Oxygen Precipitate Density Research Articles

High-sensitivity Defect Evaluation by a New Preferential Etching Technique for Highly As-doped Si Crystals

A high-sensitivity preferential etching technique is presented to evaluate crystal defects in a highly As-doped silicon crystal with a resistivity lower than 0.01 Ω· cm. For highly doped n-type Si, a conventional preferential etching technique, such as Secco etching, Wright etching or Dash etching becomes less useful because of a significant decrease in defect detection sensitivity. The new method is quite sensitive to dislocations, stacking faults and oxygen precipitates in highly As-doped crystals with a surface of either (111) or (100). In this method, copper is first decorated at the defect site, then the defect is preferentially etched by a dilute alkaline solution. The technique thus offers us a sensitive and Cr-free method, attractive from an environmental aspect. A correlation between the laser scattering method is also obtained for the oxygen precipitate density.

Spatial variations in oxygen precipitation in silicon after high temperature rapid thermal annealing

Spatial variations of oxygen precipitation have been studied in silicon wafers submitted to rapid thermal annealing (RTA) in nitrogen ambients at a temperature above 1150 °C prior to a two-step precipitation treatment. The samples submitted to high temperature preannealing show a consistent enhancement of oxygen precipitation, which is dependent on the RTA time and temperature. Oxygen precipitate density measurements show that oxygen precipitation is not homogeneous inside the wafer, but peaks near the surfaces, with a minimum in the bulk. The high treatment in N2 results in the formation of defects which act as precursors for the subsequent nucleation and growth of oxygen precipitates. There is strong evidence that these precursors are generated by the thermal nitridation of the silicon surface and subsequent vacancy injection into the bulk of the wafer.

Oxygen precipitation in Czochralski-grown silicon wafers during hydrogen annealing

In studying the effect of the ramping process on oxygen precipitation in Czochralski-grown silicon wafers in hydrogen annealing, we have found that the oxygen precipitate density in the bulk region depends on the ramping-up rate at temperatures between 900 and 1200 °C. Few oxygen defects are observed when the ramping-up rate is 30 °C/min or more. Decreasing the ramping-up rate exponentially increases the oxygen precipitate density. The nucleation for oxygen precipitates can therefore be controlled by adjusting the ramping-up rate during hydrogen annealing.

Characterization of Nickel Contamination in Float Zone and Czochralsky Silicon Wafers by Using Electrolytic Metal Tracer or Microwave Photoconductivity Decay Measurement

The influence of nickel contamination on the free carrier recombination lifetime and on the electrolytic diodes reverse dark current of electrolytic metal tracer (ELYMAT) have been studied on both float zone (FZ) and Czochralsky Conductivity Decay (CZ) wafers. The reverse currents of the ELYMAT electrolytic cell's measured on moderately doped FZ wafers are clearly increasing with nickel concentration. The recombination lifetime in both FZ wafers, and CZ wafers after oxygen precipitation (Internal gettering) treatments is influenced by nickel contamination. In CZ wafers with oxygen precipitation nickel contamination causes a drop of the lifetime which is directly related to the oxygen precipitate density. The characteristic variation of recombination lifetime dominated by oxygen precipitates as a function of injection level changes significantly after intentional nickel contamination. All these results bring new insights for the fast identification of Ni contamination in device fabrication lines.

Improvement to Bulk Oxygen Precipitate Density Necessary for Internal Gettering in Antimony Doped N/N+ Epitaxial Wafers Using the 3‐Step Technique and Ramped Nucleation

The addition of a ramped nucleation cycle, just after an initial oxidation, is shown to greatly increase the precipitation of interstitial oxygen during simulated processing on N/N+ antimony doped epitaxial wafers. When used with fully processed wafers, the ramped nucleation improves internal gettering. Oxygen precipitate density and bulk stacking fault density achieved are about a factor of 100 higher when using ramped nucleation. These results indicate that N/N+ antimony doped epitaxial wafers have an intrinsic gettering capability as good as that of lightly doped material when using an activation cycle (initial oxidation) and subsequent ramped nucleation. A method for calculating bulk stacking fault density is presented. It is shown that, at high concentration (above 107 cm−3), the square of the bulk stacking fault length is inversely proportional to their density. This finding indicates that the growth of bulk stacking faults is limited by the supply of interstitial silicon generated in the bulk during oxygen precipitate growth.

