Non-contact system and method for measuring the distance between a silicon melt and a reflector

Abstract

The measurement system includes an object that is at least partially visible through an opening of a crystal pulling apparatus. The crystal pulling apparatus includes molten silicon in a crucible and a reflector that defines a central passage for pulling up a crystal. The detector array captures light through the opening. The detector array is directed at the surface of the molten silicon and the object within the crystal pulling apparatus, and the laser selectively transmits a coherent light beam through the opening to the object, forming a reflection of the object on the surface of the molten silicon. The optical modulator pulses the coherent light beam of the laser and converts it into a discrete coherent light beam having a period, and the lock-in amplifier is connected to the detector array and filters the discrete coherent light having a period from the captured light.

Description

Cross - reference to related applications

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 357,734, filed on July 1, 2022, the disclosure of which is hereby incorporated by reference in its entirety.

Technical Field

[0002] This technical field generally relates to the manufacture of silicon ingots, and more specifically to non - contact methods and systems for measuring the distance between a silicon melt and a reflector within a crystal pulling apparatus.

Background Art

[0003] Some crystal pulling apparatuses have a reflector disposed above the silicon melt. During the operation of the crystal pulling apparatus, it may be beneficial to know the distance (referred to as "HR") between the bottom surface of the reflector and the surface of the silicon melt. The accuracy of HR measurement is usually less than 1 mm, and a more desirable accuracy is in the range of 0.1 - 0.2 mm.

[0004] Measuring the coefficient of thermal expansion is difficult with well - known methods. This is because measuring the coefficient of thermal expansion requires observing and tracking the characteristics inside the extremely high - temperature pulling apparatus under vacuum or low - pressure conditions. These conditions generally limit the types of sensors and materials that can be used inside the pulling apparatus. Since thermal expansion generally also affects parts that are not actively cooled, the values measured before the start of pulling or operation may not be usable or useful after the pulling apparatus reaches its operating temperature. Also, the resolution and accuracy of optical sensors and detector arrays used to measure distances within the crystal pulling apparatus can be affected by the energy radiation from the molten or heated materials within the crystal pulling apparatus. In particular, photoluminescence and thermal luminescence may emit incoherent light that reduces the resolution of the sensors.

[0005] Therefore, it is necessary to improve the resolution and accuracy of the optical sensors and detector arrays used to measure distances within the crystal lifting apparatus.

[0006] This section of the background art is intended to introduce readers to various aspects of technologies that may be related to various aspects of the present disclosure described and / or claimed below. This discussion is thought to be helpful in providing readers with background information for a better understanding of the various aspects of the present disclosure. Accordingly, these descriptions should be read from this perspective and should be understood, rather than as an admission of prior art.

Summary of the Invention

[0007] In one aspect, a crystal pulling apparatus includes at least one heater, a silicon melt in a crucible, and a measurement system for measuring the distance between the silicon melt and a reflector while pulling a crystal from the silicon melt. The system includes a reflector that defines a central passage and an opening through which the crystal is pulled, and a measurement assembly. The measurement system further includes an object that is at least partially visible through the opening, and a detector array that captures light through the opening. The detector array is directed at the surface of the silicon melt within the crystal pulling apparatus and the object. The measurement system further includes a laser that selectively transmits a coherent light beam from the opening toward the object to form a reflection of the object at the surface of the silicon melt. The measurement system further includes an optical modulator that pulses the coherent light beam of the laser into discrete coherent light beams having a period, and a controller connected to the detector array, the laser, and the optical modulator. The controller is programmed to control the laser to direct the discrete coherent light beam from the laser toward the object, control the optical modulator to pulse the coherent light beam of the laser into discrete coherent light beams, and control the detector array to capture light through the opening while the discrete coherent light beam is directed toward the object. The captured light includes at least a portion of the surface of the silicon melt where a reflection of the object is visible, and the controller is programmed to control the detector array to filter the discrete coherent light beams having a period from the captured light.

[0008] In another aspect, the measurement system includes an object that is at least partially visible through an opening of the crystal pulling apparatus, the crystal pulling apparatus having a silicon melt in a crucible and a reflector defining a central passage through which the crystal is pulled, and having a detector array that captures light through the opening. The detector array is directed at the surface of the silicon melt within the crystal pulling apparatus and at the object. The measurement system further includes a laser that selectively transmits a coherent light beam from the opening to the object to form a reflection of the object at the surface of the silicon melt, and an optical modulator that pulses the coherent light beam of the laser into a discrete coherent light beam having a period. The measurement system further includes a lock-in amplifier connected to the detector array and filtering the discrete coherent light having a period from the captured light. While the crystal is being pulled from the silicon melt, a controller is programmed to determine a measurement distance from the surface of the silicon melt by controlling the laser to direct the coherent light beam from the laser at a first end of the object. The first end is visible through the opening by the laser. The controller is programmed to control the optical modulator to pulse the coherent light beam of the laser, control the detector array to capture the light, and control the lock-in amplifier to filter the discrete coherent light beam having a period from the captured light. The lock-in amplifier is connected to the detector array, and the controller determines a measurement distance between the surface of the silicon melt and the bottom surface of the reflector based on the reflection position of the object.

