【発明の詳細な説明】[Detailed description of the invention]
本発明は半導体装置の製造工程におけるエピタ
キシヤル気相成長、各種絶縁膜の気相成長、ある
いは多結晶膜の気相成長等に使用されるサセプタ
ーの改良に関するものである。
従来、この種のサセプターとしては、有害ガス
の放出がなく、化学的、熱的に安定な黒鉛基材に
炭化珪素をコーテイングしたものが用いられてい
る。
しかしながら、上記サセプターを構成する炭化
珪素の熱膨張係数は4.2×10-6／℃で、他方サセ
プターの本体として使用可能な黒鉛基材の熱膨張
係数は2.4×10-6／℃〜4.1×10-6／℃範囲である
ため、このサセプターが熱影響を受けると、不可
避的に熱膨張差を生じる。その結果、炭化珪素の
コーテイング中及び加熱処理に伴ない加熱冷却サ
イクル中に炭化珪素膜にクラツクが発生し、露出
した黒鉛基材部分に含まれる吸着ガスが処理雰囲
気中に放出して半導体基板（シリコンウエハー）
を阻害する欠点がある。また、従来のサセプター
によりH2雰囲気に曝らすエピタキシヤル成長を
行なうと、炭化珪素は極く微量の鉄等が存在する
H2雰囲気下で分解が促進され、炭化珪素膜にピ
ンホールが発生して上記と同様に黒鉛基材中の吸
着ガスが放出してシリコンウエハーを阻害した
り、あるいは分解により分解により生じたカーボ
ンがシリコンウエハー中に拡散してシヤローピツ
ト等の発生原因となり、半導体装置の製造効率を
低下させる問題がある。
なお、サセプターのピンホール発生を抑制する
ために、炭化珪素膜の厚さを厚くすることが考え
られるが、炭化珪素膜を厚くすればするほど加熱
冷却時における黒鉛基板と炭化珪素膜との熱膨張
差による応力が増大し、短期間で炭化珪素膜にク
ラツクが発生する不都合さがある。
このようなことから、本発明者は上記欠点を解
消するために鋭意研究を重ねた結果、窒化珪素の
熱膨張係数が3.6×10-6／℃と一般的な製法で得
られる黒鉛の熱膨張係数（2.4×10-6／℃〜4.1×
10-6／℃）に近似しているとに着目し、この窒化
珪素を適度な気孔を有する炭素基材にコーテイグ
せしめることによつて、窒化珪素膜を厚くしても
急熱急冷サイクルによる亀裂発生を防止し、亀裂
発生に伴なう炭素基材に含まれる吸着ガスの放出
を阻止でき、しかもH2雰囲気中での窒化珪素の
分解による窒化珪素膜のピンホール発生を抑制で
きると共に分解生成物はシリコンと窒素でシリコ
ン半導体装置の品質劣化が招かず長時間安定して
使用できる強度の高いサセブターを見い出した。
すなわち、本発明のサセプターは気孔率10〜30
％の炭素基材の表面層に、厚さ30〜200μの高密
度窒化珪素膜を該窒化珪素が該炭素基材の気孔に
浸入するように形成せしめたことを特徴とするも
のである。
本発明において炭素基材の気孔率を上記範囲に
限定した理由は、その気孔率を10未満にすると、
窒化珪素のコーテイングに際して、窒化珪素が基
材中の十分浸入できるアンカー効果の高い、つま
り高強度の窒化珪素膜を形成できず、かといつて
その気孔率が35％を越えると、炭素基材自在の強
度が低下しひいては得られたサセプターの強度も
低下することになるからである。
なお、本発明における炭素材の熱膨張係数は、
2.4×10-6〜4.1×10-6／℃である。
本発明における高密度窒化珪素膜の厚さを限定
した理由は、膜厚を30μ未満にするとH2雰囲気
下での分解により短期間でピンホールを発生して
内部の炭素基材に含まれる吸着ガスが処理雰囲気
中に放出し半導体装置を汚染するからである。ま
た、200μを越えるとコスト面及びその効果は変
らないばかりか、魚熱急冷によつてクラツクが発
生し易くなるからである。
なお、本発明のサセプターをうるには、たとえ
ば炭素基材にハロゲン化珪素、水素化珪素などの
珪素系ガスと窒素、アンモニアなどの窒素系ガス
とを供給し、常圧もしくは減圧下で両ガスの反応
温度付近にて加熱し炭素基材表面層に窒化珪素膜
を蒸着する方法が採用される。
次に、本発明の実施例を説明する。
実施例 １
寸法270×680×16mmで気孔率18％、熱膨張係数
34×10-6／℃の炭素基材を、石英ガガラス管を炉
心管とした高周波加熱炉に挿入し、誘導加熱によ
り炭素基材表面を1350℃に加熱した後、炉心管内
にSiCl4を毎分５c.c.、H2を毎分500c.c.及びNH3を毎
分40c.c.供給させて炭素基材表面層に厚さ100μの
高密度窒化珪素膜を形成しサセプターを得た。
実施例 ２
寸法200×400×100mmで気孔率20％、熱膨張係
数2.4×10-6／℃の炭素基材を、アルミナ管を炉
心管とする外熱型の電気炉内に挿入し、炭素基材
表面を、1300℃に加熱した後、炉心管内を10mmＨ
ｇの減圧に保持しながら、、該管内にSiH4毎分０
c.c.、H2を毎分1000c.c.及びNH3を毎分80c.c.供させて
炭素基材表面層に厚さ80μの高密度窒化珪素膜を
形成しサセプターを得た。
実施例 １
実施例１で用いた炭素基材と同一形状で同一の
物性を有する炭素基材を石英ガラス管を炉芯管と
した高周波加熱炉に挿入し、誘導加熱により炭素
基材表面1200℃に加熱した後、炉芯内にトリクロ
ルメチルシランを毎分５c.c.、H2を毎分２c.c.供給
させ炭素基材表面層に厚さ100μの高密度炭化珪
素膜を形成しサセプターを得た。
比較例２及び３
寸法270×680×16mmで気孔率５％、熱膨張係数
3.0×10-6／℃の炭素基材に実施例１と同一条件
で基材表面に厚さ20μ（比較例２）、400μ（比較
例３）の高密度窒化珪素膜を形成し夫々のサセプ
ターを得た。
実施例１，２及び比較例１，２，３のサセプタ
ーを1200℃、HC1中で１時間、５時間及び15時間
エツチングした後、90℃の熱湯中に浸漬し１mmＨ
ｇ以下の真空にして、表面からの気泡発生の有無
によつてピンホール発生を確認した。結果をピン
ホールの発生が無い場合を〇印、ピンホールの発
生が有る場合を×印として表１に示した。
