JP2004218003A - Electroless plating bath, and method of forming metal protective film using the electroless plating bath - Google Patents
Electroless plating bath, and method of forming metal protective film using the electroless plating bath Download PDFInfo
- Publication number
- JP2004218003A JP2004218003A JP2003006703A JP2003006703A JP2004218003A JP 2004218003 A JP2004218003 A JP 2004218003A JP 2003006703 A JP2003006703 A JP 2003006703A JP 2003006703 A JP2003006703 A JP 2003006703A JP 2004218003 A JP2004218003 A JP 2004218003A
- Authority
- JP
- Japan
- Prior art keywords
- plating bath
- electroless plating
- cobalt
- phosphinate
- ions
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 238000007772 electroless plating Methods 0.000 title claims abstract description 51
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 35
- 239000002184 metal Substances 0.000 title claims abstract description 35
- 230000001681 protective effect Effects 0.000 title claims description 15
- 238000000034 method Methods 0.000 title claims description 14
- 238000007747 plating Methods 0.000 claims abstract description 37
- 239000000758 substrate Substances 0.000 claims abstract description 27
- IPRHNRJRYOAPLY-UHFFFAOYSA-L [Co++].[O-][PH2]=O.[O-][PH2]=O Chemical compound [Co++].[O-][PH2]=O.[O-][PH2]=O IPRHNRJRYOAPLY-UHFFFAOYSA-L 0.000 claims abstract description 16
- -1 phosphinate ions Chemical class 0.000 claims abstract description 15
- 229910001429 cobalt ion Inorganic materials 0.000 claims abstract description 13
- XLJKHNWPARRRJB-UHFFFAOYSA-N cobalt(2+) Chemical compound [Co+2] XLJKHNWPARRRJB-UHFFFAOYSA-N 0.000 claims abstract description 13
- 239000008139 complexing agent Substances 0.000 claims abstract description 7
- 229910001413 alkali metal ion Inorganic materials 0.000 claims abstract description 6
- 238000002844 melting Methods 0.000 claims description 10
- 230000008018 melting Effects 0.000 claims description 10
- 150000002736 metal compounds Chemical class 0.000 claims description 6
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 4
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 239000011733 molybdenum Substances 0.000 claims description 3
- 229910052721 tungsten Inorganic materials 0.000 claims description 3
- 239000010937 tungsten Substances 0.000 claims description 3
- 229910001415 sodium ion Inorganic materials 0.000 claims description 2
- 239000003870 refractory metal Substances 0.000 claims 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 abstract description 31
- 229910052802 copper Inorganic materials 0.000 abstract description 31
- 239000010949 copper Substances 0.000 abstract description 31
- 229910052783 alkali metal Inorganic materials 0.000 abstract description 9
- 150000001340 alkali metals Chemical class 0.000 abstract description 8
- 238000011109 contamination Methods 0.000 abstract description 5
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- 239000010410 layer Substances 0.000 description 12
- ACVYVLVWPXVTIT-UHFFFAOYSA-N phosphinic acid Chemical compound O[PH2]=O ACVYVLVWPXVTIT-UHFFFAOYSA-N 0.000 description 9
- 229910017052 cobalt Inorganic materials 0.000 description 7
- 239000010941 cobalt Substances 0.000 description 7
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 7
- 239000000203 mixture Substances 0.000 description 6
