R-14-RS-01

平成１４年度
故障物理研究委員会研究成果報告書－ 最新 VLSI 要素技術(酸化膜と多層配線)の信頼性と微細化限界

平成１５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メカニズムを解明し、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
SiO2系ゲート酸化膜、その代替の High − κ 絶縁膜に関わる信頼性の問題、及び銅配線技術を中心とした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。
また、最近議論が盛んな半導体技術の微細化限界について、特に信頼性から見たシリコン半導体技術の限界についてもレビューしました。
本年度の報告書は、ここ3年に渡り調査してきました内容をまとめ集大成したものです。故障現象の基礎から、故障メカニズムの説明、その対策等幅広い内容になっています。ULSIの故障モードについて、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、重要と思われる故障モ
ード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１５年３月
財団法人 日本電子部品信頼性センター
理事長 古口 榮男

平成１４年度故障物理研究委員会
目

成果報告書

次

序文
平成 14 年度故障物理委員会委員構成表
まえがき ···················································································································································1
Ⅰ 薄膜ゲート酸化膜の信頼性
1. 極薄ゲート酸化膜のブレークダウン現象（ソフトブレークダウン現象を中心に） ·····························3
1.1 はじめに ···································································································································3
1.2 ブレークダウンモード（ソフトブレークダウンとハードブレークダウン） ····································3
1.2.1 電流－電圧特性 ···············································································································3
1.2.2 面積、酸化膜厚依存性 ····································································································4
1.2.3 注入極性依存性（基板タイプ依存性） ·············································································5
1.2.4 ストレス電流（電圧）依存性 ·······························································································6
1.2.5 測定系の影響 ···················································································································7
1.3 ソフトブレークダウンとハードブレークダウンの故障メカニズム ··············································8
1.3.1 故障メカニズム ··················································································································8
1.3.2 電気伝導メカニズム ··········································································································9
1.4 統一的説明モデル ················································································································10
1.4.1 電圧トランジェントの回路モデル ····················································································10
1.4.2 面積依存性 ····················································································································· 11
1.4.3 ストレス電圧及びストレス電流依存性 ·············································································14
1.4.4 膜厚依存性 ·····················································································································15
1.4.5 消費電力と蓄積エネルギー ···························································································16
1.5 微細 MOSFET におけるブレークダウン現象と回路特性への影響 ·····································16
1.5.1 微細 MOSFET のブレークダウンモードとブレークダウン箇所 ·····································16
1.5.2 ブレークダウン現象のデジタル回路動作への影響·······················································19
1.6 ソフトブレークダウンの統計的取り扱い ·················································································20
1.7 まとめ ······································································································································23
2. 薄層ゲート酸化膜の TDDB 特性と寿命予測 ················································································26
2.1 薄層ゲート酸化膜の TDDB モデル ·······················································································26
2.1.1 はじめに ··························································································································26
2.1.2 熱化学モデル（Thermochemical model） ·······································································27
2.1.3 アノード正孔注入モデル（Anode Hole Injection（AHI）モデル） ···································28
2.1.4 トラップ発生モデル（水素乖離モデル） ··········································································32
2.2 TDDB 試験方法と工程管理への応用 ···················································································36
2.2.1 試験法の種類 ··················································································································36
2.2.1.1 電圧ランプ法·············································································································36
2.2.1.2 電流ランプ法·············································································································38
2.2.1.3 定電流ストレス法 ·······································································································39
2.2.1.4 定電圧ストレス法 ·······································································································39
2.2.1.5 薄膜酸化膜における評価法の注意点 ·····································································41
2.2.2 試料作成方法 ··················································································································42-i-2.2.3 パッケージ品での評価 ····································································································44
2.2.4 評価装置 ··························································································································44
2.2.5 工程管理への応用 ·········································································································45
2.2.5.1 TDDB モニタリング ··································································································45
2.2.5.2 プラズマ損傷モニタリング ························································································46
2.2.5.3 初期ゲートリーク電流モニタリング ···········································································46
2.3 寿命分布と予測式 ·················································································································49
2.3.1 寿命分布の起源 ··············································································································49
2.3.2 TDDB（Time Dependent Dielectric Breakdown）の寿命分布 ········································49
2.3.3 寿命予測法 ······················································································································49
2.3.4 まとめ ································································································································60
2.4 極薄ゲート酸化膜の TDDB の電圧（電界）、温度加速性－TDDB の最近の話題 ···········62
2.4.1 極薄ゲート酸化膜の TDDB 評価の困難性···································································62
2.4.2 電圧（電界）加速性 ·········································································································62
2.4.3 温度加速性 ·····················································································································64
2.4.4 まとめ ·······························································································································66
2.5 TDDB 特性から見た薄層化限界··························································································67
2.5.1 はじめに ···························································································································67
2.5.2 寿命予測方法 ··················································································································67
2.5.3 極薄ゲート酸化膜の TDDB 特性 ··················································································67
2.5.4 報告されている各種寿命予測結果················································································68
2.5.5 まとめ ································································································································72
3． P チャネル MOS トランジスタの負バイアス温度不安定性 ························································74
3.1 はじめに ·································································································································74
3.2 NBTI の劣化メカニズム ·········································································································74
3.2.1 表面チャネルと埋込みチャネル PMOS FET ··································································74
3.2.2 拡散反応モデル ··············································································································75
3.2.3 正イオン伝導モデル ·······································································································76
3.2.4 トンネル電子の電離衝突による界面準位生成モデル ··················································76
3.3 NBTI の評価方法 ··················································································································78
3.3.1 NBTI 評価回路 ···············································································································78
3.3.2 NBTI 劣化現象による特性変動 ·····················································································78
3.4 NBTI の加速モデル ·············································································································79
3.4.1 温度加速性 ······················································································································79
3.4.2 電圧加速性 ······················································································································80
3.5 NBTI 劣化要因 ·····················································································································82
3.5.1 ゲート長依存性················································································································82
3.5.2 ボロン(B)拡散の影響·······································································································83
3.5.3 窒素(N)濃度の影響·········································································································84
3.5.4 水素(H)及び重水素(D2)の影響 ·····················································································86
3.5.5 水分(H2O)の影響 ············································································································86
3.5.6 フッ素(F)の影響 ··············································································································87
3.6 まとめ ······································································································································88
付録 従来の N+ポリ Si ゲート MOS 構造のバイアス・温度不安定性現象 ································90
付録.1 はじめに ·······················································································································90
付録.2 N+ゲート MOS 構造の NBTI 及び PBTI による特性変動の特徴······························90- ii -

