A thickness uniformity detection method for VCSEL epitaxial wafer production

Abstract

The present application relates to the technical field of thickness detection, and particularly relates to a thickness uniformity detection method for VCSEL epitaxial wafer production. The method acquires a reference reflectance spectrum of a detection point of a VCSEL epitaxial wafer; acquires an interference degree according to the distribution characteristics of a reference layer and a resonant cavity layer; acquires a theoretical reflectance spectrum based on the preset thickness of each layer of the VCSEL epitaxial wafer and the refractive index dispersion relationship; acquires a deviation degree according to the difference in reflectance intensity between the theoretical reflectance spectrum and the reference reflectance spectrum and the interference degree; adjusts the preset thickness to acquire the corresponding deviation degree after each adjustment until the deviation degree meets a stop condition; and takes the preset thickness of the resonant cavity layer in the final adjustment as the reference thickness of the detection point to detect the thickness uniformity of the VCSEL epitaxial wafer production. The present application accurately acquires the reference thickness of each detection point, effectively improving the accuracy of the analysis of the thickness uniformity of the VCSEL epitaxial wafer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thickness detection, and particularly relates to a thickness uniformity detection method for VCSEL epitaxial wafer production. BACKGROUND

[0002] VCSEL (Vertical-Cavity Surface-Emitting Laser) as the third generation of semiconductor core devices, has irreplaceable application value in the fields of optical communication, 3D sensing, laser radar, etc., and the VCSEL epitaxial wafer is the core material for manufacturing such lasers, and its essence is to form a semiconductor crystal structure by depositing III-V semiconductor materials on the substrate layer by layer through epitaxial growth technology, and the core functional layer is composed of two distributed Bragg reflectors and a resonant cavity sandwiched in the middle, and the overall structure is equivalent to a high-performance Fabry-Perot optical cavity, and the optical properties of the resonant cavity layer directly determine the laser output performance of the VCSEL. For the production and manufacture of VCSEL epitaxial wafers, the thickness uniformity of the resonant cavity layer is a key quality index. This is because the resonant cavity as the core area of laser oscillation, once the thickness is not uniform, it will directly lead to the imbalance of the optical path difference in the cavity, causing unstable laser mode, increased beam divergence angle and output power fluctuation, etc., and in severe cases, it will even reduce the electro-optical conversion efficiency of the laser and shorten the service life of the device. Therefore, in the production process of the VCSEL epitaxial wafer, the precise detection of the thickness uniformity of the resonant cavity layer is a key link to ensure the consistency of the downstream device performance and reduce the production yield loss.

[0003] Existing methods employ optical interferometry as the mainstream technique for VCSEL epitaxial wafer thickness measurement. This method utilizes a broadband white light source to vertically illuminate the epitaxial wafer surface. After reflection and transmission at the interfaces of each layer, the light forms superimposed reflected light. The reflected spectrum is collected by a spectrometer, and the thickness of the resonant cavity layer corresponding to the detection point is calculated by analyzing the periodic oscillation characteristics presented in the spectrum. By measuring multiple detection points on the chip surface point by point, a two-dimensional thickness distribution map is finally generated, which is used to evaluate the thickness uniformity of the entire epitaxial wafer. However, in reality, a VCSEL epitaxial wafer is a complex system composed of multiple heterogeneous structures, including a substrate, buffer layer, n-DBR, resonant cavity layer, oxide confinement layer, p-DBR, capping layer, and contact layer. When probe light is incident on this type of multilayer structure, reflection and transmission occur at the upper and lower interfaces of each layer, forming dozens or even hundreds of reflected beams. These reflected beams superimpose and interfere with each other during propagation, and the resulting reflection spectrum is no longer an ideal periodic oscillation curve. Consequently, it is impossible to accurately extract the thickness information attributable only to the resonant cavity layer from the measured spectrum, because the interference signals generated by other layers will severely obscure or distort the spectral characteristics of the resonant cavity layer. Therefore, it is impossible to accurately obtain the thickness of the VCSEL epitaxial wafer and meet the requirements of high-precision VCSEL epitaxial wafer production quality control. Summary of the Invention

[0004] To address the problem of inaccurate thickness detection in existing VCSEL epitaxial wafer thickness measurement technologies based on optical interferometry, which fail to effectively eliminate complex multi-beam interference caused by multilayer superlattice structures, leading to difficulties in accurately extracting resonant cavity layer thickness information, this invention aims to provide a thickness uniformity detection method for VCSEL epitaxial wafer production. The specific technical solution adopted is as follows:

[0005] This invention provides a method for detecting thickness uniformity in VCSEL epitaxial wafer production, the method comprising the following steps:

[0006] Obtain the reference reflectance spectrum of each detection point on the surface of the VCSEL epitaxial wafer;

[0007] All layers in the VCSEL epitaxial wafer except the resonant cavity layer are used as reference layers. Based on the similarity of the standard spectral curves of each reference layer and the resonant cavity layer, the positional distribution and the preset thickness difference, as well as the reflection intensity in the standard spectral curve of each reference layer at each wavelength and the difference between each wavelength and the wavelength corresponding to the peak in the standard spectral curve of the resonant cavity layer, the interference degree of each reference layer on the resonant cavity layer at each wavelength is obtained.

[0008] Based on the preset thickness and refractive index dispersion relationship of each layer of the VCSEL epitaxial wafer, the theoretical reflection spectrum of the preset thickness group is obtained; the reference level of each wavelength is obtained based on the interference level; and the deviation between the preset thickness group and the corresponding detection point is obtained based on the difference in reflection intensity between the theoretical reflection spectrum and the reference reflection spectrum at each wavelength and the reference level of each wavelength.

