Aluminum gallium nitride barrier layer thickness measurement structure and method

Abstract

The application discloses an aluminum gallium nitride barrier layer thickness measurement structure and a measurement method. The measurement structure comprises a substrate, a heterojunction on the substrate, the heterojunction comprising a gallium nitride channel layer and an aluminum gallium nitride barrier layer, a two-dimensional electron gas being formed at the interface between the gallium nitride channel layer and the aluminum gallium nitride barrier layer, a first metal layer on the heterojunction, the first metal layer being electrically connected with the two-dimensional electron gas, a passivation layer on the first metal layer and the heterojunction, a second metal layer on the passivation layer, the second metal layer comprising a first metal electrode plate located in a region above the first metal layer and a second metal electrode plate located in a region above the two-dimensional electron gas. The measurement structure of the application can form a first parallel plate capacitor not containing the aluminum gallium nitride barrier layer and a second parallel plate capacitor containing the aluminum gallium nitride barrier layer, and the thickness of the aluminum gallium nitride barrier layer can be finally obtained based on voltage-capacitance characteristic testing and a parallel plate capacitor capacitance formula.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to a structure and method for measuring the thickness of an aluminum gallium nitride barrier layer. Background Art

[0002] Due to the polarization of the material, a high-concentration two-dimensional electron gas (2DEG) is formed at the aluminum gallium nitride / gallium nitride (AlGaN / GaN) heterojunction interface, and it has the characteristic of high carrier saturation mobility. It can be said that the AlGaN / GaN heterojunction structure is the cornerstone for the preparation of gallium nitride-based high electron mobility transistors (HMETs).

[0003] During epitaxial growth, the concentration of the two-dimensional electron gas (2DEG) directly depends on the thickness and Al content of the AlGaN barrier layer, which ultimately affect the current characteristics of the device. While the thickness or Al content of the AlGaN barrier layer can be measured using a number of methods, such as scanning electron microscopy (SEM), focused ion beam technology (FIB), and X-ray diffractometer (XRD), these methods require expensive equipment and are difficult to measure during actual wafer production.

[0004] In the existing technology, the voltage-capacitance (CV) characteristics can be used to measure and calculate the thickness of the AlGaN barrier layer. Specifically, metal is evaporated on the AlGaN / GaN heterojunction to form a Schottky contact, and then a parallel plate capacitor structure of Metal-AlGaN-2DEG is formed. In this structure, Metal and 2DEG are the upper and lower plates, and the AlGaN barrier layer acts as the dielectric layer. The capacitance value of the structure can be measured using an LCR meter, and then the thickness of the AlGaN barrier layer can be calculated according to the capacitance formula of the parallel plate capacitor: C=ε0εS / d. In the formula, C is the measured capacitance value, ε0 is the vacuum dielectric constant, ε is the relative dielectric constant of the AlGaN barrier layer, S is the capacitor plate area, that is, the Schottky contact area, and d is the thickness of the AlGaN barrier layer. In the above formula, the capacitance value C is obtained from actual measurement, the vacuum dielectric constant ε0 = 8.854187817E-12F / m, the plate area S is the process design value, and the AlGaN barrier layer dielectric constant ε can be obtained according to the empirical formula ε = 9.5-0.5x, where x is the Al component ratio in the AlGaN barrier layer. Therefore, the premise of using this method to measure the thickness of the AlGaN barrier layer is to know the Al component ratio in the AlGaN. However, the actual situation is that when the thickness of the AlGaN barrier layer is unknown, its Al component ratio is often unknown. In addition, if the AlGaN barrier layer is of low quality and has large leakage, or if the Schottky contact is poor, the error of the result measured and calculated by the above method will also be large.

[0005] Therefore, in order to solve the above technical problems, it is necessary to provide a structure and method for measuring the thickness of an AlGaN barrier layer. Summary of the Invention

[0006] In view of this, an object of the present invention is to provide a structure and method for measuring the thickness of an AlGaN barrier layer.

