A method for real-time control of epitaxial layer growth stress

Abstract

This invention discloses a method for real-time control of epitaxial layer growth stress. During epitaxial growth, the change in the curvature of the epitaxial film is closely related to the thickness and stress of the epitaxial film. Several 200nm quaternary InGaAsP alloys with different stresses are grown on an InP substrate, and the film stress monitoring software curvature is retrieved during the growth process. This method for real-time control of epitaxial layer growth stress summarizes the relationship between the stress of the InGaAsP quaternary alloy epitaxial layer and the rate of change of the epitaxial film curvature, and refines it into a formula; at the same time, it summarizes the relationship between epitaxial stress and epitaxial process parameters, and refines it into a formula. By applying these two formulas, on the one hand, the epitaxial growth process parameters for a given stress can be quickly located, and on the other hand, the stress can be monitored during the epitaxial growth of the quaternary alloy, and the stress can be adjusted in situ, reducing the number of growth cycles and improving growth efficiency.

Description

Technical Field

[0001] This invention belongs to the field of epitaxial layer growth stress technology, and particularly relates to a method for real-time control of epitaxial layer growth stress. Background Technology

[0002] Stress is a crucial parameter in semiconductor lasers, and its control is essential for achieving high performance and reliability. Stress is generated at every stage of the semiconductor laser fabrication process, necessitating continuous monitoring of stress accumulation and changes. Epitaxial growth is a critical step in laser fabrication, and controlling the stress in each layer significantly impacts both the final device performance and the effectiveness of subsequent processing.

[0003] Stress monitoring methods for epitaxial growth are relatively limited. Early methods typically involved XRD or profilometer stress testing after growth to characterize the stress in the epitaxial material. However, the inherent lag in these methods necessitates multiple experiments to achieve satisfactory stress control. Furthermore, changes in the reaction chamber environment can lead to stress deviations, requiring adjustments in later tests and resulting in wasted growth time. Recently, some epitaxial manufacturers have introduced Curvature, a tool that allows real-time monitoring of epitaxial growth stress. It utilizes the distance difference between two in-phase beams reflected from the wafer to obtain stress changes. However, this method is currently only one form of stress characterization and cannot directly correlate stress with actual stress levels, nor can it guide the adjustment of growth parameters.

[0004] Currently, most methods for stress control in epitaxial thin films involve first growing a monitoring wafer, then adjusting the growth on the final wafer based on the XRD test results of the monitoring wafer to achieve stress control. However, adjusting based on XRD test results after epitaxial growth is inefficient, and if the initial adjustment has a large deviation, a second adjustment is required, wasting growth cycles.

[0005] In the epitaxial growth process, if the curvature tool is used, the relationship between the results it provides and the stress needs to be adjusted according to different materials, and it cannot directly guide the adjustment of growth stress. Therefore, it can only be used as a monitoring tool in most cases, and cannot be used as a control tool. To address this, the present invention provides a method for real-time control of epitaxial layer growth stress. Summary of the Invention

[0006] The purpose of this invention is to provide a method for real-time control of epitaxial layer growth stress, so as to solve the technical problems mentioned in the background art.

[0007] To achieve the above objectives, the specific technical solution of the present invention is as follows: A method for real-time control of epitaxial layer growth stress, specifically comprising the following steps:

[0008] Step 1: During the epitaxial growth process, the change in the curvature of the epitaxial film is closely related to the thickness and stress of the epitaxial film. Several 200nm quaternary InGaAsP alloys with different stresses are grown on an InP substrate. By calling the film stress monitoring software curvature during the growth process, the relationship between the curvature curvature value and the epitaxial film stress under the same thickness is obtained.

