|Abstract: ||本研究係以砷化鎵為基板之無阻絕層銅製程之製備與性質研究。於無阻絕層砷化鎵基板上,以射頻磁控濺鍍法濺鍍銅膜,以及共濺鍍摻雜鉭,釕,氮之銅合金薄膜,經不同溫度(300~550C)及不同時間(15分~1小時)之真空退火,以低掠角X光繞射儀,與X光繞射儀確認薄膜結晶結構,以X光光電子能譜儀去鑑別銅合金薄膜之元素的化學鍵結能,並以四點探針及測量薄膜之片電阻值,以聚焦離子束儀(FIB) 觀察界面變化。同時,藉由掃瞄式電子顯微鏡(SEM)及穿透式電子顯微鏡(TEM)觀察薄膜的顯微結構。 銅與微量不互溶元素共濺鍍在薄膜中,此微量不互溶元素可抑制晶粒成長與再結晶,進而改善高溫熱穩定性。鉭已廣用於半導體界作為被動元件的材料,釕的電阻比鉭小,具有更好的熱穩定性,最近一直被用來作為研究具有挑戰性的新材料.這也是本研究選為研究對象的原因。 由實驗結果發現, Cu(TaNx)/GaAs之結構有較佳之熱穩定性,純銅膜結構(Cu/GaAs)之熱穩定性只能持續到350C一小時的退火,而摻雜TaNx 之銅膜結構能夠耐高溫到450C一小時的退火,此結果顯示微量TaNx 在薄膜中扮演一個非常重要而且關鍵性的角色。更進一步發現,Cu(RuTaNx)/GaAs的熱穩定度可達 500C。 ㄧ般而言,金屬薄膜與半導體的異質接面是具有蕭特基位障,若去測量其I-V曲線,具有類似二極體特性,當Cu(RuTaNx)/GaAs經550C退火10分鐘, 其I-V特性曲線則呈現類歐姆接觸曲線,在能量散佈光譜儀(EDS)及穿透式電子顯微鏡(TEM)觀察薄膜的顯微結構發現有一層Cu3Ga的類歐姆接觸層存在。 更進一步的研究發現,共濺鍍定量的鍺(Ge)在Cu(RuTaNx)薄膜中,而形成Cu(RuTaNx)-Ge/GaAs的結構中,經300C退火15分鐘可形成歐姆接觸,這提供了在砷化鎵產品ㄧ個實際應用之可行性。|
Barrierless copper metallization on GaAs was conducted and the film structure thus obtained characterized. Pure Cu films and Cu doped with Ta, Ru, and N were co-sputtered by R.F. magnetron sputter deposition on barrierless GaAs, followed by post-annealing for 1 hour at various temperatures (300~550C). As confirmed by X-ray diffractometry, X-ray photoelectron spectroscope (XPS), and electrical resistivity measurements made using the four-point probe method. The cross-sectional microstructure of the films was analyzed using a focused ion beam (FIB), and the microstructure of films was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Doping pure Cu film with a small amount of insoluble substances inhibits recrystallization and grain growth, improving thermal stability. Tantalum (Ta) has been adopted as a passive element in semiconductor manufacture for a long period. Ruthenium (Ru) has a lower resistivity than Ta and better thermal stability. Accordingly, several researchers have recently been using Ru. Hence, both Ta and Ru were used in this study. Experimental results reveal that Cu(TaNx) films has better stability than pure Cu. The pure Cu film on GaAs was stable up to 350C for 1 hour annealing. The Cu(TaNx) film on GaAs was more thermally stable up to 450C for 1 hour annealing. The improvement in thermal stability achieved by doping a minor amount of TaNx into Cu was confirmed and it plays a key role in this result. Afterward, in further developed, the thermal stability of Cu(RuTaNx)/GaAs structure can be up to 500C. In general, a metal film in contact with a semiconductor forms a heterojunction with a Schottky barrier. Whose I-V curve is similar to that of a diode. The I-V curve of the Cu(RuTaNx)/GaAs after annealing at 550C for 10 min is that of a quasi ohmic contact. The quasi ohmic contact formed between the Cu(RuTaNx) film and the GaAs substrate as a layer of Cu3Ga as confirmed in TEM and energy dispersive spectrometeric (EDS) analyses . In this study, co-sputtering germanium (Ge) in the Cu(RuTaNx) film yield the Cu(RuTaNx)-Ge/GaAs structure, forming an ohmic contact was formed after annealing at 300C for 15 min. The results of this study can be feasibly applied to some GaAs devices.