JPH0438133B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for forming ultra-fine patterns, and in particular, the invention relates to a method for forming ultra-fine patterns. The present invention relates to an ultra-fine pattern forming method that makes it possible to form ultra-fine patterns with a width of nm or less with good reproducibility.

[Background of the Invention] Optical and electronic devices with fine structures such as semiconductor integrated circuits, high-speed transistors, and surface acoustic wave devices are becoming more sophisticated and multifunctional year by year, and along with this, pattern widths are becoming increasingly finer. I'm following it. Today, there is a need to establish a method for forming patterns with a width of several tens of nanometers.

Lithography techniques such as ultraviolet ray exposure, electron beam exposure, and There are problems such as swelling of the resist when the resist is thick enough to be used as an etching mask.
It is extremely difficult to form a pattern of 200 nm or less.

In recent years, research has been conducted on methods in which electron beams or ion beams are focused to a diameter of approximately 10 nm to expose resists or directly etch substrates, but it is not possible to increase the beam current in order to focus the beams, and the pattern The disadvantage is that it takes a long time to form.

Recently, a new method for forming ultrafine groove patterns, which is completely different from lithography, has been developed.
This method is proposed in No. 187387 as a "method for manufacturing semiconductor devices." This proposed method will be explained with reference to FIG. Figure 1a shows a cross section of a structure in which a polycrystalline Si layer 2 is deposited on a Si substrate 1, a resist layer 3 is further formed on top of the polycrystalline Si layer 2, and a SiO ₂ film 4 is deposited on top of this using the ECR plasma deposition method. It is a diagram. When this is immersed in a buffered hydrofluoric acid solution, the SiO ₂ film 4 adhering to the sides of the pattern of the resist layer 3 is separated from the SiO ₂ film 4 deposited on other parts.
The structure shown in FIG. 1b is obtained. For example, using CBrF gas
Etch using RIE to form a groove pattern. Characteristics include a simple process, a short time required for pattern formation, and the possibility of forming patterns with a large ratio of groove depth to groove width, so-called aspect ratio.

However, when dry etching the polycrystalline Si layer 2 or the like using this method, a peculiar undercut as shown in FIG. However, due to the unique undercut, it is extremely difficult to completely fill the inside of this groove using a deposition method such as CVD, which is a fatal problem, and it has not been applied to device fabrication.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems in the prior art, and is based on an etching mask that has an inverted trapezoidal cross-sectional shape and an opening hole of an arbitrary width at the bottom, and uses dry etching to make the opening hole width. An object of the present invention is to provide an ultrafine pattern forming method for forming grooves in a processed layer that are faithful to the original pattern. By using the method of the present invention, ultrafine groove patterns with a width of several tens of nanometers can be formed with good reproducibility, and therefore, significant progress can be expected in the development of devices with ultrafine structures.

[Summary of the invention]

A feature of the present invention is that an etching mask layer is formed on the layer to be processed, and the etching mask layer has a cross section of an inverted trapezoid or a similar shape and has an opening hole of an arbitrary width at the bottom, and contains a reactive element as a constituent element. In an ultrafine pattern forming method in which ultrafine grooves are formed in a layer to be processed by dry etching using an etching gas, a thin film whose dry etching rate is higher than that of the etching mask layer and lower than that of the layer to be processed is used. The film thickness is at least G・tanθ ₂ , where G is the width of the bottom of the opening hole and θ ₂ is the larger of the angles of inclination that the slope of the opening hole makes with respect to the surface of the underlying thin film. The etching mask layer is deposited between the layer to be processed and the etching mask layer so that the etching mask layer is thick, and ultrafine grooves are formed in the layer to be processed.

[Embodiments of the invention]

The present invention will be explained below with reference to Examples.

2 P on a Si substrate covered with a 50 nm thick SiO ₂ film.
The ^first sample consisted of a ⁵⁰⁰ nm thick polycrystalline Si film doped with
Two second samples were prepared which were coated to a thickness of 500 nm and heat treated at a temperature of 200° C. for 1 hour. Thereafter, an SiO ₂ etching mask layer having microscopic openings was formed on each surface of these two samples by the following method.

