Method for measuring thickness of epitaxial wafer layer

Abstract

The invention relates to the technical field of semiconductors, and discloses an epitaxial wafer layer thickness measurement method, which comprises the following steps: providing an epitaxial layer sample of a semiconductor laser; the epitaxial layer sample comprises a plurality of epitaxial wafer layers, and two adjacent epitaxial wafer layers are different III-V compounds; obtaining a high-angle annular dark field image of the atomic scale resolution of the epitaxial layer sample in the direction of a target crystal zone axis; a target connecting line is determined in the high-angle annular dark field image along the close arrangement face of the target atoms, and the target connecting line penetrates through an interface between the adjacent epitaxial wafer layers and is connected with the multiple atoms; determining the thickness of the epitaxial wafer layer on the target connecting line according to the brightness of the reference atoms on the target connecting line; and determining the thickness of the epitaxial wafer layer according to the thickness of the epitaxial wafer layer on the target connecting line. Compared with the prior art, the thickness measurement precision of the epitaxial wafer layer can be improved, and the photoelectric performance of the laser is further improved.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a method for measuring the thickness of an epitaxial sheet layer. Background Art

[0002] In the modern III-V semiconductor laser industry, the optoelectronic performance of the laser is basically determined by the epitaxial structure. Especially for vertical cavity surface emitting semiconductor lasers and quantum cascade semiconductor lasers with complex epitaxial structures, their performance is closely related to the thickness of the epitaxial layer. Therefore, in the production process of semiconductor lasers, the accurate measurement of the epitaxial layer thickness is of great significance. First, the measured value of the epitaxial layer thickness can be compared with the design value to determine the optimization direction of the epitaxial process. Then, the measured value of the epitaxial layer thickness can be linked to the optoelectronic performance of the semiconductor laser, thereby providing a reference for the design of the epitaxial structure of the semiconductor laser.

[0003] However, most existing epitaxial layer thickness measurement methods can only achieve nanometer-scale resolution. For semiconductor lasers with complex epitaxial structures, these methods not only cannot meet the measurement needs of epitaxial wafer layers, but may also mislead the device design and process optimization of these semiconductor lasers, which is not conducive to the development and optimization of related device products. Therefore, a higher-resolution epitaxial wafer thickness measurement solution is needed to improve measurement accuracy and thus improve the optoelectronic performance of semiconductor lasers. Summary of the invention

[0004] In view of this, the present invention provides a method for measuring the thickness of an epitaxial wafer layer to solve the problem in the related art that the thickness of the epitaxial wafer layer cannot be accurately measured, thereby limiting the optical performance of the semiconductor laser.

[0005] In a first aspect, the present invention provides a method for measuring the thickness of an epitaxial wafer layer, the method for measuring the thickness of an epitaxial wafer layer comprising: Providing epitaxial layer samples of semiconductor lasers; the epitaxial layer samples include multiple epitaxial wafer layers, and two adjacent epitaxial wafer layers are different III-V group compounds; Obtain a high-angle annular dark field image of the epitaxial layer sample in the direction of the target crystal zone axis; the resolution of the high-angle annular dark field image is at the atomic scale; The target line is determined along the close-packed surface of the target atoms in the high-angle annular dark field image. The target line passes through the interface between adjacent epitaxial wafer layers and connects multiple atoms. Determine the thickness of the epitaxial layer on the target line according to the brightness of the reference atom on the target line; The thickness of the epitaxial wafer layer is determined according to the thickness of the epitaxial wafer layer on the target connection line.

[0006] The present invention provides a method for measuring the thickness of an epitaxial wafer layer. First, a high-angle annular dark field image of an epitaxial layer sample in the target crystal band axis direction is obtained; secondly, a target line is determined along a target atomic close-packed plane in the high-angle annular dark field image, wherein the target line passes through interfaces between adjacent epitaxial wafer layers and connects a plurality of atoms; finally, the thickness of the epitaxial wafer layer on the target line is determined according to the brightness of reference atoms on the target line, and the thickness of the epitaxial wafer layer is determined according to the thickness of the epitaxial wafer layer on the target line. On the one hand, the thickness measurement accuracy of the epitaxial wafer layer can reach the atomic scale resolution, thereby improving the thickness measurement accuracy of the epitaxial wafer layer and further improving the photoelectric performance of the semiconductor laser; on the other hand, the measurement error of the epitaxial wafer layer is within a crystal plane spacing, which is much less than 1nm. This high-precision epitaxial layer thickness measurement method can not only efficiently guide the adjustment of the epitaxial layer growth process, but also accurately establish the connection between the epitaxial structure and the performance of the semiconductor laser.

[0007] In an optional embodiment, the step of determining the thickness of the epitaxial layer on the target line according to the brightness of the reference atom on the target line includes: Using the Group III atoms or Group V atoms in the epitaxial layer as reference atoms, and determining the positions of the interface reference atoms on the interfaces on both sides of the epitaxial layer according to the brightness of the reference atoms on the target line; The thickness of the epitaxial layer on the target connection line is determined based on the position of the interface reference atoms.

