JPS61181131A - Etching method by molecular flow - Google Patents

Abstract

PURPOSE:To enable of non-defect anisotropic etching of silicon or silicon nitride by a method wherein a xenon difluoride molecular flow having a directional property is applied onto a substrate having silicon or silicon nitride on the surface. CONSTITUTION:An etching mask material 11 for xenon difluoride XeF2, such as a silicon dioxide film or a resist film, for instance, is formed on a silicon substrate 12. Next, the etching mask 11 is patterned. Then, a molecular flow 13 of xenon difluoride is applied. The molecular flow of xenon difluoride collides with the silicon substrate and dissociation from the XeF2 to XeF+F occurs thereon. Fluorine is combined with silicon to be SiF4, which is discharged. The silicon substrate 12 undergoes anisotropic etching in the silicon substrate, i.e. the etching depth and side etching thereof, is determined by the characteristics of the molecular flow, i.e. the velocity of the molecular flow and the ratio between an inactive gas, such as an argon gas or a nitrogen gas, used as a carrier gas, and xenon difluoride.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of etching silicon or silicon nitride using a xenon fluoride (xep) molecular stream.

(Prior art and its problems) With the manufacture of ultra-L8I level high-density integrated circuits, miniaturization of patterns is required, and it has become necessary to form patterns with sufficient control of dimensions of 1 μm or less. . In ultra-L8I manufacturing, reactive ion etching is introduced in the entire process.

However, ion irradiation damage has also become a problem.

In device isolation and trench-horizon capacitors in which reactive ion etching is performed on 8i substrates, defects generated by reactive ion etching cause leakage current, which is a major problem. Conventionally, after reactive ion etching, wet etching was performed to remove the defects. However, wet etching has the disadvantage that it is isotropic etching and the controllability of the dimensions is poor.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a method for defect-free anisotropic etching of silicon or silicon nitride.

(Structure of the Invention) According to the present invention, a mask pattern is formed on a substrate having silicon or silicon nitride on the surface, and a directional xenon fluoride molecular flow is irradiated onto the substrate to form a mask pattern on the surface of the silicon or silicon nitride. A method for etching silicon is provided.

(Principle of the Invention) The invention will be described in detail with respect to the case of etching silicon using FIGS. 1(a) to 1(c).

First, Zenon 70Lide (XeFl) is placed on the silicon substrate 12.
), an etching mask material 11, such as a silicon dioxide film or a resist film, is formed (FIG. (a)). Next, the etching mask material 11 is patterned (see (b)).

Next, a molecular stream 13 of xenon 70ride (XePt) is irradiated.

The xenone fluoride (XeF2) molecular stream collides with XeF2 = XeF + F on the silicon substrate and dissociates, and fluorine (7) combines with silicon (8i) to become 8iF4 and is discharged.

The depth of etching and the amount of side etching depend on the characteristics of the molecular flow, i.e., the molecular flow rate and the inert gas such as argon (Ar) gas or nitrogen (r'tt) gas used as a carrier gas and xenon fluoride (XeFl). ) is determined by the ratio of

The method of forming a molecular stream is generally well known, and FIG. 2 shows a schematic diagram of the molecular stream forming apparatus used in the present invention. Argon gas 21, which is an inert gas, is introduced as a carrier gas into a source chamber 22 containing Zenon 70ride (XeFl) 23, and further into a chamber 24. The chamber is divided into 24#, 25, 26, and 3gI/C, and each chamber is separated by orifices 27 and 28. A pressure difference is achieved at the orifices 27, 28, creating a molecular flow. A sample 29 is placed on the sample holder 30 in the chamber nitrogen 26.
is placed. The air chamber 26 is evacuated by a vacuum pump (31). Velocity of molecular flow, Xenon 70lide (XeFl)
) in the carrier gas is determined by the flow rate of the argon carrier gas 21, the diameter of the orifice 27, 28, and the evacuation speed of the vacuum pump.

