使用氮化處理技術改進低壓化學氣相沉積鎢及低介電常數材料作為極大型積體電路金屬接觸擴散障礙層之特性研究

Abstract

本論文研究以氮化處理改進低壓化學氣相沉積鎢與低介電常數材料作為擴散障礙層之特性，並且利用低介電材料形成一不需要擴散障礙金屬層的介電層結構；化學氣相沉積鎢於沉積時，氟元素穿透進入鎢膜下的問題也一並討論。氮化處理技術被使用作為改善耐火性金屬與介電層的熱穩定性與增加阻止擴散的能力，同時也可以抑制氟元素在沉積鎢金屬的穿透力。 對於導體擴散障礙層，一種新的化學氣相沉積似非晶鎢膜，藉由矽皖與六氟化鎢於氣相反應的方式，形成一層擴散障礙層，由適當的條件下，可沉積一層具有平整覆蓋性、高沉積速度與優異的步階覆蓋性等優點的似非晶鎢膜。在同一腔體不破真空的下，氮氣電漿處理被使用來作為填充似非晶鎢膜的晶粒介面，晶粒介面形成的快速擴散的途徑一但被填充，可降低似非晶鎢膜的擴散係數，經過二次離子質譜儀分析，經過五分鐘攝氏三百度的氮氣電漿處理後，表面約五十奈米似非晶鎢膜被轉換成氮化鎢。其中鎢與氮的原子比約為2:1。 一層雙層a-WN2/a-W的擴散障礙層介於鋁與p+n或n+p二極體間以阻擋鋁的擴散，當此結構的二極體經過575℃三十分鐘退火，有部分二極體的漏電流密度高達每單位平方公分0.1~0.01安培，這是由於鋁穿過經由耐火金屬和二氧化矽的介面，一層TEOS沉積於耐火金屬和二氧化矽之間以減少轉角上的應力，如此可防止二極體在575℃三十分鐘的退火條件下失效，這種結構在600℃三十分鐘的退火條件下開始失效。此雙層a-WN2/a-W的擴散障礙層也被應用於銅電極，這種Cu/ a-WN2/a-W/p+n結構的二極體在漏電流有較好的表現，它經過725℃三十分鐘的退火後仍大致保持良好。經由實驗證明a-WN2/a-W雙層擴散障礙層的阻止擴散的能力，是由於氮原子與過多的矽原子填充於似非晶鎢的晶粒介面所致。 以一般選擇性化學氣相沉積鎢作為閘及電集會有氟原子穿透進入閘極氧化層的嚴重問題，這會對金氧半場效電晶體與金氧半場效電容造成特性上的傷害，本實驗以化學氣相沉積似非晶鎢薄膜，與二矽化鎢相比，除降低電阻之外，也增加了阻擋氟原子擴散進入閘極二氧化矽的能力，當一般柱狀結構的化學氣相沉積鎢沉積在似非晶鎢薄膜之上，不僅保持阻擋氟原子擴散的能力，而且可進一步降低其阻抗，在此篇論文中證明上述雙層堆疊鎢結構(c-W/a-W)，展現較低的電阻係數與抗氟擴散性。 在介電層的擴張障礙層方面，HSQ與MSQ兩種低介電常數材料被選擇做為研究的主題，經過氨氮氣電漿處理，HSQ低介電常數材料能夠成功的抵擋銅金屬的擴散，同時也可以改善其漏電流，經過不同電漿處理時間，HSQ膜依然保有低介電常數材料之特性，其介電常數僅有少量的上升。對於漏電流隨氨氣電漿處理的時間的增加而減少，我們可以歸納出以下三點原因：首先是HSQ膜變得更緊密，其次是HSQ表面形成一層氮化層，最後是HSQ膜原有所含的損害經過退火處理所致。HSQ表面形成一層氮化層是改善抵抗金屬擴散的主要原因；這層經氨氣電漿處理之後所形成的氮化層的厚度約為35奈米，此氮化層抵擋銅金屬的擴散機制是以形成一層穩定保護層(passive)的方式。 使用氨氣電漿處理MSQ膜可以同時獲得兩項非常重要的優點，包括增加抵抗銅金屬擴散能力與抗灰化能力，一種Cu/MSQ/Si電容被用來研究MSQ經過灰化處理與熱處理後的電性，經實驗證明經過氨氣電漿處理的MSQ膜擁有較佳的抵抗銅金屬擴散能力與抗灰化能力。以二次離子質譜儀分析經過攝氏500度60分鐘的Cu/MSQ/Si電容結構，並無銅金屬穿透MSQ膜，此外，經過氨氣電漿處理的MSQ膜再經過灰化處理之後，MSQ膜的含碳原子的濃度不會改變；相反的，未經過氨氣電漿處理的MSQ膜再經過灰化處理之後，其所含的碳原子已經完全消失，經過氨氣電漿處理的MSQ膜，能夠抵抗銅金屬擴散能力與抗灰化能力的原因是由於MSQ膜的表面已經重新反應形成一層穩定的含碳氮化矽薄膜。

This thesis studies the barrier properties of the low pressure chemical vapor deposited tungsten film (CVD-W) and of low dielectric constant material as the dielectric layer of barrier metal-free structure for ultra-large-scale-integrated (ULSI) metal contacts applications. Fluorine penetration during CVD-W deposition was also studied Nitridation technique was used to improve the thermal stability of barrier layer (including tungsten film and low dielectric constant materials) and to suppress the fluorine penetration. For the conductive diffusion barrier, a novel chemical vapor deposited amorphous-like tungsten (CVD a-W) film was deposited by a SiH4-WF6 gas phase reaction as a diffusion barrier layer. By suitable process conditions, a conformal CVD a-W film with high deposition rate and superior step coverage is obtained. In a chamber without breaking the vacuum, nitrogen plasma treatment was used to stuff nitrogen atoms into the grain boundaries of an amorphous-like tungsten film. The nitrogen atoms eliminated the fast diffusion paths of film thus giving the amorphous-like tungsten film a smaller diffusion coefficient. The upper 50 nm of the a-W film was transformed to WNX after 5 min of N2 plasma exposure at 300℃. The atomic ratio of W to N in WNX layer was 2:1. A bi-layer a-WN2/a-W barrier was inserted between Al and p+n/n+p diodes as barrier layer. The failure of these diodes with amorphous-like WN2/W barriers was annealed at 575℃ for 30 min and had leakage currents of 107 or 108nA/cm2. These diodes failed due to the diffusion of aluminum along the sidewalls of the barriers and the field oxide interface. In a search for a solution to this problem we investigated the use of tetra-ethyl-ortho-silicate (TEOS), which was known for its thermal stability as a stress buffer. Therefore, in this experiment TEOS was formed a "contact array structure" which in turn prevented diode failure at 575℃ annealing for 30min. Further, these diodes in the 'contact array structure' only began to show the evidence of degradation at 