A method for measuring the thickness of an epitaxial layer

Abstract

The present invention relates to the field of semiconductor technology, and discloses a method for measuring the thickness of an epitaxial layer. The method for measuring the thickness of the epitaxial layer includes providing an epitaxial layer sample of a semiconductor laser; the epitaxial layer sample includes a plurality of epitaxial layers, and two adjacent epitaxial layers are different ternary and quaternary compounds; obtaining a high-angle annular dark-field image with atomic-scale resolution of the epitaxial layer sample in the direction of the target crystal zone axis; determining a target connection line along the target atomic close-packed plane in the high-angle annular dark-field image, the target connection line traverses the interface between adjacent epitaxial layers and connects a plurality of atoms; determining the thickness of the epitaxial layer on the target connection line according to the brightness of the reference atoms on the target connection line; and determining the thickness of the epitaxial layer according to the thickness of the epitaxial layer on the target connection line. Compared with the related art, the present invention can improve the measurement accuracy of the thickness of the epitaxial layer, and further improve the optoelectronic performance of the laser.

Description

Technical Field

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

[0002] In the modern III-V semiconductor laser industry, the optoelectronic performance of a laser is basically determined by the epitaxial structure. Particularly 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, precise measurement of the epitaxial layer thickness is of great significance. First, the measured value of the epitaxial layer thickness can be compared with the designed value to determine the optimization direction of the epitaxial process. Then, the measured value of the epitaxial layer thickness can be related to the optoelectronic performance of the semiconductor laser, providing a reference for the design of the epitaxial structure of the semiconductor laser.

[0003] However, most of the existing methods for measuring the epitaxial layer thickness can only achieve a resolution at the nanometer scale. For semiconductor lasers with complex epitaxial structures, these methods not only cannot meet the measurement requirements of the epitaxial layer, but may also mislead the device design and process optimization of these semiconductor lasers, which is not conducive to the research and development and optimization of related device products. Therefore, a thickness measurement scheme for epitaxial layers with higher resolution is needed to improve the 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 layer to solve the problem in the related art that the thickness of the epitaxial layer cannot be accurately measured, restricting the optical performance of semiconductor lasers.

[0005] In a first aspect, the present invention provides a method for measuring the thickness of an epitaxial layer, which includes:

[0006] Providing an epitaxial layer sample of a semiconductor laser; the epitaxial layer sample includes a plurality of epitaxial layers, and two adjacent epitaxial layers are different III-V compounds;

[0007] Obtaining a high-angle annular dark-field image of the epitaxial layer sample in the direction of a target zone axis; the resolution of the high-angle annular dark-field image is at the atomic scale;

[0008] Determining a target connection line along a target atomic close-packed plane in the high-angle annular dark-field image, the target connection line passing through the interface between adjacent epitaxial layers and connecting a plurality of atoms;

[0009] Determining the thickness of the epitaxial layer on the target connection line according to the brightness of reference atoms on the target connection line;

[0010] Determine the thickness of the epitaxial layer according to the thickness of the epitaxial layer on the target connection line.

[0011] The method for measuring the thickness of the epitaxial layer provided by the present invention first obtains a high-angle annular dark-field image of the epitaxial layer sample in the direction of the target zone axis; secondly, determines a target connection line along the target atomic close-packed plane in the high-angle annular dark-field image, the target connection line crosses the interface between adjacent epitaxial layers and connects multiple atoms; finally, determines the thickness of the epitaxial layer on the target connection line according to the brightness of the reference atoms on the target connection line, and determines the thickness of the epitaxial layer according to the thickness of the epitaxial layer on the target connection line. On the one hand, the measurement accuracy of the thickness of the epitaxial layer can reach atomic-scale resolution, improving the measurement accuracy of the thickness 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 one lattice plane spacing, far less than 1 nm. This high-precision method for measuring the thickness of the epitaxial layer 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.

[0012] In an optional embodiment, the step of determining the thickness of the epitaxial layer on the target connection line according to the brightness of the reference atoms on the target connection line includes:

[0013] Take the group III atoms or group V atoms in the epitaxial layer as reference atoms, and determine the positions of the interface reference atoms on both sides of the interface of the epitaxial layer according to the brightness of the reference atoms on the target connection line;

[0014] Determine the thickness of the epitaxial layer on the target connection line according to the positions of the interface reference atoms.

