JPH02101468A - Fine pattern forming method - Google Patents

Abstract

PURPOSE:To enable a pattern sufficient in resolution to be formed by using a resist higher in the concentration of a photosensitive group in the surface and lower in the lower part in the resist applied on one of the surfaces of a semiconductor wafer. CONSTITUTION:The diazo type photoresist 2 is applied to the semiconductor substrate 1 and the substrate 1 is baked (e) from the reverse side, preferably, at a temperature of >=90 deg.C, and cooled (d) by dry air, preferably, at a tempera ture of <=23 deg.C from the surface time, resulting in forming the layer higher in the upper part 3 in the concentration of the photosensitive group and lower in the upper part 3 in the concentration of the photosensitive group and lower in the lower part 4. This resist is exposed to ultraviolet rays l by using a size reduction projection exposure device an a reticle 4. At that time, the contrast of a latent of a reticle pattern formed in the resist pattern is enhanced as com pared to the contrast between the intensities of lights incident on the surface of the resist 2, and a resist pattern 20 is formed by developing the area exposed to light l and removing it, thus permitting the contrast in the resist pattern to be enhanced and a pattern high in resolution to be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for forming a fine pattern, and more particularly to a method for forming an island resolution resist pattern.

BACKGROUND OF THE INVENTION Recently, semiconductor devices have become more and more densely packed, and the dimensions of the fine patterns of each element are now 1 micron or less.

Conventionally, as a method for forming a pattern of 1 micron or less, a stepper having a 5x or 10x reduction projection lens is used. A step of forming a resist film on the surface of the substrate in which the concentration of photosensitive groups is distributed such that the concentration of photosensitive groups is higher on the substrate surface side and less near the substrate, and a latent image of the pattern of the semiconductor integrated circuit is formed on the resist film by a light exposure method. 3. A method for forming a fine pattern, comprising a step of generating the resist pattern, and a step of removing the resist in the mJ latent image portion exposed with a predetermined developer, and forming the resist pattern.

e) A patent claim characterized in that a photosensitive group concentration distribution in the resist is formed by applying a resist film to the surface of a semiconductor substrate, cooling the surface of the resist film, and baking the substrate side at a predetermined temperature. The fine pattern forming method according to item 1.

(3) A resist film is applied to the surface of a semiconductor substrate, and a photosensitive group concentration distribution in the resist is formed by irradiating the resist with an electron beam. A reticle pattern consisting of a semiconductor integrated circuit pattern was projected.

FIG. 4 shows how a pattern is formed in a resist using a stepper. As shown in Figure 4, the reticle (
When illumination light 43 is incident on the reticle pattern 41, the black and white pattern 41 formed in the mask) 40 is diffracted into a black pattern portion 44 on the resist surface on the semiconductor wafer, which serves as a light shielding portion on the reticle. Light also enters.

Problems to be Solved by the Invention Due to the entry of such light, exposure to the resist results in a light intensity distribution shown in the mouth 42, and sufficient contrast cannot be obtained. Furthermore, since the light incident on the resist at the same time is absorbed in the resist when propagating within the resist, the amount of light given to the resist differs between the upper layer and the lower layer of the resist. As a result, when the resist exposed by the stepper is developed with a predetermined developer, a trapezoidal pattern 46 corresponding to the light intensity distribution absorbed in the resist is formed, and sufficient resolution cannot be obtained. There was a problem.

As mentioned above, when trying to form a fine pattern of 1 μm or less using a conventional stepper (particularly an excimer stepper), a pattern with sufficient resolution cannot be formed because the contrast of the latent image of the pattern absorbed in the resist is poor. There was a problem.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an improvement in the latent image formed in a resist by reduction projection exposure using a simple process.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention uses a resist coated on one surface of a semiconductor wafer in which the concentration of photosensitive groups is higher on the resist surface and lower on the lower layer. This improves the contrast of the resist pattern after exposure.

Function The present invention makes it possible to accurately form a resist pattern of 1 μm or less with good contrast due to light absorption in the lower layer of the resist by creating a concentration gradient of photosensitive groups in the resist from the resist surface to the lower layer.

Embodiment A first embodiment of the present invention is shown in FIG. A diazo resist 2 (for example, trade name MP1.aoo), which is a photoresist, is applied to a thickness of 1.5 pm on the semiconductor substrate 1 (aJ).
Preferably 23°C from the surface while beta at 00'C
When cooled with dry air as described below, a region 3 with many photosensitive groups and a region 4 with few photosensitive groups are formed (1)). As a result, the photosensitive groups contained in the resist migrate due to crosslinking due to heating and diffusion phenomena in the resist, and the concentration of photosensitive groups on the resist surface becomes higher than that in the lower layer of the resist. Then, this resist is exposed to ultraviolet light e at about 100 mJ/CΔ using a reticle 4 using a reduction projection exposure apparatus. At this time, the contrast of the latent image of the reticle pattern formed within the resist pattern is improved more than the contrast of the intensity of light incident on the resist surface. This is because the concentration of photosensitive groups in the resist has a gradient from the surface toward the lower layer, so that absorption of light intensity in the lower layer of the resist becomes small (internal cell effect).

Then, the resist pattern 20 is formed by developing and removing the exposed portion of the light β (C).

Next, a formula expressing the basic principle of the present invention is shown. Conventionally, the interaction between the photoresist and the irradiation light in photophosphorography has been described using the model proposed by Dill et al. (@Char
activation of PositivaP
photoregist”, I.I.I. Transon Electron Devices (ITLIcIc T
ranson IElactron Devices
) vol KD-22.

