JP2004214075A - HEATING ELEMENT CONTAINING MoSi2 AS MAIN CONSTITUENT - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、発熱体の集積性が高く高温化及び温度制御が容易であり、また加熱時の変形（あばれ）やショート等の故障が少なく、さらに汚染物質（不純物）の少ない、特に半導体製造装置用熱処理炉（酸化・拡散炉を含む）に有用であるＭｏＳｉ２を主成分として８０ｗｔ％以上含む基材からなる発熱体及びコストを低減化できる同発熱体の製造方法に関する。
なお、本明細書で使用するＭｏＳｉ２を主成分として８０ｗｔ％以上含む基材は、ＭｏＳｉ２基材に絶縁性酸化物であるＳｉＯ２を含有させて電気抵抗を増加させたＭｏＳｉ２を主成分とする発熱体である。
ＭｏＳｉ２を主成分とする発熱体は、６７３°Ｋ〜８７３°Ｋの範囲で、ＭｏとＳｉの同時酸化が起こり、さらにＭｏ酸化物の蒸発減少が伴うという、ペスト（粉化現象）と言う低温酸化が起こるが、これを防止するために１５００°Ｋ以上で酸化処理して緻密なシリカ保護被膜を形成する。本発明は、このような緻密なシリカ保護被膜を形成した発熱体を含み、シリカ（ＳｉＯ２）であるガラス質成分の添加は、このような緻密なシリカ保護被膜の形成に有効である。
【０００２】
【従来の技術】
従来、半導体製造装置に使用される熱処理炉においては、金属発熱体（発熱体）が使用されることが多い。
ところが、金属発熱体を半導体製造装置の熱処理炉等に使用した場合、発熱体の発熱とともに発熱体に含有される低融点の不純物や金属酸化物等の蒸気圧が高くなり、発熱体表面から炉雰囲気中に飛散される金属化合物量が多くなる。
これらの金属化合物中の金属は、デバイスの高集積化が進むとともに、極少量でもデバイスに悪影響を及ぼすため、特に熱処理中に混入するウエハの金属汚染が問題になってきている。
発熱体から飛散した金属は、発熱体とウエハとの間にたとえ石英管やＳｉＣ管が存在しても、これらの中を拡散し、最終的にはウエハにまで到達する。特に、シリコン結晶中の拡散係数が大きいＣｕ，Ｆｅ，Ｍｎ，Ｍｇ，Ｎａ，Ｋ等の不純物元素は注意が必要であった。
【０００３】
最近、金属発熱体では上記のような金属汚染の問題があるため、また半導体デバイスの微細化及びデバイス製造時間の短縮化と省エネルギー化のために、従来の金属発熱体に替えて、ＣＶＤ装置や拡散炉等の半導体製造装置に、ＭｏＳｉ２を主成分とする高出力性能の発熱体が利用されるようになってきた。
一般に、半導体製造装置に使用される熱処理炉は炉内の温度分布を厳密に制御するなど、非常に高精度な温度特性が要求されるが、ＭｏＳｉ２を主成分とする発熱体は優れた耐熱特性を有し、金属発熱体の約１０倍の表面負荷が可能であり、また急速加熱昇温することができるという大きな特長を有するので、好適な材料と言える。
【０００４】
しかし、これまで半導体製造装置に使用される熱処理炉においては、炉内の温度分布のコントロールや製造時間短縮のための急速加熱昇温等が主としたねらいであったので、ＭｏＳｉ２を主成分とする発熱体は、そのための材料強度（耐熱性）や材料脆化現象を防止するため、あるいはペスト（粉化現象）と呼ばれている低温酸化を防止するために１５００°Ｋ以上で酸化処理して緻密なシリカ保護被膜を形成する等、発熱体自体の材料開発が主であった。
ところが、ＭｏＳｉ２を主成分とする発熱体を半導体製造装置の熱処理炉等に使用した場合、金属製発熱体よりはその傾向は小さいものの、発熱体の発熱とともに、発熱体に含有される不純物が発熱体表面から炉雰囲気中に飛散するという同様の問題を生じた。
特に、高温での急速加熱昇温を行う場合にそれが顕著であり、ウエハの金属汚染が問題になっている。したがって、従来のＭｏＳｉ２を主成分とする発熱体は、半導体製造装置の熱処理炉等の発熱体としては必ずしも良いとは言えず、問題を有していた。
このようなことからＭｏＳｉ２を主成分とする発熱体中に含有されるＦｅ、Ｃｕ、Ａｕ、Ｃａ、Ａｌ等の不純物の総量を０．１ｍａｓｓ％以下にすること、またＦｅ、Ｃｕ、Ａｕ、Ｃａ、Ａｌの不純物をそれぞれ０．０５ｍａｓｓ％以下、さらには０．０３ｍａｓｓ％以下に規制する提案がなされている（例えば、特許文献１参照）。
しかし、この程度の不純物の規定量では不十分であることが判明した。一方、これらの不純物（上記不純物元素及びそれらの酸化物等を含む）の中で、蒸気圧が１６００°Ｃで１×１０−３Ｈｇ以下であれば、上記の量以上含有されていても特に問題とならないことがないことが分かった。
【０００５】
【特許文献１】
特開平１０−３２４５７１号
【０００６】
【発明が解決しようとする課題】
本発明は、発熱体の集積性が高く高温化及び温度制御が容易であり、また加熱時の変形（あばれ）やショート等の故障が少ないというＭｏＳｉ２を主成分とする発熱体の特徴を生かすと同時に、汚染物質（不純物）の少ない、特に半導体製造装置用熱処理炉（酸化・拡散炉を含む）に有用であるＭｏＳｉ２を主成分として８０ｗｔ％以上含む発熱体及びその製造方法を提供する。
【０００７】