[0009] Adjust the preset thickness, obtain the deviation between the preset thickness group after each adjustment and each detection point, until the deviation is less than the preset deviation threshold, stop adjusting the preset thickness, and take the preset thickness corresponding to the resonant cavity layer in the final adjustment as the reference thickness of the corresponding detection point;

[0010] The thickness uniformity of VCSEL epitaxial wafer production is tested based on a reference thickness.

[0011] Furthermore, the method for obtaining the degree of interference is as follows:

[0012] Based on the similarity of the standard spectral curves of each reference layer and the resonant cavity layer, their positional distribution, and the preset thickness differences, the degree of influence of each reference layer on the resonant cavity layer is obtained.

[0013] Based on the reflection intensity in the standard spectral curve of each reference layer at each wavelength, and the difference between the wavelength of each reference layer and the wavelength corresponding to the nearest peak in the standard spectral curve of the resonant cavity layer at each wavelength, the interference analysis value of each reference layer to the resonant cavity layer at each wavelength is obtained.

[0014] The normalized product of the interference analysis value of each reference layer on the resonant cavity layer at each wavelength and the influence degree of each reference layer on the resonant cavity layer is taken as the interference degree of each reference layer on the resonant cavity layer at each wavelength.

[0015] Furthermore, the method for obtaining the degree of influence is as follows:

[0016] For any reference layer, the absolute value of the difference between the standard spectral curves of the reference layer and the resonant cavity layer is obtained by definite integration, which is taken as the spectral difference; the result of negatively correlating and normalizing the spectral difference is taken as the first influence analysis value of the reference layer on the resonant cavity layer.

[0017] The number of layers between the reference layer and the light source is taken as the first quantity; the number of layers between the resonant cavity layer and the light source is taken as the second quantity; the ratio of the first quantity to the second quantity is taken as the second influence analysis value of the reference layer on the resonant cavity layer.

[0018] The ratio of the preset thickness of the reference layer to the preset thickness of the resonant cavity layer is used as the third influence analysis value of the reference layer on the resonant cavity layer.

[0019] The product of the first influence analysis value, the second influence analysis value, and the third influence analysis value is taken as the degree of influence of the reference layer on the resonant cavity layer.

[0020] Furthermore, the method for obtaining the interference analysis values ​​is as follows:

[0021] The wavelength corresponding to each peak in the standard spectral curve of the resonant cavity layer is obtained and used as the sensitive wavelength;

[0022] For any wavelength, the difference between that wavelength and each sensitive wavelength is obtained and used as the difference for analysis;

[0023] For any reference layer, the product of the negative correlation result of the smallest analytical difference and the reflection intensity in the standard spectral curve of the reference layer at that wavelength is taken as the interference analysis value of the reference layer on the resonant cavity layer at that wavelength.

[0024] Furthermore, the method for obtaining the reference level is as follows:

[0025] For any wavelength, the sum of the interference levels of all reference layers to the resonant cavity layer at that wavelength is taken as the total interference level at that wavelength.

[0026] The result of negatively correlating and normalizing the total interference level is used as the reference level for that wavelength.

[0027] Furthermore, the method for obtaining the degree of deviation is as follows:

[0028] For any reference reflectance spectrum at any detection point and any wavelength, the square of the difference between the theoretical reflectance spectrum and the reference reflectance spectrum at that wavelength is obtained as the first difference corresponding to that wavelength.

[0029] The product of the reference level of the wavelength and the first difference is used as the deviation analysis value of the wavelength;

[0030] The result of summing and normalizing the deviation analysis values ​​of all wavelengths is used as the degree of deviation between the preset thickness group and the detection point.

[0031] Furthermore, the method for detecting the thickness uniformity of VCSEL epitaxial wafer production based on a reference thickness is as follows:

[0032] The surface of the VCSEL epitaxial wafer is mapped onto a two-dimensional coordinate system to obtain the spatial coordinates of each detection point in the two-dimensional coordinate system;

[0033] The reference thickness of each detection point is mapped to its spatial coordinates to generate a two-dimensional thickness distribution map; the reference thickness of each detection point is represented by color intensity.

[0034] The thickness uniformity of VCSEL epitaxial wafers can be visually detected by observing the color variations in a two-dimensional mapping image.

[0035] Furthermore, the method for obtaining the theoretical reflectance spectrum is as follows:

[0036] Based on the preset thickness and refractive index dispersion relationship of each layer of the VCSEL epitaxial wafer, the theoretical reflection spectrum of the preset thickness group is obtained by means of the transfer matrix method.

[0037] Furthermore, the preset thickness group is composed of the preset thickness of each layer of the VCSEL epitaxial wafer.

[0038] Furthermore, the preset thickness adjustment is achieved by automatically adjusting the preset thickness of each layer of the VCSEL epitaxial wafer using the Levenberg-Marquardt algorithm.

