高含氮量的極薄含氮氧化層的再氧化行為以及高氮靠近含氮氧化層表面之介電層技術開發

Abstract

本論文主要探討高含氮量的極薄含氮氧化層的再氧化行為，同時開發在氧化層表面形成具有高含氮量分佈的極薄含氮氧化層的製程。 極薄、高含氮的氮氧化層在快速升溫系統(RTP)下，配合氧化亞氮(N2O)以及純氧(O2)輪流再氧化的結果，發現到：(1) 不同氮化溫度下形成的氮氧化層，經由N2O以及O2再氧化結果，發現N2O的再氧化速率與氮氧化層的氮化溫度並無明顯的關聯，然而O2的再氧化的速率卻會隨著氮氧化層的氮化溫度而有所差異－氮化溫度越高，再氧化速率越慢－這暗示意味著可藉由選用適當的氮化溫度來達成控制成長極薄含氮氧化層的厚度； (2) 以N2O進行再氧化的實驗中，發現氧化層厚度呈現放射狀不均勻的現象，其位於晶片中間的部份較薄，而位於邊緣的部份較厚；(3) 輪流交互使用N2O以及O2進行對高含氮的極薄氧化層的再氧化過程中，當高含氮的極薄氧化層的厚度大約小於60埃的範圍內，N2O的再氧化速率在晶片的同一位置上是固定不變，但在其他位置上卻有所不同。氧化的次數增多時，以O2進行再氧化的氧化速度會呈現加速動作。對於上述多種現象的解釋機制如下: RTP下所成長之氧化層其厚度先天就呈現中間薄而邊緣厚，此乃由於熱應力所致，尤其當使用N2O作為氧化劑時，因N2O的放熱反應結合RTP的熱應力效應，更加劇氧化層厚度放射狀的不均勻現象。此外由於N2O的放熱反應易使N2O所產生的原子氧(atomic oxygen)在位於晶片中間的含量較低，加上原子氧的氧化行為不受限於氧化層內的含氮量，因此在含氮氧化層的厚度大約小於60埃時，其氧化速度幾乎是固定的。然而原子氧具有移走含氮氧化層中的氮的能力，因此當氧化次數增多時，氮原子的逐漸空乏促成後續以O2執行再氧化時，其氧化層成長速率會隨之增快。 高含氮量分佈的極薄含氮氧化層的製程建立在將化學氧化層(chemical oxide)先以NH3作氮化(NH3 nitridation)處理，隨即以O2作再氧化處理，藉此可將高濃度的氮原子累積在靠近含氮氧化層的表面處。其特色在於能以低的熱預算(low thermal budget)得到高品質的極薄含氮氧化層，同時兼具低介面陷位密度、低電性應力誘發漏電流效應、高時依性介電崩潰以及良好的抗硼穿透的能力等特性。本製程不僅簡單且匹配於現行的製程技術，對於閘極介電層製程開發的半導體業界，將會有極大的參考價值。

In this dissertation, we report that reoxidation behavior of high-nitrogen ultrathin oxynitride in rapid thermal process (RTP). Simultaneously, we develop a novel process to grow robust ultrathin oxynitride with high nitrogen content close to its surface. Reoxidation experiments on high-nitrogen ultrathin oxynitride, which is formed by thermally nitridizing a chemical silicon oxide with pure ammonia, are conducted using an alternation of nitrous oxide and oxygen gas in rapid thermal oxidation (RTO). The new finding herein is the zig-zag characteristic of the oxidation rate by O2 and N2O. It is clear that the N2O oxidation rate is almost independent of the concentration of nitrogen in oxynitride through out the rapid thermal oxidation process, but the O2 oxidation rate is decreased as nitrogen content increased. Furthermore, non-uniform thickness of oxynitride was also observed after N2O gas treatment. Particularly, the thickness is thinner in the center part of the wafer instead of at the edge of the wafer. It should be noted that O2 gas does not produce the same results. Any conventional oxidation model based on simple bulk diffusion and/or surface reaction mechanisms simply would not do it. The non-uniformity of N2O gas reoxidation can be explained by combining a mechanism with radial thermally induced stress, exothermic N2O oxidation and depletion of atomic oxygen. Finally, we have proposed an approach for growing robust ultrathin oxynitride, including NH3 nitridation of chemical oxide and reoxidation with O2. In this method, we obtain oxynitride with high nitrogen concentration (≈13 at.%) on the top and low interface state density (Dit=2×1010 cm-2 eV-1). The films demonstrate excellent properties in terms of low leakage current, high endurance in stressing and superior boron diffusion blocking behavior. This process does not involve any additional capital equipment. In addition, it obtains high-quality oxynitride film with low thermal budget. Most importantly, this process is simple and fully compatible with current process technology. It would be important and interesting to the process engineers who engaged in the field of gate dielectrics.