【課題を解決するための手段】
上記の課題を解決するために、本発明者らは、特定の不純物を低減することにより、特に半導体製造装置用熱処理炉（酸化・拡散炉を含む）に有用であるＭｏＳｉ２を主成分として８０ｗｔ％以上含む発熱体を低コストで提供できるとの知見を得た。
本発明はこの知見に基づき、
１．ＭｏＳｉ２を主成分として８０ｗｔ％以上含み、残余ＳｉＯ２と不純物からなる発熱体において、該発熱体中に含まれる不純物の内、１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ以上である不純物の総量が３００ｐｐｍ以下であることを特徴とするＭｏＳｉ２を主成分とする発熱体
２．半導体製造装置用熱処理炉に使用することを特徴とする上記１記載のＭｏＳｉ２を主成分とする発熱体
３．ＭｏＳｉ２原料粉を酸で洗浄し乾燥する工程、ＳｉＯ２と混合粉砕する工程、バインダーと混合し脱脂する工程、通電焼結する工程からなることを特徴とするＭｏＳｉ２を主成分とする発熱体の製造方法
４．脱脂後一次焼結する工程を含むことを特徴とする上記３記載のＭｏＳｉ２を主成分とする発熱体の製造方法
５．硫酸以外の酸で洗浄することを特徴とする上記３又は４記載のＭｏＳｉ２を主成分とする発熱体の製造方法
６．酸洗後のＭｏＳｉ２原料粉に含まれる１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ以上である不純物の総量が３００ｐｐｍ以下であることを特徴とする上記３〜５のそれぞれに記載のＭｏＳｉ２を主成分とする発熱体の製造方法を提供する。
【０００８】
【発明の実施の形態】
本発明のＭｏＳｉ２を主成分として８０ｗｔ％以上含み、残余ＳｉＯ２と不可避的不純物からなる発熱体（以下、特に記載しない限り、「ＭｏＳｉ２製発熱体」と称する。）は、該発熱体中に含まれる不純物の内、１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ以上である不純物の総量が３００ｐｐｍ以下であることを特徴とするＭｏＳｉ２を主成分とする発熱体である。
ＭｏＳｉ２製発熱体を加熱した場合に、このＭｏＳｉ２製発熱体から飛散し、半導体製造装置用熱処理炉内及び半導体ウエハを汚染する主要な物質は、１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ以上である鉄、マンガン、マグネシウム、ナトリウム、カリウム等の物質である。
【０００９】
例えば、不純物として鉄が多量に含有するＭｏＳｉ２製発熱体が石英管内で加熱された場合、石英管の内部が赤褐色に変色する現象が見られる。これは飛散する鉄が、同時に放散される酸素と結びついて酸化鉄となり赤褐色に変色したものと考えられる。したがって、このようなＭｏＳｉ２製発熱体から飛散する物質（不純物）は極力制限されなければならず、総量が３００ｐｐｍ以下であることが必要である。
【００１０】
主成分としてのＭｏＳｉ２は、好ましくは９０ｗｔ％以上とする。これは、ＳｉＯ２の体積変化を伴う相転移を考慮したもので、ＳｉＯ２の含有量が多くなり過ぎるとその影響が大きくなり、発熱体の強度に支障をきたす可能性があるためである。
１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ未満であるＴａ，Ｗ，Ｍｏ，Ｖ，Ｎｂ及び鉄等の酸化物等の不純物は、ＭｏＳｉ２製発熱体から飛散することが極めて少ないので、発熱体に含有される量は特に問題となることがなく、総量で１ｐｐｍ以上、例えば１００ｐｐｍ、１０００ｐｐｍのオーダーで含有されていても良い（許容される）。
以上によって、ＭｏＳｉ２製発熱体から飛散し、半導体製造装置用熱処理炉内及び半導体ウエハを汚染する主要な物質を防止できるという著しい効果が得られた。
【００１１】
以上の不純物には、ＭｏＳｉ２に混入する不純物及び添加されるシリカ（ＳｉＯ２）等に混入する不純物があるが、いずれも高純度の材料を使用し、不純物の量を上記に制限する。
通常、高純度シリカはガラス質形成材料として２０ｗｔ％以下、好ましくは１０ｗｔ％以下含有させる。これは、ＳｉＯ２の体積変化を伴う相転移を考慮したもので、ＳｉＯ２の含有量が多くなり過ぎるとその影響が大きくなり、発熱体の強度に支障をきたす可能性があるためである。
以上のＭｏＳｉ２製発熱体は、半導体製造装置用熱処理炉に好適であり、半導体装置への汚染を防止できるという著しい効果がある。
【００１２】
このＭｏＳｉ２製発熱体は、ＭｏＳｉ２原料粉を酸で洗浄した後これを乾燥し、次にＳｉＯ２と混合粉砕した後、バインダーと混合し、さらに例えば押出しによって棒状又は平板状に成形する。
このようにして得た成形体を脱脂、一次焼結及び通電加熱焼結することによって、密度の高いＭｏＳｉ２製発熱体を製造する。
さらに、このようにして作製した棒状又は平板状の発熱体を接合し、例えば円弧状又はＵ字形状等に製造する。このように、ＭｏＳｉ２製発熱体を各種の形状に成形した後、半導体製造装置用熱処理炉に設置する。
【００１３】
