Planar-type infrared focal plane array and method for preparing planar electrodes

Abstract

The present invention relates to the technical field of infrared focal plane detectors, and provides a mesa-type infrared focal plane array and a method for preparing mesa electrodes. The array includes: a pixel electrode region, which has a plurality of pixel mesa as pixel electrodes, and each pixel mesa is separated by a first isolation groove with a width less than a preset width and a depth greater than a preset depth; a common electrode region, which has a plurality of common electrode mesa separated by the first isolation groove or the second isolation groove, and there is at least one second isolation groove around each common electrode mesa. The width and depth of the second isolation groove are both greater than those of the first isolation groove. The first and second isolation grooves are obtained synchronously by one etching. Conductive metal is deposited on the bottom of the first isolation groove, the bottom and side walls of the second isolation groove, and the surface of the common electrode mesa in the common electrode region to lead the common electrode from the bottom of the epitaxial material to the mesa surface. To solve the problem in the related art that it is difficult for an infrared focal plane array to take into account a relatively large mesa duty cycle, a relatively small lateral diffusion current, and a relatively stable conduction path.

Description

Technical Field

[0001] The present invention relates to the technical field of infrared focal plane detectors, and particularly to a mesa-type infrared focal plane array and a method for preparing mesa electrodes. Background Art

[0002] Infrared focal plane detectors have a wide range of applications in military and civilian fields. Their components mainly consist of an infrared focal plane array and a readout circuit, and the two are electrically connected through metal electrodes. With the development of infrared focal plane detectors towards ultra-large area arrays and ultra-small pixel sizes, it is necessary to separate the pixels in the mesa-type infrared focal plane array through isolation grooves and minimize the width of the isolation grooves to increase the mesa duty cycle in order to obtain better detector response performance.

[0003] The mesa units in the infrared focal plane array can be divided into pixel mesas and common electrode mesas. The pixel mesa is the basic unit in the infrared focal plane array responsible for detecting infrared radiation and converting it into an electrical signal. The common electrode mesa is the output port connecting the common terminal electrode, which can provide a common potential reference or signal transmission path for the pixel mesa.

[0004] In the existing actual product structure, the widths of the isolation grooves between pixel mesas, between pixel mesas and common electrode mesas, and between common electrode mesas are the same. Therefore, when reducing the width of the above isolation grooves to increase the mesa duty cycle, on the one hand, the etching difficulty of the infrared focal plane array increases with the increase of the depth-to-width ratio of the isolation grooves, and on the other hand, it is difficult to prepare metal electrodes on the sidewalls of the above isolation grooves, and the prepared metal electrodes have problems such as difficult ramp-up, easy breakage of the conduction path leading to poor electrical connection, which will affect the output of the photocurrent signal in the infrared focal plane detector and thus reduce the detector performance.

[0005] In view of the problem in the related art that it is difficult for the infrared focal plane array to achieve a large mesa duty cycle, a small lateral diffusion current, and stable metal electrode conduction, no effective solution has been proposed yet. Summary of the Invention

[0006] A mesa-type infrared focal plane array and a method for preparing mesa electrodes provided by an embodiment of the present invention can at least solve the problem in the related art that it is difficult for the infrared focal plane array to achieve a large mesa duty cycle, a small lateral diffusion current, and stable metal electrode conduction.

[0007] A mesa-type infrared focal plane array provided by an embodiment of the present invention includes a pixel electrode region and a common electrode region. The pixel electrode region includes a plurality of pixel mesas, and the common electrode region includes a plurality of common electrode mesas. Each pixel mesa is separated by a first isolation groove. Among them, a conductive metal is deposited on the surface of the pixel mesa as the pixel electrode of the infrared focal plane array. The first isolation groove is an isolation groove with a width less than a preset width and a depth greater than a preset depth. Each common electrode mesa is separated by the first isolation groove or the second isolation groove, and at least one second isolation groove is etched around each common electrode mesa. Among them, the second isolation groove is an isolation groove with a width greater than the width of the first isolation groove and a depth greater than the depth of the first isolation groove. The first isolation groove and the second isolation groove are obtained synchronously by one etching. In the common electrode region, conductive metal is deposited on the bottom of the first isolation groove, the bottom and side walls of the second isolation groove, and the surface of the common electrode mesa, for leading the common electrode of the above infrared focal plane array from the bottom of the epitaxial material of the above infrared focal plane array to the surface of the common electrode mesa. It can be understood that the width of the first isolation groove is less than the preset width, that is, the first isolation groove is relatively narrow, which can improve the mesa duty ratio; the depth of the first isolation groove is greater than the preset depth, that is, the first isolation groove is etched deeper, which can reduce the lateral diffusion current; the mesa structure of the above common electrode region can provide a stable conduction path.

[0008] In the mesa-type infrared focal plane array provided by an embodiment of the present invention, the first isolation groove is an isolation groove with a uniform width; the second isolation groove is an isolation groove with a uniform width greater than the width of the first isolation groove, or a non-uniform width isolation groove with a minimum width greater than the width of the first isolation groove; the width of the non-uniform width isolation groove gradually increases in the length direction of the isolation groove, and the depth of the non-uniform width isolation groove increases with the increase of the width.

[0009] In the mesa-type infrared focal plane array provided by an embodiment of the present invention, when second isolation grooves are etched on both opposite sides of the common electrode mesa and the second isolation groove is a non-uniform width isolation groove, the ends with the minimum width of the two non-uniform width isolation grooves are respectively close to different sides of the common electrode mesa; two adjacent common electrode mesas on the same side share a second isolation groove.

[0010] In the mesa-type infrared focal plane array provided by an embodiment of the present invention, when second isolation grooves are etched on both adjacent sides of the common electrode mesa and the second isolation groove is a non-uniform width isolation groove, the ends with the minimum width of the two non-uniform width isolation grooves are adjacent, or the ends with the maximum width of the two non-uniform width isolation grooves are adjacent.