[0009] In yet another aspect, a method is determined for measuring the distance between the silicon melt in the crucible and the reflector in the crystal pulling apparatus while pulling a crystal from the silicon melt using a measurement system. This method includes the step of directing a coherent light beam from a laser at an object attached to the reflector and visible through an opening. The laser is disposed outside the crystal pulling apparatus, and the coherent light beam is pulsed into a discrete coherent light beam having a period using an optical modulator. The optical modulator is selected from a pulse width modulator and an optical chopper. The pulse width modulator is connected to the laser and pulses the coherent light beam of the laser. The optical chopper is disposed between the laser and the object and chops the coherent light beam of the laser. The scattered light is captured from the opening using a detector array disposed outside the crystal pulling apparatus while the discrete coherent light beam is directed at the object. The captured light includes at least a portion of the surface of the silicon melt where the reflection of the object is visible. The controller determines the distance between the surface of the silicon melt and the bottom surface of the reflector based on the position of the reflection of the object.

[0010] There are various improvements to the features and steps described in connection with the above aspects. Further features can also be incorporated into the above aspects. These improvements and additional features can exist individually or in any combination. For example, the various features and steps described below in connection with any of the illustrated embodiments can be incorporated into the above aspects alone or in any combination.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0012] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION OF THE INVENTION

[0013] An ingot pulling device (also more simply referred to as an "ingot pulling device" or a "crystal pulling device") for growing a single crystal silicon ingot will be described with reference to FIGS. 1-4. FIG. 1 is a cross-sectional view of an ingot pulling device generally designated 100 used to pull a single crystal silicon ingot from a silicon melt. FIGS. 2 and 3 are cross-sectional views of the ingot pulling device 100, and FIG. 4 is a partial front view of a single crystal silicon ingot grown, for example, by the Czochralski method within the ingot pulling device 100.

[0014] The ingot pulling device 100 includes a crystal pulling device housing 108 that defines a growth chamber 152 for pulling a silicon ingot 113 from a silicon melt 104. A control system 172 (also referred to as a "controller") controls the operation of the ingot pulling device 100 and its components. The ingot pulling device 100 includes a crucible 102 disposed within the growth chamber 152 for containing the silicon melt 104. The crucible 102 is supported by a susceptor 106.

[0015] The crucible 102 includes a bottom 129 and side walls 131 extending upward from the bottom 129. The side walls 131 are generally vertical. The bottom 129 includes a curved portion of the crucible 102 extending under the side walls 131. Inside the crucible 102, there is a silicon melt 104 having a melting surface 111 (i.e., a molten ingot interface). The susceptor 106 is supported by a shaft 105. The susceptor 106, crucible 102, shaft 105, and ingot 113 have a common longitudinal axis A or "lifting axis" A.

[0016] Inside the ingot pulling device 100, a pulling mechanism 114 for growing and pulling the ingot 113 from the melt 104 is arranged. The pulling mechanism 114 includes a pulling cable 118, a seed holder or chuck 120 coupled to one end of the pulling cable 118, and a seed crystal 122 coupled to the seed holder or chuck 120 to initiate crystal growth. One end of the pulling cable 118 is connected to a pulley (not shown) or drum (not shown) inside the pulling mechanism 114, or any other suitable type of lifting mechanism, such as a shaft, and the other end is connected to a chuck 120 that holds the seed crystal 122. During operation, the seed crystal 122 is lowered to contact the melt 104. The pulling mechanism 114 is activated and the seed crystal 122 rises. Thereby, the single crystal ingot 113 is pulled from the melt 104.

[0017] During heating and crystal pulling, a crucible drive unit 107 (e.g., a motor) rotates the crucible 102 and the susceptor 106. The lift mechanism 112 raises and lowers the crucible 102 along the pulling axis A during the growth process. As the ingot grows, the silicon melt 104 is consumed and the height of the melt inside the crucible 102 decreases. The crucible 102 and the susceptor 106 may be raised to maintain the melt surface 111 at or near the same position with respect to the ingot pulling device 100.

[0018] The crystal drive unit (not shown) can also rotate the lifting cable 118 and the ingot 113 in a direction opposite to the direction in which the crucible drive unit 107 rotates the crucible 102 (e.g., counterclockwise rotation). In embodiments using constant speed rotation, the crystal drive unit may rotate the lifting cable 118 in the same direction as the crucible drive unit 107 rotates the crucible 102. Further, the crystal drive unit raises and lowers the ingot 113 relative to the melt surface 111 as desired during the growth process.