[0008] The present invention provides a method for measuring the thickness of an epitaxial wafer layer. The Group III atoms or Group V atoms in the epitaxial wafer layer are used as reference atoms. The positions of interface reference atoms on the interfaces on both sides of the epitaxial wafer layer are determined according to the brightness of the reference atoms on the target line. The positions of interface reference atoms between the epitaxial wafer layers can be accurately defined, so that the measurement accuracy reaches the atomic scale, and the thickness measurement accuracy of the epitaxial wafer layer can be improved, thereby improving the photoelectric performance of the semiconductor laser. At the same time, the thickness of the epitaxial layer is determined by the positions of adjacent interface atoms on the close-packed surface of the target atoms, thereby avoiding the influence of the strain in the out-of-plane direction of the lattice in the epitaxial layer on the measurement result, and improving the accuracy of the measurement result. In addition, the error of the thickness of the epitaxial wafer layer measured by the method is within a crystal plane spacing, which is much less than 1nm. This high-precision epitaxial layer thickness measurement method can not only efficiently guide the adjustment of the epitaxial layer growth process, but also accurately establish the connection between the epitaxial structure and the performance of the semiconductor laser.

[0009] In an optional embodiment, the step of using the Group III or Group V atoms in the epitaxial wafer layer as reference atoms and determining the positions of the interface reference atoms on the interfaces on both sides of the epitaxial wafer layer according to the brightness of the reference atoms on the target line includes: Using the Group III or Group V atoms in the epitaxial layer as reference atoms, obtaining a second brightness-position curve corresponding to the brightness of the reference atoms on the target line; The positions of interface reference atoms on the interfaces on both sides of the epitaxial wafer layer are determined according to the second brightness-position curve.

[0010] In an optional embodiment, the step of taking the Group III or Group V atoms in the epitaxial wafer layer as reference atoms and obtaining a second brightness-position curve corresponding to the brightness of the reference atoms on the target line includes: Obtaining a first brightness-position curve corresponding to the brightness of each atom on the target line; The Group III or Group V atoms in the epitaxial layer are used as reference atoms, and a second brightness-position curve corresponding to the brightness of the reference atoms on the target line is extracted from the first brightness-position curve.

[0011] In an optional embodiment, the step of determining the thickness of the epitaxial wafer layer according to the thickness of the epitaxial wafer layer on the target connection line includes: Calculating the sine value of the angle between the interface between adjacent epitaxial wafer layers and the target close-packed surface; The thickness of the epitaxial wafer layer is the product of the thickness of the epitaxial wafer layer on the target line and the sine value of the angle.

[0012] In an optional embodiment, the step of providing an epitaxial layer sample of a semiconductor laser comprises: The epitaxial layer samples of semiconductor lasers are prepared by using a focused ion beam method or an ion thinning method.

[0013] In an optional embodiment, the step of obtaining a high-angle annular dark field image of the epitaxial layer sample in the target crystal zone axis direction includes: Determine the target crystal zone axis direction of the epitaxial layer sample; the out-of-plane index of the epitaxial layer in the target crystal zone axis direction is 0; The epitaxial layer sample is tilted to the target crystal zone axis direction by a transmission electron microscope; the transmission electron microscope has a condenser spherical aberration correction function; Acquire a high-angle annular dark field image of the epitaxial layer sample in the direction of the target crystal zone axis.

[0014] In an optional embodiment, for an epitaxial wafer layer with a cubic structure, the target crystal zone axis directions are

[100] ,

[110] ,

[120] and

[130] ; For hexagonal epitaxial layers, the target crystal zone axis directions are

[1000] , [10-10], [11-20], and [12-30].

[0015] In an optional embodiment, before the step of determining the target line along the target atomic close-packed plane in the high-angle annular dark field image, the step further includes: The target atomic close-packed plane is determined based on the target crystal zone axis direction and the high-angle annular dark field image.

[0016] In an optional embodiment, for an epitaxial wafer layer with a face-centered cubic structure, When the target crystal zone axis direction is the

[100] zone axis, the target atomic close-packed plane is the (010) crystal plane; When the target crystal zone axis direction is the

[110] zone axis, the target atomic close-packed plane is the (1-11) crystal plane; When the target crystal zone axis direction is the

[120] zone axis, the target atomic close-packed plane is the (2-11) crystal plane; When the target crystal zone axis direction is the

[130] zone axis, the target atomic close-packed plane is the (3-11) crystal plane.

[0017] In an optional embodiment, the epitaxial wafer layer includes a first epitaxial wafer layer and a second epitaxial wafer layer; the epitaxial layer is composed of a plurality of first epitaxial wafer layers and a plurality of second epitaxial wafer layers alternately stacked; When the group III atoms in the first epitaxial wafer layer and the second epitaxial wafer layer are the same and the group V atoms are different, the group V atoms are used as reference atoms to determine the position of the interface reference atoms; When the Group III atoms in the first epitaxial wafer layer and the second epitaxial wafer layer are different but the Group V atoms are the same, the Group III atoms are used as reference atoms to determine the position of the interface reference atoms.

[0018] In an optional embodiment, when the material of the first epitaxial layer in the epitaxial layer is In x Ga (1-x) As, the material of the second epitaxial layer is In x Al (1-x) As, or the material of the first epitaxial layer is In x Ga (1-x) As, the material of the second epitaxial layer is Al x Ga (1-x) When As, the group III atoms are used as reference atoms to determine the position of the interface reference atoms; When the material of the first epitaxial layer in the epitaxial layer is GaAs; the material of the second epitaxial layer is GaAs y P (1-y) When the five group atoms are used as reference atoms, the positions of the interface reference atoms are determined.

[0019] In an optional embodiment, the epitaxial wafer layer includes a first epitaxial wafer layer and a second epitaxial wafer layer; the epitaxial layer is composed of a plurality of first epitaxial wafer layers and a plurality of second epitaxial wafer layers alternately stacked; The material of the first epitaxial layer in the epitaxial layer is In x Ga (1-x) As, the material of the second epitaxial layer is In x Al (1-x) As; Inx Ga (1-x) Atomic columns and In x Al (1-x) The atomic column is used as a reference atom to determine the position of the interface reference atom. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the related technologies, the drawings required for use in the specific embodiments or the related technical descriptions will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 The figure is a flow chart of a method for measuring the thickness of an epitaxial wafer layer according to an embodiment of the present invention.

