Epitaxial growth method for adjusting height gradient between wafer and graphite base in real time

Abstract

The invention relates to an epitaxial growth method for adjusting the height gradient between a wafer and a graphite base in real time. The epitaxial growth method comprises the following steps: S1, installing an optical thickness analysis system above a glass observation window of an epitaxial equipment reaction chamber; s2, starting an optical thickness analysis system every time a film with a certain thickness grows on the first batch of wafers, and measuring a height gradient standard value of each wafer and the graphite base; s3, measuring the height gradient test value of each wafer and the graphite base in the next batch of wafers through the same method as the step S2, and adjusting the airflow of each planetary plate in real time in the test process so as to adjust the difference value between each height gradient test value and the height gradient standard value corresponding to the step S2; and S4, subsequently placing a batch of wafers again each time for epitaxial film growth, and performing test adjustment according to the step S3. According to the method, the dynamic adjustment of the wafer plane can be realized, and the trend that the height gradient of the top surface of the wafer and the top surface of the graphite base is increased is inhibited.

Description

Technical Field

[0001] This invention relates to an epitaxial growth method for real-time adjustment of the height gradient between a wafer and a graphite substrate, belonging to the field of epitaxial growth technology. Background Technology

[0002] Epitaxial equipment uses metal-organic chemical vapor deposition technology to grow thin films on wafers that are highly consistent with the crystal structure. These thin films are the core basic materials of the semiconductor industry and are widely used in electronic device chips, high-power devices, microwave radio frequency and other fields.

[0003] In epitaxial growth equipment, the height gradient between the planetary disk and the graphite substrate in the reaction chamber is usually fixed. During growth, this height gradient can disrupt airflow and temperature at the wafer edge, resulting in poor edge epitaxial quality. When the wafer surface is lower than or flush with the edge of the graphite substrate, airflow disturbances or stagnation zones are easily generated at the wafer edge steps, affecting the uniformity of reactant transport. Furthermore, significant heat loss occurs at the wafer edge, forming a radial temperature gradient that leads to uneven epitaxial layer thickness and doping. Conversely, when the wafer surface is slightly higher than the edge of the graphite substrate, it facilitates rotational mating between the wafer and the substrate, forming stable and uniform laminar flow and reducing eddies. It also effectively reduces heat dissipation from the wafer edge to the low-temperature environment, improving radial temperature uniformity. Currently, the mainstream optimization solution in the industry is to increase the height of the planetary disk and reduce the depth of the wafer carrier disk groove. However, as the epitaxial growth cycle increases, the material thickness at the center of the graphite substrate continuously increases, causing the height gradient between the wafer and the graphite substrate to dynamically amplify with epitaxial growth. Therefore, achieving dynamic adjustment of the height gradient between the wafer and the graphite substrate plays a crucial role in optimizing the radial uniformity of epitaxial films. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an epitaxial growth method that adjusts the height gradient between the wafer and the graphite substrate in real time. This method enables dynamic adjustment of the height gradient between the wafer and the graphite substrate, thereby reducing the edge defect effect of the epitaxial film and ultimately improving the radial uniformity of the epitaxial film.

[0005] Terminology Explanation: The EpiCurve® TT system is an in-situ optical metrology and monitoring system developed by LayTec GmbH in Germany. It is mainly used in semiconductor thin film growth equipment such as metal-organic chemical vapor deposition and molecular beam epitaxy to monitor the epitaxial growth process in real time.