[0019] The ingot lifting device 100 may include an inert gas system for introducing and withdrawing an inert gas such as argon from the growth chamber 152. The ingot lifting device 100 may include a dopant supply system (not shown) for introducing a dopant into the melt 104.

[0020] According to the Czochralski single crystal growth process, a predetermined amount of polycrystalline silicon, i.e., polysilicon, is charged into the crucible 102 (e.g., a charge of 250 kg or more). The sources of polycrystalline silicon are various, for example, granular polycrystalline silicon produced by pyrolyzing silane or halosilane in a fluidized bed reactor, or polycrystalline silicon produced in a Siemens reactor, etc. After adding polycrystalline silicon to the crucible to form a charge, the charge is heated to a temperature above the melting point of silicon (e.g., about 1412 °C) to melt it. In some embodiments, the charge (i.e., the melt) is heated to a temperature of at least about 1425 °C, at least about 1450 °C, and even at least about 1500 °C. The ingot lifting device 100 includes a bottom heat insulator 110 and side heat insulators 124 for retaining heat within the lifting device 100. In the illustrated embodiment, the ingot lifting device 100 includes a bottom heater 126 disposed below the crucible floor 129. The crucible 102 may be moved relatively close to the bottom heater 126 to melt the polycrystalline material loaded into the crucible 102.

[0021] To form an ingot, the seed crystal 122 is brought into contact with the surface 111 of the melt 104. The lifting mechanism 114 is actuated to lift the seed crystal 122 out of the melt 104. The ingot 113 includes a crown portion 142 that migrates outwardly from the seed crystal 122 and tapers to reach a target diameter. The ingot 113 includes a constant diameter portion 145 or a cylindrical "body" that grows by increasing the lifting speed. The body 145 of the ingot 113 has a relatively constant diameter. The ingot 113 includes a tail or end cone (not shown), which is a portion where the diameter of the ingot tapers after the body 145. When the diameter becomes small enough, the ingot 113 is then separated from the melt 104. The ingot 113 has a central longitudinal axis A that extends to the crown portion 142 and the end of the ingot 113.

[0022] The ingot lifting apparatus 100 includes a side heater 135 and a susceptor 106 that surrounds the crucible 102 to maintain the temperature of the melt 104 during crystal growth. The side heater 135 is disposed radially outward with respect to the side wall 131 of the crucible when the crucible 102 moves up and down along the lifting axis A. The side heater 135 and the bottom heater 126 may be any type of heater operable as described herein. In some embodiments, the heaters 135, 126 are resistance heaters. The side heater 135 and the bottom heater 126 may be controlled by a control system 172 such that the temperature of the melt 104 is controlled throughout the lifting process.

[0023] The ingot lifting apparatus 100 may be disposed within the growth chamber 152, positioned above the melt 104, and include a reflector 151 (or "thermal shield") that covers the ingot 113 during ingot growth. The reflector 151 may be partially disposed within the crucible 102 during crystal growth. The reflector 151 defines a central passage 160 for receiving the ingot 113 when the ingot 113 is lifted by the lifting mechanism 114.

[0024] The reflector 151 may be a heat shield adapted to hold heat below it and above the melt 104. Other reflector designs and structural materials (e.g., graphite) may be used without limitation. The reflector 151 has a bottom 138 (best shown in FIG. 2), and during ingot growth, the bottom 138 of the reflector 151 is spaced a distance HR from the surface of the melt. As the ingot 113 is pulled up, the distance HR increases due to the decrease in the melt 104.

[0025] The terms "light", "light emission", "coherent light", "incoherent light", and "light beam" refer to photon energy radiated from the light source and components of the ingot pulling apparatus. The emitted light may or may not be visible to the human eye. The light may be in a broad spectral region (i.e., from ultraviolet to infrared). The emitted light may be "coherent" light or "incoherent" light. Coherent light has a fixed phase difference between the waves of light from the emission source. Incoherent or non - coherent light has a non - fixed or random phase difference between the waves of light from the emission source. Coherent light may be radiated by optical enhancement of an intensified outflow of electromagnetic radiation. Incoherent light may be radiated by photoluminescence and thermal luminescence from a molten or heated source. As used herein, "captured light" or "captured image" refers to light observed by a sensor or detector.

[0026] An example of a single - crystal silicon ingot 113 manufactured by the Czochralski method is shown in FIG. 3. The ingot 113 includes a neck 116, an outwardly spreading portion 142 (synonyms "crown" or "cone"), a shoulder 119, and a body 145 having a constant diameter. The neck 116 is in contact with the melt and is attached to a seed crystal 122 that is withdrawn to form the ingot 113. The body 145 is suspended from the neck 116. When the cone portion 142 of the ingot 113 begins to form, the neck 116 ends.

