Buffer oxidation etching liquid for thinning quartz wafer

Abstract

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

Description

Technical Field

[0001] The invention belongs to the technical field of etching solutions, and in particular relates to a buffered oxidation etching solution used for thinning quartz wafers. Background Art

[0002] Quartz crystal is a non-metallic material widely used in many fields. Quartz crystal has many advantages such as good optical properties, high chemical stability, good piezoelectric properties, etc., so it is widely used in optics, electronics, chemical industry, aerospace, clocks and watches and other industries. In the electronics field, α-configuration quartz material is widely used. Its piezoelectric properties can be used to make quartz crystal oscillators, tuning fork crystal oscillators, filters and other devices. The characteristic of quartz crystal material is that its frequency is inversely proportional to its thickness, that is, the thinner the thickness of the chip, the higher its frequency. However, as the speed of electronic product updates and iterations becomes faster and faster, the frequency requirements for quartz materials are getting higher and higher, which requires the industry to develop more sophisticated quartz processing methods.

[0003] The thinning processes of quartz materials in quartz resonators mainly include mechanical grinding, wet etching, ion beam etching, laser processing, etc. Different thinning methods are used for different application scenarios. Wet etching has the advantages of low processing cost and small processing size and is widely used in the thinning process of quartz wafers. Since the crystal form of α-configuration quartz material is hexagonal, it has anisotropic etching, that is, the etching rate in different directions on the surface of the quartz material is different, which will lead to many problems such as poor uniformity of the surface morphology of the etched material, high etching roughness, and difficulty in controlling the etching rate at different positions. It will also cause large differences with different factors such as etching solution type, concentration, temperature, direction angle, opening size, etc., making it difficult to predict and monitor the etching cross-sectional morphology. For high fundamental frequency quartz crystals, the thickness of the 100MHz frequency wafer is 17um, while the thickness of the 150MHz frequency wafer is about 11um. The thinner the quartz wafer, the easier it is to break during processing due to the weakened mechanical strength, and the impact of uneven roughness and etching thickness will be greater. Because quartz composed of SiO2 can be etched by HF, BOE etching solution composed of HF and NH4F is also used in the thinning process of quartz wafers, but conventional BOE etching solution will cause triangular pyramid structure protrusions on the wafer surface, resulting in poor etching uniformity on the wafer surface. Therefore, it is necessary to find a suitable method to improve the above-mentioned shortcomings in the BOE etching solution thinning quartz crystal process. Summary of the invention

[0004] In view of the above-mentioned problems that conventional BOE etching solution for thinning quartz wafers will produce poor etching morphology, high roughness, and easy generation of triangular pyramid structure protrusions, the present invention aims to provide a buffered oxidation etching solution for thinning quartz wafers. The technical solution of the present invention is as follows: A buffered oxidation etching solution for thinning a quartz wafer, the buffered oxidation etching solution comprising the following components by mass fraction: 10%-20% hydrofluoric acid, 15%-35% ammonium fluoride, 0.1%-5% alcohol compounds, and 0.1%-2% organic acid, the balance is ultrapure water. Preferably, the buffered oxidative etching solution comprises the following components by mass fraction: 12%-18% hydrofluoric acid, 17%-25% ammonium fluoride, 0.8%-3% alcohol compounds, and 0.8%-1.5% organic acid, the balance is 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 refers to an electronic grade ammonium fluoride solution with a mass fraction of 39%-41%.

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

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

[0008] 2) The addition of acid additives in the etching solution can effectively dissolve the insoluble products generated at the solid-liquid interface during the etching process, reduce the etching micromask, and thus achieve excellent etching morphology and lower etching roughness. The etching products generated at the solid-liquid reaction interface can be dissolved and transferred in time, 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, and will not hinder the reaction, reducing the surface tension of the etching solution while reducing the etching roughness. Alcohol adsorbs on the Si-OH functional groups on the quartz material to form an adsorption layer that hinders hydrofluoric acid etching to control the corrosion rate of the quartz structure. At the same time, the appropriate molecular structure can effectively improve the anisotropic corrosion of hydrofluoric acid on the quartz wafer, thereby reducing the pits or protrusions left after the etching. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is the surface morphology of the quartz wafer to be thinned; Figure 2 This is the surface morphology after etching with the etching solution of Example 10; Figure 3 This is the surface morphology after etching with the etching solution of Comparative Example 1. DETAILED DESCRIPTION

[0011] The following will be combined with the specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The embodiments described 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 work belong to the protection scope of the present invention.

