JPS61116838A - Formation of resist pattern - Google Patents

Abstract

PURPOSE:To improve rectangularity of section by transferring a mask pattern using near ultraviolet ray beam to a resist film on an Si substrate, giving far ultraviolet ray beam to the entire part and executing the development processing. CONSTITUTION:A positive UV resist film 2 of mixture of novolac resin and orthoquinondiazide is formed on a Si substrate 1. It is baked for 100sec from the rear side of substrate at 70-80 deg.C. Thereafter, the surface is irradiated with near UV ray 4 in the wavelength of 320nm or more through the mask 3 and thereby the resist at the exposing part 2b changes to orthoquinondiazide carboxyl acid. Next, the entire part is irradiated with the far UV beam 5 with wavelength of 320nm of less from the rear surface of substrate 1 while heating at 90-110 deg.C, and the resist of unexposed portion 2a absorbs the far UV beam and shows bridging reaction, lowering solubility to the developer. When developed, only the part 2a remains. According to this structure, rectangularity of resist pattern can be improved very easily.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a method for forming a resist pattern, which is a manufacturing technology for LSIs, etc., and is intended to improve the squareness of the vertical cross-sectional shape of the resist pattern. be.

(Rono) Conventional technology In the ring 2 fin process in LSI manufacturing, a chrome pattern is usually placed on the surface of a glass substrate in order to form the required geometric shape of a resist film on a wafer (semiconductor substrate). We have a method of transferring a resist film onto a semiconductor substrate coated with ultraviolet light (UV light) using something called a mask.

A typical positive 9 UV resist (hereinafter referred to as resist) currently on the market is a mixture of a novolatile resin (polymer) that dissolves in an alkaline solution (developer) and a photosensitizer called orthoquinonediazide. When the resist film is irradiated with UV light, the photosensitive agent orthoquinone diazide reacts as shown in Figure 6, as shown in "MS Photoresin" by Takahiro Tsunoda, published by Printing Society Publishing Department, page 28. finally produces carboxyl e, which has extremely high solubility in alkaline solutions. In addition, orthoquinone diazide acts as an inhibitor of dissolution of the novolak resin in the alkaline g solution, so if the resist film is not exposed to light, it has extremely low solubility in the alkaline solution.

This = the area irradiated with light (exposed area) and the area that is not irradiated (unexposed area)
Current phosphor-fi technology uses the difference in dissolution rate of chromium in a developer to form a resist film geometrically on a substrate. Since a projection exposure method using light is used as a method of exposure, the diffraction phenomenon of light causes the light to wander into areas where it should not be irradiated, and the dissolution rate ratio of the resist (1! Since the ratio (dissolution rate of the exposed area)/(dissolution rate of the unexposed area) is not infinite but finite, the cross-sectional shape of the resist pattern obtained after development is as shown in Figure 4. , and the inclination of the side wall α) with respect to the substrate (S) has an angle θ which is not 90°.

(c) Problems to be Solved by the Invention The LSI manufacturing process consists of forming two # films on a silicon substrate and etching them. It becomes a certain shape. When a resist pattern is formed by coating, exposing, and developing a resist on the surface of the substrate with the steps, the semiconductor substrate (S) has the steps (
When the line of resist film ψ) crosses (support), 1
Because of the angle θ formed by the lIIJ wall, if the height of the step is d, then
A convergence g of 2d/lanθ (Q indicates the line width difference on one side) is caused above and below the step. Setting such a line width poses a serious problem depending on the allowable dimensional accuracy of the device to be manufactured. To date, various multilayer resist methods have been developed as a method for suppressing variations in line width due to step differences, but all of these methods increase the number of steps and reduce throughput, although they provide good dimensional accuracy. In addition, there were drawbacks such as the need for a number of expensive new devices for practical use.

The present invention seeks to provide an economical and effective method for forming resist patterns that eliminates the above-mentioned drawbacks.

