We have applied cathodoluminescence (CL) and Raman spectroscopies to shallow trench isolation (STI) processes in large scale integration to investigate crystalline defects and stresses by extracting the wafer after each process. A sample with high standby leakage current clearly showed dislocation-related luminescence lines (D lines) in the regions surrounding the memory cell. These regions contain various sizes of active and field areas ranging from 0.5to5μm. However, a normal sample showed no D lines in any region through the STI processes. The D lines were observed after liner oxidation, which was performed after trench patterning. Raman microprobe measurements showed that the trench patterning process generated a large inhomogeneous stress distribution up to 200MPa in the regions surrounding the memory cell. The inhomogeneous stress distributions caused by the trench patterning and the subsequent thermal processes are likely the main causes of dislocations. A comparison between the D lines in the CL spectra and the stress measured by a Raman microprobe clarified the mechanism of generation of crystalline defects. We can thus optimize the process conditions in STI processes by these spectroscopic methods.
The metal-oxide-semiconductor-field-effect-transistor (MOSFET) has been miniaturized for the high performance large-scale integrated-circuit (LSI). However, in the ultimately miniaturized MOSFET, the gate oxide failure with high leakage current is inevitable. In this study, we evaluated the origin of the gate oxide failure by Raman spectroscopy in conjunction with optical beam induced resistance change (OBIRCH) analysis. MOS capacitors were used as the samples. The 2.8 nm thick gate oxinitrid insulator film and the poly-Si gate electrode layer were formed on a P type Si substrate. The cobalt (Co) silicide film was formed on the poly-Si electrode. The SiH4 flow rate was 150 sccm or 350 sccm. The gate oxide integrity was evaluated by the test element group (TEG) measurements. As a result, Raman intensity increased at the failure position compared with the other positions in the sample deposited with 150 sccm of SiH4 flow rate. We consider that higher Raman intensity at the gate oxide failure positions reflects the irregular structure of poly-Si. Furthermore, the Raman peaks at failure positions shifted toward the lower wavenumber while the FWHMs are approximately constant with other positions. Thus, we found that there is no difference in the crystallinity of the poly-Si. The origin of the gate oxide failure was high tensile strain in the gate poly-Si electrode. In conclusion, we have successfully evaluated the gate oxide failure by Raman spectroscopy with a quasi-line excitation source.
Cathodoluminessence (CL) spectroscopy was applied to optimize the shallow trench isolation (STI) process. The analysis of dislocations with CL spectroscopy could be performed during STI process steps. Then, the result of CL analysis was associated with the failure of a junction leakage current. Moreover, the analysis contributed to identifying the failure, including the root cause. As the result of CL analysis, nitride film thickness used as a mask layer of patterning was controlled at 190 nm or less. The dislocation analysis with CL spectroscopy can reduce the cycle time from 50 to 5 days.
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