[0011] In the mesa-type infrared focal plane array provided by the embodiment of the present invention, when three second isolation grooves are etched around the common electrode mesa and the second isolation grooves are non-uniform-width isolation grooves, the end with the smallest width of the middle isolation groove is adjacent to the end with the smallest width of one non-uniform-width isolation groove, and the end with the largest width of the middle isolation groove is adjacent to the end with the largest width of the other non-uniform-width isolation groove, where the middle isolation groove is the non-uniform-width isolation groove located in the middle of the three non-uniform-width isolation grooves.

[0012] In the mesa-type infrared focal plane array provided by the embodiment of the present invention, a plurality of pixel mesas are arranged in a matrix in the pixel electrode region, and the pixel electrode region is rectangular; a plurality of common electrode mesas are arranged in a matrix in the common electrode region; the common electrode region is linear, L-shaped, concave, or loop-shaped; where the linear shape is a shape region in contact with one side of the rectangular pixel electrode region; the L-shaped is a shape region in contact with two adjacent sides of the rectangular pixel electrode region; the concave shape is a shape region in contact with three sides of the rectangular pixel electrode region; the loop-shaped is a shape region in contact with four sides of the rectangular pixel electrode region.

[0013] In the mesa-type infrared focal plane array provided by the embodiment of the present invention, when the common electrode region is linear, a first isolation groove or a second isolation groove is etched between adjacent common electrode mesas and pixel mesas on one side of the common electrode region adjacent to the pixel electrode region; when the common electrode region is L-shaped, a first isolation groove or a second isolation groove is etched between adjacent common electrode mesas and pixel mesas on two sides of the common electrode region adjacent to the pixel electrode region; when the common electrode region is concave, a first isolation groove or a second isolation groove is etched between adjacent common electrode mesas and pixel mesas on three sides of the common electrode region adjacent to the pixel electrode region; when the common electrode region is loop-shaped, the common electrode region surrounds the pixel electrode region, and a first isolation groove or a second isolation groove is etched between adjacent common electrode mesas and pixel mesas on four sides of the common electrode region adjacent to the pixel electrode region. On the basis of meeting the corresponding readout circuit structure, those skilled in the art can design different structures in combination with the specific shapes, numbers, and arrangement manners of the pixel mesas and the common electrode mesas.

[0014] The mesa-type infrared focal plane array provided by the embodiment of the present invention, the above infrared focal plane array is a multi-layer material structure, and the multi-layer material structure is separated into pixel mesas and common electrode mesas through a first isolation groove and a second isolation groove; the multi-layer material structure includes a substrate, and a buffer layer, a bottom electrode contact layer, a barrier layer, an absorption layer, and a top electrode contact layer grown in sequence from the substrate to the mesa direction to realize the optoelectronic characteristics of the photodiode. The bottom of the first isolation groove is etched into the interior of the bottom electrode contact layer, and the bottom of the second isolation groove is etched into a first region, and the first region is any region between the interior of the bottom electrode contact layer and the interior of the substrate. Therefore, technicians only need to precisely control the etching depth of the first isolation groove during the preparation process.

[0015] A method for preparing a mesa electrode of an infrared focal plane array provided by the embodiment of the present invention includes: coating a photoresist on the top electrode contact layer of the superlattice epitaxial wafer; performing photolithography on the photoresist according to a mask, forming a photoresist mask layer, wherein the mask is provided with patterns of a first isolation groove and a second isolation groove, the width of the first isolation groove is less than a preset width, the width of the second isolation groove is greater than the width of the first isolation groove, and the photoresist mask layer is the photoresist mask layer after the photoresist corresponding to the pattern is removed; performing dry etching on the superlattice epitaxial wafer with the photoresist mask layer through an etching gas to obtain a mesa structure with a first isolation groove and a second isolation groove, wherein the first isolation groove and the second isolation groove are obtained synchronously in one etching, the depth of the first isolation groove is greater than a preset depth, the depth of the second isolation groove is greater than the depth of the first isolation groove, each pixel mesa of the mesa structure is separated by the first isolation groove, each common electrode mesa of the mesa structure is separated by the first isolation groove or the second isolation groove, and at least one second isolation groove is etched around each common electrode mesa; depositing a metal electrode on the mesa structure to obtain the mesa electrode of the infrared focal plane array.

[0016] The method provided by the embodiment of the present invention performs dry etching on the superlattice epitaxial wafer with the photoresist mask layer through an etching gas to obtain a mesa structure with a first isolation groove and a second isolation groove, including: determining the depth of the first isolation groove; determining the time for performing dry etching according to the depth of the first isolation groove; performing dry etching on the superlattice epitaxial wafer with the photoresist mask layer through the etching gas according to the time to obtain a mesa structure with a first isolation groove and a second isolation groove.

[0017] An embodiment of the present invention provides a mesa-type infrared focal plane array and a method for preparing mesa electrodes, which designs two isolation grooves with different widths and depths that can be obtained by one etching, simplifying the etching process; the width of the first isolation groove is less than a preset width, which can increase the mesa duty cycle; the depth of the first isolation groove is greater than a preset depth, which can reduce the lateral diffusion current; in the common electrode region, a metal connection is formed between the bottom of the first isolation groove - the bottom of the second isolation groove and the side wall - the common electrode mesa after depositing a conductive metal, so that the common electrode is led from the bottom of the epitaxial material of the infrared focal plane array to the surface of the common electrode mesa, improving the conductive stability. To solve the problem in the related art that it is difficult for the infrared focal plane array to balance a relatively large mesa duty cycle, a relatively small lateral diffusion current, and relatively stable metal electrode conduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other embodiments based on these drawings without creative efforts.

[0019] Figure 1 It is a schematic diagram of the mesa topography of the pixel mesa in the embodiment of the present invention.

[0020] Figure 2 It is a schematic diagram of the mesa topography with a first isolation groove and a second isolation groove of equal width between the common electrode mesas in the embodiment of the present invention.

