Joel Kearns

Aspects of Iron Contamination Studies in Silicon by Photoluminescence Correlation to Other Techniques

Photoluminescence (PL) studies were applied to intentionally iron contaminated silicon wafers to validate the PL technique for the quantitative evaluation of bulk iron in silicon. Iron contamination ranged from 109 cm−3 to 1012 cm−3. For lightly doped p‐type and n‐type silicon a good correlation was found between Photoconductance Decay (PCD) lifetime, Surface Photo Voltage (SPV) diffusion length (DL) and iron readings and PL intensity readings. PCD, SPV and PL high‐resolution mapping was applied to build the point‐to‐point correlation. PL was shown to be sensitive to iron contamination at concentrations exceeding 1010cm−3 as calibrated by SPV using lightly doped p‐type silicon. PL may be used as high‐resolution non‐destructive technique to track down the metal contamination sources in wafers processing.

Alkali Metals Transport at High Temperatures in the Presence of an Electric Field

The transport of Sodium from silicon wafers in the presence of an electric field was studied. A dual polarity silicon boat was designed to apply the electric potential to silicon wafers during annealing. Secondary ion mass spectrometry (SIMS) and atomic absorption spectroscopy (AAS) were used to measure sodium contamination levels. Results indicate that alkali metals desorb from the silicon oxide surface, diffuse through gas boundary layer, and are transported into the gas flow. This process is strongly depends on process temperature, ambient gas pressure and electric field conditions. A DC‐electric field was found to be an effective means to manage the desorbed ionized Na+ species diffusion through the near‐surface stagnant layer and transporting it into the gas phase.

Clean Thermal Processing at Elevated Temperatures

Clean thermal processing (CTP) was developed to reduce silicon wafer metal contamination. Silicon carbide (SiC) and quartz boats were investigated to find and eliminate Fe contamination sources at 1050 and 1250°C. Contamination originates from (a) metal diffusion in direct wafer to boat contact area (MDD — Metals Direct Diffusion) and (b) as adsorption of metal species from gas phase (MAG — Metals Adsorption from Gas Phase). To reduce both, MDD and MAG contamination, additional cleaning procedures were implemented using Trans‐LC treatment at 1250°C, followed by steam oxidation. Metal contamination levels were evaluated using surface photo‐voltage (SPV), photo‐conductance decay (PCD) and photoluminescence (PL) high‐resolution mapping. SPV iron, PCD lifetime and PL intensity maps indicate cleaning procedures are effective for both Quartz and SiC boats.