2) The method for solving the problem is to transfer a mask pattern onto a resist film on a cowhide substrate using near-ultraviolet light, and then transfer the mask pattern to the part of the resist film to which near-ultraviolet light has been applied (exposed part). ) and the area to which the near-ultraviolet naked light has not been applied (unexposed area) at the same time, far-ultraviolet naked light is applied, and then the resist s is developed.

(e) Effect: When UV light is irradiated onto a resist (a mixture of a novolac resin (polymer) dissolved in an alkaline solution and a photosensitizer called orthoquinonediazide), orthoquinonediazide is converted into ionically dissociated gold and carboxylic acid. Nicum ions are generated, but when irradiated with deep ultraviolet naked light (DUV light), the ions are decomposed i11! Generates highly reactive radicals without causing any damage. (The energy tLt key per photon required to generate radicals is 3.9 eV or more, which corresponds to a wavelength of light < 320 tea (DUV light).) The generated radicals are , causing bonding between the novolac m, and also forming a hologram between radicals, increasing the molecular weight (6). A resist whose molecular weight has increased due to cross-linking has a markedly lower solubility in Gengen Soybean than an unexposed resist.

After applying UVll1￥ light, apply DUViJ to the entire half-body board.
When you hold a party, you can expect the following phenomena.

DU in the exposed area where has changed to carboxylic acid.
Since cross-linking does not occur due to V irradiation, loss-linking can be achieved selectively between the exposed and unexposed areas, or by reducing the dissolution rate of only the unexposed areas.

■ DUv light has a large absorption coefficient for resist.

-1, the register h+ where the intensity of the incident light is 1/10
Han f! i-# calculation, e, length 200-245nm and 275-10nm, 100OA, 255-10n
5000A for m, jsoo for 290-300nm
There are o people. (When forming a resist pattern on a substrate with a large step height, the resist film thickness selected is 15,000.
It is about λ. ) Due to the high absorption of υUv light into the resist, the cross-linking occurs from the boundary circle between the resist film and the semiconductor substrate, and from the resist film and the semiconductor substrate.
As we move towards the boundary curve of the air, the velocity increases due to t(t).In the upper layer of the resist film, the isostatic velocity becomes smaller.

(2) Upon irradiation with DLIV light, new carboxyl d is generated and not destroyed, and the resist film is not exposed to light.

From the above, with DUV irradiation, the dissolution rate ratio of the resist (dissolution rate of the exposed area)/(dissolution rate of the unexposed area) becomes smaller, and the dissolution rate of the exposed area becomes smaller than that of the upper layer of the resist. The angle θ formed by the sidewalls of the pattern after development becomes larger. As a result, line width variation when a resist line crosses a step is considered to be smaller than that obtained by a normal process.

(f) Example Figure 1 shows a process diagram of the zero invention method.A positive UV resist (111il), which is a mixture of a novolac resin and a photosensitizer (orthoquinonediazide), is applied to a semiconductor substrate (1) such as a silicon wafer. For example, 0F manufactured by Tokyo Ohkatai
PR-800CJ' is applied to form a resist film (2) (first step, FIG. 1A). Next, this semiconductor substrate (1) is placed in a direct hot plate baking device! 100° from the back side of the substrate at 70 to 80°C using
Bake for 2 seconds (second step, Figure 1B). The reason why the baking temperature in this baking process is set relatively low (about 90 to 110°C in normal processes) is because the baking process will be performed again in the later process, so it is not necessary to use the same process as in the normal process. This is because the decomposition of the photosensitizer and the volatilization of the solvent in the resist film (2) due to heat become excessive, resulting in a decrease in the sensitivity of the lens to light and a decrease in throughput.

Next, an exposure device using UV light is applied to the resist film (2) of the semiconductor substrate (1) through a mask (3).
) (near ultraviolet light with a wavelength of 320 nm or more).

Mask X3) has a chrome pattern (6b) on the mask substrate (6a), and the part (2a) of the resist film facing this pattern (3b) is not irradiated with UV light, while this pattern exists. UV''L is irradiated to the resist film (2b) opposite to the non-containing part.As mentioned above, orthoquinonediazide is converted to carboxylic acid in the resist film on the front part (2b). On the other hand, no such change occurs in the unexposed portion (2a) (third step, FIG. 1C).