[0006] The technical solution of the present invention is as follows: This invention provides an epitaxial growth method for real-time adjustment of the height gradient between a wafer and a graphite substrate, comprising the following steps: S1. Install an optical thickness analysis system above the glass observation window of the epitaxial equipment reaction chamber; S2. Place the first batch of wafers into the reaction chamber, set the purge gas ratio and initial gas flow of each planetary disk, control the temperature of the reaction chamber, grow a thin film on the wafer, and after each film of a certain thickness is grown, start the optical thickness analysis system to measure the height gradient between each wafer and the graphite substrate. Each height gradient is measured multiple times, and the average value of each height gradient is calculated as the standard value of the height gradient. After the epitaxial film growth is completed, take out the first batch of wafers from the reaction chamber. S3. Place another batch of wafers into the reaction chamber; set the same planetary disk purge gas ratio, initial planetary disk gas flow, and reaction chamber temperature as in step S2, and grow an epitaxial film on the wafer. After each film of the same thickness as in step S2 is grown, start the optical thickness analysis system to measure the height gradient between each wafer and the graphite substrate. Each height gradient is measured multiple times, and the average value of each height gradient is calculated as the height gradient test value. During the test, adjust the gas flow of each planetary disk in real time to adjust the difference between each height gradient test value and the height gradient standard value corresponding to step S2. After the growth of this batch of epitaxial films is completed, remove the wafers from the reaction chamber. S4. Each time a new batch of wafers is placed for epitaxial film growth, the testing and adjustment are carried out in accordance with step S3.

[0007] According to a preferred embodiment of the present invention, in step S1, the optical thickness analysis system performs optical analysis using Schahm's law.

[0008] According to a preferred embodiment of the present invention, in step S1, the measurement range of the optical thickness analysis system in the horizontal direction is 120±40mm; more preferably, the measurement range of the optical thickness analysis system in the horizontal direction is 150mm.

[0009] According to a preferred embodiment of the present invention, in step S1, a light source is provided at the bottom center of the optical thickness analysis system, and the light source is 40±20mm above the glass observation window in the vertical direction; preferably, the light source is 50mm above the glass observation window in the vertical direction; the optical thickness analysis system emits a linear beam of light without obstructing the operation and monitoring of the EpiCurve® TT system, passes through the glass observation window to perform thickness measurement and analysis on the graphite substrate and the wafer radius region, and obtains the height gradient between each wafer and the graphite substrate.

[0010] According to a preferred embodiment of the present invention, in step S2, the purge gas flow ratio of each planetary disk is set to N2:H2=0~17, and the initial gas flow of each planetary disk is set to 50~500 sccm; at this time, the wafer is higher than the graphite substrate, and the height gradient between the wafer and the graphite substrate is 10~200 μm. This reduces the height gradient while ensuring the rotation of the planetary disks, thereby reducing the edge defect effect of the epitaxial film. More preferably, the purge gas flow ratio of each planetary disk is set to N2:H2=0~2, the initial gas flow of each planetary disk is set to 50~150 sccm, and the height gradient between the wafer and the graphite substrate is 10~60 μm. Most preferably, the purge gas flow ratio of each planetary disk is set to N2:H2=1, the initial gas flow of each planetary disk is set to 100 sccm, and the height gradient between the wafer and the graphite substrate is 20~30 μm.

[0011] According to a preferred embodiment of the present invention, in step S2, a thin film with a thickness of 0.5 to 12 μm is grown on the wafer, and an optical thickness analysis system is activated after each 0.1 to 6 μm thick film is grown; more preferably, an 8 μm thick film is grown on the wafer, and an optical thickness analysis system is activated after each 4 μm thick film is grown.

[0012] According to a preferred embodiment of the present invention, in step S2, when the optical thickness analysis system is started, the initial angle of the graphite base is 0°-180°; more preferably, the initial angle of the graphite base is 0°.

[0013] According to a preferred embodiment of the present invention, in step S2, each height gradient is measured 10-15 times, and the period of each height gradient measurement is 12-180s; more preferably, each height gradient is measured 12 times, and the period of each height gradient measurement is 60s.

[0014] According to a preferred embodiment of the present invention, in step S3, the number of measurements and the period for each height gradient are the same as in step S2.

