製程參數對複晶矽TEOS介電層特性之影響

Abstract

近來，文獻指出要在成長於複晶矽上得到更可靠性的介電層可以利用沈積方式替代熱成長的方式得到。由於位於在複晶矽內的缺陷沒有併進去沈積介電層裡，且複晶矽表面沒有更粗糙化(起因於沒有複晶矽被消耗)[1]。因此。這沈積的中間介電層潛在擁有的缺陷密度是相對於底層複晶矽是無關的。在所有化學氣相沈積過程中，比較於以SiH4為主的化學氣相，利用tetraethylorthosillicate的分解被指出是最簡單和最安全沒有危險的材質。 在此論文中，我們探討利用N2O或N2氣體快速熱火的TEOS介電層特性和利用離子佈值進去底層複晶矽電極以氟化的TEOS介電層特性。 對於非發性記憶體，為了擁有好的資料儲存特性，具有低導電性和高的崩潰電壓是一當前的課題。為此，特利用N2O與N2氣體以不同溫度快速熱火處理化學氣象沉積的TEOS介電層。以此方法得到的複晶矽介電層，實驗結果顯示有著低漏電流，高的崩潰電壓，較低的電子捕獲率，及較高的崩潰電荷。 這些改善是因氮於介電層和介電層與複晶矽介面所造成得結果[2-11]。更進一步地，對於接受N2O(二氧化氮)氣體快速熱火比接受N2(氮)氣體快速熱火的有更佳得改善。這可能起因於N2O氣體熱火處理的氧原子可以修補懸浮鍵和有張力的鍵。 對於利用氟原子的離子佈值於底層複晶矽然後藉由熱火以得到的氟化TEOS介電層也被作了探討。發現這氟化過的介電層在正負偏壓下都呈現出低的漏電流與高的崩潰電壓特性[12-18]。這改善起因是氟原子的進入介電層與介面可以夠與懸浮鍵且可以破壞有張力的Si-O-Si鍵以形成較強的Si-F鍵[18-20]。同時也造成局部的應力的被釋出，所有會有較平坦的複晶矽表面。然而，氟化的介電層卻有高的電子捕獲率。這也暗示說在固定電流密度入射下，氟化的介電層有較多的電子被捕獲。雖氟化的介電層有較高一些的電子捕獲率，但其仍有較高的崩潰電荷。這可能是由於有較強的Si-F鍵的關係。

Recently, it is reported that more reliable dielectrics grown on the polysilicon can be obtained by using deposited instead of thermally grown dielectrics. Since defects located in the polysilicon are not incorporated into the deposition dielectric and the surface of the polysilicon layer is not roughened (due to no polysilicon consumption)[1]. Hence, the deposition dielectric potentionally has a defect density relatively independent of the bottom polysilicon. Among all the CVD process, the decomposition of tetraethylorthosilicate (TEOS) is reported to be the simplest and safest without any dangerous media in the process as compared with the Silane-based CVD. In this thesis, we investigated the properties of TEOS interpoly dielectric layers with N2O/N2 rapid thermal anneal and characteristics of fluorinated TEOS interpoly dielectrics through ion implantatiom into bottom polysilicon electrode. In order to obtain good data retention characteristics for nonvolatile menory, the interpoly dielectrics with low conductivity and high breakdown fileds have long been sought. Therefor, the characteristics of interpoly dielectrics deposited by pyrolysis of tera-ethyl-ortho-silicate (TEOS) instead of conventional thermal oxide layers with N2O or N2 RTA treatment have been investigated. The dielectrics were subjected to viscous rapid thermal N2O or N2 annealing temperature. Experimental results showed that the dielectrics with N2O or N2 RTA treatment exhibit desirable properties such as lower leakage current, higher breakdown field (Ebd), lower electron trapping rate, and higher charge to breakdown (Qbd). These improvements were due to the incorporation of nitrogen into polyoxide and at the polyoxide/polysilicon interface[2-11]. Moreover, the improvement is more dramatic on samples that received N2O-RTA treatment than those that received N2-RTA treatment. This is believedto be due to oxygen atoms available in N2O RTA tratment can also repair the dangling bonds and strained bonds. The effects of fluorine-incorporation through ion implantation on TEOS dielectric characteristics were investigated, also. It was found that the fluorine-implanted polyoxides had a lower leakage current and a higher electrical breakdown field for both positive and negative bias [12-18]. The improvements were due to the incorporated fluorine could passivate the danging bonds and breakdown the strained Si-O-Si bonds to form stronger Si-F bonds in the polyoxide and at the polyoxide/polysilicon interface [18-20] . This relaxes the local stress in the dielectric and makes the polsilicon/polyoxide interface morphology more smoother. However, they exhibited higher trapping rate. This implied that fluore-implanted polyoxides had higher electron trapping rate during constant current injection. Athough fluorine-implanted polyoxides had higher trapping rate, but they still exhibited higher charge to breakdown. This may be due to stronger Si-F hardly breakdown.