Shingo Sumie

Correlation of photoconductivity response of amorphous In–Ga–Zn–O films with transistor performance using microwave photoconductivity decay method

The film quality of amorphous In–Ga–Zn–O (a-IGZO), an amorphous oxide semiconductor (AOS), was studied by the microwave photoconductivity decay (μ-PCD) method. Also, μ-PCD mappings over a 6 in. wafer were undertaken. It was found that the peak signal of the decay curve had a strong correlation with the a-IGZO transistor performance and hence the film quality. The film annealed under a wet condition showed the highest mobility and had the highest peak signal. The μ-PCD method was found to be a very useful tool to evaluate the film quality and predict the performance of AOS transistors fabricated under different process conditions.

A New Method of Photothermal Displacement Measurement by Laser Interferometric Probe -Its Mechanism and Applications to Evaluation of Lattice Damage in Semiconductors

A new, highly sensitive technique for measuring photothermal displacement using a laser heterodyne interferometric probe has been developed. This technique is based on the detection of phase changes in the probe beam and is very sensitive to the presence of lattice damage in semiconductors. It has been found that the phase change is caused by the thermal expansion of a sample surface induced by absorption of a modulated pump beam. The displacements of metals and semiconductors measured by this technique coincided with the results predicted by a thermal diffusion model. These displacements simply depended upon the ratio of the thermal expansion coefficient to the thermal conductlvity of a sample.

Transient photoconductivity responses in amorphous In-Ga-Zn-O films

We studied the photoconductivity responses in amorphous In-Ga-Zn-O (a-IGZO) films using a time-resolved microwave photoconductivity decay (μ-PCD) technique. The a-IGZO film characteristics are correlated with three components in the photoconductivity response: the peak value and two decay constants. The peak value originated from the density of the photo-generated free carriers through carrier generation and recombination processes during laser pulse irradiation. Power law characteristics indicated that the peak values are attributed to recombination process related to the exponential distribution of the conduction band tail states. After the laser pulse was turned off, the reflectivity signal decreased rapidly, indicating fast recombination of the photo-generated carriers. This fast decay component is suggested to be related to the recombination processes through the deep level states. Following the fast decay, a slow decay with a decay constant on the order of microseconds appeared. This slow decay was ...

Dose and Damage Measurements in Low Dose Ion Implantation in Silicon by Photo-Acoustic Displacement and Minority Carrier Lifetime

Photo-acoustic displacement (PAD) generated with a modulated laser beam pumping is studied for As+ or B+ implanted Si. At doses above 1×1013 ions/cm2, the PAD has a close relationship to damage density. An ion implantation dose down to 2×109 ions/cm2 can be detected by the PAD measurement. Doses below 2×1010 ions/cm2 can be monitored by minority carrier lifetime measurement. A non-destructive high-sensitive dose monitor can be achieved by the PAD and minority carrier lifetime measurements. This monitoring leads to tight control of the threshold voltage of a MOS transistor.

Excess Carrier Lifetime in a Bulk p-Type 4H–SiC Wafer Measured by the Microwave Photoconductivity Decay Method

Excess carrier lifetime in a p-type 4H–SiC wafer was measured by the microwave photoconductivity decay (µ-PCD) method. The obtained excess carrier decay curve had the fast and slow components with time constants of ≤1 µs and ≥1 ms, respectively. The 1/e lifetime map for the wafer showed that the time constant of the fast component decreases around structural defects. On the other hand, the 1/e2 lifetime map showed that the time constant of the slow component does not depend on the defect distribution. We measured decay curves for the slow component at various temperatures, and fitted them to those obtained from the numerical simulation. The fitting result showed that the slow component is caused by a minority carrier trap located at 0.16 eV below the conduction band. From the measurement of samples with various surface conditions, we found that the excess carrier decay is independent of the surface condition. Thus, the excess carrier decay is caused predominantly by recombination in the bulk rather than at the surface of the wafer.