First, a SiO ₂ film was deposited using the ECR plasma deposition method.
It was deposited to a thickness of 500 nm. Subsequently, a resist pattern was formed using ultraviolet lithography, and the SiO ₂ film was etched using reactive ion etching to obtain the structure shown in FIG. 2a. In the figure, 1
4 shows a pattern formed of a Si substrate, 4 a SiO ₂ film, and 3 a resist layer. The ECR plasma deposition method was used under the conditions of SiH ₄ flow rate of 30 SCCM, O ₂ flow rate of 30 SCCM, pressure of 0.26 Pa, and power of 200 W. In addition, the conditions for reactive ion etching are CF ₄ flow rate
33 SCCM, H ₂ flow rate 11 SCCM, pressure 0.67 Pa, and power density 0.32 W/cm ² . The SiO ₂ film 4 was again deposited on the entire surface of the Si substrate 1 including the SiO ₂ film 4 and the resist pattern 3 by using the ECR plasma deposition method to obtain the structure shown in FIG. 2b. At this time, the SiO ₂ film deposited on the edges of the pattern is more fragile than the SiO ₂ film deposited on flat areas, and can be easily selectively removed by etching with a 3% buffered hydrofluoric acid solution for 30 seconds.
Next, when the sample is immersed in acetone, the resist pattern 3 and the SiO 2 film 4 on it are removed, and the resist pattern 3 and the SiO ₂ film 4 on it are removed.
As shown in the figure, the cross section is an inverted trapezoid and the opening width at the bottom is
An etching mask layer having opening holes 5 of 40 nm was formed. For the second sample in which a resist was applied on the polycrystalline Si layer, etching was performed by reactive ion etching using oxygen as a gas until the polycrystalline Si layer was exposed. The conditions for reactive ion etching at this time are O ₂ flow rate
At 20SCCM, pressure 0.13Pa, discharge power 0.3W/ ^cm2 ,
SiO ₂ was hardly etched.

Next, the polycrystalline Si films of the first and second samples were etched by parallel plate plasma etching using CCl ₂ F ₂ as a gas. The results are shown in FIG. Figure 3a shows the direct contact on the polycrystalline Si film 11.
Although this is a sample in which a SiO ₂ etching mask layer 12 is formed, a peculiar undercut is observed in the groove formed in the polycrystalline Si layer 11, and a groove with a rectangular cross section cannot be obtained. On the other hand, FIG. 3b shows a sample in which a SiO ₂ etching mask layer 12 is formed on a polycrystalline Si layer 11 via a resist layer 13.
Although undercuts are observed in the polycrystalline
The groove formed in the Si layer 11 has a width approximately equal to the width of the bottom of the opening in the etching mask layer 12 and has a rectangular cross section.

From the above results, by forming an etching mask layer on the processed layer via a resist layer,
It can be seen that grooves with extremely fine rectangular cross sections can be formed in the processed layer.

The cause of the undercut is thought to be as follows. Ions that are perpendicularly incident on the surface of the sample having an inverted trapezoidal opening are reflected by the side wall of the opening formed in the etching mask layer 22, as shown by symbol A in FIG. It is also incident on the side walls of the groove. On the other hand, electrically neutral radicals undergoing random motion are also incident on the side walls of the groove. Undercuts are caused by this interaction between ions and radicals. The radicals incident on point B in FIG. 4 are limited to those within the range of angle α determined by the shape of the opening in the etching mask layer 22 and moving in the direction of point B. As the angle α becomes larger, the amount of radicals incident on point B increases, and the speed of undercut increases. When point B is near the etching mask, the angle α
is small, the angle α becomes maximum at a certain depth, and the angle α becomes small at a sufficiently deep depth. Correspondingly, an undercut also occurs as shown in FIG. The depth at which the angle α is maximum is a line segment extending the slope of the opening hole of the etching mask layer 22 in the depth direction.
Point E where CC' intersects perpendicular line DD' passing through the edge of the opening hole
It is in the vicinity of . When the depth is twice as deep as point E, undercuts hardly occur. Therefore, in the present invention, it is particularly effective if the thickness of the resist layer 23 deposited between the layer to be processed 21 and the etching mask layer 22 is at least twice the depth of point E in FIG.