- 150000003839 salts Chemical class 0.000 description 5
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 4
- 229910000531 Co alloy Inorganic materials 0.000 description 4
- 229910021503 Cobalt(II) hydroxide Inorganic materials 0.000 description 4
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- ASKVAEGIVYSGNY-UHFFFAOYSA-L cobalt(ii) hydroxide Chemical compound [OH-].[OH-].[Co+2] ASKVAEGIVYSGNY-UHFFFAOYSA-L 0.000 description 4
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- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 3
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 235000011114 ammonium hydroxide Nutrition 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 3
- XAYGUHUYDMLJJV-UHFFFAOYSA-Z decaazanium;dioxido(dioxo)tungsten;hydron;trioxotungsten Chemical compound [H+].[H+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O XAYGUHUYDMLJJV-UHFFFAOYSA-Z 0.000 description 3
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- 229940044175 cobalt sulfate Drugs 0.000 description 2
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- KTVIXTQDYHMGHF-UHFFFAOYSA-L cobalt(2+) sulfate Chemical compound [Co+2].[O-]S([O-])(=O)=O KTVIXTQDYHMGHF-UHFFFAOYSA-L 0.000 description 2
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 2
- 238000002354 inductively-coupled plasma atomic emission spectroscopy Methods 0.000 description 2
- JKQOBWVOAYFWKG-UHFFFAOYSA-N molybdenum trioxide Chemical compound O=[Mo](=O)=O JKQOBWVOAYFWKG-UHFFFAOYSA-N 0.000 description 2
- 239000003002 pH adjusting agent Substances 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 229910001379 sodium hypophosphite Inorganic materials 0.000 description 2
- 238000004544 sputter deposition Methods 0.000 description 2
- 239000003381 stabilizer Substances 0.000 description 2
- WGTYBPLFGIVFAS-UHFFFAOYSA-M tetramethylammonium hydroxide Chemical compound [OH-].C[N+](C)(C)C WGTYBPLFGIVFAS-UHFFFAOYSA-M 0.000 description 2
- ZNOKGRXACCSDPY-UHFFFAOYSA-N tungsten trioxide Chemical compound O=[W](=O)=O ZNOKGRXACCSDPY-UHFFFAOYSA-N 0.000 description 2
- 239000000080 wetting agent Substances 0.000 description 2
- BJEPYKJPYRNKOW-REOHCLBHSA-N (S)-malic acid Chemical compound OC(=O)[C@@H](O)CC(O)=O BJEPYKJPYRNKOW-REOHCLBHSA-N 0.000 description 1
- KWSLGOVYXMQPPX-UHFFFAOYSA-N 5-[3-(trifluoromethyl)phenyl]-2h-tetrazole Chemical compound FC(F)(F)C1=CC=CC(C2=NNN=N2)=C1 KWSLGOVYXMQPPX-UHFFFAOYSA-N 0.000 description 1
- KXDHJXZQYSOELW-UHFFFAOYSA-N Carbamic acid Chemical class NC(O)=O KXDHJXZQYSOELW-UHFFFAOYSA-N 0.000 description 1
- FEWJPZIEWOKRBE-JCYAYHJZSA-N Dextrotartaric acid Chemical compound OC(=O)[C@H](O)[C@@H](O)C(O)=O FEWJPZIEWOKRBE-JCYAYHJZSA-N 0.000 description 1
- PIICEJLVQHRZGT-UHFFFAOYSA-N Ethylenediamine Chemical compound NCCN PIICEJLVQHRZGT-UHFFFAOYSA-N 0.000 description 1
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- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 1
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- 229910008482 TiSiN Inorganic materials 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- KKYXVXDDVONUGW-UHFFFAOYSA-N [Co].[PH2](=O)O Chemical compound [Co].[PH2](=O)O KKYXVXDDVONUGW-UHFFFAOYSA-N 0.000 description 1
- AQQVTZBWWYVEGR-UHFFFAOYSA-N [NH4+].[O-][PH2]=O Chemical compound [NH4+].[O-][PH2]=O AQQVTZBWWYVEGR-UHFFFAOYSA-N 0.000 description 1