[0015] The method for measuring the thickness of the epitaxial layer provided by the present invention takes the group III atoms or group V atoms in the epitaxial layer as reference atoms, and determines the positions of the interface reference atoms on both sides of the interface of the epitaxial layer according to the brightness of the reference atoms on the target connection line, which can accurately define the positions of the interface reference atoms between the epitaxial layers, making the measurement accuracy reach the atomic scale, improving the measurement accuracy of the thickness of the epitaxial layer, and further improving the optoelectronic performance of the semiconductor laser; at the same time, determining the thickness of the epitaxial layer by the positions of the adjacent interface atoms on the target atomic close-packed plane avoids the influence of the strain in the out-of-plane direction of the lattice plane in the epitaxial layer on the measurement result, and can improve the accuracy of the measurement result; in addition, the error of the thickness of the epitaxial layer measured by this method is within one lattice plane spacing, far less than 1 nm. This high-precision method for measuring the thickness of the epitaxial layer 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.

[0016] In an alternative embodiment, taking group III or group V atoms in the epitaxial layer as reference atoms, the steps of determining the positions of the interface reference atoms on both side interfaces of the epitaxial layer according to the brightness of the reference atoms on the target line include:

[0017] Taking 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;

[0018] According to the second brightness-position curve, determining the positions of the interface reference atoms on both side interfaces of the epitaxial layer.

[0019] In an alternative embodiment, taking group III or group V atoms in the epitaxial layer as reference atoms, the steps of obtaining a second brightness-position curve corresponding to the brightness of the reference atoms on the target line include:

[0020] Obtaining a first brightness-position curve corresponding to the brightness of each atom on the target line;

[0021] Taking group III or group V atoms in the epitaxial layer as reference atoms, extracting, from the first brightness-position curve, a second brightness-position curve corresponding to the brightness of the reference atoms on the target line.

[0022] In an alternative embodiment, the steps of determining the thickness of the epitaxial layer according to the thickness of the epitaxial layer on the target line include:

[0023] Calculating the sine value of the angle between the interface between adjacent epitaxial layers and the close-packed plane of the target atoms;

[0024] The thickness of the epitaxial layer is the product of the thickness of the epitaxial layer on the target line and the sine value of the angle.

[0025] In an alternative embodiment, the steps of providing an epitaxial layer sample of a semiconductor laser include:

[0026] Preparing an epitaxial layer sample of a semiconductor laser by using a focused ion beam method or an ion thinning method.

[0027] In an alternative embodiment, the steps of obtaining a high-angle annular dark-field image of the epitaxial layer sample in the direction of the target zone axis include:

[0028] Determining the direction of the target zone axis of the epitaxial layer sample; the out-of-plane index of the epitaxial layer in the direction of the target zone axis is 0;

[0029] Tilting the epitaxial layer sample to the direction of the target zone axis through a transmission electron microscope; the transmission electron microscope has a condenser spherical aberration correction function;

[0030] Obtaining a high-angle annular dark-field image of the epitaxial layer sample in the direction of the target zone axis.

[0031] In an alternative embodiment, for an epitaxial layer of cubic structure, the target zone axis directions are

[100] ,

[110] ,

[120] , and

[130] ;

[0032] For an epitaxial layer of hexagonal structure, the target zone axis directions are

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

[0033] In an alternative embodiment, before the step of determining the target connection line along the target atomic close-packed plane in the high-angle annular dark-field image, it further includes:

[0034] Determine the target atomic close-packed plane according to the target zone axis direction and the high-angle annular dark-field image.

[0035] In an alternative embodiment, for an epitaxial layer of face-centered cubic structure,

[0036] When the target zone axis direction is the

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

[0037] When the target zone axis direction is the

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

[0038] When the target zone axis direction is the

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

[0039] When the target zone axis direction is the

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

[0040] In an alternative embodiment, the epitaxial layer includes a first epitaxial layer and a second epitaxial layer; the epitaxial layer is composed of multiple first epitaxial layers and multiple second epitaxial layers stacked alternately;

[0041] When the group III atoms in the first epitaxial layer and the second epitaxial layer are the same and the group V atoms are different, the group V atoms are used as the reference atoms to determine the position of the interface reference atoms;

[0042] When the group III atoms in the first epitaxial layer and the second epitaxial layer are different and the group V atoms are the same, the group III atoms are used as the reference atoms to determine the position of the interface reference atoms.

[0043] In an alternative embodiment, when the material of the first epitaxial layer in the epitaxial layer is In x Ga (1-x) As, and 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, and the material of the second epitaxial layer is Alx Ga (1-x) When it is GaAs, the group III atoms are used as the reference atoms to determine the positions of the interface reference atoms;

[0044] When the material of the first epitaxial layer in the epitaxial layer is GaAs; and the material of the second epitaxial layer is GaAs y P (1-y) When it is, the group V atoms are used as the reference atoms to determine the positions of the interface reference atoms.