[0021] Figure 3 is Figure 2 The front view of the common electrode mesa located in the upper left corner in

[0022] Figure 4 It is a schematic diagram of the mesa topography with a first isolation groove and a second isolation groove of unequal width between the common electrode mesas in the embodiment of the present invention.

[0023] Figure 5 is Figure 4 The front view of the common electrode mesa located in the upper left corner in

[0024] Figure 6 It is a schematic diagram of the mesa topography with only second isolation grooves of unequal width between the common electrode mesas in the embodiment of the present invention.

[0025] Figure 7 is Figure 6 The front view of the common electrode mesa located in the upper left corner in

[0026] Figure 8It is a schematic diagram of the linear shape of the common electrode region in the embodiment of the present invention.

[0027] Figure 9 It is a schematic diagram of the L-shaped common electrode region in the embodiment of the present invention.

[0028] Figure 10 It is a flowchart of the steps of a method for fabricating mesa electrodes of an infrared focal plane array in the embodiment of the present invention. Detailed implementation manners

[0029] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to more thoroughly and completely understand the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not used to limit the protection scope of the present invention.

[0030] With the development of infrared focal plane detectors towards large-area arrays and ultra-small pixels, it is necessary to separate the mesa units in the mesa-type infrared focal plane array through isolation grooves and minimize the width of the isolation grooves to increase the mesa duty cycle in order to obtain better detector response performance. However, as the aspect ratio of the isolation grooves increases, the difficulty of fabricating metal electrodes on the sidewalls of the isolation grooves increases, and the fabricated metal electrodes have problems such as difficult climbing and easy breakage of the conduction path, resulting in poor electrical connection, thereby reducing the detector performance.

[0031] See Figures 1 to 9 As shown, the embodiment of the present invention provides a mesa-type infrared focal plane array to solve the above problems. The above infrared focal plane array includes a pixel electrode region and a common electrode region. The pixel electrode region includes a plurality of pixel mesas, and the common electrode region includes a plurality of common electrode mesas.

[0032] Each pixel mesa is separated by a first isolation groove. Among them, a conductive metal is deposited on the surface of the pixel mesa as the pixel electrode of the infrared focal plane array, and the first isolation groove is an isolation groove with a width less than a preset width and a depth greater than a preset depth.

[0033] Each common electrode mesa is separated by a first isolation groove or a second isolation groove, and at least one second isolation groove is etched around each common electrode mesa. Among them, the second isolation groove is an isolation groove with a width greater than the width of the first isolation groove and a depth greater than the depth of the first isolation groove, and the first isolation groove and the second isolation groove are obtained synchronously by one etching.

[0034] In the common electrode region, conductive metal is deposited on the bottom of the first isolation groove, the bottom and side walls of the second isolation groove, and the surface of the common electrode mesa, for leading the common electrode of the above infrared focal plane array from the bottom of the epitaxial material of the above infrared focal plane array to the surface of the common electrode mesa.

[0035] In the infrared focal plane array, whether it is a pixel mesa or a common electrode mesa, there can be various shapes, such as quadrilateral, rhombus, honeycomb or circular. In order to make full use of the space of the infrared focal plane array and meet the actual requirements of simple manufacturing process and easy large-scale integration, the embodiments of the present invention illustrate with the shape of the pixel mesa and the common electrode mesa being quadrilateral as the preference.

[0036] In the above preferred case, depending on the position, whether it is a pixel mesa or a common electrode mesa, there will be one or two or three or four isolation grooves around. Among them, when each mesa is arranged in a matrix form on the infrared focal plane array, there will be two or three or four isolation grooves around each mesa.

[0037] Affected by the mesa arrangement mode and the mesa shape, the shape of the connecting part between the first isolation groove and the second isolation groove, or the connecting part between the second isolation groove and the second isolation groove can have various situations, such as presenting as a rectangle, a trapezoid or an irregular polygon in the top view.

[0038] When the width of the above connecting part is greater than the first isolation groove and less than or equal to the second isolation groove, the above connecting part can be understood as a part of the adjacent second isolation groove.

[0039] When the width of the above connecting part is equal to the first isolation groove, the above connecting part can be understood as a part of the adjacent first isolation groove or a separate first isolation groove.

[0040] The isolation groove between the pixel mesa and the common electrode mesa can be the first isolation groove or the second isolation groove, and these two situations can exist simultaneously in an infrared focal plane array. The same is true for the isolation groove between the common electrode mesas, but at least one second isolation groove needs to be etched around each common electrode mesa.

[0041] Etching includes dry etching and wet etching. The equipment cost of wet etching is relatively low, and the etching rate is relatively high, but the etching accuracy is relatively low, and there are problems of photoresist swelling and drift. The equipment cost of dry etching is relatively high, but the etching accuracy is relatively high. The embodiments of the present invention illustrate with the first isolation groove and the second isolation groove obtained by dry etching as the preference.

[0042] The width of the first isolation groove is less than the preset width, and the depth of the first isolation groove is greater than the preset depth. Those skilled in the art can determine the specific values of the preset width and the preset depth according to prior values and actual situations.

[0043] Among them, in order to increase the duty cycle of the infrared focal plane array, the width of the first isolation groove should be small, such as 0.5 - 1 μm. In order to reduce the lateral diffusion current, the depth of the first isolation groove should be large, for example, the bottom of the first isolation groove is etched into the bottom electrode contact layer of the infrared focal plane array.

[0044] It can be understood that the width of the second isolation groove is greater than that of the first isolation groove, but it is limited by the area of the infrared focal plane array. At the same time, if the width of the second isolation groove is too large, the area of the common electrode mesa will be reduced. Therefore, those skilled in the art need to determine the reasonable width of the second isolation groove according to prior values and actual situations, such as 1 - 5 μm. In addition, the second isolation groove can be an equal-width isolation groove or a non-equal-width isolation groove, which will be introduced in detail in the subsequent description.

