Xinhuan Niu

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.

Dislocation of Cz-sapphire substrate for GaN growth by chemical etching method

Abstract The diameter of Czochralski (Cz) sapphire crystals is 50 mm. The sapphire substrates were lapped by using diamond powders and polished by chemical mechanical polishing(CMP) method using alkali slurry with SiO 2 abrasive. After obtaining the smooth surfaces, the chemical etching experiments were processed by using fused KOH and NaOH etchants at different temperature for different times. The dislocation was observed by means of optical microscope and scanning electron microscope. The clear and stable contrast images of sample etching pits were observed. On the whole, the dislocation density is about 10 4 –10 5 cm −2 . Comparing the results under the conditions of different etchants, temperatures and times during the etching proceeding, it was found that the optimal condition for dislocation displaying is etching 15 min with fused KOH at 290 °C. At the same time, the formation of the etch pits and the reducing method of dislocation density were also discussed.

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.

Influence of minor oxides on formation and decomposition of mineral calcium sulfoaluminate (3CaO·3Al2O3·CaSO4)

Abstract Research was done on the influence of minor oxide Fe2O3, Cr2O3, ZnO, TiO2 and CaF2 on the formation and decomposition of 3CaO·3Al2O3·CaSO4. The result showed that 3CaO·3Al2O3·CaSO4 began to form at about 1000°C, increased at approximately 1200°C, and then became almost pure 3CaO·3Al2O3·CaSO4—along with the vanishing of the transitional resultant at around 1300°C. CaF2 and Fe2O3 promoted the formation of 3CaO·3Al2O3·CaSO4 and the decomposition of CaSO4 while TiO2, ZnO and Cr2O3 restrained the forming rate of 3CaO·3Al2O3·CaSO4 because of their stabilisation effect on the transitional resultant CA. At 1400°C, 3CaO·3Al2O3·CaSO4 has already decomposed, and adding Cr2O3, ZnO and CaF2 facilitated the process. In addition, Cr2O3 and Fe2O3 decreased the decomposition temperature of 3CaO·3Al2O3·CaSO4.

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.

Study on CMP Slurry and Technique of Silicon Dioxide Dielectric for ULSI

SiO2 is a kind of widely used dielectric material in ULSI and its chemical mechanical planarization (CMP) is one of the most difficult processes. In this paper, the CMP mechanism and the effect of abrasive on SiO2 dielectric were analyzed; the different factors of affecting the CMP were analyzed. A kind of organic alkali was chosen to act as the pH regulator and complexation agent to enhance the chemical effect. The silica sol was selected as abrasive to realize no contamination, low viscidity, proper hardness and easy to clean. The effect of different concentration of abrasive on the removal rate and surface performance were studied. Further more the influence of polishing slurry flow and surfactant on removal rate were analyzed. The final planarization was realized.

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.

Influence of surfactant on Si{111} etched surface

The anisotropy etched technique of single crystal silicon in alkaline solution with high pH value has become one of the key technique for MEMS development. Production of smooth, defect-free silicon surface is essential for fabrication of all kinds of devices. In order to gain optimal silicon etched surface, non-ion surfactant was added in silicon{111} etchants, and its concentration was different and over than CMC(Critical Micelle Concentration). From the experiment results, it can be seen that the etched n-Si{111} surface was improved with increasing concentration of surfactant. Using such method the optimal etched surface can be gotten.

Study on Chemical Mechanical Polishing Technology of Copper

Chemical mechanical polishing (CMP) of copper films in alkaline slurries was investigated. In the copper CMP, the slurry was made by adding colloidal silica abrasive to de-ionized water.The organic alkali was added to adjust the pH, H2O2 was used as an oxidizer.The effects of varying polishing temperature, polishing pressure, slurry flow rate, organic alkali concentration and oxidizer concentration on removal rate were investigated in order to determine the optimum conditions for those parameters. It is shown the chemical composition of the slurry was 2%~3% oxidizer concentration, 3% organic alkali concentration and proper amount surfactant is reasonable. The solid concentration of the polishing slurry was fixed at 20% by weight. The removal rate of copper could reach 700nm/min and the surface roughness after CMP was 0.49nm.