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CN-121976285-A - Method for reducing silicon oxygen content of 8-inch lightly doped Czochralski single crystal and improving in-plane oxygen distribution uniformity and single crystal ingot

CN121976285ACN 121976285 ACN121976285 ACN 121976285ACN-121976285-A

Abstract

A thermal field structure used for reducing the silicon oxygen content of 8-inch lightly doped Czochralski single crystal and improving the in-plane oxygen distribution uniformity comprises a heater arranged on the periphery of a graphite crucible, a heat preservation cylinder arranged on the periphery of the heater, and a thermal shield arranged on the periphery of a crystal bar and above the surface of a melt, wherein the main structure of the thermal shield is in a configuration of being firstly inwards folded and then directly outwards expanded from top to bottom, the inwards folded configuration in the thermal shield accounts for 2/3-3/4 of the overall configuration height of the thermal shield, the distance from the horizontal plane of the bottommost part of the thermal shield to the surface of the melt is 40-50mm, and the thermal field structure further comprises the following technological parameters of cooperative optimization in the whole equal diameter stage of crystal bar growth, wherein the furnace pressure is set to be 1-3Torr, the argon flow rate is set to be 110-150slm, the pulling speed is set to be 0.7-0.9mm/min, the ratio of the crystal bar rotating speed to the crucible rotating speed is 2.5:1-3:1, and the linear attenuation rate of each crystal bar is reduced by 100% per 100% of crystal power along with the lowering of the surface of the melt in the crystal bar growth process.

Inventors

  • WANG ZHONGBAO
  • ZHANG YOUHAI
  • WANG LIGUANG
  • RUI YANG
  • YANG KAI
  • ZHAO NA
  • BAI YUAN
  • LI JUNLI

Assignees

  • 宁夏中欣晶圆半导体科技有限公司

Dates

Publication Date
20260505
Application Date
20260407

Claims (6)

  1. 1. A method for reducing the silicon oxygen content of an 8 inch lightly doped czochralski single crystal and improving the in-plane oxygen distribution uniformity, comprising: The thermal field structure comprises a heater arranged on the periphery of a graphite crucible, a heat preservation cylinder arranged on the periphery of the heater, and a thermal screen arranged on the periphery of a crystal bar and above the surface of a melt, wherein the main structure of the thermal screen is in a structure of being firstly internally retracted and then directly externally expanded from top to bottom, the internally retracted structure in the thermal screen accounts for 2/3-3/4 of the height of the whole thermal screen, a tapered channel from top to bottom is formed between the inner side surface of the thermal screen and the crystal bar, so that the flow velocity of argon is gradually increased when the argon flows through the area, the carrying and purging capacity of volatile matters on the surface of the melt is enhanced, and then an outwards-diffused diffusion channel is directly formed, so that the airflow is quickly diffused after leaving the surface of the melt, the airflow rebound or vortex generation is avoided, and the deposition of SiO on the lower edge of the thermal screen is reduced, wherein the distance from the horizontal plane of the bottommost part of the thermal screen to the surface of the melt is 40-50mm; the method also comprises the following technological parameters which are cooperatively optimized in the whole isodiametric stage of crystal bar growth: setting the furnace pressure to be 1-3Torr; the argon flow is set to be 110-150slm; The pulling speed is set to be 0.7-0.9mm/min; the ratio of the rotation speed of the crystal bar to the rotation speed of the crucible is 2.5:1-3:1; During ingot growth, as the melt surface was lowered, the heater power was linearly attenuated at a rate of 0.5% per 100mm of ingot growth relative to the initial power at the beginning of the isodiametric.
  2. 2. The method for reducing the silicon oxygen content of an 8-inch lightly doped Czochralski crystal and improving the uniformity of in-plane oxygen distribution as set forth in claim 1, wherein the ingot rotation speed is 12-20rpm and the crucible rotation speed is 4-8rpm.
  3. 3. The method for reducing the silicon oxygen content of an 8-inch lightly doped Czochralski crystal and improving the uniformity of in-plane oxygen distribution according to claim 1, wherein the heat shield comprises an outer cover, an inner upper cover and an inner lower cover, wherein the outer cover, the inner upper cover and the inner lower cover are all of annular structures and are connected with each other, the outer cover is cylindrical, the cross section of the inner upper cover is V-shaped and is provided with an opening at the bottom, the cross section of the inner lower cover is splayed, the top of the inner lower cover is butted with the bottom of the inner upper cover, and the bottom of the inner lower cover is butted with the bottom of the outer cover.
  4. 4. The method for reducing the silicon oxygen content of an 8-inch lightly doped czochralski crystal and improving the uniformity of in-plane oxygen distribution of claim 3, wherein the included angle α of the cross section of the inner lower housing and the horizontal direction is 20-30 degrees and the included angle β of the cross section of the inner upper housing and the vertical direction is 30-45 degrees.
  5. 5. The method for reducing the silicon oxygen content of an 8 inch lightly doped czochralski crystal and improving the uniformity of in-plane oxygen distribution of claim 3, wherein the outer cover, the inner upper cover, and the inner lower cover are all made of graphite.
  6. 6. A single crystal ingot, characterized by being drawn by the method for reducing the silicon oxygen content of 8 inch lightly doped czochralski single crystals and improving the in-plane oxygen distribution uniformity as claimed in any one of claims 1 to 5.

