At present, the production method of silicon single crystal is mainly based on the Cz method and the zone melting method (FZ), and 70% to 80% of the silicon single crystal production in the world is produced by the Czochralski method. The commonly used Czochralski method for producing silicon single crystals is a pressure-reduced pull crystal process that uses a vacuum process and a flow atmosphere process. The vacuum pull crystal process is a process in which the silicon single crystal is drawn continuously and evenly into the furnace of the single crystal furnace to make the use of high-purity argon gas. At the same time, the vacuum pump continuously extracts air from the furnace. Keep the vacuum in the furnace stable at (27 ~ 5.3) 10 Tuen This process has the characteristics of vacuum process (negative pressure in the furnace), and the characteristics of the flow atmosphere process (continuous inflation, continuous exhaust) 3. Use this In the process of growing a silicon single crystal, the process allows a high-purity argon gas stream charged into the furnace to penetrate through the entire area where the silicon single crystal is grown from the top down and promptly removes the silicon oxide and impurities generated due to the high temperature. Material, to ensure the quality of silicon single crystal.
According to the most commonly used silicon single crystal pull pull vacuum process, the vacuum system is generally equipped with a spool vacuum pump.
Therefore, the need to periodically change the vacuum pump oil to do so can also extend the life of the vacuum pump. However, the frequent replacement of vacuum pump oil is not only expensive to maintain but also cannot be achieved during a pull process. Especially when pulling heavily doped arsenic and other highly toxic doping elements of silicon single crystals, some arsenic and other highly toxic elements are incorporated into the vacuum pump oil to make the maintenance of the vacuum pump more difficult. The vacuum pump oil treatment with arsenic and other highly toxic doping elements is very Tricky thing.
3Improvement and Application Results The improved vacuum system of the water ring pump in Yu1 considers that the vacuum in the furnace is normally maintained at (2.7~5.3)x103Pa. The two-stage water ring pump can meet this requirement and therefore improve. The main pump of the vacuum system adopts a water ring pump; the task of requiring the ultimate vacuum in the furnace to reach below 67 Pa before the start of pulling crystal will be pumped by the auxiliary pump, so the auxiliary pump still uses the slide pump.
See the improved vacuum system. Its working principle is that at the beginning of work, the isolation valve between the stretching chamber and the furnace is open, and the secondary slide valve vacuum pump 7 pulls the gas in the stretching chamber and the furnace through the bypass vacuum ball valve 3 to require the ultimate vacuum in the furnace. Below 6.67Pa, check the tightness of the furnace to meet the requirements of pulling crystal; then start normal crystal pulling, Ar gas passes through the mass flow controller 9, the upper argon valve 4 passes into the stretching chamber to the furnace, and the bypass vacuum valve is closed 3 And the auxiliary slide valve vacuum pump 7, open the main water ring pump 8 through the main vacuum ball valve 1 pumping, then can ensure that the furnace vacuum is maintained at (2.7 ~ 5.3) x 103Pa. When the pulling process needs to open the stretching chamber, Operation and the same as the original vacuum system to open the lower argon valve 6, close the upper argon valve 4, can close the isolation valve, and then open the central argon valve 5 to the stretching chamber is inflated to atmospheric pressure, to close the central argon valve 5 Open the stretching chamber; after the operation is completed, close the stretching chamber, it is necessary to use the secondary slide valve pump 7 through the secondary vacuum ball valve 2 to draw the stretching chamber to a vacuum close to the hearth so that the secondary vacuum ball valve 2 and the secondary slide can be closed. Pump 7, the isolation valve is opened, and then opening the upper valve 4 argon, argon lower portion of the valve 6 closed, pulling back to the normal state.
(Continued on page 31) Manufacturing Technology Wu Xiulong (1979-) Male, from Wuhu City, Anhui Province, Master's degree in 2002, School of Electronic Science and Technology, Anhui University, Research direction: modeling and modeling of microelectronic devices; Ke Daoming (1954) - Male, Anqing City, Anhui Province, Professor, Ph.D., Master's tutor of Anhui University, 1992 graduated from Southeast University Electronic Engineering Department, has long been engaged in the simulation and modeling of semiconductor devices, and VLSI CAD research and teaching.
(Continued from page 19) In this improved vacuum system, either a water ring pump can be used as the main pump, or when the bypass vacuum ball valve 3 is closed, the slide valve pump is used as the main pump to satisfy different crystal pulling processes. need. When the water ring pump is used as the main pump, silicon oxide and impurity volatiles generated by normal crystal pulling are pumped into the water ring pump and dissolved in the water of the water ring pump. The water of the water ring pump is continuously circulated and updated, ensuring the The water cleaning makes the water ring pump work normally. It will not affect the working performance of the water ring pump because the pulling time is too long, so as to maintain the normal pumping speed and ensure the vacuum degree in the furnace is stable. Exhausted water can also be reused after treatment. This is not only easy to maintain but also low in cost. Particularly when silicon single crystals containing highly toxic elements such as arsenic are added, it is easier to separate arsenic and other highly toxic doping elements into water. Collect less environmental impact.
The improved vacuum system has been applied in the CG6000 automatic single crystal growth furnace newly designed and produced by Hangzhou Kaixus Zheda Electromechanical Co., Ltd., a joint venture between Kayex Corporation and Zhejiang University Machinery Factory. Good results. The company, which has purchased CG6000 fully automatic single crystal growth furnace from Hangzhou Kaixing Zheda Electromechanical Co., Ltd., has successfully used this technology in pulling special requirements such as large diameter and heavy doping. Silicon single crystal has achieved very good economic and social benefits.
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