[0015] According to a preferred embodiment of the present invention, in step S3, the airflow of each planetary disk is adjusted in real time during the test, thereby adjusting the difference between each altitude gradient test value and the altitude gradient standard value corresponding to step S2 to ±1μm. More preferably, the difference between each altitude gradient test value and the altitude gradient standard value corresponding to step S2 is adjusted to ±0.5μm. Most preferably, the difference between each altitude gradient test value and the altitude gradient standard value corresponding to step S2 is adjusted to ±0.2μm.

[0016] The technical features and beneficial effects of this invention are as follows: The method of this invention utilizes an external optical thickness analysis system to monitor the height of the wafer and graphite substrate in real time, while simultaneously optimizing the purge airflow at the bottom of the planetary disk. This enables dynamic adjustment of the wafer plane, suppressing the increasing height gradient between the wafer top surface and the graphite substrate top surface, reducing edge heat dissipation effects, and preventing the formation of eddies. This improves the uniformity of the wafer's radial temperature and enhances the uniformity of the epitaxial film. Furthermore, by increasing the height of the planetary disk, ensuring the wafer top surface is higher than the edge of the graphite substrate, the method also reduces the risk of defects formed on the wafer film from the graphite substrate edge material, improving film quality. In addition, the method combines real-time thickness monitoring with dynamic adjustment of the planetary disk airflow, overcoming the difficulty of increasing film edge defects with increasing epitaxial thickness, thus improving film uniformity and extending the epitaxial growth cycle. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an epitaxial device for mounting an optical thickness analysis system provided in Embodiment 1 of the present invention, where X represents the height gradient between the wafer and the graphite substrate; Figure 2 This is a schematic diagram of the epitaxial device without an optical thickness analysis system provided in Comparative Example 1 of the present invention. In the figure: 1. Graphite base, 2. Planetary disk, 3. Wafer, 4. Reaction chamber top cover, 5. Glass observation window, 6. EpiCurve® TT system, 7. Optical thickness analysis system. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments, but is not limited thereto. The described embodiments are some embodiments of the present invention. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified in the embodiments of the present invention, all can be based on existing technology. In this embodiment, the epitaxial device is existing equipment, specifically the AIXTRON AIX 2800G4 metal-organic chemical vapor deposition (MOCVD) device, and this embodiment is an improvement upon this device.

[0020] Example 1 An epitaxial growth method for real-time adjustment of the height gradient between a wafer and a graphite substrate includes the following steps: S1. An optical thickness analysis system 7 with a horizontal measurement range of 150 mm is installed above the glass observation window 5 of the reaction chamber top cover 4 to perform optical analysis using Scherm's law. A light source is set at the center of the bottom of the optical thickness analysis system 7, and the light source is set below the EpiCurve® TT system 6. The vertical distance between the EpiCurve® TT system 6 and the glass observation window 5 is 100 mm, and the vertical distance between the light source and the glass observation window 5 is 550 mm.