[0007] In order to achieve the above-mentioned purpose, the technical solution provided by one embodiment of the present invention is as follows:

[0008] A structure for measuring the thickness of an aluminum gallium nitride barrier layer, comprising:

[0009] substrate;

[0010] A heterojunction located on the substrate, the heterojunction comprising a gallium nitride channel layer and an aluminum gallium nitride barrier layer, wherein a two-dimensional electron gas is formed at an interface between the gallium nitride channel layer and the aluminum gallium nitride barrier layer;

[0011] a first metal layer located on the heterojunction, the first metal layer being electrically connected to the two-dimensional electron gas;

[0012] a passivation layer located on the first metal layer and the heterojunction;

[0013] a second metal layer located on the passivation layer, the second metal layer comprising a first metal plate located entirely or partially in a region above the first metal layer and a second metal plate located entirely or partially in a region above the two-dimensional electron gas;

[0014] The measurement structure includes a first parallel plate capacitor and a second parallel plate capacitor. The upper plate of the first parallel plate capacitor is a first metal plate, the lower plate is a first metal layer, and the dielectric layer is a passivation layer. The upper plate of the second parallel plate capacitor is a second metal plate, the lower plate is a two-dimensional electron gas, and the dielectric layer is an aluminum gallium nitride barrier layer and a passivation layer.

[0015] In one embodiment, the passivation layer includes a first passivation layer, and the thickness of the first passivation layer is 50 nm to 500 nm. Preferably, the first passivation layer is a combination of one or more of a silicon nitride layer, a silicon oxide layer, and an aluminum oxide layer.

[0016] In one embodiment, the passivation layer further includes a second passivation layer, and the thickness of the second passivation layer is 100 nm to 1 μm. Preferably, the second passivation layer is a combination of one or more of a silicon nitride layer, a silicon oxide layer, and a polyimide layer.

[0017] In one embodiment, the thickness of the gallium nitride channel layer is 50 nm to 2 μm; and / or the thickness of the aluminum gallium nitride barrier layer is 10 nm to 50 nm; and / or the aluminum gallium nitride barrier layer is Al x Ga 1-xN barrier layer, x=0.1-0.3; and / or, the thickness of the passivation layer is greater than the thickness of the AlGaN barrier layer. Preferably, the thickness of the passivation layer is greater than or equal to 4 times the thickness of the AlGaN barrier layer.

[0018] In one embodiment, a metal test block is formed on the measurement structure. The metal test block is located beside the second metal layer and penetrates the entire passivation layer to be electrically connected to the first metal layer.

[0019] In one embodiment, the area of ​​the first metal plate is equal to the area of ​​the second metal plate; and / or the area of ​​the first metal plate and the area of ​​the second metal plate are greater than or equal to 1E4 μm 2 .

[0020] In one embodiment, the first metal layer is located on the surface of the AlGaN barrier layer or at least partially inside the AlGaN barrier layer; and / or,

[0021] The substrate is a combination of one or more of silicon, sapphire, and silicon carbide; and / or,

[0022] The measurement structure includes a buffer layer between the channel layer and the substrate; and / or,

[0023] An isolation region is formed in the heterojunction except for the region directly below the second metal plate; and / or,

[0024] An isolation layer is formed between the gallium nitride channel layer and the aluminum gallium nitride barrier layer; and / or,

[0025] A cap layer is formed on the AlGaN barrier layer; and / or,

[0026] The first metal layer is an ohmic metal, and its material is a metal and / or a metal compound, wherein the metal includes one or more of gold, platinum, nickel, titanium, aluminum, palladium, tantalum, tungsten, and molybdenum, and the metal compound includes one or more of titanium nitride and tantalum nitride; and / or,

[0027] The second metal layer is a gate metal, a field plate metal or a through-hole connection metal, and is made of metal and / or metal compound. The metal includes one or more of gold, platinum, nickel, titanium, palladium, tantalum, and tungsten, and the metal compound includes one or more of titanium nitride and tantalum nitride.

