when the diameter of the SiC single crystal substrate is 4 inches (100 mm) or more. It is suitable for a large-diameter SiC single crystal substrate such as a so-called 150 mm diameter substrate or 200 mm diameter substrate that has been reported. Further, when the step density on the surface of the SiC single crystal substrate is reduced, the gas adsorbed on the surface needs to move over a long distance on the substrate to react, so that the effectiveness of the present invention similarly increases. In other words, the effect is greater as the off-angle of the SiC single crystal substrate, which is the angle inclined in the <11-20> direction with respect to the (0001) plane, is smaller. However, if the off angle is too small, the growth itself becomes difficult, so the off angle of the SiC single crystal substrate is preferably 0.5 ° or more, and the upper limit is the current mainstream of the SiC single crystal substrate. ° or less is preferable.
このようにして製造したSiCウェハ上に好適に形成されるデバイスは、例えば、ショットキーバリアダイオード、PINダイオード、MOSダイオード、MOSトランジスタ等に用いることができ、特に好適には電力制御用に用いられるデバイスである。 Devices suitably formed on the SiC wafer manufactured in this way can be used, for example, for Schottky barrier diodes, PIN diodes, MOS diodes, MOS transistors, etc., and are particularly preferably used for power control. Device.
以下、実施例に基づき本発明を説明するが、本発明はこれらの内容に制限されるものではない。 Hereinafter, the present invention will be described based on examples, but the present invention is not limited to these contents.
(実施例1)
4インチ(100mm)ウェハ用SiC単結晶インゴットから、約400μmの厚さでスライスした後、粗削りとダイヤモンド砥粒による通常研磨および化学機械研磨（CMP）を実施した、4H型のポリタイプを有するSiC単結晶基板のSi面に、エピタキシャル成長を実施した。このSiC単結晶基板のオフ角度〔(0001)面に対して＜11-20＞方向へ傾けた角度〕は4°である。成長の手順としては、エピタキシャル成長炉に上記SiC単結晶基板をセットし、成長炉内を真空排気した後、水素ガスを導入しながら圧力を7.3kPaに調整した。その後、圧力を一定に保ちながら水素ガスの流量と成長炉の温度を上げ、最終的に水素ガスは毎分150L、温度は1635℃にして水素ガス中でSiC単結晶基板のエッチングを10分行った。エッチング後、成長炉の温度、圧力は1635℃、7.3kPaで変えず、SiH4流量を毎分140cm3、C3H8流量を毎分63cm3、ドーピング用N2流量を毎分13cm3にして成長を開始し（C/Si比は1.35）、エピタキシャル層の厚さが10μmになるまで成長した。成長速度は10.9(μm/hr.)であり、P×Rは79.3(kPa・μm/hr.)であった。成長後SiH4、C3H8およびN2の導入を止め、水素ガスのみ流した状態で温度を下げた。温度が常温まで下がった後、水素ガスの導入を止め、成長室内を真空排気し、不活性ガスを成長室に導入して、成長室を大気圧に戻してから、得られたSiCウェハを取り出した。
(Example 1)
SiC single-crystal ingots for 4 inch (100mm) wafers are sliced to a thickness of about 400μm, then rough-cut, regular polishing with diamond abrasive grains, and chemical mechanical polishing (CMP). Epitaxial growth was performed on the Si surface of the single crystal substrate. The off angle [the angle inclined in the <11-20> direction with respect to the (0001) plane] of this SiC single crystal substrate is 4 °. As a growth procedure, the SiC single crystal substrate was set in an epitaxial growth furnace, the inside of the growth furnace was evacuated, and the pressure was adjusted to 7.3 kPa while introducing hydrogen gas. After that, while maintaining the pressure constant, the flow rate of hydrogen gas and the temperature of the growth furnace were increased, and finally, the hydrogen gas was set to 150 L / min, the temperature was set to 1635 ° C, and the SiC single crystal substrate was etched in hydrogen gas for 10 minutes. Was. After etching, the temperature and pressure of the growth furnace were maintained at 1635 ° C. and 7.3 kPa, the SiH 4 flow rate was 140 cm 3 per minute, the C 3 H 8 flow rate was 63 cm 3 per minute, and the N 2 flow rate for doping was 13 cm 3 per minute. Then, growth was started (C / Si ratio was 1.35), and the epitaxial layer was grown to a thickness of 10 μm. The growth rate was 10.9 (μm / hr.), And P × R was 79.3 (kPa · μm / hr.). After the growth, the introduction of SiH 4 , C 3 H 8 and N 2 was stopped, and the temperature was lowered with only hydrogen gas flowing. After the temperature drops to room temperature, the introduction of hydrogen gas is stopped, the growth chamber is evacuated, an inert gas is introduced into the growth chamber, the growth chamber is returned to atmospheric pressure, and the obtained SiC wafer is taken out. Was.
