JPH058567B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for forming a photoresist pattern, particularly for forming an opening having an inclined sidewall in a thin film such as a silicon oxide film formed on a silicon substrate. The present invention relates to a method of forming a photoresist pattern having sloped sidewalls in the openings of the photoresist coated on the thin film.

2. Description of the Related Art When forming a metal wiring layer in a 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 portions sloped surfaces to prevent breakage. In order to form a contact window or the like in which the side wall is an inclined surface, a method is often adopted in which the side wall of the resist pattern opening for forming the contact window is formed into an inclined surface.

Conventionally, this type of photoresist pattern having sloped side walls has been formed by a forming method as shown in FIG. 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 a heat treatment at a predetermined temperature for a predetermined time. This heat treatment causes a flow in the resist, and as shown in FIG. 2b, an opening 5 having an inclined side wall 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. 2 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 discontinuity 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. It was difficult to control the width.

Incidentally, when heat treatment is applied to a resist layer having a resist opening 7 with a large amount of resist surrounding it and a resist opening 8 with a small amount of resist surrounding it, as shown in FIG. 4a, the resist layer shown in FIG. Although resist openings 9 and 10 with sloped side walls are formed as shown in FIG. In the opening 9 where resist exists, the sidewall slope is gentle and the pattern width becomes narrow, whereas in the opening 10 where a small amount of resist exists around the sidewall, the sidewall slope is steep and the pattern width does not change much. becomes. Further, in this method, since the resist flows in all the openings, it is not possible to selectively process only the sidewalls of specific openings into a sloped surface shape.

Means for Solving the Problems In order to solve the above-mentioned problems, the method for forming a photoresist pattern of the present invention includes forming an opening in a novolac-based photoresist film formed on a substrate, and then forming an opening in a novolak-based photoresist film formed on a substrate. exposing a portion of the photoresist film located near the periphery of the opening including the edge with ultraviolet light having a wavelength of 350 nm or more and 450 nm or less;
In this method, a photoresist pattern is formed by further performing heat treatment at a temperature of 100° C. or higher and 150° C. or lower.

Effect According to this method, only the resist located around the resist opening and exposed to ultraviolet light flows due to the heat treatment. Therefore, if the exposure with ultraviolet light is made selective, it is possible to form a photoresist pattern that is sloped only on the sidewalls of specific openings.

EXAMPLE An example of the method for forming a photoresist pattern of the present invention will be described below with reference to FIG.

First, as shown in FIG. 1a, a silicon substrate 1
A silicon oxide film 12 is grown on the silicon oxide film 12 using a thermal oxidation method, and a novolak-based photoresist manufactured by Tokyo Ohka Co., Ltd. (product number OFPR800) is grown on the silicon oxide film 12.
is applied to form a photoresist film 13, and resist openings 1 are formed in the photoresist film 13 through exposure using a reduction projection exposure device and subsequent development treatment.
form 4. 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. 2b, the photoresist film 1
A photomask 15 that covers the resist opening 14 and has a transparent area facing a predetermined area wider than the resist opening 14 is placed on top of the resist opening 14, and a reduction projection exposure device emits ultraviolet light 1 with a wavelength of 430 nm.
Exposure is performed in Step 6. In the photoresist film 13, the portions exposed to ultraviolet light have lower heat resistance than the unexposed portions. Thereafter, by performing heat treatment at 130° C. for 30 minutes, the photoresist in the area near the periphery of the resist opening 14 and irradiated with ultraviolet light flows out. As a result, a resist opening 17 having an inclined side wall is formed as shown in FIG. 1c.

The part of the above-mentioned novolak photoresist that is not exposed to ultraviolet light has sufficient heat resistance for heat treatment at 130°C for 30 minutes;
When heat treated at ℃ for 30 minutes, the heat resistance deteriorates a little and the resist starts to flow slightly. On the other hand, the heat resistance of the part exposed to ultraviolet light is 120℃.
It flows after heat treatment at 130℃ for 30 minutes. Therefore, as mentioned above, at 130℃
Under the heat treatment condition for 1 minute, the resist opening 14
Only the resist portions located at the periphery and exposed to ultraviolet light flow, and the resist in non-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 ultraviolet light region 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.

Further, by selectively exposing only the periphery of a specific opening pattern by setting the pattern of the photomask 15, only the sidewall of the specific opening in the resist pattern can be formed into a sloped sidewall shape.

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

In the above explanation, the novolak photoresist manufactured by Tokyo Ohka Co., Ltd. (product number OFPR800) was used as an example of the novolak photoresist, but other products such as the novolak photoresist manufactured by Shipley (product number AZ1350J or AZ2400) can also be used.
According to experiments, in AZ1350J or AZ2400,
Resist areas not exposed to UV light at 150℃
After 30 minutes of heat treatment at
It was confirmed that the material began to flow after 30 minutes of heat treatment. Therefore, the heat treatment temperature after exposure to ultraviolet light depends on the type of resist and the sidewall inclination angle.
It is appropriate to set the temperature to 100°C or higher and 150°C or lower.
Note that the wider the exposed resist area and the higher the heat treatment temperature, the easier the resist will flow and the sidewall inclination angle will tend to become smaller. Therefore, the sidewall inclination angle can be controlled by the heat treatment temperature and the width of the resist around the exposed opening.

Although an example has been described in which the resist regions to be exposed to ultraviolet light are selected using a photomask, the resist may be selectively exposed directly to a beam of ultraviolet light.

Effects of the Invention As described above, according to the method for forming a photoresist pattern of the present invention, by controlling the heat treatment conditions and the width of the resist area around the opening exposed to ultraviolet light, the sidewall slope can be increased regardless of the amount of resist around the opening. A resist pattern having a resist opening whose angle and pattern width are controlled with high precision can be formed. Moreover, not only can the sidewalls of all resist openings in the resist pattern be sloped surfaces, but also only the sidewalls of specific resist openings can be sloped, which helps prevent disconnection of the metal wiring layer. A resist pattern can be formed in which the sidewall inclination angle is made gentler in areas where measurement is required, and the sidewall inclination angle is made steeper in areas where precision in pattern width is required, or where there is no inclination.

[Brief explanation of drawings]

FIG. 1 is a process diagram for explaining the method of forming a photoresist pattern according to the present invention, FIG. 2 is a process diagram for explaining a conventional method for forming a resist pattern, and FIG. FIG. 4 is a cross-sectional view showing a contact window of a silicon oxide film formed using a resist pattern formed using a conventional method. FIG. 11...Silicon substrate, 12...Silicon oxide film, 13...Photoresist film, 14...Resist opening, 15...Photomask, 16...Ultraviolet light,
17...Resist opening whose side wall is an inclined surface.

Claims (1)

[Claims] 1. After forming an opening in a novolac-based photoresist film formed on a substrate, a portion of the photoresist film located near the periphery of the opening, including at least a part of the edge, is heated with a wavelength of 350 nm or more and 450 nm.
A method for forming a photoresist pattern, which comprises exposing to the following ultraviolet light and further performing heat treatment at a temperature of 100°C or more and 150°C or less.