交流偏壓對鑽石成核影響之研究

Abstract

本實驗以交流偏壓輔助成核在微波電漿化學氣相沉積設備中合成鑽石膜於單晶矽 (100) 之基材上，主要探討交流訊號對鑽石成核是否有異於一般負偏壓之效果。藉由掃描式電子顯微鏡 (SEM)、原子力顯微鏡 (AFM)、穿透式電子顯微鏡 (TEM)、Raman 光譜儀等分析技術，試圖瞭解交流偏壓成核成長鑽石膜後在高方向性鑽石 (highly oriented diamond，HOD) 的比例、鑽石膜均勻性以及鑽石品質上的表現是否獲得改進。 實驗中先以一般負偏壓所能達之最佳偏壓成核參數 (2 % CH4/-200 V bias/17 min) 做為對照組，並以此參數同時加上交流訊號成核成長鑽石膜。從交流偏壓大小及時間的變化之實驗中發現2 % CH4/-200 50 V/21 min，可以得到31% HOD。從 DC BEN 及 DC/AC BEN 這兩組結果互相比較，觀察到加上交流訊號對於鑽石成核的情況在 HOD 及均勻性的表現上與一般負偏壓比較，只有少許的改進。以 TEM 觀察介面情況發現鑽石核種與基材間存在一層與基材有磊晶關係的 □-SiC，與一般負偏壓成核的情況相仿。磊晶之鑽石核種呈現尖錐狀，具有 {111} 之晶面，經過成長過程，發展成側向尺寸較大且表面為 {100} 晶面之鑽石晶粒。另外，在研究中我們可以發現的是，交流訊號可大幅增加最佳偏壓時間的範圍，並且明顯的減少 sp2 鍵結之碳含量，對鑽石品質有正面的影響。

In this work, diamond films were synthesized on silicon (100) substrate by microwave plasma chemical vapor deposition (MPCVD) via bias-enhanced nucleation (BEN) using direct current (DC) with alternating current (AC) on Si (100) substrate. Examination of the highly oriented diamond (HOD) percentage, uniformity and quality of the diamond films in comparison with those synthesized via DC bias were carried out using scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Raman spectrometry. It is found that the optimum condition for DC bias enhanced nucleation (BEN) is performed with 2 % CH4 concentration at the bias voltage of -200 V for 17 min, which produced 28 % HOD. The DC BEN pretreatment simultaneously added with AC biasing (60 Hz frequency and AC voltage of 35.4 Vrms, 50 V peak to peak) for various time with 2 % CH4 concentration were employed for diamond deposition. It is shown that 31% HOD can be reached, which have slight increase over those synthesized by the DC BEN. However, the Raman spectra shows that the amount of sp2 carbon species in the diamond films with AC biasing have significantly decreased, implying better film quality. Also application of the AC biasing allows the wider range of bias time for diamond deposition of similar HOD and uniformity. TEM examination shows that epitaxial □-SiC exists at the interface between the diamond nucleation and Si substrate. The epitaxial diamond nuclei have pyramid-like morphology with {111} facets, and evolve into surface morphology of rectangular shape with larger lateral size during the following growth.