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- 150000001412 amines Chemical class 0.000 description 1
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- APUPEJJSWDHEBO-UHFFFAOYSA-P ammonium molybdate Chemical compound [NH4+].[NH4+].[O-][Mo]([O-])(=O)=O APUPEJJSWDHEBO-UHFFFAOYSA-P 0.000 description 1
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- YVBOZGOAVJZITM-UHFFFAOYSA-P ammonium phosphomolybdate Chemical compound [NH4+].[NH4+].[NH4+].[NH4+].[O-]P([O-])=O.[O-][Mo]([O-])(=O)=O YVBOZGOAVJZITM-UHFFFAOYSA-P 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- 239000003945 anionic surfactant Substances 0.000 description 1
- 229910001378 barium hypophosphite Inorganic materials 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
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- UFMZWBIQTDUYBN-UHFFFAOYSA-N cobalt dinitrate Chemical compound [Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O UFMZWBIQTDUYBN-UHFFFAOYSA-N 0.000 description 1
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- AUTNMGCKBXKHNV-UHFFFAOYSA-P diazanium;3,7-dioxido-2,4,6,8,9-pentaoxa-1,3,5,7-tetraborabicyclo[3.3.1]nonane Chemical compound [NH4+].[NH4+].O1B([O-])OB2OB([O-])OB1O2 AUTNMGCKBXKHNV-UHFFFAOYSA-P 0.000 description 1
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- 150000004687 hexahydrates Chemical class 0.000 description 1
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- QRXWMOHMRWLFEY-UHFFFAOYSA-N isoniazide Chemical compound NNC(=O)C1=CC=NC=C1 QRXWMOHMRWLFEY-UHFFFAOYSA-N 0.000 description 1
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- 239000005078 molybdenum compound Substances 0.000 description 1
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- 229910052763 palladium Inorganic materials 0.000 description 1
- ACVYVLVWPXVTIT-UHFFFAOYSA-M phosphinate Chemical compound [O-][PH2]=O ACVYVLVWPXVTIT-UHFFFAOYSA-M 0.000 description 1
- DHRLEVQXOMLTIM-UHFFFAOYSA-N phosphoric acid;trioxomolybdenum Chemical compound O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.O=[Mo](=O)=O.OP(O)(O)=O DHRLEVQXOMLTIM-UHFFFAOYSA-N 0.000 description 1
- IYDGMDWEHDFVQI-UHFFFAOYSA-N phosphoric acid;trioxotungsten Chemical compound O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.OP(O)(O)=O IYDGMDWEHDFVQI-UHFFFAOYSA-N 0.000 description 1
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Images
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は無電解めっき浴及び該無電解めっき浴を用いた金属保護膜の形成方法に関する。更に詳しくは、電子回路用基板に形成された銅等の金属配線の表面に選択的にめっきを施すことを可能とし、かつ、該配線や基板のアルカリ金属による汚染を防止することができる無電解めっき浴及び当該めっき浴を用いた金属保護膜の形成方法に関する。
【０００２】
【従来の技術】
従来より、半導体ウェハなどの微細な回路パターンを有する電子回路用基板上に銅等の金属配線を形成するための手段として、基板上にあらかじめ配線溝等を形成し、この部分にめっき等の手段を用いて金属銅や銅合金を埋め込んだ後、化学機械研磨（Ｃｈｅｍｉｃａｌ Ｍｅｃｈａｎｉｃａｌ Ｐｏｌｉｓｈｉｎｇ：ＣＭＰ）等により表面の余分な銅等を除去するという手段が用いられている。
【０００３】
このＣＭＰ等による基板表面の平坦化後には、銅等の配線の表面が外部に露出するが、この上に更に埋め込み配線を形成するにあたっては、一般には、既に配線が形成された配線形成部の保護や、エッチャント等による汚染の防止のためＳｉＮ等の配線保護膜を形成されていた。
【０００４】
一方、このＳｉＮ等の保護膜を電子回路板全面に形成させると、層間絶縁膜の誘電率が上昇して配線遅延を誘発するという問題があるため、銅等の配線材料との接合が強いコバルト等の金属、特に比抵抗が低いコバルト合金膜を無電解めっきによって形成せしめて、当該めっき皮膜で露出配線の表面を選択的に覆って配線を保護する手段が提案されていた。
【０００５】
しかしながら、選択的な配線保護のために用いられる無電解めっき浴には、一般には、還元剤としてホスフィン酸ナトリウム塩（次亜りん酸ナトリウム塩）等のアルカリ金属塩が使用されているため、無電解めっきを行った際に、このアルカリ金属イオンがめっき皮膜に取り込まれるという問題があった。そしてこのようなナトリウム等のアルカリ金属による金属配線の汚染は、電子回路用基板の電気特性に悪影響を及ぼしてしまうという問題を有していた。
【０００６】
【発明が解決しようとする課題】