上記酸による洗浄は硫酸以外の酸を使用する。例えば希塩酸と硝酸の混酸を使用して洗浄する。この酸による洗浄は極めて重要であり、これによってクロム、ニッケル、鉄、マンガン、マグネシウム、ナトリウム、カリウム等の不純物を著しく低減させることができる。
ＭｏＳｉ２原料粉の酸による洗浄は、さほどの労力や費用を必要としない。それにもかかわらず、著しい不純物の除去効果がある。
例えば、ＭｏＳｉ２原料粉に含まれる１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ以上である不純物が、総量で１０００ｐｐｍ以上含有されていても、酸洗後のＭｏＳｉ２原料粉に含まれる同不純物の総量を３００ｐｐｍ以下まで低減できる効果を有する。
【００１４】
【実施例及び比較例】
以下に実施例及び比較例を説明するが、本実施例は理解を容易にするためのものであり、本発明を制限するものではない。すなわち、本発明の技術思想の範囲内での他の変形あるいは他の実施例は、当然本発明に含まれる。
【００１５】
（実施例１）
発熱体原料とするＭｏＳｉ２粉末は、純度２Ｎ〜３Ｎレベルの粉末を用いることができる。ＭｏＳｉ２粉末の主な不純物含有量を表１に示す。
表１から明らかなように、鉄（Ｆｅ）、クロム（Ｃｒ）、ニッケル（Ｎｉ）、鉄（Ｆｅ）、マンガン（Ｍｎ）、マグネシウム（Ｍｇ）、ナトリウム（Ｎａ）、カリウム（Ｋ）等の不純物がかなりの量で含有されている。これを希塩酸と硝酸の混酸で洗浄した。
酸による洗浄後の同不純物含有量を同様に表１に示す。酸による洗浄後、表１に示すように、不純物は著しく除去された。また、ＭｏＳｉ２粉末の比表面積は３０％上昇した。
一方、ＳｉＯ２粉末は市販品を用いるが、不純物を選別除去した後、さらに１６５０°Ｃ以上の高温で長時間熱処理することにより、含有する金属成分を蒸発させて精製した材料を使用した。
なお、ＳｉＯ２の高温熱処理は、ＳｉＯ２の結晶構造を石英から高温で安定なクリストバライトに相転移させるために必要である。
【００１６】
上記ＭｏＳｉ２粉９５ｗｔ％とＳｉＯ２粉末５ｗｔ％とをバインダーと混合（なお、バインダーは混合比率には計算しない。以下、同様とする。）し、この混合物を型から押出して棒状の成形体とした。
この棒状の成形体（グリーン）を脱脂、一次焼結及び通電加熱焼結することによって、ＭｏＳｉ２製棒状発熱体を得た。
このＭｏＳｉ２製棒状発熱体に使用したＭｏＳｉ２粉末には、表１に示す通り、Ｆｅ：１１０ｗｔｐｐｍ、Ｗ：１２０ｗｔｐｐｍ、Ｎｂ：４０ｗｔｐｐｍ、Ｔａ：４０ｗｔｐｐｍが含有されていた。
しかし、これらは蒸気圧が低い、すなわち１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ未満であるので、ＭｏＳｉ２製発熱体から飛散し、半導体製造装置用熱処理炉内及び半導体ウエハを汚染することは殆どない。ここでＦｅが１１０ｐｐｍあるが、これは蒸気圧の低いＦｅの化合物である。
【００１７】
他方、蒸気圧が高い、すなわち１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ以上であるＦｅ，Ｍｎ，Ｍｇ，Ｎａ，Ｋ等の不純物は、半導体製造装置用熱処理炉内及び半導体ウエハを汚染する可能性が高いと言える。
しかし、表１に示す通り、Ｃｒ：３０ｗｔｐｐｍ，Ｎｉ：１０ｗｔｐｐｍ，Ｍｎ：４ｗｔｐｐｍ，Ｍｇ：１ｗｔｐｐｍ，Ｎａ：３ｗｔｐｐｍ，Ｋ：２ｗｔｐｐｍであり、汚染物質となる量そのものが著しく低減しており、本発明の実施例においては、特に問題となるようなレベルでないことが分かる。なお、Ｆｅ１１０ｗｔｐｐｍとあるが、これは蒸気圧の低いＦｅの化合物である。
なお、発熱体中の不純物は、発熱体の製造工程において、容器や工具等からの汚染があり、表１の出発原料よりも不純物量はやや増加する。粉砕容器の内壁をＭｏでライニングすること、あるいは気流粉砕方式を用いるなどして、製造工程からの金属汚染を極力低減することが重要である。
【００１８】
【表１】
次に、汚染物質（不純物）の挙動確認のため、このようにして得た高純度ＭｏＳｉ２製棒状発熱体を石英板（３〜１０ｍｍ間）の直下に配置し、大気中で発熱体の表面温度が１６００°Ｃになるように通電加熱した。
この試験では、発熱体表面から気化し、また蒸気圧が高くなって飛散した成分が石英板に再析出するため、その石英板を観察することにより、発熱体からの金属汚染量が模擬的に評価できる。
上記発熱体を１０分間通電加熱保持した後、石英板の下面に付着した不純物量を観察（目視及びＳＥＭ観察）した。目視による石英板の変色は認められず、ＳＥＭ観察でも、なにも観察されなかった。
以上から、実施例１に示す発熱体材は、半導体製造装置用熱処理炉と使用する場合、発熱時に発熱体材から放散される不純物が被熱処理体を汚染する可能性が低く、発熱体材としては極めて好ましい材料と言える。
また、この発熱体材は室温と５００°Ｃで３０時間保持する熱サイクル特性試験において、５０サイクル後でも粉状化せず、さらに１６００°Ｃで３００時間処理後の抗折試験でも３００ＭＰａ以上であった。
【００２０】
（実施例２）
表２に示す原料、特にＷ、Ｎｂ、Ｔａの蒸気圧の低い不純物を多く含有される原料を用い、同様に酸洗してＭｏＳｉ２製棒状発熱体を作製した。
