JPH08148468A - Etching method - Google Patents

Abstract

PURPOSE: To protect a substrate against deformation caused by a micro loading effect by a method wherein an N<+> Poly-Si layer is specified in selection ratio to insulating films used under isotropic etching conditions and non-isotropic etching conditions respectively. CONSTITUTION: A film structure is composed of an Si substrate 24, a thermal SiO2 , an N<+> Poly-Si 22, and a resist layer 21, and the N<+> Poly-Si 22 is etched with a Lissajous-electron plasma device which generates high-vacuum plasma by a rotating electric field. First, a natural oxide film is removed, and a main etching operation is carried out under conditions that a selection ratio to an oxide film is kept below 20, a non-isotropic etching is performed under conditions that a selection ratio to an oxide film is kept above 30 or a solid pattern (space section) residual main etching is carried out. Thereafter, all the solid pattern (space section) is etched, and then an overetching is carried out to completely remove the residues under such conditions that a selection ratio to an oxide film is kept above 100.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method, and more particularly to a film as an etching object, which is a film of silicon or a silicon compound.

[0002]

2. Description of the Related Art Dry etching is one of the etching methods that utilizes chemical or physical reactions on the surface of gas phase and solid phase due to ions and radicals existing in plasma.
It is a microfabrication technology that etches a thin film. The most widely used dry etching techniques are reactive ion etching (RIE), electron cyclotron resonance (ECR) that uses a rotating magnetic field, recently inductively coupled plasma (ICP), and Lissajous electron that uses a rotating electric field. There is plasma (LEP) or the like, which causes a reaction by exposing the sample to high-frequency discharge plasma of an appropriate gas to remove a part of the sample surface.

In order to miniaturize dry etching, it is necessary to align the directionality of ions, but for this purpose, it is indispensable to reduce ion scattering in plasma. It is said that it is effective to increase the degree of vacuum and increase the mean free path of the ions in order to align the directionality of the ions.

On the other hand, the dry etching process is particularly important in the manufacture of semiconductor devices, and especially in the formation of the gate electrode which greatly affects the performance of the transistor, the vertical shape, high speed, high selection ratio, high dimension control, etc. Is required. In many cases, a polysilicon-based film is mainly used as the gate electrode material, and the etching method is various. The plasma source for etching is R
IE, ECR, ICP, and LEP are mainstream, and chlorine and bromine gas are mainly used as etching gas. Recently, the demand for silicon-based etching in semiconductor devices has been increasing. 0.25
For fine patterns of μm or less, a high selection ratio (versus resist,
Simultaneous realization of (anti-oxidation film), high dimension control, and vertical etching is required, but it is difficult to achieve this.

In order to achieve the above high-performance etching, a method of changing the condition once during etching is proposed in Japanese Patent Publication No. 2-57701, and the conventional dry etching will be described below.

First, an electrode film on an insulating film on a substrate (for example,
The first etching having a selectivity in the direction perpendicular to the surface of (n ⁺ polySi) is performed to selectively etch it, and this etching is stopped before the insulating film is completely exposed.
Next, after the first etching, the electrode film remaining on a part of the insulating film by the first etching is etched by the second etching in which etching of the insulating film is less likely to occur than in the first etching. Thus, the electrode film (electrode pattern) is selectively formed on the insulating film without etching the insulating film not covered with the electrode pattern.

Recently, a method of dividing the main etching (main etching, the first etching in the above-mentioned conventional example) and over-etching (residual removal etching, the second etching in the above-mentioned conventional example) into a step Has been widely and commonly used for manufacturing semiconductor devices having

Hereinafter, an example of etching by the above conventional method will be specifically described with reference to the drawings.

FIG. 2 is a schematic diagram of a Lissajous-Electron Plasma (LEP) device that uses a rotating electric field in various etching devices to generate a high vacuum plasma. 11
Is a chamber, 12, 13, 14 are side electrodes, 15 is an electrode (sample stage), and 16 is an earth electrode. Using this device system, etching was performed under the conditions shown in Table 2.

[0010]

[Table 1]

FIG. 3A shows a film structure before etching, 21 is a resist, 22 is n ⁺ PolySi, 23 is thermal SiO ₂ , and 24 is a Si substrate. 3 side electrodes 1
A LEP power having a frequency of 54.24 MHz is applied to 2, 13, and 14, and a frequency of 13.5 is applied to the electrode (sample table) 15.
An RF power of 6 MHz was applied. At the time when the first dry etching is completed, there is a micro-loading effect, so that the area around the rough pattern (open portion) is completely etched as shown in FIG. Unetched parts still remain inside the line & space). When the process proceeds to the second dry etching as it is, oxygen gas is added under this condition in order to increase the selection ratio with respect to the thermal SiO _2, and the isotropic etching component becomes dominant, so that finally, as shown in FIG. As shown in), a bite shape is generated inside the line & space.

As described above, according to the conventional method, it is possible to reproduce not only a fine pattern of 0.25 μm or less, which cannot follow high-precision etching but has a remarkable microloading effect, but also a pattern of 0.35 μm level. It is difficult to simultaneously realize high selectivity, high selection ratio, high dimensional control, and vertical etching.

