A method for monitoring the etching process of APD epitaxial material InGaAs / InAlAs

Abstract

The present invention discloses an APD that is convenient for monitoring an etching process. The present invention discloses a method for monitoring the etching progress of an APD epitaxial structure, comprising the following steps: performing photolithography on the APD that is convenient for monitoring an etching process to form a mask pattern, then immersing the APD in an etching solution for etching, then observing the APD surface, and judging the etching progress according to the APD surface conditions, specifically as follows: when a "ground glass" phenomenon is observed on the APD surface, it indicates that the etching solution etches to the interface between the InGaAsP material and the InGaAs / InAlAs material; when the "ground glass" phenomenon on the APD surface begins to fade, it indicates that the etching solution begins to etch to the interface between the InGaAs / InAlAs material and the InP material; when the APD surface is observed to become smooth and uniform again, it indicates that the InGaAs / InAlAs material has been completely etched.

Description

Technical Field

[0001] The invention relates to the technical field of wafer etching, and in particular to an APD which is convenient for monitoring an etching process, and a method for monitoring the etching progress of an APD epitaxial structure. Background Art

[0002] APD (avalanche photodiode) epitaxial structure usually grows InGaAs / InAlAs material on InP substrate. In the preparation process of APD chip, different patterns need to be etched on the epitaxial material, such as grooves, terraces, contact holes, etc.; therefore, the depth and time of etching the epitaxial material need to be strictly controlled, and generally a chemical solution with high selectivity for InGaAs / InAlAs and InP materials is used. However, when the solution etches to the interface of the two materials, no changes can be observed with the naked eye, so it is difficult to visually judge whether the InGaAs / InAlAs material has been etched to the bottom. At present, it can only be judged whether the InGaAs / InAlAs layer material has been etched to the bottom by etching multiple times and then using a step instrument to measure the depth change after each etching.

[0003] However, the above traditional etching scheme has the following disadvantages:

[0004] 1. The changes in the etching process cannot be observed intuitively;

[0005] 2. Under-etching or over-etching will cause the product to be scrapped;

[0006] 3. Multiple etching and multiple depth measurements increase process time and are inefficient.

[0007] Through long-term work, the inventors hope to make the InGaAs / InAlAs material etching process of the APD epitaxial structure visually observable in some way, especially the changes when the etching solution etches to the interface between InGaAs / InAlAs and InP can be visually displayed. Summary of the invention

[0008] The purpose of the present invention is to solve the shortcomings of the prior art and to propose an APD that is convenient for monitoring the etching process and a method for monitoring the etching progress of an APD epitaxial structure.

[0009] An APD convenient for monitoring an etching process uses an InP material as a substrate, the surface of the InP material is covered with an InGaAs / InAlAs material, and the surface of the InGaAs / InAlAs material is covered with an InGaAsP material.

[0010] Preferably, the InGaAsP material When the InGaAsP thickness is The following monitoring effect can be achieved. Although thicker InGaAsP can also meet the requirements, its epitaxial growth and material etching time will be prolonged, increasing the cost.

[0011] Preferably, a layer of InGaAsP material is grown on the surface of the InGaAs / InAlAs material by using a Metal-organic Chemical Vapor Deposition (MOCVD) method.

[0012] Specifically, InGaAsP material is formed by chemically reacting and depositing organic compounds of indium and gallium as well as arsine, phosphine, etc. in a special closed cavity at a certain temperature and pressure.

[0013] A method for monitoring the etching progress of an APD epitaxial structure, wherein the APD that is convenient for monitoring the etching process is subjected to photolithography to form a mask pattern, then immersed in an etching solution for etching, and then the APD surface is observed, and the etching progress is judged according to the APD surface condition, as follows:

[0014] When the "ground glass" phenomenon is observed on the APD surface, it indicates that the etching solution etches to the interface between the InGaAsP material and the InGaAs / InAlAs material;

[0015] When the "ground glass" phenomenon on the APD surface begins to fade, it indicates that the etching solution begins to etch to the interface between the InGaAs / InAlAs material and the InP material;

[0016] When the APD surface is observed to become smooth and uniform again, it indicates that the InGaAs / InAlAs material has been completely etched.

[0017] Preferably, the etching solution is an InGaAs / InAlAs etching solution. Conventional InGaAs / InAlAs etching solutions also have an etching effect on InGaAsP, but their etching rate is much lower than that on InGaAs / InAlAs.

[0018] Preferably, the "ground glass" phenomenon is that the APD surface appears grayish white.

[0019] The present invention adds a thin layer of InGaAsP on the APD epitaxial surface, immerses the wafer in an etching solution, and firstly, the etching solution contacts the thin layer of InGaAsP material and starts to etch slowly. When the solution etches to the interface between the InGaAsP and the InGaAs / InAlAs material, a grayish white "ground glass" phenomenon is observed on the surface of the wafer. As the etching time increases, when the etching solution etches to the interface between the InGaAs / InAlAs and the InP material, the "ground glass" phenomenon on the wafer surface gradually fades, and the surface becomes smooth and uniform again, indicating that the InGaAs / InAlAs material has been etched cleanly.