[0022] Figure 2 The present invention is a schematic diagram of a specific process of measuring the thickness of an epitaxial wafer layer according to an embodiment of the present invention.

[0023] Figure 3 It is a HAADF image of an InGaAs / InAlAs epitaxial wafer layer with atomic scale resolution in a method for measuring the thickness of an epitaxial wafer layer in an embodiment of the present invention.

[0024] Figure 4 yes Figure 3 The Fourier transform image of .

[0025] Figure 5 It is the second brightness-position curve corresponding to the brightness of the reference atom on the first target line.

[0026] Figure 6 It is a second brightness-position curve corresponding to the brightness of the reference atom on the second target line.

[0027] Reference numerals: 1. First target connection; 2. Second target connection; 10. Epitaxial wafer layer No. 1; 20. Epitaxial wafer layer No. 2; 30. Epitaxial wafer layer No. 3; 40. Epitaxial wafer layer No. 4. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0029] In the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified for the purpose of clear expression, and some details may be omitted. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships between them are only exemplary, and may be deviated due to manufacturing tolerances or technical limitations in practice, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be a middle layer / element between them. In addition, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "under" the other layer / element.

[0030] In the modern III-V semiconductor laser industry, the optoelectronic performance of the laser is basically determined by the epitaxial structure. Especially for vertical cavity surface emitting semiconductor lasers and quantum cascade semiconductor lasers with complex epitaxial structures, their performance is closely related to the thickness of the epitaxial layer. Therefore, in the production process of semiconductor lasers, the accurate measurement of the epitaxial layer thickness is of great significance. First, the measured value of the epitaxial layer thickness can be compared with the design value to determine the optimization direction of the epitaxial process. Then, the measured value of the epitaxial layer thickness can be linked to the optoelectronic performance of the semiconductor laser, thereby providing a reference for the design of the epitaxial structure of the semiconductor laser.

[0031] However, most existing epitaxial layer thickness measurement methods can only achieve nanometer-scale resolution. For semiconductor lasers with complex epitaxial structures, these methods not only cannot meet the measurement needs of epitaxial wafer layers, but may also mislead the device design and process optimization of these semiconductor lasers, which is not conducive to the development and optimization of related device products. Therefore, a higher-resolution epitaxial wafer thickness measurement solution is needed to improve measurement accuracy and thus improve the optoelectronic performance of semiconductor lasers.

[0032] like Figure 1 As shown, this embodiment provides a method for measuring the thickness of an epitaxial wafer layer, and the preparation method includes but is not limited to steps S101 to S105.

[0033] Step S101, providing an epitaxial layer sample of a semiconductor laser; the epitaxial layer sample includes a plurality of epitaxial wafer layers, and two adjacent epitaxial wafer layers are different III-V group compounds.

[0034] Step S102, obtaining a high-angle annular dark field image of the epitaxial layer sample in the direction of the target crystal zone axis; the resolution of the high-angle annular dark field image is at the atomic scale.

[0035] Step S103, determining a target line along the close-packed surface of target atoms in the high-angle annular dark field image, wherein the target line passes through the interface between adjacent epitaxial wafer layers and connects multiple atoms.

[0036] Step S104, determining the thickness of the epitaxial layer on the target line according to the brightness of the reference atom on the target line.

[0037] Step S105, determining the thickness of the epitaxial wafer layer according to the thickness of the epitaxial wafer layer on the target connection line.

[0038] The method for measuring the thickness of an epitaxial layer provided in the present embodiment first obtains a high-angle annular dark field image of an epitaxial layer sample in the target crystal band axis direction; secondly, a target line is determined along the target atomic close-packed plane in the high-angle annular dark field image, the target line passes through the interface between adjacent epitaxial layers and connects multiple atoms; finally, the thickness of the epitaxial layer on the target line is determined according to the brightness of the reference atom on the target line, and the thickness of the epitaxial layer is determined according to the thickness of the epitaxial layer on the target line. On the one hand, the thickness measurement accuracy of the epitaxial layer can reach the atomic scale resolution, thereby improving the thickness measurement accuracy of the epitaxial layer, and further improving the optoelectronic performance of the semiconductor laser; on the other hand, the measurement error of the epitaxial layer is within a crystal plane spacing, which is much less than 1nm. This high-precision epitaxial layer thickness measurement method can not only efficiently guide the adjustment of the epitaxial layer growth process, but also accurately establish the connection between the epitaxial structure and performance of the semiconductor laser.

[0039] In some optional embodiments, the step of determining the thickness of the epitaxial layer on the target line according to the brightness of the reference atom on the target line includes: Using the Group III atoms or Group V atoms in the epitaxial layer as reference atoms, and determining the positions of the interface reference atoms on the interfaces on both sides of the epitaxial layer according to the brightness of the reference atoms on the target line; The thickness of the epitaxial layer on the target connection line is determined based on the position of the interface reference atoms.

[0040] In a specific implementation, the interface reference atoms on the interfaces on both sides of the epitaxial wafer layer refer to the interface reference atoms on the interface between the epitaxial wafer layer and its adjacent epitaxial wafer layer. Figure 3 The interface between the No. 1 epitaxial wafer layer 10 and the No. 2 epitaxial wafer layer 20 is L1.

