JPH0263056A - Formation of resist pattern - Google Patents

Abstract

PURPOSE:To increase similarity of a pattern shape to rectangular shape and to improve resolution thereof by using plural positive photoresists having different dissolution velocity in an alkaline developing soln. to each other for a same exposure and forming the resists on a substrate the nearer it is to the substrate the larger its dissolution velocity is. CONSTITUTION:Positive photoresists 1, 2, 3 contain respective esterified product of naphthoquinone diazide and hydroxybenzophenone having each different dissolution velocity in an alkali developing soln. for same exposure. The higher the dissolution velocity of the resist 1 is, the nearer the resist 1 is formed to the substrate side 7. Thus, the difference between the dissolution velocity of the resist at the surface side 3 and the substrate side 7 of the resist becomes smaller, so the pattern shape after development can be more similar to a rectangular shape and the resolution can be improved. Further, since the resist layer has high sensitivity as a whole, less light quantity is required for the exposure. By this constitution, the shape of fine pattern is made more similar to a rectangular shape, and a desired resist pattern is obtd. easily and stably.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a resist pattern forming method, and in particular,
The present invention relates to a resist pattern forming method suitable for forming fine structures such as semiconductor integrated circuits.

[Prior Art] FIGS. 6A, 6B, and 6C are cross-sectional views for forming a conventional photoresist pattern.

Next, a conventional photoresist pattern forming method will be described with reference to FIGS. 6A to 6C.

First, referring to FIG. 6A, one type of positive photoresist is applied onto the substrate 7 to be processed to form the resist layer 6. As shown in FIG. Next, with reference to FIG. 6B, the desired mask 5 is
The resist layer 6 is exposed to light through. Next, the resist layer 6 is developed with an alkaline developer, and in the resist layer 6,
The exposed areas are removed. As a result, a cyst pattern 9 shown in FIG. 6C is obtained.

Typically, photoresist is exposed using monochromatic light to reduce lens aberrations. Therefore, the seventh
As shown in the figure, the light incident on the photoresist 6 and the substrate 7
A standing wave is created by the interaction with the light reflected from the surface of the photoresist layer 6, and layers with relatively high exposure intensity and layers with relatively low exposure intensity are formed alternately in the photoresist layer 6, as shown in FIG. .

The numbers 30 to 100 shown in FIG. 8 indicate the relative values of the exposure intensity within the photoresist 6 when a certain amount of light is incident. If the thickness of the resist layer 6 is 1.2 μm and G-line (wavelength λ-436 nm) is used as the incident light,
The standing waves create nine layers (stripes).

As shown in FIG. 8, the exposure intensity is higher on the surface side of the photoresist 6 than on the substrate 7 side. When a positive photoresist is exposed to light, it has the property of being eluted into an alkaline developer, so the rate of dissolution is high in areas where the amount of exposure is large, and the rate of dissolution is slow in areas where the amount of exposure is small. Therefore, as shown in FIG. 9, the dissolution rate of the photoresist layer 6 in the exposed area is higher on the surface side and lower on the substrate side, and changes to maximum and minimum values in response to the standing waves. have

[Problems to be Solved by the Invention] FIG. 10 shows the exposure intensity and the resist pattern written after development. As the size S of the mask pattern becomes smaller, the contrast of the optical image 8 becomes smaller due to light diffraction phenomena, and portions that should not normally be exposed are slightly exposed.

Therefore, the resist pattern 9a after development does not have a rectangular shape, but has a rounded top.

Furthermore, as described above, the exposure amount, that is, the amount of light absorption is greater on the resist surface side than on the substrate 7 side, so the difference in dissolution rate shown in FIG. 9 occurs, resulting in the resulting resist pattern 9a. The shape of is close to a triangle.

JP-A-61-55922 discloses an improved photoresist pattern forming method. In this method, at least two layers of pattern forming materials having different dissolution rates in the same developer are laminated on a substrate to be processed. A positive type pattern forming material consisting of a homogeneous mixture of a photosensitive resin having a carboxyl group in its side chain and an additive selected from at least one of divalent metal oxides, metal halides, and organic acid salts. A resist composition is used.