付録.3-BT エージングによる正の固定電荷及び界面準準位密度増加現象のバイアス・温度加速性 ··························································································93
付録.4 劣化機構 ······················································································································96
4．ホットキャリア不安定性 ·····················································································································99
4.1 従来の長チャネル MOSFET のホットキャリア不安定性·······················································99
4.1.1 ホットキャリア劣化現象····································································································99
4.1.2 ホットキャリア劣化モデル ······························································································102
4.2 デープサブミクロン MOSFET のホットキャリア不安定性····················································103
4.2.1 デープサブミクロン MOSFET のホットキャリア劣化現象 ·············································103
4.2.2 ホットキャリア劣化メカニズム ·························································································106
4.3 最新 SoC 技術のホットキャリア不安定性 ············································································108
付録－ ホットキャリア不安定性評価・予測方法 ·······································································109
5. 最近の話題···································································································································· 112
5.1 高誘電率（high-k）ゲート絶縁膜の動向と信頼性 ······························································· 112
5.1.1 High-k 材料に求められる特性···················································································· 112
5.1.2 高誘電率ゲート絶縁膜材料と論文紹介 ······································································· 115
5.1.3 高誘電体膜の信頼性 ··································································································· 119
5.1.3.1 高誘電体膜の電荷トラップ特性及び NBTI ························································ 119
5.1.3.2 高誘電体膜の降伏特性·······················································································124
5.1.3.3 TDDB 特性 ··········································································································126
5.1.4 まとめ ······························································································································131
5.2 不揮発性強誘電体メモリ技術と信頼性 ··············································································133
5.2.1 はじめに ························································································································133
5.2.2 強誘電体膜材料 ···········································································································133
5.2.3 強誘電体メモリセル技術·······························································································139
5.2.4 強誘電体メモリの製造技術 ··························································································142
5.2.5 強誘電体膜の信頼性 ···································································································151
5.3 高速、高信頼性、低コスト SiGe/Si システム ······································································158
5.3.1 SiGe/Si システムの重要性 ···························································································158
5.3.2 SiGe 混晶の基本特性·································································································159
5.3.3 歪 Si の基本特性 ··········································································································163
5.3.4 SiGe-HBT の信頼性に関する論文紹介 ·····································································164
5.3.5 結び ·······························································································································167
Ⅱ ULSI 多層配線技術と信頼性
1. はじめに ·········································································································································169
2. エレクトロマイグレーションの基礎物理モデル ·············································································171
2.1 通常の導線と LSI 配線の比較 ···························································································171
2.2 物理現象としてみたエレクトロマイグレーション ··································································172
2.3 多結晶薄膜におけるエレクトロマイグレーション ·································································173
2.4 エレクトロマイグレーションにより起こる故障のモード ·························································174
2.5 エレクトロマイグレーションを説明するモデルとその役割 ···················································176
2.6 質量移動の基本式と Blech の逆流応力 ············································································178
2.7 寿命予測の基本式 ··············································································································179
2.8 まとめ ····································································································································180- iii -