[0045] In an alternative embodiment, the epitaxial layer includes a first epitaxial layer and a second epitaxial layer; the epitaxial layer is composed of multiple first epitaxial layers and multiple second epitaxial layers stacked alternately;

[0046] The material of the first epitaxial layer in the epitaxial layer is In x Ga (1-x) As, and the material of the second epitaxial layer is In x Al (1-x) As;

[0047] Taking the In x Ga (1-x) atomic column and the In x Al (1-x) atomic column as the reference atoms to determine the positions of the interface reference atoms. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the related art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the related art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0049] Figure 1 FIG. is a flowchart of a method for measuring the thickness of an epitaxial layer according to an embodiment of the present invention.

[0050] Figure 2 FIG. is a specific flowchart of a method for measuring the thickness of an epitaxial layer according to an embodiment of the present invention.

[0051] Figure 3 FIG. is a HAADF image of the atomic scale resolution of an InGaAs / InAlAs epitaxial layer in a method for measuring the thickness of an epitaxial layer according to an embodiment of the present invention.

[0052] Figure 4 is Figure 3 the Fourier transform image of.

[0053] Figure 5is the second luminance-position curve corresponding to the luminance of the reference atom on the first target connection line.

[0054] Figure 6 is the second luminance-position curve corresponding to the luminance of the reference atom on the second target connection line.

[0055] Reference numerals:

[0056] 1. First target connection line; 2. Second target connection line; 10. No. 1 epitaxial layer; 20. No. 2 epitaxial layer; 30. No. 3 epitaxial layer; 40. No. 4 epitaxial layer. Detailed implementation manners

[0057] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Additionally, it should be noted that for the convenience of description, only the parts related to the present invention rather than all the structures are shown in the accompanying drawings.

[0058] In the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention. Various structural schematic diagrams according to the embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, where for the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are only exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can 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 can be directly on the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element can be "under" the other layer / element.

[0059] In the modern III-V semiconductor laser industry, the optoelectronic performance of a 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 precise measurement of the epitaxial layer thickness has 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 establish a connection with the optoelectronic performance of the semiconductor laser, thereby providing a reference for the design of the epitaxial structure of the semiconductor laser.

[0060] However, the vast majority of existing measurement methods for the thickness of epitaxial layers can only achieve nanoscale resolution. For semiconductor lasers with complex epitaxial structures, these methods not only fail to meet the measurement requirements of epitaxial layers, but may also mislead the device design and process optimization of these semiconductor lasers, which is not conducive to the research and development and optimization of related device products. Therefore, a thickness measurement scheme for epitaxial layers with higher resolution is needed to improve the measurement accuracy and further improve the optoelectronic performance of semiconductor lasers.

[0061] As Figure 1 shown, this embodiment provides a method for measuring the thickness of an epitaxial layer, and the preparation method includes but is not limited to steps S101 to S105.

[0062] Step S101: Provide an epitaxial layer sample of a semiconductor laser; the epitaxial layer sample includes a plurality of epitaxial layers, and two adjacent epitaxial layers are different ternary and quaternary compounds.

[0063] Step S102: 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.

[0064] Step S103: Determine a target connection line in the high-angle annular dark-field image along the target atomic close-packed plane. The target connection line crosses the interface between adjacent epitaxial layers and connects multiple atoms.

[0065] Step S104: Determine the thickness of the epitaxial layer on the target connection line according to the brightness of the reference atoms on the target connection line.

[0066] Step S105: Determine the thickness of the epitaxial layer according to the thickness of the epitaxial layer on the target connection line.

[0067] The method for measuring the thickness of the epitaxial layer provided in this embodiment first obtains a high-angle annular dark-field image of the epitaxial layer sample in the direction of the target crystal zone axis; secondly, determines a target connection line in the high-angle annular dark-field image along the target atomic close-packed plane. The target connection line crosses the interface between adjacent epitaxial layers and connects multiple atoms; finally, determines the thickness of the epitaxial layer on the target connection line according to the brightness of the reference atoms on the target connection line, and determines the thickness of the epitaxial layer according to the thickness of the epitaxial layer on the target connection line. On the one hand, it can make the thickness measurement accuracy of the epitaxial layer reach atomic-scale resolution, improve the thickness measurement accuracy of the epitaxial layer, and further improve the optoelectronic performance of semiconductor lasers; on the other hand, the measurement error of the epitaxial layer is within one crystal plane spacing, far less than 1 nm. 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 semiconductor lasers.

[0068] In some alternative embodiments, the steps of determining the thickness of the epitaxial layer on the target connection line according to the brightness of the reference atoms on the target connection line include:

[0069] Taking 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 two side interfaces of the epitaxial layer according to the brightness of the reference atoms on the target connection line;

[0070] Determining the thickness of the epitaxial layer on the target connection line according to the positions of the interface reference atoms.

[0071] Specifically, the interface reference atoms on the two side interfaces of the epitaxial layer refer to the interface reference atoms on the interface between the epitaxial layer and its adjacent epitaxial layer. For example, Figure 3 The interface between the No. 1 epitaxial layer 10 and the No. 2 epitaxial layer 20 in the figure is L1.

