化学腐蚀后的表面状态对硅片Fe沾污的影响

Surface Stateof Silicon Waferwith Chemical Etching Processon Fe Contamination

利用不同的酸腐蚀和碱腐蚀条件对硅片进行了腐蚀,分析了腐蚀后的硅片表面状态对Fe沾污的影响。实验结果表明,不同酸腐蚀条件的硅片经过以HF酸结尾的改进型RCA(Radio Corporation of America)清洗法清洗后,表面疏水性增强,相对不易附着Fe离子,而当酸腐蚀硅片表面经过SC-1溶液处理后,表面亲水性增强,附着的Fe离子较多,且难以通过超纯水冲洗去除;随着酸腐蚀硅片表面粗糙度的增大,表面吸附的Fe离子也增多。不同碱腐蚀条件的硅片去除量越小,表面残留的研磨造成的机械损伤层厚度则越大,损伤层厚度较大时,表面吸附的Fe离子也越多,且难以通过超纯水冲洗去除;在90℃下腐蚀40 s的硅片,由于去除量约为4.2μm,研磨过程中造成的表面损伤层沾污没有完全去除,残留在损伤层中的Fe沾污经过改进型RCA清洗后也无法去除,沾污会在退火过程中扩散进入硅片体内。

With the development of very large-scale integrated circuits(VLSI),the integration of the circuit was getting higher andhigher,and the yield of the device was more and more sensitive to the metal impurities and defects in the silicon wafer.As a commonmetal impurity in the process of integrated circuits(IC)manufacturing,iron(Fe)had a large diffusion coefficient at high temperatureand easy to diffuse into the bulk of wafer through surface contamination.Through different etching processes,the effect of the surfacestate of the etched silicon wafer on Fe contamination was studied.The surface photovoltage(SPV)method was used to analyze the Feconcentration in silicon wafer.All experimental silicon wafers were first etched under different acid and alkali etching conditions.Thenall silicon wafers were cleaned by an improved Radio Corporation of America(RCA)cleaning method,mainly through two SC-1 solu-tions(5% NH_(4)OH and 10% H_(2)O_(2)),one SC-2 solution(volume ratio of HCl∶H_(2)O_(2)∶H_(2)O=1∶1∶20),one dilute HF solution(containing 1% HF)and several times quickly drain(QDR)cleaning.The first part of the experiment:the cleaned acid-etched silicon wafers weredivided into five groups,and each group contains silicon wafers with four different acid etching conditions.The first group of silicon wa-fers were directly annealed;The second group of silicon wafers were contaminated by FeCl_(3) solution with a concentration of 5×10^(-9) mol·L^(-1) for 10 min and then annealed.The third group of silicon wafers were contaminated by FeCl_(3) solution and rinsed with ultrapure waterfor 10 s,and then annealed;The fourth and fifth group of silicon wafers were contaminated by the FeCl_(3) solution after respectively im-mersing half and whole of silicon wafers in the SC-1 solution for 2 min,and then annealed after rinsing with ultrapure water.The sec-ond part of the experiment:the cleaned alkali-etched silicon wafers were divided into three groups,and each group contains silicon wa-fers with four different alkali etching conditions.The first group of silicon wafers were directly annealed;The second group of siliconwafers were contaminated by FeCl_(3) solution with a concentration of 5×10^(-9) mol·L^(-1) for 10 min and then annealed.The third group of sili-con wafers were contaminated by FeCl_(3) solution and rinsed with ultrapure water for 10 s,and then annealed.The silicon wafers weredried in air before annealing at 650 ℃ for 30 min.The annealed silicon wafers were polished and measured for Fe by SPV method.Theresults of the Groups 1~3 in the first part of the experiment showed that the average concentration of bulk Fe of silicon wafers contami-nated with FeCl_(3) solution was higher than 9.1×10^(10) atom·cm-3 after annealing.The roughness of silicon wafers with a removal amount of 30μm was smaller than that of silicon wafers with a removal amount of 15 μm.And when the removal amount was the same,the roughness ofsilicon wafers etched by the new acid was smaller than that of silicon wafers etched by the exhausted acid.And silicon wafers with a small-er roughness had a lower degree of Fe contamination.The experimental results of the fourth and fifth group of silicon wafers showed thatthe surface hydrophilicity of acid-etching silicon wafers was enhanced by immersion in SC-1 solution.After silicon wafers were contami-nated by FeCl_(3) solution,the Fe ions adsorbing on the surface could not be cleaned by ultra-pure water.The average bulk Fe concentrationof silicon wafers was more than 1×10^(11) atom·cm-3 after annealing.And the contamination amount of the whole silicon wafer immersed inSC-1 solution was larger than that of half of the silicon wafer immersed in SC-1 solution.The results of Groups 1~3 in the second part ofthe experiments showed that the surface removal amount of silicon wafers is 4.2 μm after alkali-etching at 90 ℃ for 40 s.And as the sili-con wafers cleaned by improved RCA cleaning,the average concentration of bulk Fe was still high after annealing.When silicon waferswere contaminated with FeCl_(3) solution,the average concentration of bulk Fe of silicon wafers washed by ultrapure water was lower thanthat of silicon wafers without being washed by ultrapure water.But it was still higher than the initial level of silicon wafers.And the con-tamination degree of silicon wafers with larger amount of surface removal was lower.The surface hydrophobicity of silicon wafers with dif-ferent acid etching conditions enhanced after an improved RCA cleaning method ending with HF acid,and Fe ions were relatively diffi-cult to adhere to the surface,while the acid etching wafers were treated with SC-1 solution,the surface hydrophilicity of the wafers en-hanced and more Fe ions adhering to the surface could not be removed by rinsing with ultra-pure water.As the surface roughness of acidetching silicon wafers increased,the Fe ions adhering to the surface also increased.The smaller removal amount of the silicon wafers withdifferent alkali etching conditions,the greater residual thickness of the mechanical damage layer caused by the surface grinding and themore Fe ions adsorbed on the surface.The Fe ions could not be removed by rinsing with ultra-pure water.After etching the silicon wafersfor 40 s at 90 ℃,the contamination of surface damage layer caused by the grinding process was not completely removed due to the 4.2 μmremoval amount.The Fe contamination in the damage layer also could not be removed after an improved RCA cleaning,and would diffuseinto the bulk of silicon wafers during the annealing process.