[0028] Another embodiment of the present invention provides a technical solution as follows:

[0029] A method for measuring the thickness of an AlGaN barrier layer is applied to the above-mentioned measurement structure, and the measurement method includes:

[0030] S1, obtaining a first capacitance value C1 of the first parallel plate capacitor and a second capacitance value C2 of the second parallel plate capacitor;

[0031] S2, according to C1 = ε r1 S1 / d1, to obtain the dielectric permittivity ε of the dielectric layer in the first parallel-plate capacitor r1 S1 is the area of the first metal electrode plate in the region above the first metal layer, and d1 is the thickness of the passivation layer;

[0032] S3, according to C2 = ε r2 S2 / d2, to obtain the total thickness d2 of the aluminum gallium nitride barrier layer and the passivation layer, and the dielectric permittivity ε of the second parallel-plate capacitor r2 , which is equal to the dielectric permittivity ε of the first parallel-plate capacitor r1 S2 is the area of the second metal electrode plate in the region above the two-dimensional electron gas;

[0033] S4, according to d AlGaN = d2-d1, to obtain the thickness d AlGaN of the aluminum gallium nitride barrier layer.

[0034] In an embodiment, the measurement method further comprises:

[0035] measuring the thickness d AlGaN of the aluminum gallium nitride barrier layer in the measurement structure with different thicknesses and / or different numbers of passivation layers, respectively.

[0036] In an embodiment, the first capacitance value C1 and / or the second capacitance value C2 are measured by a probe station and an LCR tester.

[0037] The present application has the following beneficial effects:

[0038] The measurement structure of the present application can form a first parallel-plate capacitor not containing an aluminum gallium nitride barrier layer and a second parallel-plate capacitor containing an aluminum gallium nitride barrier layer, and the thickness of the aluminum gallium nitride barrier layer can be finally obtained based on voltage-capacitance characteristic testing and a parallel-plate capacitor capacitance formula;

[0039] The measurement instrument only needs a probe station and an LCR tester, the measurement method is simple and easy to operate, and the measurement process does not need the Al component content in the aluminum gallium nitride barrier layer, the measurement structure is compatible with most GaN HMET process flows, and the thickness of the aluminum gallium nitride barrier layer obtained by using the measurement structure and the measurement method has high accuracy and consistency. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiment or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.

[0041] Figure 1 Schematic diagram of the structure of the measurement structure of the present invention;

[0042] Figure 2 Schematic diagram of the specific structure of the measurement structure in Example 1 of the present invention;

[0043] Figure 3 Schematic diagram of the planar structure of the measurement structure in Example 1 of the present invention;

[0044] Figure 4 Schematic diagram of the specific structure of the measurement structure in Example 2 of the present invention;

[0045] Figure 5 Schematic diagram of the planar structure of the measurement structure in Example 2 of the present invention;

[0046] Figure 6 This is a flow chart of the AlGaN barrier layer thickness measurement method of the present invention. DETAILED DESCRIPTION

[0047] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0048] The present invention discloses a structure for measuring the thickness of an aluminum gallium nitride barrier layer, comprising:

[0049] substrate;

[0050] A heterojunction located on the substrate, the heterojunction comprising a gallium nitride channel layer and an aluminum gallium nitride barrier layer, wherein a two-dimensional electron gas is formed at the interface between the gallium nitride channel layer and the aluminum gallium nitride barrier layer;

[0051] a first metal layer located on the heterojunction, the first metal layer being electrically connected to the two-dimensional electron gas;

[0052] a passivation layer located on the first metal layer and the heterojunction;

[0053] a second metal layer located on the passivation layer, the second metal layer comprising a first metal plate located entirely or partially in a region above the first metal layer and a second metal plate located entirely or partially in a region above the two-dimensional electron gas;

[0054] The measurement structure comprises a first parallel-plate capacitor and a second parallel-plate capacitor, the upper electrode plate of the first parallel-plate capacitor is a first metal electrode plate, the lower electrode plate is a first metal layer, the dielectric layer is a passivation layer, the upper electrode plate of the second parallel-plate capacitor is a second metal electrode plate, the lower electrode plate is a two-dimensional electron gas, and the dielectric layer is an aluminum gallium nitride barrier layer and a passivation layer.