その純度を表２に示す。表２に示す通り発熱体中には、Ｗ、Ｎｂ、Ｔａが多量に含まれている。実施例１と同様に、このＭｏＳｉ２製棒状発熱体を石英板（３〜１０ｍｍ間）の直下に配置し、大気中で発熱体の表面温度が１６００°Ｃになるように通電加熱した。そして、その後石英板の下面に付着した不純物量を観察（目視及びＳＥＭ観察）した。
しかし、この発熱体からは石英板への付着物は観察されなかった。これらのことからＷ、Ｎｂ、Ｔａ等の１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ未満である不純物が、たとえ発熱体の中に多く含有されていても、これらが加熱中に飛散することがなく、不純物として悪影響を与えないことが分かった。
【００２１】
【表２】
（比較例１）
一般に高純度と言われている市販品のＭｏＳｉ２粉末９５ｗｔ％（Ｆｅ６００ｗｔｐｐｍ）と、同様に市販品であるＳｉＯ２粉末５ｗｔ％とを微粉砕後、バインダーと混合し、この混合物を型から押出して棒状の成形体とした。
この棒状の成形体（グリーン）を脱脂、一次焼結及び通電加熱焼結することによって、ＭｏＳｉ２製棒状発熱体を得た。
同様に、表１に不純物の分析値を示す。表１に示す通り、このＭｏＳｉ２製棒状発熱体には、Ｆｅ：６００ｗｔｐｐｍ，Ｗ：２０ｗｔｐｐｍ、Ｃｒ：３０ｗｔｐｐｍ、Ｎｉ：１０ｗｔｐｐｍ、Ｎｂ：１０ｗｔｐｐｍ、Ｔａ：３ｗｔｐｐｍ，Ｍｎ：１０ｗｔｐｐｍ，Ｍｇ：６ｗｔｐｐｍ，Ｎａ：１ｗｔｐｐｍ，Ｋ：１ｗｔｐｐｍが含有されていた。これらの中には、酸化物も含まれる。
【００２３】
次に、このようにして得たＭｏＳｉ２製棒状発熱体を石英板直下に配置し、大気中で発熱体の表面温度が１６００°Ｃになるように通電加熱した。上記実施例と同様に、上記発熱体を１０分間通電加熱保持した後、石英板に付着した不純物量を観察（目視及びＳＥＭ観察）した。
石英板は目視で茶色に変色しており、発熱体の真上に位置した部分には一面に多量の不純物が付着していた。またこれらの付着物を分析すると、ここでは主にＦｅであることが分かった。
以上から、半導体製造装置用熱処理炉と使用する場合、発熱時に発熱体材から放散される不純物が被熱処理体を汚染する可能性が高く、発熱体材としては好ましくない結果が得られた。
【００２４】
以上に示す通り、ＭｏＳｉ２製棒状発熱体を加熱することによって、不純物の量が多い、特に１６００°Ｃにおける蒸気圧が１．０×１０−３ｍｍＨｇ以上である不純物の含有量が多い発熱体については、近傍に配置した石英板が変色するほどに、該発熱体からの不純物の飛散があり、これらは半導体ウエハ等に混入し、悪影響を与えることは必須である。
本発明は、ＭｏＳｉ２を主成分として８０ｗｔ％以上、好ましくは９０ｗｔ％以上含む、やや純度の低いＭｏＳｉ２粉末材料から半導体装置製造に影響を与える不純物を低コストで減少させ、かつ発熱体の集積性が高く高温化及び温度制御が容易であり、また加熱時の変形（あばれ）やショート等の故障が少ないというＭｏＳｉ２を主成分とする発熱体の特徴を生かすことのできるという優れた特徴を有している。
【００２５】
【発明の効果】
本発明のＭｏＳｉ２を主成分として８０ｗｔ％以上含み、残余ＳｉＯ２からなる発熱体は、発熱体の集積性が高く高温化及び温度制御が容易であり、また加熱時の変形（あばれ）やショート等の故障が少ないというＭｏＳｉ２を主成分とする発熱体の特徴を生かすと同時に、やや純度の低いＭｏＳｉ２粉末材料から半導体装置製造に影響を与える不純物を低コストで減少させ、汚染物質（不純物）の少ない、特に半導体製造装置用熱処理炉（酸化・拡散炉を含む）に有用である発熱材料を提供できるという優れた効果を有する。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention has a high heat-generating property, is easy to raise the temperature and control the temperature, and has few failures such as deformation during heating (shortening) and short-circuiting, and further has little contaminants (impurities). The present invention relates to a heating element composed of a base material containing MoSi 2 as a main component and containing 80 wt% or more, which is useful for a heat treatment furnace (including an oxidation / diffusion furnace), and a method for manufacturing the heating element, which can reduce costs.