従って、埋め込み配線構造を有する電子回路用基板に形成された銅等の金属配線に対して、当該配線の表面にめっき皮膜を選択的に形成するとともに、アルカリ金属による当該配線の汚染の問題が起こらない無電解めっき浴の開発が求められていた。
【０００７】
【課題を解決するための手段】
本発明者らは、上記の課題を解決すべく、無電解めっき浴の成分について鋭意検討した結果、コバルトイオン及びホスフィン酸イオンの主供給源としてホスフィン酸コバルトを利用しためっき浴で無電解めっきを行うことにより、上記の課題が解決できることを見出し、本発明を完成した。
【０００８】
すなわち本発明は、コバルトイオン、ホスフィン酸イオン及び錯化剤を含有する無電解めっき浴であって、コバルトイオン及びホスフィン酸イオンの主供給源としてホスフィン酸コバルトを用い、めっき浴中に実質的にアルカリ金属イオンを含有しないことを特徴とする無電解めっき浴を提供するものである。
【０００９】
また、本発明は、電子回路用基板に形成された金属配線の表面に選択的に金属保護膜を形成する方法であって、上記の無電解めっき浴を用いて無電解めっきを行うことを特徴とする金属保護膜の形成方法を提供するものである。
【００１０】
【発明の実施の形態】
本発明の無電解めっき浴は、コバルトイオン、ホスフィン酸イオン及び錯化剤を必須成分とするものであり、そのコバルトイオン及びホスフィン酸イオンの主供給源としてホスフィン酸コバルト（次亜リン酸コバルト）を用い、めっき浴中に実質的にアルカリ金属イオンを含有しないものである。
【００１１】
本発明の無電解めっき浴におけるコバルトイオン及びホスフィン酸イオンは、ホスフィン酸コバルト（Ｃｏ（Ｈ２ＰＯ２）２）を主供給源とするものであるが、かかるホスフィン酸コバルトは、例えば、次亜リン酸（ホスフィン酸）に水酸化コバルトを加えてホスフィン酸コバルトを得る手段や、次亜リン酸バリウムと硫酸コバルトの複分解反応等の手段を用いることにより調製することができる。
【００１２】
本発明の無電解めっき浴は、上記のコバルトイオン及びホスフィン酸イオンの主供給源としてホスフィン酸コバルトを用いるものであるが、これら成分の一方を増加させる場合には、コバルトやホスフィン酸を含む他の成分を、必要に応じて使用することができる。例えば、めっき浴中のコバルトイオンのみの濃度を増加させたい場合は、硫酸コバルト、硝酸コバルト、塩化コバルトなどのコバルト塩を使用すれば良く、また、ホスフィン酸イオンのみの濃度を増加させたい場合は、ホスフィン酸、ホスフィン酸アンモニウムなどを適宜添加すればよい。但し、これらの添加成分は、ナトリウム等のアルカリ金属を含有するものであってはならない。
【００１３】
また、本発明の無電解めっき浴に添加される錯化剤としては、例えば、酢酸、しゅう酸、マロン酸等のカルボン酸及びこれらの塩、酒石酸、くえん酸、リンゴ酸等のヒドロキシカルボン酸及びこれらの塩、グリシン、アラニン等のアミノカルボン酸及びこれらの塩、エチレンジアミン等のアミン及びこれらの塩、アンモニア等を挙げることができる。また、これらは一種を単独で使用してもよく、または二種類以上を組み合わせて使用してもよい。
【００１４】
本発明の無電解めっき浴における、ホスフィン酸およびコバルトの配合量は、０．００１〜１ｍｏｌ／Ｌ程度であり、特に０．０１〜０．３ｍｏｌ／Ｌであることが好ましい。また、錯化剤の配合量は、０．００１〜１．５ｍｏｌ／Ｌ程度であり、特に０．０１〜１ｍｏｌ／Ｌであることが好ましい。
【００１５】
本発明の無電解めっき浴には、以上の必須成分に加え、高融点金属化合物を含有させることができ、これにより、コバルトと高融点金属の合金からなるめっき皮膜を析出させることができる。
【００１６】
この高融点金属化合物に含まれる高融点金属としては、例えば、タングステンやモリブデンを挙げることができる。このうち、タングステンを含む化合物としては、例えば、三酸化タングステン、タングステン酸、タングステン酸アンモニウム、パラタングステン酸アンモニウム等を挙げることができる。
【００１７】
一方、モリブデンを含む化合物としては、例えば、三酸化モリブデン、モリブデン酸、モリブデン酸アンモニウム、パラモリブデン酸アンモニウム等のモリブデン化合物を挙げることができる。
【００１８】
更に、高融点金属化合物として、リンタングステン酸、リンタングステン酸アンモニウム、けいタングステン酸、けいタングステン酸アンモニウム、りんモリブデン酸、りんモリブデン酸アンモニウム等のヘテロポリ酸及びそれらの塩を用いることもできる。
【００１９】
これらの高融点金属化合物の濃度は、本発明の無電解めっき浴の組成において、浴中の高融点金属元素の濃度として０．０００１〜１ｍｏｌ／Ｌであることが好ましく、０．００１〜０．１ｍｏｌ／Ｌであることがより好ましい。
【００２０】
本発明の無電解めっき浴は、上記の基本構成成分のほかに、必要に応じて、ｐＨ調整剤やｐＨ緩衝剤を、本発明の効果を妨げない範囲で適宜添加することができる。
【００２１】
ｐＨ調整剤としては、例えば、アンモニア水や、水酸化テトラメチルアンモニウム、水酸化テトラエチルアンモニウム、コリンなどの有機アルカリを用いることができる。また、ｐＨ緩衝剤としては、例えば、ほう酸、硫酸アンモニウム、四ほう酸アンモニウム等を用いることができる。
【００２２】
また、本発明の無電解めっき浴には、上記成分に加えて、更に、浴安定化剤、湿潤剤等の公知の添加剤を、本発明の効果を妨げない範囲で適宜添加することができる。浴安定剤としては、例えば、鉛（Ｐｂ）またはビスマス（Ｂｉ）等の重金属を含む化合物や、チオジグリコール酸等の硫黄を含む化合物などが挙げられる。また、湿潤剤としては、例えば、非イオン性界面活性剤、アニオン界面活性剤、カチオン界面活性剤等の各種界面活性剤などが挙げられる。
【００２３】
しかしながら、上記のｐＨ調整剤等の各任意成分においても、ナトリウム等のアルカリ金属が含まれていないものを選択すべきであることはいうまでもない。
【００２４】
本発明の無電解めっき浴の調製方法や無電解めっきの実施方法は、特に制限はなく、通常の無電解コバルトめっきあるいは無電解コバルト合金めっきと同様でよい。例えば、めっき浴の調製は、上記した各成分を混合させるなど、通常用いられる方法で行えば良く、この無電解めっき浴のｐＨは、７〜１４程度、特に８〜１２とすることが好ましい。
【００２５】
また、無電解めっきの実施にあたっては、無電解めっき浴の浴温を２０〜１００℃程度、特に、５０〜９０℃とすることが好ましい。
【００２６】
本発明の無電解めっきの好ましい組成の例を挙げれば次の通りである。
（ 無電解めっき浴組成 ）
ホスフィン酸コバルト ０．０１〜０．３ｍｏｌ ／Ｌパラタングステン酸アンモニウム ０．００１〜０．０１ ｍｏｌ／Ｌ
（（ＮＨ４）Ｗ１２Ｏ４１）
クエン酸（錯化剤） ０．０１〜１ｍｏｌ／Ｌホスフィン酸 ０〜０．０５ｍｏｌ／Ｌ
【００２７】
以上説明した本発明の無電解めっき浴を用いて、電子回路用基板に形成された金属配線の表面に選択的に金属保護膜を形成する方法を実施するための好ましい手段について説明する。
【００２８】
本発明の金属保護膜の形成方法の対象となる電子回路用基板は、その表面に、微細な溝（以下「配線溝」ということもある）等の埋め込み配線構造が設けられ、かかる配線溝内に金属銅や銅合金が埋められることにより回路配線が形成されるシリコンウェハ等の半導体基板等である。
【００２９】
この電子回路用基板としては、例えば、幅が０．１〜０．５μｍ程度、深さが０．５〜２μｍ程度（アスペクト比として１〜５程度）の配線溝を有しているものが挙げられる。
【００３０】