[0027] The constant-diameter portion 145 of the ingot 113 has a peripheral edge portion 150, a central axis A parallel to the peripheral edge portion 150, and a radius R extending from the central axis A to the peripheral edge portion 145. The central axis A also passes through the conical portion 142 and the neck 116. The diameter of the main ingot body 145 varies, and in some embodiments, the diameter may be about 150 mm, about 200 mm, about 300 mm, greater than about 300 mm, about 450 mm, or greater than about 450 mm.

[0028] The single-crystal silicon ingot 113 may generally have any resistivity. The single-crystal silicon ingot 113 may or may not be doped.

[0029] FIG. 5 is an example of a computing device 400 that may be used as, or as part of, control system 172. Computing device 400 includes a processor 402, a memory 404, a media output component 406, an input device 408, and a communication interface 410. Other embodiments include different components, additional components, and / or do not include all of the components shown in FIG. 5. Processor 402 is configured to execute instructions. In some embodiments, the executable instructions are stored in memory 404. Processor 402 may include one or more processing units (e.g., a multi-core configuration). As used herein, the term “processor” refers to a central processing unit, a microprocessor, a microcontroller, a reduced instruction set circuit (RISC), an application specific integrated circuit (ASIC), a programmable logic circuit (PLC), and other circuits or processors capable of performing the functions described herein. The foregoing are merely examples and are not intended to limit the definition and / or meaning of the term “processor” in any way. Memory 404 stores non-transitory computer-readable instructions for execution of the techniques described herein. When such instructions are executed by processor 402, processor 402 is caused to perform at least a portion of the methods described herein. In some embodiments, memory 404 stores computer-readable instructions for providing a user interface to a user via media output component 406 and receiving and processing input from input device 408. Memory 404 may include, but is not limited to, random access memory (RAM) such as dynamic RAM (DRAM) or static RAM (SRAM), read only memory (ROM), erasable and programmable read only memory (EPROM), electrically erasable and programmable read only memory (EEPROM), and non-volatile RAM (NVRAM).Although shown separately from processor 402, in some embodiments, memory 404 may be combined with processor 402, such as a microcontroller or microprocessor, but may still be referred to separately. The above memory types are merely examples and do not limit the types of memory that can be used to store computer programs. Media output component 406 is configured to present information to a user (e.g., an operator of the system). Media output component 406 is any component that can communicate information to the user. In some embodiments, media output component 406 includes output adapters such as video adapters and / or audio adapters. The output adapter is operably connected to processor 402 and can be operably connected to an output device such as a display device (e.g., a liquid crystal display (LCD), a light emitting diode (LED) display, an organic light emitting diode (OLED) display, a cathode ray tube (CRT), an "electronic ink" display, one or more light emitting diodes (LEDs)) or an audio output device (e.g., speakers or headphones).

[0030] Computing device 400 includes or is connected to an input device 408 for receiving input from a user. Input device 408 is any device that enables computing device 400 to receive analog and / or digital commands, instructions, or other input from a user, such as visual, auditory, tactile, button presses, stylus taps, etc. Input device 408 may include, for example, a variable resistor, an input dial, a keyboard / keypad, a pointing device, a mouse, a stylus, a touch-sensitive panel (e.g., a touch pad or a touch screen), a gyroscope, an accelerometer, a position detector, an audio input device, or any combination thereof. A single component such as a touch screen may function as both an output device of media output component 406 and an input device 408.

[0031] Through the communication interface, computing device 400 can communicate with remote devices and systems such as remote sensors, remote databases, and remote computing devices. The communication interface may include multiple communication interfaces for interacting with multiple remote devices or systems. The communication interface is a wired or wireless communication interface, enabling computing device 400 to communicate directly or via a network with remote devices and systems. The wireless communication interface may include a radio frequency (RF) transceiver, a Bluetooth® adapter, a Wi-Fi transceiver, a ZigBee® transceiver, a near field communication (NFC) transceiver, an infrared (IR) transceiver, and / or other devices and communication protocols for wireless communication (Bluetooth is a registered trademark of the Bluetooth Special Interest Group of Kirkland, Washington, and ZigBee is a registered trademark of the ZigBee Alliance of San Ramon, California). The wired communication interface can use any suitable wired communication protocol, such as USB, RS232, I2C, SPI, analog, and proprietary I / O protocols, for direct communication. In some embodiments, the wired communication interface includes a wired network adapter that couples computing device 400 to a network such as the Internet, a local area network (LAN), a wide area network (WAN), a mesh network, and / or any other network, enabling communication with remote devices and systems via the network.

[0032] The computer systems described herein may include additional, fewer, or alternative features, including those described elsewhere herein. The computer systems described herein may be included or implemented by, or via, computer-executable instructions stored on a non-transitory computer-readable medium or media.