[0041] In the epitaxial structure of III-V semiconductor lasers, the difference between heteroepitaxial layers is mainly the difference in group III or group V atoms. In addition, the contrast of the high-angle annular dark field image (HAADF image) obtained by a transmission electron microscope is related to the atomic number of the epitaxial layer. The larger the atomic number in the epitaxial layer, the larger the relative mass of the atom, and the brighter the corresponding epitaxial layer in the image. In particular, when the HAADF image of the epitaxial layer enters the atomic scale resolution, different atoms in the heteroepitaxial layer can be distinguished by the brightness of the atomic image.

[0042] Since the essence of TEM imaging is the projection of the epitaxial layer, the atomic points in the HAADF image are the projections of the atomic columns in the epitaxial layer. For the inside of the epitaxial layer, the atoms are uniformly and orderly distributed, and the brightness of the atomic columns can correspond to the composition. Since the growth of different epitaxial layers is achieved by switching different growth sources, the atomic columns at the interface between the epitaxial layers are a uniform mixture of Group III or Group V atoms from two different epitaxial layers, and the brightness of the corresponding atomic columns is between the brightness of the corresponding atomic columns in the epitaxial layers on both sides. In summary, the brightness of the interface reference atom should be close to the average brightness of the corresponding atoms in the epitaxial layers on both sides of the interface.

[0043] In particular, Group III atoms or Group V atoms as reference atoms refer to Group III atoms and solid solution atoms of other Group III, or Group V atoms and solid solution atoms of other Group V as reference atoms.

[0044] Specifically, the Group III atoms or Group V atoms can be used as reference atoms, either a single type of Group III atoms or a single type of Group V atoms as reference atoms, or solid solution atoms composed of different Group III atoms or solid solution atoms composed of different Group V atoms as reference atoms.

[0045] The method for measuring the thickness of an epitaxial wafer provided in the present embodiment uses the Group III atoms or Group V atoms in the epitaxial wafer as reference atoms, and determines the positions of the interface reference atoms on the interfaces on both sides of the epitaxial wafer according to the brightness of the reference atoms on the target line, so as to accurately define the positions of the interface reference atoms between the epitaxial wafers, so that the measurement accuracy reaches the atomic scale, and the thickness measurement accuracy of the epitaxial wafer can be improved, thereby improving the photoelectric performance of the semiconductor laser; at the same time, the thickness of the epitaxial layer is determined by the positions of the adjacent interface atoms on the close-packed plane of the target atoms, so as to avoid the influence of the strain in the out-of-plane direction of the lattice in the epitaxial layer on the measurement result, and the accuracy of the measurement result can be improved; in addition, the error of the thickness of the epitaxial wafer measured by the present method is within one crystal plane spacing, which is much less than 1nm. This high-precision epitaxial layer thickness measurement method can not only efficiently guide the adjustment of the epitaxial layer growth process, but also accurately establish the connection between the epitaxial structure and the performance of the semiconductor laser.

[0046] In some optional embodiments, the step of using the Group III or Group V atoms in the epitaxial wafer layer as reference atoms and determining the positions of the interface reference atoms on the interfaces on both sides of the epitaxial wafer layer according to the brightness of the reference atoms on the target line comprises: Using the Group III or Group V atoms in the epitaxial layer as reference atoms, obtaining a second brightness-position curve corresponding to the brightness of the reference atoms on the target line; The positions of interface reference atoms on the interfaces on both sides of the epitaxial wafer layer are determined according to the second brightness-position curve.

[0047] In specific implementation, since the brightness of the atoms at the interface should be close to the average brightness of the corresponding atoms in the epitaxial wafer layers on both sides of the interface, the positions of the interface reference atoms on the interfaces on both sides of the epitaxial wafer layers can be determined according to the second brightness-position curve and the average brightness of the reference atoms. The interface reference atoms are the reference atoms that are closest to the average brightness line of the reference atoms.

[0048] In one example, it is necessary to measure four stacked epitaxial wafer layers, such as Figure 3 As shown, the interfaces between the four epitaxial wafer layers are L1, L2, L3, and L4, respectively, wherein the interface between the epitaxial wafer layer 10 and the epitaxial wafer layer 20 is L1, the interface between the epitaxial wafer layer 20 and the epitaxial wafer layer 30 is L2, the interface between the epitaxial wafer layer 30 and the epitaxial wafer layer 20 is L3, and the interface between the epitaxial wafer layer 40 and other structural layers is L4. Among them, the interface reference atom on the L1 interface is A1, the interface reference atom on the L2 interface is A2, the interface reference atom on the L3 interface is A3, and the interface reference atom on the L4 interface is A4.

[0049] The Group III or Group V atoms in the four epitaxial layers are used as reference atoms, and the second brightness-position curves corresponding to the brightness of the reference atoms on the first target line 1 and the second target line 2 are obtained respectively, such as Figure 5 and Figure 6 As shown. Among them, Figure 5 is the second brightness-position curve corresponding to the brightness of the reference atom on the first target line 1, Figure 6 It is a second brightness-position curve corresponding to the brightness of the reference atom on the second target line 2.

[0050] like Figure 5 As shown, when the thickness of epitaxial wafer layer 20 No. 2 needs to be measured, the interface reference atoms A1 and A2 on the interfaces L1 and L2 on both sides of epitaxial wafer layer 20 No. 2 are determined based on the second brightness-position curve and the average brightness of the reference atoms. According to the same method, the interface reference atoms on both sides of each epitaxial wafer layer can be found respectively.

