CN101972754A - Surface cleaning method after carrying out chemical-mechanical polishing (CMP) on lithium niobate wafer in alkalinity - Google Patents

Abstract

The invention relates to a surface cleaning technique after lithium niobate chemical-mechanical polishing liquor is used to precisely finish and polish a lithium niobate wafer. Water polishing is adopted to achieve the clean of the surface, the main chemical components of water polishing liquor comprise an active agent, a chelant, a corrosion resistance agent and deionized water. After alkaline polishing is just completed, the water polishing liquor is immediately used and a method of large flow amount of water polishing is adopted, thereby washing the residual polishing slurry away and simultaneously rapidly reducing surface tension, forming a monomolecular passive film and leading metal ions to form soluble chelate to cleanly and perfectly polish the surface. The water polishing method has the advantages of low cost, no pollution of environment and no corrosion of equipment.

Description

Surface Cleaning Method of Lithium Niobate Wafer After Alkaline CMP

technical field

The invention belongs to the cleaning technology of wafer surface after CMP, in particular to the technology of obtaining clean surface after basic CMP of lithium niobate crystal.

Background technique

Lithium niobate crystal is a rare artificial crystal like single crystal silicon. Because of its ferroelectric, piezoelectric, pyroelectric, electro-optic, acousto-optic and photorefractive effects, it is widely used in the production of various surface acoustic wave, electro-optic and nonlinear optical devices. In recent years, with the improvement of rare earth doping engineering, domain engineering, and near-stoichiometric crystal growth and post-processing technology, the research on the function and performance of _LiNbO3 waveguide, _LiNbO3 optoelectronic and photonic devices has increased dramatically, making it possible to become Optical silicon materials for key components in the fields of optical communications, military countermeasures, optical data storage, optical gyroscopes, optical remote sensing, and laser technology.

With the development of optoelectronic technology, the demand for lithium niobate crystals to make ultra-precision components is increasing day by day. Such components not only require extremely high precision and extremely low surface roughness, but also require no subsurface damage. Due to the following processing characteristics of lithium niobate crystals: low hardness (Mohs hardness is 5), it is easy to produce wedge crystals with small angles during processing, resulting in sand roads. At the same time, it is prone to defects such as scratches and edge collapse. In particular, latent scratches are not easy to find, and may affect device performance, stability, and reliability during subsequent use, and even cause greater losses; high toughness, slow processing speed; sensitive to temperature, prone to microdomain inversion .

Therefore, in the actual processing and production of _LiNbO3 wafers, problems such as low processing efficiency and yield, and difficult control of processing quality are often prone to occur. At present, the domestic polishing of lithium niobate crystals mostly uses diamond micropowder as an abrasive with a high price, and precision processing is achieved through traditional processing methods. A few of them use polishing liquid for chemical mechanical polishing (CMP), but the effect Unsatisfactory, the former can only reach grade 3, and the latter's surface roughness cannot meet the requirements.

Therefore, in order to meet the needs of making ultra-precision components with lithium niobate crystals, the chemical-mechanical polishing (CMP) technology and post-polishing treatment technology of lithium niobate crystals have become important issues to be solved urgently. As one of the surface treatment technologies, the surface cleaning technology after polishing is particularly important. At present, after mass polishing of lithium niobate wafers, the surface energy of the wafers is high, the surface tension is large, the residual polishing liquid is unevenly distributed, and metal ions are contaminated, which will increase the cost of subsequent processing and reduce the yield of devices.

Contents of the invention

The present invention aims to solve the known problems of high wafer surface energy, high surface tension, uneven distribution of residual polishing fluid, contamination of metal ions and the like after CMP of lithium niobate wafers, and discloses a simple and pollution-free lithium niobate wafer Post-CMP surface cleaning method.

The implementation steps of the surface cleaning method after CMP of the lithium niobate wafer of the present invention are as follows:

(1) Take a certain amount of deionized water, add active agent, chelating agent, corrosion inhibitor while stirring, the addition of active agent is 5-30g/L, the addition of chelating agent is 5-30g/L, the inhibitor The amount of etchant added is 5-30g/L;

(2) After alkaline CMP, use the above-mentioned water agent to perform water throwing cleaning at a flow rate of 1000g/min-4000g/min, and the water throwing time is 30-60s to obtain a clean surface.

The active agent is commercially available FA/O surfactant, Oπ-7((C ₁₀ H ₂₁ -C ₆ H ₄ -O-CH ₂ CH ₂ O) ₇ -H) from Tianjin Jingling Microelectronics Materials Co., Ltd. , Oπ-10((C ₁₀ H ₂₁ -C ₆ H ₄ -O-CH ₂ CH ₂ O) ₁₀ -H), O-20(C _12-18 H _25-37 -C ₆ H ₄ -O-CH ₂ CH ₂ O) ₇₀ -H), a kind of polyoxyethylene secondary alkyl alcohol ether (JFC).

