Study On Gettering Of Low Contamination By Helium-implantation-formed Cavities In Silicon

Metal impurities unintentionally introduced into Si wafers during various device process steps are very harmful to device performances. Many gettering techniques have been widely studied to overcome these problems by removing metal impurities from the active region of a device. Reduction in device size and introduction of new moralization processes require more efficient gettering techniques working at lower temperatures. Recently, a new gettering technique, which cavities formed by high-dose helium-implantation and subsequent annealing at lower temperature is efficiently at gettering metal impurities, has been concentrated. Some previous experiments have showed that cavities had more efficient gettering than P-diffusion, mechanical damage and ion implantation. Most of studies about cavities gettering are concentrated on the peculiarity of cavities gettering metal impurities intentionally into silicon wafer from the viewpoint of basic study. This technique especially applied to low-contamination process, however, has not been carefully studied, which should be important to the semiconductor manufacturing.In this work, the reversed leakage-current of silicon planar diode was used to indicate the metal-contamination. An optimization of thermal process was obtained, which made the cavities have the best gettering performance in the experiments. Some of the silicon planar diodes made on the double sides polished wafer wereimplanted with 1 l017/cm2 He+ ions of lOOkeV energy and the others without implantation were used as control samples. Cavity-gettering was studied by comparing varies of reversed leakage-current JR of above two kinds of diodes before and after thermal process.All of the samples were firstly annealed at 700 1hr to form cavities band in silicon. The samples that annealed at different temperatures and different cooling ways (fast or slow), separately, was compared. The experimental results showed that the temperature and the cooling-way of the gettering process were very important for the gettering efficiency. Thus, an optimized gettering process obtained was 800 and following a slow cooling. The efficiency and the homogeneity of cavities gettering were analyzed by measuring the leakage-current for the diodes in a wafer, which was thermally treated at the optimal condition, that is 700 1hr, then 800 6hr and slow cooling down. The results of the experiments were that leakage-currents of the 77% diodes have obviously reduced in form 0.08 ~ 11 A/cm2 to a value smaller than 0.032 A/cm2 . Therefore, the gettering efficiency and homogeneity has been demonstrated on devices. It was also concluded that, from the experiments, the cavities band for gettering on the polished backside of the wafer was more efficient than that on the rough side. Three orders decreasing of the leakage-current value has indicated strong ability of cavity gettering.