[0039] The present invention has the following beneficial effects:

[0040] This invention first uses all layers in the VCSEL epitaxial wafer except the resonant cavity layer as reference layers for better subsequent description. Based on the similarity of the standard spectral curves of each reference layer and the resonant cavity layer, their positional distribution, and the preset thickness differences, as well as the reflection intensity in the standard spectral curve of each reference layer at each wavelength, and the difference between each wavelength and the corresponding wavelength of the peak in the standard spectral curve of the resonant cavity layer, the interference level of each reference layer on the resonant cavity layer at each wavelength is obtained. This accurately reflects the interference of each reference layer on the resonant cavity layer at each wavelength, facilitating accurate analysis of the reference significance of each wavelength and preparing for accurate determination of the resonant cavity layer thickness. Furthermore, based on the preset thickness and refractive index dispersion relationship of each layer in the VCSEL epitaxial wafer, the theoretical reflection spectrum of the preset thickness group is obtained, accurately preparing for subsequent analysis of the reasonableness of the preset thickness group. Further, based on the interference level, the reference level of each wavelength is obtained, accurately reflecting the referenceability of each wavelength. Then, based on the theoretical reflection... By analyzing the difference in reflection intensity between the reflected light spectrum and the reference reflection spectrum, and considering the reference level of each wavelength, the deviation between the preset thickness group and the corresponding detection point is obtained, accurately reflecting the matching status between the preset thickness group and the corresponding detection point. To more accurately determine the resonant cavity layer thickness corresponding to each detection point, the preset thickness is adjusted, and the deviation between the preset thickness group and each detection point after each adjustment is obtained until the deviation is less than the preset deviation threshold. The preset thickness corresponding to the resonant cavity layer in the final adjustment is then used as the reference thickness for the corresponding detection point. This effectively improves the accuracy of obtaining the resonant cavity layer thickness corresponding to the detection point, which is beneficial for subsequent more accurate analysis of the quality of VCSEL epitaxial wafer production. Furthermore, based on the reference thickness, the thickness uniformity of VCSEL epitaxial wafer production can be accurately detected, and areas of uneven thickness in VCSEL epitaxial wafers can be accurately and efficiently located, which is beneficial for targeted process optimization and effectively meets the requirements of high-precision VCSEL epitaxial wafer production quality control. Attached Figure Description

[0041] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic flowchart illustrating a thickness uniformity detection method for VCSEL epitaxial wafer production, provided as an embodiment of the present invention.

[0043] Figure 2 A flowchart illustrating a method for obtaining the degree of interference according to an embodiment of the present invention;

[0044] Figure 3 This is a structural diagram of a thickness uniformity detection system for VCSEL epitaxial wafer production, provided in one embodiment of the present invention.

[0045] Figure 4 This is a schematic diagram of a computer device provided according to an embodiment of the present invention. Detailed Implementation

[0046] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a thickness uniformity detection method for VCSEL epitaxial wafer production proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0048] The following describes in detail, with reference to the accompanying drawings, a specific scheme for a thickness uniformity detection method for VCSEL epitaxial wafer production provided by the present invention.

[0049] Example 1:

[0050] This invention proposes a method for detecting thickness uniformity in VCSEL epitaxial wafer production. Please refer to [link to relevant documentation]. Figure 1 The diagram illustrates a schematic flowchart of a thickness uniformity detection method for VCSEL epitaxial wafer production according to an embodiment of the present invention. The method includes the following steps:

[0051] Step S1: Obtain the reference reflectance spectrum of each detection point on the surface of the VCSEL epitaxial wafer.

[0052] Specifically, to ensure the accuracy and reliability of VCSEL epitaxial wafer thickness measurement, the spectroreflectometer must be systematically calibrated before formal measurement. The specific calibration procedure is as follows: First, a standard calibration piece with known optical parameters is placed on the instrument's sample stage, and the standard measurement procedure is executed. By comparing the spectral data measured by the instrument with the theoretical model of the standard piece, system parameters such as light source intensity, detector response, and optical path can be calibrated, thereby establishing a benchmark for the instrument's response function and eliminating system errors. Then, after calibration, the standard piece is removed, and the VCSEL epitaxial wafer to be measured is taken out of its growth reaction chamber and placed flat on the calibrated instrument's sample stage. It should be noted that the sample stage usually has a vacuum adsorption function, which uses negative pressure to firmly and flatten the VCSEL epitaxial wafer, ensuring that the sample surface is perpendicular to the optical path during measurement and avoiding measurement errors caused by sample tilting or warping. Finally, in the measurement software of the control computer, a specific measurement scheme is defined according to the detection requirements. In this embodiment, a two-dimensional grid matrix covering the area to be measured is set with the center of the VCSEL epitaxial wafer as the origin, and the number, spacing, and distribution pattern of the detection points are clearly specified. These can be set according to the actual situation and are not limited here. After the measurement program is started, the instrument platform will move automatically, positioning the probe spot sequentially to each detection point. At each detection point, a broadband white light source emits a beam that is perpendicularly incident on the sample surface, and the spectrometer simultaneously acquires and records the reference reflectance spectrum of each detection point. This process ensures the high quality and high consistency of the original spectral data on which the subsequent thickness analysis is based.

[0053] Step S2: Take all layers in the VCSEL epitaxial wafer except the resonant cavity layer as reference layers. Based on the similarity of the standard spectral curves of each reference layer and the resonant cavity layer, the positional distribution and the preset thickness difference, as well as the reflection intensity in the standard spectral curve of each reference layer at each wavelength and the difference between each wavelength and the wavelength corresponding to the peak in the standard spectral curve of the resonant cavity layer, obtain the degree of interference of each reference layer to the resonant cavity layer at each wavelength.

[0054] Specifically, the thickness of the resonant cavity layer directly determines the laser wavelength emitted by the VCSEL epitaxial wafer. If the thickness of the resonant cavity layer is uneven, VCSEL chips at different locations on the epitaxial wafer will emit light of different wavelengths. Furthermore, even minute changes in the resonant cavity layer significantly affect core performance indicators such as the device's threshold current, output power, and beam quality. Moreover, the resonant cavity layer is the most sensitive and critical indicator for evaluating the uniformity and stability of the epitaxial growth process. Therefore, ensuring the extreme uniformity of the resonant cavity layer thickness is the primary task in producing high-performance, high-yield VCSEL chips. This embodiment indirectly determines the thickness uniformity of the VCSEL epitaxial wafer production by analyzing the uniformity of the resonant cavity layer thickness.