The present invention relates to improvements in susceptors used in epitaxial vapor phase growth, vapor phase growth of various insulating films, vapor phase growth of polycrystalline films, etc. in the manufacturing process of semiconductor devices. Conventionally, as this type of susceptor, a graphite base material coated with silicon carbide, which does not emit harmful gases and is chemically and thermally stable, has been used. However, the thermal expansion coefficient of silicon carbide constituting the susceptor is 4.2×10 -6 /℃, while the thermal expansion coefficient of the graphite base material that can be used as the main body of the susceptor is 2.4×10 -6 /℃ ~ 4.1×10 -6 /°C range, so when this susceptor is affected by heat, a difference in thermal expansion inevitably occurs. As a result, cracks occur in the silicon carbide film during coating of silicon carbide and during heating and cooling cycles associated with heat treatment, and the adsorbed gas contained in the exposed graphite base material portion is released into the processing atmosphere, causing the semiconductor substrate to silicon wafer)
There are drawbacks that hinder this. Furthermore, when epitaxial growth is performed using a conventional susceptor and exposed to an H 2 atmosphere, silicon carbide contains extremely small amounts of iron, etc.
Decomposition is accelerated in an H 2 atmosphere, pinholes are generated in the silicon carbide film, and the adsorbed gas in the graphite base material is released in the same manner as above, inhibiting the silicon wafer, or carbon generated by decomposition due to decomposition. There is a problem in that the particles diffuse into the silicon wafer and cause shallow pits and the like to occur, reducing the manufacturing efficiency of semiconductor devices. In order to suppress the occurrence of pinholes in the susceptor, it is possible to increase the thickness of the silicon carbide film, but the thicker the silicon carbide film, the more the heat between the graphite substrate and the silicon carbide film during heating and cooling increases. There is a disadvantage that stress due to the expansion difference increases and cracks occur in the silicon carbide film in a short period of time. For this reason, the inventor of the present invention has conducted intensive research to eliminate the above drawbacks, and has found that the thermal expansion coefficient of silicon nitride is 3.6 × 10 -6 /℃, which is the thermal expansion coefficient of graphite obtained by a general manufacturing method. Coefficient (2.4×10 -6 /℃~4.1×
10 -6 /℃), and by coating this silicon nitride on a carbon substrate with appropriate pores, even if the silicon nitride film is thick, it will not crack due to rapid heating and cooling cycles. It is possible to prevent the occurrence of pinholes in the silicon nitride film due to the decomposition of silicon nitride in an H 2 atmosphere, and to prevent the release of adsorbed gases contained in the carbon base material due to the generation of cracks. They discovered a strong susceptor made of silicon and nitrogen that can be used stably for long periods of time without causing quality deterioration of silicon semiconductor devices. That is, the susceptor of the present invention has a porosity of 10 to 30.
