Buffered oxidation etching solution for quartz wafer thinning

Abstract

The application relates to a buffer oxidation etching solution for quartz wafer thinning, 10%-20% hydrofluoric acid, 15%-35% ammonium fluoride, 0.1%-5% alcohol compound, 0.1%-2% organic acid, and the balance is ultrapure water. The etching solution is used for maintaining a proper etching rate for the quartz wafer, and the etched quartz wafer has better morphology and etching roughness, and the three-prism structure protrusions existing on the wafer surface after conventional BOE etching are improved.

Description

Technical Field

[0001] This invention belongs to the field of etching solution technology, specifically relating to a buffered oxidation etching solution for thinning quartz wafers. Background Technology

[0002] Quartz crystal is a non-metallic material widely used in various fields. Due to its excellent optical properties, high chemical stability, and good piezoelectric characteristics, quartz crystal is widely used in optics, electronics, chemical industry, aerospace, and watchmaking. In the electronics field, α-configuration quartz is widely used. Its piezoelectric properties are utilized to fabricate quartz crystal oscillators, tuning fork oscillators, filters, and other devices. A key characteristic of quartz crystal is that its frequency is inversely proportional to its thickness; that is, the thinner the crystal, the higher the frequency. However, with the increasingly rapid pace of electronic product development, the frequency requirements for quartz materials are becoming increasingly stringent, necessitating the development of more refined quartz processing methods.

[0003] The thinning processes for quartz materials in quartz resonators mainly include mechanical polishing, wet etching, ion beam etching, and laser processing. Different thinning methods are used for different applications. Wet etching is widely used in the thinning process of quartz wafers due to its advantages of low processing cost and small processing size. Because α-quartz materials have a hexagonal crystal structure, they exhibit anisotropic etching, meaning that the etching rate varies in different directions on the quartz material surface. This leads to many problems such as poor surface morphology uniformity, high etching roughness, and difficulty in controlling the etching rate at different locations. Furthermore, the etching rate varies significantly with factors such as the type, concentration, temperature, orientation angle, and aperture size of the etching solution, making it difficult to predict and monitor the morphology of the etched cross-section. For high-frequency quartz crystals, the wafer thickness is 17µm for 100MHz and approximately 11µm for 150MHz. Thinner quartz wafers have reduced mechanical strength, making them more prone to breakage during processing, and the impact of uneven roughness and etching thickness becomes more pronounced. Because quartz, composed of SiO2, can be etched by HF, BOE etchant, composed of HF and NH4F, is also used in the thinning process of quartz wafers. However, conventional BOE etchant causes triangular pyramidal protrusions on the wafer surface, resulting in poor etching uniformity. Therefore, it is necessary to find a suitable method to improve the above-mentioned shortcomings of BOE etchant in the thinning process of quartz crystals. Summary of the Invention

[0004] In view of the above-mentioned drawbacks of conventional BOE etching solution in thinning quartz wafers, such as poor etching morphology, high roughness, and easy formation of triangular pyramidal protrusions, the present invention aims to provide a buffered oxidation etching solution for thinning quartz wafers. The technical solution of this invention is as follows: A buffered oxide etchant for thinning quartz wafers, the buffered oxide etchant comprising the following components by mass fraction: 10%-20% hydrofluoric acid, 15%-35% ammonium fluoride, 0.1%-5% alcohols, and 0.1%-2% organic acids, with the balance being ultrapure water. Preferably, the buffered oxidation etching solution comprises the following components by mass fraction: 12%-18% hydrofluoric acid, 17%-25% ammonium fluoride, 0.8%-3% alcohols, and 0.8%-1.5% organic acids, with the balance being ultrapure water. Preferably, the hydrofluoric acid is an electronic-grade hydrofluoric acid solution with a mass fraction of 48%-50%.

[0005] Preferably, the ammonium fluoride is an electronic-grade ammonium fluoride solution with a mass fraction of 39%-41%.

[0006] Preferably, ultrapure water refers to ultrapure water with a resistivity of 18 megohms or higher at 25°C.

[0007] Preferably, the alcohol compound includes one or a mixture of several of 1,2-propanediol, triethylene glycol, 1,2-nonanediol, 1,2,3-butanetriol, mestribenzyl alcohol, 1,2,3-butanetriol, and tripentaerythritol. Preferably, the alcohol compound is one or a mixture of several of the following: propionic acid, nonanoic acid, succinic acid, citric acid, 1,3,5-benzenetricarboxylic acid, and ethylenediaminetetraacetic acid. Compared with the prior art, the beneficial effects of the present invention are: 1) Hydrofluoric acid is used to etch quartz wafers, while ammonium fluoride is used to maintain the hydrofluoric acid concentration, stabilize the film etching rate, and improve etching uniformity.

[0008] 2) The addition of acid additives to the etching solution can effectively dissolve the insoluble products generated at the solid-liquid interface during the etching process, reducing the etching micromask and thus achieving excellent etching morphology and low etching roughness. It can also promptly dissolve and transfer the etching products generated at the solid-liquid reaction interface, avoiding the formation of etching product micromasks and further improving the etching uniformity of the quartz surface.