[0072] In the epitaxial structure of a III-V semiconductor laser, the difference between heteroepitaxial layers is mainly the difference in group III or group V atoms. In addition, for the high-angle annular dark-field image (HAADF image) obtained by transmission electron microscopy, its contrast is related to the atomic number of the epitaxial layer. When the atomic number of the atoms in the epitaxial layer is larger, the relative atomic mass is larger, and the corresponding epitaxial layer is brighter 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.

[0073] Since the essence of transmission electron microscopy imaging is the projection of the epitaxial layer, the atomic dots 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 of two different epitaxial layers, and the brightness of the corresponding atomic columns is between the brightness of the corresponding atomic columns in the two side epitaxial layers. In summary, the brightness of the interface reference atoms should be close to the average value of the brightness of the corresponding atoms in the epitaxial layers on both sides of the interface.

[0074] Specifically, taking group III atoms or group V atoms as reference atoms means taking group III atoms and other group III solid solution atoms, or group V atoms and other group V solid solution atoms as reference atoms.

[0075] Specifically, taking group III atoms or group V atoms as reference atoms can be taking a single group III atom or a single group V atom as a reference atom, or taking solid solution atoms composed of different group III atoms or solid solution atoms composed of different group V atoms as reference atoms.

[0076] The thickness measurement method of the epitaxial layer provided in this embodiment uses group III or group V atoms in the epitaxial layer as reference atoms. According to the brightness of the reference atoms on the target line, the positions of the interface reference atoms on both interfaces of the epitaxial layer are determined, which can accurately define the positions of the interface reference atoms between the epitaxial layers, enabling the measurement accuracy to reach the atomic scale, improving the thickness measurement accuracy of the epitaxial layer, and further improving the optoelectronic performance of the semiconductor laser. At the same time, by determining the epitaxial layer thickness through the positions of adjacent interface atoms on the close-packed plane of the target atoms, the influence of the strain in the out-of-plane direction of the lattice plane in the epitaxial layer on the measurement result is avoided, which can improve the accuracy of the measurement result. In addition, the error of the epitaxial layer thickness measured by this method is within one crystal plane spacing, far less than 1 nm. 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.

[0077] In some alternative embodiments, the steps of using group III or group V atoms in the epitaxial layer as reference atoms and determining the positions of the interface reference atoms on both interfaces of the epitaxial layer according to the brightness of the reference atoms on the target line include:

[0078] Using 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;

[0079] According to the second brightness-position curve, determine the positions of the interface reference atoms on both interfaces of the epitaxial layer.

[0080] 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 layers on both sides of the interface, the positions of the interface reference atoms on both interfaces of the epitaxial layer can be determined according to the second brightness-position curve and the average brightness of the reference atoms. The interface reference atom is the reference atom closest to the average brightness line of the reference atoms.

[0081] In one example, four stacked epitaxial layers need to be measured, as Figure 3 shown. The interfaces between the four epitaxial layers are L1, L2, L3, and L4 respectively. Among them, the interface between the 1st epitaxial layer 10 and the 2nd epitaxial layer 20 is L1, the interface between the 2nd epitaxial layer 20 and the 3rd epitaxial layer 30 is L2, the interface between the 3rd epitaxial layer 30 and the 4th epitaxial layer 20 is L3, and the interface between the 4th epitaxial 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.

[0082] Taking the group-III or group-V atoms in the four epitaxial layers as reference atoms, the second luminance-position curves corresponding to the luminance of the reference atoms on the first target connection line 1 and the second target connection line 2 are respectively obtained, as Figure 5 and Figure 6 shown. Among them, Figure 5 is the second luminance-position curve corresponding to the luminance of the reference atoms on the first target connection line 1, Figure 6 is the second luminance-position curve corresponding to the luminance of the reference atoms on the second target connection line 2.

[0083] As Figure 5 shown, when it is necessary to measure the thickness of the No. 2 epitaxial layer 20, according to the second luminance-position curve and the average luminance of the reference atoms, the interface reference atoms A1 and A2 on the interfaces L1 and L2 on both sides of the No. 2 epitaxial layer 20 are determined. According to the same method, the interface reference atoms on both sides of each epitaxial layer can be found respectively.

[0084] In some alternative embodiments, the steps of taking the group-III or group-V atoms in the epitaxial layer as reference atoms and obtaining the second luminance-position curve corresponding to the luminance of the reference atoms on the target connection line include:

[0085] Obtaining the first luminance-position curve corresponding to the luminance of each atom on the target connection line;

[0086] Taking the group-III or group-V atoms in the epitaxial layer as reference atoms, and extracting the second luminance-position curve corresponding to the luminance of the reference atoms on the target connection line from the first luminance-position curve.

