JPS6224628A - Formation of photoresist pattern - Google Patents

Abstract

PURPOSE:To incline the side wall of an opening by a method wherein, after an opening has been formed on a photoresist film which absorbs far ultraviolet ray with specified wavelength, a part other than that near the opening is exposed to ultraviolet ray with specified wavelength, and then the unexposed part is flowed, and the exposed part is heat-treated within the temperature range without flow. CONSTITUTION:A silicon oxide film 12 is formed on a silicon substrate 11, a photoresist film 13 is formed on the film 12, and an opening 14 is formed in the film 13. Then, the upper part of the film 13 is provided with a photomask 15 whose region that is facing a specified region wider than the opening 14 is opaque and undergoes the exposure with far ultraviolet ray 16 with wavelength of 300nm. After that, the photoresist in the region near the opening 14 where no ultravillet ray is directed flows out when being heat-treated at the temperature of 180 deg.C for 30min. As a result of this, an opening section 17 with the side wall as an inclined plane is formed, thereby providing a resist pattern with an opening whose side wall inclination angle and pattern width are controlled with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a photoresist pattern, and more particularly to a method for forming a photoresist pattern having sloped sidewalls at openings in the photoresist.

When a metal wiring layer is formed in a conventional monolithic semiconductor device, breaks tend to occur in the metal wiring layer at gaps such as contact windows. For this reason, a method is often used to improve so-called step coverage by making the side walls of the difference portion sloped to prevent breakage. In order to form a contact window or the like in which the sidewall is a sloped surface, a method is often used in which the sidewall of a resist pattern opening for forming the contact window is formed into a sloped surface.

Conventionally, this type of photoresist pattern with sloped side walls has been formed by a forming method as shown in FIG.
It was being done. First, a photoresist film 3 is formed over the entire area of a silicon oxide film 2 covering a silicon substrate 1, and then an opening 4 having vertical side walls is formed using a photoresist film through exposure using a reduction projection exposure device and subsequent development processing. This photoresist pattern is then subjected to heat treatment at a predetermined temperature for a predetermined period of time. This heat treatment causes a flow in the resist, and as shown in FIG. 2(b), an opening 6 whose side wall has an inclined surface is formed. By using the photoresist with the side wall of the opening as a sloped surface as a mask and performing reactive ion etching with the same etching rate for the photoresist film and the silicon oxide film and under anisotropic etching conditions, the etching process shown in FIG. A contact window 6 having a sloped sidewall as shown in FIG. 1 is formed in the silicon oxide film 2.

If a metal wiring layer is formed in a semiconductor device having such a contact window, there will be no disconnection because the difference portion is an inclined surface, and good step coverage of the metal wiring layer can be maintained.

Problems to be Solved by the Invention However, in such conventional methods of forming photoresist patterns, the pattern is formed by causing the entire resist to flow through heat treatment. width) was difficult to control.

Next, as shown in FIG. 4(,), when heat treatment is applied to the resist layer having resist openings 7 around which a large amount of resist exists and resist openings 8 around which a small amount of resist exists, a fourth As shown in Figure (b), resist openings 9 and 10 with sloped side walls are formed, but the amount of resist that flows into the openings during heat treatment varies depending on the amount of resist around the openings. In the opening 9, where there is a large amount of resist around the opening, the sidewall slope is gentle and the pattern width is narrow.On the other hand, in the opening 1o, where there is a small amount of resist around the opening, the sidewall is steep and the pattern width is narrow. The result is a resist pattern that does not change much.Also, with this method, the resist flows in all the openings, so it is not possible to selectively process only the side walls of specific openings into a sloped surface shape. Ta.

Means for Solving the Problems The method for forming a photoresist pattern of the present invention to solve the above problems involves forming an opening in a photoresist film formed on a substrate that strongly absorbs deep ultraviolet light with a wavelength of 300 nm or less. After forming a portion, the photoresist film portion located in a portion excluding the vicinity of the periphery of the opening including at least a part of the edge thereof is exposed to ultraviolet light having a wavelength of 300 nm or less, and then the far ultraviolet light is exposed to ultraviolet light having a wavelength of 300 nm or less. In this method, a photoresist pattern is formed by performing heat treatment in a temperature range in which the photoresist portion that is not irradiated flows and the photoresist portion that is irradiated with the deep ultraviolet light does not flow.

According to this method, the heat resistance of the resist in the portions irradiated with deep ultraviolet light is improved, so that only the resist located around the resist openings and not exposed to deep ultraviolet light is 70-treated by heat treatment. Therefore, if the exposure with deep ultraviolet light is made selective, it is possible to form a photoresist pattern in which only the sidewalls of specific openings are sloped. Seventh Embodiment An embodiment of the method for forming a photoresist pattern according to the present invention will be described below with reference to FIG.

First, as shown in FIG. 1(, ), a silicon oxide film 12 is grown on a silicon substrate 11 using a thermal oxidation method, and a novolac-based photoresist manufactured by Tokyo Ohka Co., Ltd. (product number 0FPRsoo) is applied on the silicon oxide film 12. is applied to form a photoresist film 13, and exposed using a reduction projection exposure device;
Through the subsequent development process, resist openings 14 are formed in the photoresist film 13. Since a reduction projection exposure device is used as the exposure device, the resist opening 14 has a cross-sectional shape in which the side walls are nearly vertical.

