Crystal length measuring device for a single crystal growth furnace

Abstract

The utility model discloses a crystal length measuring device of single crystal growth furnace, aims at solving the accumulated error problem of traditional measurement method because of the thermal -mechanical deformation of suspension cable. The device includes the non -contact range sensor of fixed installation relative to the furnace body, and with the target component rigid connection of crystal. The sensor emits the detection light beam to the target surface of target component top and receives the reflected light beam, thereby directly, real -time measurement target component's vertical position, and then accurately calculates the growth length of crystal. The utility model fundamentally eliminates the accumulated error, provides high -precision real -time length data, and simple structure, strong compatibility can be integrated in closed loop control system to promote the process control level.

Description

Technical Field

[0001] This utility model relates to the field of semiconductor manufacturing equipment technology, and more particularly to a process monitoring and control device for a single crystal growth furnace. More specifically, this utility model discloses a device for high-precision, real-time measurement of crystal length during the Czochralski crystal growth process. This device utilizes a non-contact optical sensing system to directly measure the vertical position of components mechanically coupled to the crystal, overcoming the inherent limitations of traditional measurement techniques and thus achieving more precise process control. Background Technology

[0002] The Czochralski process is the mainstream technology in industry for producing large-size, high-purity single-crystal silicon, germanium, and various synthetic gemstones. The core process is as follows: First, high-purity raw materials (e.g., semiconductor-grade polycrystalline silicon) are placed in a crucible, typically made of quartz, and melted at a high temperature (silicon's melting point is approximately 1425°C). Then, a seed crystal, mounted at the end of a lifting rod, is immersed in the melt surface and slowly pulled upwards while rotating. To homogenize the melt temperature and composition, the crucible is usually rotated in the opposite direction. The entire growth process takes place in a sealed furnace filled with an inert gas (usually argon) to prevent oxidation or contamination of the melt and the growing crystal. This process can grow large cylindrical single-crystal ingots up to 2 meters in length.

[0003] In current industrial practice, crystal length is generally measured using an indirect estimation method. This method relies on tracking the vertical displacement of the crystal pulling mechanism outside the furnace. Specifically, a high-precision rotary encoder is typically coupled to the output shaft of the motor or gearbox of the crystal pulling system. These encoders themselves have extremely high resolution and measurement accuracy, enabling them to accurately record the rotation angle of the pulling mechanism's drive shaft.

[0004] However, this method has a fundamental flaw, which does not stem from the encoder's own accuracy, but rather from a disconnect between the physical object it measures and the truly important target parameter—the crystal's actual vertical position within the furnace. The encoder precisely measures the length of the suspension cable "released" by the lifting mechanism, but it cannot directly measure the crystal's actual vertical position within the hot zone of the furnace. This separation between the measurement point and the target point leads to a crucial, dynamically changing deviation between the measurement result and the crystal's actual length.

[0005] The primary source of this deviation is the thermo-mechanical deformation of the suspension cable. In a Czochralski furnace, the growing crystal and its associated components are suspended by a high-strength cable, typically made of tungsten wire. Despite tungsten's excellent high-temperature resistance, the tungsten wire cable is still subjected to significant thermo-mechanical combined stress under the harsh environment of the Czochralski furnace, resulting in deformation. This deformation is the core source of error in traditional encoder measurement methods, primarily due to two coupled physical phenomena. First, there is temperature-dependent elastic deformation. As the crystal grows, its weight increases, and the tensile load on the tungsten wire cable also increases. According to Hooke's Law, the cable will elastically elongate. However, the Young's modulus of tungsten is not constant; it decreases significantly with increasing temperature. Inside the furnace, the tungsten wire cable traverses a region of sharp temperature gradients, making it extremely complex and unreliable to simply calculate its elongation using the elastic modulus. Second, there is high-temperature creep, which is the most critical and also the most insidious source of error. Creep refers to the slow and permanent plastic deformation of a material over time under high temperature and sustained load. The conditions inside the Czochralski furnace—temperatures exceeding 1500°C and subjected to a continuously increasing tensile stress—provide ideal conditions for high-temperature creep in tungsten. This deformation is irreversible and accumulates throughout the entire crystal growth cycle, which can last for several days.

[0006] The core issue lies not merely in the elongation of the cable, but in the fact that this elongation process is dynamic, nonlinear, and path-dependent. The initial error introduced by elastic elongation is amplified over time by the continuous, permanent deformation caused by high-temperature creep. At any given moment, the total deformation of the cable depends not only on the current crystal weight but also on the temperature and load history of the entire growth process prior to that moment. This means that the measurement error caused by cable deformation is not a simple, fixed offset that can be eliminated with a single calibration, but a complex, dynamic error that accumulates over time. It is precisely this materials science phenomenon, which cannot be compensated for by software, that fundamentally limits the effectiveness of encoder-based indirect measurement methods in achieving high-precision control.

