Baimei Tan

Method of surface treatment on sapphire substrate

Sapphire single crystals are widely used in many areas because of the special physic properties and important application value. As an important substrate material, stringent surface quality requirements, i.e. surface finish and flatness, are required. The use of CMP technique can produce high quality surface finishes at low cost and with fast material removal rates. The sapphire substrate surface is treated by using CMP method. According to sapphire substrate and its product properties, SiO2 sol is chosen as abrasive. The particle size is 15-25 nm and the concentration is 40%. According to the experiment results, pH value is 10.5-11.5. After polishing and cleaning the sapphire surface, the surface roughness was measured by using AFM method and the lowest value of Ra 0.1 nm was obtained. From the results, it can be seen that using such method, the optimal sapphire surface can be gotten, which is advantageous for epitaxial growth and device making-up.

Effect of surfactant on removal of particle contamination on Si wafers in ULSI

The adsorption mechanism of particle on the surface of silicon wafer after polishing or grinding whose surface force field is very strong was discussed, and the removal method of particle was studied. Particle is deposited on the wafer surface by interactions, mainly including the Van der Waals forces and static forces. In order to suppress particles depositing on the wafer surface, it is essential that the wafer surface and the particles should have the same polarity of the zeta potential. According to colloid chemistry and lots of experiments, this can be achieved by adding surfactants. Nonionic complex surfactant was used as megasonic cleaning solution, and the adsorptive state of particle on Si wafers was effectively controlled. The efficiency and effect of megasonic particle removal is greatly improved. A perfect result is also obtained in wafer cleaning.

Effect of annealing temperature on microstructure and thermoelectric properties of bismuth–telluride multilayer thin films prepared by magnetron sputtering

Abstract N-type bismuth–telluride (Bi–Te) multilayer thin films with total thickness of about 900 nm were deposited on amorphous structure glass substrate by magnetron sputtering at room temperature. The films were annealed at different temperatures under Ar ambient for 1 hour. The effect of annealing temperature was investigated for Bi–Te multilayer thin films by surface topography, chemical composition, crystal structure and thermoelectric properties. The results show that the Bi–Te multilayer thin films are all transformed into Bi–Te-based compounds. With the annealing temperature increasing, the films undergo an island growth mode with column structure, and grain size increases from 16·4 to 23·1 nm; in addition, the electrical conductivity and carrier mobility increase monotonously. The maximum Seebeck coefficient (−98·5 μV K−1) and power factor (14·47 μW K−2 cm−1) can be obtained for stoichiometric Bi2Te3 films annealed at 150°C.

Slurry and processing technique of CLBO crystal

CsLiB6O10(CLBO) is a new-type nonlinear optical crystal material. CLBO has many good performances, especially the frequency multiplication performance in deep ultraviolet band. CLBO has important application prospect on solid-state UV laser, broad band tunable laser and laser nucleus flame igniter. Though, CLBO will be air slaking and cracking when the ambient humidity is more than 40%, which brings more difficult on CLBO surface finishing. According to the performance and structure characteristic of CLBO crystal, a new water-free slurry applying for CLBO crystal chemical mechanical polishing(CMP) was investigated. The abrasive is SiO2. The influence of polishing processing parameter on polishing process for CLBO crystal was discussed, and the parameter optimal value of polishing plate speed, pressure, pH value and abrasive concentration were determined. Through such parameters, high efficiency and precision plane polishing was gotten. The CLBO CMP process was studied, the results show that low pressure and high speed can improve the CLBO crystal surface removal rate and flatness.