このようにしてエピタキシャル成長を行った膜のドーピング密度の面内分布を測定した。測定はHgプローブを用いたCV法によって行い、図4に示すように、得られたSiCウェハについて、同心円状のパターンで合計25点測定した。その結果、測定した25点から求めたσ/mean（標準偏差/平均値）は4.7％と良好であった。 The in-plane distribution of the doping density of the epitaxially grown film was measured. The measurement was performed by the CV method using an Hg probe, and as shown in FIG. 4, a total of 25 points were measured on the obtained SiC wafer in a concentric pattern. As a result, σ / mean (standard deviation / average value) obtained from the measured 25 points was as good as 4.7%.
(実施例2〜11)
実施例1と同様にスライス、粗削り、通常研磨、CMPを行った、4H型のポリタイプを有するSiC単結晶基板のSi面に、エピタキシャル成長を実施した。成長前エッチングから成長終了までの手順と成長膜厚は実施例1と同様であるが、基板のオフ角、口径、成長時のSiH4、C3H8、N2流量、C/Si比、成長圧力を表1のように変化させた。得られたSiCウェハについて、実施例1と同様にしてエピタキシャル膜のドーピング密度の面内分布を測定した。成長後に確認した成長速度とそこから算出したP×R値、ドーピング密度のσ/meanを表1にあわせて示している。表1より、σ/meanは全て10％以下に入っており良好であった。なお、6インチ基板を評価する時は、図4におけるrを14mm、28mm、42mm、56mm、70mmとして、全測定点数は41点である。
(Examples 2 to 11)
Epitaxial growth was performed on the Si surface of a 4H-type polycrystalline SiC single crystal substrate that had been sliced, roughly cut, normally polished, and CMP in the same manner as in Example 1. The procedure from the pre-growth etching to the completion of the growth and the grown film thickness are the same as those in Example 1, but the off-angle of the substrate, the aperture, the SiH 4 , C 3 H 8 , N 2 flow rate during the growth, the C / Si ratio, The growth pressure was varied as shown in Table 1. For the obtained SiC wafer, the in-plane distribution of the doping density of the epitaxial film was measured in the same manner as in Example 1. Table 1 also shows the growth rate confirmed after the growth, the P × R value calculated therefrom, and the σ / mean of the doping density. From Table 1, all the σ / mean values were 10% or less, which was good. When a 6-inch substrate is evaluated, r in FIG. 4 is 14 mm, 28 mm, 42 mm, 56 mm, and 70 mm, and the total number of measurement points is 41 points.