[0021] S2. The first batch of wafers 3 are placed in the reaction chamber. The purge gas ratio of each planetary disk 2 is set to N2:H2=1, and the initial gas flow of the planetary disk 2 is set to 100 sccm. The reaction chamber temperature is maintained at 690℃, and TMAl, TMGa, TMIn, and PH3 are introduced. When an 8μm thick epitaxial film is grown on the wafer 3, and the epitaxial film reaches a thickness of 4μm, the optical thickness analysis system 7 is activated to measure the height gradient between the eight wafers 3 and the graphite substrate 1 in the reaction chamber. The radial angles of the eight wafers 3 are 0° (360°), 45°, 90°, 135°, 180°, 225°, 270°, and 315°, respectively. The initial height gradient of the graphite substrate 1 at the start of the measurement is... With an angle of 0°, each height gradient is measured 12 times, with a measurement cycle of 60 seconds. The average value of the eight height gradients is calculated as the standard height gradient value (x10, x20, x30, x40, x50, x60, x70, x80). When the epitaxial film is grown to an 8 μm thickness, the optical thickness analysis system 7 is activated to measure the height gradient between the eight wafers 3 and the graphite substrate 1 in the reaction chamber. Each height gradient is measured 12 times, with a measurement cycle of 60 seconds. The average value of the eight height gradients is calculated as the standard height gradient value (x11, x21, x31, x41, x51, x61, x71, x81). The first batch of wafers 3 is then removed from the reaction chamber. S3. A new batch of wafers 3 is placed in the reaction chamber. The purge gas flow ratio of each planetary disk 2 is set to N2:H2=1, and the initial gas flow of the planetary disk 2 is set to 100 sccm. The reaction chamber temperature is maintained at 690℃, and TMAl, TMGa, TMIn, and PH3 are introduced. An 8μm thick epitaxial film is grown on the wafers 3. After the epitaxial film reaches a thickness of 4μm, the optical thickness analysis system 7 is activated to measure the height gradient between the eight wafers 3 and the graphite substrate 1 in the reaction chamber. Each height gradient is measured 12 times, with a measurement cycle of 60s. The average of eight height gradients is calculated as the height gradient test value (x12, x22, x32, x42, x52, x62, x72, x82). During the test, the optical thickness analysis system 7 transmits the height gradient test values ​​to the computer's data processing system for processing. The computer then controls the epitaxial device to adjust the airflow of each planetary disk 2 in real time, increasing the airflow of each planetary disk 2 by 7 sccm. This ensures that the difference between each height gradient test value and the height gradient standard value corresponding to step S2 is controlled within 0.2 μm, i.e., x12 - x10≤0.2μm, x22-x20≤0.2μm, x32-x30≤0.2μm, x42-x40≤0.2μm, x52-x50≤0.2μm, x62-x60≤0.2μm, x72-x70≤0.2μm, x82-x80≤0.2μm; After growing an epitaxial film to a thickness of 8μm, the optical thickness analysis system 7 is activated to measure the height gradient between the eight wafers 3 and the graphite substrate 1 in the reaction chamber. Each height gradient is measured 12 times, with a measurement cycle of 60s. The average value of the eight height gradients is calculated as the standard value of the height gradient (x13, x23, x33, x43, x53, x63, x73, x83). The airflow in each planetary disk 2 is increased by 7sccm to ensure that the difference between each height gradient test value and the height gradient standard value corresponding to step S2 is controlled within 0.2μm, i.e., x13- x11≤0.2μm, x23-x21≤0.2μm, x33-x31≤0.2μm, x43-x41≤0.2μm, x53-x51≤0.2μm, x63-x61≤0.2μm, x73-x71≤0.2μm, x83-x81≤0.2μm; 3 wafers from this batch were removed from the reaction chamber. S4. Subsequently, each time a new batch of wafers 3 is placed in for epitaxial film growth, tests and adjustments are performed in accordance with step S3.

[0022] Comparative Example An epitaxial growth method includes the following steps: S1. Place a batch of wafers 3 into the reaction chamber, set the purge gas flow ratio of each planetary disk 2 to N2:H2=1, and set the initial gas flow of planetary disk 2 to 100sccm; maintain the reaction chamber temperature at 690℃, and introduce TMAl, TMGa, TMIn, and PH3 to grow an 8μm thick epitaxial film on wafers 3.

[0023] S2. Subsequently, each time a new batch of wafers is placed, epitaxial thin film growth is performed in accordance with step S1.

[0024] The difference between this comparative example and Example 1 is that the epitaxial device was not equipped with an optical thickness analysis system 7, and the airflow of each planetary disk 2 was not adjusted in real time.

[0025] Test case Epitaxial growth was performed on multiple batches of wafers using the methods of Example 1 and Comparative Example 1. During the epitaxial growth of each batch of wafers, an epitaxial film of the same thickness as the wafer was attached to the graphite substrate. The thickness of the epitaxial film on the graphite substrate accumulated with the increase of batches. When the accumulated epitaxial film thickness on the graphite substrate reached 150 μm and 300 μm, the temperature difference ΔT between the center and edge of the eight wafers, the wavelength consistency ΔWL of the epitaxial wafer, and the film thickness consistency ΔTh were observed through the epitaxial equipment system. The results are shown in Tables 1-3.