3. Al 多層配線のエレクトロマイグレーション ···················································································181
3.1 Al 配線の信頼性 ·················································································································181
3.2 プロセス技術の変遷とエレクトロマイグレーション ·······························································181
3.3 エレクトロマイグレーションによる配線抵抗の挙動 ·····························································184
3.4 添加金属の優先拡散モデル ······························································································189
3.5 内因性応力モデル ··············································································································192
3.6 まとめ ····································································································································198
4. Al 配線のストレスマイグレーション ······························································································200
4.1 高温モード ···························································································································200
4.2 低温モード ···························································································································200
4.3 ボイドの形状 ························································································································201
4.4 微細配線の応力状態 ··········································································································202
4.5 Al 配線におけるストレスマイグレーション対策 ···································································202
4.6 Al 配線のストレスマイグレーションまとめ ············································································202
5. Cu 配線技術と信頼性 ···················································································································204
5.1 はじめに ·······························································································································204
5.2 Cu 配線技術 ························································································································204
5.3 Cu 配線のエレクトロマイグレーション ··················································································205
5.3.1 Cu 配線と Al 配線の比較 ·····························································································205
5.3.2 電流密度加速性の変化（加速限界） ···········································································207
5.3.3 配線の溶断電流 ···········································································································208
5.3.4 材料・プロセス条件の依存性 ·······················································································209
5.3.5 多層配線のエレクトロマイグレーション ·········································································217
5.3.6 Cu 配線の Critical Product ···························································································219
5.4 Cu ドリフト現象 ·····················································································································222
5.5 まとめ ····································································································································225
6. Cu 配線のストレスマイグレーション ·····························································································226
6.1 高温モード ···························································································································226
6.2 低温モード ···························································································································227
6.3 Cu 配線におけるストレスマイグレーション対策 ··································································233
6.4 Cu 配線のストレスマイグレーションまとめ ···········································································236
Ⅲ 微細化・薄膜化技術対応の物理分析技術
1．故障解析技術のトレンド ·················································································································239
2．故障位置特定化の新技術 ·············································································································240
2.1 レーザービーム励起 SQUID 検出法 ··················································································240
2.2 Laser Voltage Probing 法 ··································································································241
3．電子ビーム関連物理解析技術 ······································································································241
3.1 電子銃の高性能化 ···············································································································242
3.2 SEM のアプリケーション例 ····································································································242
４．走査プローブ顕微鏡での故障解析技術 ······················································································244
4.1 ホール底部の観察の試行 ···································································································244
4.2 酸化膜電気的特性評価法···································································································245
5．今後の故障解析技術の展望 ·········································································································245- iv -

