Depth Profiling Analysis of Transition Metals in Thermally Treated Silicon Wafer

• Main Authors: I-Long Chang, 張宜隆
• Other Authors: Mo-Hsiung Yang
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/23448562154642735508

碩士 === 國立清華大學 === 原子科學系 === 91 === Abstract Metallic contamination in silicon wafer is a well-known cause of device failure and performance degradation in semiconductor manufacturing. During high temperature processing, trace transition metals can diffuse rapidly into silicon substrates from surface contamination and cause changes in electrical characteristics. In order to investigate the diffusion behavior of trace transition metals in silicon wafer upon thermal processing, a depth profiling analysis consisted of successive anodic oxidation of a wafer followed by inductively coupled plasma mass spectrometry (ICP-MS) determination is highly desired. In this study the anodic oxidation technique for growing uniform silicon oxide layers on silicon wafer was investigated. In order to ensure good homogeneity and rapid growth of oxide layers, a series of studies on the effect of current density and electrolysis time were undertaken. The thermal diffused silicon wafers (6-inch p-type) were used as testing samples for anodic oxidation in constant current mode with 80 % ethylene glycol and 20% H2O as electrolyte. The thickness of oxide layer formed was measured both by scanning electron microscopy (SEM) and inductively coupled plasma optical emission spectrometry (ICP-OES). From the results, it shows that the thickness of silicon oxide layers grown steadily increases with increasing the current density in the tested region from 1.38 mA/cm2 to 6.2 mA/cm2. A similar increasing trend was also observed by prolonging the electrolysis time from 10 to 50 min at the constant current density of 6.2 mA/cm2. Though higher current density and longer electrolysis time are advantageous to the formation of oxide layer with thickness suitably used for depth profiling analysis purpose, it may cause deterioration of the quality of oxide layer so obtained. The anodization at constant current density of about 4.14 mA/cm2 with electrolysis time of 60 min has been proven to be a favorable condition, which can produce oxide layer thickness of about 2600 Å with good surface uniformity and homogeneity. After anodic oxidation, the trace transition elements (Cr, Zn, Ni, Co, Cu) in the oxide layers was dissolved in 2% HF+3% H2O2. In order to decrease the interference effects caused by the silicon and HF matrix in the dissolved solution, an in-line membrane separation technique (neutralizer system) was introduced to achieve effective separation of analytes from the interferents. Successively repeating the processes of layer formation, dissolution, matrix removal and measurement steps, the concentrations of analytes in the respective layers of silicon wafer were obtained. On the basis of the analytical results obtained by anodic oxidation-neutralizer-ICP-MS, its shows that a general diffusion behavior of decreasing metal concentration with increase of depth in the wafers, treated under the temperature between 600℃ to 1000℃ is obtained. The diffusion coefficients of various transition metals in silicon wafer were estimated to be in the order of 10-14-10-15 cm2/sec.