[0026] Table 1 Results of temperature difference ΔT between wafer center and edge Table 2 Results of Epitaxial Wavelength Consistency ΔWL Table 3 Results of film thickness uniformity ΔTh As shown in Table 1, when the cumulative epitaxial thickness of the graphite substrate reaches 150 μm, the temperature uniformity of each wafer in Example 1 is in the range of 0.1℃-0.3℃, and the temperature uniformity of each wafer in Comparative Example 1 is in the range of 1.1℃-1.7℃; when the cumulative epitaxial thickness of the graphite substrate reaches 300 μm, the temperature uniformity of each wafer in Example 1 is in the range of 0.2℃-0.5℃, and the temperature uniformity of each wafer in Comparative Example 1 is in the range of 1.7℃-2.6℃.

[0027] As shown in Table 2, when the cumulative epitaxial thickness of the graphite substrate reaches 150 μm, the wavelength consistency of each epitaxial wafer in Example 1 is in the range of 1.9 nm to 2.7 nm, and the wavelength consistency of each epitaxial wafer in Comparative Example 1 is in the range of 3.0 nm to 4.5 nm; when the cumulative epitaxial thickness of the graphite substrate reaches 300 μm, the wavelength consistency of each epitaxial wafer in Example 1 is in the range of 2.2 nm to 3.0 nm, and the wavelength consistency of each epitaxial wafer in Comparative Example 1 is in the range of 3.7 nm to 5.0 nm.

[0028] Table 3 shows that when the cumulative epitaxial thickness of the graphite substrate reaches 150 μm, the thickness consistency of the thin films on each wafer in Example 1 is in the range of 11 nm to 17 nm, and the thickness consistency of the thin films on each wafer in Comparative Example 1 is in the range of 24 nm to 37 nm; when the cumulative epitaxial thickness of the graphite substrate reaches 300 μm, the thickness consistency of the thin films on each wafer in Example 1 is in the range of 12 nm to 18 nm, and the thickness consistency of the thin films on each wafer in Comparative Example 1 is in the range of 39 nm to 49 nm.

[0029] In summary, the epitaxial growth method of the present invention significantly improves the radial temperature uniformity of the wafer, the wavelength consistency of the epitaxial wafer, and the film thickness consistency by detecting the height gradient between the wafer and the graphite substrate and optimizing the wafer height.

Claims

1. An epitaxial growth method for real-time adjustment of the height gradient between a wafer and a graphite substrate, characterized in that, Including the following steps: S1. Install an optical thickness analysis system above the glass observation window of the epitaxial equipment reaction chamber; S2. Place the first batch of wafers into the reaction chamber, set the purge gas ratio and initial gas flow of each planetary disk, control the temperature of the reaction chamber, grow a thin film on the wafer, and after each film of a certain thickness is grown, start the optical thickness analysis system to measure the height gradient between each wafer and the graphite substrate. Each height gradient is measured multiple times, and the average value of each height gradient is calculated as the standard value of the height gradient. After the epitaxial film growth is completed, take out the first batch of wafers from the reaction chamber. S3. A new batch of wafers is placed in the reaction chamber. The same planetary disk purge gas ratio, initial planetary disk gas flow, and reaction chamber temperature as in step S2 are set. An epitaxial thin film is grown on the wafer. After each film of the same thickness as in step S2 is grown, an optical thickness analysis system is activated to measure the height gradient between each wafer and the graphite substrate. Each height gradient is measured multiple times, and the average value of each height gradient is calculated as the height gradient test value. During the test, the gas flow of each planetary disk is adjusted in real time to adjust the difference between each height gradient test value and the corresponding height gradient standard value in step S2. After the growth of this batch of epitaxial thin films is completed, the wafers are removed from the reaction chamber. (The last sentence appears to be incomplete and possibly refers to a different process.) S4. Each time a new batch of wafers is placed for epitaxial film growth, the testing and adjustment are carried out in accordance with step S3.