[0045] It can be understood that the first isolation groove in the pixel electrode region is used to separate the pixel mesa. The first isolation groove and the second isolation groove in the common electrode region are used, on the one hand, to separate the common electrode mesa, and on the other hand, to deposit metal electrodes to realize the electrical connection between the infrared focal plane array and the readout circuit.

[0046] In the common electrode region, the small width of the first isolation groove results in a large aspect ratio, making it difficult for the metal electrode to be deposited on the sidewall near the bottom of the first isolation groove, resulting in difficulties for the metal electrode to climb along the path of the bottom of the first isolation groove - the sidewall of the first isolation groove - the common electrode mesa. While the width of the second isolation groove is greater than that of the first isolation groove, and the aspect ratio is relatively small, which can enable the metal electrode deposited at the bottom of the first isolation groove to achieve electrical connection along the path of the bottom of the first isolation groove - the bottom of the second isolation groove - the sidewall of the second isolation groove - the common electrode mesa, thereby improving the conduction stability.

[0047] In addition, in the specific structure of the above infrared focal plane array, both the depth and width of the second isolation groove are greater than those of the first isolation groove, but during the preparation process, only the width of the second isolation groove being greater than that of the first isolation groove needs to be considered. The reason is that since the width of the second isolation groove is greater than that of the first isolation groove, the etching area of the second isolation groove is larger than that of the first isolation groove, making the etching rate of the second isolation groove greater than that of the first isolation groove. Therefore, under the same etching time, the etching depth of the second isolation groove will be greater than that of the first isolation groove.

[0048] For the above reasons, the first isolation groove and the second isolation groove provided in the embodiment of the present invention can be synchronously formed in one etching, and the aspect ratio of the second isolation groove is less than that of the first isolation groove.

[0049] In order to obtain isolation grooves with two different depths, the related art needs to use etching twice or even multiple times, and each etching after the first etching will greatly increase the preparation difficulty. Compared with multiple etchings, setting patterns with different line widths on the mask plate to correspond to the first isolation groove and the second isolation groove has little impact on the preparation process. Therefore, the above infrared focal plane array provided by the embodiment of the present invention has significant advantages in the preparation process.

[0050] It can be understood that the bottom of the epitaxial material of the above infrared focal plane array refers to the bottom electrode contact layer, or the buffer layer located at the bottom of the bottom electrode contact layer, or the substrate located at the bottom of the buffer layer, which will be specifically described later.

[0051] In summary, the above infrared focal plane array provided by the embodiment of the present invention creates two isolation grooves with different widths and depths that can be obtained through one etching, simplifying the etching process; the width of the first isolation groove is less than the preset width, and a smaller value can be taken according to the actual situation to increase the mesa duty cycle and enhance the response performance; the depth of the first isolation groove is greater than the preset depth, and a larger value can be taken according to the actual situation to reduce the lateral diffusion current; the width of the second isolation groove is greater than that of the first isolation groove, which can provide a larger bottom electrode contact area and reduce the difficulty of preparing the common electrode; depositing a conductive metal between the bottom of the first isolation groove - the bottom of the second isolation groove and the side wall - the common electrode mesa in the common electrode area to form a metal connection can lead the common electrode from the bottom of the epitaxial material of the infrared focal plane array to the surface of the common electrode mesa, improving the conductive stability.

[0052] Exemplarily, in order to simplify the process, the first isolation groove is an isolation groove with a constant width, such as Figure 1 the first isolation grooves between the 9 pixel mesas shown are all isolation grooves with a constant width.

[0053] Exemplarily, the second isolation groove is an isolation groove with a constant width greater than the width of the first isolation groove, such as Figure 2 there are a first isolation groove and a second isolation groove between the 9 common electrode mesas shown, and the second isolation grooves are all isolation grooves with a constant width greater than the width of the first isolation groove. Taking the common electrode mesa in the upper left corner in Figure 2 as an example, the front view is as shown in Figure 3 The width d2 of the second isolation groove is greater than the width d1 of the first isolation groove, and the depth h2 of the second isolation groove is greater than the depth h1 of the first isolation groove. Figure 3The dark shadow indicates that the corresponding part is deposited with a metal electrode. It can be seen that due to the large aspect ratio of the first isolation groove, it is difficult to deposit the metal electrode on the bottom sidewall of the first isolation groove. The width d2 of the second isolation groove is greater than the width d1 of the first isolation groove, and the aspect ratio is relatively large. The metal electrode can also be well covered on the bottom sidewall of the second isolation groove, thus ensuring a stable conduction path between the bottom electrode contact layer and the top electrode contact layer of the common electrode mesa.

[0054] Preferably, the second isolation groove is a non-uniform-width isolation groove with a minimum width greater than the width of the first isolation groove. The width of the non-uniform-width isolation groove gradually increases in the length direction of the isolation groove, and the depth of the non-uniform-width isolation groove increases with the increase of the width.

[0055] It can be understood that the length of the second isolation groove can be less than or equal to or greater than the length of the adjacent side of the adjacent common electrode mesa.

[0056] Exemplarily, as Figure 4 shown, there are a first isolation groove and a second isolation groove between 9 common electrode mesas, and the second isolation groove is the above-mentioned non-uniform-width isolation groove. Taking the common electrode mesa located in the upper left corner in Figure 4 as an example, the front view is as Figure 5 shown. The width of the second isolation groove gradually increases from d3 to d2 in the length direction of the isolation groove, the depth increases with the increase of the width, and the bottom of the second isolation groove is of a slope type. Figure 5 The dark shadow in Figure 5 indicates that the corresponding part is deposited with a metal electrode. The width of the connection part between the first isolation groove and the second isolation groove in

[0057] is between d3 and d2, and the depth is between h1 and h2. Wherein, d3 is the minimum width of the second isolation groove, and d1 < d3 < d2. Figure 5 shown, it is difficult to deposit the metal electrode in the area corresponding to the width close to d3 on the bottom sidewall of the second isolation groove, which is the same reason as the difficulty of depositing the metal electrode on the bottom sidewall of the first isolation groove. At the same time, since the other areas on the bottom sidewall of the second isolation groove are easy to deposit the metal electrode, the conduction path is still stable enough.

