Apparatus and method for manufacturing silicon-doped single crystal rods

Abstract

The present invention relates to an apparatus and method for producing doped crystals according to the Czochralski method, comprising a pressure vessel, a crucible in the pressure vessel capable of containing liquid silicon, and an apparatus for doping the melt, the apparatus for doping comprising a housing, a storage container for holding a dopant, a conveyor belt for transporting the dopant, an apparatus for forming a filling layer on the conveyor belt, and a tube, the first end of which can receive the dopant from the conveyor belt, the second end of which faces the liquid silicon and is closed against the liquid silicon by a porous separating element.

Description

Technical Field

[0001] The present invention relates to a process for manufacturing a single crystal ingot of silicon, which process comprises melting polysilicon in a crucible, doping the silicon, and pulling a single crystal from the melt heated in the crucible onto a seed crystal, according to the Czochralski method.

Background Art

[0002] Single crystal silicon, which is the starting material for most methods of manufacturing electronic semiconductor components, is typically produced by the Czochralski method ("CZ"). In this method, polycrystalline silicon ("polysilicon") is placed in a crucible and melted, a seed crystal is brought into contact with the molten silicon, and a single crystal is grown by slowly withdrawing it.

[0003] The crucible typically consists of a material containing silicon dioxide such as quartz. The crucible is generally filled with chunks and / or granules of polycrystalline silicon, which is melted by a lateral heater arranged around the crucible and a bottom heater arranged under the crucible. After a thermal stabilization stage of the melt, a single crystal seed crystal is immersed in the melt and withdrawn. In this procedure, silicon crystallizes at the end of the seed crystal wetted by the melt. The crystallization rate is greatly influenced by the rate at which the seed crystal is withdrawn (crystal withdrawal rate) and the temperature of the interface at which the molten silicon crystallizes. By appropriately controlling these parameters, a portion called the "neck" is first withdrawn to remove dislocations, then the conical portion of the single crystal, and finally the cylindrical portion of the single crystal are withdrawn, from which a semiconductor wafer is later obtained.

[0004] For example, as described in US5954873A, the corresponding operating parameters of the crystal withdrawal process are adjusted so that the defect distribution in the resulting crystal is radially uniform.

[0005] In particular, care should be taken to ensure that even if aggregates of vacancies, also known as COP (Crystal Originated Particles), are formed, their number is below the detection limit. The detection limit for COP is 1000 defects / cm². 3 It is considered to be less than that density.

[0006] At the same time, care is taken to ensure that any interstitial silicon atom aggregates called LPITs, if they do occur, are kept below the detection limit. The detection limit is 1 defect / cm². 2 This is considered to be below the LPIT density.

[0007] In certain applications, a certain amount of dopant is added to the molten silicon to achieve a desired resistivity in the silicon crystal. Traditionally, the dopant is introduced into the molten silicon from a filling hopper located several meters above the height of the molten silicon. However, this procedure is undesirable for volatile dopants because such dopants tend to evaporate uncontrollably into the surrounding environment, which can lead to the formation of oxide particles (i.e., suboxides), which can fall into the molten silicon and be incorporated into the growing crystal. These particles become heterogeneous nucleation sites and can ultimately lead to failure of the crystal pulling operation, for example, by causing dislocations.

[0008] Certain known dopant systems introduce volatile dopants into the growth chamber in gaseous form. However, such systems require manual replenishment after each doping procedure. Furthermore, such systems cannot be replenished during operation. As a result, the amount of dopant that can be loaded for each growth operation is limited in such systems. Therefore, the size of the growable silicon block is limited in such systems. Moreover, such systems tend to supply dopants uncontrolledly during growth operations, thereby causing uncontrolled increases in dopant concentration along the longitudinal axis of the grown ingot.

[0009] WO2009 / 113441A1 describes a silicon doping process and doping apparatus, in which the dopant is sublimated and supplied to the molten material in gaseous form.

[0010] WO2014 / 141309A1 describes a crystal pulling apparatus which includes a dopant supply system including a dopant conduit with a specific chamber system so that solid dopants do not fall into the molten material, but gaseous dopants can access the molten material.