Described chelating agent is to be commercially available FA/O chelating agent of Tianjin Jingling Microelectronics Material Co., Ltd., tetrakis (tetrahydroxyethylethylenediamine) of ethylenediaminetetraacetic acid, and structural formula is as follows:

The corrosion inhibitor is hexamethylenetetramine or benzotriazole, wherein hexamethylenetetramine C ₆ H ₁₂ N ₄ , structural formula:

Benzotriazole C ₆ H ₅ N ₃ , structural formula:

The effect of technology adopted in the present invention is:

After alkaline polishing of lithium niobate crystals, there are problems such as high energy, high surface tension, uneven distribution of residual polishing fluid, and contamination of metal ions on the wafer surface. Immediately after the alkaline polishing is completed, add surfactants, chelating agents, corrosion inhibitors, etc. to the water polishing liquid, and use a large-flow water throwing method to wash away the residual polishing liquid and quickly reduce the surface. Tension, forming a single-molecule passivation film, and allowing metal ions to form soluble chelates, so as to achieve a clean and perfect polished surface.

Beneficial effect and advantage of the present invention:

1. After CMP, choose water agent containing surfactant, chelating agent, composite corrosion inhibitor, etc., and use large-flow water throwing to clean the surface of the wafer, which will not corrode the equipment, and can remove the unevenly distributed polishing solution remaining on the surface of the wafer Rinses away quickly for a clean, perfectly polished finish.

2. The selection of surfactant can quickly reduce the high surface tension of the polished wafer surface, reduce the damaged layer, and improve the uniformity of the wafer surface quality;

3. The selected chelating agent can react with the metal ions remaining on the surface of the chip to form a soluble macromolecular chelate, which is separated from the chip surface under the action of a large flow of water agent.

4. The selected corrosion inhibitor can form a monomolecular passivation film on the surface of the polished wafer, preventing the unevenly distributed polishing solution on the wafer surface from continuing to react with the substrate, and improving the perfection of the polished wafer surface.

Detailed ways

The present invention is further illustrated below with examples.

Embodiment 1: prepare 2000g lithium niobate crystal water-soluble surface cleaning liquid

Take 1800g of deionized water, put in 50g of FA/O surfactant and 40g of FA/O chelating agent while stirring, then weigh 10g of hexamethylenetetramine corrosion inhibitor, dilute it with 100g of deionized water and pour it into the above-mentioned mixture while stirring. liquid. After stirring evenly, 2000g of silicon water-soluble surface cleaning solution is obtained, and the flow rate of 2000g/min is used for water polishing for 60s, and the surface is smooth and free of corrosion.

Embodiment 2: preparation 4000g lithium niobate crystal water-soluble surface cleaning liquid

Take deionized water 3700g, put into Oπ-7 ((C ₁₀ H ₂₁ -C ₆ H ₄ -O-CH ₂ CH ₂ O) ₇ -H) surfactant 70g while stirring, FA/O chelating agent 60g, Then weigh 70g of benzotriazole corrosion inhibitor and dilute it with 100g of deionized water and pour it into the liquid while stirring. After stirring evenly, 4000g of silicon water-soluble surface cleaning solution was obtained. After water polishing at a flow rate of 4000g/min, the surface was smooth and free of corrosion.

Claims (4)

1. a method for cleaning the surface of lithium niobate wafer alkaline CMP, is characterized in that, according to the following steps, carry out (weight wt%): (1) Prepare water throwing liquid: get a certain amount of deionized water, add activator, chelating agent and corrosion inhibitor while stirring, the add-on of activator is 5-30g/L, the add-on of chelating agent is 5- 30g/L, the amount of corrosion inhibitor added is 5-30g/L; (2) After the alkaline CMP of the lithium niobate wafer, use the above-mentioned water polishing liquid to carry out water polishing and cleaning at a flow rate of 1000g/min-4000g/min, and the water polishing time is 30-60s. 2. the surface cleaning method after alkaline CMP of lithium niobate wafer according to claim 1, is characterized in that: the active agent of described step (1) is the commercially available FA/O surfactant of Tianjin Jingling Microelectronics Material Co., Ltd. agent, Oπ-7((C ₁₀ H ₂₁ -C ₆ H ₄ -O-CH ₂ CH ₂ O) ₇ -H), Oπ-10((C ₁₀ H ₂₁ -C ₆ H ₄ -O-CH ₂ CH ₂ O) ₁₀ -H), O-20(C _12-18 H _25-37 -C ₆ H ₄ -O-CH ₂ CH ₂ O) ₇₀ -H) or JFC. 3. The method for cleaning the surface of a lithium niobate wafer after alkaline CMP according to claim 1, wherein the chelating agent in the step (1) is a commercially available FA/O chelating agent from Tianjin Jingling Microelectronics Materials Co., Ltd. 4. The method for cleaning the surface of a lithium niobate wafer after alkaline CMP according to claim 1, characterized in that: the corrosion inhibitor in the step (1) is hexamethylenetetramine or benzotriazole.