[0058] Compared with Figure 2 and Figure 3 shown in the case where the second isolation groove is an equal-width isolation groove, the above non-uniform-width isolation groove can allow the common electrode mesa to have a larger area, and the metal electrode conduction is also more stable.

[0059] Exemplarily, as Figure 6 shown, the second isolation grooves between 9 common electrode mesas are all the above-mentioned non-uniform-width isolation grooves.Figure 6 Taking the common electrode mesa located in the upper left corner as an example, the front view is as Figure 7 shown, and the minimum width portions of the two second isolation grooves are connected.

[0060] It can be understood that, compared with the situations shown in Figure 4 and Figure 5 , the common electrode mesa shown in Figure 6 and Figure 7 enhances the conductivity stability of the metal electrode and is beneficial to the preparation of the electrode on the common electrode mesa.

[0061] It can be understood that the two situations where the second isolation groove is an equal-width isolation groove and the second isolation groove is a non-equal-width isolation groove can exist simultaneously on an infrared focal plane array. Two or three or four second isolation grooves around the same common electrode mesa can also include the above two situations at the same time. Those skilled in the art can design different-shaped second isolation grooves in combination with the specific shape, quantity, and arrangement of the common electrode mesa.

[0062] Preferably, when second isolation grooves are etched on both opposite sides of the common electrode mesa and the second isolation groove is a non-equal-width isolation groove, the ends with the minimum width of the two non-equal-width isolation grooves are respectively close to different sides of the common electrode mesa, and two adjacent common electrode mesas on the same side share one second isolation groove, as Figure 4 shown. It can enhance the conductivity stability of the metal electrode while allowing the common electrode mesa to have a larger area.

[0063] Preferably, when second isolation grooves are etched on both adjacent sides of the common electrode mesa and the second isolation groove is a non-equal-width isolation groove, the ends with the minimum width of the two non-equal-width isolation grooves are adjacent, or the ends with the maximum width of the two non-equal-width isolation grooves are adjacent, as shown in the common electrode mesas located at the four corners in Figure 6 . It can enhance the conductivity stability of the metal electrode while allowing the common electrode mesa to have a larger area.

[0064] Preferably, when three second isolation grooves are etched around the common electrode mesa and the second isolation groove is a non-equal-width isolation groove, the end with the minimum width of the middle isolation groove is adjacent to the end with the minimum width of a non-equal-width isolation groove, and the end with the maximum width of the middle isolation groove is adjacent to the end with the maximum width of another non-equal-width isolation groove, where the middle isolation groove is the non-equal-width isolation groove located in the middle of the three non-equal-width isolation grooves, as shown in the four common electrode mesas adjacent to the common electrode mesa located in the middle in Figure 6 . Adjacent means that these four common electrode mesas are adjacent to the common electrode mesa located in the middle edge to edge. It can enhance the conductivity stability of the metal electrode while allowing the common electrode mesa to have a larger area.

[0065] It can be understood that, as Figure 6 shown by the common electrode mesa in the middle in the four second isolation grooves are etched around the common electrode mesa, and when the second isolation grooves are non-uniform-width isolation grooves, every two adjacent non-uniform-width isolation grooves are adjacent at the end with the minimum width or at the end with the maximum width. It is possible to enhance the conductive stability of the metal electrode while allowing the common electrode mesa to have a relatively large area.

[0066] Preferably, a plurality of pixel mesas are arranged in a matrix form in the pixel electrode region, and the pixel electrode region is rectangular; a plurality of common electrode mesas are arranged in a matrix form in the common electrode region, and the common electrode region is linear or L-shaped or concave-shaped or loop-shaped.

[0067] Among them, the linear shape is a shape region in contact with one side of the rectangular pixel electrode region; the L-shaped is a shape region in contact with two adjacent sides of the rectangular pixel electrode region; the concave-shaped is a shape region in contact with three sides of the rectangular pixel electrode region; the loop-shaped is a shape region in contact with four sides of the rectangular pixel electrode region.

[0068] It can be understood that the shapes and layouts of the pixel electrode region and the common electrode region can both be adjusted by those skilled in the art according to actual requirements.

[0069] Specifically, when the common electrode region is linear, on one side of the common electrode region adjacent to the pixel electrode region, a first isolation groove or a second isolation groove is etched between adjacent common electrode mesas and pixel mesas. Exemplarily, Figure 8 shown is the case where a plurality of first isolation grooves are etched between adjacent common electrode mesas and pixel mesas. The pixel electrode region has 5×3 pixel mesas, and the common electrode region has 4×1 common electrode mesas.

[0070] Specifically, when the common electrode region is L-shaped, on two sides of the common electrode region adjacent to the pixel electrode region, a first isolation groove or a second isolation groove is etched between adjacent common electrode mesas and pixel mesas. Exemplarily, Figure 9 shown is the case where a plurality of first isolation grooves and second isolation grooves are etched between adjacent common electrode mesas and pixel mesas. The pixel electrode region has 3×3 pixel mesas, and the common electrode region has 1×3 + 4×2 common electrode mesas.

[0071] It can be understood that in actual situations, the number of pixel mesas arranged in the pixel electrode region and the number of common electrode mesas arranged in the common electrode region far exceed the above examples and can reach 10 6 pieces. The above examples are only examples made to clearly show the distribution of the isolation grooves in the drawings.

[0072] Specifically, when the common electrode region is concave, a first isolation groove or a second isolation groove is etched between adjacent common electrode platforms and pixel platforms on three sides of the common electrode region adjacent to the pixel electrode region.

