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

利用高分辨RBS/沟道技术研究了超低能离子注入Si（001）过程中的非晶化过程。结果表明，非晶化是从表面开始的，与高能离子注入非晶化不同。对这种反常的表面非晶化现象的解释有以下几种可能：（1）离子轰击引起的晶格缺陷向表面移动。(2)氧原子的影响。(3)TRIM模拟不能给出超低能离子注入的准确结果。为了验证这一点，我们在3-5 keV Ar^+轰击下，通过高分辨率RBS原位观察，研究了有和没有自然氧化层的Si（001）晶体的非晶化。通过比较Ar的深度分布，研究了氧的影响，并检验了TRIM程序的准确性，发现非晶化是从表面开始的，而与自然氧化层无关，观察到的Ar分布比TRIM程序的浅20- 30%，指出在使用TRIM程序模拟超低能注入时应注意的问题。

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.