The peculiar undercut mentioned above is especially 0.1 μm.
This is noticeable in the following dimension ranges. This can be inferred because, in a pattern with a width of 0.1 μm or more, ions reflected from the side walls of the openings collide with other particles and lose energy before reaching the side walls of the grooves. Therefore, the present invention is particularly effective for pattern formation in the size range of 0.1 μm or less.

In the above discussion of FIG. 4, the inclination angles θ ₁ and θ ₂ of the slope of the opening hole with respect to the upper surface of the resist layer were considered to be approximately equal. However, if the inclination angles θ ₁ and θ ₂ are not equal, , a line segment that is an extension of the slope with the larger slope angle θ ₂ of slope angles θ ₁ and θ ₂
Depth from the bottom layer of the mask determined by the intersection E of CC' and the perpendicular line DD' drawn from the point (or line) where the other mask end that is paired with this mask end is in contact with the upper surface of the resist layer 23 That is, by setting the resist layer 23 to have a film thickness that is at least thicker than G·tanθ ₂ , where G is the width of the bottom of the opening hole, the above-described effect can be produced. Further, in this example, a resist layer 23 was deposited on the layer to be processed 21, but this resist layer 23 had a dry etching rate higher than that of the etching mask layer 22, and a dry etching rate slower than that of the layer to be processed 21. Any material can be used as long as it is a thin film. In addition, as the dry etching method, reactive ion etching, reactive sputter etching, reactive ion beam etching, plasma etching, reactive ion shower etching, etc., which perform etching by the interaction of ions and radicals, can be used. .

〔Effect of the invention〕

As explained above, according to the present invention, ultrafine grooves having a rectangular cross section, particularly a rectangular cross section with a width of 100 nm or less, can be formed with good reproducibility and faithfully to the width of the opening in the etching mask layer. It can be applied to the manufacturing of devices with ultra-fine structures such as semiconductor integrated circuits, optical integrated circuits, high-speed transistors, surface acoustic wave devices, and diffraction gratings, and can significantly accelerate future device development.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a mask pattern having inverted trapezoidal openings according to the conventional method, and a, b, and c indicate the manufacturing order. FIG. 2 is a diagram showing the manufacturing order of the openings used in the present invention. The figures are diagrams for explaining embodiments of the present invention, in which a is a cross-sectional view of a pattern when the present invention is not used, b is a cross-sectional view of a pattern when the present invention is used, and FIG. 4 is a diagram illustrating the undercut phenomenon. <Explanation of symbols>, 1...Si substrate, 2...polycrystal
Si layer, 3... resist layer, 4... SiO ₂ film, 5...
... Opening hole, 11 ... Polycrystalline Si film, 12 ... Etching mask layer.

Claims (1)

[Claims] 1. On the layer to be processed, an etching mask layer having an inverted trapezoidal cross section or a similar shape and an opening hole of an arbitrary width at the bottom is formed, and an etching gas containing a reactive element as a constituent element is used. In an ultrafine pattern forming method in which ultrafine grooves are formed in a layer to be processed using a dry etching method, a thin film having a dry etching rate higher than that of the etching mask layer and a dry etching rate lower than that of the layer to be processed is formed so as to have a film thickness as described above. The bottom hole width of the open hole is G, and the larger of the angles of inclination that the slope of the open hole makes with respect to the underlying thin film surface is θ ₂ , so that the thickness is at least greater than G·tan θ ₂ . A method for forming an ultra-fine pattern, characterized in that the layer is deposited between the layer to be processed and the etching mask layer.