[0073] Specifically, when the common electrode region is in a loop shape, the common electrode region surrounds the pixel electrode region, and a first isolation groove or a second isolation groove is etched between adjacent common electrode platforms and pixel platforms on four sides of the common electrode region adjacent to the pixel electrode region.

[0074] Preferably, the above infrared focal plane array is a multi-layer material structure. The multi-layer material structure is separated into pixel platforms and common electrode platforms through the first isolation groove and the second isolation groove; the multi-layer material structure includes a substrate, and a buffer layer, a bottom electrode contact layer, a barrier layer, an absorption layer, and a top electrode contact layer grown in sequence along the direction from the substrate to the platform. The bottom of the first isolation groove is etched into the inside of the bottom electrode contact layer, and the bottom of the second isolation groove is etched to a first region, where the first region is any region between the inside of the bottom electrode contact layer and the inside of the substrate.

[0075] While realizing the optoelectronic characteristics of the photodiode, the above multi-layer material structure has good stability and compatibility. Among them, the buffer layer is grown on the substrate, which can further relieve the lattice mismatch and stress between the substrate and the subsequent grown layers, and improve the crystal quality of the material.

[0076] Since the depth of the second isolation groove is greater than that of the first isolation groove, when the bottom of the second isolation groove is etched into the inside of the bottom electrode contact layer, it can be understood that the bottom of the first isolation groove is etched into the upper half of the bottom electrode contact layer, and the bottom of the second isolation groove is etched into the lower half of the bottom electrode contact layer.

[0077] In the infrared focal plane array provided by the embodiment of the present invention, the bottom of the second isolation groove can penetrate through the bottom electrode contact layer and reach the buffer layer or even the substrate. Therefore, during the preparation process, technicians only need to precisely control the etching depth of the first isolation groove, thereby reducing the preparation difficulty and being beneficial to large-scale production.

[0078] Specifically, in the pixel electrode region, a conductive metal is deposited on the surface of the pixel platform; in the common electrode region, a conductive metal is deposited on the bottom of the first isolation groove, the bottom and side walls of the second isolation groove, and the surface of the common electrode platform, which can ensure the stability of the electrical connection between the infrared focal plane array and the readout circuit. The conductive metal includes but is not limited to titanium, platinum, and gold.

[0079] It can be understood that the surface of the pixel platform and the surface of the common electrode platform refer to the upper surface of the platform, which is the side of the platform away from the isolation groove.

[0080] See Figure 10As shown in the figure, the embodiment of the present invention also provides a method for preparing a mesa electrode of an infrared focal plane array, including: Step S101, applying a photoresist on the top electrode contact layer of the superlattice epitaxial wafer.

[0081] Step S102, performing photolithography on the photoresist according to a mask plate to form a photoresist mask layer. Among them, the mask plate is provided with patterns of a first isolation groove and a second isolation groove. The width of the first isolation groove is less than a preset width, and the width of the second isolation groove is greater than the width of the first isolation groove. The photoresist mask layer is the photoresist mask layer after the corresponding part of the pattern of the photoresist is removed.

[0082] Step S103, performing dry etching on the superlattice epitaxial wafer with the photoresist mask layer through an etching gas to obtain a mesa structure with a first isolation groove and a second isolation groove. Among them, the first isolation groove and the second isolation groove are obtained synchronously in one etching. The depth of the first isolation groove is greater than a preset depth, and the depth of the second isolation groove is greater than the depth of the first isolation groove. Each pixel mesa of the mesa structure is separated by the first isolation groove, and each common electrode mesa of the mesa structure is separated by the first isolation groove or the second isolation groove, and at least one second isolation groove is etched around each common electrode mesa.

[0083] Step S104, depositing a metal electrode on the mesa structure to obtain the mesa electrode of the infrared focal plane array.

[0084] It can be understood that the superlattice epitaxial wafer is the basic material of the infrared focal plane array, and is a semiconductor thin film with a superlattice structure grown on a substrate by using epitaxial growth technology. The superlattice structure refers to an artificial periodic structure formed by alternating growth of two or more different semiconductor materials with a thickness on the nanometer scale.

[0085] The above preparation method provided by the embodiment of the present invention can obtain two isolation grooves with different widths and depths through one etching, which simplifies the etching process; the width of the first isolation groove is less than the preset width, and a smaller value can be taken according to the actual situation to increase the mesa duty cycle and enhance the response performance. At the same time, the depth of the first isolation groove is greater than the preset depth, that is, a deep etching process is adopted to reduce the influence of the lateral diffusion current between the pixel mesas; the width of the second isolation groove is greater than that of the first isolation groove, providing a larger bottom electrode contact area, thereby improving the detector stability and reducing the energy loss; the metal electrode deposited at the bottom of the first isolation groove in the common electrode region can realize electrical connection along the path of the bottom of the first isolation groove - the bottom of the second isolation groove - the side wall of the second isolation groove - the common electrode mesa, improving the conductive stability.

[0086] Preferably, before step S101, wet cleaning is performed on the superlattice epitaxial wafer with a multi-layer material structure, which can effectively remove impurities.

[0087] Specifically, the above multi-layer material structure includes a substrate, and a buffer layer, a bottom electrode contact layer, a barrier layer, an absorption layer, and a top electrode contact layer that are sequentially grown in the direction from the substrate to the mesa.

[0088] Preferably, in step S101, applying a photoresist on the top electrode contact layer of the superlattice epitaxial wafer includes: spin-coating the photoresist on the surface of the superlattice epitaxial wafer using a spin coater with a spin speed of 3000 rpm and a resist thickness of 2 μm. The applied photoresist is subjected to soft bake curing, with a soft bake curing temperature of 120 °C and a time of 100 s.

[0089] Exemplarily, the above photoresist is AZ-5214E, TI 35 ESX, or AZ NL of 2000.