Incidentally, 80 wt% or more comprises a base material MoSi 2 to be used herein as the main component is composed mainly of a MoSi 2 substrate contain a SiO 2 which is an insulating oxide MoSi 2 having an increased electrical resistance Heating element.
A heating element containing MoSi 2 as a main component is referred to as a plague (pulverization phenomenon), in which simultaneous oxidation of Mo and Si occurs in the range of 673 ° K to 873 ° K, and the evaporation of Mo oxide is accompanied by a decrease. Oxidation at a low temperature occurs at 1500 ° K or higher to prevent low-temperature oxidation, thereby forming a dense silica protective coating. The present invention includes a heating element having such a dense silica protective film formed thereon, and the addition of a vitreous component which is silica (SiO 2 ) is effective for forming such a dense silica protective film.
[0002]
[Prior art]
Conventionally, in a heat treatment furnace used for a semiconductor manufacturing apparatus, a metal heating element (heating element) is often used.
However, when a metal heating element is used in a heat treatment furnace or the like of a semiconductor manufacturing apparatus, the heat generated by the heating element increases the vapor pressure of low-melting impurities and metal oxides contained in the heating element. The amount of the metal compound scattered in the atmosphere increases.
Metals in these metal compounds are becoming more highly integrated in devices and, even in very small amounts, adversely affect the devices, so metal contamination of wafers mixed during heat treatment has become a problem.
The metal scattered from the heating element diffuses inside the heating element and the wafer even if a quartz tube or a SiC tube exists between the heating element and the wafer, and finally reaches the wafer. In particular, attention must be paid to impurity elements such as Cu, Fe, Mn, Mg, Na, and K having a large diffusion coefficient in the silicon crystal.
[0003]
In recent years, metal heating elements have the above-described metal contamination problem, and in order to miniaturize semiconductor devices, shorten device manufacturing time, and save energy, a conventional metal heating element is replaced with a CVD device or the like. 2. Description of the Related Art A high-performance heating element mainly composed of MoSi 2 has been used in a semiconductor manufacturing apparatus such as a diffusion furnace.
Generally, heat treatment furnaces used in semiconductor manufacturing equipment require extremely high-precision temperature characteristics, such as strict control of the temperature distribution in the furnace. However, heating elements mainly composed of MoSi 2 have excellent heat resistance. It is a suitable material because it has characteristics such as a surface load of about 10 times that of a metal heating element and a rapid heating and temperature rise.
[0004]
However, in the heat treatment furnaces used in semiconductor manufacturing equipment, MoSi 2 has been mainly used to control the temperature distribution in the furnace and to rapidly raise the temperature to shorten the manufacturing time. The heating element is oxidized at 1500 ° K or more to prevent material strength (heat resistance) and material embrittlement, or to prevent low-temperature oxidation called pest (powdering). The main purpose was to develop a material for the heating element itself, for example, to form a dense silica protective film.
However, when a heating element mainly composed of MoSi 2 is used in a heat treatment furnace of a semiconductor manufacturing apparatus, the tendency is smaller than that of a metal heating element. A similar problem of scattering from the surface of the heating element into the furnace atmosphere occurred.
In particular, this is remarkable when rapid heating and heating are performed at a high temperature, and metal contamination of the wafer is a problem. Therefore, the conventional heating element mainly composed of MoSi 2 is not always good as a heating element of a heat treatment furnace or the like of a semiconductor manufacturing apparatus, and has a problem.
For this reason, the total amount of impurities such as Fe, Cu, Au, Ca, and Al contained in the heating element containing MoSi 2 as a main component is set to 0.1 mass% or less, and Fe, Cu, Au, Proposals have been made to regulate the impurities of Ca and Al to 0.05 mass% or less, respectively, and further to 0.03 mass% or less (for example, see Patent Document 1).
However, it has been found that such a specified amount of impurities is insufficient. On the other hand, among these impurities (including the above-mentioned impurity elements and their oxides), if the vapor pressure is 1 × 10 −3 Hg or less at 1600 ° C., even if the content is more than the above-mentioned amount, particularly It turned out that there was nothing wrong.
[0005]
[Patent Document 1]
JP-A-10-324571
[Problems to be solved by the invention]
INDUSTRIAL APPLICABILITY The present invention makes use of the characteristics of a heating element containing MoSi 2 as a main component, which has high integration of the heating element, facilitates high temperature and temperature control, and has few failures such as deformation (roughness) and short-circuit during heating. At the same time, the present invention provides a heating element containing less than 80 wt% of MoSi 2 as a main component, which is low in contaminants (impurities) and is particularly useful for a heat treatment furnace (including an oxidation / diffusion furnace) for a semiconductor manufacturing apparatus, and a method for manufacturing the same.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have reduced the amount of specific impurities so that MoSi 2 , which is particularly useful in a heat treatment furnace (including an oxidation / diffusion furnace) for a semiconductor manufacturing apparatus, has a main component of 80 wt%. % Of heat generating elements can be provided at low cost.
