Patent Application
20240018689
This disclosure claims a priority to Chinese Patent Application No. 202111146606.2 filed on Sep. 28, 2021, the disclosures of which are incorporated in their entirety by reference herein.
The present disclosure relates to the field of semiconductor silicon wafer production, and in particular to a crystal puller for pulling monocrystalline silicon ingots.
Silicon wafers used for producing of semiconductor electronic components such as integrated circuits are mainly produced by slicing monocrystalline silicon ingots pulled by the Czochralski method. The Czochralski method includes melting polysilicon in a quartz crucible to acquire a silicon melt, immersing a monocrystalline seed into the silicon melt, and continuously pulling the seed to move away from the surface of the silicon melt, thereby a monocrystalline silicon ingot is grown at the phase interface during pulling.
In the production process described above, it is advantageous to provide such a silicon wafer that has a Denuded Zone (DZ) extending into the body from the front surface and a Bulk Micro Defect (BMD) zone adjacent to the DZ and further extending into the body. The front surface refers to a surface of the silicon wafer on which electronic components are to be formed. The above-mentioned DZ is important, the reasons are as follows: in order to form electronic components on a silicon wafer, it is required that there is no crystal defects in the formation area of electronic components, otherwise it will lead to circuit breakage and other faults. Thus, the electronic components can be formed in the DZ to avoid the influence of crystal defects. The effect of the above-mentioned BMD is that it can produce an Intrinsic Getter (IG) effect on metal impurities to keep metal impurities in silicon wafers away from the DZ. Thus, the adverse effects such as the increase of leakage current and the reduction of gate oxide film quality caused by metal impurities can be avoided.
In the process of producing the above-mentioned silicon wafers with BMD zones, it is advantageous to dope silicon wafers with nitrogen. For example, in the case of a silicon wafer doped with nitrogen, it is possible to promote the formation of BMD with nitrogen as the core, so that the BMD can reach a certain density and effectively play a role as a source for absorbing metal impurities. Moreover, it is also have a beneficial effect on the density distribution of the BMD, such as making the density of the BMD more uniformly distributed in the radial direction of the silicon wafer, for another example, making the density of the BMD higher in the region adjacent to the DZ and gradually decreasing toward the inside of silicon wafer, etc.
In addition, during the silicon wafer production process, the BMD density of nitrogen-doped silicon wafers can be further increased by subjecting the nitrogen-doped silicon wafers to a heat treatment, because if such silicon wafers are subjected to the heat treatment, the supersaturated oxygen in the silicon wafer will precipitate out as oxygen precipitates, and such oxygen precipitates are also known as BMD. However, in the prior art, the heat treatment of silicon wafers needs to be performed in a heat treatment furnace being separated from the crystal puller. The existing heat treatment furnaces can be broadly classified into horizontal and vertical types according to the structure of the furnace inside. Both horizontal and longitudinal heat treatment furnaces can perform heat treatment upon only hundreds of silicon wafers at one time due to structural limitations, which is low efficient. Moreover, when the heat treatments are performed upon a batch of wafers, cross contamination may easily occur, which means impurities on some wafers may affect other wafers. In addition, since wafers are usually placed in a wafer boat in the heat treatment furnace and preformed heat treatment, slip dislocations of crystal lattices caused by thermal stress may be induced in the part of the wafer that is in contact with the wafer boat.
In order to solve the above-mentioned technical problems, embodiments of the present disclosure provide a crystal puller for pulling a monocrystalline silicon ingot, which solves the problem of low efficiency of heat treatment of silicon wafer, avoids the problem of cross contamination and the problem of slip dislocations of crystal lattices that may be caused by contacting between a wafer and a wafer boat during heat treatment of a silicon wafer.
The technical solutions of the present disclosure are as follow.
Embodiments of the present disclosure provide a crystal puller for pulling monocrystalline silicon ingots, the crystal puller comprises a heater configured with a heat treatment chamber, in which the heater is arranged in the crystal puller such that the monocrystalline silicon ingots are accessible to the heat treatment chamber by moving along a direction of crystal growth.
The embodiments of the present disclosure provide a crystal puller for pulling a monocrystalline silicon ingot which further includes a heater configured with a heat treatment chamber, which differs from the conventional crystal pullers. Therefore, unlike a way in which heat treatment is performed on the silicon wafers using a conventional technology, by using the crystal puller according to the present disclosure, the monocrystalline silicon ingot is pulled from melt, and then is heat treated in the crystal puller. Since the heat treatment chamber is arranged inside the crystal puller, there is unnecessary to transfer the monocrystalline silicon ingots into a conventional furnace. Moreover, the heat treatment may be performed on the entire monocrystalline silicon ingot in the crystal puller, thus greatly improving the efficiency of the heat treatment. In addition, since the heat treatment is performed on the monocrystalline silicon ingots instead of the silicon wafers, cross contamination and possible slip dislocations of crystal lattice caused by the contact between wafers and wafer boats are avoided during heat treatment of the wafers.
The technical solutions in the embodiments of the present disclosure will be described hereinafter in conjunction with the drawings in the embodiments of the present disclosure in a clear and complete manner.