[0090] Preferably, in step S102, performing photolithography on the photoresist according to a mask to form a photoresist mask layer includes using a photolithography mask to block a preset mesa area for exposure with an exposure time of 7 s, and then developing in a developer for 90 s. Subsequently, it is baked at a preparation temperature of 120 °C for 100 s to obtain a photoresist mask layer with a thickness of 2 μm. Among them, the first isolation groove is an equal-width isolation groove with a width of 1 μm, the second isolation groove is an equal-width isolation groove with a width of 2 μm, or a non-equal-width isolation groove with a width gradually changing from 1 μm to 2 μm.

[0091] Preferably, in step S103, dry etching the superlattice epitaxial wafer with a photoresist mask layer through an etching gas to obtain a mesa structure with a first isolation groove and a second isolation groove includes: step S1031, determining the depth of the first isolation groove.

[0092] It can be understood that the bottom of the first isolation groove in the common electrode region can contact the bottom electrode contact layer of the superlattice epitaxial wafer so that the subsequently deposited metal electrode can cover the bottom electrode contact layer. The depth of the first isolation groove can be determined by the thickness difference between the top electrode contact layer and the bottom electrode contact layer, and the thicknesses of the bottom electrode contact layer, the top electrode contact layer, and the functional layers between them can all be determined during the material growth process. Therefore, those skilled in the art can relatively easily and accurately determine the depth of the first isolation groove.

[0093] Step S1032, determining the time for dry etching according to the depth of the first isolation groove.

[0094] Step S1033, dry etching the superlattice epitaxial wafer with a photoresist mask layer through the etching gas according to the above time to obtain a mesa structure with a first isolation groove and a second isolation groove.

[0095] Exemplarily, the above etching gas is Cl2 / BCl3 or CH4 / H2.

[0096] Preferably, in step S104, metal electrodes are deposited on the mesa structure to obtain the mesa electrodes of the infrared focal plane array, including: step S1041, performing deposition pretreatment on the mesa structure to obtain a product to be deposited, specifically: removing the photoresist on the mesa structure to obtain a first-process product; passivating the first-process product to obtain a second-process product with a passivation film; opening holes in the passivation film of the second-process product to obtain the product to be deposited, wherein the area of the passivation film exposed due to the opening corresponds to the area where the metal electrodes need to be deposited.

[0097] Step S1042, depositing metal electrodes on the product to be deposited to obtain the mesa electrodes of the infrared focal plane array, specifically: by means of thermal evaporation or magnetron sputtering, sequentially depositing conductive metals titanium, platinum, and gold on the bottom of the first isolation groove in the common electrode region, the bottom and side walls of the second isolation groove, the common electrode mesa, and the pixel mesa in the pixel electrode region to obtain the mesa electrodes of the infrared focal plane array.

[0098] Exemplarily, a metal electrode is formed by a process of photolithography, deposition, and stripping.

[0099] The specific method for forming the metal electrode is as follows: First, a layer of photoresist is coated on the surface of the passivation film, then the required metal electrode pattern is formed on the photoresist through development, then a metal electrode layer is deposited on the pattern formed by the photoresist, and finally the unnecessary part of the metal electrode layer and the photoresist are stripped to form the required metal electrode. Among them, the metal electrode layer can be formed by deposition processes such as chemical vapor deposition, physical vapor deposition, plasma-enhanced chemical vapor deposition, or atomic layer deposition, and the materials can be titanium, platinum, gold, tin, chromium, aluminum, etc.

[0100] The embodiment of the present invention also provides an infrared detector, which includes the above mesa-type infrared focal plane array and a readout circuit with a substrate. The above mesa-type infrared focal plane array and the above readout circuit are electrically connected through the mesa electrodes prepared according to the above method. The above mesa electrodes can be led out from the side wall of the common electrode mesa to the surface of the common electrode mesa, which can effectively improve the electrode contact of the infrared detector.

[0101] It should be noted that the term "including" and its variants used in the embodiments of the present invention are open-ended, that is, "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". The modifications of "one" and "a plurality" mentioned in the embodiments of the present invention are illustrative rather than restrictive. Those skilled in the art should understand that, unless clearly stated otherwise in the context, it should be understood as "one or more". The descriptions of "first", "second", etc. are only for descriptive purposes and should not be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features.

[0102] The user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the embodiments of the present invention are all information and data that have been authorized by the user or fully authorized by all parties. And the collection, use, and processing of relevant data need to comply with the relevant laws, regulations, and standards of relevant countries and regions, and corresponding operation entrances are provided for users to choose to authorize or refuse.

[0103] The various steps recorded in the method implementation manners provided in the embodiments of the present invention can be executed in different orders and / or executed in parallel. In addition, the method implementation manners may include additional steps and / or omit the steps shown. The protection scope of the present invention is not limited in this regard.

[0104] The term "embodiment" in this specification means that the specific features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of the present invention. The phrase appears in various positions in the specification does not necessarily mean the same embodiment, nor does it mean being independent or alternative to other embodiments and mutually exclusive. The various embodiments in this specification are all described in a related manner, and the same or similar parts between the various embodiments are referred to each other. In particular, for device, equipment, and system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and the relevant parts refer to the partial description of the method embodiments.

[0105] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation of the protection scope. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A mesa-type infrared focal plane array, characterized in that, It includes a pixel electrode region and a common electrode region. The pixel electrode region includes a plurality of pixel mesa surfaces, and the common electrode region includes a plurality of common electrode mesa surfaces; Each of the pixel mesa surfaces is separated by a first isolation groove. Among them, a conductive metal is deposited on the surface of the pixel mesa surface as the pixel electrode of the infrared focal plane array. The first isolation groove is an isolation groove with a width less than a preset width and a depth greater than a preset depth; Each of the common electrode mesa surfaces is separated by the first isolation groove or a second isolation groove, and at least one of the second isolation grooves is etched around each common electrode mesa surface. Among them, the second isolation groove is an isolation groove with a width greater than the width of the first isolation groove and a depth greater than the depth of the first isolation groove. The first isolation groove and the second isolation groove are obtained synchronously by one etching; In the common electrode region, conductive metal is deposited on the bottom of the first isolation groove, the bottom and side walls of the second isolation groove, and the surface of the common electrode mesa surface, for leading the common electrode of the infrared focal plane array from the bottom of the epitaxial material of the infrared focal plane array to the surface of the common electrode mesa surface.