Carrier Lifetime and Material Study in Intrinsically Gettered Silicon Wafers for High Precipitate Density

Cz-grown Si wafers, subjected to several ramped heat treatment procedures and having high oxygen preciptate density, are tested to determine the gettering efficiency. The methods used are preferential etching, infrared absorption spectroscopy and carrier lifetime measurement at high-injection levels. The wafer warpage is also measured. The investigations show that the number of precipitates is reduced and the width of precipitate free zone is increased in two narrow regions of the intial oxygen concentration. This effect is caused by a reduction of the small-sixe defect concentration peak in the precipitate profile. This phinomenon is attributed to an interaction between native point defects and interstitial oxygen. It is shown that the carrier lifetime in bulk decreases sublinearily with the bulk oxygen precipitate density in the range between 106 and 108 cm−2. the dependence of wafer warpage on oxygen density is increased for an initial oxygen density Oi ≧ 9 × 1017 cm−9. [Russian text Ignored.]

Quantitative determination of high-temperature oxygen microprecipitates in Czochralski silicon by micro-Fourier transform infrared spectroscopy

Oxygen content in the bulk of Czochralski silicon was analyzed by using micro-Fourier transform infrared spectroscopy in a transversal wafer cross-section configuration. This technique locally distinguishes between interstitial oxygen and oxygen precipitates in wafers used as substrates for epitaxial layer growth. Systematic measurements performed in the 5000–700 cm−1 wavenumber range clearly indicate the presence of oxygen microprecipitates in the bulk of the processed silicon wafers. Quantitative determination of oxygen precipitate density is reported and compared with the measured interstitial oxygen concentration.

Heavy metal contamination during integrated-circuit processing: Measurements of contamination level and internal gettering efficiency by surface photovoltage

Crystallographic defects present in device active areas form localized dark current generation sites. The current generation rate is a function of decoration of these defects by heavy metals. These defects cause yield degradation of the integrated circuits. The surface photovoltage (SPV) method, which measures minority-carrier diffusion lengths, has been applied successfully to monitoring in real time the heavy metal contamination level in processing lines, and to identifying sources of heavy metals. Heavy metal contamination has been monitored on the control floating zone (FZ) wafers, which were exposed to certain critical processing steps. A threshold contamination level exists beyond which the probability of crystallographic defect decoration and the formation of stacking faults increases dramatically. This level is different for the different defects, processes and different types of silicon wafers (i.e. those obtained by FZ, magnetic Czochralski (MCZ), internal gettering (IG), Czochralski and epitaxy methods). Surface photovoltage was also used to measure non-destructively, in real time, the denuded zone depth in IG wafers. In IG wafers, values of diffusion length are proportional to the denuded zone depth. Bulk oxygen precipitate densities were also measured by SPV. Prior to these measurements the denuded zone was removed from the back of the wafer by etching. Good correlation between the yield reduction charge-coupled device imagers, complementary metal-oxide-semiconductors, dynamic random access memories and bipolar devices and increases in the contamination level as measured by SPV has been reported in literature. Also, good correlation between the yield of these circuits and the efficiency of IG, as measured by SPV in IG wafers after completion of the fabrication sequence, was established. These issues will be discussed in this paper.

The effect of 1300-1380 degrees C anneal temperatures and material contamination on the characteristics of CMOS/SIMOX devices

The characteristics of CMOS transistors fabrication on silicon implanted with oxygen (SIMOX) materials were measured as a function of the silicon superficial layer contamination levels. In addition, postimplant anneal temperatures of 1300 degrees C, 1350 degrees C, and 1380 degrees C were examined. It is found that the transistor leakage currents as well as the integrity of the gate oxide and implanted SIMOX oxide are functions of the carbon content in the starting material. Leakage currents below 1.0*10/sup -12/ A/ mu m of channel width have been measured when the carbon concentration is reduced to 2*10/sup 18//cm/sup 2/. In addition, the integrity of the transistor gate dielectric, SIMOX implanted oxide, and oxygen precipitate density are seen to be a function of the postimplant anneal temperature. A gate dielectric breakdown field of 10 MV/cm has been achieved when the postimplant temperature is increased to 1380 degrees C. >

New oxygen donors formed at 700 °C in silicon

Donor formation at 700 °C was studied by infrared absorption, etching, transmission electron microscope, resistivity, and spreading resistance measurements in Czochralski grown silicon. The donor concentration is related to the oxygen-precipitate density, oxygen reduction, and carbon reduction by annealing at 700 °C. The donor distribution corresponds to the distribution of oxygen precipitates observed after annealing. The proposed donor is an oxygen precipitate nucleated at a carbon site. The oxygen-related donor formation not only occurs in the bulk of samples but also in the denuded zone. Donor-related microdefects do not seriously influence the threshold voltage in metal-oxide-silicon field-effects-transistors, but are expected to decrease carrier lifetime at the surface of the denuded zone.