[0020] During the InGaAs / InAlAs etching process, the "ground glass" phenomenon can be visually observed with the naked eye. When the "ground glass" phenomenon fades, it indicates that the InGaAs / InAlAs material has been etched cleanly. By visually observing the changes in the InGaAs / InAlAs etching process, under-etching or over-etching can be effectively avoided, and the etching target can be achieved in one time, thus shortening the process time and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a photo of the abnormality on the wafer surface when the InP material is etched before the InGaAs / InAlAs material is completely etched.

[0022] Figure 2 This is the normal etching pattern when checking the etching degree under a metallographic microscope.

[0023] Figure 3 This is the over-etched pattern when checking the etching degree under a metallographic microscope.

[0024] Figure 4 This is a real photo of the wafer surface with an off-white color similar to the "frosted glass" phenomenon, where the off-white area is the "frosted glass" area (Note: This phenomenon can be observed very obviously with the naked eye in actual operation, but the effect is not good after being captured by a camera and converted to grayscale).

[0025] Figure 5 This is a picture of the "ground glass" area on the wafer surface under a metallographic microscope.

[0026] Figure 6 This is a picture of the wafer surface under a metallographic microscope after the "ground glass" phenomenon has completely faded. DETAILED DESCRIPTION

[0027] The present invention will be further explained below in conjunction with specific embodiments.

[0028] The existing method for monitoring the etching progress of APD epitaxial structure uses a highly selective etching solution for etching. However, when etching to the interface between InGaAs / InAlAs and InP materials, no changes can be observed by the naked eye. At this time, three situations may occur: under-etching, normal etching, and over-etching:

[0029] 1. It is difficult to distinguish the under-etching of InGaAs / InAlAs materials with the naked eye, but when etching the next layer of material, the under-etched area of ​​InGaAs / InAlAs materials will show abnormalities. Figure 1 As shown, when the InGaAs / InAlAs material is not completely etched and then the InP material is etched, an uneven black block abnormality appears on its surface.

[0030] 2. Over-etching is identified by special monitoring patterns placed on the wafer surface, such as Figure 2 and Figure 3 shown. Figure 2 To check the etching degree under a metallographic microscope, the normally etched pattern is used to monitor the integrity of the pattern; Figure 3 It is the case of over-etching when checking the etching degree under a metallographic microscope, and the monitoring pattern is damaged and falling off.

[0031] It should be noted that whether over-etching occurs cannot be directly observed with the naked eye during the etching process, but can only be inspected and confirmed under a metallographic microscope after the etching is completed. Once over-etching occurs, the product will be scrapped.

[0032] The present invention provides a method for monitoring the etching progress of an APD epitaxial structure, comprising the following steps:

[0033] A layer with a thickness of 1000 nm is deposited on the surface of the APD epitaxial structure (with InP material as substrate and InGaAs / InAlAs material covering the surface of the InP material). InGaAsP material;

[0034] The APD epitaxial structure deposited with the InGaAsP material is subjected to photolithography to form a mask pattern, and then immersed in an InGaAs / InAlAs etching solution for etching, and then the wafer surface is observed, and the etching progress is determined according to the wafer surface condition, as follows:

[0035] When the wafer surface is observed to be grayish white similar to the "frosted glass" phenomenon, such as Figure 4 As shown in the figure, it means that the etching solution has etched to the interface between the InGaAsP material and the InGaAs / InAlAs material, and the InGaAs / InAlAs material here has not been etched cleanly. At this time, the frosted glass area on the wafer surface is observed using a metallographic microscope (200×). Figure 5 As shown, you will find that its surface is rough and uneven.

[0036] If InGaAsP material is not deposited on the surface of the APD epitaxial structure, this phenomenon cannot be observed during the InGaAs / InAlA etching process.

[0037] When the "ground glass" phenomenon on the wafer surface begins to fade, it indicates that the etching solution begins to etch to the interface between the InGaAs / InAlAs material and the InP material;

[0038] When the "frosted glass" phenomenon on the wafer surface is completely removed, it indicates that the InGaAs / InAlAs material has been completely etched, the rough surface becomes smooth and flat, and the wafer surface becomes smooth and uniform again. At this time, use a metallographic microscope to observe the wafer surface (200×). Figure 6 As shown, you will find that its rough surface becomes smooth and flat.

[0039] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for monitoring the etching progress of an APD epitaxial structure, wherein the APD uses an InP material as a substrate, and the surface of the InP material is covered with an InGaAs / InAlAs material, characterized in that: The surface of the InGaAs / InAlAs material is covered with InGaAsP material; The method comprises the following steps: performing photolithography on the APD to form a mask pattern, then immersing the APD in an etching solution for etching, then observing the APD surface, and judging the etching progress according to the APD surface condition, as follows: When the frosted glass phenomenon is observed on the APD surface, it indicates that the etching solution etches to the interface between the InGaAsP material and the InGaAs / InAlAs material; the frosted glass phenomenon is that the APD surface appears grayish white; When the frosted glass phenomenon on the APD surface begins to fade, it indicates that the etching solution begins to etch the interface between the InGaAs / InAlAs material and the InP material; When the APD surface is observed to become smooth and uniform again, it indicates that the InGaAs / InAlAs material has been completely etched; The etching solution is InGaAs / InAlAs etching solution.

2. The method for monitoring the etching progress of the APD epitaxial structure according to claim 1, characterized in that: The thickness of InGaAsP material is ≥50-100Å.

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