[0033] 。 As shown in FIGS. 1-4, the ingot lifting device is used as part of a measurement system for determining the distance between the reflector 151 or the object 200 and the surface 111 of the melt 104, and includes a measurement assembly 170. As shown in FIGS. 2 and 3, the measurement assembly 170 can be used to determine the distance between the bottom surface 138 of the reflector 151 and the surface of the melt during the growth of the ingot (i.e., to determine HR). The measurement assembly 170, system, and method described herein can also be used to determine other distances from the surface 111 of the melt 104 within the crystal pulling device 100. The measurement assembly 170 can be configured to measure any vertical distance (parallel to the axis X in FIG. 1) using the system and method, as described in more detail below.

[0034] The measurement assembly 170 and the controller 172 constitute a measurement system. The measurement assembly 170 is used by the controller 172 to determine the distance between the bottom surface 138 of the reflector 151 and the surface 111 of the silicon melt 104. The measurement assembly 170 includes an object 200 disposed within the growth chamber 152 of the ingot pulling device 100, a detector array 210 disposed outside the growth chamber 152 for capturing light within the growth chamber 152, a laser 208 disposed within the growth chamber 152 for selectively transmitting a coherent light beam to the object 200, and an optical modulator 212 for pulsing the coherent light beam of the laser into discrete coherent light beams having a period. The lock-in amplifier 214 is connected to the detector array 210 and can filter the discrete coherent light beams having a period from the captured light. The lock-in amplifier 214 can amplify the discrete coherent light beams having a period from the non-coherent light present within the growth chamber 152.

[0035] Generally, a laser 208 (such as a laser diode) is focused on an object 200 that projects a laser dot onto a molten surface 111. The object 200 is translucent or opaque, and when light from the laser is focused on a first end 202 or point of the object 200, the light refracts to a second end 204 or a point on the opposite side of the first end 202. The refracted light from the second end 204 or point projects light onto the molten surface 111. As shown in FIGS. 2 and 3, a projection 201 is displayed on the molten surface 111. This projection 201 can have a diameter and shape substantially equal to that of the second end 204 of the object 200, emits coherent light by refraction, and this coherent light can be detected by a detector array 210. The first end 202 of the object 200 also reflects the coherent light from the laser, and this coherent light is detectable by the detector array 210.

[0036] The laser 208 is preferably a diode laser having 5 milliwatts, a wavelength of 520 nm, a divergence angle of less than 0.3, and three beam dimensions, and can irradiate the object 200 with a coherent light beam. Since the melt is generally reddish in color, a green laser makes the contrast between the dot and the melt easier to visually recognize than other colors. In other embodiments, other suitable color lasers may be used.

[0037] The detector array 210 is disposed outside the crystal pulling apparatus housing 108 and is directed to capture light emitted from at least the first end 202 of the object 200 and the projection 210 on the molten surface 111. The detector array 210 is disposed to view the growth chamber 152 through an opening 109 in the crystal pulling apparatus housing 108 (shown in FIG. 1). During the remainder of the operation, the laser dot is constantly tracked by a camera to determine the HR. This measurement system does not rely on contact with the melt to determine the HR.

[0038] The detector array 210 is preferably a photodiode or a position sensor for detecting and measuring the wavelength of light along the spectrum. The detector array 210 converts the wavelength measurement value into a distance measurement value between the detector array 210 and the light-emitting element. In some embodiments, the detector array 210 is a charge-coupled device (CCD) camera or a charge-injection device (CID) camera. CCD and CID cameras utilize image sensors that record visible light as an electronic signal and convert that light into a two-dimensional pixelated image. Each image includes the surface of the silicon melt, the object, and the reflection of the object on the silicon melt within the crystal pulling apparatus.

[0039] The object 200 may be a quartz pin made from a stock rod. The object 200 is optically transparent. In other embodiments, the object 200 may be made of any refractory material for high temperatures, such as silicon carbide (SiC), silicon nitride (SiN), tungsten carbide, tantalum carbide, quartz, sapphire, boron nitride, or other optically transparent and heat-resistant materials. Generally, the pin material should produce a strong and distinct reflection at the melt surface at all interesting stages of crystal growth. As an example, the material of the quartz rod is a 3 mm rod. Alternatively, rod materials of other diameters can also be used. The pin may have a head made or formed from the rod, for example, when a long optical path length pin is required. In this case, although the laser light needs to be visible from the pin tail, since the laser light is displayed on the pin head, the pin is not a welded sphere, but a single continuous part such that when the laser irradiates the pin head, the laser light is guided to the bottom of the pin.