[0055] Referring to the drawings, the present application further discloses an aluminum gallium nitride barrier layer thickness measurement method applied to the measurement structure, and the measurement method comprises the following steps: Figure 6

[0056] S1, obtaining a first capacitance value C1 of the first parallel-plate capacitor and a second capacitance value C2 of the second parallel-plate capacitor;

[0057] S2, obtaining a dielectric constant ε r1 S1 / d1 of the dielectric layer in the first parallel-plate capacitor according to C1=ε r1 S1 / d1, wherein S1 is the area of the first metal electrode plate in the region above the first metal layer, and d1 is the thickness of the passivation layer;

[0058] S3, obtaining the total thickness d2 of the aluminum gallium nitride barrier layer and the passivation layer according to C2=ε r2 S2 / d2, wherein the dielectric constant ε r2 S2 / d2 of the second parallel-plate capacitor is equal to the dielectric constant ε r1 S1 / d1 of the first parallel-plate capacitor, and S2 is the area of the second metal electrode plate in the region above the two-dimensional electron gas;

[0059] S4, obtaining the thickness d AlGaN of the aluminum gallium nitride barrier layer according to d AlGaN .

[0060] The present application is further described below in combination with specific embodiments.

[0061] Embodiment 1

[0062] Referring to the drawings, the present application further discloses an aluminum gallium nitride barrier layer thickness measurement method applied to the measurement structure, and the measurement method comprises the following steps: Figure 1

[0063] a substrate 10, which is silicon (Si), sapphire (Al2O3), silicon carbide (SiC) or the like;

[0064] a heterojunction on the substrate, the heterojunction comprising a gallium nitride channel layer 30 and an aluminum gallium nitride barrier layer 40, a two-dimensional electron gas (2DEG) being formed at the interface between the gallium nitride channel layer 30 and the aluminum gallium nitride barrier layer 40, the thickness of the gallium nitride channel layer being 50 nm to 2 μm, and the aluminum gallium nitride barrier layer being Al x Ga 1-x ​​N (x=0.1-0.3) barrier layer, thickness is 10nm-50nm.

[0065] The measurement structure in this embodiment further includes a buffer layer 20 located between the substrate and the heterojunction. The buffer layer is mainly nitride, including gallium nitride, aluminum nitride, aluminum gallium nitride, etc.

[0066] Furthermore, an isolation layer, such as an aluminum nitride isolation layer (AlN spacer), is formed between the gallium nitride channel layer and the aluminum gallium nitride barrier layer; a cap layer, such as a gallium nitride cap layer (GaN cap), is formed on the aluminum gallium nitride barrier layer; and an epitaxial layer such as p-type gallium nitride (p-GaN) can also be formed on the aluminum gallium nitride barrier layer.

[0067] Combine Figure 2 As shown, the measurement structure of this embodiment further includes a first metal layer 50 , a first passivation layer 61 , a second metal layer, and a metal test block 80 .

[0068] The first metal layer 50 is located on the heterojunction, and the first metal layer 50 is electrically connected to the two-dimensional electron gas.

[0069] The first metal layer is typically an ohmic metal and may be made of gold (Au), platinum (Pt), nickel (Ni), titanium (Ti), aluminum (Al), palladium (Pd), tantalum (Ta), tungsten (W), molybdenum (Mo), or metal compounds such as titanium nitride (TiN) and tantalum nitride (TaN). The metal layer may be formed by evaporation or sputtering. After formation, the photoresist and excess metal may be removed by stripping, or metal etching may be used to remove the metal outside the source and drain regions.

[0070] The first metal layer may be located on the surface of the AlGaN barrier layer, or may be partially located inside the AlGaN barrier layer, depending on whether an ohmic etching process is performed before forming the ohmic contact in an actual process.

[0071] The first passivation layer 61 is located on the first metal layer and the heterojunction. The first passivation layer is one of the insulating media such as silicon nitride layer, silicon oxide layer, aluminum oxide layer, etc., and can also be a composite medium composed of multiple insulating media.

[0072] It is worth noting that the thickness of the first passivation layer should be as thick as possible than the thickness of the AlGaN barrier layer. In this embodiment, the thickness of the first passivation layer is 50 nm to 500 nm.

[0073] The second metal layer is located on the first passivation layer 61 , and includes a first metal plate 71 located entirely or partially in an area above the first metal layer and a second metal plate 72 located entirely or partially in an area above the two-dimensional electron gas.

[0074] Preferably, in this embodiment, the first metal plate 71 is entirely located in the region above the first metal layer, the second metal plate 72 is entirely located in the region above the two-dimensional electron gas, and the area of ​​the first metal plate 71 is equal to the area of ​​the second metal plate 72 .