[0011] WO2020 / 123074A1 presents an evolution of the above specification, which includes a porous separation element fitted into the dopant conduit instead of the chamber system used. The porous separation element prevents solid dopant granules, which move violently during the sublimation process, from leaking out of the chamber system. If these granules leak out of the chamber system, they may fall into the molten material and potentially form particles that can, firstly, impair the consistency of the dopant operation, and secondly, cause crystal dislocations.

[0012] The specification EP0170856A1 describes an apparatus for refilling a crucible with silicon during crystal pulling using a conveyor belt. A drawback of this configuration is that the amount of silicon added may vary, and therefore it is not suitable for use as a dopant refilling unit.

[0013] Therefore, improvements are needed in the dopant supply system for producing doped silicon blocks by doping molten silicon using the Czochralski process. [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] Therefore, an object of the present invention is to provide a process and apparatus that enables the production of single crystal ingots by the Czochralski pulling method with minimal axial change of the dopant. [Means for solving the problem]

[0015] This objective is achieved by the process and apparatus described in the claims. Features shown in relation to the above embodiments of the process of the present invention can be appropriately replaced in the product of the present invention. Conversely, features shown in relation to the above embodiments of the product of the present invention can be appropriately replaced in the process of the present invention. These and other features of embodiments according to the present invention are made apparent in the description of the drawings and the claims. Individual features can be realized separately or in combination as embodiments of the present invention. They can also describe advantageous configurations that can be protected independently. [Brief explanation of the drawing]

[0016] [Figure 1] This figure shows the configuration of the present invention for continuous silicon doping. [Figure 2] This figure shows a reservoir container (204) filled with dopant. [Figure 3] This diagram shows the connection between the conveyor belt and the molten material. [Modes for carrying out the invention]

[0017] Detailed description of exemplary embodiments of the present invention Apparatus for pulling doped Czochralski crystals and enabling continuous metering and addition of dopants during pulling includes apparatus for pulling crystals by the Czochralski method.

[0018] As shown in Figure 1, the crystal (105) is pulled up from the molten material (101) with one or more heat shields (102) containing the radiant heat. Doping of the molten material (101) is achieved by conveying the dopant from a reservoir container (108) in a housing (107) to a collection hopper (110) via a conveyor belt (106), from where the dopant falls onto a porous separation element (104) via a pipe. The Czochralski crystal pulling section includes a crucible (113) in a pressure vessel (103) filled with liquid silicon (101). The crystal (105) is pulled up from the molten material (101) with one or more heat shields (102) containing the radiant heat. Doping with the molten material (101) is achieved by transporting the dopant from a reservoir container (108) located within the housing (107) to a collection hopper (110) via a conveyor belt (106), from where the dopant falls onto a porous separation element (104) via a pipe. Typical conditions at the location where the porous separation element (104) is positioned are such that the dopant sublimates. The gas thus obtained dops the liquid silicon, and therefore the crystals. A device (109) for forming a dump layer on the conveyor belt is mounted above the conveyor belt, which forms a distinct cone of the dumped dopant onto the conveyor belt (106) without causing further contamination. Pressure equalization between the housing and the pressure vessel is optionally possible by a compensating valve (111) further mounted on the gas line (112) between the pressure vessel and the housing. A blocking device (203) allows the dopant to access a connecting pipe (202) to a device (201) for forming a dump layer on the conveyor belt, which ensures that a distinct dump layer (208) of the dopant is formed on the conveyor belt (205). The open side (207) of the half-pipe of the device for forming the dump layer on the conveyor belt faces the direction of travel (206) of the conveyor belt. The dopant falls from the conveyor belt into a collection hopper (304), passes through a pipe (302) to access a porous separation element (301), where it can be sublimated.The device is held by a holding device (303).

[0019] An important feature of the present invention is the conveyor belt (106). Its function is to convey the dopant. The dopant is preferably arsenic and more preferably can consist of lumps having an appropriate particle size distribution or can consist of particles of arsenic or suitable compounds such as arsenic silicide, arsenic oxide, or arsenate. Even more preferred dopants include the following, namely Se, Bi.

[0020] The belt material of the conveyor belt is preferably configured to function in the environment of the lifting section. More specifically, this function is to be chemically resistant to the selected dopant compound under vacuum (lower limit 10 mbar) and at a radiant temperature of up to 150 °C, and should not release particles or volatile substances. The inventors have recognized that the preferred belt material in this context consists of dry fluorine rubber.

