JPH0279045A - Resist pattern forming method - Google Patents

Abstract

PURPOSE:To make it possible to perform patterning of a lower resist layer with high accuracy, even in the case that the lower resist layer is a thick layer, by selectively forming a reinforcing layer on the surface part of the lower layer resist, and then subjecting the lower resist layer to patterning through the reinforcing layer as a mask by aeolotropically etching it. CONSTITUTION:A 1st. resist 4 is applied on the surface of a substrate 1 so as to be flattened it, and then the thinner 2nd. resist layer 5 is applied on the surface of the 1st. resist layer 4, and is subjected to patterning, and further impregnated with a cross-linking initiator 6, followed by being irradiated the layer 5 with UV rays. And the 1st. resist 4 is selectively etched through the 2nd. resist layer 5' strengthened by advancing a cross-linking reaction, as the mask by means of an aeolotropic dry etching method. Thus, the resist pattern with high accuracy is formed even on the uneven substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of forming a resist pattern, and particularly to the formation of a fine pattern by a multilayer resist method.

In semiconductor integrated circuits, as the density of semiconductor integrated circuits increases, patterns become finer, and line width and line spacing (line and spacing) increase.
For e), lithography technology is required to form a pattern of 0.5 μm or less, but for e), the unevenness of the substrate surface becomes extremely large due to the multilayered wiring structure, and the photoresist has a fine structure. This makes patterning difficult.

In other words, a resist layer applied to an uneven surface will inevitably have a large thickness, but it is necessary to increase the numerical aperture of the optical system in order to increase the resolution of the optically transferred image. ,
As the numerical aperture becomes larger, the depth of focus becomes shallower, making it impossible to expose a thick resist layer uniformly in the depth direction, making it impossible to improve the dimensional accuracy of the resist pattern.

To realize the 0.5μm rule, l (λ-3650)
In this case, the numerical aperture is 0.45, and a resist pattern with good dimensional accuracy is formed directly on a resist layer thick enough to eliminate the unevenness of the substrate. is almost impossible.

A processing method called a multilayer resist method has been developed as a method to deal with this situation. In this method, a relatively thin upper resist layer is applied over a lower resist layer that has been applied thickly enough to flatten the unevenness of the substrate, and the lower resist layer is patterned using the pattern formed on the upper resist layer as a mask.

With this processing method, the upper layer resist patterned by photolithography can be made thinner, so
The pattern formation accuracy of the upper resist layer is high, and the lower layer resist pattern formed using this as a mask is also high precision.

[Conventional technology]

There are two types of multilayer resist methods: a three-layer method in which an intermediate layer having different etching characteristics is interposed, and a two-layer method in which no intermediate layer is used.

In the three-layer method, by using a material with dry etching resistance for the intermediate layer, it becomes possible to pattern the lower resist layer by anisotropic dry etching such as RIE, which improves pattern accuracy, but the process is complicated.

On the other hand, the two-layer method has a relatively simple processing process, but there are restrictions on the materials and processing methods used, and the pattern accuracy is even worse.The present invention is related to the improvement of the two-layer method.
Here, the conventional technology of the two-layer method will be explained. FIG. 3 is a schematic cross-sectional view showing the steps of a known two-layer resist method, and this drawing will be referred to hereinafter.

As shown in the same figure (al), for example, a polycrystalline Si (poly-Si) layer 2 is partially formed on the surface of the substrate l,
A lower resist 4 is applied thickly to the surface covered with the layer 3 so as to eliminate the difference in level, thereby making the surface flat. The thickness of the lower resist layer is 2 to 3 μm, and its material is, for example, a polymethyl methacrylate (PMMA)-based positive resist. Further, layer 230 is selectively etched using the lower resist pattern formed in the subsequent process as a mask.

After baking the lower resist layer, a positive upper resist layer 5 is applied using a spin code and patterned using photolithography. A novolac type resist is used for the upper layer resist, and its thickness is 0.5 to 1.0 μm.

Next, as shown in tb+ of the same figure, ultra-ultraviolet light (DUV
) when the entire surface is irradiated, the upper layer resist with a large absorption coefficient acts as a mask, and the lower layer resist in areas without a pattern is selectively exposed. By developing this,
As shown in the same figure (C1), a pattern of the lower resist is formed.

[Problem to be solved by the invention]

In the above process, both the upper layer resist and the lower layer resist are made of organic polymer compounds, and dry etching with a high selectivity cannot be performed, so patterning of the lower layer resist has to rely on selective exposure and wet development, which requires pattern accuracy. decline is inevitable.

An object of the present invention is to provide a 2N resist method for patterning a lower resist layer by dry etching, and to provide a processing method that can form a highly accurate resist pattern even on an uneven substrate.

[Means to solve the problem]

In order to achieve the above object, in - of the present invention, a first resist is coated on the substrate surface so that the surface becomes flat, a thinner second resist layer is coated on top of the first resist layer, and then patterned. The second resist is impregnated with a crosslinking initiator and irradiated with ultraviolet light, and the first resist is selected by an anisotropic dry etching method using the second resist, which has been strengthened through crosslinking reaction, as a mask. Etching is performed.