[0009] Step 2: The relationship between the change value of the curvature of the thin film surface during the growth process and the stress value of the epitaxial layer after the experiment was obtained. The Stoney formula was used to input the quaternary alloy material parameters obtained by ourselves. By searching the data, the corresponding data values ​​of InGaAsP material were obtained, and the following relationship between the curvature change value and the strain of the epitaxial layer was obtained. The specific formula of the relationship (1) is as follows:

[0010] Δδ=(3.4656 / hs^2) ε+a(1)

[0011] Where Δδ is the change in curvature, in units of (km(- 2 hs is the thickness of the substrate in km; ε is the strain of the epitaxial layer on the substrate; a is the correction term for substrate stress, with a specific value of 1E+09, dimensionless.

[0012] Step 3: Based on the results obtained from XRD testing of the epitaxial material used in the above experiments, and the corresponding growth parameters, obtain the relationship between growth parameters and stress, and generate a table showing the stress magnitude and the proportion of In atoms and Ga atoms in the InGaAsP quaternary alloy epitaxial film.

[0013] Step 4: Based on the percentage table generated in Step 3, we obtain the following formula (2):

[0014] ε = -526.02x + 7.605 + b(2)

[0015] Where ε is the strain of the epitaxial layer on the substrate layer, dimensionless; x is the In / Ga molar ratio of the growth parameter, dimensionless; b is the correction term for the molar ratio parameter, with a base value of 0, dimensionless.

[0016] Step 5: Adjust stress during the growth process according to formulas (1) and (2).

[0017] Preferably, the InP substrate in step one has a thickness of 625 μm, and several different stress values ​​include 0.54%, 0.33%, 0.17%, -0.49%, and -1%, where negative values ​​represent compressive stress.

[0018] Preferably, the Stoney formula in step two is as follows:

[0019] ε = σ / E + αΔT, where ε is strain, σ is stress, E is Young's modulus, α is the coefficient of linear expansion, and ΔT is the temperature change;

[0020] Where αΔT is 0, a constant is introduced as a compensation correction term, σ stress is the stress caused by lattice changes between the epitaxial film and the substrate during actual growth, and its calculation formula is (af-as) / as, ε represents strain, which is the ratio of the change in film length to the initial length. The relationship between strain, stress and radius curvature is derived as follows:

[0021]

[0022] Among them, R c The curvature change value can be obtained through curvature, h f and h s E represents the thickness of the epitaxial film and the substrate, respectively. f and E s They represent biaxial modulus, ε represents strain, and a f and a s Representing the lattice constants of the epitaxial film and the substrate, respectively, (a f -a s ) / a s Represents stress.

[0023] 4. Preferably, the specific operation steps for real-time stress control in step five are as follows:

[0024] S1. Based on the design, the target value of the epitaxial layer stress is obtained. The corresponding growth parameter value is calculated according to formula (2), and the parameter value is 1. The corresponding curvature value is calculated according to formula (1), and the change value is 1, which is used as a reference value.

[0025] S2. Use parameter value 1 to write a program to prepare the program, place the substrate, run the program, heat up, and start growth after the temperature stabilizes.

[0026] S3. After growth begins, the EpiTT software will automatically open a new page displaying curves such as temperature, reflectivity, and curvature. Drag the stress-related curvature curve corresponding to the position of the small disk to the new display interface to display the stress monitoring curve. After retrieving the stress monitoring curve, after the required epitaxial layer begins to grow, read the curvature value of the epitaxial layer through the data on the curvature / km^-1 axis on the left side of the curve, which is the change value of Δδ.

[0027] S4. If the actual change value 1 of curvature and the calculated change value 1 are the same or similar, then growth can be carried out under this condition. If the actual change value 1 of curvature and the calculated change value 1 are far apart, then the corresponding new stress value 2 needs to be calculated using formula (1) based on the actual change value 1 of curvature. Then, using (stress value 2, parameter 1) as a data point, it is substituted into formula (2) to calculate the latest substrate correction parameter b1. Then, the growth parameter 2 is calculated based on the corrected formula (2) and the target stress value.

