化學氣相沉積鎢膜及矽化鎢膜在極大型積體電路之應用

Abstract

本論文研究化學氣相沉積鎢膜(CVD-W)及矽化鎢膜(CVD-WSix)在極大型積體電路之應用 。首先，我們探討鎢膜及矽化鎢膜的薄膜特性及熱穩定性。其次，我們探討以鎢膜及矽化 鎢膜作為鋁銅擴散障礙層之高溫穩定性。另外，我們提出以WSiN/WSix/W多層結構來進一 步提升對金屬銅的擴散障礙效果。再者，對於以濺鍍法之鉭膜及氮化鉭膜對金屬銅的阻障 能力亦加以探討。最後，我們整合選擇性鎢膜沉積與化學機械研磨之技術，也對於銅膜的 化學機械研磨作初步討論。在化學氣相沉積鎢膜及矽化鎢膜方面，我們發現不同的SiH4/W F6流量比可以得到不同的鎢膜晶相。在沉積溫度為300℃及沉積壓力為100mTorr的條件下 ，α-W 晶相鎢膜與非晶相矽化鎢膜可分別在SiH4/WF6流量比小於一與大於二之沉積條件 下得到。在矽化鎢膜的薄膜特性方面，我們發現在SiH4和WF6流量分別為每分鐘6毫升合2 毫升及沉積壓力為12mTorr之條件下，矽化鎢膜的沉積活化能約為3千卡/莫耳，且沉積所 得之WSix膜具有低應力、低電阻率及優異的步階覆蓋性等特點。 在銅的擴散障礙層研究方面，我們首先探討以矽化鎢膜作為銅和矽基板之間的擴散障礙 層之高溫穩定性，其中矽化鎢膜係以化學氣相沉積法沉積所得。研究結果顯示，以矽化鎢 膜充當銅的擴散障礙層，可使Cu/WSix(50 nm)/p+-n二極體的高溫穩定性達500℃。對矽化 屋鎢膜作氮氣電漿處理，可進一步提昇擴散障礙層的熱穩定性，使所得之Cu/WSiN/WSix/W /p+-n二極體的高溫穩定性提昇到600℃以上。再者，如以選擇性化學氣相鎢膜沉積法在元 件工作區的窗口內填充一層450 nm厚度的鎢膜，然後再作矽化鎢膜沉積及氮氣電漿處理而 製成Cu/WSiN/WSix(75 nm)/W(450 nm)/p+-n結構的二極體，則其高溫穩定性可達700℃以 上。 最後， 我們整合選擇性鎢膜沉積和化學機械研磨技術，將選擇性鎢膜沉積所可能發生的選擇性損 失以及填充管洞造成之鎢膜溢出，以化學機械研磨法去除，完成ULSI多層金屬連線所需之 平坦化。此一新穎技術，不但可以提高產能，還可以降低研磨墊的損耗、減少研磨漿消耗 ，從而降低稱成本。在銅膜的化學機械研磨方面，初步的研究結果顯示：研磨漿中氧化劇 的種類及濃度對銅膜之腐蝕速率、研磨速率、及表面粗糙度皆具重大影響。

This thesis studies the properties and thermal stability of chemically vapor deposited (CVD) W and WSix films. In addition, barrier capability of the W and WSix films used as diffusion barrier between Al and Si substrate as well as Cu and Si substrate are investigated, and the effects of in-situ N2 plasma treat- ment on the barrier efffectiveness of the W and WSix films are also evaluatd.F urthermore, a WSiN/WSix/W stack-layer structure is proposed to further improv- e the barrier capability against Cu diffusion For compaarison, barrier proper- ties of sputtered Ta and TaN films used as barriers are also investigated. Fi- nally, a noval process thst combines selective CVD-W with chemical mechanical polishing of W (W-CMP) technique is developed; moreover, an initial study of C u-CMP is also included. To start with, properties of W and WSix films chemical ly vapor deposited (CVD) at various deposited temperatures, chamber pressure, and SiH4/WF6 reactant gas flow ratios are investigated. It is found that the a -W phase and amorphous WSix phase can be obtained by the SiH4 reduction of WF6 with SiH4/WF6 flowratio lower than 1 and higher than 2, respectively. For the WSix deposition process with a SiH4/WF6 flow rate higher than 2 and a total g as pressure of 12mTorr, the activation energy of the CVD-WSix process is deter mined to be 3.0 kcal/mole. The CVD-WSix film has a low residual stress, low el ectrical resist-ivity, and excellent step coverage. For the applications of CV D-WSix layers as diffusion barrier against Cu diffusion, the thermal stabil-it y of Cu/WSix(50 nm)/p+-n junctions is investigated, in which the WSix layeris depo+-n junction diodes heir composition and is decreasing with SiH4/WF6atio f or the ratiosgreater than 3. For the amorphous WSix barrier layers deposited w ith the SiH4-/WF6flow ratio of 3, the Cu/WSix(50 nm)/p+-n junction diodes are able to sus-taina 30 min thermal annealing at temperatures up to 500 C without causing degradation to the electrical charateristics. With an in-situ N2 plas ma treat-ment applied to the WSix barrier, the Cu/WSiN/WSix(50 nm)/p+-n juncti on diodesare able to remain inact up to at least 600 C. To improve the barrier capability against Cu diffusion, the use of selective CVD-W(450 nm) layres as well as WSiN/WSix(75 nm)/W(450 nm) stacked-layers are investigated. It is fou- nd that the Cu/W(450 nm)/p+-n junction diodes are able to sustain a 30 min fu- rance annealing up to 650 C without causing degradation in electrical charact- eristics. The use of WSiN/WSix/W stacked-layers as diffusion layers further im prove the thermal stability of Cu/WSiN/WSix/W/p+-n junction diodes up to at 70 0 C. Finally, chemical mechanical polishing (CMP) of W and Cu is investigated. A novel process that combines CMP technique with selective CVD-W is used to r- emove nail heads due to W overgrowth and W-particles on the surface of dielec- tric due to selectivity loss. This novel process not only improve the through- put of W-CMP dramatically, but also extends the pad lifetime and reduce the consumption of slurry; thus, the process cost of W-CMP can be reduced. Copper chemical mechanical polishing (Cu-CMP) is investigated using slurries conyain- ing Al2O3 abrasive and various types and concentrations of oxidizer. The resu- lts of this study indicate that the corrosion rate, polishing rate and surface roughness of copper films are sensitively dependent on the type and concentra- tion of oxidizer.