2. The mesa-type infrared focal plane array according to claim 1, characterized in that The first isolation groove is an isolation groove with a constant width; The second isolation groove is an isolation groove with a constant width greater than the width of the first isolation groove, or a non-constant-width isolation groove with a minimum width greater than the width of the first isolation groove; The width of the non-constant-width isolation groove gradually increases in the length direction of the isolation groove, and the depth of the non-constant-width isolation groove increases with the increase of the width.

3. The mesa-type infrared focal plane array according to claim 1, characterized in that, When the second isolation grooves are etched on both opposite sides of the common electrode mesa surface and the second isolation groove is a non-constant-width isolation groove, the ends with the minimum width of the two non-constant-width isolation grooves are respectively close to different sides of the common electrode mesa surface; Two adjacent common electrode mesa surfaces on the same side share one of the second isolation grooves.

4. The mesa-type infrared focal plane array according to claim 1, wherein, When the second isolation grooves are etched on both adjacent sides of the common electrode mesa surface and the second isolation groove is a non-constant-width isolation groove, the ends with the minimum width of the two non-constant-width isolation grooves are adjacent, or the ends with the maximum width of the two non-constant-width isolation grooves are adjacent.

5. The mesa-type infrared focal plane array according to claim 1, wherein When three of the second isolation grooves are etched around the common electrode mesa surface and the second isolation groove is a non-constant-width isolation groove, the end with the minimum width of the middle isolation groove is adjacent to the end with the minimum width of one of the non-constant-width isolation grooves, and the end with the maximum width of the middle isolation groove is adjacent to the end with the maximum width of the other non-constant-width isolation groove. Among them, the middle isolation groove is a non-constant-width isolation groove located in the middle of the three non-constant-width isolation grooves.

6. The mesa-type infrared focal plane array according to claim 1, wherein, The plurality of pixel mesa surfaces are arranged in a matrix in the pixel electrode region, and the pixel electrode region is rectangular; The plurality of common electrode mesa surfaces are arranged in a matrix in the common electrode region; The common electrode region is linear, L-shaped, concave, or loop-shaped; among them, the linear shape is a shape region in contact with one side of the rectangular pixel electrode region; the L-shaped is a shape region in contact with two adjacent sides of the rectangular pixel electrode region; the concave shape is a shape region in contact with three sides of the rectangular pixel electrode region; the loop-shaped is a shape region in contact with four sides of the rectangular pixel electrode region.

7. The mesa-type infrared focal plane array according to claim 6, wherein When the common electrode region is linear, on one side of the common electrode region adjacent to the pixel electrode region, the first isolation groove or the second isolation groove is etched between adjacent common electrode mesa and pixel mesa. When the common electrode region is L-shaped, on two sides of the common electrode region adjacent to the pixel electrode region, the first isolation groove or the second isolation groove is etched between adjacent common electrode mesa and pixel mesa. When the common electrode region is concave, on three sides of the common electrode region adjacent to the pixel electrode region, the first isolation groove or the second isolation groove is etched between adjacent common electrode mesa and pixel mesa. When the common electrode region is loop-shaped, the common electrode region surrounds the pixel electrode region, and on four sides of the common electrode region adjacent to the pixel electrode region, the first isolation groove or the second isolation groove is etched between adjacent common electrode mesa and pixel mesa.

8. The mesa-type infrared focal plane array according to claim 1, wherein, The infrared focal plane array is a multi-layer material structure, and the multi-layer material structure is separated into the pixel mesa and the common electrode mesa through the first isolation groove and the second isolation groove. The multi-layer material structure includes a substrate, and a buffer layer, a bottom electrode contact layer, a barrier layer, an absorption layer, and a top electrode contact layer that are sequentially grown along the direction from the substrate to the mesa. The bottom of the first isolation groove is etched into the inside of the bottom electrode contact layer, and the bottom of the second isolation groove is etched into the first region, and the first region is any region between the inside of the bottom electrode contact layer and the inside of the substrate.

9. A method for preparing mesa electrodes of an infrared focal plane array, characterized in that, Including: Coating photoresist on the top electrode contact layer of the superlattice epitaxial wafer. Performing photolithography on the photoresist according to a mask plate to form a photoresist mask layer, wherein the mask plate is provided with patterns of the first isolation groove and the second isolation groove, the width of the first isolation groove is less than a preset width, the width of the second isolation groove is greater than the width of the first isolation groove, and the photoresist mask layer is the photoresist mask layer after the photoresist corresponding to the patterns is removed. The superlattice epitaxial wafer with the photoresist mask layer is dry-etched with an etching gas to obtain a mesa structure having the first isolation groove and the second isolation groove, wherein the first isolation groove and the second isolation groove are synchronously obtained in one etching, the depth of the first isolation groove is greater than a preset depth, the depth of the second isolation groove is greater than the depth of the first isolation groove, each pixel mesa of the mesa structure is separated by the first isolation groove, each common electrode mesa of the mesa structure is separated by the first isolation groove or the second isolation groove, and at least one of the second isolation grooves is etched around each common electrode mesa; a metal electrode is deposited on the mesa structure to obtain a mesa electrode of an infrared focal plane array.

10. The method according to claim 9, wherein Dry-etching the superlattice epitaxial wafer with the photoresist mask layer by an etching gas to obtain a mesa structure having the first isolation groove and the second isolation groove, including: Determining the depth of the first isolation groove; Determining the time for dry-etching according to the depth of the first isolation groove; Dry-etching the superlattice epitaxial wafer with the photoresist mask layer by the etching gas according to the time to obtain a mesa structure having the first isolation groove and the second isolation groove.

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