第２実施形態に係るサセプタ７は、ＳｉＣが被覆された黒鉛からなるサセプタ本体２と、ウェハを上部に載置する部分となる部材８と、部材８の上部の外周に沿って接合するように設けられるＳｉＣからなる環状部材９とを備えてなり、これらサセプタ本体２と、部材８と、環状部材９とによりザグリ部８ａが形成されるものである。
The susceptor 7 according to the second embodiment is joined along the susceptor main body 2 made of graphite coated with SiC, the member 8 serving as a portion on which the wafer is placed, and the outer periphery of the upper portion of the member 8. An annular member 9 made of SiC is provided, and a counterbore portion 8 a is formed by the susceptor body 2, the member 8, and the annular member 9.
部材８は、ＴａＣからなる円盤状部材であり、その断面は略Ｔ字型となるように形成されていて、環状部材９とともにサセプタ本体２に嵌合されたとき、サセプタ７においてウェハを載置するのに最適な形状を有するザグリ部８ａを形成できる。このザグリ部８ａは、載置するウェハと同じ大きさの平面形状である必要はなく、やや大きい平面形状を有するものであってもよい。なお、この部材８も上述した部材３と同様に、図２に示すように、ＴａＣ被膜５が黒鉛６表面に被覆されているＴａＣ被覆黒鉛材からなる部材４であってもよい。このとき、ＴａＣ被膜の厚さは１０〜１００μｍが好ましく、さらに好ましくは３０〜１００μｍである。
The member 8 is a disk-shaped member made of TaC, and its cross section is formed to be substantially T-shaped. When the member 8 is fitted to the susceptor body 2 together with the annular member 9, the wafer is placed on the susceptor 7 . The counterbore part 8a having an optimum shape for the formation can be formed. The counterbore 8a does not need to have a planar shape having the same size as the wafer to be placed, and may have a slightly larger planar shape. The member 8 may be a member 4 made of a TaC-coated graphite material in which a TaC coating 5 is coated on the surface of the graphite 6 as shown in FIG. At this time, the thickness of the TaC film is preferably 10 to 100 μm, and more preferably 30 to 100 μm.
次に、図８に示す測定装置の動作、及び、サセプタのガス透過率の測定方法について説明する。測定試料には、サセプタを直径３０ｍｍ以上の円板状に加工し、測定前に十分乾燥したものを用いた。測定試料をセル２６内に設置し、ゲートバルブ３２と排気バルブ３１を開けてロータリー式真空ポンプ２４で粗引きする。１００Ｐａ以下まで真空引きした後、排気バルブ３１を閉めて排気バルブ３３、３４を開けてセル一次側配管２５および二次側のタンク２７をロータリー式の真空ポンプ２９およびターボ分子ポンプ２８で一定の高真空値になるまで減圧する。次いで、電離真空計２３で高真空まで到達したことを確認したら、排気バルブ３３、３４とゲートバルブ３２を閉めた後に真空ポンプ２９とターボ分子ポンプ２８を停止する。ストップバルブ３０を開けて一次側配管２５に一次側真空計２１で確認しながらＮ2ガスを一定の試験圧で加える。Ｎ2ガスは一次側から、セル２６内の測定試料を透過して、二次側のタンク２７へと移動し、二次側のタンク２７の圧力が上昇し始める。その圧力上昇率を二次側圧力計２２で測定する。このように測定装置を動作させた後、測定試料のガス透過率（Ｋ）を次の式（１）、（２）にしたがって算出する。
Ｋ＝（ＱＬ）／（ΔＰＡ）…（１）
Ｑ＝｛（ｐ2−ｐ1）Ｖ0｝／ｔ…（２）
ここで、Ｋは窒素ガス透過率、Ｑは通気量、ΔＰは一次側タンクと二次側タンクの圧力差、Ａは透過面積、Ｌは測定試料の厚さ、ｐ1は二次側タンクの初期圧力、ｐ2は二次側タンクの最終圧力、Ｖ0は二次側タンクの容積、ｔは測定時間である。
被膜の窒素ガス透過率（Ｋ2）を求めるには、まず、黒鉛基材上に被膜を設けたＳｉＣおよびＴａＣ被覆黒鉛材の窒素ガス透過率（Ｋ0）を測定し、次いで研磨により上記被膜を除去し、黒鉛基材のみの窒素ガス透過率（Ｋ1）を測定する。そして、次の関係式（３）からＫ2を算出する。
（Ｌ1＋Ｌ2）／Ｋ0＝Ｌ1／Ｋ1＋Ｌ2／Ｋ2…（３）
ここで、Ｌ1は黒鉛基材の厚さ、Ｌ2はＳｉＣおよびＴａＣの被膜の厚さである。
Next, the operation of the measuring apparatus shown in FIG. 8 and the method for measuring the gas permeability of the susceptor will be described. As a measurement sample, a susceptor processed into a disk shape having a diameter of 30 mm or more and sufficiently dried before measurement was used. A measurement sample is placed in the cell 26, and the gate valve 32 and the exhaust valve 31 are opened and roughed by the rotary vacuum pump 24. After evacuating to 100 Pa or less, the exhaust valve 31 is closed, the exhaust valves 33 and 34 are opened, and the cell primary side piping 25 and the secondary side tank 27 are fixed at a certain level by the rotary vacuum pump 29 and the turbo molecular pump 28. Depressurize until vacuum is reached. Then, confirm that it has reached to a high vacuum by ionization gauge 23 stops the vacuum pump 2 9 and a turbo molecular pump 2 8 after closing the exhaust valve 33 and the gate valve 32. The stop valve 30 is opened, and N 2 gas is added to the primary side pipe 25 at a constant test pressure while checking with the primary side vacuum gauge 21. The N 2 gas permeates the measurement sample in the cell 26 from the primary side and moves to the secondary side tank 27, and the pressure in the secondary side tank 27 starts to rise. The pressure increase rate is measured by the secondary pressure gauge 22. After operating the measuring apparatus in this way, the gas permeability (K) of the measurement sample is calculated according to the following equations (1) and (2).