% of the carbon base material, a high-density silicon nitride film with a thickness of 30 to 200 μm is formed so that the silicon nitride penetrates into the pores of the carbon base material. The reason why the porosity of the carbon base material is limited to the above range in the present invention is that if the porosity is less than 10,
When coating with silicon nitride, it is not possible to form a silicon nitride film with a high anchoring effect that allows silicon nitride to sufficiently penetrate into the base material, that is, a high strength silicon nitride film, and if the porosity exceeds 35%, it becomes difficult to use the carbon base material. This is because the strength of the susceptor decreases, and as a result, the strength of the obtained susceptor also decreases. In addition, the thermal expansion coefficient of the carbon material in the present invention is
It is 2.4×10 -6 to 4.1×10 -6 /°C. The reason for limiting the thickness of the high-density silicon nitride film in the present invention is that if the film thickness is less than 30 μm, pinholes will be generated in a short period of time due to decomposition in an H 2 atmosphere, and adsorption contained in the internal carbon base material will occur. This is because the gas is released into the processing atmosphere and contaminates the semiconductor device. Moreover, if it exceeds 200μ, not only will the cost and effectiveness remain the same, but cracks will be more likely to occur due to rapid cooling of the fish. In order to obtain the susceptor of the present invention, for example, a silicon-based gas such as silicon halide or silicon hydride and a nitrogen-based gas such as nitrogen or ammonia are supplied to a carbon base material, and both gases are mixed under normal pressure or reduced pressure. A method is employed in which a silicon nitride film is deposited on the surface layer of a carbon base material by heating at around the reaction temperature of . Next, examples of the present invention will be described. Example 1 Dimensions: 270 x 680 x 16 mm, porosity 18%, coefficient of thermal expansion
A carbon base material of 34×10 -6 /°C was inserted into a high-frequency heating furnace with a quartz glass tube as the core tube, and after the surface of the carbon base material was heated to 1350℃ by induction heating, SiCl 4 was injected into the core tube. A susceptor was obtained by forming a high-density silicon nitride film with a thickness of 100 μm on the carbon substrate surface layer by supplying H 2 at 500 c.c./min and NH 3 at 40 c.c./min. . Example 2 A carbon base material with dimensions of 200 x 400 x 100 mm, porosity of 20%, and thermal expansion coefficient of 2.4 x 10 -6 /°C was inserted into an externally heated electric furnace with an alumina tube as the core tube. After heating the base material surface to 1300℃, the inside of the furnace tube was heated to 10mmH.
SiH 4 per minute is injected into the tube while maintaining a reduced pressure of 0 g per minute.
A susceptor was obtained by supplying cc, H 2 at 1000 c.c./min and NH 3 at 80 c.c./min to form a high-density silicon nitride film with a thickness of 80 μm on the carbon substrate surface layer. Example 1 A carbon base material having the same shape and same physical properties as the carbon base material used in Example 1 was inserted into a high frequency heating furnace with a quartz glass tube as the furnace core, and the surface of the carbon base material was heated to 1200°C by induction heating. After heating, trichloromethylsilane was supplied into the furnace core at 5 c.c./min and H 2 was supplied at 2 c.c./min to form a high-density silicon carbide film with a thickness of 100 μm on the surface layer of the carbon base material. I got it. Comparative Examples 2 and 3 Dimensions: 270 x 680 x 16 mm, porosity 5%, thermal expansion coefficient
A high-density silicon nitride film with a thickness of 20μ (Comparative Example 2) and 400μ (Comparative Example 3) was formed on the surface of the carbon substrate at 3.0 × 10 -6 /℃ under the same conditions as in Example 1, and the respective susceptors were I got it. The susceptors of Examples 1 and 2 and Comparative Examples 1, 2, and 3 were etched in HC1 at 1200°C for 1 hour, 5 hours, and 15 hours, and then immersed in hot water at 90°C for 1 mmH.
The vacuum was set to less than g and the occurrence of pinholes was confirmed by the presence or absence of air bubbles from the surface. The results are shown in Table 1 with the mark ◯ indicating that no pinholes were generated and the mark x indicating that pinholes were present.
