Ｒ－１２－ＲＳ－０１

平成１２年度
故障物理研究委員会 成果報告書

平成１３年３月
財団法人

日本電子部品信頼性センター

序文

近年、半導体の微細加工技術や多層金属配線技術等の開発が益々向上し、半導体集積回路の高集積化・高機能化・高性能化・高速化・低消費電力化が著しく進展し、新たな需要分野を喚起しております。
このような技術により集積されたＵＬＳＩの信頼性を確保するためには、ＵＬＳＩの設計・製造プロ
セスの開発段階で信頼性を作り込むことが重要な手法になってきました。そのためには、各種故障モード及び故障機構を解明し、早急に対策を立てていく必要があります。そのため、半導体故
障物理の研究が益々重要視されるようになってまいりました。
このような背景において、当センターでは、かねてより半導体メーカ、研究所、大学などから故障
物理の専門家にお集まりいただき、研究会を組織して、最新半導体デバイスで問題となる信頼性問題について調査・研究を進めてまいりました。本年は、特に近年薄層化が進んでいるゲート酸化膜に関わる信頼性の問題、さらには最近注目されている銅配線技術を含んだ多層配線技術の信頼性に着目し、内外の文献調査及び検討を進めてまいりました。
ここに、平成１２年度の成果を取りまとめました。平成１１年度資料を補強し、内容を充実させました。酸化膜信頼性と多層配線信頼性について、必ずしも全項目をカバーしているわけではありま
せんが、重要と思われる項目は取り上げたつもりです。本報告書が広く関係方面のご参考になり、活用されることを期待致します。
なお、本事業の遂行に当たり、「故障物理研究委員会」の木村 忠正委員長を始め、委員の皆様の多大なご尽力に対し、深謝致します。

平成１３年３月
財団法人 日本電子部品信頼性センター
理事長 佐々木 元平成１２年度故障物理研究委員会 成果報告
目次

まえがき ·········································································································

1

Ｉ． 薄膜ゲート酸化膜の信頼性
1. 酸化膜の物性 ····························································································

3

1.1 酸化膜の伝導機構 ···················································································

3

1.1.1 酸化膜の構造 ···················································································

3

1.1.2 絶縁体の電気伝導 ·············································································

3

1.1.3 LSIのゲート酸化膜に流れる電流 ····························································

4

1.1.4 直接トンネル電流とFNトンネル電流の境界（膜厚依存性） ·······························

9

1.2 MOS電荷の分類及びキャリアトラップの特性 ··················································· 11
1.2.1 MOS電荷の分類 ··············································································· 11
1.2.2 酸化膜トラップ電荷 ············································································· 12
1.2.2.1 酸化膜トラップ電荷の測定方法及び電荷分布中心の評価方法 ·················· 12
1.2.2.2 正孔トラップ ················································································ 16
1.2.2.3 電子トラップ ················································································ 19
1.2.2.4 FN電子注入により観測される電荷 ···················································· 23
1.2.2.5 薄い酸化膜のトラップ発生モデル ························································ 25
1.2.2.6 まとめ ························································································ 27
1.3 極薄酸化膜MOS構造のC-V特性 ·································································· 29
1.3.1 はじめに ···························································································· 29
1.3.2 量子効果 ··························································································· 29
1.3.3 ポリSi空乏効果 ··················································································· 30
1.3.4 C-V特性のシミュレーション ····································································· 31
1.3.5 実測C-V特性との比較 ·········································································· 31
1.3.6 C-V特性を利用した酸化膜厚評価 ···························································· 31
1.3.7 まとめ ······························································································· 34
2. FNストレスによる薄層ゲート酸化膜のリーク電流増加現象 ········································ 35
2.1 リーク電流増加現象と機構 ·········································································· 35
2.1.1 SILCとソフトブレークダウン ···································································· 36
2.1.2 SILCの伝導メカニズム ·········································································· 37
2.1.3 SILCの時間変化················································································· 39
2.1.4 正電荷トラップの時間減衰 ······································································ 42(i)2.1.5 ソフトブレークダウン現象 ········································································ 43
2.2 ソフトブレークダウン後の伝導機構（パーコレーションモデル） ································ 47
2.2.1 はじめに ·························································································· 47
2.2.2 パーコレーションモデル ········································································ 47
2.2.3 まとめ ······························································································ 53
3. TDDBモデルと寿命予測 ················································································· 55
3.1 TDDB寿命の電界依存性 ··········································································· 55
3.2 熱化学Eモデル（低電界TDDBモデル）） ························································· 57
3.2.1 はじめに ·························································································· 57
3.2.2 構造と結合エネルギ ············································································ 58
3.2.3 SiO2の誘電特性 ················································································ 60
3.2.4 熱化学モデル ··················································································· 64
3.2.5 熱化学モデル（歪んだ結合状態との混合） ················································· 69
3.3 統一モデル ····························································································· 77
3.3.1 はじめに ·························································································· 77
3.3.2 TDDBの統一モデル ··········································································· 77
3.3.3 欠陥モデル ······················································································ 80
3.3.4 薄い酸化膜（<5 nm）に対する見直し ······················································· 82
3.4 正確なアノードホール注入（Anode Hole Injection）モデル ·································· 84
3.4.1 はじめに ···························································································· 84
3.4.2 AHIモデルのフェルミレベル依存 ····························································· 84
3.4.3 ダメージの挙動 ··················································································· 87
3.4.4 低、高電界でのTBDスケーリング ······························································· 89
3.4.5 膜厚、極性依存 ··················································································· 91
3.4.6 TBDに対する電圧スケーリングと普遍的な形状·············································· 92
3.4.7 まとめ ······························································································· 92
3.5 相補モデル ····························································································· 94
3.5.1 誘電劣化の分子モデル ········································································· 94
3.5.2 酸化膜への電子、ホールの注入 ······························································ 97
3.5.3 TDDBにおけるホール捕獲の役割 ··························································· 98
3.5.4 TDDBの相補モデル ············································································ 99
3.6 まとめ································································································· 104