The rate of dissolution of such patterning materials can be controlled by varying the amount of additives used or the processing temperature after application of the patterning material. The stacked two-layer pattern forming material is irradiated with an electron beam scanned in a line. The patterning material is then developed, resulting in a photoresist pattern.

According to this method, it is possible to control the dissolution rate, but there are problems in that the additive causes precipitation in the photosensitive resin, making it difficult to apply the pattern-forming material and deteriorating its stability.

Further, the dissolution rate can be changed by changing the amount of additive, but the variation range of the dissolution rate is only about one order of magnitude, so there is a problem of lack of versatility.

Furthermore, in the method of changing the heat treatment temperature of the pattern forming materials of the first layer and the second layer in order to control the dissolution rate, the first layer is also heat treated at the same time when the second layer is heat treated, so the first layer is heat treated at the same time. It is very difficult to achieve the desired dissolution rate of the layer.

JP-A-61-6830 also discloses a technique for forming a resist pattern using two photoresists having different dissolution rates.

However, in this method, the first layer of photoresist must be heat-treated at a high temperature of 130°C to 160°C before coating the second layer of photoresist on the first layer of photoresist. There is a problem that stability is significantly impaired.

Therefore, an object of the present invention is to provide a resist pattern forming method that can approximate the shape of a fine pattern to a rectangle and can easily and stably obtain a desired resist pattern.

[Means for Solving the Problem] The present invention is a method of forming a resist pattern using a resist containing an esterified product of naphthoquinone diazide and hydroxybenzophenone as a photosensitive material, and a resist pattern is formed on a substrate with a dissolution rate in an alkaline developer. A first resist prepared to be relatively large is applied, and the first resist is
forming a resist layer on the first resist layer having a dissolution rate in an alkaline developer of the first resist layer;
forming a second resist layer by applying a second resist prepared to be smaller than the resist; exposing the first and second resist layers to light through a photomask; The exposed first and second resist layers are developed with an alkaline developer to form the first and second resist layers.
and removing the exposed portion of the resist layer.

[Effect]

In this invention, a plurality of positive photoresists having different dissolution rates in an alkaline developer at the same exposure amount are used, and the resist with a high dissolution rate is formed on which substrate side, thereby dissolving the resist surface side and the substrate side. The difference in speed is reduced, the pattern shape after development can be made closer to a rectangle, and the resolution is improved.

Further, according to the present invention, since the resist layer as a whole has high sensitivity, the amount of light required for exposure can be small.

[Embodiments of the Invention] As an embodiment of the present invention, a method of forming a photoresist pattern using three types of photoresists having different dissolution rates will be described.

Each photoresist used in this example consists of a resin soluble in an alkaline developer, a photosensitive material, and a solvent. In this embodiment, Talesol novolac resin is used in common for each photoresist as a resin soluble in an alkaline developer. In this embodiment, a different photosensitive material is used for each photoresist. Next, methods for synthesizing the three types of photosensitive substances used in this example will be explained.

(a) Synthesis of photosensitive material A of the following formula (1) 2,3,4.4' droxybenzophenone 2. Og (8°) and 2.2 g (8°2 mmo) of 1,2-naphthoquinonediazide-5-sulfonic acid chloride represented by the following formula (2)
1 L) and 60 mQ of dioxane, add 3.2 g of triethylamine without stirring (while stirring), and continue the reaction at 25°C to 27°C for 1 hour. Next, add 100 ml of water and dissolve the reaction mixture. was precipitated, this was divided into four parts, and the reaction product was washed with water until the pH of the washing solution became 7.Finally, the reaction product was suspended washed in 100 ml (L) of ethanol, and then separated into four parts and dried. As a result of analyzing the photosensitive material A obtained as a reaction product by liquid chromatography, the average esterification rate was 5% from 1.

(b) Synthesis of Photosensitive Substance B In the synthesis of Photosensitive Substance A, the amount of 1.2-naphthoquinonediazide-5-sulfonic acid chloride was 1.7 g (6
A photosensitive material B was obtained under the same conditions except that the photosensitive material was changed to 3 mm (3 mm). The average esterification rate was 75%.

(e) Synthesis of Photosensitive Substance C In the synthesis of Photosensitive Substance A, the amount of 1,2-naphthoquinonediazide-5-sulfonic acid chloride was added to 1°5 g (5,
A photosensitive material C was obtained under the same conditions except that the photosensitive material was 6 mmof). The average esterification rate was 55%.

