JPH0821533B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention aims to improve the resolution and contrast of a resist in a resist mask forming step of a semiconductor device manufacturing process to form a fine resist pattern having a high aspect ratio. A method of manufacturing a semiconductor device is provided.

2. Description of the Related Art Conventionally, a resist pattern is generally formed by applying a single-layer photoresist on a substrate and performing an exposure / development process. In this method, since the exposure amount and the film reduction amount of the unexposed portion have a gradient in the depth direction of the resist, the resolution is low and the resolution required in the current VLSI process cannot be obtained. As a high-resolution process that replaces the single-layer photoresist, the multi-layer resist method and CEL (Contras
t Enhanced Lithography) process is under consideration.

Problems to be Solved by the Invention However, these new processes have a problem in terms of mass productivity, in addition to complexity of steps and poor stability.

The present invention is intended to solve the above problems,
The present invention provides a method for manufacturing a semiconductor device, which maintains the simplicity of the single-layer resist method, improves the contrast of the resist, and stably forms a resist pattern having a high aspect ratio.

Means for Solving the Problems In order to solve the above problems, the present invention applies a novolac resin-based positive photoresist to the semiconductor substrate main surface,
While holding the semiconductor substrate at 80 ° C or higher and 130 ° C or lower,
This is a method for manufacturing a semiconductor device in which the photoresist is entirely irradiated with far-ultraviolet light having a wavelength range of 200 nm to 320 nm, exposed to a normal pattern, and then developed.

Effect According to the present invention, the boundary portion between the exposed portion and the non-exposed portion of the positive resist has a solubility gradient with respect to the developing solution due to the diffraction effect of light during normal pattern exposure. However, it is possible to form a fine resist pattern having a high contrast and a high aspect ratio because the inclination in the opposite direction can be given by the irradiation of far-ultraviolet light performed before the normal pattern exposure. .

Examples Details of the present invention will be described with examples. As shown in FIG. 1, a positive photoresist 2 was spin-coated on a silicon substrate 1 to a thickness of 1 μm. After that, baking was performed on the hot plate 3 at 100 ° C. for 60 seconds. Thereafter, as shown in FIG. 2, while the substrate 1 was kept at 100 ° C., far-ultraviolet light irradiation was performed for 2 to 5 seconds. The illuminance at this time was about 10 mw / cm ^{2 as} measured using a 245 nm sensor. Then, as shown in FIG. 3, exposure was performed through a reticle using a stepper having an exposure wavelength of 436 nm and a lens numerical aperture of 0.35. The exposure time at this time was increased by 10 to 30% as compared with the case where light irradiation was not carried out, and then development was carried out by the usual static paddle method.
After development, by post-baking at 120 ° C for 90 seconds,
A resist pattern as shown in FIG. 4 was obtained. As the photoresist, a positive photoresist OFPR-5000 manufactured by Tokyo Ohka Co., Ltd. was used, but a similar effect can be obtained if it is a novolak positive photoresist.

Generally, a positive photoresist based on novolac resin contains a photoconductor called PAC (Photo Active Conpaund). This photoconductor inhibits the dissolution of novolac resin in a developing solution, but it is known that when it receives light, it changes into an acid and loses its dissolution inhibiting property in the developing solution. Therefore, in the case of a positive type resist, the resist in the portion that receives light, that is, is exposed, is soluble in the developing solution. However, it is known that this reaction does not occur in all photoconductors in the resist, and that it occurs at about 80 ° C. or lower in air. Chemically, as shown in FIG. 5, the photoconductor contained in the photoresist releases nitrogen to become a ketene by the received light, and further reacts with water present in the air to generate an acid (carboxylic acid). )become. In such a reaction, the acid concentration is high depending on the exposure dose, that is, on the surface of the film, and the acid concentration is low in the deep part of the film, that is, near the substrate surface. On the other hand, due to the diffraction effect of light, the acid concentration at the boundary between the exposed portion and the unexposed portion has a distribution that decreases from the exposed portion to the unexposed portion,
The shape of the resist after development will be determined.

On the other hand, on the other hand, when irradiation with far-ultraviolet light was performed while the substrate was kept at a high temperature of 80 ° C. or higher, the reaction with water as described above did not proceed, and as shown in FIG. The esterification reaction between ketene and the hydroxyl group in the skeleton molecule of the photoconductor proceeds. This reaction is driven by the energy of far-ultraviolet light, but when the entire surface is irradiated from the resist surface, a gradient of the irradiation amount (large near the surface and small near the substrate) occurs in the resist film in the depth direction. Progresses much near the surface. This reaction increases the molecular weight and has the effect of decreasing the solubility during the subsequent pattern exposure.

In the development carried out after the usual pattern exposure, the resist pattern is reduced by the developer in the remaining pattern, and the contrast is generally lowered. As described above, this development occurs because the acid concentration becomes higher on the surface of the exposed portion during pattern exposure and the acid digs into the resist side of the unexposed portion. However, in the present invention, since the solubility in the developing solution can be lowered closer to the surface of the resist, such film loss can be reduced. As a result, it is possible to obtain a high-contrast rectangular pattern in which the shoulder (near the surface) above the remaining pattern is firmly left.

It is not clear why far-ultraviolet light irradiation was effective, but due to its short wavelength, its energy was strong and an esterification reaction that sufficiently offsets the solubility gradient in the developing solution occurred. Infer.

Although one example of the contrast improvement of the photoresist according to the present invention has been shown above, what is important in the present invention is that after applying the positive photoresist of the novolak resin to the main surface of the semiconductor substrate, the substrate temperature is 80 ° C. or higher and 130 ° C. or lower. Far ultraviolet light irradiation is carried out while the above temperature is maintained, and then ordinary pattern exposure and development are carried out. Needless to say, if the photoresist is a novolac-based positive photoresist, the same contrast improving effect can be seen.

Effects of the Invention According to the method of the present invention, in the conventional single-layer resist method, resolution and contrast can be improved, a fine resist pattern can be stably formed with good reproducibility, and its industrial value is high.

[Brief description of drawings]

1 to 4 are process sectional views of an embodiment of the present invention,
FIG. 5 is a diagram showing a state in which the photoconductor contained in the photoresist is converted into a carboxylic acid, and FIG. 6 is a diagram showing an esterification reaction. 1 ... Silicon substrate, 2 ... Photoresist, 3 ... Hot plate, 4 ... Reticle.

Continuation of the front page (72) Inventor Yukio Takashima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electronics Industrial Co., Ltd. (56) Reference JP-A-61-61154 (JP, A)

Claims (2)

[Claims] 1. A novolac resin-based positive photoresist is applied to the main surface of the semiconductor substrate, and the semiconductor substrate is heated to 80 ° C. or higher.
While maintaining at 0 ℃ or less, 200nm ~ 32nm to the photoresist
A method for manufacturing a semiconductor device, which comprises irradiating the entire surface with far-ultraviolet light including a wavelength range of 0 nm, performing normal pattern exposure, and then developing. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the wavelength of irradiation of far-ultraviolet light is shorter than that of normal pattern exposure.