[0040] As shown in FIG. 2, the object 200 is positioned at the edge of the bottom surface 138 of the reflector 151. As shown in FIG. 3, the object 200 can be positioned and extended through the opening 139 of the reflector 151. The opening 139 is sized such that the detector array 210 can visually recognize at least the first end 202 and the protrusion 201 of the object displayed on the melt surface 111. The opening 139 of the reflector 151 is a compound angle, allowing the object 200 to be visually recognized from the side edges of the ports where the detector array 210 and the laser 208 are attached. Unlike known dipstick laser systems that use an "open" hot zone with a reflector of poor insulation, this system is used in a "closed" hot zone where the reflector 151 fills the area above the melt 104 with an insulator as much as possible. The open hot zone system uses the outer periphery of the maximum crystal diameter of the crystal as seen from the port on the opposite side of the crystal as the object 200 and looks at the reflection of the bottom surface of the object 200 illuminated by the laser 208 in the melt. In an exemplary embodiment, while closing the hot zone, the laser dot reflection can be made visible from the same port while maintaining high-resolution HR capabilities despite a sharp cut-off angle. In other embodiments, multiple ports (e.g., placing the camera and the laser in different ports) can be used.

[0041] By using a bright laser, a stable signal can be obtained on the melt. Green wavelength lasers (wavelengths of 520 nm to 532 nm) with various rated outputs commonly available on the market are usually bright enough under all conditions. This can avoid problems caused by some known detector arrays, optical sensors, and camera systems that visually observe the characteristics of the hot zone where the light intensity may change due to reflection or the emission of the silicon melt. A change in light intensity can cause a shadow, making the object in the hot zone appear to have moved by one or two pixels. This can result in false movement (i.e., HR change). The optical modulator 212 is selected from a pulse width modulator or an optical chopper. The pulse width modulator is connected to the laser 208 or is integral with the laser 208, and pulses the coherent light beam of the laser into discrete coherent light beams having a period. The optical chopper is disposed between the laser 208 and the object 200, and chops the coherent light beam of the laser into discrete coherent light beams having a period. In either configuration, the coherent light beam is blocked for a certain period, and essentially momentary flicker occurs. This period is on the order of a fraction of a second and, in some embodiments, is invisible to the human eye. The flicker of the coherent light emitted from the laser 208 and refracted by the object 200 is also converted into a projection 201 displayed on the molten surface 111.

[0042] The lock-in amplifier 214 can extract coherent light having a period from the environment by synchronizing the lock-in amplifier 214 with the period of the optical modulator 212, thereby separating the discrete coherent light beam having a period from the light in the growth chamber 152 and improving the accuracy and sensitivity of the detector array 210.

[0043] The lock-in amplifier 214 can also filter light driven by an alternating voltage having a specific frequency. Generally, electrical components operating with direct current and alternating voltage emit light according to the operating frequency. The heater operates with a direct current voltage and can thus emit light having no frequency, and the laser operates with an alternating voltage and can thus emit a coherent light beam having a frequency. The emitted coherent light beam having a frequency can be filtered from incoherent light and DC light.

[0044] FIG. 6 is a schematic view of the fields of view of detector array 210 and laser 208. Detector array 210 is positioned so that object 200 and projections 201 displayed on melt surface 111 are within the field of view. Detector array 210 captures light through opening 109 of crystal puller housing 108. The light captured by the detector array includes non-interfering light from heater 135 and bottom heater 126, as well as interfering light emitted by laser 208. The field of view of detector array 210 includes first end 202 of object 200 and projections 201 (designated as (ZD) and (ZE)) at various distances from second end 204 of object 200. Laser 208 transmits a selected coherent light beam 230 through the opening to object 200, forming a reflection 201 of the object on surface 111 of the silicon melt. Optical modulator 212 pulses coherent light beam 230 of laser 208 into discrete coherent light beams 232 having a period. Lock-in amplifier 214 filters coherent light beam 232 having a period from non-coherent light.

[0045] To use the measurement system, the height (PH) of object 200, the diameter (PD) of first end 202 of object 200, and the distance (H) that object 200 extends from the bottom of the reflector are known. Laser 208 and optical modulator 212 are turned on, and discrete coherent light beams having a period are irradiated onto first end 202 of object 200. The discrete coherent light beams refract through object 200 (up to second end 204), and projections 201 are displayed on melt surface 111. As crucible lift 112 moves crucible 102 and melt surface 111 relative to bottom surface 138 of reflector 151, the measured distance changes (as illustrated by (ZD) and (ZE) in FIG. 6).

[0046] In some embodiments, instead of directly finding the center, the controller 172 finds the tangent edges and uses the previously measured pupil diameter (PD) of the object 200 to find the pupil center. The center of the lower end of the pin is found using a known value of the diameter of the pin (measured or unmeasured since it is made from stock material with a known diameter). The measured distances from the light captured by the detector array 210 can be used to triangulate the length of the height (PH) of the object 200 and establish reference numbers for calculating the unknown distances (ZD) and (ZE) using ratios. When the detector array 210 is a camera, the distances obtained as a result of the projection 201 can be represented by pixel positions that correlate with the aforementioned points.

