The influence of the modulation efficiency in scanning capacitance microscopy on the observation of p-n junctions

掃描電容顯微術(scanning capacitance microscopy, SCM)是一項藉由電壓調制技術來量測半導體材料電性的分析方法，對於電容變化的靈敏度極高，可用於電子元件與材料的電性分析，例如觀察半導體的p-n接面並量測接面深度、二維載子分布以及等效通道長度等。調制效率是掃描電容顯微術在訊號偵測能力上的一項重要指標，與p-n接面的SCM訊號平衡原理結合，所得的總電容變化關係，有利於討論調制效率對p-n接面深度觀察的影響。在本研究中，藉由調制範圍的增加，探討SCM樣品的載子濃度分布以及表面氧化層與背電極接觸之製備方式對調制效率的影響，並深入觀察調制電壓引致接面偏移的現象。研究結果顯示，由於SCM訊號的非單調性行為，調制效率因調制區域的載子濃度而異，造成接面深度的分析結果隨著調制範圍的擴大而往樣品中的低調制效率區域移動；在相同的氧化層製備條件下，表面氧化層對p型與n型樣品造成的氧化速率也不同，導致p型與n型區域的調制效率差異；不同的背電極接觸矽基板時，因功函數差異也導致p型與n型區域的調制效率差異。藉由探討上述各項變因對SCM調制效率的影響，可以得知調制效率對p-n接面觀察與量測的重要性。With voltage modulation technology, scanning capacitance microscopy (SCM) is a metrology method analyzing electrical properties of semiconductor materials. SCM is extremely sensitive to capacitance variation and capable of electrical analyses of electronic devices and materials, such as observing p-n junctions and two-dimensional carrier distributions in semiconductors, as well as measuring the junction depth and effective channel length in electronic devices. Modulation efficiency (ME) is an important indicator of the signal detection in SCM. Combining the ME with the principle of signal balance at p-n junctions, one can establish the relation between the ME and the change in total capacitance, being helpful for discussing the influence of the ME on the observation of p-n junction depths. In this thesis, I discussed the influence of the carrier concentration distribution, the preparation processes of the surface oxide layer and the specimen contact electrode on the ME by increasing the modulation area. The modulation-voltage-induced junction shifts were also studied. Experimental results showed that the ME varied with carrier concentration in modulated area due to the non-monotonic behavior of the SCM signals. Therefore, the junction depth increased with the modulated area and hence shifted toward the area with a lower ME. With the same oxidation process, the surface oxide layer resulted in different oxidation rates for p-type and n-type specimens, leading to different ME values in p-type and n-type regions. For different electrodes contacting with a silicon substrate, the work function difference between the contact electrode and the silicon substrate leaded to different ME for p-type and n-type regions. According to the discussion on the factors influencing the ME, the importance of the ME to the observations and the measurements of p-n junctions was revealed.致謝 i 摘要 ii Abstract iii 目錄 iv 圖目錄 vii 表目錄 x 第一章 前言 1 1.1研究背景 1 1.2研究動機 3 第二章 文獻回顧 5 2.1淺接面製程 5 2.1.1低能量離子佈植技術 5 2.1.2熱退火技術的演進 5 2.2.掃描電容顯微術 6 2.2.1 p-n接面影像 6 2.2.2光擾現象 8 2.2.3調制電壓與調制效率 10 2.3樣品處理 11 2.3.1樣品氧化層處理 11 2.3.2樣品背電極處理 12 第三章 實驗方法 14 3.1試片結構 14 3.1.1淺佈植p+ / n接面 15 3.1.2圖型化定義 16 3.1.3微波退火處理 17 3.2橫截面樣品 17 3.2.1橫截面氧化層製備 18 3.2.2橫截面背電極製備 19 3.3檢測分析系統 22 3.3.1原子力顯微鏡 22 3.3.2掃描電容顯微術 23 3.3.3導電探針規格 26 3.3.4四點探針片電阻分析儀 26 第四章 結果與討論 28 4.1調制效率與p-n接面 28 4.1.1阻抗比與訊號比 28 4.1.2 p-n接面位置的定義 31 4.2影響橫向接面深度觀察的變因 36 4.2.1載子濃度 36 4.2.2表面氧化層製備方式 39 4.2.3背電極接觸材料 47 4.3影響縱向接面深度觀察的變因 52 4.3.1載子濃度 52 4.3.2表面氧化層製備方式 55 4.3.3背電極接觸材料 60 第五章 結論與建議 64 5.1結論 64 5.2未來研究建議 64 參考文獻 67 相關出版目錄 7