RU2313851C2 - Method for removing crystallites from silicon wafer surface - Google Patents

Abstract

FIELD: semiconductor device manufacture; silicon-wafer surface post-oxidation etching, boron and phosphor sublimation.

SUBSTANCE: proposed method for removing crystallites from silicon wafer surface includes pre-oxidation of wafer surface in oxygen environment at temperature of 850 °C for 20 minutes followed by chemical treatment in hydrofluoric acid and ammonium fluoride solution, proportion of ingredients being 1 : 6.

EFFECT: provision for complete removal of crystallites from silicon wafer surface after heat treatment, reduced wafer treatment time.

1 cl

Description

The invention relates to the manufacturing technology of semiconductor devices, in particular to the processes of etching the surface of silicon wafers after operations: oxidation, distillation of boron, distillation of phosphorus. On the surface of the semiconductor wafer after this operation, the formation of a dull appearance and dark dots and dimples under the microscope are observed. This type of defect is called crystallites; they are the reason for the formation of irregular crystals.

Numerous solutions, acids, alkalis are known that are used in technology to remove various types of defects on the surfaces of semiconductor wafers. One of them is the selective Sirtl etch [1], which is used to identify and remove various types of defects: dislocations, packaging defects, lemon slices.

Another etchant [1] is known, which consists of the following components: hydrofluoric acid (HF), nitric acid (HNO ₃ ) and acetic acid (CH ₃ COOH), used to remove crystallites at a ratio of components of 3: 5: 3. Removal time is 45 minutes. The total number of defects is 300 ÷ 10,000 pcs / cm ² .

The main disadvantage of the etchants used is that they do not provide complete removal of crystallites from the surface of the plates, do not provide the opportunity to obtain a smooth, undisturbed surface, and the processing process is time-consuming.

The aim of the invention is the complete removal of crystallites from the surface of the plate after thermal processes and the reduction of the processing time of the plates.

This goal is achieved by conducting preliminary low-temperature oxidation at a temperature of 850 ° C of the surface of the silicon wafer and then etching into a chemical solution until the crystallites are completely removed.

The chemical solution was selected by experimental data and consists of the following components: hydrofluoric acid (HF) and ammonium fluoride (NH ₄ F) in a ratio of 1: 6, and the optimal time of the chemical process (20 minutes) was chosen until the crystallites were completely removed.

The essence of the method lies in the fact that the cassette with semiconductor wafers is loaded into a diffusion furnace and kept in an oxygen environment with an oxygen flow rate of 15 l / h. Then, after unloading, a chemical treatment process is carried out. Then, silicon wafers are loaded into clean cassettes and washed in deionized water and the drying process is carried out in a nitrogen atmosphere. Cleaning control is carried out under a beam of focused light. To do this, control plates are selected from the batch using vacuum tweezers and the number of luminous points is counted, and for counting defects, which include crystallites, a working magnification of the microscope in the range of 100-400 ^{x is} chosen.

Next, determine the diameter of the field of view of the microscope (D) for which:

1) set the object of the micrometer on the microscope stage and direct sharpness;

2) count the number of integer divisions of the scale that fit in diameter;

3) multiply the number of division by the division price of the scale of the micrometer object, equal to 1 × 10 ^-3 cm;

4) determine the area (S, cm ² ) of the eyepiece according to the formula:

After that, the number of defects is counted on the control plates.

EXAMPLE 1

Semiconductor wafers are loaded into a diffusion furnace and incubated in oxygen with an oxygen flow rate of 15 l / h, at a temperature of 850 ° C for 20 minutes. Then, after unloading, a chemical treatment was carried out for 15 min in a solution of hydrofluoric acid and ammonium fluoride in a ratio of 1: 6. Then, silicon wafers were loaded into clean cassettes and washed in deionized water. The drying process was carried out in a nitrogen atmosphere. Cleaning control was carried out under a beam of focused light. The number of defects on the control plates was 130 pcs / cm ² .

The proposed method of crystallite removal using the process of preliminary low-temperature oxidation and etching in a selected chemical solution can reduce the time of the process. Thanks to this method, it is possible to remove completely crystallites from the surface of the plates, makes it possible to obtain a smooth, undisturbed surface, which allows to increase the yield of suitable devices, as well as to improve the surface quality of diffusion and epitaxial structures.

Literature

1. Z.Yu. Gotra. Technology of microelectronic devices. Moscow, “Radio and Communications, 1991, p. 128.

Claims (1)

A method for removing crystallites from the surface of a silicon wafer, including a chemical treatment process, characterized in that the surface of the wafer is pre-oxidized in oxygen at a temperature of 850 ° C for 20 minutes, and then a chemical treatment is carried out in a solution of hydrofluoric acid and ammonium fluoride in a ratio of 1: 6.