The present invention is based on this finding,
1. In a heating element containing 80 wt% or more of MoSi 2 as a main component and composed of residual SiO 2 and impurities, of the impurities contained in the heating element, when the vapor pressure at 1600 ° C. is 1.0 × 10 −3 mmHg or more. 1. A heating element containing MoSi 2 as a main component, wherein the total amount of certain impurities is 300 ppm or less. 2. The heating element containing MoSi 2 as a main component as described in 1 above, which is used in a heat treatment furnace for a semiconductor manufacturing apparatus. A heating element comprising MoSi 2 as a main component, comprising a step of washing and drying the MoSi 2 raw material powder with an acid, a step of mixing and crushing with SiO 2 , a step of mixing with a binder and degreasing, and a step of electrical sintering. Production method 4. 4. The method for producing a heating element containing MoSi 2 as a main component as described in 3 above, which comprises a step of primary sintering after degreasing. 5. The method for producing a heating element containing MoSi 2 as a main component as described in 3 or 4 above, wherein the heating element is washed with an acid other than sulfuric acid. Each of the above items 3 to 5, wherein the total amount of impurities having a vapor pressure at 1600 ° C. of 1.0 × 10 −3 mmHg or more contained in the MoSi 2 raw material powder after pickling is 300 ppm or less. The present invention provides a method for producing a heating element containing MoSi 2 as a main component.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The heating element of the present invention containing MoSi 2 as a main component at 80 wt% or more and comprising residual SiO 2 and unavoidable impurities (hereinafter referred to as “a heating element made of MoSi 2 ” unless otherwise specified) is included in the heating element. Is a heating element containing MoSi 2 as a main component, wherein the total amount of impurities having a vapor pressure at 1600 ° C. of 1.0 × 10 −3 mmHg or more is 300 ppm or less.
When the heating element made of MoSi 2 is heated, the main substance that scatters from the heating element made of MoSi 2 and contaminates the heat treatment furnace for semiconductor manufacturing equipment and the semiconductor wafer has a vapor pressure of 1.0 × at 1600 ° C. It is a substance such as iron, manganese, magnesium, sodium, potassium and the like having a hardness of 10 −3 mmHg or more.
[0009]
For example, when a MoSi 2 heating element containing a large amount of iron as an impurity is heated in a quartz tube, a phenomenon in which the inside of the quartz tube turns reddish brown is observed. This is thought to be due to the fact that the scattered iron was combined with oxygen that was simultaneously released and turned into iron oxide, which turned reddish brown. Therefore, substances (impurities) scattered from such a heating element made of MoSi 2 must be limited as much as possible, and the total amount must be 300 ppm or less.
[0010]
MoSi 2 as a main component is preferably at least 90 wt%. This is because a phase transition accompanied by a change in volume of SiO 2 is taken into consideration, and if the content of SiO 2 is too large, its influence becomes large, which may hinder the strength of the heating element.
Impurities such as oxides such as Ta, W, Mo, V, Nb and iron having a vapor pressure of less than 1.0 × 10 −3 mmHg at 1600 ° C. are scattered very little from the MoSi 2 heating element. Therefore, the amount contained in the heating element does not matter in particular, and may be contained in a total amount of 1 ppm or more, for example, on the order of 100 ppm or 1000 ppm (acceptable).
As described above, a remarkable effect of being able to prevent a main substance that scatters from the MoSi 2 heating element and contaminates the inside of the heat treatment furnace for a semiconductor manufacturing apparatus and the semiconductor wafer is obtained.
[0011]
The above-mentioned impurities include impurities mixed into MoSi 2 and impurities mixed into silica (SiO 2 ) to be added, and a high-purity material is used, and the amount of the impurities is limited to the above.
Usually, high-purity silica is contained in an amount of 20 wt% or less, preferably 10 wt% or less as a vitreous forming material. This is because a phase transition accompanied by a change in volume of SiO 2 is taken into consideration, and if the content of SiO 2 is too large, its influence becomes large, which may hinder the strength of the heating element.
The MoSi 2 heating element described above is suitable for a heat treatment furnace for a semiconductor manufacturing apparatus, and has a remarkable effect of preventing contamination of the semiconductor device.
[0012]
The heating element made of MoSi 2 is obtained by washing the MoSi 2 raw material powder with an acid, drying it, mixing and pulverizing it with SiO 2 , mixing it with a binder, and further extruding it into a rod or a flat plate, for example.
The formed body thus obtained is degreased, subjected to primary sintering and electrically heated and sintered to produce a high-density MoSi 2 heating element.
Further, the rod-shaped or flat-shaped heating element thus manufactured is joined to produce, for example, an arc shape or a U-shaped shape. As described above, after the MoSi 2 heating element is formed into various shapes, it is set in a heat treatment furnace for a semiconductor manufacturing apparatus.
[0013]
The acid cleaning uses an acid other than sulfuric acid. For example, cleaning is performed using a mixed acid of dilute hydrochloric acid and nitric acid. This acid cleaning is extremely important, and can significantly reduce impurities such as chromium, nickel, iron, manganese, magnesium, sodium, and potassium.
Cleaning the MoSi 2 raw material powder with acid does not require much labor and cost. Nevertheless, there is a significant impurity removal effect.
For example, an impurity vapor pressure at 1600 ° C contained in the MoSi 2 raw material powder is 1.0 × 10 -3 mmHg or more, be contained in a total amount 1000ppm or more, contained in the MoSi 2 raw powder after pickling This has the effect of reducing the total amount of the same impurity to 300 ppm or less.