[0055] Considering that a VCSEL epitaxial wafer is a structure composed of a substrate layer, a buffer layer, an n-DBR layer, a resonant cavity layer, an oxide confinement layer, a p-DBR layer, a capping layer, and a contact layer, when probe light is incident on a detection point, each layer may experience light reflection and transmission. Complex multi-beam interference effects will occur between different layers. Therefore, other layers of the VCSEL epitaxial wafer will affect the reflection and refraction of the resonant cavity layer, making it impossible to accurately measure the thickness of the resonant cavity layer corresponding to each detection point. To accurately obtain the thickness of the resonant cavity layer, it is necessary to accurately analyze the influence of each layer in the VCSEL epitaxial wafer other than the resonant cavity layer on the resonant cavity layer. For better description, this embodiment uses all layers in the VCSEL epitaxial wafer other than the resonant cavity layer as reference layers.

[0056] It is known that the more similar the standard spectral curves of a reference layer are to those of a resonant cavity layer, the closer the optical properties (such as refractive index and extinction coefficient) are to those of the reference layer, or that the structural characteristics of the reference layer lead to a strong optical coupling effect. This spectral similarity can cause significant optical interference. On the one hand, there is optical crosstalk, where reference layers with similar optical properties under incident light excitation produce reflection and transmission responses similar to those of the resonant cavity layer, causing optical signals from different layers to mix in the detector, making it extremely difficult to identify characteristic signals purely originating from the resonant cavity layer from the composite spectrum. On the other hand, there is the multiple interference effect, where light undergoes multiple reflections and transmissions at multiple interfaces in a complex multilayer VCSEL structure, forming complex multi-beam interference. If the optical response of a reference layer overlaps with that of the resonant cavity layer, the additional interference fringes generated by the reference layer will be superimposed on the inherent interference modes of the resonant cavity layer, resulting in distortion of the final measured spectrum and an increased deviation from the ideal single-layer interference spectrum. Therefore, the more similar the standard spectral curve of a reference layer is to that of the resonant cavity layer, the stronger the shielding and interference effect of the reference layer on the optical behavior of the resonant cavity layer. This interference will mask the key spectral features corresponding to the thickness information of the resonant cavity layer, directly reducing the accuracy and reliability of thickness measurement based on the spectral inversion algorithm. It should be noted that the standard spectral curve of each layer of the VCSEL epitaxial wafer is known and will not be elaborated further.

[0057] In the multilayer structure of VCSEL epitaxial wafers, the difference in distance between each layer and the light source leads to significant differences in how the corresponding layers interact with incident light and their interference effects on the resonant cavity layer. When the light source is incident, the layers closer to the light source in the epitaxial wafer will preferentially interact directly with the incident light. The propagation path of light in the near-light source layer is shorter, resulting in only direct optical effects (such as single reflection and refraction). Therefore, the interference with the optical signal and subsequent resonant cavity layer detection is weaker and the impact range is smaller. Conversely, although the direct interaction with the incident light is weaker in the layers farther from the light source, the light undergoes multiple reflections and refractions between the far-light source layers after passing through the near-light source layer. The interference effect of the far-light source layer on the light accumulates continuously with the propagation of the light, eventually forming a stronger comprehensive interference effect. This has a more significant impact on the optical signal characteristics and thickness detection accuracy of the resonant cavity layer, resulting in more interference compared to the near-light source layer.

[0058] This embodiment first sets a preset thickness for each layer of the VCSEL epitaxial wafer. The implementer can set the preset thickness for each layer according to actual conditions; no limitation is imposed here. When the preset thickness of a reference layer relative to the resonant cavity layer is larger, it indicates that the reference layer significantly interferes with the spectral characteristics of the resonant cavity layer. This is because when the thickness of the reference layer is larger, the propagation path of light within the reference layer is correspondingly longer. This increases the probability of light interacting with the reference layer, and more photons participate in the reflection, refraction, and other processes induced by the reference layer. Simultaneously, it prolongs the residence time of light within the reference layer, further increasing the interaction time between light and the reference layer. This makes the interference effect of the reference layer on the spectral characteristics of the resonant cavity layer more significant, thus having a greater impact on the accurate detection of the resonant cavity layer thickness.

[0059] Furthermore, in the spectral analysis of VCSEL epitaxial wafers, different wavelengths of light correspond to specific energies, and their effects on the resonant cavity layer vary significantly. When a certain wavelength is close to the peak wavelength corresponding to the standard spectral curve of the resonant cavity layer, it indicates that this wavelength has extremely high sensitivity to the optical response of the resonant cavity layer and is a key wavelength for accurately capturing the optical characteristics of the resonant cavity layer. When the reflection intensity in the standard spectral curve of a reference layer at this wavelength is greater, the optical interference generated by that reference layer will be greater, which may cause a significant deviation between the actual measured spectrum and the standard spectrum of the resonant cavity layer. This, in turn, interferes with the accurate identification of the periodic characteristics of the resonant cavity layer. Since the periodic characteristics of the resonant cavity layer are the core basis for calculating its thickness, the enhancement of periodic interference will directly undermine the basis of thickness calculation, ultimately leading to errors in the thickness measurement results of the resonant cavity layer.