上記電子回路基板に銅配線を形成するにあたっては、まず、上記のような仕様の電子回路用基板の配線溝に、Ｔｉ、ＴｉＮ、Ｔａ、ＴａＮ、ＷＮ、ＴｉＳｉＮ等から選ばれたバリア層、次いで電解めっきの給電層としての銅シード層を、スパッタリング、化学気相蒸着法（Ｃｈｅｍｉｃａｌ Ｖａｐｏｒ Ｄｅｐｏｓｉｔｉｏｎ：ＣＶＤ）等の手段により形成する。
【００３１】
次に、当該基板に、銅等の金属めっきを施すことにより、電子回路用基板の配線溝内に金属を充填させる。その後、ＣＭＰ等により、絶縁膜上に析出した金属を除去するとともに、配線溝に充填させた金属層の表面と絶縁膜の表面とをほぼ同一平面にする。これにより、電子回路基板上に銅シード層と、銅等の金属層からなる配線が形成されることになる。
【００３２】
そして、以上の手段により銅シード層と銅等の金属層からなる銅配線が形成された電子回路基板を、上記した本発明の無電解めっき浴に浸漬させて無電解めっきを行うことにより、銅配線の表面に対して選択的に金属めっき皮膜を形成させることができる。
【００３３】
【実施例】
次に実施例及び参考例を挙げて本発明を更に詳しく説明するが、本発明はこれら実施例等に何ら制約されるものではない
【００３４】
参 考 例 １
ホスフィン酸コバルト（Ｃｏ（Ｈ２ＰＯ２）２）の調製：
ホスフィン酸（Ｈ３ＰＯ２）水溶液に水酸化コバルト（Ｃｏ（ＯＨ）２）を、ホスフィン酸と水酸化コバルトのモル比が２：１となるように添加、混合した。水酸化コバルトをホスフィン酸水溶液に溶解させた後、この溶液を、６０℃に加熱して水分を除去して乾固させ、粉末状のホスフィン酸コバルト（Ｃｏ（Ｈ２ＰＯ２）２）を調製した。
【００３５】
得られたホスフィン酸コバルトについてのＸ線回析の結果を図１に示すが、大部分はＣｏ（Ｈ２ＰＯ２）２であり、一部がその６水塩であった。
【００３６】
実 施 例 １
（ａ）微細回路基板サンプルの調製：
微細回路基板サンプルとして、幅０．５μｍ、深さ１μｍの配線溝を設けたシリコンウェハを用意した。この基板サンプルに対し、常法に従って銅シード層を形成した後、銅めっきを施し、配線溝を銅で埋め込んで回路配線を形成した。これを、ＣＭＰにより基板表面を研磨して、配線溝部分のみ銅が埋め込まれた微細回路基板サンプルを得た。
【００３７】
（ｂ）金属保護膜の形成：
上記（ａ）で得た基板サンプルに対し、参考例１で得られたホスフィン酸コバルトを含有する下記組成の２種類のめっき浴（本発明品１及び２）を用い、下記のめっき条件により無電解めっきを施した。なお、無電解めっきに先立ち、常法に従ったパラジウム処理を行った。
【００３８】
めっき後、その表面形態の観察と、エネルギー分散Ｘ線分光法（ＥＤＳ）による元素分析を行ったこの結果を図２に示す。
【００３９】
（ 本発明品１の無電解めっき浴の組成 ）
成 分 濃 度
参考例１で調製したホスフィン酸コバルト ０．１ｍｏｌ／Ｌ
クエン酸 ０．２ｍｏｌ／Ｌ
ｐＨ ８（注）
（注）アンモニア水で調整
【００４０】
（ めっき条件 ）
温度 ： ９０℃
めっき時間 ： ６０秒間
【００４１】
（ 本発明品２の無電解めっき浴の組成 ）
成 分 濃 度
参考例１で調製したホスフィン酸コバルト ０．１ｍｏｌ／Ｌ
クエン酸 ０．２ｍｏｌ／Ｌ
パラタングステン酸アンモニウム ０．００５ｍｏｌ／Ｌ
（（ＮＨ４）１０Ｗ１２Ｏ４１）
ホスフィン酸 ０．４ｍｏｌ／Ｌ
ｐＨ １０（注）
（注）アンモニア水で調整
【００４２】
（ めっき条件 ）
温度 ： ９０℃
めっき時間 ： ６０秒間
【００４３】
図２の結果から明らかなように、銅部分にのみコバルトを含むめっき皮膜が析出しており、選択的にめっきされていることが示された。
【００４４】
実 施 例 ２
（ａ）微細回路基板サンプルの調製：
微細回路基板サンプルとして、幅０．５μｍ、深さ１μｍの配線溝が存在する直径２００ｍｍのシリコンウェハを用意した。この基板サンプルに、まず、ＴａＮのバリア層を２０ｎｍの厚さで形成し、さらに、スパッリタングで、銅シード層を５０ｎｍの厚さで形成した。
【００４５】
銅シード層を形成した上記サンプルに対し、常法を用いて銅めっきを施し、配線溝に対して銅を埋め込んで回路配線を形成した後、ＣＭＰにより基板表面を研磨して、微細回路基板サンプルを得た。
【００４６】
（ｂ）金属保護皮膜の形成：
上記（ａ）で得た基板サンプルに対して、前記本発明品２を用い、無電解めっきを行った。無電解めっきは、基板サンプルを５０％メタノール水溶液で５分間超音波洗浄し、次いで室温で１０％硫酸に１分間浸漬した後、Ｐｄ触媒液に攪拌しながら１０秒間浸漬し、再び室温で１０％硫酸に１分間浸漬した後行った。
【００４７】
無電解めっき浴を用いてめっきした基板サンプルの銅配線部を、走査型電子顕微鏡（ＳＥＭ）を用いて観察した結果を図３に示す。この結果より、銅配線の表面にのみ選択的に金属保護膜が形成されていることが確認できた。
【００４８】
また、形成された金属保護膜を硝酸／クエン酸の混酸に溶解させ、ＩＣＰ−ＡＥＳ（誘導結合プラズマ原子発光分析）法を用いてナトリウム等のアルカリ金属の存在の有無を確認したところ、アルカリ金属の検出量は検出限界以下であった。
【００４９】
【発明の効果】
本発明の無電解めっき浴は、銅等の金属配線の表面のみに選択的にめっきを施すことを可能とするものであるが、めっき浴のコバルトイオンおよびホスフィン酸イオンの主供給源としてホスフィン酸コバルトを用いているので、めっき浴中にナトリウムイオン等のアルカリ金属イオンが存在することなく、金属配線のアルカリ金属による汚染を防止することができるものである。また、めっき浴の連続使用においてめっき浴成分を補給した場合であっても、硫酸ナトリウム等の副生成物の生成が起こらないため、長期間にわたってめっき浴を使用することが可能となる。
【００５０】
更に、高融点金属化合物を含む本発明の無電解めっき浴を使用した場合は、高融点金属がめっき皮膜中に共析し、合金化することで、めっき皮膜の熱安定性が向上するという利点がある。
【００５１】
従って、本発明の無電解めっき浴は、電子回路用基板上の銅配線等の保護用皮膜形成のために有利に使用することができるものである。
【図面の簡単な説明】
【図１】ホスフィン酸コバルトのＸ線回析結果を示す図面。
【図２】実施例１により、銅表面にのみコバルトまたはコバルト合金が析出した状態を示す図面（写真）。
【図３】実施例２で無電解めっきを行った後のサンプル基板の銅配線部の断面写真。
以 上[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electroless plating bath and a method for forming a metal protective film using the electroless plating bath. More specifically, it is possible to selectively plate the surface of a metal wiring such as copper formed on a substrate for an electronic circuit and to prevent the wiring and the substrate from being contaminated by an alkali metal. The present invention relates to a plating bath and a method for forming a metal protective film using the plating bath.