[0014]
[Examples and Comparative Examples]
EXAMPLES Hereinafter, Examples and Comparative Examples will be described. However, the present Examples are intended to facilitate understanding, and do not limit the present invention. That is, other modifications or other embodiments within the technical idea of the present invention are naturally included in the present invention.
[0015]
(Example 1)
As the MoSi 2 powder used as a heating element material, a powder having a purity level of 2N to 3N can be used. Table 1 shows the main impurity contents of the MoSi 2 powder.
As is clear from Table 1, impurities such as iron (Fe), chromium (Cr), nickel (Ni), iron (Fe), manganese (Mn), magnesium (Mg), sodium (Na), and potassium (K). Is contained in a considerable amount. This was washed with a mixed acid of dilute hydrochloric acid and nitric acid.
Table 1 also shows the impurity contents after washing with an acid. After washing with acid, impurities were significantly removed, as shown in Table 1. Further, the specific surface area of the MoSi 2 powder increased by 30%.
On the other hand, as the SiO 2 powder, a commercially available product is used, but a material purified by evaporating a contained metal component by performing a heat treatment at a high temperature of 1650 ° C. or more for a long time after selectively removing impurities is used.
Incidentally, the high-temperature heat treatment of SiO 2 is required to phase transition crystal structure of SiO 2 of silica in a stable cristobalite at high temperatures.
[0016]
95% by weight of the MoSi 2 powder and 5% by weight of the SiO 2 powder are mixed with a binder (the binder is not calculated in a mixing ratio; the same applies hereinafter), and the mixture is extruded from a mold to form a rod-shaped molded body. did.
The rod-shaped molded body (green) was degreased, primary sintered, and electrically heated and sintered to obtain a MoSi 2 rod-shaped heating element.
The MoSi 2 powder used in this MoSi 2 made rod-shaped heating element, as shown in Table 1, Fe: 110wtppm, W: 120wtppm, Nb: 40wtppm, Ta: 40wtppm was contained.
However, since these have a low vapor pressure, that is, the vapor pressure at 1600 ° C. is less than 1.0 × 10 −3 mmHg, they are scattered from the heating element made of MoSi 2 , and the inside of the heat treatment furnace for a semiconductor manufacturing apparatus and the semiconductor wafer are removed. Very little pollution. Here, Fe is 110 ppm, which is a compound of Fe having a low vapor pressure.
[0017]
On the other hand, impurities such as Fe, Mn, Mg, Na, and K having a high vapor pressure, that is, a vapor pressure at 1600 ° C. of 1.0 × 10 −3 mmHg or more are contained in a heat treatment furnace for a semiconductor manufacturing apparatus and a semiconductor wafer. Can be said to be highly contaminated.
However, as shown in Table 1, Cr was 30 wtppm, Ni was 10 wtppm, Mn was 4 wtppm, Mg was 1 wtppm, Na was 3 wtppm, and K was 2 wtppm, and the amount itself as a pollutant was significantly reduced. It can be seen that the level is not particularly problematic in the embodiment. The content of Fe is 110 wtppm, which is an Fe compound having a low vapor pressure.
Note that the impurities in the heating element are slightly contaminated from the starting materials in Table 1 due to contamination from containers, tools, and the like in the manufacturing process of the heating element. It is important to reduce the metal contamination from the manufacturing process as much as possible by lining the inner wall of the pulverizing container with Mo, or by using an air current pulverization method.
[0018]
[Table 1]
Next, in order to confirm the behavior of the contaminants (impurities), the high-purity MoSi 2 rod-shaped heating element thus obtained was placed immediately below a quartz plate (between 3 and 10 mm), and the surface of the heating element was exposed in air. Electric heating was performed so that the temperature became 1600 ° C.
In this test, the vaporized material from the heating element surface and the scattered components due to the high vapor pressure are reprecipitated on the quartz plate.By observing the quartz plate, the amount of metal contamination from the heating element can be simulated. Can be evaluated.
After heating and holding the heating element for 10 minutes, the amount of impurities attached to the lower surface of the quartz plate was observed (visual and SEM observation). No discoloration of the quartz plate was visually observed, and nothing was observed even by SEM observation.
From the above, when the heating element material shown in Example 1 is used with a heat treatment furnace for a semiconductor manufacturing apparatus, there is a low possibility that impurities radiated from the heating element material at the time of heat generation contaminate the heat treatment target. Is a very preferable material.
In addition, in the heat cycle characteristics test in which the heating element material was kept at room temperature and 500 ° C. for 30 hours, it did not become powdered even after 50 cycles, and in the bending test after treatment at 1600 ° C. for 300 hours, it did not exceed 300 MPa. there were.
[0020]
(Example 2)
Using a raw material shown in Table 2, particularly a raw material containing a large amount of impurities with low vapor pressures of W, Nb and Ta, pickling was similarly performed to produce a MoSi 2 rod-shaped heating element.
The purity is shown in Table 2. As shown in Table 2, the heating element contains a large amount of W, Nb, and Ta. In the same manner as in Example 1, this MoSi 2 rod-shaped heating element was placed immediately below a quartz plate (between 3 and 10 mm), and was heated by heating so that the surface temperature of the heating element was 1600 ° C. in the atmosphere. Then, the amount of impurities attached to the lower surface of the quartz plate was observed (visual and SEM observation).