[0060] Based on the above analysis, this embodiment obtains the degree of interference of each reference layer to the resonant cavity layer at each wavelength by considering the similarity of the standard spectral curves of each reference layer and the positional distribution and preset thickness differences, as well as the reflection intensity in the standard spectral curve of each reference layer at each wavelength and the difference between each wavelength and the wavelength corresponding to the peak in the standard spectral curve of the resonant cavity layer. This provides a basis for accurate analysis of the thickness uniformity of the VCSEL epitaxial wafer in the future.

[0061] Preferably, in one feasible embodiment, the method for obtaining the interference level is described in [reference needed]. Figure 2 The document presents a flowchart of a method for obtaining the degree of interference provided in this embodiment. The method includes the following steps:

[0062] Step S201: Based on the similarity of the standard spectral curves of each reference layer and the resonant cavity layer, their positional distribution, and the preset thickness difference, obtain the degree of influence of each reference layer on the resonant cavity layer.

[0063] The greater the impact, the greater the spectral interference of the reference layer on the resonant cavity layer.

[0064] In one possible implementation of this embodiment, the method for obtaining the degree of influence is as follows: For any reference layer, the absolute value of the difference between the standard spectral curves of the reference layer and the resonant cavity layer is obtained by definite integral, which is taken as the spectral difference; the smaller the spectral difference, the more similar the standard spectral curves of the reference layer and the resonant cavity layer are, and the greater the influence of the reference layer on the resonant cavity layer; then, the result of negatively correlated and normalized spectral differences is taken as the first influence analysis value of the reference layer on the resonant cavity layer; in this embodiment, the negative number of the spectral difference is taken as the power of an exponential function with the natural constant as the base, and the output of the exponential function is the result of negatively correlated and normalized spectral differences; further, the number of layers between the reference layer and the light source is taken as the first quantity; the number of layers between the resonant cavity layer and the light source is taken as the second quantity; when the first quantity is larger than the second quantity, it indicates that the reference layer is farther away from the light source and has a greater influence on the resonant cavity layer; then, the ratio of the first quantity to the second quantity is taken as the second influence analysis value of the reference layer on the resonant cavity layer; it should be noted that if the reference layer is the layer closest to the light source in the VCSEL epitaxial wafer, then the first quantity is 1. In addition, the ratio of the preset thickness of the reference layer to the preset thickness of the resonant cavity layer is obtained as the third influence analysis value of the reference layer on the resonant cavity layer;

[0065] When the first, second, and third influence analysis values ​​are all larger, it indicates that the reference layer has a greater influence on the resonant cavity layer. In order to characterize the influence of the reference layer on the resonant cavity layer as a whole, the product of the first, second, and third influence analysis values ​​is taken as the degree of influence of the reference layer on the resonant cavity layer.

[0066] This allows us to determine the extent to which each reference layer affects the resonant cavity layer.

[0067] Step S202: Based on the reflection intensity in the standard spectral curve of each reference layer at each wavelength, and the difference between the wavelength corresponding to the nearest peak in the standard spectral curve of each wavelength in the resonant cavity layer, obtain the interference analysis value of each reference layer to the resonant cavity layer at each wavelength.

[0068] The larger the interference analysis value, the greater the degree of optical interference from the corresponding reference layer to the resonant cavity layer at the corresponding wavelength.

[0069] In one possible implementation of this embodiment, the interference analysis value is obtained as follows: The wavelength corresponding to each peak in the standard spectral curve of the resonant cavity layer is obtained and used as the sensitive wavelength; for any wavelength, the absolute value of the difference between that wavelength and each sensitive wavelength is obtained and used as the analysis difference; the smaller the minimum analysis difference, the more sensitive that wavelength is to the optical response of the resonant cavity layer; when the minimum analysis difference is small, the greater the reflection intensity corresponding to the standard spectral curve of a certain reference layer at that wavelength, the greater the interference of the reference layer to the resonant cavity layer at that wavelength; then, the product of the negative correlation result of the minimum analysis difference and the reflection intensity in the standard spectral curve of the reference layer at that wavelength is used as the interference analysis value of the reference layer to the resonant cavity layer at that wavelength. In this embodiment, the negative of the minimum analysis difference is used as the power of an exponential function with the natural constant as the base, and the output of this exponential function is the negative correlation result of the minimum analysis difference.

[0070] At this point, the interference analysis values ​​of each reference layer to the resonant cavity layer at each wavelength are obtained.

[0071] Step S203: Normalize the product of the interference analysis value of each reference layer on the resonant cavity layer at each wavelength and the influence degree of each reference layer on the resonant cavity layer, and use the result as the interference degree of each reference layer on the resonant cavity layer at each wavelength.

[0072] It is known that the larger the interference analysis value, the greater the optical interference of the corresponding reference layer on the resonant cavity layer at the corresponding wavelength; the greater the influence, the greater the spectral interference of the corresponding reference layer on the resonant cavity layer. To comprehensively characterize the interference of each reference layer on the resonant cavity layer at each wavelength, the product of the interference analysis value and the influence of each reference layer on the resonant cavity layer at each wavelength is normalized to represent the interference level of each reference layer on the resonant cavity layer at each wavelength. This embodiment uses a norm normalization function to normalize the product of the interference analysis value and the influence level.

[0073] At this point, the interference level of each reference layer on the resonant cavity layer at each wavelength is obtained.

[0074] Step S3: Based on the preset thickness and refractive index dispersion relationship of each layer of the VCSEL epitaxial wafer, obtain the theoretical reflection spectrum of the preset thickness group; obtain the reference level of each wavelength based on the interference level; and obtain the deviation between the preset thickness group and the corresponding detection point based on the difference in reflection intensity between the theoretical reflection spectrum and the reference reflection spectrum at each wavelength and the reference level of each wavelength.