IV 電子デバイスの微細化限界
１．デバイス構造の微細化限界 ······································································································247
1.1 電子デバイスの過去と将来·································································································247
1.2 スケーリング則 ·····················································································································248
1.3 消費電力の限界 ··················································································································249
1.3.1 現状································································································································249
1.3.2 可逆計算…0 Joule/switch ····························································································250
1.3.3 断熱論理…漸近的に 0 Joule/switch ···········································································251
1.3.4 熱力学的考察によるスイッチング消費電力限界…0.00065 fJ/switch·························251
1.3.5 半導体ロードマップによるスイッチング消費電力限界…0.002 fJ/switch ····················252
1.4 リーク消費電力 ····················································································································252
1.4.1 サブスレッショルド電流 ·································································································253
1.4.2 ゲートリーク電流 ···········································································································254
1.5 酸化膜 ·································································································································254
1.5.1 層間絶縁膜 ···················································································································254
1.5.2 DRAM 酸化膜 ··············································································································255
1.5.3 ゲート酸化膜 ·················································································································256
1.6 ドーピング ····························································································································257
1.6.1 ソース・ドレイン領域のドーピング ·················································································257
1.6.2 チャネルドーピング ·······································································································258
1.6.3 ゲート材料 ·····················································································································260
2. 配線微細化限界 ···························································································································263
2.1 はじめに ·······························································································································263
2.2 配線問題 ·····························································································································263
2.3 基礎的な性能限界に関する検討 ·······················································································263
2.3.1 光速度制約 ···················································································································263
2.3.2 エネルギーからみた限界······························································································264
2.3.3 ノイズからみた限界 ·······································································································264
2.3 4 配線の寸法と物理定数からみた性能検討 (逆スケーリング則) ·································265
2.4 材料による性能限界に関する検討 ····················································································265
2.4.1 抵抗率 ···························································································································265
2.4.2 材料の信頼性 ···············································································································266
2.4.3 配線材料 ·······················································································································266
2.4.4 Cu 配線 MPU ················································································································267
2.4.5 層間絶縁膜 ···················································································································267
2.5 プロセスによる性能限界に関する検討···············································································268
2.5.1 SON (Silicon On Nothing) ····························································································268
2.5.2 配線構造 ·······················································································································268
2.5.3 Cu 配線構造 MPU ········································································································269
2.5.4 解像度限界 ···················································································································269
2.6 レイアウトによる性能限界に関する検討 ·············································································270
2.6.1 斜め配線 ·······················································································································270
2.7 デバイスによる性能限界に関する検討 ··············································································271
2.7.1 RC 効果·························································································································271-v-

2.7.2 多層配線構造 ···············································································································272
2.7.3 配線スケーリング ···········································································································272
2.7.4 IR ドロップ ····················································································································274
2.7.5 インダクタンス効果 ········································································································274
2.7.6 配線設計制約 ················································································································275
2.8 回路による性能限界に関する検討 ·····················································································277
2.8.1 リピータの挿入 ···············································································································277
2.8.2 消費電力限界 ···············································································································277
2.8.3 クロック周波数と配線長 ································································································277
2.8.4 RC 線路の限界 ·············································································································278
2.8.5 配線遅延 ·······················································································································278
2.8.6 電磁波伝送 ···················································································································279
2.9 システムによる性能限界に関する検討···············································································280
2.9.1. 2D-IC の製造限界 ·······································································································280
2.9.2 3D-IC ·····························································································································280
2.9.3 3D-IC の配線遅延限界 ································································································281
2.9.4 システム集積 ·················································································································281
2.9.5 3D-SiP ···························································································································282
2.10 将来の配線技術の研究動向 ····························································································283
2.10.1 光配線チップ ··············································································································283
2.10.2 光配線の遅延時間 ·····································································································283
2.11 まとめ··································································································································284
あとがき ················································································································································287- vi -

