Deep Levels Study in Float Zone Si Used for Fabrication of CCD Imagers

Goldsmith

et al. 1984

The effect of internal gettering on circuit performance has been studied for I2L and linear logic bipolar circuits. The gettering has been introduced by controlled precipitation of oxygen in silicon wafers during processing, and its effect has been measured as reduction of circuit leakage current, which has been reflected in yield improvement. The efficiency of internal gettering has been found to be a strong function of the amount of precipitated oxygen and precipitate's morphology. It has also been found that the same factors affect the mechanical strength (warpage) of silicon wafers. The best gettering and yield improvement was obtained for relatively low amounts of precipitated oxygen (about 10 ppm), which resulted in the desired precipitate's morphology. An increase in the amount of precipitated oxygen decreased the gettering efficiency and also reduced the mechanical strength of the silicon wafers. The present work showed that, in addition to well‐known factors, such as the interstitial oxygen concentration in virgin wafers, oxygen‐precipitation kinetics during bipolar processing is strongly affected by other factors, such as concentration of nucleation centers for oxygen precipitation. They control the rate of oxygen precipitation and precipitate's morphology. Since the concentration of these centers is related to the crystal‐growth conditions, differences in precipitation kinetics are found in the wafers provided by various commercial suppliers. This can lead to unusual results. For instance, lower amounts of precipitated oxygen have been found in wafers with an initial oxygen concentration of 40 ppm than in wafers with 28 or 31 ppm coming from different suppliers. We believe that our results clearly demonstrate that internal gettering after optimization can be used to improve circuit yield in bipolar processing lines.

mentioning

confidence: 99%

Internal Gettering in Bipolar Process: Effect on Circuit Performance and Relationship to Oxygen Precipitation Kinetics

Goldsmith

et al. 1984

“…wafer thickness (around 525 ~m), it is not surprising that the diffusion length measured at the back of a SIMOX wafer corresponds to the concentration of heavy metals which are implanted into the front of a SIMOX wafer. It is well known that heavy metal precipitates contribute to defect nucleation and decoration (12)(13)(14)(15). These defects cause excessive junction leakage (8,(16)(17)(18).…”

Section: Discussionmentioning

confidence: 99%

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

Cullen

1990

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...

“…Manuscript submitted May 7, 1986; revised manuscript received Aug. 2, 1986. This was Paper 418 presented at the Las Vegas, NV, Meeting of the Society, Oct. [13][14][15][16][17][18]1985.…”

Section: Discussionmentioning

confidence: 99%

“…Mechanical strength.--The mechanical strength of silicon wafers affects breakage (line yield) of wafers thinned to 10 ~m and susceptibility of silicon to generation of slip Heat-treatments involved during processing and virgin wafer characteristics and dislocations. The amount of low contrast white spots/line failures is related to the amount of dislocations and their decoration by heavy metals (14). In addition, the mechanical strength of silicon wafers can also affect resolution failures.…”

Section: Defect Originmentioning

confidence: 99%

See 1 more Smart Citation

Silicon Wafers for CCD Imagers

Cullen

et al. 1987

The sensitivity to defects in CCD imagers is about two orders of magnitude higher than in the most sophisticated DRAM circuits. This makes CCD imagers one of the most difficult and challenging VLSI circuits to manufacture. In the present work, we discuss the origin of the material-related defects that affect CCD imager performance in the various types of silicon wafers. The following silicon starting materials have been evaluated: internally gettered CZ, MCZ, FZ, FZ doped with nitrogen, and epitaxial silicon on internally gettered substrates. The assets and liabilities in the use of these various types of material were assessed. Issues addressed were mechanical strength (susceptibility to defect generation and wafer breakage), presence of residual defects in as-grown crystals, presence of inhomogeneities, and gettering potential. The best results were obtained using MCZ wafers and epitaxial layers grown on internally gettere-d ~ubstrates. The CCD imagers made on these wafers had the least problems related to materials defects. This can be attributed to the absence of inhomogeneities, the presence of oxygen pinning of dislocations (which provides good mechanical strength, i.e., low wafer breakage, and resistance to dislocation generation), and low grown-in defect density for MCZ silicon and gettering ability for the epilayers on IG-CZ.