However, no deposit on the quartz plate was observed from this heating element. From these facts, even if impurities such as W, Nb, Ta and the like whose vapor pressure at 1600 ° C. is less than 1.0 × 10 −3 mmHg are contained in the heating element in a large amount, these impurities may be generated during heating. It was found that it did not scatter and had no adverse effects as impurities.
[0021]
[Table 2]
(Comparative Example 1)
A commercially available MoSi 2 powder 95 wt% (Fe 600 wt ppm), which is generally called high purity, and similarly a commercially available SiO 2 powder 5 wt% are finely pulverized, mixed with a binder, and extruded from a mold. A rod-shaped molded body was obtained.
The rod-shaped formed body (green) was degreased, primary-sintered, and electrically heated and sintered to obtain a MoSi 2 rod-shaped heating element.
Similarly, Table 1 shows the analysis values of impurities. As shown in Table 1, the MoSi 2 rod-shaped heating element includes Fe: 600 wtppm, W: 20 wtppm, Cr: 30 wtppm, Ni: 10 wtppm, Nb: 10 wtppm, Ta: 3 wtppm, Mn: 10 wtppm, Mg: 6 wtppm, Na: 1 wtppm, K: 1 wtppm. These include oxides.
[0023]
Next, the MoSi 2 rod-shaped heating element thus obtained was placed immediately below the quartz plate, and was heated by heating so that the surface temperature of the heating element was 1600 ° C. in the atmosphere. In the same manner as in the above example, the heating element was heated and maintained for 10 minutes, and then the amount of impurities attached to the quartz plate was observed (visual and SEM observations).
The quartz plate had visually turned brown, and a large amount of impurities had adhered to the entire surface of the portion located directly above the heating element. Analysis of these deposits revealed that it was mainly Fe here.
From the above, when used with a heat treatment furnace for a semiconductor manufacturing apparatus, there is a high possibility that impurities released from the heating element material at the time of heat generation contaminate the object to be heat treated, and an undesirable result as a heating element material was obtained.
[0024]
As described above, by heating the MoSi 2 rod-shaped heating element, the heating element having a large amount of impurities, in particular, having a large vapor content at 1600 ° C. of 1.0 × 10 −3 mmHg or more has a large content of impurities. With regard to (2), the more the quartz plate disposed in the vicinity is discolored, the more the impurities are scattered from the heating element, and it is essential that these impurities are mixed into the semiconductor wafer or the like and have an adverse effect.
The present invention reduces the impurities affecting the semiconductor device production from MoSi 2 powder material containing MoSi 2 as a main component at 80% by weight or more, preferably 90% by weight or less at a low cost, and integrates heating elements. It has excellent characteristics that it can easily take advantage of the characteristics of the heating element mainly composed of MoSi 2, which has high heat resistance, is easy to raise the temperature and control the temperature, and has few failures such as deformation (roughness) and short-circuit during heating. Have.
[0025]
【The invention's effect】
A heating element containing 80 wt% or more of MoSi 2 as a main component of the present invention and made of residual SiO 2 has high integration of the heating element, is easy to raise the temperature and control the temperature, and has a deformation (roughness) and a short circuit during heating. In addition to taking advantage of the characteristics of the heating element containing MoSi 2 as a main component, which has few failures, such as MoSi 2 as a main component, impurities that affect semiconductor device production can be reduced at a low cost from a somewhat low-purity MoSi 2 powder material, and contaminants (impurities) can be reduced. ), Which is an excellent effect of being able to provide a heat generating material which is particularly useful for a heat treatment furnace for semiconductor manufacturing equipment (including an oxidation / diffusion furnace).
Claims (6)
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| JPH10324571A (en) * | 1997-05-23 | 1998-12-08 | Riken Corp | Molybdenum disilicide ceramic heat generating body and its production |
| JPH11317282A (en) * | 1998-02-20 | 1999-11-16 | Riken Corp | Molybdenum disilicide composite ceramic heating element and its manufacture |
| JPH11322431A (en) * | 1998-05-21 | 1999-11-24 | Japan Energy Corp | Pyrogenous material composed of molybdenum disilicide as major part having low oxygen diffusible vitreous coating layer |
| JP2000243538A (en) * | 1999-02-22 | 2000-09-08 | Japan Energy Corp | HEATER CONTAINING MoSi2 AS MAIN COMPONENT AND MANUFACTURE THEREOF |
-
2003
- 2003-01-07 JP JP2003000935A patent/JP2004214075A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0136981B2 (en) * | 1983-12-26 | 1989-08-03 | Toshiba Ceramics Co | |
| JPH03174364A (en) * | 1989-11-30 | 1991-07-29 | Kyocera Corp | Silicon nitride-based sintered body |
| JPH10324571A (en) * | 1997-05-23 | 1998-12-08 | Riken Corp | Molybdenum disilicide ceramic heat generating body and its production |
| JPH11317282A (en) * | 1998-02-20 | 1999-11-16 | Riken Corp | Molybdenum disilicide composite ceramic heating element and its manufacture |
| JPH11322431A (en) * | 1998-05-21 | 1999-11-24 | Japan Energy Corp | Pyrogenous material composed of molybdenum disilicide as major part having low oxygen diffusible vitreous coating layer |
| JP2000243538A (en) * | 1999-02-22 | 2000-09-08 | Japan Energy Corp | HEATER CONTAINING MoSi2 AS MAIN COMPONENT AND MANUFACTURE THEREOF |
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