【表】
この表からも明らかな様に、本発明のサセプタ
ーではHC1で15時間のエツチング後においてもピ
ンホールの発生は確認されなかつたのに対し、炭
化珪素膜を形成した比較例１のサセプター及び膜
厚20μの窒化珪素膜を形成した比較例２のサセプ
ターでは、５時間のエツチングでピンホールの発
生が確認された。また、膜厚400μの密化珪素膜
を形成した比較例３のサセプターでは、本発明の
サセプターと同様15時間のエツチング後もピンホ
ールの発生は認められなかつたが、本発明のサセ
プターーと比較して急熱急冷に弱くクラツクが発
生し易いものであつた。
比較例４及び５
寸法270×680×16mm熱膨張係数3.0××10-6／
℃で気孔率５％の炭素基材（比較例４）と気孔率
40％の炭素基材（比較例５）を実施例１と同一条
件で基材表面に膜厚100μで、高密度窒化珪素膜
を形成しサセプターを得た。比較例４で得られた
サセプターはエピタキシヤル気相成長における昇
温、降温の過程で時間の使用で剥離し使用に耐え
るものではなかつた。また、比較例５で得られた
サセプターは機械的強度が弱く、割れ易いため実
用的ではなかつた。
また、本実施例１，２のサセプター及び炭素基
材に炭化珪素膜を形成したサセプター（比較例
６）を用いて、シリコンウエハーをH2雰囲気中
でエピタキシヤル気相成長させ、各サセプター表
面膜の亀裂、ピンホール発生、及びシリコンウエ
ハーのシヤローピツト発生を調べた。その結果、
本実施例１，２のサセプターは窒化珪素膜のクラ
ツク、ピンホール発生が抑制され、従来の炭化珪
素膜を形成したサセプターに比して1.5〜２倍の
耐用度を示し、しかもその間のシリコンウエハー
のシヤローピツト発生は皆無であることがわかつ
た。
以上詳述した如く、本発明よれば炭素基材の保
護膜としての窒化珪素膜を厚くしても急熱急冷サ
イクルによる亀裂発生を防止し、亀裂発生に伴な
う炭素基材に含まれる吸着ガスの放出及びウエハ
ーの特性を劣化させる炭素基材の分解ガスの発生
を阻止でき、しかもH2雰囲気中での窒化珪素の
分解によるピンホール発生を抑制できると共に分
解生成物は無害なシリコンと窒素でシリコン半導
体装置の品質劣化の誘発を防止でき、もつて耐用
寿命が長く、シヤローピツト等のない高品質の半
導体装置を長期間安定して製造し得る実用性の高
いサセプターを提供できるものである。[Table] As is clear from this table, no pinholes were observed in the susceptor of the present invention even after 15 hours of etching with HC1, whereas the susceptor of Comparative Example 1 on which a silicon carbide film was formed In the susceptor of Comparative Example 2 in which a silicon nitride film with a thickness of 20 μm was formed, pinholes were observed to occur after 5 hours of etching. In addition, in the susceptor of Comparative Example 3 in which a densified silicon film with a film thickness of 400μ was formed, no pinholes were observed even after 15 hours of etching, similar to the susceptor of the present invention, but compared to the susceptor of the present invention. It was susceptible to rapid heating and cooling and was prone to cracks. Comparative Examples 4 and 5 Dimensions: 270 x 680 x 16 mm Coefficient of thermal expansion: 3.0 x x 10 -6 /
Carbon substrate with porosity of 5% at °C (Comparative Example 4) and porosity
A susceptor was obtained by forming a high-density silicon nitride film with a thickness of 100 μm on the surface of a 40% carbon base material (Comparative Example 5) under the same conditions as in Example 1. The susceptor obtained in Comparative Example 4 peeled off over time during the temperature rising and falling process during epitaxial vapor phase growth, and was not durable for use. Furthermore, the susceptor obtained in Comparative Example 5 had low mechanical strength and was easily broken, making it impractical. In addition, using the susceptors of Examples 1 and 2 and a susceptor in which a silicon carbide film was formed on a carbon base material (Comparative Example 6), a silicon wafer was epitaxially grown in an H 2 atmosphere, and each susceptor surface film was The occurrence of cracks, pinholes, and shallow pits in silicon wafers was investigated. the result,
The susceptors of Examples 1 and 2 suppress the occurrence of cracks and pinholes in the silicon nitride film, and exhibit 1.5 to 2 times the durability compared to susceptors formed with conventional silicon carbide films. It was found that there was no occurrence of shallow pits. As described in detail above, according to the present invention, even if the silicon nitride film as a protective film for the carbon base material is thickened, crack generation due to rapid heating and cooling cycles can be prevented, and the adsorption of the carbon base material that accompanies crack generation can be prevented. It can prevent the release of gas and the generation of decomposition gas from the carbon base material that deteriorates the characteristics of wafers. Furthermore, it can suppress the generation of pinholes due to the decomposition of silicon nitride in an H2 atmosphere, and the decomposition products are harmless silicon and nitrogen. Therefore, it is possible to provide a highly practical susceptor that can prevent quality deterioration of silicon semiconductor devices, has a long service life, and can stably manufacture high-quality semiconductor devices without shallow pits or the like over a long period of time.