Refer to
When the monocrystalline silicon ingots are pulled using the crystal puller 1, the process includes the following steps. First of all, placing the high purity polysilicon raw material into the crucible 10, and the crucible 10 is continuously heated by the graphite heater 20 while the crucible rotation mechanism 30 drives the crucible 10 rotating, to melt the polysilicon raw material contained in the crucible 10 into a molten state, i.e., melting into molten liquid S2. The heating temperature is maintained at about more than one thousand degrees Celsius. The gas filled in the puller is usually an inert gas that allows the polysilicon to melt and without generating unwanted chemical reactions. When the liquid surface temperature of the molten liquid S2 is controlled at the critical point of crystallization by controlling the hot zone provided by the graphite heater 20, by pulling the monocrystalline seed S1 located on the liquid surface upward along the direction T, the molten liquid S2 grows into the monocrystalline silicon ingot S3 in the crystal direction of the monocrystalline seed S1 as the mono-crystalline seed S1 is lifted upward. In order to finally produce silicon wafers with high BMD density, it may be optionally doped with nitrogen in raw material during the pulling process of monocrystalline silicon ingots, for example by filling the puller chamber of the crystal puller 1 with nitrogen gas during the pulling process, or by doping the silicon melt in the crucible 10 with nitrogen, so that the pulled monocrystalline silicon ingots and the silicon wafers slicing from the monocrystalline silicon ingots will be doped with nitrogen.
In order to further increase the BMD density within the monocrystalline silicon ingots, the embodiments of the present disclosure proposes a crystal puller with a heat treatment chamber, in which the monocrystalline silicon ingots are pulled from melt and heat treated in the crystal puller subsequently. Specifically, referring to
In the embodiment illustrated in
The monocrystalline silicon ingot S3 is heat-treated in heat treatment chamber 501 through the heater 50, whereby the supersaturated oxygen in the monocrystalline silicon ingot S3 precipitates as oxygen precipitates, i.e. precipitates BMD, to achieve the BMD density in monocrystalline silicon ingots S to the required level. It is unnecessary to slice the monocrystalline silicon ingots into silicon wafers and then transfer them in a separate heat treatment furnace for performing heat treatment. Thus the efficiency of heat treatment is improved and cross contamination problems and possible slip dislocations of crystal lattice caused by contact with the crystal boat due to the heat treatment in the silicon wafer form can be avoided.
In order to achieve movement of the monocrystalline silicon ingot S3 along the direction of crystal growth T, refers to
In order to make the monocrystalline silicon ingot S3 being heat treated under the predetermined conditions, optionally, the pulling mechanism 60 is configured to allow the entire monocrystalline silicon ingot S3 to stay in the heat treatment chamber 501 for a period of time as the heat treatment is required. As shown in
Since the monocrystalline silicon ingot S3 enters the heat treatment chamber 501 along the direction of crystal growth, the different parts of the monocrystalline silicon ingot S3 in the length direction actually enter the heat treatment chamber 501 at different time points. In order to ensure each part of the monocrystalline silicon ingot S3 to experience heat treatment under the same conditions, the time that individual part of the monocrystalline silicon ingot S3 stays in the heat treatment chamber 501 should be the heat treatment time as required.
In this regard, in the preferred embodiments of the present disclosure, the crystal pulling mechanism 60 is configured to move the monocrystalline silicon ingot S3 through the heat treatment chamber 501 at a constant speed, such that any cross section of the monocrystalline silicon ingot S3 stays in the heat treatment chamber 501 for a period of time as the heat treatment is required. As a result, the actual stay time of each part of the monocrystalline silicon ingot S3 in the heat treatment chamber 501 is the same, ensuring that the monocrystalline silicon ingot S3 is heat treated overall uniformly.
In the heat treatment process, in addition to the need to control the heat treatment time, the control of the heating temperature is also important. In the preferred embodiment of the present disclosure, refer to
As shown in
In order to further precisely control the heat treatment temperature provided by the heater 50, in the preferred embodiments of the present disclosure, the heater 50 may be controlled by the controller 80 such that different portions of the heater 50 along the direction of crystal growth T provide different temperatures simultaneously. As a result, if the actual temperatures of different portions of the mono-crystalline silicon ingot S3 along the direction of crystal growth T are different during the heat treatment process, the various portions of the heater 50 are able to provide heating temperatures based on these actual temperatures so that the actual experienced heat treatment temperatures of each part of the monocrystalline silicon ingot S3 are the same.
In the preferred embodiments of the present disclosure, the heat treatment temperature of the monocrystalline silicon ingot may be about 800 degrees Celsius.
In the preferred embodiments of the present disclosure, the heat treatment time may be about 2 hours.
In one embodiment of the present disclosure, the crystal puller 1′ is arranged to enable the entire mono-crystalline silicon ingot S3 to undergo the heat treatment simultaneously in the heat treatment chamber 501. Preferably, as shown in
By using the crystal puller according to embodiments of the present disclosure, the BMD density within the mono-crystalline silicon ingot S3 is further increased. Preferably, the monocrystalline silicon ingot S3 has a BMD density of not less than 1E8ea/cm3 (1E8/cm3) after being performed heat treatment in the heat treatment chamber 501.
It should be noted that the technical solutions described in the embodiment of the present disclosure may be combined in any way without conflict.
The above description is merely the specific embodiment of the present disclosure, but the scope of the present disclosure is not limited thereto. Moreover, any person skilled in the art would readily conceive of modifications or substitutions within the technical scope of the present disclosure, and these modifications or substitutions shall also fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be determined by the scope of the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202111146606.2 | Sep 2021 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2022/122175 | 9/28/2022 | WO |