&7 P, 445-P, 452, July 19
75) is widely used as a reaction model for diazo resists. This is calculated as follows using the concentration M of naphthoquinone diazizo, which is a photosensitive group in the diazo resist, its light absorption efficiency, the light absorption efficiency B of the base material, and the reaction rate G of the photosensitive group. It is expressed as follows.

Here, 2 is the depth in the vertical direction from the resist surface, and t is the time from the start of exposure. Further, M is the intensity of light and M is the concentration of the photosensitive group. Furthermore, according to Dill et al., the parameters Person, B, and C are as follows.

becomes. Here, ko is the light intensity at the resist surface, τ(
t) represents the light transmittance of the resist, and d represents the film thickness of the resist. Therefore, when a resist having a thickness of d is irradiated with light, M, B, and C can be obtained by measuring the intensity of the light and measuring the change in transmittance over time, that is, the so-called bleaching characteristic.

For a commonly used diazo resist in the ultraviolet region, for example, trade name MP2400 (Shipley), the parameters of mJ A, B, and C are actually measured: = 0.27 (μm), B:= 1.77 (
-μm-1], C-0,0018Cc, A/mJ]
becomes.

As mentioned above, the relationship between light absorption within the resist and photosensitive group concentration is expressed by equation (1), but in the present invention, (1)
) By distributing the photosensitive group concentration gradient from the surface to the bottom surface, absorption of light intensity within the resist can be optimized and the shape of the resist pattern after development can be improved.

Next, a second embodiment of the present invention is shown in FIG. A layer of photoresist (for example, product name MP1400) is applied on the semiconductor substrate 6.
．． Spin code to a thickness of 24 m and pre-bake at 100°C for 12 minutes (a). Next, the electron beam 9 is
is irradiated at 1x1o C/c with an acceleration energy of 20keY. The irradiation amount at this time is the irradiation amount that is not developed by the developer, but due to the influence of backscattered electrons from the substrate, the exposure amount of the resist near the substrate is higher than that of the resist surface.As a result, the photosensitive group concentration on the resist surface side is higher than that on the substrate side. There are also many. In the figure, 7 is a region with a high concentration of photosensitive groups, and 8 is a region with a low concentration (b). Next, 100mJ was applied using a reduction projection exposure device.
When exposed at /ca and developed with a desired developer, a resist pattern 21 with good contrast is formed as shown in the first embodiment.
is formed.

Next, a third embodiment of the present invention will be described. A photoresist 11 (for example, product name MP1400) is applied 1. on the semiconductor substrate 10.
Pre-bake for 2 minutes at 2 μm μm Bispin Code 00'C e). At this time, it is not necessarily necessary to pre-bake. An aqueous solution 12 containing photosensitive groups as the main component (for example, a mixture of diazonium salt in polyvinyl alcohol) is applied on top of the resist, and baguing is carried out at 100'C for 2 minutes to diffuse the photosensitive groups into the resist. A resist 14 and a small resist 13 are used. Conventional reduction projection exposure fR
The film is exposed to light at 150 mJ/cJ and developed with a desired developer. As a result, a resist pattern 22 with good resolution is formed as shown in the first embodiment.

In this embodiment, an aqueous solution containing a photosensitive group as a main component was applied onto the resist, but a solution containing a photosensitive group dissolved in an organic solvent may also be used.

Effects of the Invention As described above, according to the present invention, by adding an extremely easy process, the contrast in the resist pattern in the reduction projection exposure method can be improved and a high-resolution pattern can be formed. This greatly contributes to the production of

[Brief explanation of drawings]

1, 2, and 3 are the first and second embodiments of the present invention, respectively.
．． FIG. 4 is a process sectional view showing the pattern forming method of the third embodiment, and a schematic diagram showing the pattern forming method in conventional reduction projection exposure. 1.6,10... Semiconductor substrate, 2,5.11
...Photoresist, 3. Completion, 14... Part with many photosensitive groups, 4, 8.13... Part with few photosensitive groups, 20.21.22... Pattern after exposure and development. Name of agent: Patent attorney Shigetaka Awano and 1 other person 1st
Figure 4 f゛° - The chief on the mask, the human body 1 blade V to the surface of the tar 7 beresist is distributed e-・Lice- body ↑ light

Claims (4)

[Claims] (1) A process of forming a resist film on the surface of a semiconductor substrate in which the concentration of photosensitive groups is distributed such that the concentration of photosensitive groups is high on the substrate surface side and low near the substrate, and a pattern of a semiconductor integrated circuit is formed on the resist film using a light exposure method. 1. A method for forming a fine pattern, comprising the steps of: generating a latent image; and removing the resist in the latent image portion exposed with a predetermined developer to form the resist pattern. (2) A patent characterized in that a photosensitive group concentration distribution in the resist is formed by applying a resist film to the surface of a semiconductor substrate, cooling the surface of the resist film, and baking the substrate side at a predetermined temperature. A method for forming a fine pattern according to claim 1. (3) A photosensitive group concentration distribution in the resist is formed by coating a resist film on the surface of a semiconductor substrate and irradiating the resist with an electron beam. Fine pattern formation method. (4) applying a resist film on the surface of a semiconductor substrate, applying a solution containing a photosensitive group as a main component on the resist film, and diffusing the photosensitive group into the resist by heating the semiconductor substrate; 2. The fine pattern forming method according to claim 1, wherein a distribution of photosensitive group concentration is formed in the resist.