[0047] The controller 172 is connected to the detector array 210, the laser 208, and the optical modulator 212 and is programmed to perform the following functions. The laser 208 is controlled to direct a discrete coherent light beam from the laser 208 towards the object 200, the optical modulator 212 is controlled to pulse the coherent light beam of the laser 208 into a discrete coherent light beam, the detector array 210 is controlled to capture light through the aperture while the discrete coherent light beam is directed towards the object 200, the detector array 210 is controlled to filter the discrete coherent light beam having a period from the captured light, and the lock-in amplifier is controlled to filter the discrete coherent light having a period from the captured light. The controller calculates the measured distance between the surface of the silicon melt and the bottom surface of the reflector based on the position of the reflection 201 of the object 200, for example using a processor.

[0048] The exemplary method 500 shown in FIG. 7 is a method for determining the distance between the silicon melt in the crucible and the reflector in the crystal pulling apparatus while pulling a crystal from the silicon melt. This method includes step 502 of directing a coherent light beam from a laser towards an object attached to the reflector and visible through an opening, step 504 of using an optical modulator to pulse the coherent light beam from the laser into a discrete coherent light beam having a period, and step 506 of using a detector array located outside the crystal pulling apparatus to capture scattered light through the opening while directing the discrete coherent light beam towards the object. This method also includes step 508 of determining the distance between the surface of the silicon melt and the bottom surface of the reflector based on the reflection position of the object by a controller. This method may also include step 510 of filtering the discrete coherent light beam using a lock-in amplifier connected to the detector array.

[0049] The exemplary method does not require a specific order of steps, or a sequential order. Further, other steps may be included or steps may be excluded from the method described, and other components may be added or removed from the system described. It will be understood that the above-described embodiments, which have been described in particular detail, are merely exemplary or possible embodiments, and that there are many other combinations, additions, or alternatives.

[0050] Also, a specific name of a component, the capitalization of terms, attributes, data structures, or other programming or structural aspects are not essential and not important either. The mechanisms implementing the present disclosure or its features may have different names, formats, or protocols. Further, the system may be implemented by a combination of hardware and software as described above, or may be implemented entirely by only hardware elements. Also, the specific division of functions among the various system components described herein is merely an example and not essential. Functions performed by a single system component may instead be performed by a plurality of components, and functions performed by a plurality of components may instead be performed by a single component.

[0051] The approximating language used throughout this specification and the claims may be applied to modify quantitative expressions that can vary within a range that is allowed without changing the relevant basic function. Accordingly, values modified by terms such as "about" or "substantially" are not limited to the specific exact values. In at least some instances, the approximating expression may correspond to the precision of the means for measuring the value. Throughout this specification and the claims, range limitations may be combined and / or interchanged, and such ranges are specified and include all sub-ranges contained therein, unless the context or expression indicates otherwise.

[0052] Various changes, modifications, and alterations in the teachings of the present disclosure may be envisioned by those skilled in the art without departing from the intended spirit and scope. The present disclosure is intended to embrace such changes and modifications.

[0053] This specification illustrates the disclosure and describes, including the best mode, the manufacture and use of the apparatus or system and the execution of the incorporated methods so that those skilled in the art can practice the disclosure. The patentable scope of the disclosure is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be included within the scope of the claims if they have structural elements that do not differ from the language of the claims or if they include equivalent structural elements that do not have a substantial difference from the language of the claims.

Claims

1. A crystal pulling apparatus comprising at least one heater, a silicon melt in a crucible, and a measuring system for measuring the distance between the silicon melt and a reflector while pulling a crystal from the silicon melt, wherein the system is A reflector defining the central passage through which the crystal is pulled and the opening; and, A measuring assembly, An object that is visible, at least partially, through an opening; A detector array that captures light through an aperture, and is directed towards the surface of the silicon melt and the object in a crystal pulling apparatus; A laser that selectively transmits a coherent light beam to an object through the same aperture that the detector array uses to capture light, forming a reflection of the object on the surface of the silicon molten material; An optical modulator that pulses a coherent laser beam to create a periodic discrete coherent light beam; Measurement assemblies including, A controller connected to a detector array, laser, and optical modulator, Controlling a laser to direct a discrete coherent beam of light from the laser towards an object. Controlling an optical modulator to pulse a laser's coherent light beam into discrete coherent light beams. The method involves directing a discrete coherent light beam towards an object and controlling a detector array to capture the light through an aperture, wherein the captured light includes at least a portion of the surface of a silicon melt where the reflection of the object is visible, and Controlling the detector array to filter out periodic discrete coherent light beams from the captured light, A controller programmed to perform the following actions; A crystal pulling apparatus that includes [a specific component].

2. The crystal pulling apparatus according to claim 1, wherein a discrete coherent light beam is directed from a laser towards the object, thereby projecting the reflection of the object onto the surface of a silicon melt.

3. The crystal pulling apparatus according to claim 2, wherein the controller is programmed to determine the measurement distance between the surface of the silicon melt and the bottom surface of the reflector based on the projection position of the object in the captured light.