[0075] Specifically, to obtain the thickness corresponding to each detection point, i.e., the thickness of the resonant cavity layer corresponding to each detection point, this embodiment indirectly determines the thickness corresponding to each detection point by analyzing the rationality of the preset thickness. First, based on the preset thickness and refractive index dispersion relationship of each layer of the VCSEL epitaxial wafer, the theoretical reflection spectrum of the preset thickness group is obtained by using the transfer matrix method. The preset thickness group is composed of the preset thicknesses of each layer of the VCSEL epitaxial wafer arranged in order from top to bottom. The implementer can set the arrangement order of the preset thicknesses in the preset thickness group according to the actual situation, which is not limited here. The transfer matrix method is well-known and will not be elaborated further. It should be noted that the refractive index dispersion relationship of each layer is known and can be obtained in advance by measuring the single-layer thin film sample with an ellipsometry, which is not limited here.

[0076] By analyzing the similarity of reflection intensity at each wavelength between the theoretical reflection spectrum and the reference reflection spectrum at a specific detection point, the reasonableness of the preset thickness setting is determined. When the reflection intensity of the theoretical reflection spectrum and the reference reflection spectrum at a specific detection point is more equal at the same wavelength, it indicates that the preset thickness of each layer of the VCSEL epitaxial wafer is more accurate, indirectly suggesting that the preset thickness of the resonant cavity layer is more likely to be its true thickness. However, considering that the interference degree of each reference layer on the resonant cavity layer is different at each wavelength in reality, to obtain the resonant cavity layer thickness more accurately, a reference degree for each wavelength is obtained based on the interference degree of each reference layer on the resonant cavity layer at each wavelength. The greater the reference degree, the more meaningful the corresponding wavelength is. Therefore, based on the difference in reflection intensity between the theoretical reflection spectrum and the reference reflection spectrum at each wavelength and the reference degree for each wavelength, the deviation between the preset thickness group and the corresponding detection point is obtained. The smaller the deviation, the more accurate the preset thickness in the preset thickness group, and the more likely the thickness of the resonant cavity layer at the corresponding detection point is the preset thickness of the resonant cavity layer in the preset thickness group.

[0077] Preferably, in one feasible embodiment of this invention, the method for obtaining the reference level is as follows: for any wavelength, the sum of the interference levels of all reference layers on the resonant cavity layer at that wavelength is taken as the total interference level for that wavelength; the greater the total interference level, the less meaningful the wavelength is for reference, and the result of negatively correlated and normalized total interference level is taken as the reference level for that wavelength. In this embodiment, the negative of the total interference level is taken as the power of an exponential function with the natural constant as the base, and the output of the exponential function is the result of negatively correlated and normalized total interference level.

[0078] At this point, the reference level for each wavelength has been obtained.

[0079] Preferably, in one feasible embodiment of this invention, the method for obtaining the degree of deviation is as follows: for any reference reflectance spectrum at any detection point and any wavelength, the square of the difference between the theoretical reflectance spectrum and the reference reflectance spectrum at that wavelength is obtained as the first difference corresponding to that wavelength; the product of the reference degree of that wavelength and the first difference is obtained as the deviation analysis value of that wavelength; in order to analyze the deviation between the theoretical reflectance spectrum and the reference reflectance spectrum as a whole, the deviation analysis values ​​of all wavelengths are added together and normalized, and the result is used as the degree of deviation between the preset thickness group and the detection point. In this embodiment, the sum of the deviation analysis values ​​of all wavelengths is normalized using the norm normalization function.

[0080] Step S4: Adjust the preset thickness, obtain the deviation between the preset thickness group after each adjustment and each detection point, until the deviation is less than the preset deviation threshold, stop adjusting the preset thickness, and take the preset thickness corresponding to the resonant cavity layer in the final adjustment as the reference thickness of the corresponding detection point.

[0081] Specifically, to obtain the thickness corresponding to each detection point, this embodiment automatically adjusts the preset thickness of each layer of the VCSEL epitaxial wafer using the Levenberg-Marquardt algorithm. After each adjustment, the deviation between the adjusted preset thickness group and each detection point is obtained until the deviation is less than a preset deviation threshold. At this point, the adjustment of the preset thickness stops, and the preset thickness corresponding to the resonant cavity layer in the final adjustment is used as the reference thickness for the corresponding detection point. This embodiment sets the preset deviation threshold to 0.2. Implementers can set the size of the preset deviation threshold according to actual conditions; it is not limited here. The Levenberg-Marquardt algorithm is a well-known technique and will not be described in detail here.

[0082] At this point, the reference thickness for each detection point is obtained.

[0083] Step S5: Detect the thickness uniformity of VCSEL epitaxial wafer production based on the reference thickness.

[0084] Specifically, to analyze the thickness uniformity of VCSEL epitaxial wafer production and accurately assess the quality of VCSEL epitaxial wafer manufacturing, the surface of the VCSEL epitaxial wafer is mapped onto a two-dimensional coordinate system to obtain the spatial coordinates of each detection point. Then, the reference thickness of each detection point is correlated with its spatial coordinates to generate a two-dimensional thickness distribution map. The reference thickness of each detection point is represented by color intensity; the color change and the reference thickness change present an intuitive correspondence. This embodiment uses a gradient color spectrum from light to dark to reflect the change in reference thickness. By observing the color intensity changes in the two-dimensional map, the thickness uniformity of the VCSEL epitaxial wafer production can be intuitively detected. Furthermore, it can accurately and efficiently locate areas of uneven thickness in the VCSEL epitaxial wafer, facilitating targeted process optimization.