[0028] S5. Input growth parameter 2 into the program and adjust the parameters in a timely manner, and observe the subsequent changes in curvature value.

[0029] The method for real-time control of epitaxial layer growth stress according to the present invention has the following advantages:

[0030] 1. This method for real-time control of epitaxial layer growth stress can quickly obtain the growth process parameters of the target stress by using the relationship between the stress of the quaternary alloy epitaxial film and the epitaxial process parameters obtained by this invention.

[0031] 2. This method for real-time control of epitaxial layer growth stress summarizes the relationship between stress and curvature change rate of InGaAsP quaternary alloy epitaxial layer and extracts it into a formula; at the same time, it summarizes the relationship between epitaxial stress and epitaxial process parameters and extracts it into a formula. By applying these two formulas, on the one hand, the epitaxial growth process parameters for a given stress can be quickly located, and on the other hand, the stress can be monitored and adjusted in situ during the epitaxial growth of quaternary alloy, reducing the number of growth cycles and improving growth efficiency. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the stress monitoring curve of the present invention;

[0034] Figure 2 This is a data curve of the 200nm quaternary InGaAsP alloy thin film in this invention;

[0035] Figure 3 This is a table showing the proportions of In atoms and Ga atoms in this invention. Detailed Implementation

[0036] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0037] In the description of the embodiments of the present invention, it should be understood that the terms "length", "vertical", "horizontal", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0039] In this embodiment of the invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this embodiment of the invention according to the specific circumstances.

[0040] The following disclosure provides many different implementations or examples for carrying out different structures of the embodiments of the present invention. To simplify the disclosure of the embodiments of the present invention, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the embodiments of the present invention. Furthermore, reference numerals and / or reference letters may be repeated in different examples of the embodiments of the present invention; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various implementations and / or arrangements discussed.

[0041] To better understand the purpose, structure, and function of this invention, the following detailed description of a method for real-time control of epitaxial layer growth stress is provided in conjunction with the accompanying drawings.

[0042] like Figures 1-3As shown, a method for real-time control of epitaxial layer growth stress according to the present invention specifically includes the following steps:

[0043] Step 1: During epitaxial growth, the curvature of the epitaxial film is closely related to its thickness and stress. Several 200nm quaternary InGaAsP alloy films with different stresses were grown on an InP substrate (all alloy films were in an unstressed state). The relationship between the curvature value and the epitaxial film stress at the same thickness was obtained by retrieving the curvature from the film stress monitoring software, Curvature, during the growth process. The InP substrate thickness was 625µm, and the different stress values ​​included 0.54%, 0.33%, 0.17%, -0.49%, and -1%, with negative values ​​representing compressive stress. The data curves for the 200nm quaternary InGaAsP alloy films are shown below. Figure 2 As shown.

[0044] like Figure 1 As shown, the bottom line from the left is the curve of the curvature value, which reflects the stress change in real time during the growth of the stress layer. The solution in this invention also calculates and adjusts the parameters based on the value of this curve during the growth process.

[0045] Step 2: The relationship between the change in surface curvature of the thin film during the growth process and the stress value of the epitaxial layer after the experiment was obtained. The Stoney formula was used, with the quaternary alloy material parameters obtained independently. The Stoney formula is as follows:

[0046] ε = σ / E + αΔT, where ε is strain, σ is stress, E is Young's modulus, α is the coefficient of linear expansion, and ΔT is the temperature change;

[0047] In this case, since we aim to adjust the stress in real time during the growth process, there is actually no temperature change, where αΔT is 0. A constant is introduced as a compensation correction term. σ stress is the stress caused by lattice changes between the epitaxial film and the substrate during actual growth, and its calculation formula is (af-as) / as, which is dimensionless. ε represents strain, which is the ratio of the change in film length to the initial length. The relationship between strain, stress, and radius curvature is derived as follows:

[0048]