(Embodiment) FIGS. 3(a) to ω are cross-sectional views showing an embodiment of the present invention.

Currently, the development of highly integrated elements having deep diffusion layer regions, such as complementary FIMO transistors, is progressing. In order to increase the integration of devices having such deep diffusion layer regions, an element isolation method is required that has fine element dimensions and a sufficient element isolation function in the depth direction.

Figure 3 is an example.

First, a Pfi silicon single crystal substrate 3 is used as a semiconductor crystal substrate.
1-, and a silicon dioxide film 32 is formed on its surface by thermal oxidation.
After forming a silicon nitride film 33 and a silicon dioxide film 33A on the surface thereof by the CVD method, the portions other than the groove formation region were covered with a photoresist film 34 ((a)). figure).

Next, using the photoresist film 34 as an etching-resistant mask, the silicon dioxide film 33, the silicon nitride film 33,
The silicon dioxide film 32 is etched away, and the photoresist film 34 and the silicon dioxide film 33 are etched away.
Using A as an etching-resistant mask, the silicon substrate 21 was etched away to form a groove A, and then the photoresist film 34 was removed (FIG. 3B). For etching to form the grooves, reactive sputter etching is used which causes small lateral inward expansion during etching. Next, in order to remove the damage caused by reactive ion etching, molecular flow etching of xenone fluoride using a human carrier was performed ((C)
figure). The substrate is placed close enough to the oriice to use the parallel component of the molecular flow. Since the molecular stream is not a perfectly parallel beam, the sidewalls of the grooves are also slightly etched, and any damage to the sidewalls is removed. Moreover, the mask film 33A
't 33'? Since there is a thickness of 32',
Side wall work.

The etching can be kept small by isotropic etching such as wet etching, and the controllability of dimensions is good. The machining and ching damage to be removed is mainly on the bottom of the groove, and the depth is at most 0.1 μm. In this embodiment, since the molecular flow etching rate is approximately 0.1 μm/min, etching may be performed for 1 minute, and the time required is extremely short. Furthermore, the parallelism of the molecular flow can be further improved by using a nozzle instead of an oriice.

Next, a thin silicon film 3 is formed on the grooved surface by thermal oxidation.
5 is formed, and further, boron B, for example, is ion-implanted as a channel stopper at the bottom of the groove as a conductive impurity, and then thick polycrystalline silicon 36 is formed on the entire wafer by CVD. Filled the gap (Figure (d))
.

Next, the polycrystalline silicon 36 is formed into the silicon nitride film 33'.
The polycrystalline silicon 36' was removed by etching up to the vicinity of the surface, leaving the polycrystalline silicon 36' only in the groove area (Figure (C)).

Next, the silicon dioxide film 33A' was removed by etching (Figure (f)).

Next, using the silicon nitride film 33' as an oxidation-resistant mask, the polycrystalline silicon 36' formed in the trench was oxidized by thermal oxidation to form a thick silicon dioxide film 37 on the top of the trench ((ω diagram)) According to the method described above, there is no defect in grooving, and the dimensional controllability of the groove is also good.

In this embodiment, etching of Si is shown, but the same applies to silicon nitride.

(Effects of the Invention) By using the present invention, defect-free anisotropic etching of silicon or silicon nitride can be achieved.

[Brief explanation of the drawing]

FIGS. 1(a) to 1(c) are cross-sectional views showing the process of molecular flow etching. FIG. 2 is a diagram showing an example of an apparatus for forming a molecular flow. Figures 3 (1) to (- are cross-sectional views showing an example in which molecular flow etching is applied to the formation of grooves for device isolation. Figure 1 (α) Figure 3 (α) (b) (C) 5Pi3 diagram

Claims (1)

[Claims] A mask pattern is formed on a substrate having surface silicon or silicon nitride, and the silicon or silicon nitride is anisotropically etched by irradiating the substrate with a directional xenon fluoride molecular flow. Molecular flow etching method.