4. TDDB寿命に及ぼすパルスおよびACストレス効果 ·················································· 105
4.1 試験セットアップ························································································ 105
4.2 試験結果 ································································································ 106
4.2.1 パルス波形および周波数依存 ································································· 106(ii)

4.2.2 電界依存 ··························································································· 107
4.2.3 酸化膜厚依存 ····················································································· 108
4.2.4 温度依存 ··························································································· 108
4.3 パルスおよびACストレス効果のメカニズム ························································ 109
5. TDDB試験方法 ···························································································· 112
5.1 試験法の種類 ·························································································· 112
5.1.1 電圧ランプ法 ······················································································ 112
5.1.2 電流ランプ法 ······················································································ 114
5.1.3 定電流ストレス法 ················································································· 115
5.1.4 定電圧ストレス法 ················································································· 115
5.1.5 薄酸化膜における評価法の注意点 ··························································· 117
5.2 試料作成方法 ·························································································· 118
5.3 パッケージ品での評価 ················································································ 121
5.4 評価装置 ································································································ 121
6. 寿命分布と予測式 ······················································································· 122
6.1 寿命分布の起源 ······················································································ 122
6.2 TDDBの寿命分布 ··················································································· 122
6.3 寿命予測法 ···························································································· 122
6.4 まとめ································································································· 134

7. pMOSトランジスタの負バイアス不安定性 ····························································· 136
7.1 はじめに ································································································· 136
7.2 NBTIの劣化メカニズム ··············································································· 136
7.2.1 拡散反応モデル ·················································································· 136
7.2.2 正イオン伝導モデル ············································································· 137
7.2.3 トンネル電子の電離衝突による界面準位生成モデル ····································· 137
7.3 NBTI劣化要因 ························································································ 138
7.3.1 ゲート長依存性 ··················································································· 138
7.3.2 ボロン（B）拡散の影響 ··········································································· 139
7.4 まとめ································································································· 140

8. 最近の話題（高誘電体膜の信頼性） ·································································· 142
8.1 はじめに ································································································ 142
8.2 高誘電率絶縁膜の種類 ············································································· 143
8.3 高誘電体膜を用いた製造技術 ···································································· 145
8.4 高誘電体膜の信頼性 ················································································ 148(iii)

