RU2486287C2 - Method to treat surface of semiconductor plates and regeneration of etching solutions - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes etching of semiconductor plates in a bath with a solution NH₄HF₂, continuously injected with a flow of an ozone-oxygen mixture with ozone concentration of 15.9 vol. %, and their flushing with deionised water. Also in the method regeneration of the treated etching solution of NH₄HF₂ is carried out by contact deposition of iron and copper ions at rejected silicon plates, placed into a bath with the specified solution, continuously injected with the ozone-oxygen mixture flow.

EFFECT: invention provides for treatment of a surface of semiconductor plates from metal contaminants, and also makes it possible to create a closed technology of treatment of specified plates and regeneration of treated etching solutions with minimum consumption of chemical agents.

2 cl, 2 dwg, 1 ex

Description

The invention relates to the manufacture of printed circuit boards, specifically to cleaning the surface of silicon semiconductor wafers from metal contaminants and the regeneration of etching solutions, and can be used in radio engineering, electrical and other industries for the separation of metal contaminants from spent etching solutions with the subsequent return of the etching solution to the process.

It is known that the problem of removing various types of contaminants from the surface of semiconductor wafers in the technology for their manufacture is relevant at the present time. One of the important stages is the stage of removing contaminants in the form of molecules, ions and atoms adsorbed from solutions of etchants, deionized water, and organic solvents. The nature and patterns of the adsorption process and the amount of adsorbed impurities in the etching solutions strongly depend on the state of the surface, which is determined by the degree of oxidation and hydration of the surface, the dissolution rate, and the value of the electrode potential. The latter factors depend on the composition and nature of the etchant and the etching conditions. The maximum allowable level of adsorption of impurities on the surface of a semiconductor wafer is ≤10 ^-12 at / cm ² , therefore it is necessary to use reagents with a total content of basic impurities of 10 ^-5 -10 ^-6 % [1].

One of the main difficulties is to maintain this degree of purity during transportation, storage and use of reagents and deionized water.

Another difficulty is the adsorbed impurities of heavy metals (Cu, Fe, etc.) adversely affect the electrophysical characteristics of the surface of semiconductor wafers, which greatly degrades the parameters of semiconductor devices, up to failure.

It is known that to remove impurities of heavy metals from the surface of silicon semiconductor wafers, the following multi-stage scheme is used [2]:

Significant disadvantages of this technology are:

- multi-stage;

- significant energy consumption, since it is required to heat the etching solutions to 100 ° C;

- low efficiency due to the high consumption of hydrogen peroxide as a result of catalytic decomposition at high temperatures;

- significant costs of hydrochloric and nitric acids due to the high volatility of their vapors at high temperatures.

A known method in which the cleaning solution contains water, hydrogen peroxide, an alkaline compound and 2,2-bis- (hydroxyethyl) - (iminotris) - (hydroxymethyl / methane) as a chelating agent. Preferably, the alkaline compound is selected from the group consisting of organic base, ammonia, ammonium hydroxide, tetramethyl ammonium hydroxide, more preferably from the group consisting of ammonia and ammonium hydroxide. The chelating additive is contained in an amount of 1000-3000 ppm (1-3 g / l). The method includes treating the semiconductor substrates with a cleaning solution and drying said semiconductor substrate after washing with water. The technical result is an increase in the stability of the solution at elevated temperature and an increase in the degree of surface cleaning [3].

Disadvantages:

- the use of organic substances environmentally hazardous;

- the complex composition of the etching solutions;

- high material costs;

- complicated and expensive technology for the regeneration of pickling solutions.

The closest in technical essence and the achieved result is a method in which etching solutions of the following composition are used: BHF - 63%, HF - 6%, NH ₄ F - 30%, to remove metal (Cu, Fe) contaminants from the surface of silicon semiconductor wafers [four].

Disadvantages:

- lack of a method (technology) for the regeneration of etching solutions;

- significant costs for the regeneration of pickling solutions.