[0087] In some alternative embodiments, the steps of determining the thickness of the epitaxial layer according to the thickness of the epitaxial layer on the target connection line include:

[0088] Calculating the sine value of the angle between the interface between adjacent epitaxial layers and the close-packed plane of the target atoms;

[0089] The thickness of the epitaxial layer is the product of the thickness of the epitaxial layer on the target connection line and the sine value of the angle.

[0090] Specifically, as Figure 3 shown, the angle between the interface and the close-packed plane of the target atoms is α, and the thickness of the epitaxial layer is the thickness of the epitaxial layer on the target connection line multiplied by sinα.

[0091] Among them, the sine value of the angle sinα can be directly calculated by using the coordinates of different normal vectors in the Fourier transform, or the sine value of the angle sinα can be obtained by calculating the specific value of the angle according to the coordinates of the interface reference atoms.

[0092] Continuing with the above example, as Figure 5As shown, after determining the interface reference atoms A1 and A2 on the interfaces L1 and L2 on both sides of the epitaxial layer 20 of the No. 2 epitaxial wafer, subtracting the coordinates of A1 and A2 gives the thickness of the epitaxial layer on the target connection line as 3.28 nm, α = 53°, sinα = 0.79864, and finally the calculated thickness of the epitaxial layer is 3.28 nm × 0.79864 = 2.62 nm.

[0093] In some alternative embodiments, the step of providing an epitaxial layer sample of a semiconductor laser includes:

[0094] Preparing an epitaxial layer sample of a semiconductor laser by using a focused ion beam method or an ion thinning method.

[0095] In some alternative embodiments, the step of obtaining a high-angle annular dark-field image of an epitaxial layer sample in a target zone axis direction includes:

[0096] Determining the target zone axis direction of the epitaxial layer sample; the out-of-plane index of the epitaxial layer in the target zone axis direction is 0;

[0097] Tilting the epitaxial layer sample to the target zone axis direction through a transmission electron microscope; the transmission electron microscope has a condenser spherical aberration correction function;

[0098] Obtaining a high-angle annular dark-field image of the epitaxial layer sample in the target zone axis direction.

[0099] In some alternative embodiments, for an epitaxial layer of a cubic structure, the target zone axis directions are

[100] ,

[110] ,

[120] , and

[130] ;

[0100] For an epitaxial layer of a hexagonal structure, the target zone axis directions are

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

[0101] In some alternative embodiments, before the step of determining the target connection line along the target atom close-packed plane in the high-angle annular dark-field image, it further includes:

[0102] Determining the target atom close-packed plane according to the target zone axis direction and the high-angle annular dark-field image.

[0103] In some alternative embodiments, for an epitaxial layer of a face-centered cubic structure,

[0104] When the target zone axis direction is the

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

[0105] When the target zone axis direction is the

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

[0106] When the target zone axis direction is the

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

[0107] When the target zone axis direction is the

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

[0108] In some alternative embodiments, the epitaxial layer includes a first epitaxial layer and a second epitaxial layer; the epitaxial layer sample is composed of a plurality of first epitaxial layers and a plurality of second epitaxial layers stacked alternately;

[0109] When the group III atoms in the first epitaxial layer and the second epitaxial layer are the same and the group V atoms are different, the group V atoms are used as the reference atoms to determine the positions of the interface reference atoms;

[0110] When the group III atoms in the first epitaxial layer and the second epitaxial layer are different and the group V atoms are the same, the group III atoms are used as the reference atoms to determine the positions of the interface reference atoms.

[0111] In specific implementation, for the ternary - quinary semiconductor compound, the group III atoms and the group V atoms occupy different positions respectively. The group III atoms form a set of cubic lattices, and so do the group V atoms. Therefore, the positions at the interface need to be calibrated by different atoms. When the group III atoms are different, the group III atoms are needed to determine the interface. When the group V atoms are different, the group V atoms are needed to determine the interface.

[0112] In some alternative embodiments, when the material of the first epitaxial layer in the epitaxial layer sample is In x Ga (1-x) As, and the material of the second epitaxial layer is In x Al (1-x) As, or when the material of the first epitaxial layer is In x Ga (1-x) As, and the material of the second epitaxial layer is Al x Ga (1-x) As, the group III atoms are used as the reference atoms to determine the positions of the interface reference atoms;

[0113] When the material of the first epitaxial layer in the epitaxial layer sample is GaAs; and the material of the second epitaxial layer is GaAs y P (1-y) at this time, the group V atoms are used as the reference atoms to determine the positions of the interface reference atoms.

[0114] In specific implementation, when the epitaxial layer is the InGaAs / InAlAs system, the InGaAs / AlGaAs system, etc., the brightness of the group III atoms is selected as a reference to determine the positions of the atoms at the interface. When the epitaxial layer is the GaAs / GaAsP system, etc., the brightness of the group V atoms is selected as a reference to determine the positions of the atoms at the interface.