[0075] In other embodiments, the first metal plate 71 may be partially located in the region above the first metal layer, and the second metal plate 72 may be partially located in the region above the two-dimensional electron gas.

[0076] The second metal layer can be a gate metal, field plate metal, or via metal, depending on the actual process flow. Materials include gold (Au), platinum (Pt), nickel (Ni), titanium (Ti), palladium (Pd), tantalum (Ta), tungsten (W), and metal compounds such as titanium nitride (TiN) and tantalum nitride (TaN). The metal can be formed by evaporation or sputtering. After formation, the photoresist and excess metal can be removed by stripping, or by metal etching.

[0077] The metal test block 80 is located adjacent to the second metal layer and extends through the entire first passivation layer 61 to electrically connect to the first metal layer 50. In this embodiment, the metal test block 80 is made of the same material as the second metal layer. The metal test block 80 is formed by first etching the first passivation layer down to the first metal layer, and then simultaneously forming the metal test block with the second metal layer through evaporation or sputtering.

[0078] At this point, the measurement structure can form a first parallel plate capacitor (excluding the AlGaN barrier layer) and a second parallel plate capacitor (including the AlGaN barrier layer), specifically:

[0079] The upper plate of the first parallel plate capacitor is the first metal plate 71, the lower plate is the first metal layer 50, and the dielectric layer is the first passivation layer 61;

[0080] The upper plate of the second parallel plate capacitor is the second metal plate 72 , the lower plate is the two-dimensional electron gas (2DEG), and the dielectric layer is the AlGaN barrier layer 40 and the first passivation layer 61 .

[0081] Since the first metal plate 71 in this embodiment is entirely located in the area above the first metal layer, and the second metal plate 72 is entirely located in the area above the two-dimensional electron gas, the plate area of ​​the first parallel plate capacitor is the area of ​​the first metal plate 71, and the plate area of ​​the second parallel plate capacitor is the area of ​​the second metal plate 72.

[0082] In other embodiments, when the first metal plate 71 partially overlaps with the first metal layer 50, the plate area of ​​the first parallel plate capacitor is the overlapping area of ​​the two; when the second metal plate 72 partially overlaps with the two-dimensional electron gas (2DEG), the plate area of ​​the second parallel plate capacitor is the overlapping area of ​​the two.

[0083] Furthermore, an isolation region 90 is formed in the heterojunction outside the area directly below the second metal plate. Specifically, during the fabrication process, the first parallel plate capacitor region can be isolated. Isolation can be achieved by ion implantation of strongly electronegative elements such as O or F, or by etching using gases such as BCl3 or Cl2. Because the second parallel plate capacitor utilizes a two-dimensional electron gas as the lower plate, the gas must be retained, so this region cannot be isolated.

[0084] Ginseng Figure 3 The figure shows a schematic diagram of the top view of the measurement structure. The left area is the upper plate of the first parallel plate capacitor, and the right area is the upper plate of the second parallel plate capacitor. The lower plates of the two capacitors are electrically connected through the metal test block in the middle.

[0085] The shapes of the first metal plate 71 and the second metal plate 72 can be rectangular, circular or other irregular shapes. The shapes should be convenient for calculating the plate area. The area of ​​the first metal plate 71 and the second metal plate 72 should be as large as possible. 2 If the area is too small, the capacitance will be too small, which will affect the actual measurement and calculation.

[0086] Based on the above measurement structure, the AlGaN barrier layer thickness measurement method is based on the voltage-capacitance (CV) characteristic test and the parallel plate capacitor capacitance formula, and specifically includes the following steps:

[0087] S1. Obtain a first capacitance value C1 of a first parallel plate capacitor and a second capacitance value C2 of a second parallel plate capacitor.

[0088] The first capacitance value C1 and the second capacitance value C2 are measured by a probe station and an LCR meter.

[0089] S2, according to C1 = ε r1 S1 / d1, the dielectric constant ε of the dielectric layer in the first parallel plate capacitor is obtained r1 , S1 is the area of ​​the first metal plate located in the area above the first metal layer, and d1 is the thickness of the first passivation layer.