600℃. Bi-layer barriers of a-WN2/a-W and TEOS also inserted between Cu and p+n diode. The Cu/a-WN2/a-W/p+n diodes showed better characteristics in leakage current. It retained integrity up to 725℃. As the experimental results, the effectiveness of a-WN2/a-W bi-layer diffusion barrier is attributed to stuff grain boundary with N atoms and excess Si atoms as well as to eliminate the rapid diffusion by using CVD a-W material. A serious problem of typical CVD tungsten film is fluorine contamination of the gate oxide. This shifts the characteristics of the MOSFET and MOS capacitors. In this experiment, amorphous-like tungsten films were deposited by CVD process. We then found a reduction of the resistance, compared with WSi2, and increased blocking of the fluorine atoms diffusing into the gate oxide. However, when the amorphous-like tungsten film was deposited prior to typical CVD tungsten film with columnar structure, it not only showed excellent barrier characteristics for fluorine impurities but also the resistance was substantially lower than a single layer of a-W film. Therefore, this bi-layer film of typical CVD tungsten/amorphous -like CVD tungsten makes a better wordline structure with substantially lower levels of resistivity and fluorine contamination. For the dielectric diffusion barrier, hydrogen silsesquioxane (HSQ) and (MSQ) were chosen to study its characteristics after plasma treatment. Hydrogen silsesquioxane, a material with low dielectric constant, can successfully suppress Cu diffusion without using barrier metal through NH3 plasma treatment. Lower leakage current and better barrier capability can be achieved by hydrogen silsesquioxane film after NH3 plasma treatment. Having been treated with different plasma exposure times, this film can still maintain its original dielectric constant with little changes. The decrease in leakage current with increasing exposure time can be attributed to the following mechanisms: dielectric film becomes densier, nitride film is formed on the hydrogen silsesquioxane, and the bulk damage of hydrogen silsesquioxane is annealed out. A thin layer of nitride formed on the dielectric is the cause for having better barrier capability. The thickness of the nitride layer on hydrogen silsesquioxane is about 35 nm, and it can prevent the Cu diffusion/migration into the underlying dielectric. The role of our nitride film is to act as the passive diffusion barriers. Simultaneously, Using NH3 plasma treatment, two extremely important advantages were achieved in spin-on organic polymer－methyl(CH3) phenyl(C6H5) silsesquioxane (MSQ), including the reduction of copper diffusion and the improvement of ashing resistance. A copper/MSQ/Si capacitor structure is used to study the electrical characteristics of MSQ film after ashing treatment or post-anneal. Higher barrier capability and better ashing resistance can be achieved by MSQ layer after NH3 plasma treatment. After annealing at 500℃ for 60 min, SIMS depths profile shows that the Cu atoms do not penetrate into the MSQ when they are pre-treated by NH3 plasma. Furthermore after ashing step, the carbon atoms in the MSQ film almost remain the same when they are pre-treated by NH3 plasma. On the other hand, the concentration of carbon in as-cured MSQ is no longer seen. The reason of improving ashing resistance and better barrier capability was due to the organic polymer film rearranging to form a carbon contained silicon nitride film. Chinese Abstract ......................................... i English Abstract ......................................... iv Acknowledgements ......................................... vii Contents ................................................. viii Table Captions ........................................... x Figure Captions .......................................... xi Chapter 1 Introduction 1.1 General Background ................................. 