製程氣氛與活性金屬鍍層對硬焊合金在鑽石上擴展能力之影響

Abstract

本實驗採用微波電漿化學氣相沉積法,以CH4/H2為反應氣體,使用 Si(100) N-type之Si晶片作底材,並變化沉積時間,CH4/H2濃度,微波功率, 進行鑽石膜之沉積,以 -step,SEM,XRD,Raman光鑑定鑽石之品質及其特性, 利用E-gun在鑽石膜表面鍍上活性金屬鍍層(Ti,Cr,Mo,Ni),進行硬焊合金( Ag-Cu-Ti,AWS-BAg-4,BAg-5,BAg-22)擴展能力之研究.就鑽石膜表面粗糙 度,加熱溫度,持溫時間和預度介層等參數,探討微波加熱法與電阻加熱法, 不同環境氣氛下,硬焊合金在鑽石膜表面擴展能力之影響.針對鑽石膜與硬 焊合金之界面及破裂面進行EDX分析.並利用示差熱分析(DTA)進一步瞭解 硬焊合金與鑽石膜間之反應性. 實驗結果顯示,在微波電漿系統中,鑽 石膜對AWS BAg-4,BAg-5和BAg-22三種硬焊合金之擴展能力分別約為0.603 ~0.823 cm2/g , 0.257~0.366 cm2/g和1.30~1.61 cm2/g.顯示Ag-Cu-Ti合 金在鑽石膜表面具良好之擴展性.主要歸因於Ti元素與鑽石間良好的潤濕 性,且Ti原子可提供d-層軌域空位與碳形成混成軌域. 結果亦顯示擴展 能力與鑽石膜表面粗糙度,溫度,持溫時間有密切的關係,擴展能力隨著粗 糙度增加至一最大值,然後遞減再趨於定值.在粗糙度約1000A左右,可得最 佳擴展特性(22.5cm2/g);主要歸因於毛細作用與粗糙度的影響效應.就溫 度與持溫時間的影響,結果亦顯示Ag-Cu-Ti硬焊合金在鑽石膜之擴展能力, 隨溫度與持溫時間的增加而增加,至最大值後,逐漸下降而後趨於定值.一 般而言,熔融合金隨著溫度升高流動性越佳,且需要足夠的時間才能讓熔融 合金擴展到平衡位置.然而在長時間高溫加熱情況下,會使鑽石膜品質下 降.而氣氛中之氧含量亦會影響鑽石膜之品質,並與硬焊合金中的活性金屬 產生氧化作用.在5分鐘持溫時間下,900C可得最佳之擴展能力(24.2 cm2/ g).在850C下,15分鐘可得最佳的擴展能力(23.9 cm2/g). 就加熱方法 而言,結果顯示用電阻式加熱法比起微波電漿加熱法Ag-Cu-Ti之擴展能力 顯著下降.這是因為電阻加熱法是在大氣下用Ar-3%H2氣氛保護之,氧的含 量明顯較高所致. 就介金屬膜的影響,Ag-Cu-Ti硬焊合金對於鑽石膜預 鍍不同金屬膜(Ti,Cr,Ni,Mo)後之擴展能力,分別為13.2 cm2/g , 10.5 cm2/g , 9.18 cm2/g 和7.42 cm2/g , 顯示比起沒預鍍的情形明顯下降. 且對於AWS BAg-4,BAg-5和BAg-22硬焊合金亦無明顯改善趨勢,這可能歸因 於加熱氣氛的氧分壓太高,使得這些金屬膜產生氧化作用所致. 就Ag- Cu-Ti硬焊合金與鑽石膜的相互反應,X-ray繞射圖譜顯示形成TiC鍵結,且 經EDX分析確實發現Ti元素聚集在鑽石膜和硬焊合金之介面,其他合金元素 亦發現有相互擴散之情形.DTA圖譜亦顯示合金及鑽石膜之間有反應的跡 象.這顯示Ag-Cu-Ti將是良好的硬焊合金材料兼具優良的鍵結,潤濕性和擴 展能力. Diamond films were deposited on N-type Si(100) substrates by microwave plasma chemical vapor deposition (MPCVD) system with CH4 and H2 as the reactantgases. Diamond films were characterized by -step , SEM , XRD and Raman Spectroscopy. A layer of metal films (Ti , Cr , Ni or Mo) was deposited byan E- gun system on some of the diamond films to determine its effect on spreadingability of brazing alloys. The various film interfaces of the specimens wereexamined by EDX. The possible interactions between diamond film and brazing alloy were investigated by a differential thermal analyzer (DTA). The spreadingexperiments were carried out in a furnace with resistance heating or microwaveplasma heating. The experimential results indicate that the spreading under microwave plasmaheating atmospheres for AWS BAg-4,BAg-5 and BAg-22 brazing alloys are rangingfrom 0.603~0.823 cm2/g , 0.257~0.366 cm2/g and 1.30~1.61 cm2/g , respectively.The corresponding spreading abilities for Ag-Cu-Ti alloys have a better spreadingability. This is due to the fact that Ti atoms have good wettability with diamond, and the imcomplete d-shell of Ti atoms can interact with outer electrons ofcarbon atoms to form the hybrid orbital. The results also reveal that the spreading ability of Ag-Cu-Ti brazing alloyis depending upon the surface roughness of diamond films , heating temperatureand time. The spreading ability increases with the surface roughness up toa maximum value and then decreases slightly down to a constant value. This mayresult from the effects of capillary reaction with the surface roughness. The spreading ability also have a tendency to increase with the heating temperatureand the holding time up to a maximum valve , and then decreases slightly down toa constant value. It is well known that the fluidity of the melt increases withdegree of superheating , and there is a minimum time required to let the melt toreach the equilibrium position. However , at higher temperatures and longer times, the quility of diamond films will be declined by interactions with oxygen inthe heating atmosphere , and oxygen may also interact with active metals in the brazing alloy to form oxides. At 5 min holding time , the spreading ability at900C (24.2 cm2/g) was the best one. At 850C , the spreading ability after 15 minholding time (23.9 cm2/g) was also the best one. By comparing microwave plasma heating and resistance heating methods , theresults show that the spreading abilites of Ag-Cu-Ti brazing alloys are much smaller for resistance heating method. This is due to the fact that the atmospherefor resistance heating furnace is Ar-3%H2 under one atm. pressure , which has a significant higher oxygen content. In terms of interlayer effects , the spreading abilities of Ag- Cu-Ti brazingalloy on diamond films precoated with a layer of metals are ranging from 13.2 cm2/g, 10.5 cm2/g , 9.18 cm2/g and 7.42 cm2/g , for diffrent interlayer metals (Ti,Cr,Ni,Mo) , respectively. It is obvious that the interlayer metal films are deterimential to the spreading ability. This may be due to the fact that the activeinterlayer metals are in pure state which has the highest activity , so that easyto reach with oxygen in the atmosphere. As for interactions between diamond films and Ag-Cu-Ti brazing alloys , theresults of X-ray diffraction analysis show TiC compound formation. This is inagreement with the EDX analysis that Ti atoms are accumulated around the diamondfilm-brazing alloy interface. DTA analysis also indicates a strong exothermic reactions between them. Threrfore , it is concluded that Ag-Cu-Ti alloys will bea good candidate for brazing alloys , pocessing good bonding , wettability andspreading ability.