(比較例1〜6)
実施例1と同様にスライス、粗削り、通常研磨、CMPを行った、4H型のポリタイプを有するSiC単結晶基板のSi面に、エピタキシャル成長を実施した。成長前エッチングから成長終了までの手順と成長膜厚は実施例1と同様であるが、基板のオフ角、口径、成長時のSiH4、C3H8、N2流量、C/Si比、成長圧力を表2のように変化させた。得られたSiCウェハについて、実施例1と同様にしてエピタキシャル膜のドーピング密度の面内分布を測定した。その結果、比較例1、2については、P×R値が小さすぎるためσ/meanが10％より大きくなっていることが分かる。比較例3ではC/Si比が小さいため残留不純物の影響を受けて、P×R値が45以上であるがσ/meanが大きくなっており、比較例4ではC/Si比が大きいためキラー欠陥が多数発生し、σ/meanが大きくなっている。更に比較例5では成長温度が低すぎてキラー欠陥が多数発生したため、比較例6では成長温度が高すぎて表面荒れが生じたため、P×R値は条件を満たすもののσ/meanが大きくなっている。比較例7では、P×R値が大きすぎ、すなわち高い成長圧力の下で高い成長速度を設定したために、原料のSiH4が二次元核を形成し、Siドロップレットが発生して鏡面状のエピタキシャル膜が得られず、ドーピングも正常に行われなかった結果σ/meanが大きくなっている。
(Comparative Examples 1 to 6)
Epitaxial growth was performed on the Si surface of a 4H-type polycrystalline SiC single crystal substrate that had been sliced, roughly cut, normally polished, and CMP in the same manner as in Example 1. The procedure from the pre-growth etching to the completion of the growth and the grown film thickness are the same as those in Example 1, but the off-angle of the substrate, the aperture, the SiH 4 , C 3 H 8 , N 2 flow rate during the growth, the C / Si ratio, The growth pressure was varied as shown in Table 2. For the obtained SiC wafer, the in-plane distribution of the doping density of the epitaxial film was measured in the same manner as in Example 1. As a result, in Comparative Examples 1 and 2, it was found that σ / mean was larger than 10% because the P × R value was too small. In Comparative Example 3, the P / R value was 45 or more but σ / mean was large due to the influence of residual impurities due to the small C / Si ratio. Many defects occur, and σ / mean is large. Furthermore, in Comparative Example 5, the growth temperature was too low, and many killer defects occurred.In Comparative Example 6, the growth temperature was too high, and the surface was roughened. I have. In Comparative Example 7, since the P × R value was too large, that is, a high growth rate was set under a high growth pressure, the raw material SiH 4 formed a two-dimensional nucleus, Si droplets were generated, and a mirror-like surface was formed. Since an epitaxial film was not obtained and doping was not performed normally, σ / mean was increased.
この発明によれば、 SiC単結晶基板上へのエピタキシャル成長において、ドーピング密度の面内均一性に優れた高品質エピタキシャル膜を有するSiCウェハを作成することが可能である。そのため、このようなSiCウェハ上に電子デバイスを形成すればデバイスの特性及び歩留まりが向上することが期待できる。 According to the present invention, it is possible to produce a SiC wafer having a high-quality epitaxial film having excellent in-plane uniformity of doping density in epitaxial growth on a SiC single crystal substrate. Therefore, if an electronic device is formed on such a SiC wafer, it can be expected that device characteristics and yield will be improved.
Claims (2)
前記炭化珪素単結晶基板のオフ角度を4°以下とし、
前記炭化珪素単結晶基板の直径を4インチ（100mm）以上とし、
前記材料ガス中の炭素と珪素の原子数比（C/Si比）を1.2以上1.8以下とし、
前記熱CVD法での成長温度を1580℃以上1680℃以下とし、
前記エピタキシャル成長の成長条件をエピタキシャル成長時の成長炉内圧力P（kPa）と得られるエピタキシャル層の成長速度R（μｍ/hr.）との積が45以上100以下（45≦P×R≦100）の範囲となるように、Pを6kPa以上12kPa以下、Rを7μm/hr.以上14μm/hr.以下に調整して、エピタキシャル膜のドーピング密度面内均一性（標準偏差/平均値（σ/mean））を10%以下として炭化珪素をエピタキシャル成長させることを特徴とするエピタキシャル炭化珪素単結晶ウェハの製造方法。 The silicon carbide single crystal substrate of an epitaxial growth furnace, and the material gas silicofluoride Motokei and carbon, and doping gas, by flowing the carrier gas, with silicon carbide was epitaxially grown by thermal CVD, epitaxial silicon carbide single In a method of manufacturing a crystal wafer,
Off angle of the silicon carbide single crystal substrate is 4 ° or less,
The diameter of the silicon carbide single crystal substrate is 4 inches (100 mm) or more,
The atomic ratio of carbon and silicon (C / Si ratio) in the material gas is set to 1.2 or more and 1.8 or less,
The growth temperature in the thermal CVD method is 1580 ° C or higher and 1680 ° C or lower,
The growth condition of the epitaxial growth is such that the product of the pressure P (kPa) in the growth furnace during the epitaxial growth and the growth rate R (μm / hr.) Of the obtained epitaxial layer is 45 to 100 (45 ≦ P × R ≦ 100). to be in the range, 6 kPa or more 12kPa or less P, by adjusting the R to 7 [mu] m / hr. or more 14 [mu] m / hr. or less, doping density radial uniformity of the epitaxial layer (standard deviation / average value (sigma / mean) ) Of 10% or less, and epitaxially growing silicon carbide.
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