Excess Carrier Lifetime Measurement of Bulk SiC Wafers and Its Relationship with Structural Defect Distribution

Excess carrier lifetime in bulk 2-in. SiC wafers was measured by microwave photoconductivity decay (?-PCD). The mapping technique was used to obtain the lifetime distribution in the entire wafer. We observed the birefringence image and X-ray topograph of the wafers in order to determine the structural defect distribution, and the net donor concentration distribution was also observed by capacitance?voltage measurements. By comparison of lifetime maps with the structural defect distribution, it was found that relatively long lifetime regions correspond to regions with high-density structural defects. The net donor concentration did not show a clear influence on the carrier lifetimes. We confirmed that surface recombination has a negligible effect on the carrier lifetimes, and therefore the lifetimes obtained from mapping measurements are mainly dominated by carrier recombination behavior in the bulk of the wafers.

ANALYSIS OF LATTICE DEFECTS INDUCED BY ION IMPLANTATION WITH PHOTO-ACOUSTIC DISPLACEMENT MEASUREMENTS

Subsurface lattice defects in silicon induced by ion implantation were studied by the use of the photo‐acoustic displacement (PAD) method based on the sensitive measurements of the surface displacement due to the absorption of laser‐light energy. A definite correlation between PAD and displaced atoms density (DAD) was found because PAD reflects the change in thermal conductivity associated with the net amount of displaced atoms in the crystal lattice beneath the surface. According to the linear dependence of 1/PAD on DAD, defects below a DAD of 1014/cm2 (corresponding to implant doses of 2×1011, 8×1010, and 6×1010 ions/cm2 for 100 keV B+, P+, and As+, respectively) were concluded to be point defects. After the DAD reached 1014/cm2, the PAD showed a gentle increase, and this can be attributed to the growth of point‐defect clusters. A marked dependence of the PAD on the DAD was not observed beyond a DAD of 1016/cm2. In this region, the presence of an amorphous layer was observed by cross‐sectional transmiss...

Bulk carrier lifetime measurement by the microwave reflectance photoconductivity decay method with external surface electric field

We attempted to measure the bulk carrier recombination lifetime of Si wafers by the microwave reflectance photoconductivity decay (PCD) method. Voltage was applied between an external electrode and a Si wafer to suppress surface recombination. Before the measurement, the surface state density was reduced by a chemical treatment using NH4OH–H2O2–H2O and diluted HF solutions. Carrier lifetime as long as 1 ms was measured by the present method for a wafer with a bare surface. Comparison with results for oxidized wafers show that the present method can suppress surface recombination more effectively than thermal oxidation, which has been often used for surface passivation in PCD measurements.

Characterization of Si wafer Surfaces after Wet Chemical Treatment by the Microwave Reflectance Photconductivity Decay Method with Surface Electric Field.

Voltage is applied between an external electrode and a Si wafer to control surface recombination, and carrier lifetime is measured by the microwave reflectance photconductivity decay (µ-PCD) method. The voltage dependence of the lifetime changes depending on the surface Fermi level and the surface state density. We apply this method to Si wafers with various chemical treatments, and qualitatively characterize the surface properies from the dependence of lifetime on applied voltage. The change in the surface properties with time after the treatment is also investigated.

Comparison of Silicon-on-Insulator Wafer Mappings between Photoluminescence Intensity and Microwave Photoconductivity Decay Lifetime

We characterized the nonuniformities of state-of-the-art ultrathin silicon-on-insulator (SOI) wafers by photoluminescence (PL) intensity mapping and microwave photoconductivity decay (µ-PCD) lifetime mapping. Both mapping techniques revealed characteristic patterns with extreme sensitivity. The PL and µ-PCD mapping patterns on the substrate were almost exactly alike for all the measured wafers. There was also a strong resemblance between the two mapping patterns on the top Si layer for most wafers. A higher PL intensity region corresponded to a longer lifetime area. The quantitative relationship between the PL intensity and µ-PCD lifetime was obtained not only for comparison within a wafer but also for wafer-to-wafer comparison. The mapping pattern on the substrates varied greatly depending on the wafer fabrication method. We believe that the pattern on the top Si layer originates in the distribution of microdefects such as HF defects in the layer, the variation in layer thickness, and/or the nonuniformity produced during the thermal process for surface passivation.