[0002]
[Prior art]
Conventionally, as a means for forming metal wiring such as copper on an electronic circuit substrate having a fine circuit pattern such as a semiconductor wafer, a wiring groove or the like is previously formed on the substrate, and a means such as plating is formed on this portion. After embedding metallic copper or a copper alloy using a method, a method of removing excess copper or the like on the surface by chemical mechanical polishing (CMP) or the like is used.
[0003]
After the surface of the substrate is flattened by the CMP or the like, the surface of the wiring such as copper is exposed to the outside. However, when forming a further buried wiring thereon, generally, the wiring forming portion where the wiring is already formed is formed. A wiring protection film such as SiN is formed for protection and prevention of contamination by an etchant or the like.
[0004]
On the other hand, if this protective film such as SiN is formed on the entire surface of the electronic circuit board, there is a problem that the dielectric constant of the interlayer insulating film is increased and a wiring delay is induced. For example, there has been proposed means for forming a metal, such as a cobalt alloy film having a low specific resistance, by electroless plating, and selectively covering the surface of the exposed wiring with the plating film to protect the wiring.
[0005]
However, in an electroless plating bath used for selective wiring protection, an alkali metal salt such as sodium phosphinate (sodium hypophosphite) is generally used as a reducing agent. There has been a problem that the alkali metal ions are taken into the plating film when performing the electrolytic plating. The contamination of the metal wiring by the alkali metal such as sodium has a problem that the electrical characteristics of the electronic circuit board are adversely affected.
[0006]
[Problems to be solved by the invention]
Therefore, for a metal wiring such as copper formed on an electronic circuit substrate having an embedded wiring structure, a plating film is selectively formed on the surface of the wiring, and the problem of contamination of the wiring by an alkali metal occurs. The development of an electroless plating bath was not required.
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on the components of the electroless plating bath in order to solve the above-mentioned problems, and as a result, have conducted electroless plating in a plating bath using cobalt phosphinate as a main source of cobalt ions and phosphinate ions. The inventors have found that the above-mentioned problems can be solved by performing the present invention, and completed the present invention.
[0008]
That is, the present invention relates to an electroless plating bath containing a cobalt ion, a phosphinate ion and a complexing agent, wherein cobalt phosphinate is used as a main source of the cobalt ion and the phosphinate ion, and the plating bath substantially contains the same. An electroless plating bath characterized by not containing an alkali metal ion is provided.
[0009]
Further, the present invention is a method for selectively forming a metal protective film on a surface of a metal wiring formed on an electronic circuit substrate, wherein the electroless plating is performed using the above electroless plating bath. And a method of forming a metal protective film.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The electroless plating bath of the present invention contains cobalt ion, phosphinate ion and complexing agent as essential components, and uses cobalt phosphinate (cobalt hypophosphite) as a main source of the cobalt ion and phosphinate ion. And a plating bath containing substantially no alkali metal ion.
[0011]
The cobalt ion and the phosphinate ion in the electroless plating bath of the present invention are mainly composed of cobalt phosphinate (Co (H 2 PO 2 ) 2 ). It can be prepared by using a means such as adding cobalt hydroxide to phosphoric acid (phosphinic acid) to obtain cobalt phosphinate or a means such as a metathesis reaction between barium hypophosphite and cobalt sulfate.
[0012]
The electroless plating bath of the present invention uses cobalt phosphinate as a main supply source of the above-mentioned cobalt ions and phosphinate ions, but when one of these components is increased, other components containing cobalt or phosphinic acid are used. Can be used as needed. For example, when it is desired to increase the concentration of only cobalt ions in the plating bath, a cobalt salt such as cobalt sulfate, cobalt nitrate, or cobalt chloride may be used, or when it is desired to increase the concentration of only phosphinate ions. , Phosphinic acid, ammonium phosphinate and the like may be appropriately added. However, these additional components must not contain an alkali metal such as sodium.
[0013]
Further, as the complexing agent added to the electroless plating bath of the present invention, for example, carboxylic acids such as acetic acid, oxalic acid, malonic acid and salts thereof, tartaric acid, citric acid, hydroxycarboxylic acid such as malic acid and These salts include aminocarboxylic acids such as glycine and alanine and salts thereof, amines such as ethylenediamine and salts thereof, and ammonia. These may be used alone or in a combination of two or more.
[0014]
The amount of phosphinic acid and cobalt in the electroless plating bath of the present invention is about 0.001 to 1 mol / L, and particularly preferably 0.01 to 0.3 mol / L. The compounding amount of the complexing agent is about 0.001 to 1.5 mol / L, and particularly preferably 0.01 to 1 mol / L.