In another aspect of the present invention, a first resist layer is applied to the substrate surface so that the surface becomes flat, a thinner second resist layer is applied thereon and patterned, and then the first resist layer is applied to the substrate surface so that the surface becomes flat. The portions of the first resist that are not covered by resist No. 2 are impregnated with a crosslinking initiator and irradiated with ultraviolet light, and using the portions of the first resist where the crosslinking reaction has progressed and strengthened as a mask, The laminated body of the resist and the second resist is selectively etched by an anisotropic dry etching method.

[For production]

Since the second resist among the two types of resists described above is applied relatively thinly, the original pattern to be transferred in the subsequent process can be formed with high precision by photolithography.

When a novolac resist is used as a resist impregnated with a crosslinking initiator and 41 azidobiphenyl sulfide is used as a crosslinking initiator, both dissolve in a common solvent, and 4°azidobiphenyl sulfide It is possible to impregnate a novolak resist.

When this is irradiated with ultraviolet light, a crosslinking reaction progresses in the novolak resist due to the action of 4'azidobiphenyl sulfide, forming a strong layer that is resistant to oxygen plasma, so that the crosslinked layer pattern R with mask
IH makes it possible to etch the resist in which the crosslinking reaction has not progressed. Since RIE has remarkable anisotropy, the upper layer pattern is accurately transferred to the lower resist.

In the first invention of this patent application, a cross-linking reaction is caused to proceed on a resist patterned by photolithography, and this is used as a mask for RIB to selectively etch the lower resist. The pattern is used as a mask when impregnating the lower resist with a crosslinking initiator, and the reinforced portion of the lower resist formed complementary to the pattern of the upper resist is subjected to RI.
It is used as a mask for selective etching by E.

A combination of the first resist and the second resist is selected so that they do not mix with each other, and furthermore, their behavior toward the crosslinking initiator must be different.

That is, since the present invention utilizes the fact that the impregnation rate of the crosslinking initiator is significantly different or the progress rate of the crosslinking reaction is significantly different, the present invention cannot be applied to combinations of resists in which such differences are not clear. This effect will not occur.

When a novolac resin is used as a resist for the crosslinking reaction, for example, PMM is used as the other resist.
If resin A is used, the above conditions are satisfied and it becomes possible to form a resist pattern with high precision using RTE.

When etching a PSG layer or the like using the resist pattern thus formed as a mask, for example, even if a fluorine-based etching gas is used, the etching speed of these resins can be reduced under processing conditions that quickly etch PSG. It is possible to do this, and it will function satisfactorily as a mask for selective etching.

〔Example〕

FIG. 1 is a schematic cross-sectional view showing the steps of a first embodiment corresponding to claim 1 of the present invention. The steps of the embodiment will be described below with reference to the drawings.

As shown in the figure fat, for example, a poly-Si layer 2 is partially formed on the surface of a substrate 1 and covered with a PSG layer 3, and then a lower resist 4 is applied thickly enough to eliminate the step difference. , flatten the surface.

The thickness of the lower resist layer is 2 to 3 μm, and the material thereof is, for example, non-photosensitive polyimide. Further, the PSG layer is selectively etched using the lower resist pattern formed in the following steps as a mask.

After baking the lower resist at 250-300°C,
An upper resist 5 is applied using a spin code and patterned using ultraviolet photolithography. The resist has a photosensitive characteristic to ultraviolet light, and, for example, Novolanc-based TSMR-8900 (trade name, manufactured by Tokyo Ohka) is suitable, and the thickness is 0.4 to 1.0 μm.

Subsequently, as shown in the same figure (bl), the entire surface of the substrate was treated with 4′ dissolved in ethyl cell solve acetate (E CA).
Covered with azidobiphenyl sulfide 0 is shown as crosslinking initiator 6 in the drawing. In this treatment, the solution may be dropped onto the substrate to adhere to the substrate surface due to surface tension, or the solution may be immersed in the solution. Since ECA serves as a solvent for the novolak resin, by maintaining this state, 4'azidobiphenyl sulfide is impregnated into the patterned resist. On the other hand, the lower resist using a different solvent is hardly impregnated.

After this treatment, when irradiated with DUV, a crosslinking reaction progresses in the novolak resist layer impregnated with 4'' azidobiphenyl sulfide, forming a reinforced layer 5' with excellent resistance to dry etching (Fig. (C1) In the figure, the entire patterned resist layer is depicted as a reinforcing layer, but it is not necessary for the reinforcing layer to be formed over the entire upper resist, and the surface of the pattern is completely covered. It would be good if it were done.

Using the pattern of the upper resist layer strengthened by the above process as a mask, the lower resist layer is selectively etched by RIE using oxygen plasma.The reinforced layer has sufficient resistance to this dry etching, so it can be etched by RIE with remarkable anisotropy.
The pattern is accurately transferred to the lower resist layer by H ((di) in the same figure).