[0051] In some optional embodiments, the step of using the Group III or Group V atoms in the epitaxial wafer layer as reference atoms and obtaining a second brightness-position curve corresponding to the brightness of the reference atoms on the target line includes: Obtaining a first brightness-position curve corresponding to the brightness of each atom on the target line; The Group III or Group V atoms in the epitaxial layer are used as reference atoms, and a second brightness-position curve corresponding to the brightness of the reference atoms on the target line is extracted from the first brightness-position curve.

[0052] In some optional implementations, the step of determining the thickness of the epitaxial wafer layer according to the thickness of the epitaxial wafer layer on the target connection line includes: Calculating the sine value of the angle between the interface between adjacent epitaxial wafer layers and the target close-packed surface; The thickness of the epitaxial wafer layer is the product of the thickness of the epitaxial wafer layer on the target line and the sine value of the angle.

[0053] When implementing it, Figure 3 As shown, the angle between the interface and the target close-packed surface is α, and the thickness of the epitaxial layer is the thickness of the epitaxial layer on the target connection line multiplied by sinα.

[0054] Among them, the sine value sinα of the angle can be directly calculated using the coordinates of different normal vectors in Fourier transform, or the specific value of the angle can be calculated based on the coordinates of the interface reference atom and then the sine value sinα of the angle can be obtained.

[0055] Using the above example, Figure 5 As shown, after determining the interface reference atoms A1 and A2 on the interfaces L1 and L2 on both sides of epitaxial wafer layer No. 2 20, the coordinates of A1 and A2 are subtracted to obtain the thickness of the epitaxial wafer layer on the target line as 3.28nm, α=53°, sinα=0.79864, and finally the calculated thickness of the epitaxial wafer layer is 3.28nm×0.79864=2.62nm.

[0056] In some optional embodiments, the step of providing an epitaxial layer sample of a semiconductor laser comprises: The epitaxial layer samples of semiconductor lasers are prepared by using a focused ion beam method or an ion thinning method.

[0057] In some optional embodiments, the step of acquiring a high-angle annular dark field image of the epitaxial layer sample in the direction of the target crystal zone axis includes: Determine the target crystal zone axis direction of the epitaxial layer sample; the out-of-plane index of the epitaxial layer in the target crystal zone axis direction is 0; The epitaxial layer sample is tilted to the target crystal zone axis direction by a transmission electron microscope; the transmission electron microscope has a condenser spherical aberration correction function; Acquire a high-angle annular dark field image of the epitaxial layer sample in the direction of the target crystal zone axis.

[0058] In some optional embodiments, for the epitaxial wafer layer with a cubic structure, the target crystal zone axis directions are

[100] ,

[110] ,

[120] and

[130] ; For hexagonal epitaxial layers, the target crystal zone axis directions are

[1000] , [10-10], [11-20], and [12-30].

[0059] In some optional embodiments, before the step of determining the target line along the target atomic close-packed plane in the high-angle annular dark field image, the step further includes: The target atomic close-packed plane is determined based on the target crystal zone axis direction and the high-angle annular dark field image.

[0060] In some optional embodiments, for an epitaxial wafer layer with a face-centered cubic structure, When the target crystal zone axis direction is the

[100] zone axis, the target atomic close-packed plane is the (010) crystal plane; When the target crystal zone axis direction is the

[110] zone axis, the target atomic close-packed plane is the (1-11) crystal plane; When the target crystal zone axis direction is the

[120] zone axis, the target atomic close-packed plane is the (2-11) crystal plane; When the target crystal zone axis direction is the

[130] zone axis, the target atomic close-packed plane is the (3-11) crystal plane.

[0061] In some optional embodiments, the epitaxial wafer layer includes a first epitaxial wafer layer and a second epitaxial wafer layer; the epitaxial layer sample is composed of a plurality of first epitaxial wafer layers and a plurality of second epitaxial wafer layers alternately stacked; When the group III atoms in the first epitaxial wafer layer and the second epitaxial wafer layer are the same and the group V atoms are different, the group V atoms are used as reference atoms to determine the position of the interface reference atoms; When the Group III atoms in the first epitaxial wafer layer and the second epitaxial wafer layer are different but the Group V atoms are the same, the Group III atoms are used as reference atoms to determine the position of the interface reference atoms.

[0062] In specific implementation, in a group III semiconductor compound, group III atoms and group V atoms occupy different positions respectively. Group III atoms form a set of cubic lattices, and so do group V atoms, so the position at the interface needs to be calibrated by different atoms. When the group III atoms are different, group III atoms are needed to define the interface, and when the group V atoms are different, group V atoms are needed to define the interface.

[0063] In some optional embodiments, when the material of the first epitaxial layer in the epitaxial layer sample is In x Ga (1-x) As, the material of the second epitaxial layer is In xAl (1-x) As, or the material of the first epitaxial layer is In x Ga (1-x) As, the material of the second epitaxial layer is Al x Ga (1-x) When As, the group III atoms are used as reference atoms to determine the position of the interface reference atoms; When the material of the first epitaxial layer in the epitaxial layer sample is GaAs; the material of the second epitaxial layer is GaAs y P (1-y) When the five group atoms are used as reference atoms, the positions of the interface reference atoms are determined.

[0064] In specific implementation, when the epitaxial wafer layer is an InGaAs / InAlAs system, an InGaAs / AlGaAs system, etc., the brightness of the Group III atoms is used as a reference to determine the position of the atoms at the interface. When the epitaxial wafer layer is a GaAs / GaAsP system, etc., the brightness of the Group V atoms is used as a reference to determine the position of the atoms at the interface.