K = (QL) / (ΔPA) (1)
Q = {(p 2 −p 1 ) V 0 } / t (2)
Here, K is the nitrogen gas permeability, Q is the air flow rate, ΔP is the pressure difference between the primary side tank and the secondary side tank, A is the permeation area, L is the thickness of the measurement sample, and p 1 is the secondary side tank. Initial pressure, p 2 is the final pressure of the secondary tank, V 0 is the volume of the secondary tank, and t is the measurement time.
In order to obtain the nitrogen gas permeability (K 2 ) of the coating, first, the nitrogen gas permeability (K 0 ) of the SiC and TaC-coated graphite material provided with the coating on the graphite substrate is measured, and then the above-mentioned coating is obtained by polishing. And the nitrogen gas permeability (K 1 ) of only the graphite substrate is measured. Then, K 2 is calculated from the following relational expression (3).
(L 1 + L 2 ) / K 0 = L 1 / K 1 + L 2 / K 2 (3)
Here, L 1 is the thickness of the graphite substrate, and L 2 is the thickness of the SiC and TaC coatings.
また、それぞれのエピタキシャル成長したＳｉＣ層の窒素とホウ素濃度を測定した。その結果を上記表５に示す。測定にはＳＩＭＳ分析法を用いた。実施例５のサセプタを使用した場合のＳｉＣ層の窒素濃度とホウ素濃度は、それぞれ５．２×１０15と３．４×１０14ａｔｏｍｓ／ｃｍ3であり、高純度なものであった。しかし、比較例５のサセプタを使用した場合のＳｉＣ層の窒素濃度とホウ素濃度は、高くなっており、ＳｉＣ被膜の昇華や黒鉛基材からのガス放出が原因で不純物濃度が高くなっていた。また、比較例５と比較例６のサセプタを使用した場合のエピタキシャル成長したＳｉＣ層の窒素濃度とホウ素濃度は、５．８×１０17〜５．６×１０18ａｔｏｍｓ／ｃｍ3と高くなっており、ＴａＣ被膜を透過した黒鉛基材からのガス放出が原因で不純物濃度が高くなっていた。
Further, the nitrogen and boron concentrations of each epitaxially grown SiC layer were measured. The results are shown above Symbol Table 5. The SIMS analysis method was used for the measurement. When the susceptor of Example 5 was used, the nitrogen concentration and boron concentration of the SiC layer were 5.2 × 10 15 and 3.4 × 10 14 atoms / cm 3 , respectively, and were high purity. However, when the susceptor of Comparative Example 5 was used, the nitrogen concentration and boron concentration of the SiC layer were high, and the impurity concentration was high due to sublimation of the SiC coating and outgassing from the graphite substrate. Further, when the susceptor of Comparative Example 5 and Comparative Example 6 is used, the nitrogen concentration and boron concentration of the epitaxially grown SiC layer are as high as 5.8 × 10 17 to 5.6 × 10 18 atoms / cm 3. The impurity concentration was high due to outgassing from the graphite base material permeated through the TaC coating.
１、７、１０ サセプタ
２ サセプタ本体
３、４、８ 部材
３ａ、８ａ、１１ ザグリ部
５ ＴａＣ被膜
１２ ＴａＣ被膜又はＳｉＣ被膜
６、１３ 黒鉛
９ 環状部材
２１ 一次側真空計
２２ 二次側真空計
２３ 電離真空計
２４、２９ ロータリーポンプ
２５ 一次側配管
２６ 透過セル
２７ 二次側タンク
２８ ターボ分子ポンプ
３０ ストップバルブ
３１、３３、３４ 排気バルブ
３２ ゲートバルブ
1, 7, 10 Susceptor 2 Susceptor body 3, 4, 8 Member 3a, 8a, 11 Counterbore part 5 TaC coating
12 TaC coating or SiC coating 6, 13 Graphite 9 Annular member 21 Primary vacuum gauge 22 Secondary vacuum gauge 23 Ionization vacuum gauge 24, 29 Rotary pump 25 Primary piping 26 Permeation cell 27 Secondary tank 28 Turbo molecular pump 30 Stop valve 31, 33, 34 Exhaust valve 32 Gate valve