[0015]
The electroless plating bath of the present invention can contain a high melting point metal compound in addition to the above essential components, whereby a plating film composed of an alloy of cobalt and a high melting point metal can be deposited.
[0016]
Examples of the high melting point metal contained in the high melting point metal compound include tungsten and molybdenum. Among these, examples of the compound containing tungsten include tungsten trioxide, tungstic acid, ammonium tungstate, and ammonium paratungstate.
[0017]
On the other hand, examples of the compound containing molybdenum include molybdenum compounds such as molybdenum trioxide, molybdic acid, ammonium molybdate, and ammonium paramolybdate.
[0018]
Further, heteropolyacids such as phosphotungstic acid, ammonium phosphotungstate, silicotungstic acid, ammonium silicotungstate, phosphomolybdic acid, ammonium phosphomolybdate, and salts thereof can be used as the high melting point metal compound.
[0019]
In the composition of the electroless plating bath of the present invention, the concentration of these high melting point metal compounds is preferably 0.0001 to 1 mol / L, more preferably 0.001 to 0.1 mol / L, as the concentration of the high melting point metal element in the bath. More preferably, it is 1 mol / L.
[0020]
In the electroless plating bath of the present invention, in addition to the above basic components, a pH adjuster or a pH buffering agent can be appropriately added, if necessary, as long as the effects of the present invention are not hindered.
[0021]
As the pH adjuster, for example, aqueous ammonia, or an organic alkali such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, or choline can be used. Further, as the pH buffer, for example, boric acid, ammonium sulfate, ammonium tetraborate and the like can be used.
[0022]
In addition, in addition to the above components, known additives such as a bath stabilizer and a wetting agent can be appropriately added to the electroless plating bath of the present invention as long as the effects of the present invention are not impaired. . Examples of the bath stabilizer include compounds containing heavy metals such as lead (Pb) or bismuth (Bi), and compounds containing sulfur such as thiodiglycolic acid. Examples of the wetting agent include various surfactants such as a nonionic surfactant, an anionic surfactant, and a cationic surfactant.
[0023]
However, it goes without saying that, among the optional components such as the above-mentioned pH adjusters, those which do not contain alkali metals such as sodium should be selected.
[0024]
The method for preparing the electroless plating bath and the method for performing the electroless plating according to the present invention are not particularly limited, and may be the same as ordinary electroless cobalt plating or electroless cobalt alloy plating. For example, the plating bath may be prepared by a commonly used method such as mixing the above-mentioned components, and the pH of the electroless plating bath is preferably about 7 to 14, particularly preferably 8 to 12.
[0025]
In carrying out the electroless plating, the bath temperature of the electroless plating bath is preferably set to about 20 to 100 ° C, particularly preferably 50 to 90 ° C.
[0026]
Preferred examples of the composition of the electroless plating of the present invention are as follows.
(Electroless plating bath composition)
Cobalt phosphinate 0.01-0.3 mol / L Ammonium paratungstate 0.001-0.01 mol / L
((NH 4 ) W 12 O 41 )
Citric acid (complexing agent) 0.01-1 mol / L phosphinic acid 0-0.05 mol / L
[0027]
Preferred means for implementing a method for selectively forming a metal protective film on the surface of a metal wiring formed on an electronic circuit substrate using the electroless plating bath of the present invention described above will be described.
[0028]
An electronic circuit substrate that is a target of the method for forming a metal protective film of the present invention is provided with an embedded wiring structure such as a fine groove (hereinafter sometimes referred to as a “wiring groove”) on the surface thereof. And a semiconductor substrate such as a silicon wafer on which circuit wiring is formed by embedding metallic copper or a copper alloy.
[0029]
Examples of the electronic circuit substrate include a substrate having a wiring groove having a width of about 0.1 to 0.5 μm and a depth of about 0.5 to 2 μm (approximately 1 to 5 in aspect ratio). Can be
[0030]
In forming a copper wiring on the electronic circuit board, first, a barrier layer selected from Ti, TiN, Ta, TaN, WN, TiSiN or the like is formed in a wiring groove of the electronic circuit board having the above specifications, A copper seed layer as a power supply layer for electrolytic plating is formed by a method such as sputtering or chemical vapor deposition (CVD).
[0031]
Next, a metal is filled in the wiring groove of the electronic circuit substrate by plating the substrate with a metal such as copper. Then, the metal deposited on the insulating film is removed by CMP or the like, and the surface of the metal layer filled in the wiring groove and the surface of the insulating film are made substantially flush. As a result, a wiring composed of a copper seed layer and a metal layer such as copper is formed on the electronic circuit board.
[0032]
Then, by performing the electroless plating by immersing the electronic circuit board on which the copper wiring made of the copper seed layer and the metal layer such as copper is formed by the above-described means in the above-described electroless plating bath of the present invention, A metal plating film can be selectively formed on the surface of the wiring.
[0033]
【Example】
Next, the present invention will be described in more detail with reference to Examples and Reference Examples, but the present invention is not limited to these Examples and the like.
Reference example 1
Preparation of Cobalt phosphinic acid (Co (H 2 PO 2) 2):
Cobalt hydroxide (Co (OH) 2 ) was added to and mixed with a phosphinic acid (H 3 PO 2 ) aqueous solution such that the molar ratio of phosphinic acid to cobalt hydroxide was 2: 1. After dissolving cobalt hydroxide in an aqueous solution of phosphinic acid, this solution is heated to 60 ° C. to remove moisture and dried to prepare powdery cobalt phosphinate (Co (H 2 PO 2 ) 2 ). did.
