JPH0391233A - Formation of pattern - Google Patents

Abstract

PURPOSE:To improve the accuracy by a method wherein after a lower-layer resist is applied onto a material to be processed and exposed at the circumferential edge part of a wafer, isotropic etching is done to form an undercut under the lower-layer resist prior to formation of an intermediate layer by use of a liquid-layer growing method and the resultant cavity is filled with the lower-layer resist by giving fluidity to the resist through heat treatment. CONSTITUTION:After the surface of a silicon substrate 1 where an aluminum film 2 is formed is spin-coated with a novolak resin 6, pre-baking is done. Next, the substrate is immersed in an etching solution to remove the aluminum film 2 on the circumferential edge part of the silicon substrate and to form a cavity 5 as a result. Then, baking is done to give fluidity to a novolak resin 6 and to fill the cavity with novolak resin 6. After that, the substrate is immersed in a supersaturated solution of silicon oxide so as to form a silicon oxide film 4. Furthermore, after forming a resist layer 7, pattern transfer is effected to form a resist pattern 8. Next, after etching the silicon oxide film 4 by RIE using the resist pattern 8 as a mask, a polymer layer 6 is etched by RIE using the silicon oxide film as a mask, thereby obtaining a pattern 6. Thus, etching from the circumferential edge part of a material to be processed can be prevented and pattern formation of high accuracy becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a pattern forming method, and particularly to the formation of a lithography mask pattern in the manufacturing process of a semiconductor integrated circuit.

(Prior Art) As semiconductor technology advances, semiconductor devices are becoming faster and more highly integrated.

Along with this, the need for finer patterns is increasing, and highly accurate pattern formation is being required.

Current processes use reactive ion etching (RIE) using a photosensitive polymer (resist) pattern as a mask.
) etching the underlying thin film.

Therefore, it is necessary to form a fine resist pattern with a high aspect ratio and with high dimensional accuracy even on a surface with steps.

Therefore, we first flatten the surface and apply a thick resist film for the base to absorb the reflected light from the base.
A process called a multilayer resist method has been proposed in which a high-resolution resist is coated on top of this and patterned.

This method aims to divide the roles assigned to the resist by forming multiple layers.
A resist layer is provided to a thickness of m to flatten the blocking surface step and absorb reflected light from the underlying layer. Then, by forming a high-resolution resist layer on top of this and patterning the base resist layer with this pattern, exposure and development can be performed under ideal conditions separated from the base, resulting in high resolution and good dimensional accuracy. This is to obtain a similar pattern.

This is the basic idea of the multilayer resist method, but the specific methods vary depending on the number of layers and the method of pattern transfer to the underlying layer.

Here, as a typical multilayer process, there is a three-layer resist method in which an intermediate layer is provided between upper and lower resist layers. In this method, pattern transfer from the upper layer to the intermediate and lower layers is performed by two-step reactive ion etching.

Here, the intermediate layer prevents interaction between the upper and lower resist layers,
Its role is to provide pressure resistance to reactive ion etching of the underlying resist layer.

Therefore, as a material for the intermediate layer, an SOG (Spin on glass organic silicon glass) film, which can be formed by a spin coating method, is most widely used.

This method is a fairly stable process compared to other technologies, but because alkyl groups remain in SOG, it does not result in a pure silicon oxide film, and the RIE resistance to the underlying resist is insufficient. It is. For this reason, SOG
There were problems such as the pattern dimensions not being maintained and the RIE processed shape having a taper.

As a means to solve this problem, a method has also been proposed in which a silicon oxide film is formed by immersing it in a supersaturated solution of silicon oxide and using a so-called liquid layer growth method, which allows the formation of a film closer to a silicon oxide film.

In this method, for example, as shown in FIG. 2(a), a lower resist layer 3 is formed on the surface of the workpiece material 2 formed on the surface of the substrate 1, and as shown in FIG. 2(b), When immersing in a liquid layer growth solution to form the silicon oxide film 4 as an intermediate layer, this liquid layer growth solution is acidic (hydrofluoric acid type) and the immersion time is extremely long, at least one hour. [Especially when the material 2 to be applied] is a metal such as aluminum, there is a problem that the liquid layer growth liquid wraps around from the peripheral edge of the substrate and the material to be applied (aluminum layer) 2 is etched. A new birth.

Since the liquid layer growth time takes a long time, approximately 2 hours to grow a 0.2 μm silicon oxide film, the aluminum film is etched away over several mans from the periphery of the substrate, resulting in many defective chips. There was a problem that occurred.

(Problems to be Solved by the Invention) As described above, in the conventional multilayer resist process in which a silicon oxide layer is formed as an intermediate layer by liquid layer growth, the liquid layer growth solution is removed from the peripheral edge of the substrate during the liquid layer growth process. There was a problem that the workpiece material would be etched due to encircling.

The present invention was made in view of the above-mentioned circumstances, and is capable of preventing etching from the periphery of a workpiece in a multilayer resist process using a silicon oxide layer formed by a liquid layer growth method as an intermediate layer, thereby producing a highly accurate pattern. An object of the present invention is to provide a pattern forming method that allows pattern formation.