[0009] 3) The addition of alcohol additives to the etching solution can form a uniform adsorption layer at the solid-liquid interface without hindering the reaction, thereby reducing the surface tension of the etching solution while reducing the etching roughness. The alcohol adsorbs onto the Si-OH functional groups on the quartz material, forming an adsorption layer that inhibits hydrofluoric acid etching, thus controlling the corrosion rate of the quartz structure. Simultaneously, an appropriate molecular structure can effectively improve the anisotropic corrosion of the quartz wafer by hydrofluoric acid, thereby reducing pits or protrusions left after etching. Attached Figure Description

[0010] Figure 1 This is a surface morphology image of the quartz wafer to be thinned; Figure 2 This is a surface morphology image of the surface after etching with the etching solution in Example 10; Figure 3 This is a diagram of the surface morphology after etching with the etching solution in Comparative Example 1. Detailed Implementation

[0011] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. These embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0012] First, prepare the etching solution according to its composition and stir for 60 minutes. Place the PFA bottle containing the etching solution into a low-temperature constant temperature bath (50℃) and keep it at that temperature for 3 hours. Then, place the quartz wafer to be etched into the etching solution and slowly stir and etch, recording the etching time with a stopwatch. After etching, observe the morphology of the quartz wafer using a scanning electron microscope and measure the etching roughness using an atomic force microscope.

[0013] Surface tension testing: The surface tension of the etching solution at 25°C was tested using a surface tension meter.

[0014] To better understand the present invention, the content of the present invention will be further described below in conjunction with Examples 1-14 and Comparative Examples 1-6. However, the content of the present invention is not limited to the following examples and comparative examples. Some of the examples and comparative examples conceived in the present invention are shown in Table 1 below.

[0015] Table 1

[0016] The etching rate, etching roughness, and surface tension of the etching solutions prepared for each embodiment and comparative example on the quartz wafers are shown in Table 2.

[0017] Table 2

[0018] Examples 1 to 5 show that the number of functional groups and the chemical structure of additive 1 have a significant impact on the etching rate of the quartz wafer. As the number of hydroxyl groups in additive 1 increases, the etching rate of the quartz wafer gradually decreases from approximately 0.19 μm / min to approximately 0.18 μm / min. Examples 5 and 7 show that the structure of additive 2 itself has a significant impact on the roughness of the quartz wafer after etching; the longer the structure of additive 2, the higher the roughness after etching. Examples 6 to 11 show that the more carboxyl groups additive 2 has, the greater the decrease in roughness after etching, indicating that the etching roughness of the quartz wafer is closely related to the number of carboxyl groups, with the etching roughness ranging from approximately 2.811 nm to 1.411 nm. The combination of tribenzyl alcohol and 1,2,3-butanetriol in additive 1 with 1,3,5-benzenetricarboxylic acid and citric acid in additive 2 can achieve low etching roughness and a low etching rate. Examples 12 to 14 show that further increasing the number of hydroxyl groups in alcohol additives does not necessarily reduce etching roughness. It requires combination with acid additives of different structures to achieve better results. Furthermore, increasing the number of hydroxyl groups also leads to a slight increase in etching rate, possibly due to the thickening of the Si-OH adsorption layer. The experimental results for acid additives are similar to those for alcohols, indicating that etching roughness is not only related to the number of functional groups, but the additive structure also has a significant impact on the etching effect. The lower etching roughness in Example 14 may be due to the ability of ethylenediaminetetraacetic acid (EDTA) to complex metals, which can further reduce the thickness of the micromask on the etched surface.

[0019] The technical solutions of the present invention have been explained through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above specific embodiments to be implemented. Any improvements made by those skilled in the art based on the present invention, or equivalent substitutions for the materials selected in the present invention, fall within the scope of patent protection.

Claims

1. A buffered oxidation etching solution for thinning quartz wafers, characterized in that: The buffered oxidation etching solution comprises the following components by mass fraction: 10%-20% hydrofluoric acid, 15%-35% ammonium fluoride, 0.1%-5% alcohols, 0.1%-2% organic acids, with the balance being ultrapure water; the alcohols include one or a mixture of several of 1,2-propanediol, triethylene glycol, 1,2-nonanediol, 1,2,3-butanetriol, mesitylene alcohol, 1,2,3-butanetriol, and tripentaerythritol; The organic acid is one or a mixture of several of the following: propionic acid, nonanoic acid, succinic acid, citric acid, 1,3,5-benzenetricarboxylic acid, and ethylenediaminetetraacetic acid.

2. The buffered oxidation etching solution for thinning quartz wafers according to claim 1, characterized in that: The buffered oxidation etching solution comprises the following components by mass fraction: 12%-18% hydrofluoric acid, 17%-25% ammonium fluoride, 0.8%-3% alcohols, and 0.8%-1.5% organic acids, with the balance being ultrapure water.

3. The buffered oxidation etching solution for thinning quartz wafers according to claim 1, characterized in that: The hydrofluoric acid is an electronic-grade hydrofluoric acid solution with a mass fraction of 48%-50%. Ammonium fluoride refers to an electronic-grade ammonium fluoride solution with a mass fraction of 39%-41%. Ultrapure water refers to water with a resistivity of 18 megohms or higher at 25°C.

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