4. The crystal pulling apparatus according to claim 1, wherein the capture light from the detector array includes at least non-coherent light emitted from the silicon melt and discrete coherent light beams from a laser and an optical modulator.

5. The crystal pulling apparatus according to claim 4, wherein a lock-in amplifier is connected to a detector array and filters a periodic discrete coherent light beam from the captured light.

6. The crystal pulling apparatus according to claim 1, wherein a lock-in amplifier is connected to a detector array and filters the periodic discrete coherent light beam from the captured light by amplifying the periodic discrete coherent light beam.

7. The crystal pulling apparatus according to claim 1, wherein the object has a first end and a second end opposite to the first end, the object is attached to a reflector, and the object refracts light between the first end and the second end.

8. The crystal pulling apparatus according to claim 7, wherein the projection of the object from the second end of the object's reflection forms a reflection of the object on the surface melt.

9. The crystal pulling apparatus according to claim 1, wherein the detector array is an optical sensor that converts light captured through the aperture of a reflector into a pixelated image, each image including the surface of the silicon melt in the crystal pulling apparatus, the object, and the reflection of the object on the silicon melt.

10. The crystal pulling apparatus according to claim 1, wherein the optical modulator is selected from a pulse width modulator or an optical chopper, the pulse width modulator is connected to a laser and pulses the coherent light beam of the laser, and the optical chopper is placed between the laser and the object and chops the coherent light beam of the laser.

11. A measurement system, An object visible at least partially through the opening of a crystal pulling apparatus, the crystal pulling apparatus comprising a silicon melt in a crucible and a reflector defining a central passage through which the crystal is pulled; A detector array that captures light through an aperture, the detector array directed at the surface of the silicon melt in a crystal pulling apparatus and the object; A laser that selectively transmits a coherent light beam from the aperture to the object through the same aperture through which the detector array captures light, forming a reflection of the object on the surface of the silicon melt; An optical modulator that pulses a coherent laser beam into a periodic discrete coherent beam; and, A lock-in amplifier connected to a detector array, which filters out periodic discrete coherent light from the captured light; Includes, The controller is The laser is controlled to direct a coherent beam of light from the laser towards a first end of the object, so that the first end can be seen by the laser through the opening; Control the optical modulator to pulse the coherent beam of the laser; Control the detector array to capture light; A lock-in amplifier is controlled to filter the periodic discrete coherent light beam from the captured light, and the lock-in amplifier is connected to the detector array; and, The controller determines the measurement distance between the surface of the silicon melt and the bottom surface of the reflector based on the reflection position of the object; A measurement system programmed to determine the measurement distance from the surface of the silicon melt while the crystal is being drawn out of the silicon melt.

12. The measurement system according to claim 11, wherein the captured light includes light emitted from the silicon melt and a periodic discrete coherent light beam, and a lock-in amplifier filters the light emitted from the silicon melt.

13. The measurement system according to claim 12, wherein the second end of the object extends a certain length from the bottom surface of the reflector.

14. The measuring system according to claim 13, wherein the measuring distance is determined at least in part on the reflection position of the first end of the target and the known dimensions of the object.

15. The measurement system according to claim 13, wherein the measurement distance is determined by triangulation from the first end of the object and the reflection of the object on the surface of the silicon melt.

16. The measurement system according to claim 11, wherein the control device is programmed to control the crucible lift to move the crucible and change the measurement distance between the surface of the silicon melt and the bottom surface of the reflector.

17. A method for determining the distance between the silicon melt in the crucible and the reflector in the crystal pulling apparatus while pulling a crystal from the silicon melt, the following measurement system: A coherent light beam from a laser is directed onto a visible object through an aperture mounted on a reflector, with the laser positioned outside the crystal pulling apparatus; Modulation of a coherent light beam from a laser into a periodic discrete coherent light beam using an optical modulator, wherein the optical modulator is selected from a pulse width modulator and an optical chopper, the pulse width modulator is connected to the laser and pulses the laser's coherent light beam, and the optical chopper is placed between the laser and the object and chops the laser's coherent light beam; While a discrete coherent light beam is irradiated onto the object, a detector array positioned outside the crystal pulling apparatus is used to capture discrete light passing through the same aperture on which the coherent light beam is detected, wherein the captured light includes at least a portion of the surface of the silicon melt on which the reflection of the object is visible; and, The controller determines the distance between the surface of the silicon melt and the bottom surface of the reflector based on the position of the reflection of the object; How to use it.

18. The method according to claim 17, wherein the light captured by the detector array includes a discrete coherent light beam emitted from a laser and light emitted from a silicon melt.

19. The method according to claim 18, further comprising filtering a discrete coherent light beam using a lock-in amplifier connected to a detector array.

20. The method according to claim 17, wherein the determination step includes triangulation based on a first end of the object and the reflection of the object on the surface of the silicon melt.

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