[Structure of the invention]

(Means for Solving the Problems) Therefore, in the present invention, after applying a lower layer resist to the workpiece exposed at the periphery of the wafer, and prior to forming an intermediate layer resist by a liquid layer growth method, the lower layer is etched by isotropic etching. An undercut is created under the resist, and the resulting cavity is filled by fluidizing the lower resist through heat treatment, so that the workpiece is completely covered with the lower resist.

(Function) According to the above method, when forming the intermediate resist layer by the liquid layer growth method, the workpiece is completely embedded in the lower resist layer, so that the liquid layer growth liquid at the wafer periphery is Penetration is suppressed, and a good intermediate layer can be formed without etching of the peripheral edge of the workpiece.

In this way, since a silicon oxide film grown by liquid layer growth can be used as an intermediate layer, when etching the lower resist layer, the etching resistance in RIE using oxygen plasma is greatly improved compared to the conventional SOG film, resulting in higher precision etching. It becomes possible to perform the following pattern formations.

(Example) Hereinafter, a method for forming a resist pattern according to an example of the present invention will be described in detail with reference to the drawings.

First, as shown in FIG. 1(a), a novolac resin is applied as a first polymer layer to the surface of a silicon substrate 1 on which an aluminum film 2 with a thickness of 0.8 μm is formed by vapor deposition as a base film for pattern formation. 6, rotation speed 400Or
After spin-coding with pm and forming a film with a thickness of 1.5 μm, the temperature was 90°C.

Pre-bake for 10 minutes.

Next, as shown in FIG. 1(b), the silicon substrate was immersed in an etching solution consisting of a mixed solution of phosphoric acid, hydrofluoric acid, and nitric acid for 5 minutes to etch away the aluminum film 2- on the periphery of the silicon substrate. Cavity part 5 due to undercut of lZ m
form.

Next, baking is performed at 200° C. for 20 minutes to give fluidity to the novolac resin 6, fill the cavity, and fill the first
As shown in Figure (C), the ends of the aluminum film 2 are embedded in the novolac resin 6 without being exposed.

Thereafter, as shown in FIG. 1(d), it was immersed in a supersaturated solution of silicon oxide for 2 hours to form a silicon oxide film 4 having a thickness of 0.2 μm.

Furthermore, as shown in FIG. 1(e), an upper resist layer 7 is formed.

After that, as shown in FIG. 1(f), a pattern is transferred to the upper resist layer 7 using a light stepper with light 4 having a wavelength of 436 nm to form a latent image of the mask pattern.
A resist pattern 8 is formed by post-baking and kinging at 5° C. for 90 seconds and development. Next, as shown in FIG. 1(g), using this resist pattern 8 as a mask, 80% by volume of tetrafluor The intermediate silicon oxide film 4 is etched using RIE using a mixed gas of ormethane (CF4) and 20% by volume of oxygen.

Thereafter, as shown in FIG. 1(h), the first polymer layer 6 is etched by RIE using oxygen gas using the intermediate silicon oxide film 4 as a mask to obtain a first polymer layer pattern 6. .

In this way, a highly accurate pattern of 0.4 μm could be obtained on the photomask with great fidelity to the pattern.

By etching the base film by reactive ion etching using the resist pattern thus obtained as a mask, it becomes possible to form a good pattern with extremely high precision.

Further, in the above embodiment, when pattern exposure is performed, a wavelength of 43
Although 6 nm light was used, the K
Desired light may be selected from light in the photosensitive region, such as rF excimer laser light with a wavelength of 248 cm.

〔Effect of the invention〕

As explained above, according to the method of the present invention, after applying the lower resist to the workpiece exposed at the periphery of the wafer, and prior to forming the intermediate layer by the liquid layer growth method, the lower resist is etched by isotropic etching. By creating an undercut at the bottom and filling the resulting cavity by fluidizing the lower resist through heat treatment, the workpiece is completely covered with the lower resist, allowing the height to be faithful to the photomask. It becomes possible to form precision patterns.

[Brief explanation of drawings]

1(a) to 1(h) are diagrams showing the resist pattern forming process according to the method of the embodiment of the present invention, and FIG. 2(a)
FIGS. 2(b) to 2(b) are diagrams showing a resist pattern forming process by a conventional method. 1... Silicon substrate, 2... Aluminum film, 4...
... silicon oxide cavity, 5 ... cavity, 6 ... novolac resin (first polymer layer), 7 ... resist layer, 8
...Resist pattern.

Claims (1)

[Claims] A method for forming a resist pattern on a substrate to be processed includes a lower resist coating step of applying a lower resist onto the substrate on which the processed material has been formed, and a resist pattern to be processed by isotropic etching. an etching process of etching the material to form a cavity by undercutting at the peripheral edge of the substrate; a fluidization process of heating and fluidizing the lower resist to fill the cavity; and forming a silicon oxide film on the lower resist by a liquid layer growth method. an upper layer resist forming step of forming an upper layer resist on the intermediate layer; an upper layer pattern forming step of transferring a pattern to the upper resist and developing it to form an upper resist pattern; an intermediate layer pattern forming step of etching the intermediate layer using the pattern as a mask to form an intermediate layer pattern; and a lower layer pattern forming step of etching the lower resist using the intermediate layer resist pattern as a mask to form a lower resist pattern. Characteristic pattern formation method.