Next, as shown in FIG. 2(b), the photoresist film 13
A photomask 15 that covers the resist opening 14 and has an opaque region facing a predetermined region wider than the resist opening 14 is placed on top of the resist opening 14, and is exposed to deep ultraviolet light with a wavelength of 300 nm using a 1/1 projection exposure device. Exposure is performed with light 16.

In the photoresist film 13, the portion exposed to deep ultraviolet light has improved heat resistance compared to the unexposed portion. After this, 18
By performing heat treatment at 0° C. for 30 minutes, the photoresist in the area not irradiated with deep ultraviolet light flows out near the resist opening 140. As a result, a resist opening 17 having an inclined side wall is formed as shown in FIG. 1(c).

Note that the portion of the novolac photoresist exposed to deep ultraviolet light has sufficient heat resistance to heat treatment at 27C) for 30 minutes. On the other hand, the heat resistance of the portion not exposed to deep ultraviolet light is improved by heat treatment at 180 tl for 30 minutes.

Therefore, under the heat treatment conditions of 180'C for 30 minutes as described above, only the resist portions located around the resist openings 14 and not exposed to deep ultraviolet light flow, and the resist in the exposed portions is not thermally deformed.

Therefore, only the side wall of the selected opening can have an inclined surface shape. Furthermore, by controlling the width of the far-ultraviolet light exposure area of the resist layer around the opening, the inclination angle of the formed sidewall surface and the pattern width of the resist opening can be controlled with high precision.

Furthermore, by selectively exposing the photomask 16 by setting the pattern, only the sidewall of a specific opening in the resist pattern can be formed into a sloped sidewall shape.

In this way, reactive ion etching (RIE) is performed using a resist pattern in which the sidewalls of the openings are sloped.
), a contact window similar to the resist pattern shown in Figure 3 is formed in the silicon oxide film by performing an anisotropic etching process in which the etching rate is the same for the photoresist film and the silicon oxide film. be able to.

In addition, in the above explanation, the novolac photoresist manufactured by Tokyo Ohka Kaiyo Co., Ltd. (product number 0FPR) is used as the novolac photoresist.
800), but novolac photoresists manufactured by Shipley (product number AZ1350T or AZ2400) are used as examples.
) can also be used. According to experiments,
AZ136011! In II or AZ2400, the resist portions not exposed to deep ultraviolet light were heated to 30°C at 160°C.
After heat treatment for 30 minutes, the resist portion begins to flow slightly, while the resist portion exposed to deep ultraviolet light does not change shape even after heat treatment at 270° C. for 30 minutes. Therefore, the heat treatment temperature after exposure to deep ultraviolet light is appropriately set to 100° C. or higher and 150° C. or lower depending on the type of resist and the side wall inclination angle. In addition, there is a large resist area that is not exposed to deep ultraviolet light.
The higher the heat treatment temperature, the easier the resist flows, and the sidewall inclination angle tends to become smaller. Therefore, the sidewall inclination angle can be controlled by the heat treatment temperature and the width of the resist around the opening that is not exposed to deep ultraviolet light.

Note that the selection of resist areas that will not be exposed to deep ultraviolet light is
Although an example has been described in which the photomask is used, the resist may be selectively exposed directly to an ultraviolet beam.

Effects of the Invention As described above, according to the photoresist film (turn formation method) of the present invention, the amount of resist around the opening can be influenced by controlling the heat treatment conditions and the width of the resist area around the opening that is not exposed to deep ultraviolet light. It is possible to form resist layer turns with resist openings whose sidewall inclination angles and pattern widths are controlled with high precision. Of course, only the sidewalls of specific resist openings can be sloped, so in places where it is necessary to prevent disconnection of the metal wiring layer, the sidewall slope angle is made gentler, and the precision of the pattern width can be improved. Where necessary, the sidewall inclination angle can be made steep, or a resistive turn can be formed with no inclination.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the photoresist film (turn formation method) according to the present invention in the order of processing steps; FIG. 2 is a cross-sectional view of the photoresist film (turn formation method) of the present invention; FIG. 4 is a cross-sectional view showing a contact window of a silicon oxide film formed using a resist pattern with sloped sidewalls. FIG. It is a sectional view for explaining that the turn changes. 11...Silicon substrate, 12...Silicon oxide film, 13...Photoresist film, 14.
...Resist opening, 16...Photomask, 16...Deep ultraviolet light 117...Resist opening whose side wall is an inclined surface.

Claims (1)

[Claims] After forming an opening in a photoresist film formed on a substrate that strongly absorbs deep ultraviolet light with a wavelength of 300 nm or less, The photoresist film part has a wavelength of 3
The photoresist pattern is exposed to deep ultraviolet light of 00 nm or less, and further heat-treated at a temperature range in which the photoresist portions not exposed to the far ultraviolet light flow and the photoresist portions exposed to the far ultraviolet light do not flow. Formation method.