[0012] First, prepare the etching solution according to the composition, stir and mix for 60 minutes, put the PFA bottle containing the etching solution into a low-temperature thermostatic bath (50°C) for 3 hours, put the quartz wafer to be etched into the etching solution and slowly stir and etch, and record the etching time with a stopwatch. After etching, use a scanning electron microscope to observe the morphology of the quartz wafer, and use an atomic force microscope to measure the etching roughness.

[0013] Surface tension test: Use a surface tension meter to test the surface tension of the etching solution at 25°C.

[0014] For a better understanding of 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, but the content of the present invention is not limited to the following examples and comparative examples. Some embodiments and comparative examples conceived by the present invention are shown in Table 1 below.

[0015] Table 1

[0016] The etching rate, etching roughness and surface tension of the quartz wafer by the etching solutions prepared in various embodiments and comparative examples are shown in Table 2.

[0017] Table 2

[0018] From Examples 1 to 5, it can be seen that the number of functional groups and chemical structure in Additive 1 have a great influence on the etching rate of the quartz wafer. When the number of alcoholic hydroxyl groups in Additive 1 is more, the etching rate of the quartz wafer by the etching solution gradually decreases from about 0.19um / min to about 0.18um / min. From Examples 5 and 7, it can be seen that the structure of Additive 2 itself has a great influence on the roughness of the quartz wafer after etching. When the structure of Additive 2 is longer, the roughness after etching will also be higher. From Examples 6 to 11, it can be seen that the more carboxyl groups in Additive 2, the greater the downward trend of the roughness after etching, indicating that the etching roughness of the quartz wafer is greatly related to the number of carboxyl groups, and the etching roughness is about 2.811nm-1.411nm. After compounding with 1,3,5-benzenetricarboxylic acid and citric acid in Additive 2, both benzyl alcohol and 1,2,3-butanetriol in Additive 1 can achieve a lower etching roughness, and the etching rate is also in a lower range. It can be seen from Examples 12 to 14 that continuing to increase the number of hydroxyl groups in the alcohol additive does not necessarily reduce the etching roughness. It needs to be combined with acid additives of different structures to achieve better results. At the same time, the increase in the number of hydroxyl groups will also lead to a small increase in the etching rate, which may be caused by the thickening of the Si-OH adsorption layer. The experimental effect of acid additives is similar to that of alcohols, that is, the etching roughness is not only related to the number of functional groups, but the structure of the additive also has a great influence on the etching effect. The lower etching roughness of Example 14 may be due to the ability of ethylenediaminetetraacetic acid to complex metals, which can further reduce the thickness of the micromask on the etching surface.

[0019] The technical solution of the present invention is 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 technicians in the relevant field based on the present invention, or equivalent replacement of the materials selected by the present invention, etc., fall within the scope of protection of the patent.

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% alcohol compounds, 0.1%-2% organic acid, and the balance is ultrapure water.

2. The buffered oxidation etching solution for quartz wafer thinning 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% alcohol compounds, and 0.8%-1.5% organic acid, the balance is ultrapure water.

3. The buffered oxidation etching solution for quartz wafer thinning 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 electronic grade ammonium fluoride solution with a mass fraction of 39%-41%; Ultrapure water refers to ultrapure water with a resistivity of 18 megohms or above at 25°C.

4. The buffered oxidation etching solution for quartz wafer thinning according to claim 1, characterized in that: The alcohol compound includes one or a mixture of 1,2-propylene glycol, triethylene glycol, 1,2-nonanediol, 1,2,3-butanetriol, isotribenzyl alcohol, 1,2,3-butanetriol and tripentaerythritol.

5. The method for preparing a porous negative electrode material derived from high silicon slag according to claim 1, characterized in that: The alcohol compound is one or a mixture of propionic acid, nonanoic acid, succinic acid, citric acid, 1,3,5-benzenetricarboxylic acid and ethylenediaminetetraacetic acid.

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