[0021] This function is made possible by the drive performed by a motor, which is more preferably arranged outside the vacuum region of the lifting section.

[0022] The driving force is transmitted by a shaft designed as a vacuum rotary passage. The drive motor itself is preferably configured as an electric motor and more preferably as what is called a stepper motor. The torque is preferably increased by a transmission device. The transmission device can preferably be composed of gears. A chain drive type or a belt drive type is equally possible.

[0023] The device (109) for forming a dump layer on the conveyor belt is extremely important for the flow of the dopant and, as a result, for the cross-section of the resulting dump layer (208). Particularly preferably, a shut-off device (203) that can be used to stop the continuous flow of the dopant is integrated for assembly purposes. This configuration is a control means having on / off limits and is preferably configured as a tap or a slide.

[0024] The inner diameter of the pipe conduit must be large enough so that the dopant can flow through without stopping. For example, in the case of granules, this diameter is at least 5 times the diameter of the maximum particle size of the specified particle size distribution.

[0025] The dopant is conveyed by the continuous movement on the conveyor belt and continues to flow through the pipe. In the equipment (109, 201) for determining the cross-section, it is ensured that a dump layer (208) is formed which has the maximum uniformity in cross-section over its entire length, thereby guaranteeing a linear correlation between the forward speed and the doping mass. The beginning and end of the dump layer where this correlation is not yet linear or is no longer linear should not exceed 20% of the length of the dump layer.

[0026] The inventors have recognized that an apparatus for forming a dump layer on the conveyor belt is particularly advantageous if it is a half-pipe having a diameter smaller than the width of the conveyor belt. What is particularly important here is that the apparatus is arranged on the conveyor belt such that one side of the apparatus is closed and the other side is open, and the open side faces the conveying direction of the dopant. This ensures that the dopant can be transported without further significant contamination and that the shape of the formed dump layer of the dopant has the maximum possible uniformity over its entire length.

[0027] The position of the apparatus for forming the dump layer is preferably set on the conveyor belt such that the minimum distance from the conveyor belt is smaller than the lower limit of the particle size distribution of the dopant. This prevents, on the one hand, the granules from being trapped between the apparatus and the conveyor belt and becoming immobile, and on the other hand, prevents the dopant from falling over the conveyor belt.

[0028] Here, the lower end of the apparatus for forming the dump layer is preferably configured to form a minimum opening angle of less than 3°, more preferably less than 1°, with the conveyor belt in the conveying direction.

[0029] The apparatus for forming the damp layer is more preferably made from borosilicate glass (laboratory glass, e.g., Duran®).

[0030] The reservoir container (108) includes a dopant reservoir. The mass of the reservoir is at least equivalent to the mass required for the lifting operation.

[0031] The reservoir container is preferably designed to be suitable for filling in a toxicologically compliant filling station. Ideally, the reservoir container should further take into account specific requirements for purity (metals) and cleanroom (particles).

[0032] A preferred material for the reservoir container is borosilicate glass (laboratory glass, e.g., Duran®). Particularly preferred is that not only the reservoir container (108) but also the shutoff mechanism (203) are integrated with the apparatus (109) for forming the dump layer.

[0033] The housing (107) is an extension of the vacuum region of the pulling section. This allows the mechanism described above to be operated during the crystal pulling process.

[0034] The housing (107) is more preferably designed with a water-carrying cooling system, for example, in the form of a jacket. Windows for viewing moving parts facilitate operation and monitoring. All moving parts (conveyor belt, vacuum rotating passage, transmission, and drive motor) are mechanically mounted to the housing.

[0035] Preferably, a collection mechanism (110) is located directly beneath a small conveyor belt, which may be configured as a collection hopper and transfer to a pipe (302). The upper diameter of the collection mechanism is preferably at least equal to the width of the dopant dump layer, and preferably at least three times larger.

[0036] The diameter of the pipe (302) is preferably selected so as not to cause blockage during operation. This can be ensured by making the inner diameter of the pipe at least five times the upper limit of the particle size distribution of the dopant used.

[0037] The pipe (302) guides the dopant, which is initially still solid, into a defined area of ​​the crystal pulling section above the molten material, where ambient conditions (pressure, temperature, and partial pressure of the dopant vapor) ensure the sublimation of the dopant. The defined area of ​​the crystal pulling section is preferably selected so that the sublimation process can be visually monitored through a viewing window.