[0115] In some alternative embodiments, the epitaxial layer includes a first epitaxial layer and a second epitaxial layer; the epitaxial layer is composed of a plurality of first epitaxial layers and a plurality of second epitaxial layers stacked alternately;

[0116] The material of the first epitaxial layer in the epitaxial layer sample is In x Ga (1-x) As, and the material of the second epitaxial layer is In x Al (1-x) As;

[0117] Taking the In x Ga (1-x) atomic column and the In x Al (1-x) atomic column as the reference atoms, the positions of the interface reference atoms are determined.

[0118] In specific implementation, the epitaxial layer is of the InGaAs / InAlAs system, and the brightness of group III atoms is selected as the reference to determine the positions of the atoms at the interface. Therefore, the In x Ga (1-x) atomic column containing Ga and the In x Al (1-x) atomic column are used as the reference atoms to determine the positions of the interface reference atoms.

[0119] In some alternative embodiments, after measuring the thicknesses of a plurality of epitaxial 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 the epitaxial layers.

[0120] As Figure 2 shown, the present invention also provides a schematic flow chart of a method for measuring the thickness of an epitaxial layer, including but not limited to steps S201 to S208.

[0121] Step S201, providing an epitaxial layer sample of a semiconductor laser; the epitaxial layer sample includes a plurality of epitaxial layers, and two adjacent epitaxial layers are different ternary and quaternary compounds.

[0122] In specific implementation, the epitaxial layer includes a first epitaxial layer and a second epitaxial layer; the epitaxial layer sample is composed of a plurality of first epitaxial layers and a plurality of second epitaxial layers stacked alternately.

[0123] In one example, an epitaxial layer structure of an active region of a quantum cascade laser is provided. The material of the first epitaxial layer is In x Ga (1-x) As, and 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 / Inx Al (1-x) As. The epitaxial layer structure includes four epitaxial layers, namely the 1st epitaxial layer 10, the 2nd epitaxial layer 20, the 3rd epitaxial layer 30, and the 4th epitaxial layer 40, with designed thicknesses of 1.60 nm, 2.95 nm, 1.45 nm, and 2.10 nm respectively.

[0124] Step S202: Obtain the high-angle annular dark-field image of the epitaxial layer sample in the direction of the target zone axis; determine the target atomic close-packed plane based on the target zone axis direction and the high-angle annular dark-field image.

[0125] Specifically, when implemented, the atomic-scale resolution HAADF image of the In x Ga (1-x) As / In x Al (1-x) As epitaxial layer was obtained under the

[130] zone axis by a spherical aberration corrected transmission electron microscope, as Figure 3 shown. Based on the Fourier transform of this HAADF image, the diffraction spots of the In x Ga (1-x) As / In x Al (1-x) As epitaxial layer were obtained, as Figure 4 shown. Combining the lattice parameters of In x Ga (1-x) As / In x Al (1-x) As and calibrating the diffraction spots, it can be determined that the crystal plane index of the interface in the epitaxial layer is (002), and the crystal plane index of the atomic close-packed plane passing through the interface is (3 - 11).

[0126] Step S203: Determine the target connection line along the target atomic close-packed plane in the high-angle annular dark-field image. The target connection line crosses the interface between adjacent epitaxial layers and connects multiple atoms.

[0127] Specifically, when implemented, two straight lines were selected as the target connection lines along the (3 - 11) close-packed plane in the HAADF image of the In x Ga (1-x) As / In x Al (1-x) As epitaxial structure by Gatan DigitalMicrograph software. As Figure 3 shown, the left straight line is the first target connection line 1, and the right straight line is the second target connection line 2.

[0128] Step S204: Obtain the first brightness-position curve corresponding to the brightness of each atom on the target connection line.

[0129] In specific implementation, the curve of the brightness and position of different pixel points on the straight line is obtained through the Profile function of the Gatan DigitalMicrograph software, that is, the first brightness-position curve.

[0130] Step S205: Take the group III or group V atoms in the epitaxial layer as reference atoms, and extract the second brightness-position curve corresponding to the brightness of the reference atoms on the target connection line in the first brightness-position curve.

[0131] In specific implementation, take In x Ga (1-x) atomic columns and In x Al (1-x) atomic columns as reference atoms. In the above first brightness-position curve, select the horizontal and vertical coordinates of In x Ga (1-x) atomic columns and In x Al (1-x) atomic columns to plot a graph, and then the curve of the brightness of the reference atomic column with respect to the position can be obtained, that is, the second brightness-position curve, and at the same time, the average brightness of the reference atomic column is obtained, as Figure 5 and Figure 6 shown.

[0132] Step S206: Determine the positions of the interface reference atoms on both sides of the epitaxial layer according to the second brightness-position curve.