2. The epitaxial growth method for real-time adjustment of the height gradient between the wafer and the graphite substrate according to claim 1, characterized in that, In step S1, the optical thickness analysis system performs optical analysis using Schahm's law.

3. The epitaxial growth method for real-time adjustment of the height gradient between the wafer and the graphite substrate according to claim 1, characterized in that, In step S1, the measurement range of the optical thickness analysis system in the horizontal direction is 120±40mm; more preferably, the measurement range of the optical thickness analysis system in the horizontal direction is 150mm.

4. The epitaxial growth method for real-time adjustment of the height gradient between the wafer and the graphite substrate according to claim 1, characterized in that, In step S1, a light source is provided at the bottom center of the optical thickness analysis system, and the light source is 40±20mm above the glass observation window in the vertical direction; preferably, the light source is 50mm above the glass observation window in the vertical direction.

5. The epitaxial growth method for real-time adjustment of the height gradient between the wafer and the graphite substrate according to claim 1, characterized in that, In step S2, the purge gas flow ratio of each planetary disk is set to N2:H2=0~17, and the initial gas flow of each planetary disk is set to 50~500 sccm. At this time, the wafer is higher than the graphite substrate, and the height gradient between the wafer and the graphite substrate is 10~200 μm. This reduces the height gradient while ensuring the rotation of the planetary disk, thereby reducing the edge defect effect of the epitaxial film. More preferably, the purge gas flow ratio of each planetary disk is set to N2:H2=0~2, the initial gas flow of each planetary disk is set to 50~150 sccm, and the height gradient between the wafer and the graphite substrate is 10~60 μm. Most preferably, the purge gas flow ratio of each planetary disk is set to N2:H2=1, the initial gas flow of each planetary disk is set to 100 sccm, and the height gradient between the wafer and the graphite substrate is 20~30 μm.

6. The epitaxial growth method for real-time adjustment of the height gradient between the wafer and the graphite substrate according to claim 1, characterized in that, In step S2, a thin film with a thickness of 0.5~12μm is grown on the wafer, and the optical thickness analysis system is activated after each 0.1~6μm thick film is grown; more preferably, an 8μm thick film is grown on the wafer, and the optical thickness analysis system is activated after each 4μm thick film is grown.

7. The epitaxial growth method for real-time adjustment of the height gradient between the wafer and the graphite substrate according to claim 1, characterized in that, In step S2, when the optical thickness analysis system is started, the initial angle of the graphite base is 0°-180°; more preferably, the initial angle of the graphite base is 0°.

8. The epitaxial growth method for real-time adjustment of the height gradient between the wafer and the graphite substrate according to claim 1, characterized in that, In step S2, each height gradient is measured 10-15 times, and the period of each height gradient measurement is 12-180s; more preferably, each height gradient is measured 12 times, and the period of each height gradient measurement is 60s.

9. The epitaxial growth method for real-time adjustment of the height gradient between the wafer and the graphite substrate according to claim 8, characterized in that, In step S3, the number of measurements and the period for each height gradient are the same as in step S2.

10. The epitaxial growth method for real-time adjustment of the height gradient between the wafer and the graphite substrate according to claim 1, characterized in that, In step S3, the airflow of each planetary disk is adjusted in real time during the test, thereby adjusting the difference between each height gradient test value and the height gradient standard value corresponding to step S2 to ±1μm. More preferably, the difference between each height gradient test value and the height gradient standard value corresponding to step S2 is adjusted to ±0.5μm; most preferably, the difference between each height gradient test value and the height gradient standard value corresponding to step S2 is adjusted to ±0.2μm.

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