Yoh-Ichiro Ogita

Bulk lifetime and surface recombination velocity measurement method in semiconductor wafers

A noncontact and nondestructive measurement method is proposed to separately determine the bulk lifetime τb, and the front and backsurface recombination velocities S0 and Sw in the semiconductor wafer with different surface recombination velocities in the front and backsurfaces. The method is deduced based on a new analytical solution for photoconductivity decays derived for the wafer with different surface recombination velocities. The solution gives the expressions for a photoconductivity decay and a carrier profile under pulse laser excitation. The analytical relationship between the apparent (or effective) lifetime, S0, Sw, τb and a wafer thickness is given. The photoconductivity decay curve dependencies on various values of S0, Sw, and τb have been demonstrated. The algorithm is shown to separately extract τb, S0, and Sw. The algorithm is characterized by the measurement of two photoconductivity decay curves for pulse laser excitation on both surfaces of the wafer. The influence of the laser pulse wi...

Al2O3 formation on Si by catalytic chemical vapor deposition

Abstract Catalytic chemical vapor deposition (Cat-CVD) has been developed to deposit alumina (Al 2 O 3 ) thin films on silicon (Si) crystals using N 2 bubbled tri-methyl aluminum [Al(CH 3 ) 3 , TMA] and molecular oxygen (O 2 ) as source species and tungsten wires as a catalyzer. The catalyzer dissociated TMA at approximately 600 °C. The maximum deposition rate was 18 nm min −1 at a catalyzer temperature of 1000 °C and substrate temperature of 800 °C. Metal oxide semiconductor (MOS) diodes were fabricated using gates composed of 32.5-nm-thick alumina film deposited at a substrate temperature of 400 °C. The capacitance measurements resulted in a relative dielectric constant of 7.4, fixed charge density of 1.74×10 12 cm −2 , small hysteresis voltage of 0.12 V, and very few interface trapping charges. The leakage current was 5.01×10 −7 A cm −2 at a gate bias of 1 V.

Photoconductivity characterization of silicon wafer mirror-polishing subsurface damage related to gate oxide integrity

The correlation between gate oxide integrity, photoconductivity amplitude and surface microroughness was systematically measured with 9 SC1 cleanings to remove residual subsurface damage induced by mirror polishing on the subsurface of silicon wafers. The same measurements were also carried out for as-epitaxial wafers as a comparison. Measured gate oxide integrity and photoconductivity amplitude in polished wafers increased with increase in the number of cleaning times and saturated after 3 cleanings, however, those for the epitaxial wafers did not vary throughout the 9 cleanings. Surface microroughness increased continuously throughout the 9 cleanings for both wafers. The 3 SC1 cleanings did remove the damage layer whose thickness was determined to be 21 nm, and the photoconductivity amplitude well reflected the removal of this damage and the behavior of the gate oxide integrity. The images of the polished epitaxial wafers observed by the optical shallow defect analyzer showed many scratches which disappeared after 3 SC1 cleanings. This result gave direct evidence of the existence of residual damage and the behavior of photoconductivity amplitude and gate oxide integrity when the damage was removed.

Subsurface Damage Profile Characterization of Si Wafers with Uv/Millimeter-Wave Technique and Light Scattering Topography

We have characterized subsurface damage profiles of hydrogen-ion implanted silicon wafers by using a non-contact UV/Millimeter-Wave Technique and Light Scattering Topography (LST). A subsurface damage profile that was less than one micrometer was controlled by chemical mechanical polishing after hydrogen-ion implantation. On the area with the subsurface damage, the Photoconductivity Amplitude (PCA) signals measured by the UV/Millimeter-Wave Technique drastically weakened and the haze values measured by LST increased. A clear correlation has been found between the peak depth of the subsurface damage and the haze value. The spectral analyses of the surface images obtained by Atomic Force Microscopy (AFM) were carried out in order to separate the influences of surface micro roughness and subsurface damage on the haze value. The contribution of subsurface damage to the haze value can be formulated as the convolution of the damage profile and the transparency function of the incident laser in silicon crystal.

Silicon wafer subsurface characterization with blue-laser/microwave and UV-laser/millimeter-wave photoconductivity techniques

Chemomechanical mirror polishing damages in a subsurface of silicon wafers have been revealed by photoconductivity amplitude with blue-laser/microwave photoconductivity technique and also revealed by photoconductivity technique and also revealed by photoconductivity amplitude and initial carrier lifetime with UV/millimeter photoconductivity decay technique. These noncontact techniques also have revealed subsurface damages as to be drastically influential on gate- oxide layer breakdown in MOSFET.