[0133] In specific implementation, in the curve of the atomic column brightness with respect to the position, by comparing the average value of the brightness of In x Ga (1-x) atomic columns and In x Al (1-x) atomic columns (the dotted lines in Figure 3 and Figure 4 ) with the average brightness of the reference atomic column in the curve, the position of the interface reference atom can be judged.

[0134] As Figure 5 shown, according to the second brightness-position curve corresponding to the brightness of the reference atoms on the first target connection line 1 and the average brightness of the reference atoms, determine the interface reference atoms A1, A2, A3, and A4 on both sides of the 1st epitaxial layer 10, 2nd epitaxial layer 20, 3rd epitaxial layer 30, and 4th epitaxial layer 40. As Figure 6 shown, use the same method to determine the interface reference atoms A1, A2, A3, and A4 on the second target connection line 2.

[0135] Since In x Ga (1-x) atomic columns and In x Al (1-x)The dotted line of the average brightness of the atomic columns must pass through the middle of the brightness coordinates of adjacent atomic columns (that is, the dotted line of the average brightness can pass through the middle of the adjacent atomic brightness, which means that the dotted line of the average brightness and the atomic brightness - distance curve must have an intersection, and the ordinate of the intersection must also be between the brightness of the ordinates of two adjacent atomic points). Therefore, the error of this measurement method lies above and below the average brightness of the atomic columns, and adjacent atoms are misjudged as interface atoms. Correspondingly, the error of the entire test is within the lattice plane spacing in one epitaxial growth direction.

[0136] Step S207: Determine the thickness of the epitaxial layer on the target line according to the positions of the interface reference atoms.

[0137] In specific implementation, based on the subtraction of the position coordinates of adjacent interface atoms, the lengths of different epitaxial layers on the (3-11) close-packed atomic plane can be calculated. As Figure 5 shown, according to the coordinates of the interface reference atoms A1, A2, A3, and A4, the thicknesses of the 1st epitaxial layer 10, 2nd epitaxial layer 20, 3rd epitaxial layer 30, and 4th epitaxial layer 40 on the first target line 1 are 2.19 nm, 3.28 nm, 1.59 nm, and 1.95 nm respectively. As Figure 6 shown, according to the coordinates of the interface reference atoms A1, A2, A3, and A4, the thicknesses of the 1st epitaxial layer 10, 2nd epitaxial layer 20, 3rd epitaxial layer 30, and 4th epitaxial layer 40 on the second target line 2 are 2.18 nm, 3.29 nm, 1.58 nm, and 1.97 nm respectively.

[0138] Step S208: Determine the thickness of the epitaxial layer according to the thickness of the epitaxial layer on the target line: calculate the sine value of the angle between the interface between adjacent epitaxial layers and the target atomic close-packed plane; the thickness of the epitaxial layer is the product of the thickness of the epitaxial layer on the target line and the sine value of the angle.

[0139] In specific implementation, through the sine value sinα of the angle α between the (3-11) close-packed atomic plane and the (002) interface, according to the thickness of each epitaxial layer on the first target line 1, the thicknesses of the 1st epitaxial layer 10, 2nd epitaxial layer 20, 3rd epitaxial layer 30, and 4th epitaxial layer 40 are 1.74 nm, 2.62 nm, 1.27 nm, and 1.56 nm respectively; according to the thickness of each epitaxial layer on the second target line 2, the thicknesses of the 1st epitaxial layer 10, 2nd epitaxial layer 20, 3rd epitaxial layer 30, and 4th epitaxial layer 40 are 1.74 nm, 2.62 nm, 1.26 nm, and 1.57 nm respectively.

[0140] Therefore, in this embodiment, the thicknesses of the first epitaxial layer to the fourth epitaxial layer obtained by measuring twice according to the first target connection line 1 on the left and the second target connection line 2 on the right are 1.74 nm, 2.62 nm, 1.27 nm, and 1.56 nm, and 1.74 nm, 2.62 nm, 1.26 nm, and 1.57 nm respectively, while the designed thicknesses of the relevant epitaxial layers are 1.60 nm, 2.95 nm, 1.45 nm, and 2.10 nm. Since the lattice plane spacing of the (002) atomic close-packed plane in the epitaxial layer is about 0.3 nm (considering the influence of strain), it can be seen that the actual thicknesses of the second epitaxial layer and the fourth epitaxial layer are respectively 1 and 2 atomic layer thicknesses different from the designed thicknesses.

[0141] Table 1 Comparison of the thickness measurement results of the epitaxial layers

[0142]

[0143] In the description of this specification, the description referring to terms such as "this embodiment", "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. means that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do 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, without contradiction, 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. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" can explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0144] In the above description, technical details such as the layout 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 the required shapes. In addition, in order to form the same structure, those skilled in the art can also design methods that are not exactly the same as the methods described above. In addition, although the above embodiments are described separately, this does not mean that the measures in each embodiment cannot be used advantageously in combination.