[0065] In some optional embodiments, the epitaxial wafer layer includes a first epitaxial wafer layer and a second epitaxial wafer layer; the epitaxial layer is composed of a plurality of first epitaxial wafer layers and a plurality of second epitaxial wafer layers alternately stacked; The material of the first epitaxial layer in the epitaxial layer sample is In x Ga (1-x) As, the material of the second epitaxial layer is In x Al (1-x) As; In x Ga (1-x) Atomic columns and In x Al (1-x) The atomic column is used as a reference atom to determine the position of the interface reference atom.

[0066] In the specific implementation, the epitaxial layer is an InGaAs / InAlAs system, and the brightness of the three-group atoms is used as a reference to determine the position of the atoms at the interface. x Ga (1-x) Atomic columns and In x Al (1-x) The atomic column is used as a reference atom to determine the position of the interface reference atom.

[0067] In some optional embodiments, after measuring the thickness of multiple epitaxial wafer layers, the thickness of the epitaxial layer sample can be calculated, and the thickness of the epitaxial layer sample is the sum of the thicknesses of all epitaxial wafer layers.

[0068] like Figure 2As shown, the present invention also provides a specific flow chart of a method for measuring the thickness of an epitaxial wafer layer, including but not limited to steps S201 to S208.

[0069] Step S201, providing an epitaxial layer sample of a semiconductor laser; the epitaxial layer sample includes a plurality of epitaxial wafer layers, and two adjacent epitaxial wafer layers are different III-V Group compounds.

[0070] In a specific implementation, the epitaxial wafer layer includes a first epitaxial wafer layer and a second epitaxial wafer layer; the epitaxial layer sample is composed of a plurality of first epitaxial wafer layers and a plurality of second epitaxial wafer layers alternately stacked.

[0071] In one example, an epitaxial layer structure of an active region of a quantum cascade laser is provided, wherein the material of the first epitaxial layer is In x Ga (1-x) As, the material of the second epitaxial layer is In x Al (1-x) As, that is, the system of the epitaxial layer is In x Ga (1-x) As / In x Al (1-x) The epitaxial layer structure includes four epitaxial wafer layers, namely epitaxial wafer layer No. 1 10, epitaxial wafer layer No. 2 20, epitaxial wafer layer No. 3 30, and epitaxial wafer layer No. 4 40, and the designed thicknesses are 1.60 nm, 2.95 nm, 1.45 nm, and 2.10 nm, respectively.

[0072] Step S202, obtaining a high-angle annular dark field image of the epitaxial layer sample in the target crystal zone axis direction; determining the target atomic close-packed plane according to the target crystal zone axis direction and the high-angle annular dark field image.

[0073] In the specific implementation, the In was obtained under the

[130] crystal axis using a spherical aberration corrected transmission electron microscope. x Ga (1-x) As / In x Al (1-x) Atomic-scale resolution HAADF image of the As epitaxial layer, such as Figure 3 Based on the Fourier transform of the HAADF image, we can get In x Ga (1-x) As / In x Al (1-x) The diffraction spots of the As epitaxial layer are as follows: Figure 4 As shown. Combined with In x Ga (1-x) As / In x Al (1-x)The lattice parameters of As and by calibrating the diffraction spots, it can be determined that the crystal plane index of the interface in the epitaxial layer is (002), while the crystal plane index of the atomic close-packed plane crossing the interface is (3-11).

[0074] Step S203, determining a target line along the close-packed surface of target atoms in the high-angle annular dark field image, wherein the target line passes through the interface between adjacent epitaxial wafer layers and connects multiple atoms.

[0075] In the specific implementation, Gatan DigitalMicrograph software was used to x Ga (1-x) As / In x Al (1-x) In the HAADF image of the As epitaxial structure, two straight lines are selected along the (3-11) close-packed plane as target lines. Figure 3 As shown, the straight line on the left is the first target line 1, and the straight line on the right is the second target line 2.

[0076] Step S204, obtaining a first brightness-position curve corresponding to the brightness of each atom on the target line.

[0077] In specific implementation, a curve of brightness and position of different pixel points on a straight line, ie, a first brightness-position curve, is obtained through the Profile function of Gatan Digital Micrograph software.

[0078] Step S205 , taking the Group III or Group V atoms in the epitaxial layer as reference atoms, extracting a second brightness-position curve corresponding to the brightness of the reference atoms on the target line from the first brightness-position curve.

[0079] In the specific implementation, the In x Ga (1-x) Atomic columns and In x Al (1-x) The atomic column is used as the reference atom. In the first brightness-position curve, In x Ga (1-x) Atomic columns and In x Al (1-x) By plotting the horizontal and vertical coordinates of the atomic column, we can obtain the curve of the brightness of the reference atomic column with respect to the position, that is, the second brightness-position curve, and at the same time obtain the average brightness of the reference atomic column, such as Figure 5 and Figure 6 shown.

[0080] Step S206, determining the positions of interface reference atoms on the interfaces on both sides of the epitaxial wafer layer according to the second brightness-position curve.

[0081] In the specific implementation, in the curve of atomic column brightness with respect to position, In x Ga (1-x) Atomic columns and In x Al (1-x) The average value of the atomic column brightness ( Figure 3 and Figure 4 By comparing the average brightness of the reference atomic column in the curve (the dotted line in the figure) with that of the reference atomic column in the curve, the position of the interface reference atom can be determined.

[0082] like Figure 5 As shown, according to the second brightness-position curve corresponding to the brightness of the reference atoms on the first target line 1 and the average brightness of the reference atoms, the interface reference atoms A1, A2, A3 and A4 on both sides of the epitaxial wafer layer 10, the epitaxial wafer layer 20, the epitaxial wafer layer 30 and the epitaxial wafer layer 40 are determined. Figure 6 As shown, the interface reference atoms A1, A2, A3 and A4 on the second target line 2 are determined in the same way.