In this example, only the patterned upper layer resist h is strengthened by crosslinking, but in order to selectively proceed with the crosslinking reaction in this way, it is necessary to selectively impregnate a crosslinking initiator or to impregnate both resists. However, on the other hand, it is sufficient if the combination does not function as a crosslinking initiator, and on the other hand, the difference in the effect of the crosslinking initiator on both resists does not have to be so extreme that it can be used. It is sufficient if there is a difference, and these points are the same in the second embodiment described below.

FIG. 2 schematically shows the steps of a second embodiment corresponding to claim 2 of the present invention. This embodiment will be described below with reference to FIG.

As shown at ta+ in the same figure, for example, a poly-Si layer 2 is partially formed on the surface of the substrate 1, and covered with a PSG layer 3, the lower resist 4 is thickened to such an extent that the level difference is eliminated.
Apply and smooth the surface.

The PSG layer is selectively etched using the lower resist pattern formed in the following process as a mask. These circumstances and the fact that the thickness of the lower layer resist is 2 to 3 μm are the same as in the first embodiment, but in this example, the lower resist is impregnated with a crosslinking initiator to strengthen it. A novolak type is used.

Lightly heat the lower resist, spin code the PMMA photoresist to a thickness of 0.4 to 1.0 μm, and apply DU.
A patterned upper layer resist 5 is formed by V lithography. It is desirable to limit the heat treatment of the lower resist layer to such an extent that mixing with the PMMA resist coated above is suppressed.

Next, as shown in the same figure (bl), the entire surface of the substrate was subjected to EC.
covered with 4'azidobiphenyl sulfide dissolved in A;
This is also designated as crosslinking initiator 6 in the drawing. The specific treatment is the same as in the previous embodiment, and either a dropping method or a dipping method may be used.

Unlike the first example, in this example, 4° azidobiphenyl sulfide is hardly impregnated into PMMA, which is the upper layer resist, but is impregnated into the novolac resin, that is, the lower layer resist, which is dissolved in EAC. At this time, the upper resist layer functions as a mask for impregnation, and impregnation proceeds selectively.

After this treatment, when irradiated with DUV, a crosslinking reaction progresses to the lower resist impregnated with 4゛azidobiphenyl sulfide, and a reinforcing layer 4 is applied only to the portions not covered by the upper resist.
' is formed ((C) in the same figure).

The thickness of the reinforcing layer corresponds to the depth of impregnation, so 0.5
It is possible to form it to about μm.

Furthermore, when RIE processing using oxygen plasma is performed, the upper resist layer and the lower resist layer immediately below it are etched at a relatively high speed, whereas the reinforcing layer partially formed on the surface of the lower resist layer resists this dry etching. Since the resistance is sufficient, the lower layer pattern directly under the reinforcing layer remains without being etched. That is, even in this embodiment, in which a pattern that is an inversion of the pattern of the upper layer resist is formed on the lower layer resist, as shown in FIG.

〔Effect of the invention〕

As explained above, in the present invention, a reinforcing layer is selectively formed on the surface of the lower resist, and the lower resist is patterned by anisotropic etching using this as a mask. patterning is performed, and the object of the present invention is achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional diagram showing the steps of the first embodiment, FIG. 2 is a schematic cross-sectional diagram showing the steps of the second embodiment, and FIG. 3 is a schematic cross-sectional diagram showing the steps of the prior art. In the figure, 1 is the substrate, 2 is poly Si%, and 3 is PSG. 4 is a lower resist layer, 4' is a reinforcing layer, 5 is an upper resist layer, 5' is a reinforcing layer, and 6 is a crosslinking initiator. Fig. 1 is a schematic cross-sectional diagram showing the process of the first embodiment. Fig. 2 is a schematic cross-sectional diagram showing the process of the second embodiment.

Claims (3)

[Claims] (1) A step of applying a first resist to the substrate surface so that the surface is flat, and applying a second resist on the first resist layer so as not to mix with the first resist. , a step of patterning the second resist layer, a step of impregnating a substance that functions as a crosslinking initiator for the second resist into the patterned second resist layer, irradiating with an energy beam, A step of allowing the second resist impregnated with the crosslinking initiator to proceed with a crosslinking reaction, and using the second resist layer in which the crosslinking reaction has proceeded as a mask, the first resist layer is subjected to an anisotropic dry etching method. 1. A resist pattern forming method comprising a step of etching. (2) a step of applying a first resist to the substrate surface so that the surface is flat; applying a second resist on the first resist layer so as not to mix with the first resist; , patterning the second resist layer, adding a substance that functions as a crosslinking initiator to the first resist layer to a portion of the first resist layer that is not covered by the patterned second resist layer; a step of irradiating the first resist layer impregnated with the crosslinking initiator with an energy beam to cause a crosslinking reaction to proceed partially; The method is characterized by including a step of etching the patterned second resist layer and a portion of the first resist layer covered by the resist layer by an anisotropic dry etching method using the patterned second resist layer as a mask. Resist pattern formation method. (3) The crosslinking initiator according to claim 1 or 2, wherein the crosslinking initiator is preferentially impregnated into one of the first or second resist or has the effect of chemically promoting the crosslinking reaction. Resist pattern formation method.