STUDY ON ULTRA-LOW ENERGY ION IMPLANTATION USING HIGH-RESOLUTION RBS

我们用高分辨RBS/沟道技术研究了超低能离子注入过程中Si(001)的非晶化过程。结果表明，与高能离子注入的非晶化不同，非晶化是从表面进行的。有几种可能性可以解释这种反常的表面非晶化：(1)离子轰击引起的晶格缺陷向表面移动。(2)嵌套氧原子的影响。(3)对于超低能离子注入，TRIM模拟不能给出准确的结果。为了找出合理的解释，用高分辨RBS原位观测方法研究了3-5keV Ar~(++)轰击过程中Si(001)晶体的非晶化过程。结果表明，非晶化过程是从表面开始的，而非晶化过程与自然氧化层无关，比TRIM模拟的结果浅20%~30%，说明TRIM程序在模拟超低能注入时应引起注意。

We have investigated the amorphization process of Si(001) during ultra-low energy ion implantation using high-resolution RBS/channeling. It was found that the amorphization proceeds from the surface different from the amorphization by high energy ion implantation. There are several possibilities to explain this anomalous surface amorphization : (1) Lattice defects induced by ion bombardment move to surface. (2) Effects of the knoked-in oxygen atoms. (3) TRIM simulation does not give accurate results for ultra-low energy ion implantation. In order to see which explanation is the case, the amorphization of Si(001) crystals with and without native oxide layer was studied by in situ observation by high-resolution RBS during 3-5 keV Ar^+ bombardment. The effects of kocked-in oxygen was investigated and the accuracy of TRIM code was also examined by comparing the observed and simulated Ar depth profiles.It was found that the amorphization proceeds from the surface irrespective of the native oxide layer.The observed Ar distribution is shallower than that of TRIM simulation by 20-30 %, indicating that attention should be gave when TRIM code is used for simulation of the ultra-low energy implantation.