Description

Method for reducing silicon oxygen content of 8-inch lightly doped Czochralski single crystal and improving in-plane oxygen distribution uniformity and single crystal ingot Technical Field The invention relates to the technical field of monocrystalline silicon manufacture, in particular to a method for reducing 8-inch lightly doped Czochralski silicon oxygen content and improving in-plane oxygen distribution uniformity and a monocrystalline rod. Background In the process of preparing 8 inch lightly boron or phosphorus doped monocrystalline silicon by a Czochralski method, a quartz crucible reacts with a high temperature silicon melt in the quartz crucible to generate volatile silicon monoxide (SiO), part of the SiO volatilizes from the surface of the melt and is carried out of the system by argon, and the other part of the SiO dissolves into the silicon melt and finally enters a grown crystal bar to form interstitial oxygen, wherein the oxygen content in the crystal bar directly influences the electrical and mechanical properties of subsequent devices. For high-end power devices (e.g., fast recovery diodes), an 8 inch substrate ingot is required to have not only a relatively low oxygen content, i.e., less than 10ppma, but also an in-plane uniform oxygen content, i.e., less than 5% oxygen radial gradient ORG. At present, common technological means for reducing oxygen content in the industry mainly comprise the steps of reducing the rotating speed of a crucible to slow down the reaction speed of a crucible wall and a silicon melt, reducing the generation of SiO, increasing the flow rate of argon and reducing the furnace pressure to promote the volatilization and discharge of SiO, however, the methods introduce other problems that the excessive reduction of the crucible rotation weakens forced convection of the melt, so that the temperature field and the oxygen concentration in the melt are uneven, the uniformity of the oxygen distribution in the crystal rod surface is further deteriorated, particularly in the existing thermal field structure, the bottom of a traditional thermal screen is in a straight configuration, the excessive reduction of the furnace pressure and the increase of the flow rate of argon easily cause the volatilized SiO to be accumulated at the bottom of the thermal screen, and can not be discharged in time along an optimal path, so that the risk of falling back to the melt is remarkably increased, the SiO concentration in the melt is increased, the uniformity of the oxygen distribution is destroyed, and finally the oxygen distribution uniformity is reduced, therefore, the oxygen content in the crystal rod surface of 8-inch light boron-doped or phosphorus-ppmsilicon crystal rod prepared by the conventional means is much higher than 10 a, the ORG is 5% to 10%, and the requirement of a high-end 8-inch crystal power substrate cannot be met. Therefore, how to realize low oxygen content and ensure higher oxygen distribution uniformity in the surface of the crystal bar at the same time becomes a key technical problem to be solved in the preparation of 8-inch lightly doped Czochralski silicon. Disclosure of Invention In view of the foregoing, it is desirable to provide a method and a single crystal ingot for reducing the silicon oxygen content of 8 inch lightly doped czochralski single crystal and improving the uniformity of in-plane oxygen distribution, so as to realize low oxygen content and ensure the uniformity of in-plane oxygen distribution of the ingot, and meet the requirements of high-end power devices on the oxygen content and the uniformity of in-plane oxygen distribution of 8 inch substrate ingots. According to one aspect of the invention, a method for reducing the silicon oxygen content of 8-inch lightly doped Czochralski single crystal and improving the in-plane oxygen distribution uniformity is provided, the adopted thermal field structure comprises a heater arranged at the periphery of a graphite crucible, a heat preservation cylinder arranged at the periphery of the heater and a thermal shield arranged above the surface of a crystal bar, wherein the main structure of the thermal shield is in a configuration of being internally retracted from top to bottom and then directly expanding outwards, the internally retracted configuration in the thermal shield accounts for 2/3-3/4 of the height of the whole thermal shield configuration, a gradually-reduced channel from top to bottom is formed between the inner side surface of the thermal shield and the crystal bar, so that the flow speed of argon is gradually increased when the argon flows through the area, the carrying and purging capacity of volatile matters on the surface of a melt are enhanced, and then a diffusion channel which diffuses outwards is directly formed, the air current is rapidly diffused after leaving the surface of the melt, the air current rebound or vortex generation is avoided, and the deposition of SiO on the lower e