The general formula of the esterified product synthesized by the above-mentioned synthesis method is shown in the following formula (3).

Here, R is H or Q-'l? ).

O Let photoresists containing photosensitive substances A, B, and C, respectively, be resist A, resist B, and resist C, respectively.

Note that the content of quinonediazide was made to be the same in each resist.

FIG. 2 shows the dissolution rate of each resist A, B, and C in an alkaline developer. Referring to FIG. 2, resist A
, resist B, and resist C have higher dissolution rates for the same exposure amount.

From Figure 2, the variation range of dissolution rate for each resist is 103
It is understood that the number is about 104, which is large.

Next, with reference to FIG. 1A, FIG. 1B, and FIG. 1C,
A method for forming a photoresist pattern will be explained.

Referring to FIG. 1A, a resist C is applied onto a silicon substrate 7 and baked at 100° C. for 60 seconds using a hot plate. As a result, the first resist layer 1 having a thickness of 0.4 μm is formed on the silicon substrate 7. Next, resist B is applied onto the first resist layer 1 and baked at 100° C. for 70 seconds using a hot plate.

As a result, a film thickness of 0.4μ is formed on the first resist layer 1.
m second resists 2 are formed. Next, resist A is applied onto the second resist layer 2 and baked at 100° C. for 80 seconds using a pot plate. As a result, a third resist layer 3 having a thickness of 0.4 μm is formed on the second resist layer 2. In this way, a resist layer having a total thickness of 1.2 μm is formed on the silicon substrate 7.

The above-mentioned baking temperature is preferably 80-120°C. When the temperature is lower than 80° C., most of the solvent contained in the photoresist remains in the resist layer without being scattered, and therefore the difference in dissolution rate between exposed and unexposed areas becomes smaller. If the temperature is higher than 120'C, naphthoquinone contained in the photoresist layer will thermally decompose, making it impossible to form a resist pattern.

Next, referring to FIG. 1B, resist layers 1.2 and 3
is exposed through a desired photomask 5. For exposure, a reduction projection exposure apparatus is used, the lenses of which have numerical apertures N and A of 0°42, and which irradiates g-rays (436 nm). The dissolution rate for a given exposure dose of each resist layer stacked on the substrate is higher on the substrate side, so the sensitivity of the upper part of the stacked resist layer can be made the same as that of a conventional single-layer resist. In this case, the sensitivity of the laminated resist layer is higher overall than when a single resist layer is used. Therefore, the amount of light required for exposure is less than when using a single resist layer. Upon exposure to light, the above esterified quinone diazide shown on the left side of the following formula (5) becomes the acid shown on the right side, and then added to an alkaline developer at 2.38% by weight, as shown in Figure 1C.
Resist layers 1.2 and 3 are developed with an aqueous solution of tetramethylammonium hydroxide, thereby obtaining resist pattern 9. In FIG. 1C, the photoresist pattern has a nearly rectangular shape, and its width Wa is approximately 0.5 μm.

As shown in FIG. 3, the difference in dissolution rate of the resist layer according to this example is small between the surface side of the resist layer and the substrate side. The reason why the dissolution rate was uniform is that a resist having a high dissolution rate was used on the substrate side, which was exposed to a small amount of light. In this way, in this example, the dissolution rate is controlled by changing the esterification rate of the photosensitive substance. Therefore, depending on the choice of resist,
An overhang pattern can also be formed by further increasing the dissolution rate on the substrate side.

The photoresist pattern forming method of the present invention can be widely applied to the formation of semiconductor integrated circuits.
If applied to the area shown in the figure, great effects can be achieved.

FIG. 4 shows an example in which there is a large step difference in the substrate within the wafer and a large difference in the thickness of the resist layer.

In this example, a wiring layer made of, for example, tungsten silicide is formed in a region 11 of the stepped portion or in regions 12 and 13 of different heights sandwiching the stepped portion. The tungsten silicide film 14 has a
There are steps. When a resist is applied on this tungsten silicide film 14, the resist layer 15 has a density of 5,000 to 70%.
There is a difference in the film thickness of 00 people. Even if there is such a difference in film thickness, if the dissolution rate of the layer 152 on the substrate 10 side of the resist layer 14 is made higher than that of the surface layer 151, a rectangular pattern can be formed even in the thick film region. can do.