[0090] S3, according to C2 = ε r2 S2 / d2, the total thickness d2 of the AlGaN barrier layer and the first passivation layer is obtained, and the dielectric constant ε of the second parallel plate capacitor is obtained. r2 The dielectric constant ε of the first parallel plate capacitor is r1 , S2 is the area of ​​the second metal plate located in the region above the two-dimensional electron gas.

[0091] Since the thickness of the first passivation layer is as large as possible from the thickness of the AlGaN barrier layer, preferably, the thickness of the first passivation layer is greater than or equal to 4 times the thickness of the AlGaN barrier layer, the dielectric constant of the AlGaN barrier layer has little effect on the capacitance, so ε r2 ≈ε r1 .

[0092] S4, according to d AlGaN =d2-d1, the thickness of the AlGaN barrier layer is obtained as d AlGaN .

[0093] In a specific embodiment, the first capacitance value C1 and the second capacitance value C2 are measured to be 3.6 pF and 3.48 pF respectively. In addition, the area S1 of the first metal plate and the area S2 of the second metal plate are both 4000 μm 2 , the thickness d1 of the first passivation layer is 0.5 μm.

[0094] According to C1=ε r1 S1 / d1 can be used to obtain the dielectric constant ε of the dielectric layer in the first parallel plate capacitor. r1 =104.4F / m, then the dielectric constant ε of the second parallel plate capacitor r2 ≈ε r1 =104.4F / m.

[0095] According to C2=ε r2 S2 / d2, the total thickness of the AlGaN barrier layer and the first passivation layer can be obtained as d2 = 0.517241 μm.

[0096] The thickness of the final AlGaN barrier layer d AlGaN =d2-d1=0.017241μm.

[0097] Example 2:

[0098] In actual processes, the thickness of the first passivation layer may be relatively small. The second passivation layer may be used to increase the test structure group. The test results of multiple groups of test structures may be compared and verified with each other.

[0099] Combine Figure 4 As shown, the measurement structure of this embodiment is substantially the same as the measurement structure in Embodiment 1, except that a second passivation layer 62 is further formed on the first passivation layer 61 .

[0100] The second passivation layer may be made of insulating media such as silicon nitride, silicon oxide or polyimide, or a composite medium composed of multiple insulating media, and may have a thickness of 100 nm to 1 μm.

[0101] Ginseng Figure 5The figure shows a schematic diagram of the top view of the measurement structure. The left area is the upper plate of the first parallel plate capacitor, and the right area is the upper plate of the second parallel plate capacitor. The lower plates of the two capacitors are electrically connected through the metal test block in the middle.

[0102] In the measurement structure of this embodiment, the composition and thickness of the AlGaN barrier layer, and the material and thickness of the first passivation layer are exactly the same as those in Example 1. The difference is that in this embodiment, a second passivation layer 62 with a thickness of 0.2 μm is further epitaxially grown on the first passivation layer 61 with a thickness of 0.5 μm.

[0103] In addition, the metal test block 80 in this embodiment includes the metal test block in the first embodiment, and a new metal test block is formed simultaneously when a new second metal layer is formed.

[0104] Based on the above measurement structure, the AlGaN barrier layer thickness measurement method is based on the voltage-capacitance (CV) characteristic test and the parallel plate capacitor capacitance formula, and specifically includes the following steps:

[0105] S1. Obtain a first capacitance value C1 of a first parallel plate capacitor and a second capacitance value C2 of a second parallel plate capacitor.

[0106] The first capacitance value C1 and the second capacitance value C2 are measured by a probe station and an LCR meter.

[0107] S2, according to C1 = ε r1 S1 / d1, the dielectric constant ε of the dielectric layer in the first parallel plate capacitor is obtained r1 , S1 is the area of ​​the first metal plate located in the area above the first metal layer, and d1 is the total thickness of the first passivation layer and the second passivation layer.

[0108] S3, according to C2 = ε r2 S2 / d2, the total thickness d2 of the AlGaN barrier layer, the first passivation layer, and the second passivation layer is obtained, and the dielectric constant ε of the second parallel plate capacitor is obtained. r2 The dielectric constant ε of the first parallel plate capacitor is r1 , S2 is the area of ​​the second metal plate located in the region above the two-dimensional electron gas.