[0145] The above is only the preferred embodiment of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the above specific embodiments, and various obvious changes, re-adjustments, combinations with each other, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, it may also include more other equivalent embodiments, and the protection scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for measuring the thickness of an epitaxial layer, characterized in that Including: Providing an epitaxial layer sample of a semiconductor laser; The epitaxial layer sample includes a plurality of epitaxial layers, and two adjacent epitaxial layers are different ternary and quaternary compounds; 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; Determining a target connection line along a target atomic close-packed plane in the high-angle annular dark-field image, the target connection line traverses the interface between adjacent epitaxial layers and connects a plurality of atoms; Determining the thickness of the epitaxial layer on the target connection line according to the brightness of the reference atoms on the target connection line; Determining the thickness of the epitaxial layer according to the thickness of the epitaxial layer on the target connection line.

2. The method for measuring the thickness of an epitaxial layer according to claim 1, wherein: The step of determining the thickness of the epitaxial layer on the target connection line according to the brightness of the reference atoms on the target connection line includes: Taking 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 both sides of the epitaxial layer according to the brightness of the reference atoms on the target connection line; Determining the thickness of the epitaxial layer on the target connection line according to the positions of the interface reference atoms.

3. The method for measuring the thickness of an epitaxial layer according to claim 2, wherein: The step of taking the group III or group V atoms in the epitaxial layer as reference atoms and determining the positions of the interface reference atoms on both sides of the epitaxial layer according to the brightness of the reference atoms on the target connection line includes: 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 connection line; Determining the positions of the interface reference atoms on both sides of the epitaxial layer according to the second brightness-position curve.

4. The method for measuring the thickness of an epitaxial layer according to claim 3, wherein: 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 connection line includes: Obtaining a first brightness-position curve corresponding to the brightness of each atom on the target connection line; Taking the group III or group V atoms in the epitaxial layer as reference atoms, and extracting the second brightness-position curve corresponding to the brightness of the reference atoms on the target connection line from the first brightness-position curve.

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

6. The method for measuring the thickness of an epitaxial layer according to claim 1, wherein: The step of providing an epitaxial layer sample of a semiconductor laser includes: Preparing an epitaxial layer sample of a semiconductor laser by using a focused ion beam method or an ion thinning method.

7. The thickness measurement method of the epitaxial layer according to claim 1, characterized in that the step of obtaining the high-angle annular dark-field image of the epitaxial layer sample in the target zone axis direction includes: determining the target zone axis direction of the epitaxial layer sample; the out-of-plane index of the epitaxial layer in the target zone axis direction is 0; tilting the epitaxial layer sample to the target zone axis direction through a transmission electron microscope; the transmission electron microscope has a condenser spherical aberration correction function; obtaining the high-angle annular dark-field image of the epitaxial layer sample in the target zone axis direction.

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

9. The thickness measurement method of the epitaxial layer according to claim 1, characterized in that before the step of determining the target connection line along the target atomic close-packed plane in the high-angle annular dark-field image, it further includes: determining the target atomic close-packed plane according to the target zone axis direction and the high-angle annular dark-field image.

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

11. The thickness measurement method of the epitaxial layer according to claim 2, characterized in that the epitaxial layer includes a first epitaxial layer and a second epitaxial layer; the epitaxial layer sample is composed of a plurality of first epitaxial layers and a plurality of second epitaxial layers stacked alternately; when the group III atoms in the first epitaxial layer and the second epitaxial layer are the same and the group V atoms are different, taking the group V atoms as the reference atoms to determine the position of the interface reference atoms; when the group III atoms in the first epitaxial layer and the second epitaxial layer are different and the group V atoms are the same, taking the group III atoms as the reference atoms to determine the position of the interface reference atoms.

12. The thickness measurement method of the epitaxial layer 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 and the material of the second epitaxial layer is In x Al (1-x) As, or when the material of the first epitaxial layer is In x Ga (1-x) As and the material of the second epitaxial layer is Al x Ga (1-x) As, taking group III atoms as reference atoms, determine the positions 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, taking the group-V atoms as the reference atoms, determine the positions of the interface reference atoms 13. The thickness measurement method of the epitaxial layer according to claim 2, characterized in that the epitaxial layer includes a first epitaxial layer and a second epitaxial layer; the epitaxial layer is composed of a plurality of first epitaxial layers and a plurality of second epitaxial layers stacked alternately; The material of the first epitaxial layer in the epitaxial layer sample is In x Ga (1-x) As, and the material of the second epitaxial layer is In x Al (1-x) As; Take In x Ga (1-x) atomic columns and In x Al (1-x) atomic columns as reference atoms to determine the positions of the interface reference atoms.

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