[0007] To address the complexity of controlling the Czochralski process, other advanced monitoring technologies have been developed, but they do not solve the specific problem of directly and accurately measuring the vertical length of the crystal. For example, gravimetric methods estimate the mass growth rate by measuring changes in crystal or melt weight, which is used to control the crystal diameter. Machine vision systems, on the other hand, accurately measure the real-time diameter of the crystal by observing the meniscus at the solid-liquid interface. These advanced technologies explicitly focus on the radial dimension or mass of the crystal, rather than its axial (vertical) length. Utility Model Content

[0008] The purpose of this invention is to provide a high-precision crystal length measuring device for a single crystal growth furnace, so as to solve the problem of systematic and cumulative measurement errors caused by the thermo-mechanical deformation of the suspension cable in the prior art.

[0009] To achieve the above objectives, the present invention provides a high-precision crystal length measuring device for a single crystal growth furnace, applicable to a single crystal growth furnace comprising a furnace body, a lifting mechanism disposed above the furnace body, a suspension cable extending from the lifting mechanism into the furnace body, and a seed crystal chuck connected to the suspension cable. The device includes: a target component rigidly connected to the seed crystal chuck, the target component having an upward-facing target surface; and a non-contact distance sensor fixedly mounted relative to the furnace body, the sensor being configured to emit a probe beam toward the target surface and receive the probe beam reflected from the target surface to determine the distance between the sensor and the target surface.

[0010] By directly measuring the vertical position of the target component rigidly connected to the crystal, the measurement results of this invention are completely decoupled from any tensile or creep behavior of the suspension cable, thereby fundamentally eliminating the main sources of error in traditional measurements.

[0011] The beneficial effects of this utility model include: Eliminating cumulative errors: By directly measuring the position of the target component, the measurement results are not affected by the deformation of the suspension cable, thus fundamentally eliminating the cumulative errors in traditional measurements.

[0012] High-precision real-time data: Employing laser ranging technology based on the time-of-flight principle, it can provide high-precision measurement data and high-frequency data updates, providing the process control system with true, real-time data on crystal length.

[0013] Simple structure and strong compatibility: This device requires minimal modification to existing Czochralski furnaces, only the installation of sensors on the top of the furnace body and replacement of standard target components (such as counterweights) are needed, resulting in good equipment compatibility.

[0014] Enhanced process control capabilities: Precise length data can be fed back to the main controller of the furnace, making the control of each growth stage more accurate, which is expected to improve crystal quality and yield.

[0015] Enhanced system reliability: The non-contact measurement method and the use of robust and durable industrial-grade components ensure that the device can operate stably and reliably for a long time in the harsh furnace environment. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the structure of a crystal length measuring device for a single crystal growth furnace according to an embodiment of the present invention. It shows the relative positional relationship between the non-contact ranging sensor, the target component (weight), the seed crystal chuck, the suspension cable, the furnace body, and the lifting mechanism, as well as the emission and reflection paths of the probe beam. Detailed Implementation

[0017] The technical solution of this utility model will be clearly and completely described below with reference to the accompanying drawings.

[0018] In the first embodiment according to the present invention, referring to Figure 1 This embodiment discloses a crystal length measuring device for a single crystal growth furnace. The device is applied to a typical Czochralski furnace, which includes a furnace body 5, a lifting mechanism 6 disposed above the furnace body 5, a suspension cable 3 (typically a tungsten wire cable) extending from the lifting mechanism 6 into the furnace body 5, and a seed crystal chuck 7 connected to the suspension cable 3. The seed crystal chuck 7 holds a seed crystal, and a single crystal 4 grows on the base of the seed crystal.

[0019] The core components of this device include a non-contact ranging sensor 1 and a target component 2.

[0020] In terms of system architecture and integration, the non-contact ranging sensor 1 is rigidly fixed to the top flange of the furnace body 5 of the Czochralski furnace or to an auxiliary support structure. More advantageously, it can be rigidly fixed to a platform used to fix the pyrometer of the Czochralski furnace. The installation position of the non-contact ranging sensor 1 is precisely adjusted to ensure that the emitted probe beam DR propagates vertically and approximately coincides with the central axis of crystal pulling. In this embodiment, the target component 2 can be a counterweight of the Czochralski furnace, which hangs from the lower end of the tungsten wire rope to serve as a counterweight, tension the tungsten wire rope, and prevent swaying, and is rigidly connected to the seed crystal chuck 7. The top of the target component 2 is designed as a stable, flat target surface 21, such as a plane, to serve as a reliable measurement reference for the probe beam. Since the target component 2 is rigidly connected to the seed crystal chuck 7, measuring the vertical position of the target component 2 corresponds to the position of the top of the single crystal 4.