[0038] A pipe retaining device (303) is installed between the enlarged region and the pipe, so the pipe only needs to be fixed there. The pipe retaining device (303) is preferably made of a polymer ring and has an airtight seal with the housing.

[0039] On the side of the pipe facing the molten material, the pipe is sealed with a porous separation element (301), which prevents particles from accessing the molten material but allows gas (sublimated dopant) to pass through and diffuse.

[0040] The inventors recognized that the material used for this porous separation element is extremely important. For example, if only solid materials are used, as suggested in WO20123074A1, then, however, minute particles, possibly formed upon collision with the solid barrier, may pass through the porous separation element into the molten material, causing crystalline dislocations (and thus complete fracture) in the molten material.

[0041] Therefore, the porous separation element (301) is preferably made of silica glass wool. More preferably, the porous separation element (301) is made of a hard porous material, preferably quartz glass, on the side facing silicon, and of silica glass wool on the side farther from silicon.

[0042] When the dopant sublimes, its gas mixes with the already present gas, and the dopant can diffuse through the porous separation element (301) towards the liquid silicon.

[0043] The typical gas in the crystal pulling section is, in principle, argon. Under certain circumstances, a mixture of nitrogen may also be present.

[0044] In the Czochralski crystal pulling section, oxygen and silicon (Si) are generated from liquid silicon. x O y It is especially important to remove the gas flow, which is composed of the ) components, as quickly as possible. Otherwise, deposits may form in the pulling section, which could cause problems when the pulling section is opened after the crystals have been pulled.

[0045] Therefore, preferably, argon also functions as a carrier gas applied to the reservoir vessel and pipes. Particularly preferably, a gas flow is established in the pipes leading towards the liquid silicon. This has two effects: firstly, it prevents gases formed during crystal pulling from being carried into the doping apparatus (whereas this could lead to problems in decomposition and refilling); and secondly, it ensures that the sublimated dopant does not backflow into the reservoir vessel or pipes (backflow can result in consequences involving considerable toxicological risks (arsenic)).

[0046] To prevent the undesirable event of the pressure difference between the reservoir container and the lifting section becoming too large, an overpressure valve or compensation valve (111) for pressure equalization is preferably installed in an additional line between the reservoir container and the lifting section.

[0047] The side of the tube (302) facing the liquid silicon is preferably located below the heat shield (102). This allows the dopant-enhanced transport gas to come into direct contact with the molten material, as only in this way can the desired increase in concentration in the molten material be achieved.

[0048] To prevent etching effects on the surface of the crystal (105) during growth by arsenic vapor, the end position of the guide pipe should not be too close to the crystal.

[0049] The inventors have found that the apparatus described for doping crystals during Czochralski crystal pulling is particularly advantageous. The economic benefits of using this apparatus are greatest when the crystal diameter exceeds 250 mm.

[0050] A preferred method involves pulling up a first crystal and doping it with a first dopant using the apparatus described above during the pulling process, with the conveyor belt speed correlated with the length of the growing crystal. This is preferably done so that the target speed of the conveyor belt is first defined, particularly at predetermined support points where the crystal will later be cut into ingot pieces. The target values ​​of the conveyor belt speed outside the support points are interpolated.

[0051] Therefore, the support point forms a 2-tuple composed of the crystal length and the conveyor belt speed.

[0052] Once the first crystal is pulled up, the ingot is measured to determine its resistivity. For this purpose, it is preferable to cut the ingot into pieces whose end faces will be subjected to resistance measurement.

[0053] The measured values ​​obtained are then compared with the desired resistance profile along that axis, and the difference between the measured values ​​and the desired values ​​is formed.

[0054] This difference is then used to create a new, modified support point for the second crystal. Particularly preferably, this process can be repeated to produce a crystal that is as close as possible to the desired resistance profile along the crystal axis.

[0055] A process in which the second dopant is mixed with polysilicon in a crucible is particularly preferred. This process can, for example, produce crystals having a particularly flat axial resistance profile.

[0056] The first dopant is preferably arsenic. The second dopant more preferably contains boron.