[0083] Due to In x Ga (1-x) Atomic columns and In x Al (1-x) The dotted line of the average brightness of the atomic column must pass through the middle of the brightness coordinates of the adjacent atomic columns (that is, the dotted line of the average brightness can pass through the middle of the adjacent atomic brightness, that is, the dotted line of the average brightness and the curve of atomic brightness-distance must have an intersection, and the ordinate of the intersection must be located between the ordinate brightness of the two adjacent atomic points). Therefore, the error of this measurement method lies above and below the average brightness of the atomic column, and the adjacent atoms are misjudged as interface atoms. Accordingly, the error of the entire test is within the crystal plane spacing in one epitaxial growth direction.

[0084] Step S207, determining the thickness of the epitaxial wafer layer on the target connection line according to the position of the interface reference atoms.

[0085] In specific implementation, the lengths of different epitaxial layers on the (3-11) close-packed atomic plane can be calculated based on the subtraction of the position coordinates of adjacent interface atoms. Figure 5 As shown, according to the coordinates of the interface reference atoms A1, A2, A3 and A4, the thicknesses of epitaxial wafer layer 10, epitaxial wafer layer 20, epitaxial wafer layer 30 and epitaxial wafer layer 40 on the first target line 1 are calculated to be 2.19nm, 3.28nm, 1.59nm and 1.95nm respectively. Figure 6 As shown, according to the coordinates of the interface reference atoms A1, A2, A3 and A4, the thicknesses of epitaxial wafer layer No. 10, epitaxial wafer layer No. 20, epitaxial wafer layer No. 30 and epitaxial wafer layer No. 40 on the second target line 2 are calculated to be 2.18nm, 3.29nm, 1.58nm and 1.97nm respectively.

[0086] Step S208, determining the thickness of the epitaxial wafer layer according to the thickness of the epitaxial wafer layer on the target line: calculating the sine value of the angle between the interface between adjacent epitaxial wafer layers and the target close-packed plane; the thickness of the epitaxial wafer layer is the product of the thickness of the epitaxial wafer layer on the target line and the sine value of the angle.

[0087] In specific implementation, through the sine value sinα of the angle α between the (3-11) close-packed atomic plane and the (002) interface, the thickness of epitaxial wafer layer No. 10, epitaxial wafer layer No. 20, epitaxial wafer layer No. 30 and epitaxial wafer layer No. 40 can be calculated as 1.74nm, 2.62nm, 1.27nm and 1.56nm respectively according to the thickness of each epitaxial wafer layer on the first target line 1; the thickness of epitaxial wafer layer No. 10, epitaxial wafer layer No. 20, epitaxial wafer layer No. 30 and epitaxial wafer layer No. 40 can be calculated as 1.74nm, 2.62nm, 1.26nm and 1.57nm respectively according to the thickness of each epitaxial wafer layer on the second target line 2.

[0088] Therefore, the thickness of epitaxial wafer layer No. 1 to epitaxial wafer layer No. 4 measured twice according to the first target line 1 on the left and the second target line 2 on the right in this embodiment are 1.74nm, 2.62nm, 1.27nm and 1.56nm, and 1.74nm, 2.62nm, 1.26nm and 1.57nm, respectively, while the designed thickness of the relevant epitaxial layer is 1.60nm, 2.95nm, 1.45nm and 2.10nm. Because the interplanar spacing of the (002) atomic close-packed plane in the epitaxial layer is about 0.3nm (considering the influence of strain), it can be seen that the actual thickness of epitaxial layer No. 2 and epitaxial layer No. 4 differs from the designed thickness by 1 and 2 atomic layer thicknesses, respectively.

[0089] Table 1 Comparison of epitaxial wafer thickness measurement results

[0090] In the description of this specification, the description with reference to the terms "this embodiment", "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples, unless otherwise clearly and specifically defined. In addition, the terms "first" and "second" are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0091] In the above description, the technical details of the patterning and etching of each layer are not described in detail. However, those skilled in the art should understand that various technical means can be used to form layers, regions, etc. of desired shapes. In addition, in order to form the same structure, those skilled in the art can also design methods that are not completely the same as the methods described above. In addition, although the various embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage.

[0092] The above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described above, and that various obvious changes, readjustments, combinations and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention is described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may also include more other equivalent embodiments without departing from the concept of the present invention. The scope of protection of the present invention is determined by the scope of the attached claims.

Claims

1. A method for measuring the thickness of an epitaxial layer, characterized in that: include: Providing epitaxial layer samples for semiconductor lasers; The epitaxial layer sample comprises a plurality of epitaxial wafer layers, and two adjacent epitaxial wafer layers are different III-V group compounds; Acquire a high-angle annular dark field image of the epitaxial layer sample in the direction of the target crystal zone axis; the resolution of the high-angle annular dark field image is at the atomic scale; Determining a target line along a close-packed surface of target atoms in the high-angle annular dark field image, wherein the target line passes through an interface between adjacent epitaxial wafer layers and connects a plurality of atoms; Determining the thickness of the epitaxial layer on the target line according to the brightness of the reference atom on the target line; The thickness of the epitaxial wafer layer is determined according to the thickness of the epitaxial wafer layer on the target connection line.

2. The method for measuring the thickness of an epitaxial wafer according to claim 1, characterized in that: The step of determining the thickness of the epitaxial layer on the target line according to the brightness of the reference atom on the target line comprises: Using the Group III atoms or Group V atoms in the epitaxial layer as reference atoms, and determining the positions of interface reference atoms on the interfaces on both sides of the epitaxial layer according to the brightness of the reference atoms on the target line; The thickness of the epitaxial wafer layer on the target connection line is determined according to the position of the interface reference atoms.

