JPH04326519A - Etching method of polysilicon on vertical high step-difference - Google Patents

Abstract

PURPOSE:To etch polysilicon on a vertical step-difference without leaving deposit in the vicinity of the step-difference. CONSTITUTION:When poly silicon deposited on a vertical step-difference is etched, a deposition film 3 left in the vicinity of the step-difference is treated by using hydrofluoric acid and eliminated in the course of etching. Supplementary etching is performed in succession, thereby eliminating polysilicon residue 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dry etching polysilicon used in the manufacturing process of electronic devices and the like.

0002

[Prior Art] Conventionally, the steps of a Si device with a step structure have a gentle structure, and when polysilicon deposited on the entire surface of the step is dry-etched with halogen gas, additional etching is required to avoid leaving residue on the side walls of the step. Even if the process was carried out as is, there was no problem of formation of a fence-like deposited film near the step sidewall. However, as the degree of integration increases, the step structure of the device becomes almost vertical, and if additional etching is performed to avoid leaving residue on the sidewalls of the step, as shown in FIG. A fence-shaped deposited film 3, which is presumed to be an oxide film, is formed at a distance about the same as the thickness of the polysilicon film, and as a result, polysilicon residue 4
becomes more likely to occur.

0003

[Problems to be Solved by the Invention] As the miniaturization of elements progresses, the structure of the device becomes three-dimensional and has a steep step structure, but dry etching of polysilicon grown on the vertical step structure As a result, a fence-like deposited film is formed near the step, resulting in polysilicon residue, which has the disadvantage of lowering the manufacturing yield and reliability of the device. An object of the present invention is to provide a method for etching polysilicon on a vertical high step, which solves the above-mentioned problems.

0004

[Means for Solving the Problems] The present invention selectively etches polysilicon deposited on a step on a semiconductor substrate with an etching gas containing halogen until just before etching is completed, and then etches it with hydrofluoric acid at a predetermined concentration. This method of etching polysilicon on a vertical high step includes etching for a predetermined time and then continuing etching for a desired time using the etching gas to remove polysilicon deposited on the sidewall of the step.

[0005]

[Operation] In the present invention, when dry etching polysilicon deposited on a substantially vertical step with halogen gas, wet etching is performed for a predetermined period of time with hydrofluoric acid at a predetermined concentration immediately before the completion of etching to remove polysilicon residues on the side walls of the step. By removing the deposited film that is considered to be an oxide deposited on the surface, the formation of a fence-like deposited film is prevented. After such treatment, additional dry etching is performed to remove polysilicon residue on the sidewalls of the step, thereby completely etching away the polysilicon on the sidewalls of the step.

[0006]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a cross-sectional view of a sample used in the method of the present invention. For the sample, a Si oxide film is deposited on a silicon substrate 1 by the LPCVD method, then a photoresist layer is formed, a mask is formed by patterning by photolithography technology, and the steps of the Si oxide film are removed by dry etching. 2 was formed. On this step, there is an n+ polysilicon film 5 having a sheet resistance of 20Ω/□, which is made by thermally diffusing phosphorus into polysilicon deposited by the LPCVD method.
+Si oxide film 6, which serves as an etching mask for polysilicon film 5, was formed by photolithography and dry etching. As a dry etching apparatus for etching the n+ polysilicon film 5, a 13.56 MHz cathode couple batch processing type parallel plate etcher was used. HBr gas was used as the etching gas, and the HBr gas was heated at 20S by a mass flow controller.
Etching was performed using CCM flow, a pressure of 7 Pa, and an RF power of 550 W. Immediately before the etching was completed, diluted hydrofluoric acid (H
Wet etching was performed for 2 minutes and 30 seconds using F:H2O=1:400), and then the thickness of the film to be etched was 25 mm in order to remove the polysilicon residue deposited on the side walls of the step.
0% additional etching was performed. In the obtained sample, as shown in FIG. 3, the fence-like deposited film 3 in FIG. 2 was completely removed, and no polysilicon residue was observed on the step sidewalls. The concentration of hydrofluoric acid is HF:H2O=1:200, 1:100
However, the above effects are of course present, and the wet etching time can be changed arbitrarily depending on the concentration of hydrofluoric acid. In this embodiment, n+ polysilicon is used, but the effects of the present invention will not change even if p+ polysilicon or non-doped polysilicon is used. Further, in the present invention, H is added to the halogen gas.
Although Br was used, the present invention is effective even if other halogen gases such as HCl and HF are used. Further, although the dry etching apparatus uses RF high-frequency discharge, the effects of the present invention will not change even if an etching apparatus using discharge with a magnetic field is used.

[0007]

As explained above, according to the present invention, it is possible to prevent the formation of a fence-like deposited film, and the polysilicon on the step sidewalls is completely etched away. Therefore, it is possible to improve device manufacturing yield and reliability for future three-dimensional device structures.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor chip for explaining a conventional etching method.

FIG. 2 is a cross-sectional view of a semiconductor chip for explaining the method of the present invention.

FIG. 3 is a cross-sectional view of a semiconductor chip obtained by the method of the present invention.

[Explanation of symbols]

1 board
2 Step 3 Palisade-like deposited film
4 Polysilicon residue

Claims (1)

[Claims] 1. Selectively etching polysilicon deposited on a step on a semiconductor substrate with an etching gas containing halogen until immediately before etching is completed, then etching with hydrofluoric acid at a predetermined concentration for a predetermined time, and then etching the polysilicon deposited on a step on a semiconductor substrate. 1. A method for etching polysilicon on a vertical high level difference, characterized in that polysilicon deposited on the sidewall of the level difference is removed by continuing etching with a gas for a desired time.