[0021] In this embodiment, the non-contact ranging sensor 1 employs an industrial-grade Time-of-Flight (ToF) laser ranging sensor. The ToF sensor works by emitting a brief light pulse and precisely measuring the time elapsed from the emission of the pulse to the reception of its reflected signal. This time can be directly converted into absolute distance using the speed of light. A significant advantage of this measurement method is that its results are largely independent of the target object's color, material, or reflectivity, exhibiting strong universality.

[0022] To ensure long-term reliable operation of the device in harsh industrial environments, the key technical specifications of the laser ranging sensor subsystem can be as follows: The sensor type is a time-of-flight (ToF) sensor, providing absolute distance measurement with strong anti-interference capabilities. The laser wavelength is preferably in the 940 nm infrared band, invisible to the human eye, effectively reducing interference from the high-temperature light-emitting environment inside the furnace. The update frequency is preferably greater than or equal to 30 Hz to provide smooth, real-time dynamic data. The output interface can be a standard industrial interface such as IO-Link or 4-20mA, facilitating integration with modern industrial control systems (such as PLCs).

[0023] The material selection for target component 2 must meet the requirements of thermal stability and dimensional stability at high temperatures. The preferred materials are molybdenum or tungsten-based alloys, which have extremely low coefficients of thermal expansion and excellent creep resistance, ensuring that the target surface 21 on its top remains flat and stable throughout the entire crystal growth cycle.

[0024] To obtain a stable, reliable, and persistent laser reflection signal, the design of the target surface 21 is crucial. In this embodiment, the design of the target surface 21 is... Figure 1 The target surface 21 on top of the target component 2 shown is treated as a diffuse reflective surface. This can be achieved through controlled sandblasting or microbead peening. The diffuse reflective surface uniformly scatters the incident laser light in all directions. A significant advantage of this design is that it makes the measurement results extremely insensitive to minute angular tilts or wobbles that may occur during the rotation of the target component 2. Regardless of the slight wobbling of the target surface 21, sufficient light will always be scattered back to the sensor's receiver, ensuring signal continuity and stability. This design directly addresses a potential failure mode—signal interruption due to mechanical vibration—signally improving the reliability and industrial applicability of the entire measuring device.

[0025] Reference Figure 1 The device also includes a data processing unit 11, which can be a standalone microprocessor or directly integrated into the main controller 12 (such as a PLC) of the furnace body. The data processing unit 11 is communicatively connected to the non-contact ranging sensor 1.

[0026] The data processing unit 11 is configured to calculate the growth length of the crystal based on the current distance value measured by the non-contact ranging sensor 1 at the current moment and the pre-stored initial distance value.

[0027] At the zero moment of the process start (t=0), that is, when the seed crystal just contacts the melt surface, the device records an initial laser ranging reading, denoted as D. initial At any subsequent time t, the instantaneous growth length L of the crystal... crystal (t) can be directly calculated using the following formula: L crystal (t)=D(t)-D initial Where D(t) is the real-time distance reading of the non-contact ranging sensor 1 at that moment. This direct calculation process completely eliminates any assumptions about the mechanical behavior of the cable, and is therefore inherently accurate.

[0028] The true value of this high-precision, real-time length data lies in its ability to be used for proactive process control. An advanced implementation method is to integrate this device into a closed-loop feedback control loop. The specific implementation is as follows.

[0029] First, the real-time crystal length L is calculated. crystal (t) is input to the main controller 12. Then, the data processing unit 11 or the main controller 12 can calculate the actual crystal pulling rate (V) by performing time differentiation on the length data. actual =dL / dt). Then, the main controller 12 will use this actual rate V. actual The target lifting rate V set in the process formulation target A comparison is made, and an error signal (Error=V) is generated. target -V actual Finally, the main controller 12 uses a standard proportional-integral-derivative control algorithm to dynamically adjust the motor speed of the lifting mechanism 6 according to the error signal until the error is eliminated.

[0030] In this way, the system ensures that the crystal grows at the precise rate required by the process, rather than relying solely on the motor speed setting under open-loop control. Considering that crystal quality (especially the type and density of point defects) is highly sensitive to the ratio of growth rate (V) to the axial temperature gradient (G) at the solid-liquid interface (i.e., the V / G theoretical ratio), precise control of the actual growth rate V is crucial for optimizing crystal quality and improving yield. This closed-loop control scheme elevates the value of this device from providing a "more accurate ruler" to constructing a "more intelligent growth control system."