まえがき
シリコン集積回路の縮小化の原理的限界が､物理､材料特性､プロセス､あるいは､回路の面から盛んに検討され､それを打破するための新しい材料､プロセス､デバイス構造､実装の開発が日々行われている。
しかし､そのような新しい材料や技術も､その実用化には､コスト､再現性､歩留まり､環境問題､そして信頼性という厳しい基準をクリアする必要がある。特性､性能がよいという点で期待された材料､デバイス､技術が実際の製品に採用されない多くのケースを我々は見てきている。
シリコン集積回路では､ゲート酸化膜の厚さが 2 nm を切り､もれ電流と TDDB(time dependent dielectric
breakdown: 誘電体膜経時破壊)寿命の減少､静電破壊耐性の脆弱化などの信頼性の面から､Si-N 膜､高誘電体膜(high-k)材料への切り替えが検討されている。また､メモリとして､強誘電体膜､強磁性体膜の研究開発も盛んである。しかし､シリコン酸化膜以外の新しい誘電体膜の採用は､特に､信頼性の面から難航している。一番の問題点は､基板シリコンと誘電体界面の特性劣化である。一方で､配線幅や厚さの縮小による配線抵抗の増加､配線間距離の短縮による配線間容量増加を避けるために､Al から伝導率のより小さな Cu へ､配線間の酸化膜から低誘電率(low-k)膜への転換が可能なところから採用されている。Cu
配線におけるプロセス技術の問題はかなり解決され､信頼性の面でもエレクトロマイグレーション耐性が Alよりも優れ､ストレスマイグレーションも一時は騒がれたが技術的にほぼ解決されている。しかし､ここでも､
low-k 膜の信頼性は検討課題である。
このような当初期待されたシリコン酸化膜以外の新しい誘電体材料や新しい Cu 配線膜の導入には､それ自体あるいは周辺技術にまだまだ種々の問題があり､長年培った技術､ノウハウが蓄積されている Al 配線やシリコン酸化膜でどこまで縮小化が可能かの再検討も盛んである。
情報技術におけるデータ伝送の高速化､大容量化に対応するために使われている GaAs､InP 系の高速
電界効果トランジスタやヘテロ接合バイポーラトランジスタも､場合によっては､Si 系のトランジスタへ置き換
わる可能性も現われている。シリコンよりも移動度が 2 倍程度大きな SixGe1-x や歪シリコン材料の低温成長技術が開発され､実用化も始まっているが、これらはシリコン集積回路作成プロセスがそのまま利用でき､また､シリコン CMOS との集積化が可能であり､信頼性､コストなどの実用化面でも GaAs,InP 系デバイスより多くのメリットがあるからである。
このように､集積化や性能限界を打破するために､新しい材料､プロセス､デバイス構造が提案され､研究､試作､試験されているが、その中の少数の技術が実際に採用され生き延びていく。実用化における問題で､特に民生品では信頼性とコストが重要なファクタとなっている。
電子部品信頼性センターの故障物理研究委員会では､平成 12 年度から､シリコン集積回路の微細化限界について物理､構造､配線､回路､信頼性の面から文献調査を主体に検討してきた。特に､微細化で問題となるゲート酸化膜､high-k 誘電体膜､low-k 誘電体膜の TDDB､ホットエレクトロン劣化､NBTI(negative
bias temperature instability)等の信頼性､Al､ Cu 配線膜のエレクトロマイグレーション､ストレスマイグレーシ
ョン劣化を､その故障物理の基礎から実用化対策まで調査し､その成果を､報告書やセミナで､随時､報告してきた。平成 14 年度の成果報告書は､この 3 年間の故障物理研究委員会において調査したシリコン集積回路の誘電体膜､配線膜の信頼性をまとめ､集大成したものである。単なる文献調査報告書ではなく､故障現象の物理的理解から､故障モード､メカニズム､加速試験方法､寿命予測､対策などについて分かり
やすくまとめてあり､シリコン集積回路のさまざまな分野の技術に従事する方々にとって貴重な資料となると委員会委員一同願っている。

-1-