JPS63115336A - Resist hardening process - Google Patents

Abstract

PURPOSE:To prevent a resist damage from occuring during cure process by a method wherein the ultraviolet ray curing of resist pattern during the resist process is performed in the pressurereduced condition. CONSTITUTION:By means of UV-cure processing in pressure-reduced condition, H2O and any residual solvent are removed at the temperature lower than usual and the resist bridge reaction is accelerated effectively to improve the degassing of N2, H2O the residual solvent, etc. The wavelength of ultraviolet rays for UV-cure processing may be the same as that in case of conventional processing. During the UV-cure processing, any water and residual solvent in resist are vaporized sufficiently at the temperature not exceeding 100 deg.C so that a resist resin may be bridge-reacted with a sensitizing solution to harden the resin. The acceptable degassing effect can be achieved at the reduced pressure not exceeding 1 Torr especially 0.5 Torr. Furthermore, the pressure shall be reduced without fail at the initial phase of UV proceeding but the normal pressure may be applicable at the final phase thereof wherein resin hardening has advanced already.

Description

[Detailed Description of the Invention] [Summary] Ultraviolet rays (
By performing UV) curing under reduced pressure, H2O and residual solvent that impede UV curing are removed, and the generation of gases such as Nz and I(zO) generated during light irradiation is promoted, and the resist during the curing process is prevent damage.

[Industrial application field]

TECHNICAL FIELD This invention relates to resist processing, and more particularly, to a method of hardening a pattern in photoresist. - [Prior Art] In the manufacturing process of semiconductor devices, dry etching is performed using a photoresist pattern as a mask in order to etch oxides, polysilicon, aluminum, etc. There is a problem in that the photoresist is heated by reaction heat during dry etching, resulting in a decrease in the accuracy of the resist pattern. As a countermeasure to this problem, as a curing means to improve the heat resistance and dry etching resistance of the photoresist, after forming the resist pattern, UV
- A cure process is performed. This treatment is based on irradiating the resist pattern with ultraviolet rays having a wavelength of 200 to 400 nm to cause a crosslinking reaction of the novolac resin. Such treatment hardens the resist resin and improves its heat resistance and dry etch resistance. Furthermore, it is also known that by heating the resist resin to a temperature of 100° C. or more during or before the curing treatment, water that interferes with the crosslinking reaction can be evaporated from the resist resin to efficiently carry out the reaction.

[Problem that the invention seeks to solve]

The present inventor obtained the following knowledge in the process of researching conventional UV-curing treatment.

If N20 is contained in the resist to be UV-cured, the crosslinking reaction will be hindered and efficient resist hardening will not be possible. Furthermore, it has been found that if the resist is heated to 100 DEG C. or higher in order to carry out UV-curing treatment while evaporating HzO, which interferes with such a crosslinking reaction, the following disadvantages occur.

That is, in recent years, when a resist resin with a low molecular weight is used to improve resolution, the heat resistance of the resist resin becomes low, so that heating at 100° C. or higher causes thermal flow in the resist and deforms the pattern.

Further, even with a resist resin having a normal molecular weight, when the coating film thickness is large, the volume of the resist pattern becomes large and the pattern is easily destroyed, resulting in destruction of the resist pattern.

Furthermore, since the ultraviolet light source used in the UV-cure treatment includes a wavelength sensitive to the resist, naphthoquinone diazide, which is a photosensitizer, is decomposed and N2 is generated. On the other hand, the photocrosslinking reaction proceeds from the resist surface due to the photocrosslinking reaction promoting wavelength (230 to 400 nm in the case of novolac resin) contained in the ultraviolet light source.

Thus, as shown in FIGS. 2 and 3, the resist (1)
The Nz(2) generated as described above accumulates inside the resist pattern that has been hardened by the photo-crosslinking reaction that proceeds from the surface. Figure) will be destroyed. In addition, after UV-curing treatment, further heating (120
℃ or higher), the residual solvent in the resist (ethylene glycol ethyl ether acetate, etc.) will exceed the boiling point (ethylene glycol ethyl ether acetate: boiling point 145℃) and evaporate, causing the resist to evaporate in the same way as when N2 accumulates. It breaks through the hardened portion of the surface and destroys the resist pattern.

[Means for solving problems]

The inventor believes that the above problem is due to the presence of N20 and residual solvent in the resist during UV-curing, and that N2,
We found that this is due to poor gas release of HzO, residual solvent, etc.And by performing UV-curing treatment under reduced pressure, it can be cured at a lower temperature than before.
0, remove residual solvent and effectively promote resist crosslinking reaction, N2. We have completed a method characterized by improving t+□0 and gas release of residual solvent.

Hereinafter, conditions for carrying out the present invention will be explained.