[0057] The crystal obtained in this way is preferably cut into ingot pieces with a saw, and then cut into semiconductor wafers with a wire saw. The resulting semiconductor wafers are preferably polished and optionally have epitaxially grown silicon layers. [Explanation of Symbols]

[0058] Abbreviation 101 Silicon molten 102 Heat Shield 103 Pressure vessel 104 Porous separation element 105 Crystal 106 Conveyor Belt 107 Housing 108 Reservoir containers 109 Apparatus for forming a dump layer on a conveyor belt 110 Collection hopper, collection mechanism 111 Compensation valve for pressure equalization 112 Gas line between pressure vessel and housing 113 Crucible 201 Apparatus for forming a dump layer on a conveyor belt 202 Connecting pipe 203 Circuit breaker 204 Reservoir container 205 Conveyor Belt 206 Direction of travel of the conveyor belt 207 Open side of the half-pipe of the device for forming a dump layer on a conveyor belt 208 Dopant Dump Layer 301 Porous separation element 302 Pipes that carry Dopants 303 Pipe holding device 304 Collection hopper, collection mechanism

Claims

1. Apparatus for producing doped Czochralski crystals, Pressure vessel (103) and A crucible (113) located inside the pressure vessel, capable of containing molten liquid silicon (101), The apparatus for doping the molten material is provided, Housing (107) and A reservoir container (108) for holding the dopant, A conveyor belt (106) for transporting the dopant, An apparatus (109) for forming a dump layer, which is a stacked layer of the dopant, on the conveyor belt, The system includes a pipe (110), the first end of which is accessible to the dopant from the conveyor belt, and the second end which faces the liquid silicon (101) and is closed off from the liquid silicon by a porous separation element (104). The apparatus (109) for forming the dump layer on the conveyor belt includes a half-pipe having a diameter smaller than the width of the conveyor belt (106, 205), the half-pipe is connected to the reservoir container (108) via a connecting pipe, the dopant is introduced into the half-pipe via the connecting pipe, the half-pipe is closed on one longitudinal side and has a first opening on the other side, the apparatus (109) is positioned on the conveyor belt (106, 205) such that the first opening faces the conveying direction (206) of the dopant (208), and the connecting pipe and the half-pipe communicate via a second opening in the width direction of the half-pipe.

2. The apparatus according to claim 1, characterized in that the minimum distance between the half-pipe and the conveyor belt (106, 205) is smaller than the minimum size of the dopant particle size distribution.

3. The apparatus according to claim 1 or claim 2, characterized in that the apparatus (109) for forming the dump layer on the conveyor belt (106, 205) can be closed by a shutoff device (203), thereby stopping further flow of the dopant.

4. The apparatus according to any one of claims 1 to 3, characterized in that the conveyor belt (106, 205) is made of dry fluororubber.

5. The apparatus according to any one of claims 1 to 4, characterized in that the porous separation element (104) is made of quartz glass wool.

6. The apparatus according to any one of claims 1 to 5, characterized in that the housing (107) includes a water-carrying cooling system.

7. The apparatus (109) for forming the dump layer is made of borosilicate glass, as described in any one of claims 1 to 6.

8. A process for manufacturing silicon-doped single-crystal ingots, In the Czochralski pulling section, the first crystal is pulled from the crucible, The present invention comprises doping the first crystal with the first dopant using the apparatus described in claim 1, The speed of the conveyor belt is determined by the target speed at the position where the first crystal being lifted is cut into ingot pieces and the length of the ingot pieces of the first crystal. The first crystal is configured to have a desired axial resistance profile, and the process further, Measuring the axial resistance profile of the first crystal, The target velocity is modified according to the difference between the measured axial resistance profile of the first crystal and the desired axial resistance profile. A process comprising pulling up a second crystal using the modified target rate.

9. The process according to claim 8, characterized in that, before each time the first crystal and the second crystal are pulled up, the crucible is filled with polysilicon mixed with a predetermined amount of the second dopant.

10. The process according to claim 9, characterized in that the first dopant mainly contains arsenic and the second dopant mainly contains boron.

11. The process according to claim 9, wherein the second crystal is cut into ingot pieces.

12. The process according to claim 9, characterized in that the second crystal is pulled up to have a diameter greater than 250 mm.

13. The process according to claim 11, characterized in that the ingot piece is cut into a semiconductor wafer by a wire saw, polished, and an epitaxially grown silicon layer is optionally provided.

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