[0013]

In view of the above problems, the present invention does not cause shape defects due to the microloading effect and has good reproducibility. Furthermore, high selection ratio, high dimension control, and vertical etching are performed. An etching method to be realized is provided.

[0014]

In order to solve the above problems, in a substrate having silicon or a silicon compound formed on an insulating film, the silicon or silicon compound not covered with an etching mask is etched. In this case, the first step is to remove the natural oxide film on the silicon or silicon compound, and the second step is to selectively etch the silicon or silicon compound under the condition that the selectivity ratio to the oxide film is 20 or less. The insulating film is completely exposed around the rough pattern (open area),
Also, due to the loading effect, the dense pattern area (line &
In the space part), the bulk part is not completely exposed before the etching, and the third step is to perform the third step under the condition that there is no isotropic etching component with a selectivity ratio to the oxide film of 30 or more (line & space part). ) Is completely exposed and the residue is removed around the rough pattern (open part). The fourth step is overetching around the rough pattern under the condition that there is an isotropic etching component but the selectivity ratio to the oxide film is 100 or more. The etching method is used by dividing into the steps of removing the residue.

Further, in the present invention, it is desirable that the same pressure is applied in all etching steps. Further, it is desirable that the total gas flow rate be the same.

[0016]

According to the present invention, with the above-described structure, the remaining portion around the dense pattern (line & space portion) is etched under the etching condition where the selection ratio with respect to the underlying oxide film is 50 or more and side etching does not occur. The silicon or silicon compound by subjecting the silicon or silicon compound to an overetch condition,
Stable and vertical etching, high selectivity and high dimension control etching are possible.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An etching method according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic diagram of a Lissajous-electron plasma (LEP) apparatus for applying the etching method of the present invention to generate a high vacuum plasma using a rotating electric field. is there.

Using this apparatus, n ⁺ Poly-Si etching was performed. Table 1 shows the etching conditions at that time.

[0020]

[Table 2]

FIG. 1A shows a film structure before etching, 21 is a resist, 22 is n ⁺ Poly-Si, and 23.
Is thermal SiO ₂ and 24 is a Si substrate. The etching conditions are shown in Table 2. LEP power having a frequency of 54.24 MHz was applied to the three side electrodes 12, 13 and 14, and RF power having a frequency of 13.56 MHz was applied to the electrode (sample stage) 15.

First, after removing the natural oxide film, main etching is performed under the condition that the selectivity ratio to the oxide film is 20 or less.
As shown in (4), the rough pattern (open portion) is completely etched, but the dense pattern (inner portion of the line & space) still has an unetched portion.

Next, under the condition that the selective ratio to the oxide film is 50 or more, the etching without the isotropic etching component, that is, the main etching with the remaining dense pattern (space portion) is performed for 15 seconds.
After that, after all the dense pattern (space portion) is etched, overetching is performed to further increase the selectivity with respect to the oxide film to 170 to completely remove the residue.

With such an etching step, the present invention has a step of performing the main etching for etching the unetched portion in the dense pattern portion, so that there is no unetched portion in the overetching. Therefore, even when overetching is performed, a bite-shaped portion does not occur, and a good vertical shape without a constricted shape can be obtained with a high selection ratio. That is, it is possible to perform etching with high accuracy even when an unetched portion is generated due to the microloading effect.

Although the film to be etched is a silicon film in this embodiment, it goes without saying that the same effect can be obtained with a silicon compound film such as polycide.

Further, in order to increase the throughput, it is advantageous to make the pressure and the total flow rate the same in each etching step.

[0027]

As described above, in the etching method according to the present invention, the micro loading effect is canceled and a good vertical shape can be realized under a high selection ratio and a high dimensional control.
Further, according to the present invention, a high-performance gate electrode can be processed and a device with less variation in electrical characteristics can be realized.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of dry etching in an example of the present invention.

FIG. 2 is a schematic structural view of a dry etching apparatus according to the present invention.

FIG. 3 is a schematic sectional view of dry etching in a conventional example.

[Explanation of symbols]

11 Chambers 12, 13, 14 Side Electrodes 15 Electrodes (Sample Stand) Electrodes to which High Frequency Power of 100 MHz is Applied 16 Earth Electrodes 21 Resists 22 n ⁺ Poly-Si 23 Thermal SiO ₂ 24 Si Substrate

[Procedure amendment]

[Submission date] December 8, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

Claims (3)

[Claims] 1. A step of forming silicon or a silicon compound having an insulating film formed on the surface thereof, a step of forming a resist on the silicon or silicon compound, and the step of not covering the resist with the resist as a mask. A first etching step of main etching silicon or a silicon compound, and a selection ratio between the first etching step and the insulating film that is free of isotropic etching components and is 30
The second etching step in which etching is performed under the above conditions, and the third etching step in which etching is performed under the conditions that the isotropic etching component is included after the second etching step and the selection ratio to the insulating film is 100 or more An etching method having: 2. The etching method according to claim 1, wherein the pressures under the first, second and third etching conditions are the same. 3. The etching method according to claim 1 or 2, wherein the total gas flow rates under the first, second and third etching conditions are the same.