electrolytic in-process dressing (elid) grinding for silicon wafers.
by：QY Precision 2020-01-02
1. The introduction of advanced precision grinding technology, especially those designed to improve the polishing process of silicon wafers, plays an important role in replacing traditional loose grinding processes such as grinding and polishing (Inasaki, 1987). In addition, the latest manufacturing process for semiconductors and optical components requires ultra-precision grinding to be able to meet three performance requirements at the same time: * good surface finish; * High surface accuracy; * Low underground damage. A new grinding technology of silicon wafer is proposed. Processing feedback (ELID-grinding). The technology is expected to meet strict performance requirements by using: * fine grits wheels with rigid metal bonds; * Electrolysis- Process dressing; * Super Precision Grinder. This paper describes the electrolysis- As a practical ultra-precision mirror grinding technology for silicon wafer, process trimming is studied by studying the surface topography, subsurface damage and removal mechanism (Dobrescu et al. , 2009). 2. ELID- Grinding Technology Figure 1 shows ELID- Grinding principle, which was invented by the application of cast iron bonded diamonds (CIB-D) The wheel of the silicon wafer. By smoothly touching its surface with a brush, the wheels become positive. The electrode fixed below the surface of the wheel is the negative electrode. In the gap of about 0. 1mm between the two electrodes, electrolysis occurs through the supply of conductive fluid. The ELID- The grinding system consists of the basic elements that produce a typical electrolytic phenomenon. These are: metal bonded grinding wheels, power supplies, grinding fluids, and electrodes ( Dashen Nakagawa, 1990). [ Figure 1 slightly] The author proposed ELID- Grinding with CIB D-wheel with fine grain. Relatively rough grinding wheels can also be usedgrinding. In order to ensure the success of the fine grinding operation, the following factors should be considered: * the type of metal bond in the wheel used affects the electrolysis rate; * DC power supply that needs to generate high frequency pulse voltage for electrolytic grinding-Process dressing; * Chemical-solution- The type grinding coolant diluted with water is used as grinding fluid and electrolyte; * For negative poles that are not self-electrolytic, materials with good conductivity, such as copper and graphite, are used. The metal bonding wheel is pre- Electric trimming before grinding operation. Before that After about 20 minutes of trimming, the working current of the electrolysis is reduced by about 5 times. This is because, depending on the ionization of the metal Bond, an isolation layer consisting of hydroxide and oxide is produced on the surface of the wheel. After ELID- At the beginning of the grinding, the isolation layer is scraped through the friction between the wheel and the surface of the workpiece. Therefore, the working current will recover even in the ultra-fine grinding, and the particle protrusion can be obtained. 3. Figure 2 of the experimental equipment shows the type of grinding used by ELIDgrinding. Ultra-precision Rotary surface grinder with ELID-Using the system ( Dobrescu & Dorin, 2007). This CNC machine has air. Spindle and feed-Resolution of 0. 1 micron closure Loop feedback system. CIB- Dwheels with different granularity from 400 to 120000 are used. The wheel size is 143mm in diameter and 3mm in width. Grind the wafer workpiece. Surface measuring instruments using a laser and a diamond stylus with a 2 micron radius were used in the ground survey. X- In order to detect underground damage, the ray was applied and the angle-Sanding and steps Etching of silicon wafers (Dobrescu, 1998). [ Figure 2:4. Experimental procedure each wheel is bonded by 325 bronze Diamond wheels and waspre- Electrolytic wear. The total cutting depth of each wheel is set to 20 microns. Wheel sand size and ELID- The grinding conditions are shown in Table 1. Detection and evaluation of underground damage by X- Ray terrain and angle Polished separately. The X- Ray topology diagram of 152 silicon wafer. The wheels with a diameter of 4mm, 4000, 6000 and 8000 were evaluated and compared until 2000. The surface of each ELID grinding silicon wafer produced by 2000, 4000, 6000 and 8000 wheels is polished by angle and chemically etched, and the depth of cracks in surface damage is evaluated and compared. Step- Etching is used to evaluate the depth of the damaged subsurface layer on the silicon wafer produced by the ultra-fine grinding wheel. Chemical processes combined with chemistry Mechanical polishing, chemical etching and heat treatment are all used to reduce damage. Under constant cutting depth and constant pressure grinding, 120000 and 3000000 wheels were tested and the surface quality produced was compared. Traditional grinder with anELID-for constant pressure grinding The system and the 120000 metal bonding wheel are used. Surface accuracy was also evaluated in ultra-fine grinding. The accuracy of the plane is detected by laser interferometer. This surface is made by elid- Grind with 8000 and 40000 CIB D-wheel and ultra-precision Rotary surface grinder. Table 2 shows the use of elid- Grinding of different particle sizes. The results show that the grinding surface finish can be increased proportionally according to the particle size, and in Rmax, 2 the surface finish is 18 nm. 8 nm in Ra was obtained by using 40000 CIB-D wheels. 5. Conclusion The surface finish caused by wheel particle size and the silicon wafer Mirror produced by ultra-fine grinding are studied. Smooth surface of 2. 8 nm in Ra and 18 nm in Rmax were obtained through 40000 rounds. Sub-surface damage in grinding silicon wafers was examined by x-ray and angle-polish. The crack layer can be reduced using the afiner particle size and the depth of the crack layer is evaluated as 1. 3, 1. 1, 1. 0, 0. 4 microns, produced using 2000, 4000, 6000 and 8000 wheels, respectively. The use of fine grinding wheels can improve the surface finish and quality at the same time, and 8000 of the wheels produce cracks below 1 micron. After etching with a depth of 1 micron on anELID-all damaged layers are completely removed Ground wafers produced in round 40000; As a result, damagedlayer has been shown to be less than 1 micron in total. Surface differences due to materials were studied. Through surface analysis and grinding surfaces of about 3, the advantages of constant pressure grinding for overweight wheels such as 120000 and 3000000 are proved. 3 angstroms in Ra, 23. 5 angstroms were successfully implemented in rmax. Using constant pressure grinding is easier to obtain better surface finish than constant cutting depth. The surface accuracy of grinding silicon wafer with ultra-fine grinding wheel was detected by laser interferometer. High surface accuracy of 158. 2 nm is also achieved by grinding with ultra-fine metal bonding wheels and ELID of 60mm diameter silicon wafers. 6. References Dobrescu, T. (1998). Cercetari privind optimizarea masinilor de superfinisat materiale fragile, doctoral thesis, University \"polehnica\" semaranda dobescu, Romania. ; Dorin, A. (2007). Record of 2007 DAAAM yearbook and 18 DAAAM International Symposium intelligent manufacturing and automation: focus on the creativity, Responsibility and Ethics of engineers, Katalinic, B. (Ed. ), pp. 229-230, ISBN 3-901509-58- 5. Zadar, Croatia, published by DAAAM International, Vienna, Austria, October 2007; Enciu, G. ; Nicolescu, A. (2009). Selection of process parameters for grinding ceramics, DAAAM 2009 chronicles & 20 international DAAAM seminar \"intelligent manufacturing and automation: focus on theory, practice and education\" record(Ed. ), pp. 0361-0362, ISBN978-3-901509- 704, Vienna, Austria, November 2009, published by DAAAMInternational, Vienna, Austria. (1987). Grinding of hard and brittle materials, CIRP Annals, no. 36, pp. 463-471 Ohmori, H. ; Nakagawa, T. (1990). Mirror grinding of Electrolytic In-silicon wafer Process dressing room, Annual Report of China Radiation Protection Research Institute, No. 39, pp. 329-