[0031] In the second embodiment of the present invention, in order to broaden the scope of protection of the present invention and adapt to different application scenarios, the target surface 21 of the target component 2 may adopt other designs.

[0032] First, a specular reflective surface can be used as an alternative. The target surface 21 can also be highly polished to form a mirror. Although specular reflection can provide a stronger echo signal under ideal alignment conditions, it is extremely sensitive to angular deviations; even slight wobbling can cause the reflected beam to deviate from the receiver, resulting in signal loss.

[0033] Secondly, there are specially shaped surfaces. The geometry of the target surface 21 can also be designed to be non-planar. For example, designing the target surface 21 as concave can help focus the reflected laser energy back to the sensor, especially at longer measurement distances, potentially improving the signal-to-noise ratio. Alternatively, designing the target surface 21 as conical or convex can provide different scattering characteristics, potentially offering advantages in specific optical configurations. A more advanced embodiment integrates a high-temperature resistant retroreflective material (e.g., special ceramic microspheres) onto the target surface 21, or makes the target surface 21 composed of such a high-temperature resistant retroreflective material. Retroreflective materials can reflect the incident beam parallel to its direction of origin, almost unaffected by the incident angle. This provides excellent robustness against the swaying and tilting of the target component 2.

[0034] The following table compares the performance of different target surfaces in 21 embodiments.

[0035]

[0036] Table 1: Comparison of 21 Target Surface Examples In a third embodiment of the present invention, the device can also be designed and provided as a modular retrofit kit for upgrading existing Czochralski single crystal furnaces. This kit configuration has significant commercial value. The kit may include: a sensor subassembly comprising a non-contact ranging sensor 1 and its integrated optical protection assembly; one or more replacement target components 2 having a pre-treated target surface 21 (e.g., a diffuse reflective surface) on top; and an optional independent data processing unit 11 or main controller 12 for interfacing with single crystal furnaces whose control systems are outdated and difficult to integrate directly.

[0037] The table below compares different methods of measuring crystal length to highlight the unique advantages of this invention.

[0038]

[0039] Table 2: Comparison of Crystal Length Measurement Methods The table clearly shows that there is an unmet technological gap in the existing technology for direct, high-precision measurement of crystal length. Traditional encoder methods are limited by uncompensated cumulative errors, while other advanced technologies focus on measuring completely different process parameters. This invention solves the problem of "lack of accurate and direct length measurement methods," filling a real and persistent technological gap in the field of Czochralski process control.

[0040] It should be noted that the technical solutions described in this utility model can be combined arbitrarily without conflict.

[0041] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the protection scope of the claims.

Claims

1. A crystal length measuring device for a single crystal growth furnace, applied in a single crystal growth furnace including a furnace body, a lifting mechanism disposed above the furnace body, a suspension cable extending from the lifting mechanism into the furnace body, and a seed crystal chuck connected to the suspension cable, characterized in that, The device includes: The target component is rigidly connected to the seed crystal chuck, and the target component has an upward-facing target surface; and A non-contact ranging sensor is fixedly mounted relative to the furnace body. The non-contact ranging sensor is configured to emit a probe beam toward the target surface and receive the probe beam reflected from the target surface to determine the distance between the non-contact ranging sensor and the target surface.

2. The crystal length measuring device for a single crystal growth furnace according to claim 1, characterized in that, The non-contact ranging sensor is a laser ranging sensor.

3. The crystal length measuring device for a single crystal growth furnace according to claim 2, characterized in that, The laser rangefinder operates based on the time-of-flight principle.

4. The crystal length measuring device for a single crystal growth furnace according to claim 2, characterized in that, The detection beam emitted by the laser ranging sensor is an infrared laser.

5. The crystal length measuring device for a single crystal growth furnace according to claim 1, characterized in that, The data update frequency of the non-contact ranging sensor is greater than or equal to 30 Hz.

6. The crystal length measuring device for a single crystal growth furnace according to claim 1, characterized in that, The non-contact ranging sensor is installed on the top flange of the furnace body.

7. The crystal length measuring device for a single crystal growth furnace according to claim 1, characterized in that, The target component is the weight set on the suspension cable in the single crystal growth furnace.

8. The crystal length measuring device for a single crystal growth furnace according to claim 1, characterized in that, The target surface has a planar geometry.

9. The crystal length measuring device for a single crystal growth furnace according to claim 1, characterized in that, The device also includes a data processing unit that is communicatively connected to the non-contact ranging sensor.

10. The crystal length measuring device for a single crystal growth furnace according to claim 9, characterized in that, The data processing unit is configured to calculate the growth length of the crystal based on the current distance value measured by the non-contact ranging sensor at the current moment and the pre-stored initial distance value.

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