[0109] Since the total thickness of the first passivation layer and the second passivation layer is as large as possible from the thickness of the AlGaN barrier layer, preferably, the total thickness of the first passivation layer and the second passivation layer is greater than or equal to 4 times the thickness of the AlGaN barrier layer, the dielectric constant of the AlGaN barrier layer has little effect on the capacitance, so ε r2 ≈ε r1 .

[0110] S4, according to d AlGaN=d2-d1, the thickness of the AlGaN barrier layer is obtained as d AlGaN .

[0111] In a specific embodiment, the first capacitance value C1 and the second capacitance value C2 are measured to be 2.43 pF and 2.49 pF respectively. In addition, the area S1 of the first metal plate and the area S2 of the second metal plate are both 4000 μm 2 The total thickness d1 of the first passivation layer and the second passivation layer is 0.7 μm.

[0112] According to C1=ε r1 S1 / d1 can be used to obtain the dielectric constant ε of the dielectric layer in the first parallel plate capacitor. r1 =100.845F / m, then the dielectric constant of the second parallel plate capacitor ε r2 ≈ε r1 =100.845F / m.

[0113] According to C2=ε r2 S2 / d2, the total thickness of the AlGaN barrier layer, the first passivation layer and the second passivation layer can be obtained as d2=0.717284 μm.

[0114] The final thickness of the AlGaN barrier layer is d AlGaN =d2-d1=0.017284μm.

[0115] It can be seen that the thicknesses of the AlGaN barrier layer finally measured in the two embodiments can be verified with each other. After verification, the measurement results are basically consistent with the actual thickness of the AlGaN barrier layer (0.017000 μm).

[0116] Since the dielectric constant of the AlGaN barrier layer has a smaller impact on the capacitance as the thickness of the passivation layer increases, the thickness error of the AlGaN barrier layer decreases. When testing multiple sets of embodiments, if the errors between the multiple measurement results are large, the measured value with the larger passivation layer thickness can be selected as the final AlGaN barrier layer thickness. If the errors between the multiple measurement results are small, the average of the measured AlGaN barrier layer thicknesses can be taken.

[0117] It should be understood that the above embodiments are described using measurement structures with one passivation layer and two passivation layers as examples. In other embodiments, measurement structures with three or more passivation layers may also be used, which will not be described one by one here.

[0118] In addition, by applying high voltage on one end plate (first metal layer or second metal layer) of the parallel plate capacitor, the voltage withstand and leakage performance of the dielectric layer of the parallel plate capacitor can be tested.

[0119] It can be seen from the above technical solutions that the present invention has the following advantages:

[0120] The measurement structure of the present invention can form a first parallel plate capacitor without an AlGaN barrier layer and a second parallel plate capacitor including an AlGaN barrier layer. Based on the voltage-capacitance characteristic test and the parallel plate capacitor capacitance formula, the thickness of the AlGaN barrier layer can be finally obtained.

[0121] The measurement instruments only require a probe station and an LCR meter. The measurement method is simple and easy to operate, and the measurement process does not require the Al component content in the AlGaN barrier layer. The measurement structure is compatible with most GaN HMET process flows. The AlGaN barrier layer thickness obtained using the measurement structure and measurement method has high accuracy and consistency.

[0122] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0123] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for measuring the thickness of an AlGaN barrier layer, applied to a measurement structure, characterized in that: The measurement structure includes: substrate; A heterojunction located on the substrate, the heterojunction comprising a gallium nitride channel layer and an aluminum gallium nitride barrier layer, wherein a two-dimensional electron gas is formed at an interface between the gallium nitride channel layer and the aluminum gallium nitride barrier layer; a first metal layer located on the heterojunction, the first metal layer being electrically connected to the two-dimensional electron gas; a passivation layer located on the first metal layer and the heterojunction; a second metal layer located on the passivation layer, the second metal layer comprising a first metal plate located entirely or partially in a region above the first metal layer and a second metal plate located entirely or partially in a region above the two-dimensional electron gas; The measurement structure includes a first parallel plate capacitor and a second parallel plate capacitor, wherein the upper plate of the first parallel plate capacitor is a first metal plate, the lower plate is a first metal layer, and the dielectric layer is a passivation layer; the upper plate of the second parallel plate capacitor is a second metal plate, the lower plate is a two-dimensional electron gas, and the dielectric layer is an aluminum gallium nitride barrier layer and a passivation layer; The measuring method comprises: S1, obtaining a first capacitance value C1 of the first parallel plate capacitor and a second capacitance value C2 of the second parallel plate capacitor; S2, according to C1=ε r1 S1 / d1, the dielectric constant ε of the dielectric layer in the first parallel plate capacitor is obtained r1 , S1 is the area of ​​the first metal plate located in the region above the first metal layer, and d1 is the thickness of the passivation layer; S3, according to C2=ε r2 S2 / d2, the total thickness d2 of the AlGaN barrier layer and the passivation layer is obtained, and the dielectric constant ε of the second parallel plate capacitor is obtained. r2 The dielectric constant ε of the first parallel plate capacitor is r1 , S2 is the area of ​​the second metal plate located in the region above the two-dimensional electron gas; S4, according to d AlGaN =d2-d1, the thickness of the AlGaN barrier layer is obtained as d AlGaN .