1 1.2 Barrier Mechanisms ................................. 3 1.3 Using Chemical Vapor Deposited Tungsten as Diffusion Barrier ................................................ 4 1.4 Using Low Dielectric Material Formed Barrier Metal-Free Structure .............................................. 6 1.5 Thesis Organization ................................ 9 References ............................................. 10 Chapter 2 Reaction Chemistry of Chemical Vapor Deposited Tungsten and Characteristics of Low Dielectric Materials 2.1 Chemical Vapor Deposited Tungsten .................. 13 2.2 Low Dielectric Constant Material .................... 14 References ............................................. 10 Chapter 3 Barrier Characteristics of Chemical Vapor Deposited Amorphous-like Tungsten with in situ Nitrogen Plasma Treatment for Al metallization 3.1 Introduction ....................................... 13 3.2 Experiment ......................................... 15 3.3 Results and Discussion ............................. 16 3.4 Summary ............................................ 22 References ............................................. 24 Chapter 4 Thermal stability of amorphous-like WNX/W bilayered diffusion barrier for chemical vapor deposited-tungsten/p+-Si contact and for Cu metallization system 4.1 Introduction ....................................... 26 4.2 Experiment ......................................... 27 4.3 Results and Discussion ............................. 29 4.4 Summary ............................................ 37 References .............................................. 39 Chapter 5 The Characteristics of Chemical Vapor Deposited Amorphous-like Tungsten Film as a Gate Electrode 5.1 Introduction ....................................... 41 5.2 Experiment ......................................... 42 5.3 Results and Discussion ............................. 43 5.4 Summary ............................................ 47 References .............................................. 48 Chapter 6 Suppression of Fluorine Penetration by Use of In Situ Stacked Chemical Vapor Deposited Tungsten Film 6.1 Introduction ....................................... 49 6.2 Experiment ......................................... 50 6.3 Results and Discussion .............................. 52 6.4 Summary ............................................ 57 References .............................................. 58 Chapter 7 Using NH3 Plasma Treatment to Improve the Characteristics of Hydrogen Silsesquioxane for Copper Interconnection Application 7.1 Introduction ....................................... 60 7.2 Experiment ......................................... 61 7.3 Results and Discussion ............................. 62 7.4 Summary ............................................ 65 References ............................................ 67 Chapter 8 A Novel Pretreatment Technology for Organic Low-Dielectric Material to Suppress Copper Diffusion and Improve Ashing Resistance 8.1 Introduction ....................................... 69 8.2 Experiment ......................................... 70 8.3 Results and Discussion ............................. 71 8.4 Summary ............................................ 75 References .............................................. 76 Chapter 9 Conclusion and Suggestions for Future Work 9.1 Conclusion ......................................... 78 9.2 Suggestion for Future Work ......................... 80