The objective of the invention is to develop a method for cleaning the surface of semiconductor wafers from metal contaminants and regeneration of spent pickling solution for its subsequent return to production with the regeneration process without additional costs for reagents and electricity.

This task is achieved in that the surface of the semiconductor wafers is cleaned of metal contaminants by etching the semiconductor wafers in a bath with a solution of NH ₄ HF ₂ , a continuously injected stream of ozone-oxygen mixture with an ozone concentration of 15.9%, and their washing with deionized water. The spent NH ₄ HF ₂ etching solution is regenerated by contact deposition of iron and copper ions onto defective silicon wafers placed in the bath with the said solution, continuously injected with an ozone-oxygen mixture stream.

Example

Samples of silicon wafers are placed in a bath with a solution of NH ₄ HF ₂ , a continuously injected stream of ozone-oxygen mixture with an ozone concentration of 15.9%. After 20 minutes, the samples are removed from the bath and washed with deionized water.

The surface of silicon samples was studied by secondary ion mass spectrometry. Figure 1 presents the mass spectrum of the secondary (positive and negative) ions.

The following main fragments with M / e are recorded on the mass spectra of secondary ions: 12 - C ^- ; 13 - CH ^- ; 16 - O ^- ; 17 - OH ^- ; 19 - F ^- ; 24 - SS ⁺ ; 40 - Si-C ⁺ . There are no fragments with M / e: 55.8 - Fe ⁺ , 63.5 - Cu ⁺ .

Thus, the etching solutions of NH ₄ HF ₂ activated by ozone make it possible to clean the surface of silicon wafers from metal contaminants.

After saturation of the etching solution with metallic impurities (Cu ^{+ 2} , Fe ⁺³ ), the spent NH ₄ HF ₂ etching solution is regenerated by contact deposition of iron and copper ions on the defective silicon wafers placed in the bath with the solution, continuously injected with an ozone-oxygen mixture stream. During regeneration, defective silicon wafers are kept in solution for 30 minutes or more. Figure 2 shows the redox potentials of ions Cu ⁺² , Fe ⁺³ in solution with continuous injection of a stream of ozone-oxygen mixture.

The redox potentials of Cu ^{+ 2} ions - curve 1 and Fe ⁺³ - curve 2 in solutions with continuous injection of the ozone-oxygen mixture stream.

As you can see, Cu ^{+ 2} , Fe ⁺³ ions have high electropositive potentials and spontaneously contact deposition on silicon wafers having a more negative potential of -0.4 V. A fairly high thickness of the deposited metals is visually observed.

Thus, a closed-loop technology for cleaning the surface of silicon wafers from metal contamination of Cu ⁺² , Fe ⁺³ and regeneration of spent pickling solutions with a minimum of chemical consumption is proposed.

Used sources

1. O.K. Mokeev, A.S. Romanov. Chemical processing and photolithography in the manufacture of semiconductor devices and integrated circuits. M. Higher School, 1986

2. T. Takebe // J. Electrochem. Soc. 1992, v. 139, p. 1195.

3. Berner Mark, Kilian Rudolph, Rain Rudolph, Arnold Lucius, Schuster Michael, Leopold Alexander. Patent No. 23219298, C11D 7/18, "Surface treatment of semiconductors and the mixture used in this", publ. 07/20/2008.

4. T. Ohmi, J. Electrochem. Soc. 1992, v. 139, p. 3317, “Metallic impurities segregation at the interface between win Si water and liquid during wet cleaning”.

Claims (2)

1. A method of cleaning the surface of semiconductor wafers from metal contaminants, including etching the semiconductor wafers in a bath with a solution of NH ₄ HF ₂ , a continuously injected stream of ozone-oxygen mixture with an ozone concentration of 15.9 vol.%, And washing them with deionized water. 2. The method according to claim 1, in which the regeneration of the spent etching solution of NH ₄ HF _{2 is} carried out by contact deposition of iron and copper ions on the defective silicon wafers placed in the bath with the solution, continuously injected with a stream of ozone-oxygen mixture.

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