2. The method for measuring the thickness of the AlGaN barrier layer according to claim 1, wherein: The measuring method further comprises: The thickness d of the AlGaN barrier layer is measured in measurement structures with different thicknesses and / or different numbers of passivation layers. AlGaN .

3. The method for measuring the thickness of the AlGaN barrier layer according to claim 1, wherein: The first capacitance value C1 and / or the second capacitance value C2 are measured by a probe station and an LCR meter.

4. The method for measuring the thickness of the AlGaN barrier layer according to claim 1, wherein: The passivation layer includes a first passivation layer, the thickness of the first passivation layer is 50nm-500nm, and the first passivation layer is a combination of one or more of a silicon nitride layer, a silicon oxide layer, and an aluminum oxide layer.

5. The method for measuring the thickness of the AlGaN barrier layer according to claim 4, wherein: The passivation layer further includes a second passivation layer. The thickness of the second passivation layer is 100 nm to 1 μm. The second passivation layer is a combination of one or more of a silicon nitride layer, a silicon oxide layer, and a polyimide layer.

6. The method for measuring the thickness of the AlGaN barrier layer according to claim 1, wherein: The thickness of the gallium nitride channel layer is 50nm~2μm; and / or the thickness of the aluminum gallium nitride barrier layer is 10nm~50nm; and / or the aluminum gallium nitride barrier layer is Al x Ga 1-x N barrier layer, x=0.1~0.3; and / or, the thickness of the passivation layer is greater than the thickness of the AlGaN barrier layer, and the thickness of the passivation layer is greater than or equal to 4 times the thickness of the AlGaN barrier layer.

7. The method for measuring the thickness of the AlGaN barrier layer according to claim 1, wherein: A metal test block is formed on the measurement structure. The metal test block is located beside the second metal layer and penetrates the entire passivation layer to be electrically connected to the first metal layer.

8. The measurement structure according to claim 1, characterized in that The area of ​​the first metal plate is equal to the area of ​​the second metal plate; and / or the area of ​​the first metal plate and the area of ​​the second metal plate are greater than or equal to 1E4 μm 2 .

9. The method for measuring the thickness of the AlGaN barrier layer according to claim 1, wherein: The first metal layer is located on the surface of the AlGaN barrier layer or at least partially inside the AlGaN barrier layer; and / or, The substrate is a combination of one or more of silicon, sapphire, and silicon carbide; and / or, The measurement structure includes a buffer layer between the channel layer and the substrate; and / or, An isolation region is formed in the heterojunction except for the region directly below the second metal plate; and / or, An isolation layer is formed between the gallium nitride channel layer and the aluminum gallium nitride barrier layer; and / or, A cap layer is formed on the AlGaN barrier layer; and / or, The first metal layer is an ohmic metal, and its material is a metal and / or a metal compound, wherein the metal includes one or more of gold, platinum, nickel, titanium, aluminum, palladium, tantalum, tungsten, and molybdenum, and the metal compound includes one or more of titanium nitride and tantalum nitride; and / or, The second metal layer is a gate metal, a field plate metal or a through-hole connection metal, and is made of metal and / or metal compound. The metal includes one or more of gold, platinum, nickel, titanium, palladium, tantalum, and tungsten, and the metal compound includes one or more of titanium nitride and tantalum nitride.

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