Ⅱ．最近の多層配線技術と信頼性
1. Ａｌ多層配線のエレクトロマイグレーション ···························································· 151
1.1 はじめに ································································································ 151
1.2 プロセス技術の変遷とエレクトロマイグレーション ··············································· 151
1.2.1 Al中のCu添加 ···················································································· 152
1.2.2 高融点金属によるバリアメタル ································································· 152
1.2.3 W-Plug Via/Contactの採用 ································································· 152
1.2.4 CMPによる平坦化 ··············································································· 153
1.3 Al配線のエレクトロマイグレーション ································································ 153
1.3.1 Al配線の構造モデル ············································································ 154
1.3.2 エレクトロマイグレーション試験における抵抗変動 ·········································· 154
1.3.3 Incubation time················································································· 155
1.3.4 ドリフト期間 ························································································ 158
1.3.5 抵抗飽和期間 ····················································································· 159
1.4 基礎物理モデル ······················································································· 160
1.4.1 故障モデル ························································································ 160
1.4.2 力学的ストレスモデル ············································································ 161
1.4.3 Kawasaki/Huモデル ··········································································· 162
1.4.4 抵抗飽和モデル ·················································································· 163
1.5 LSI設計への応用 ····················································································· 165
1.5.1 Incubation timeの予測 ········································································ 165
1.5.2 Critical Productによる設計マップ ··························································· 165
1.5.3 Wachnikらの抵抗飽和マップ ································································· 166
1.5.4 適用の範囲と方針例について ································································· 167
1.6 まとめ ····································································································· 168
1.7 Al配線の今後の展望 ················································································· 168
1.7.1 Alダマシン配線の報告例 ······································································· 168
1.7.2 Al配線とCu配線におけるエレクトロマイグレーションの相違······························ 170
2. Cu配線技術と信頼性 ··················································································· 173
2.1 Cu配線技術 ··························································································· 173
2.2 Cu配線のエレクトロマイグレーション ······························································ 175
2.3 Cuドリフト ······························································································ 179
あとがき ·········································································································· 187
平成12年度故障物理研究委員会構成表 ································································ 188
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まえがき
本報告書は、第 I 部で、極薄酸化膜の TDDB の故障物理から始まり、プロセス、加速式、寿命分布等についての最近の文献を参考に委員会で議論した成果をまとめている．第 II
部では、最近の LSI の多層配線構造の進歩による Al 配線のエレクトマイグレーションの故障メカニズム、故障モードの変化とそれに伴う寿命予測式の変化、さらに、近年、注
目を浴びている Cu 配線膜のエレクトロマイグレーション信頼性について、最近の研究
論文を調査し紹介した．
集積回路の縮小化の進展は、ついにゲート Si 酸化膜厚さの限界である約 2 nm に達しよ
うとしている．さらに窒化膜、その他の高誘電率材料の開発で、2008 年頃には 酸化膜換
算で 1 nm を切ると技術予測されている．しかし、当面は、薄くなる Si ゲート酸化膜の信頼性を確保するために、Si ゲート酸化膜の作製方法の見直し、酸窒化膜の導入、ある
いは電源電圧の低減、回路の工夫など種々の点からの対策が検討されている．一方、～5
nm よ り 薄 い （ 極 薄 ） Si 酸 化 膜 の 経 時 破 壊 （ TDDB : Time Dependent Dielectric
Breakdown） 現象とそのメカニズムは、～5 nm 以上の Si 酸化膜と大きく異なり、故障モ
ード、劣化のメカニズム、種々のパラメータ依存、加速試験、寿命予測、信頼性限界に対する考え方の大幅な見直しが必要である．
厚いゲート Si 酸化膜では、陰極からの電子注入は基本的に FN（Fowler-Nordheim）トン
ネル注入であり、ゲート電圧が高い．したがって、陽極（基板 Si）に到達する電子のエ
ネルギーも大きく、この電子エネルギーによる衝突励起で基板 Si に生成された正孔や解放された界面水素原子の酸化膜への再注入が劣化の主要因となった．Si 酸化膜が薄くなるとともに ゲートからの電子注入が FN トンネル注入から直接トンネル注入に変わり、ゲート電圧も減少した．その結果、厚い膜の故障モードは正常から破壊へと短時間で移る
ハードブレークダウンであったが、薄い膜では、酸化膜中に生成されるトラップを介したトンネルによるリーク電流の増加（SILC: Stress Induced Leakage Current）、すなわちソフ
トブレークダウンが先ず観測され、SILC が徐々に増加した後にハードブレークダウンとなる．
酸化膜厚の減少による TDDB 信頼性の低下のために、実使用の低電界（あるいは電圧）における TDDB 寿命をできる限り正確に予測する式、すなわち、低電界（電圧）まで適用できる電界（電圧）加速式が要求される． ～10 nm 以上の厚い膜に対する FN 電子注
入理論に基づいて導かれた寿命（MTTF: Mean Time to Failure） の電界（E ）加速式は、1/E モデル （ MTTF =AE 2exp（B/E ）、 A、B は定数） が使われていたが、10 nm 以下の膜の低電界 （E <～5 MV/cm）での TDDB 実験データは、 MTTF として 1/E モ
デルより厳しい（予測寿命の小さい）E モデル加速式 （ MTTF=C exp（-E ）、C、 は定数）に近く、これを説明する物理モデルの検討が多くなされた．しかし、～5 nm 以下の酸化膜では、故障モードがソフトブレークダウンに変化すると共に、寿命はゲート電界
でなくゲート電圧の関数であるという実験データが報告され、これを指示する物理的モデルも報告されるようになってきている．さらに、TDDB 寿命分布も～5 nm 以下の薄膜ではこれまでと異なることが見出されている．

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このように、～5 nm 以下の極薄酸化膜に対する信頼できる TDDB 寿命データの取得、電界あるいは電圧加速式の導出、寿命予測は、現在、TDDB における大きな課題であり、これらに関して最近の論文を中心に委員会での研究成果を第 I 部にまとめた．
第 II 部では、Al、Cu 配線のエレクトマイグレーションについての調査研究成果をまとめた．Al 配線は、最近の平坦化技術の進歩に伴う LSI 多層構造の大きな変化が、エレク
トロマイグレーション故障メカニズム、故障モードとそれに伴う寿命予測式の変化をもたらしている．一方、Cu 配線膜は Al より低抵抗であり低誘電率の層間絶縁膜との併用で高速化が期待できるとともに、また、エレクトロマイグレーション耐性が Al に比べて格段に高いという特徴を持ち、配線への適用に対する活発な検討が進められている．Cu 配
線の大きな問題点は層間膜中の Cu のドリフトで、これを抑えることが重要な課題であり、この点についても報告書では調査検討した．

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