[0085] In summary, this embodiment obtains the reference reflection spectrum of the detection point of the VCSEL epitaxial wafer; obtains the interference level based on the distribution characteristics of the reference layer and the resonant cavity layer; obtains the theoretical reflection spectrum based on the preset thickness and refractive index dispersion relationship of each layer of the VCSEL epitaxial wafer; obtains the deviation level based on the difference in reflection intensity and interference level between the theoretical reflection spectrum and the reference reflection spectrum; adjusts the preset thickness, obtains the corresponding deviation level after each adjustment, until the deviation level meets the stopping condition, and uses the preset thickness corresponding to the resonant cavity layer in the final adjustment as the reference thickness of the detection point to detect the thickness uniformity of the VCSEL epitaxial wafer production. This invention effectively improves the accuracy of VCSEL epitaxial wafer thickness uniformity analysis by accurately obtaining the reference thickness of each detection point.

[0086] Example 2:

[0087] This invention also proposes a thickness uniformity detection system for VCSEL epitaxial wafer production; please refer to [link to relevant documentation]. Figure 3 The diagram illustrates a thickness uniformity detection system for VCSEL epitaxial wafer production according to an embodiment of the present invention. The system includes: a reference reflectance spectrum acquisition module 10, an interference level acquisition module 20, a deviation level acquisition module 30, a reference thickness acquisition module 40, and a detection module 50.

[0088] The reference reflectance spectrum acquisition module 10 is used to acquire the reference reflectance spectrum of each detection point on the surface of the VCSEL epitaxial wafer.

[0089] The interference level acquisition module 20 is used to take all layers in the VCSEL epitaxial wafer except the resonant cavity layer as reference layers, and obtain the interference level of each reference layer on the resonant cavity layer at each wavelength based on the similarity of the standard spectral curves of each reference layer and the position distribution and preset thickness difference, as well as the reflection intensity in the standard spectral curve of each reference layer at each wavelength and the difference between each wavelength and the wavelength corresponding to the peak in the standard spectral curve of the resonant cavity layer.

[0090] The deviation degree acquisition module 30 is used to acquire the theoretical reflection spectrum of the preset thickness group based on the preset thickness and refractive index dispersion relationship of each layer of the VCSEL epitaxial wafer; acquire the reference degree of each wavelength based on the interference degree; and acquire the deviation degree between the preset thickness group and the corresponding detection point based on the difference in reflection intensity between the theoretical reflection spectrum and the reference reflection spectrum at each wavelength and the reference degree of each wavelength.

[0091] The reference thickness acquisition module 40 is used to adjust the preset thickness, acquire the deviation between the preset thickness group after each adjustment and each detection point, until the deviation is less than the preset deviation threshold, and stop adjusting the preset thickness. The preset thickness corresponding to the resonant cavity layer in the final adjustment is used as the reference thickness of the corresponding detection point.

[0092] The detection module 50 is used to detect the thickness uniformity of VCSEL epitaxial wafer production based on a reference thickness.

[0093] It should be noted that the system provided in the above embodiments is only an example of the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the computer device can be divided into different functional modules to complete all or part of the functions described above. In addition, the thickness uniformity detection system for VCSEL epitaxial wafer production and the thickness uniformity detection method for VCSEL epitaxial wafer production provided in the above embodiments belong to the same concept, and the specific implementation process is detailed in the method embodiments, which will not be repeated here.

[0094] Example 3:

[0095] This invention also proposes a thickness uniformity detection device for VCSEL epitaxial wafer production. The device includes a memory and a processor. The memory stores executable program code, and the processor calls and executes the executable program code to perform a thickness uniformity detection method for VCSEL epitaxial wafer production provided in the embodiments of this application. Specifically, the device may be a chip, component, or module. The chip may include a connected processor and memory; the memory stores instructions, and when the processor calls and executes the instructions, the chip can perform the thickness uniformity detection method for VCSEL epitaxial wafer production provided in the above embodiments.

[0096] Furthermore, this application also protects a computer device; please refer to [link to relevant documentation]. Figure 4 The computer device includes a memory 401, a processor 402, and a computer program 403 stored in the memory 401 and running on the processor 402. When the processor 402 executes the computer program 403, the computer device can execute any of the thickness uniformity detection methods for VCSEL epitaxial wafer production described above.

[0097] Example 4:

[0098] This embodiment also provides a computer-readable storage medium storing computer program code. When the computer program code is run on a computer, the computer executes the above-described related method steps to implement the thickness uniformity detection method for VCSEL epitaxial wafer production provided in the above embodiment.

[0099] Example 5:

[0100] This embodiment also provides a computer program product that, when run on a computer, causes the computer to perform the aforementioned steps to implement the thickness uniformity detection method for VCSEL epitaxial wafer production provided in the above embodiment.

[0101] In this embodiment, the device, computer-readable storage medium, computer program product, or chip are all used to execute the corresponding methods provided above. Therefore, the beneficial effects they can achieve can be referred to the beneficial effects in the corresponding methods provided above, and will not be repeated here.