[0049] Among them, R c The curvature change value can be obtained through curvature, h f and h s E represents the thickness of the epitaxial film and the substrate, respectively. f and E s They represent biaxial modulus, ε represents strain, and af and a s Representing the lattice constants of the epitaxial film and the substrate, respectively, (a f -a s ) / a s Represents stress;

[0050] By searching for relevant data, the corresponding data values ​​of InGaAsP material were obtained, and the following relationship between curvature change value and epitaxial layer strain was obtained. The specific formula (1) of the relationship is as follows:

[0051] Δδ=(3.4656 / hs^2) ε+a(1)

[0052] Where Δδ is the rate of change of curvature, in km(- 2 hs is the thickness of the substrate in km; ε is the strain of the epitaxial layer on the substrate; a is the correction term for substrate stress, with a specific value of 1E+09, dimensionless.

[0053] Step 3: Based on the XRD results obtained from the epitaxial materials used in the above experiments, and the corresponding growth parameters, obtain the relationship between growth parameters and stress, and produce a table showing the stress magnitude and the proportion of In and Ga atoms in the InGaAsP quaternary alloy epitaxial thin film. (Table follows) Figure 3 As shown:

[0054] Step 4: Based on the percentage table generated in Step 3, we obtain the following formula (2):

[0055] ε = -526.02x + 7.605 + b(2)

[0056] Where ε is the strain of the epitaxial layer on the substrate layer, dimensionless; x is the In / Ga molar ratio of the growth parameter, dimensionless; b is the correction term for the molar ratio parameter, with a base value of 0, dimensionless.

[0057] Step 5: Based on formulas (1) and (2), stress adjustment during the growth process is guided. The specific steps for real-time stress control are as follows:

[0058] S1. Based on the design, the target value of the epitaxial layer stress is obtained. The corresponding growth parameter value is calculated according to formula (2), and the parameter value is 1. The corresponding curvature value is calculated according to formula (1), and the change value is 1, which is used as a reference value.

[0059] S2. Use parameter value 1 to write a program to prepare the program, place the substrate, run the program, heat up, and start growth after the temperature stabilizes.

[0060] S3. After growth begins, the EpiTT software will automatically open a new page displaying curves for temperature, reflectivity, and curvature. Drag the stress-related curvature curve corresponding to the small disk's position to the new display interface to generate stress monitoring curves. Figure 1 As shown, the two curves from the top left are temperature curves, the curve at the second highest point from the left is the reflectivity curve of the growth substrate and epitaxial layer, and the curve at the bottom left is the curvature curve of the epitaxial layer. After retrieving the stress monitoring curve, after the required epitaxial layer begins to grow, the curvature value of the epitaxial layer is read through the data on the curvature / km^-1 axis on the left side of the curve, which is the change value of Δδ.

[0061] S4. If the actual change value 1 of curvature and the calculated change value 1 are the same or similar, then growth can be carried out under this condition. If the actual change value 1 of curvature and the calculated change value 1 are far apart, then the corresponding new stress value 2 needs to be calculated using formula (1) based on the actual change value 1 of curvature. Then, using (stress value 2, parameter 1) as a data point, it is substituted into formula (2) to calculate the latest substrate correction parameter b1. Then, the growth parameter 2 is calculated based on the corrected formula (2) and the target stress value.

[0062] S5. Input growth parameter 2 into the program and adjust the parameters in a timely manner, and observe the subsequent changes in curvature value.

