超臨界二氧化碳應用在半導體製程及場發射元件上之研究

Abstract

本論文研究低介電常數材料HSQ (hydrogen silsesquioxane)薄膜與超臨界二氧化碳流體 (Supercritical CO2 fluid)在積體電路製程整合的技術和可靠性分析。在傳統的多層導體連線微影製程中，去除光阻的步驟是無法避免的，而在去除光阻的過程中，氧電漿灰化是主要的製程方法，但此製程會造成低介電常數材料特性的劣化。實驗中發現對於硬烤過的光阻，超臨界二氧化碳流體在適當條件下具有去除能力，且製程中僅需使用少量的溶劑。相對於氧電漿處理，本製程對低介電常數材料的影響較小，具有較小的介電常數和漏電流的改變，在可靠度上超臨界二氧化碳流體制程更是在電性上明顯優於氧電漿處理。可預期地，超臨界二氧化碳流體的特殊特性將使其在積體電路製程整合中具有其優勢。另外，在以HSQ為低介電材料的實驗中，研究另一套利用Trimethylchlorosilane (TMCS)對氧電漿灰化過的HSQ作後續處理，透過化學鍵結的方式，對薄膜作修補的效應，使其介電常數及漏電流回復接近理想的數值。此外，在最後一個研究中將利用超臨界流體的物理特性，對奈米碳管(CNTs)作後續的清潔動作，以降低CNTs對水氣的吸收，與傳統加熱的方法相較，利用超臨界流體可更有效提升CNTs的場發射效應。

In this thesis, we will investigate on reliability and process integration of low dirlrctric constant material HSQ (hydrogen silsesquioxane) and Supercritical CO2 fluid. In the traditional lithography process for integrated circuit manufacture, photoresist removal step is an inevitable process. O2 plasma ashing is the main method to remove the photoresist during photoresist stripping process. In the experiment, we confirm that hard-baked photoresist can be stripped by supercritical CO2 fluid in the special condition, and it needs a small amount of solvents in the process. Comparing with oxygen plasma treatment, the process has little impact on HSQ film, and has little change in the dielectric constant and leakage current. On the reliability, the electrical properties of supercritical CO2 fluid process are better than that of O2 plasma ashing process. With the excellent characteristic, supercritical CO2 fluid will has the advantage to integrate into the IC manufacturing processes. Since O2 plasma ashing and chemical wet stripper are commonly performed to remove photoresist (PR) in integrated circuit fabrication. However, O2 plasma or wet stripper will attack function groups and cause Si–OH group formation in HSQ film during PR removal processing. The Si–OH groups often lead to moisture uptake and consequently dielectric degradation will occur in HSQ film. Trimethylchlorosilane (TMCS) treatment can negate the damage in the HSQ film after the PR removal process. In addition, chemical TMCS can react with Si–OH groups and reduces moisture uptake so that the dielectric characteristic of HSQ can be maintained. Besides, supercritical carbon dioxide (SCCO2) fluids technology is studied to reduce the moisture adsorbed in CNTs, and compared with traditional thermal annealing process. Experimental results have demonstrated field emission enhancement of CNT emitters is effectively achieved by the SCCO2 treatment compared to the heating process, due to minimizing residue moisture uptake in CNTs.