[0035]
The results of X-ray diffraction of the obtained cobalt phosphinate are shown in FIG. 1, and most of the cobalt phosphinate was Co (H 2 PO 2 ) 2 , and a part thereof was its hexahydrate.
[0036]
Example 1
(A) Preparation of fine circuit board sample:
As a fine circuit board sample, a silicon wafer provided with a wiring groove having a width of 0.5 μm and a depth of 1 μm was prepared. After forming a copper seed layer on the substrate sample according to a conventional method, copper plating was performed, and wiring grooves were filled with copper to form circuit wiring. The substrate surface was polished by CMP to obtain a fine circuit board sample in which copper was embedded only in the wiring groove portion.
[0037]
(B) Formation of metal protective film:
The substrate sample obtained in the above (a) was treated with two kinds of plating baths (products 1 and 2 of the present invention) containing the cobalt phosphinate obtained in Reference Example 1 and having the following composition. Electroplating was performed. Prior to electroless plating, palladium treatment was performed according to a conventional method.
[0038]
After plating, the surface morphology was observed, and elemental analysis was performed by energy dispersive X-ray spectroscopy (EDS). The results are shown in FIG.
[0039]
(Composition of electroless plating bath of product 1 of the present invention)
Component Concentration Cobalt phosphinate prepared in Reference Example 1 0.1 mol / L
Citric acid 0.2mol / L
pH 8 (Note)
(Note) Adjusted with aqueous ammonia
(Plating conditions)
Temperature: 90 ° C
Plating time: 60 seconds
(Composition of electroless plating bath of product 2 of the present invention)
Component Concentration Cobalt phosphinate prepared in Reference Example 1 0.1 mol / L
Citric acid 0.2mol / L
Ammonium paratungstate 0.005mol / L
((NH 4 ) 10 W 12 O 41 )
Phosphinic acid 0.4mol / L
pH 10 (Note)
(Note) Adjusted with ammonia water
(Plating conditions)
Temperature: 90 ° C
Plating time: 60 seconds
As is clear from the results of FIG. 2, a plating film containing cobalt was deposited only on the copper portion, indicating that the plating was selectively performed.
[0044]
Example 2
(A) Preparation of fine circuit board sample:
As a fine circuit board sample, a silicon wafer having a diameter of 200 mm and a wiring groove having a width of 0.5 μm and a depth of 1 μm was prepared. First, a TaN barrier layer was formed with a thickness of 20 nm on this substrate sample, and further, a copper seed layer was formed with a thickness of 50 nm by sputtering.
[0045]
The above-mentioned sample on which the copper seed layer is formed is subjected to copper plating using a conventional method, and copper is buried in the wiring groove to form a circuit wiring. Then, the substrate surface is polished by CMP to obtain a fine circuit board sample. Got.
[0046]
(B) Formation of metal protective film:
The substrate sample obtained in the above (a) was subjected to electroless plating using the product 2 of the present invention. In the electroless plating, the substrate sample was ultrasonically cleaned with a 50% aqueous methanol solution for 5 minutes, then immersed in 10% sulfuric acid at room temperature for 1 minute, immersed in a Pd catalyst solution for 10 seconds with stirring, and again immersed in 10% Performed after immersion in sulfuric acid for 1 minute.
[0047]
FIG. 3 shows the result of observing the copper wiring portion of the substrate sample plated using the electroless plating bath using a scanning electron microscope (SEM). From this result, it was confirmed that the metal protective film was selectively formed only on the surface of the copper wiring.
[0048]
Further, the formed metal protective film was dissolved in a mixed acid of nitric acid / citric acid, and the presence or absence of an alkali metal such as sodium was confirmed using ICP-AES (inductively coupled plasma atomic emission spectrometry). Was below the detection limit.
[0049]
【The invention's effect】
The electroless plating bath of the present invention is capable of selectively plating only the surface of metal wiring such as copper. However, phosphinic acid is mainly used as a source of cobalt ions and phosphinate ions in the plating bath. Since cobalt is used, there is no alkali metal ion such as sodium ion in the plating bath, so that contamination of the metal wiring with the alkali metal can be prevented. Further, even when the plating bath components are replenished in the continuous use of the plating bath, generation of by-products such as sodium sulfate does not occur, so that the plating bath can be used for a long period of time.
[0050]
Furthermore, when the electroless plating bath of the present invention containing a high melting point metal compound is used, the high melting point metal is eutectoidized in the plating film and alloyed, thereby improving the thermal stability of the plating film. There is.
[0051]
Therefore, the electroless plating bath of the present invention can be advantageously used for forming a protective film such as copper wiring on an electronic circuit substrate.
[Brief description of the drawings]
FIG. 1 is a drawing showing the results of X-ray diffraction of cobalt phosphinate.
FIG. 2 is a drawing (photograph) showing a state in which cobalt or a cobalt alloy is precipitated only on a copper surface according to Example 1.
FIG. 3 is a cross-sectional photograph of a copper wiring portion of a sample substrate after performing electroless plating in Example 2.
that's all
Claims (5)
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006033465A1 (en) * | 2004-09-22 | 2006-03-30 | Ebara Corporation | Semiconductor device and method for manufacturing the same, and treatment liquid |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006033465A1 (en) * | 2004-09-22 | 2006-03-30 | Ebara Corporation | Semiconductor device and method for manufacturing the same, and treatment liquid |
| JP2006093357A (en) * | 2004-09-22 | 2006-04-06 | Ebara Corp | Semiconductor device and manufacturing method thereof, and processing solution |
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