Monitoring of Heavy Metals in As‐Implanted Simox with Surface Photovoltage

Abstract

Heavy metals in concentrations of E-16-E-18 cm 3 are commonly found in SIMOX samples implanted in high current implanters (100 mA). In the present study, surface photovoltage (SPV) was used successfully to measure the heavy metal concentration in as-implanted SIMOX. An initial correlation has been established between the minority carrier diffusion length measured on the back of a SIMOX wafer and Fe concentration measured by SIMS and spark source mass spectrometry in as-implanted SIMOX films. A correlation between the leakage current of MOS transistors and the heavy metal contamination level as measured by SPV was established. SPV measurements are quick, nondestructive, and do not require any additional sample preparation. They can therefore be used as a QC method to monitor heavy metals in asimplanted SIMOX layers.Heavy metals in concentrations of E-16-E-18 cm -3 are often found in SIMOX samples implanted in high current implanters (100 mA) (1). The heavy metals are introduced into SIMOX due to the interaction of the oxygen ion beam with metallic parts of an implanter (2). The heavy metal concentration in SIMOX is usually measured by SIMS, spark source mass spectrometry, or neutron activation analysis (NAA). These measurements are destructive and time consuming. They are commonly used as a diagnostic tool, but they cannot be used for quality control (QC) since QC measurements have to be nondestructive and quick.In our study, surface photovoltage technique (SPV) (3) was used successfully to measure heavy metal concentrations in as-implanted SIMOX. SPV was used previously as a QC technique to monitor heavy metal contamination and IC gettering on IC processing lines (4-9). An initial correlation has been established between a diffusion length of minority carriers measured on the back of SIMOX wafers and the heavy metal concentration measured by a SIMS and spark source mass spectroscopy in as-implanted SIMOX films. SPV measurements are quick, nondestructive, and do not require any additional sample preparation. They can be used easily as a QC method to monitor heavy metals in as-implanted SIMOX layers.A correlation between MOS device performance and heavy metal contaminations measured by SPV was established.* Electrochemical Society Active Member. Experimental Procedure and ResultsSIMOX wafers were made by implantation of 1.6 E-18 cm -2 of oxygen with energies of 150 and 200 keV at temperatures between 580 ~ and 610~ The implants were made into 10 cm diam, 525 ~m thick, p-type, 10 t2cm Si substrates. The implantation was carried out in a 100 mA implanter at IBIS Corporation. Implantation temperatures were controlled by the oxygen beam; therefore, for implants with an identical dose an increase of implantation temperature was related to a reduction of an implantation time. A typical implantation time for a dose of 1.6 E-18 cm -2 at 150 keV is around 5h at 610~ and 6h at 580~Heavy metal concentrations were measured by SIMS and spark source mass spectroscopy in the silicon film and the oxide, up to a 1 ~tm dist...

Electrical and Optical Characterization of Thin Semiconductor Layers for Advanced ULSI Devices

“…Moreover, performing additional measurements with long-wavelength excitation from the backside yields information on the substrate and back-interface recombination properties. Also the Surface Photovoltage (SPV) technique -which is typically operated at low injection level -has been applied to SOI material [17], whereby recent methods use contactless voltage measurements, based on a Kelvin probe [18]. The limitations of SPV for the characterization of ultra-thin (50 nm) SOI wafers have been pointed out by Lukasiak et al [19].…”