Next, 620 llL stripes were applied to the exposed portion (2b) and unexposed portion (2a) of the resist film (2) on the semi-substrate substrate Ill.
Far ultraviolet naked light (DUv''''Jt, ) smaller than nm!
51, the substrate (1)? Irradiation is performed while heating from the back side (fourth step, FIG. 1D). Although the unexposed area (2a) is not exposed to light by this irradiation with DUV light, it absorbs this DUV light and exhibits a crosslinking reaction, reducing its solubility in the imaging solution. Baking is performed to promote cross-ringing and extend the DUV% processing time to the full time.The baking temperature is important because the softening temperature (beyond this temperature, the resist begins to flow) differs depending on the type of resist. The standard is not determined, but it is 90 to 1 for those commonly used at present.
10°C is suitable. For the fourth step, commercially available D
UV light full surface exposure equipment (FUSI (IN SEMICOND)
MICROLI of DUCTORSYSTEM C0RP
TE PH0TO5TABILIZERMODEL
12 (conducted using SPC etc., D for about 60 seconds
By irradiating with UV light, it is possible to obtain cross ringing in the unexposed portions of the resist film 12). Development is carried out using a developer effective for the UV resist (for example, NMD 2.68%).
) The whole flight is carried out (5th step, fJi diagram E). Only the portion of the resist film on the semiconductor substrate 11) to which the near-UV light has been applied is removed, leaving the unexposed portion. FIG. 2 is a partially enlarged sectional view of the semiconductor substrate after development. In the figure,
The squareness of the resist film is improved compared to the conventional example shown by the broken line. In addition, even if this resist film is placed across the stepped portion on the semiconductor substrate, the width of the resist film above and below the step will not change significantly.

The above-mentioned improvement in squareness can be achieved because cross-ringing of the resist film caused by DUV light lowers the solubility of the original portion and the surface side of the resist film in a developing solution.

(g) Effects of the invention As explained above, the present invention provides
Using a mask to protect the cyst from the outside, apply it to the selected surface, then irradiate the exposed and unexposed areas with deep ultraviolet light at the same time, and remove the surface layer of the unexposed area.
Since the solubility in the developer is reduced, the squareness of the vertical cross section of the resist pattern after development can be improved very easily.In other words, the number of additional steps is 1
Only one DUV irradiation process is required, and the only equipment required for analysis is a DUV irradiation device i+t+.

[Brief explanation of drawings]

S+ Figures A-E are process diagrams of Hon@Meikagayo, Figure 2 is a partial cross-sectional view of the semiconductor substrate after the development process, and Figure 6 is photolysis of the photosensitive agent in the resist film against UV light t! 4 degree diagram, %4
The figure is a vertical cross-sectional view of a resist pattern obtained by a conventional method.
Figure A%Bfl is a flat curved view and a v--2 sectional view of a semiconductor substrate using this resist pattern. 11)...Semiconductor substrate, (2)...Resist film.

Claims (4)

[Claims] (1) A first step in which a resist film is attached on one surface of a semiconductor substrate.
a second step of heating the resist film on the semiconductor substrate; a third step of selectively applying near-ultraviolet light to the resist film according to a pattern on a mask; a fourth step of simultaneously applying far-ultraviolet light to a portion to which near-ultraviolet light has been applied and a portion to which the near-ultraviolet light has not been applied, and removing the portion of the resist film to which the near-ultraviolet light has been applied; A resist pattern forming method comprising: a fifth step of forming a resist pattern; (2) The resist pattern forming method according to claim (1), wherein the fourth step is performed while heating the resist film. (3) The heating conditions in the second step are set at a lower temperature than the heating conditions in the fourth step, and are set at a temperature of 70 to 80 ℃.
The resist pattern forming method according to claim (2), wherein the temperature is set within a range of .degree. (4) The resist constituting the resist film is a mixture of a novolac resin and orthoquinone diazide dissolved in an alkaline solution, and a dye that absorbs ultraviolet light is added thereto. (2) or the resist pattern forming method described in item (3).