[0102] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0103] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A method for detecting thickness uniformity in VCSEL epitaxial wafer production, characterized in that, The method includes the following steps: Obtain the reference reflectance spectrum of each detection point on the surface of the VCSEL epitaxial wafer; All layers in the VCSEL epitaxial wafer except the resonant cavity layer are used as reference layers. Based on the similarity of the standard spectral curves of each reference layer and the resonant cavity layer, the positional distribution and the preset thickness difference, as well as the reflection intensity in the standard spectral curve of each reference layer at each wavelength and the difference between each wavelength and the wavelength corresponding to the peak in the standard spectral curve of the resonant cavity layer, the interference degree of each reference layer on the resonant cavity layer at each wavelength is obtained. Based on the preset thickness and refractive index dispersion relationship of each layer of the VCSEL epitaxial wafer, the theoretical reflection spectrum of the preset thickness group is obtained; the reference level of each wavelength is obtained based on the interference level; and the deviation between the preset thickness group and the corresponding detection point is obtained based on the difference in reflection intensity between the theoretical reflection spectrum and the reference reflection spectrum at each wavelength and the reference level of each wavelength. Adjust the preset thickness, obtain the deviation between the preset thickness group after each adjustment and each detection point, until the deviation is less than the preset deviation threshold, stop adjusting the preset thickness, and take the preset thickness corresponding to the resonant cavity layer in the final adjustment as the reference thickness of the corresponding detection point; The thickness uniformity of VCSEL epitaxial wafer production is tested based on a reference thickness. The method for obtaining the level of interference is as follows: Based on the similarity of the standard spectral curves of each reference layer and the resonant cavity layer, their positional distribution, and the preset thickness differences, the degree of influence of each reference layer on the resonant cavity layer is obtained. Based on the reflection intensity in the standard spectral curve of each reference layer at each wavelength, and the difference between the wavelength of each reference layer and the wavelength corresponding to the nearest peak in the standard spectral curve of the resonant cavity layer at each wavelength, the interference analysis value of each reference layer to the resonant cavity layer at each wavelength is obtained. The normalized product of the interference analysis value of each reference layer to the resonant cavity layer at each wavelength and the influence degree of each reference layer on the resonant cavity layer is used as the interference degree of each reference layer to the resonant cavity layer at each wavelength. The method for obtaining the degree of influence is as follows: For any reference layer, the absolute value of the difference between the standard spectral curves of the reference layer and the resonant cavity layer is obtained by definite integration, which is taken as the spectral difference; the result of negatively correlating and normalizing the spectral difference is taken as the first influence analysis value of the reference layer on the resonant cavity layer. The number of layers between the reference layer and the light source is taken as the first quantity; the number of layers between the resonant cavity layer and the light source is taken as the second quantity; the ratio of the first quantity to the second quantity is taken as the second influence analysis value of the reference layer on the resonant cavity layer. The ratio of the preset thickness of the reference layer to the preset thickness of the resonant cavity layer is used as the third influence analysis value of the reference layer on the resonant cavity layer. The product of the first influence analysis value, the second influence analysis value, and the third influence analysis value is taken as the degree of influence of the reference layer on the resonant cavity layer. The method for obtaining the interference analysis values ​​is as follows: The wavelength corresponding to each peak in the standard spectral curve of the resonant cavity layer is obtained and used as the sensitive wavelength; For any wavelength, the difference between that wavelength and each sensitive wavelength is obtained and used as the difference for analysis; For any reference layer, the product of the negative correlation result of the smallest analytical difference and the reflection intensity in the standard spectral curve of the reference layer at that wavelength is taken as the interference analysis value of the reference layer on the resonant cavity layer at that wavelength.

2. The method for detecting thickness uniformity in VCSEL epitaxial wafer production as described in claim 1, characterized in that, The method for obtaining the reference level is as follows: For any wavelength, the sum of the interference levels of all reference layers to the resonant cavity layer at that wavelength is taken as the total interference level at that wavelength. The result of negatively correlating and normalizing the total interference level is used as the reference level for that wavelength.

3. The thickness uniformity detection method for VCSEL epitaxial wafer production as described in claim 1, characterized in that, The method for obtaining the degree of deviation is as follows: For any reference reflectance spectrum at any detection point and any wavelength, the square of the difference between the theoretical reflectance spectrum and the reference reflectance spectrum at that wavelength is obtained as the first difference corresponding to that wavelength. The product of the reference level of the wavelength and the first difference is used as the deviation analysis value of the wavelength; The result of summing and normalizing the deviation analysis values ​​of all wavelengths is used as the degree of deviation between the preset thickness group and the detection point.

4. The thickness uniformity detection method for VCSEL epitaxial wafer production as described in claim 1, characterized in that, The method for detecting the thickness uniformity of VCSEL epitaxial wafer production based on reference thickness is as follows: The surface of the VCSEL epitaxial wafer is mapped onto a two-dimensional coordinate system to obtain the spatial coordinates of each detection point in the two-dimensional coordinate system; The reference thickness of each detection point is mapped to its spatial coordinates to generate a two-dimensional thickness distribution map; the reference thickness of each detection point is represented by color intensity. The thickness uniformity of VCSEL epitaxial wafers can be visually detected by observing the color variations in a two-dimensional mapping image.

5. The method for detecting thickness uniformity in VCSEL epitaxial wafer production as described in claim 1, characterized in that, The method for obtaining the theoretical reflectance spectrum is as follows: Based on the preset thickness and refractive index dispersion relationship of each layer of the VCSEL epitaxial wafer, the theoretical reflection spectrum of the preset thickness group is obtained by means of the transfer matrix method.

6. The method for detecting thickness uniformity in VCSEL epitaxial wafer production as described in claim 1, characterized in that, The preset thickness group is composed of the preset thickness of each layer of the VCSEL epitaxial wafer.

7. The method for detecting thickness uniformity in VCSEL epitaxial wafer production as described in claim 1, characterized in that, The preset thickness adjustment is achieved by automatically adjusting the preset thickness of each layer of the VCSEL epitaxial wafer using the Levenberg-Marquardt algorithm.

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