FIG. 5 shows an example of a contact hole where the contrast of light is reduced. One side of the insulating film 18 is 0.8 μm.
When forming the following contact holes, since the opening area of the mask 5 is small, the optical image is greatly degraded and the contrast of light is reduced.

Therefore, the intensity of light differs greatly between the upper and lower parts of the resist layer 15. Even in such a case, the resist layer 15
By making the dissolution rate of the lower part higher than the dissolution rate of the upper part, an opening can be formed perpendicularly to the substrate 10.

In the above example, an esterified product of 1,2-naphthoquinonediazide-5-sulfonic acid chloride and 2,3,4,4'-tetrahydroxybenzophenone was used as the photosensitive material of the positive resist. In short, this invention is characterized by changing the dissolution rate by changing the structure of the esterified product of naphthoquinonediazide and hydroxybenzophenone. The same effect as described above can also be obtained.

In addition, in the above example, each resist was made with the same quinonediazide content, and the resist containing a compound with a small esterification rate was applied to the lower layer, but resists with different quinonediazide contents were Making,
A resist with a high content of quinonediazide may be applied to the lower layer.

Furthermore, as a photosensitive material, we used an amidation product of sulfonic acid of a quinonediazide-containing compound and an amino-containing compound such as p-aminodiphenylamine, and used a resist with a large Zs' (-T ratio) of a compound with a small amidation ratio. A resist containing a large amount of quinonediazide may be applied to the lower layer.

In the above embodiments, a silicon substrate is used as the substrate to be processed, but aluminum or other metal substrates may be used, or an inorganic compound may be used.

The substrate may be made of an organic compound.

[Effects of the Invention] As described above, according to the present invention, a plurality of positive photoresists having different dissolution rates in an alkaline developer at the same exposure amount are used, and the resist having a high dissolution rate is formed on the substrate side. By doing so, the pattern shape can be approximated to a rectangular shape when forming a fine pattern, so that resolution can be improved. Since the resist layer as a whole has high sensitivity, the amount of light required for exposure is small.

[Brief explanation of the drawing]

FIGS. 1A, 1B, and 1C are cross-sectional views for explaining a resist pattern forming method according to an embodiment of the present invention. FIG. 2 is a graph showing the dissolution rate of the resist used in one embodiment of the present invention. Figure 3 is 1A
FIG. 1C is a diagram showing the relationship between the depth of the resist and the dissolution rate of the resist in the resist pattern forming process shown in FIGS. 1C to 1C. FIGS. 4 and 5 are diagrams for explaining the manufacturing process of a semiconductor device to which an embodiment of the present invention is applied. FIGS. 6A, 6B, and 6C are cross-sectional views for explaining a method of forming a photoresist pattern, which is the background of the present invention. FIG. 7 is a diagram for explaining the principle of generation of standing waves within the photoresist layer. FIG. 8 is a diagram showing the exposure intensity distribution within the photoresist layer. FIG. 9 is a diagram showing the relationship between the depth of the resist and the dissolution rate of the resist in the resist pattern forming process shown in FIGS. 6A to 6C. FIG. 10 is a diagram showing the exposure intensity and the resist pattern obtained after development when forming a fine pattern using the resist pattern forming method which is the background of the present invention. In the figure, 1 is a first resist layer made of resist C;
2 is a second resist layer made of resist B, 3 is a third resist layer made of resist A, 5 is a photomask, 7 is a silicon substrate, and 9 is a resist pattern 6 obtained after development. Figure 1B

Claims (1)

[Claims] A method for forming a resist pattern using a resist containing an esterified product of naphthoquinone diazide and hydroxybenzophenone as a photosensitive material, the resist pattern being formed on a substrate so that the rate of dissolution in an alkaline developer is relatively high. Applying the first resist prepared in
forming a first resist layer; applying a second resist prepared such that its dissolution rate in an alkaline developer is lower than that of the first resist on the first resist layer; forming a resist layer; exposing the first and second resist layers to light through a photomask; and developing the exposed first and second resist layers with an alkaline developer; A resist pattern forming method comprising the step of removing exposed portions of first and second resist layers.