The wavelength of ultraviolet light for UV-curing may be the same as for conventional methods. 1 during UV-curing as in the conventional method.
Although heating may be performed at a temperature of 00°C or higher, even without such heating, the crosslinking reaction between the resist resin and the photosensitive agent can be achieved by sufficiently evaporating water and residual solvent in the resist at a temperature of 100°C or lower. and curing of the resin. There is no particular restriction on the type of resist resin as long as the above-mentioned crosslinking reaction occurs.
The method of the present invention can also be applied to B resists, DUV resists, X-ray resists, and resins. Regarding the molecular weight of the resin, the method of the present invention can be applied to resists made of low molecular weight resins that lack heat resistance when heated to temperatures of 100°C or higher, and resists made of high molecular weight resins. Even when the method of the present invention is applied to resists having high heat resistance, the advantages of improved heat resistance and dry etching resistance can be obtained.

Regarding pressure reduction, which is the most characteristic feature of the present invention, the effect can be obtained at less than 1 atm, but less than 1 torr, especially 0.
A good degassing effect can be obtained at less than 5 torr. Also, depressurization must be performed at the beginning of UV treatment,
At the final stage of the process when the resin has hardened, reduced pressure may not be applied and the process may be carried out at normal pressure.

According to vacuum UV-curing, N20, residual solvent and N
Removal of 2 increases reaction efficiency, so even for resist patterns that require heating in conventional methods, heating may be omitted and UV-curing may be performed at room temperature.

Of course, heating may be performed depending on the thickness of the resist pattern, the type of constituent resin, etc. In this case, the crosslinking reaction proceeds efficiently by the effects of both reduced pressure and temperature.

Note that heating can be performed simultaneously with or after the UV-curing step. On the other hand, if a heating process is performed before the UV-curing process, there is a risk that the resist pattern will be destroyed by the action of the above-mentioned irradiation gas, which is not preferable. The gas that remains in the UV-cure treatment equipment under reduced pressure is air, and even if the air in the UV-cure treatment equipment is replaced with another gas and then the reduced-pressure UV-cure is performed, it will not be as effective as in the case of air. No difference observed.

The present invention will be further explained below with reference to Examples.

〔Example〕

Experiments were conducted using a UV-cure apparatus schematically shown in FIG. In the figure, 3 is a UV lamp, 4 is a hot plate, 5 is a wafer, 6 is a heater, 7 is an exhaust port connected to a vacuum pump (not shown), 8 is a filter, and 9 is a resist pattern.

Pattern 9 of a novolak positive type photoresist having a thickness of 2.0 μm and a pattern size of 10 μm was cured under the following conditions.

Below margin UV-lamp (3): Xe-Hg lamp (illuminance 25,
(0 mw/d, wavelength 350 nm) Reduced pressure state (pressure): 0.1 torr Hot plate (4) Temperature = 80°C Irradiation time: 2 300 sec Reduced pressure UV - In order to examine the heat resistance of the cured resist, the resist pattern 9 was coated. When the deposited wafer 5 was heat-treated at 250° C., no change in the shape of the resist pattern 9 was observed.

For comparison, only the internal pressure under the above conditions was changed to normal pressure, and changes in shape were investigated. As a result, the pattern size locally increased or decreased within a range of 10±3 μm due to a significant change in shape.

Furthermore, using the low pressure UV-cured resist pattern 9 under the above conditions and the resist pattern of the comparative experiment,
When the aluminum pattern was sized by dry etching using RIE (reactive ion etching) using a gas containing boron trichloride and chlorine, only the low pressure UV-cured resist pattern was able to obtain the designed dimensions. Ta.

As is clear from the above experiments, according to the present invention, a resist pattern with excellent heat resistance and dry etching resistance can be formed in an accurate desired shape.

〔Effect of the invention〕

The present invention enhances the effect of UV-curing and promotes crosslinking reactions. Therefore, it becomes possible to form a resist pattern with improved heat resistance and dry etching resistance.

Additionally, the present invention prevents pattern destruction during UV-curing. Therefore, it becomes possible to accurately form a desired fine pattern.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a UV-curing device, and FIGS. 2 and 3 are diagrams illustrating how nitrogen gas accumulates in a resist pattern during UV-curing and destroys the pattern. 3...UV-lamp, 4...Hot plate, 5...Wafer, 6...Heater, 7
...Exhaust port, 8...Filter, 9.
...Resist pattern.

Claims (1)

[Scope of Claims] 1. A resist hardening method, which includes a step of irradiating ultraviolet rays under reduced pressure in a UV curing step of irradiating the resist with ultraviolet rays (UV) after forming a pattern using a photoresist. 2. The resist hardening method according to claim 1, wherein the UV curing step is performed at room temperature. 3. The resist hardening method according to claim 1, wherein the UV curing step is performed at a temperature higher than room temperature and lower than 250°C. 4. The resist hardening method according to claim 2, further comprising the step of heating at a temperature higher than room temperature and less than 300° C. after the UV curing step.