3. The method for measuring the thickness of an epitaxial wafer according to claim 2, characterized in that: The step of using the Group III or Group V atoms in the epitaxial wafer layer as reference atoms and determining the positions of the interface reference atoms on the interfaces on both sides of the epitaxial wafer layer according to the brightness of the reference atoms on the target line comprises: Taking the Group III or Group V atoms in the epitaxial layer as reference atoms, obtaining a second brightness-position curve corresponding to the brightness of the reference atoms on the target line; The positions of interface reference atoms on both side interfaces of the epitaxial layer are determined according to the second brightness-position curve.

4. The method for measuring the thickness of an epitaxial wafer according to claim 3, characterized in that: The step of taking the Group III or Group V atoms in the epitaxial layer as reference atoms and obtaining a second brightness-position curve corresponding to the brightness of the reference atoms on the target line comprises: Obtaining a first brightness-position curve corresponding to the brightness of each atom on the target line; The Group III or Group V atoms in the epitaxial layer are used as reference atoms, and a second brightness-position curve corresponding to the brightness of the reference atoms on the target line is extracted from the first brightness-position curve.

5. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: The step of determining the thickness of the epitaxial wafer layer according to the thickness of the epitaxial wafer layer on the target connection line comprises: Calculating the sine value of the angle between the interface between adjacent epitaxial wafer layers and the target close-packed plane; The thickness of the epitaxial wafer layer is the product of the thickness of the epitaxial wafer layer on the target line and the sine value of the angle.

6. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: The step of providing an epitaxial layer sample of a semiconductor laser comprises: The epitaxial layer samples of semiconductor lasers are prepared by using a focused ion beam method or an ion thinning method.

7. The method for measuring the thickness of an epitaxial wafer according to claim 1, characterized in that: The step of obtaining a high-angle annular dark field image of the epitaxial layer sample in the target crystal zone axis direction comprises: Determining a target crystal zone axis direction of the epitaxial layer sample; the out-of-plane index of the epitaxial layer in the target crystal zone axis direction is 0; The epitaxial layer sample is tilted to the target crystal zone axis direction by a transmission electron microscope; the transmission electron microscope has a condenser spherical aberration correction function; A high-angle annular dark field image of the epitaxial layer sample in the direction of the target crystal zone axis is obtained.

8. The method for measuring the thickness of an epitaxial wafer according to claim 7, characterized in that: For the epitaxial wafer layer with a cubic structure, the target crystal zone axis directions are [100], [110], [120] and [130]; For the epitaxial wafer layer with a hexagonal structure, the target crystal zone axis directions are [1000], [10-10], [11-20] and [12-30].

9. The method for measuring the thickness of an epitaxial wafer according to claim 1, characterized in that: Before the step of determining the target line along the target atomic close-packed plane in the high-angle annular dark field image, the step further includes: The target atomic close-packed plane is determined according to the target crystal zone axis direction and the high-angle annular dark field image.

10. The method for measuring the thickness of an epitaxial wafer according to claim 9, characterized in that: For the epitaxial layer of face-centered cubic structure, When the target crystal zone axis direction is the [100] zone axis, the target atomic close-packed plane is the (010) crystal plane; When the target crystal zone axis direction is the [110] zone axis, the target atomic close-packed plane is the (1-11) crystal plane; When the target crystal zone axis direction is the [120] zone axis, the target atomic close-packed plane is the (2-11) crystal plane; When the target crystal zone axis direction is the [130] zone axis, the target atomic close-packed plane is the (3-11) crystal plane.

11. The method for measuring the thickness of an epitaxial wafer according to claim 2, characterized in that: The epitaxial wafer layer includes a first epitaxial wafer layer and a second epitaxial wafer layer; the epitaxial layer sample is composed of a plurality of first epitaxial wafer layers and a plurality of second epitaxial wafer layers alternately stacked; When the Group III atoms in the first epitaxial wafer layer and the second epitaxial wafer layer are the same but the Group V atoms are different, the Group V atoms are used as reference atoms to determine the position of the interface reference atoms; When the Group III atoms in the first epitaxial wafer layer and the second epitaxial wafer layer are different and the Group V atoms are the same, the Group III atoms are used as reference atoms to determine the position of the interface reference atoms.

12. The method for measuring the thickness of an epitaxial wafer according to claim 11, characterized in that: When the material of the first epitaxial layer in the epitaxial layer sample is In x Ga (1-x) As, the material of the second epitaxial layer is In x Al (1-x) As, or the material of the first epitaxial layer is In x Ga (1-x) As, the material of the second epitaxial layer is Al x Ga (1-x) When As, the Group III atom is used as the reference atom to determine the position of the interface reference atom; When the material of the first epitaxial sheet layer in the epitaxial layer sample is GaAs; The material of the second epitaxial layer is GaAs y P (1-y) When the Group V atom is used as the reference atom, the position of the interface reference atom is determined.

13. The method for measuring the thickness of an epitaxial wafer according to claim 2, characterized in that: The epitaxial wafer layer comprises a first epitaxial wafer layer and a second epitaxial wafer layer; the epitaxial layer is composed of a plurality of first epitaxial wafer layers and a plurality of second epitaxial wafer layers alternately stacked; The material of the first epitaxial layer in the epitaxial layer sample is In x Ga (1-x) As, the material of the second epitaxial layer is In x Al (1-x) As; In x Ga (1-x) Atomic columns and In x Al (1-x) The atomic column is used as a reference atom to determine the position of the interface reference atom.

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