[0063] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for real-time control of epitaxial layer growth stress, characterized in that: Specifically, the steps include the following: Step 1: Grow several 200nm quaternary InGaAsP alloys with different stresses on an InP substrate. During the growth process, use the thin film stress monitoring software curvature to obtain the relationship between the curvature curvature value and the epitaxial film stress at the same thickness. Step 2: The relationship between the change value of the curvature of the thin film surface during the growth process and the stress value of the epitaxial layer after the experiment was obtained. The Stoney formula was used to input the quaternary alloy material parameters obtained by ourselves. By searching the data, the corresponding data values ​​of InGaAsP material were obtained, and the following relationship between the curvature change value and the strain of the epitaxial layer was obtained. The specific formula of the relationship (1) is as follows: Δδ=(3.4656 / hs^2)×ε+a(1) Where Δδ is the change in curvature, in km. -2 hs is the thickness of the substrate in km; ε is the strain of the epitaxial layer on the substrate; a is the correction term for substrate stress, with a specific value of 1E+09, dimensionless. Step 3: Based on the results obtained from XRD testing of the epitaxial material and the corresponding growth parameters, obtain the relationship between growth parameters and stress, and generate a table showing the stress magnitude and the proportion of In atoms and Ga atoms in the InGaAsP quaternary alloy epitaxial film. Step 4: Based on the percentage table generated in Step 3, we obtain the following formula (2): ε = -526.02x + 7.605 + b(2) Where ε is the strain of the epitaxial layer on the substrate layer, dimensionless; x is the In / Ga molar ratio of the growth parameter, dimensionless; b is the correction term for the molar ratio parameter, with a base value of 0, dimensionless. Step 5: Adjust stress during the growth process according to formulas (1) and (2); The specific steps for real-time stress control in step five are as follows: S1. Based on the design, the target value of the epitaxial layer stress is obtained. The corresponding growth parameter value is calculated according to formula (2), and the parameter value is 1. The corresponding curvature value is calculated according to formula (1), and the change value is 1, which is used as a reference value. S2. Use parameter value 1 to write a program to prepare the program, place the substrate, run the program, heat up, and start growth after the temperature stabilizes. S3. After growth begins, the EpiTT software will automatically open a new page displaying curves of temperature, reflectivity, and curvature. Drag the stress-related curvature curve corresponding to the position of the small disk to the new display interface to display the stress monitoring curve. After retrieving the stress monitoring curve, after the required epitaxial layer begins to grow, read the curvature value of the epitaxial layer through the data on the curvature / km^-1 axis on the left side of the curve, which is the change value of Δδ. S4. If the actual change value 1 of curvature and the calculated change value 1 are the same or similar, then growth can be carried out under this condition. If the actual change value 1 of curvature and the calculated change value 1 are far apart, then the corresponding new stress value 2 needs to be calculated using formula (1) based on the actual change value 1 of curvature. Then, using (stress value 2, parameter 1) as a data point, it is substituted into formula (2) to calculate the latest substrate correction parameter b1. Then, the growth parameter 2 is calculated based on the corrected formula (2) and the target stress value. S5. Input growth parameter 2 into the program and adjust the parameters in a timely manner, and observe the subsequent changes in curvature value.

2. The method for real-time control of epitaxial layer growth stress according to claim 1, characterized in that: In step one, the InP substrate has a thickness of 625 μm, and several different stress values ​​include 0.54%, 0.33%, 0.17%, -0.49%, and -1%, where negative values ​​represent compressive stress.

3. The method for real-time control of epitaxial layer growth stress according to claim 1, characterized in that: The Stoney formula in step two is as follows: ε = σ / E + αΔT, where ε is strain, σ is stress, E is Young's modulus, α is the coefficient of linear expansion, and ΔT is the temperature change; Where αΔT is 0, a constant is introduced as a compensation correction term, and σ stress is the stress caused by lattice changes between the actual grown epitaxial film and the substrate, and its calculation formula is (a f -a s ) / a s ε represents strain, which is the ratio of the change in film length to the initial length. The relationship between strain, stress, and radius of curvature is derived as follows: Among them, R c The curvature change value is obtained through curvature, h f and h s E represents the thickness of the epitaxial film and the substrate, respectively. f and E s They represent biaxial modulus, ε represents strain, and a f and a s Representing the lattice constants of the epitaxial film and the substrate, respectively, (a f -a s ) / a s Represents stress.

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