X光圖罩多矽氮化矽鼓膜與鎢─鉭─氮吸收層之應力控制

Abstract

X光微影具有解像度佳（線寬0.05微米或更小）、聚焦深度長、繞射現象小、幾無基材反射、幾無駐波效應及曝光範圍大等優點，未來製備1Gbit DRAM（線寬要求0.18微米）主要技術之一。X光微影中，圖罩製備為主要關鍵技術。本論文重點在研製低應力X光圖罩，以多矽氮化矽(Silicon-Rich Nitride)為鼓膜並以鎢-鉭-氮(W-Ta-N)做為X光之吸收層。 由於氮化矽(Si3N4)薄膜應力過大，並不適合做為圖罩鼓膜，因此，藉由增加氮化矽薄膜中之矽含量，降低氮化矽薄膜應力，做為X光圖罩鼓膜。本文利用低壓化學氣相沈積系統(LPCVD)，調變其沈積氣體流量比率、沈積溫度、沈積壓力，以製備低應力、可供光學對準之高光學透光率之多矽氮化矽鼓膜。實驗結束在SiH2Cl2/NH3＝98/22 sccm、溫度900℃、壓力160mtorr條件下得到低張應力多矽氮化矽薄膜(+50MPa)。 利用濺鍍系統濺鍍鎢、鉭，並通入氮氣，製備X光圖罩吸收層，可避免純鎢及純鉭薄膜應力隨時間改變之缺點。在直流功率，鎢150W、鉭250W，濺鍍氣體Ar/N2＝50/10sccm，反應腔壓力4mtorr條件下，濺鍍後鎢-鉭-氮(W-Ta-N)薄膜應力約在-250 MPa左右，經過250℃半小時的回火，可將應力調整在約+20MPa。此鎢-鉭-氮薄膜應力穩定，並在200℃升降溫重複三次，應力依然不改變。 本論文實驗控制X光圖罩鼓膜及吸收層應力，並建立完整之X光圖罩製程。

X-ray lithography has the advantages of better resolution (limited at 0.05 um and below), larger depth of focus, less diffraction effect, nearly no substrate reflection, nearly no standing wave, and larger exposure area etc. X-ray lithography will be one of the major technologies to fabricate IGbit DRAM (design rule 0.18 um) in the future. In x-ray lithography, mask fabrication is the key issue. This thesis studies the fabrication low stress x-ray mask. Using silicon-rich nitride as membrane and W-Ta-N allov as absorber. The stress of silicon nitride(Si3N4) is too large to be used as membrane of x-ray mask, hence, by increasing the amount of silicon in silicon nitride the stress could be reduced. Using low pressure chemical vapor deposition (LPCVD) system to deposit silicon-rich nitride, the ratio of gases flow, temperature and pressure of chamber were modified to fabricate low stress, high optical transmittance membranes. Under SiH2Cl2/NH3=98/22 sccm, temperature 900℃, pressure 160 mtorr, low tensile stress of silicon-rich nitride membrane around 50 MPa was obtained. Sputtering W, Ta in the present of N2 gas to fabricate x-ray mask absorbers can prevent from the problems of unstable W or Ta thin film stress changing time by time. Under DC power, tungsten 150W, tantalum 250 W, sputtering gases Ar/N2=50/10 sccm, chamber pressure 4 mtorr, the film stress is around -250 MPa, after annealing in 250℃ half an hour, W-Ta-N stress reduced to about +20MPa. The alloy thin film could keep about the same stress after rising to 200℃ three times. In this thesis the control of the stress of membrane and absorber and the fabrication processes of x-ray mask were accomplished.