潔淨室凝結性有機污染物之晶圓表面吸附沈積行為探討

Abstract

半導體產業已成為我國最重要的經濟發展產業，其中積體電路製造技術的快速發展，使我國早已躍升成為世界晶圓代工重鎮之一，然而當製程的關鍵線寬尺寸突破0.1微米而正式進入奈米等級之際，傳統針對微粒污染控制所設計之潔淨室將無法符合氣態分子污染物之潔淨需求，其中凝結性有機分子污染物質(organic airborne molecular contaminants)一旦沈積吸附於晶圓表面，將導致元件缺陷與製程良率下降。 本研究利用自動熱脫附氣相層析質譜儀(ATD-GC/MS)來完成半揮發性高沸點有機污染物之微量分析技術開發、並進行環境濃度與晶圓表面之污染偵測技術與潔淨室內材質之釋氣分析探討，以了解常見凝結性有機分子污染之種類、濃度大小與其潛在污染來源。其中針對半揮發性高沸點有機污染物(DEP、DBP)分析，本研究在環境中採樣體積為0.1 m3時，其偵測極限約可達0.05 □g m-3;而在六吋(150-mm)晶圓上，其表面沈積密度之偵測極限可達0.03 ng cm-2。 藉由微環境(mini-environment)晶圓曝露實驗，本研究亦完成凝結性有機物表面沈積量與環境濃度、曝露時間、晶圓表面狀況、污染物種吸附特性等各項參數之關係探討，並建立單一物種之凝結性oAMCs表面吸附沈積動力模式，來描述凝結性oAMCs於表面沈積吸附行為。研究結果顯示較高分子量之凝結性oAMCs具有較大之吸附能力;而較低分子量之凝結性oAMCs則在曝露初期具有較高之吸附速率，故在短曝露時間內，其吸附沈積量將大於較高分子量之凝結性oAMCs，因此在微污染的控制上，較低分子量之凝結性有機物質，將成為短時間曝露時主要污染控制對象。此外，利用吸附沈積動力模式計算，將獲得晶圓於製程中最大允許濃度或最大可曝露時間建議值，此結果可提供國內半導體相關產業在解決日漸嚴重oAMCs問題與發展微污染控制技術之參考。

Semiconductor industry has been a central figure to the economic growth in Taiwan, especially for the fabrication sector of integrated circuit (IC) that has evolved into world-leading status. The fabrication technology advances so far that the feature size (or critical line-width) of IC devices has now broken the 0.1 □m barrier and into the nano-scale age. This progress discloses that the traditional definition of a “cleanroom” environment may become increasingly inadequate because prevention of particulate contamination may no longer be a critical issue. As the condensable organic airborne molecular contaminants (oAMCs) depositing on wafer surfaces, it results in deterioration on device performance and reduces semiconductor device yield.

Using auto thermal-desorption coupled with a gas chromatography- mass spectrometry (GC-MS) instrument, an analytical technique for trace quantity of semi-volatile high boiling-point organic compounds was developed. The analytical methods for the determination of ambient oAMC concentrations and their surface density on wafer surfaces, as well as the outgassing analyses of materials used in the cleanroom, were also evaluated. The analytical method for the trace analyses of the target contaminants, namely diethyl and dibutyl phthalates, was capable of achieving detection limits of 0.05 □g m-3 for 0.1 m3 air samples and 0.03 ng cm-2 for 150-mm wafer surface density in this study.

The correlations between surface density, ambient concentration, exposure duration, and wafer surface preparation were determined from the wafer exposure studies in mini-environment. The deposition kinetics of single compound (DEP or DBP) was also developed. The results revealed that the condensable oAMCs with relatively higher molecular-weight possess greater sticking capability or potential, while those with relatively lower molecular-weight generally have greater adsorption rate at the initial exposure stage. Consequently, for short exposure time the lower molecular-weight condensable oAMCs may be a more important contamination problem than the higher molecular-weight condensable ones.

The suggested threshold limits for the allowable maximum ambient concentrations and wafer exposure times were proposed based on the deposition kinetics and simulation. The results provide practical information on resolving the progressively device deterioration caused by the oAMCs contamination, and on the development of control technologies for micro-contaminants in semiconductor cleanrooms.