JPH07106235A - Formation of pattern - Google Patents

Abstract

PURPOSE:To realize a high-resolution and high-accuracy pattern formation technique without being affected by reflection from a substrate. CONSTITUTION:A chemically amplified resist 3 having a low transmittance is exposed by a KrF excimer laser 11 and an acid is produced 15 in the surface of the resist. After the exposure, an anode 18 and a cathode 19 are installed horizontally to a substrate to apply a DC voltage to the resist, the substrate is heated by a hot plate 20 and the acid in the surface of the resist is vertically moved to the lower part of the resist. During the movement 16 of the acid, the resist is changed into a substance soluble in alkali by the acid. When the resist is developed with an alkali developing solution, high-accuracy patterns can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithographic technique for microfabrication of semiconductor devices, and more particularly to a pattern forming method utilizing the surface resolution of a resist.

[0002]

2. Description of the Related Art A photolithography technique is an essential technique for mass production of LSI because it uses a reticle to project a pattern by step-and-repeat in a reduced scale and has a high throughput and can form a fine pattern. When the wavelength of light is λ and the numerical aperture of the lens is NA, the resolution R of photolithography has a relational expression of R = k ₁ λ / NA. However, k ₁ is a constant depending on the resist material and process. As can be seen from this relational expression, as miniaturization progresses, photolithography using a light source with a shorter wavelength is required. Currently, i-line (365 nm) or KrF excimer laser (248
(nm) is used as a light source, and a VLSI is being developed by a single-layer resist process. As a resist, a chemically amplified resist that uses an acid catalyst is widely used because of the problem of high sensitivity and light absorption at the exposure wavelength (for example, Taku Ueno, Semicon NEWS 1989.12 p24).
-28).

A conventional pattern forming method using a chemically amplified resist utilizing an acid catalyst will be described with reference to the drawings.

FIG. 5 is a sectional view showing the steps of a conventional pattern forming method. A positive two-component chemically amplified resist will be described as an example. On the Si substrate 14, a resist 13 containing an acid generator and a polymer that becomes alkali-soluble by an acid is applied. The chemically amplified resist is composed of an onium salt as an acid generator and polyvinylphenol protected with a tert-butoxycarbonyl group (tBOC) as a polymer. The pattern of the mask 12 is exposed on the resist 13 using the KrF excimer laser 11. When the acid generator is exposed to light, acid generation 15 occurs (FIG. 5 (a)). By heating the substrate, the generated acid attacks the tBOC group, which is a protective group of the polymer, to form a phenolic hydroxyl group. No acid is consumed in this reaction, and one acid attacks many tBOC groups and the reaction proceeds. In this way, the acid acts as a catalyst, so the sensitivity is increased. Therefore, since the tBOC protecting group can be removed from the exposed portion, the exposed portion becomes alkali-soluble, and a positive resist pattern is formed when developing with an alkali developing solution (FIG. 5B).

[0005]

In the above-mentioned structure, unless the transmittance of the resist for exposure light is increased,
It is not possible to obtain a vertical resist pattern. Conversely, if the transmittance is increased, a good pattern shape can be obtained, but if the transmittance is high, the following two problems occur.

The first point is that the pattern size varies due to the standing wave effect. The standing wave effect will be described with reference to FIGS. When exposure light is incident on a semiconductor substrate coated with a resist, it is first reflected at the interface between the resist and the substrate, and then on the resist surface. Thus, multiple interference occurs between the resist-substrate interface and the resist surface (FIG. 6). When the resist film thickness is changed, the absorbed energy of light changes periodically.
That is, the pattern dimension changes due to the fluctuation of the resist film thickness (FIG. 7). This is called the standing wave effect. In an actual semiconductor device, since a step is formed on the substrate, there is a difference in resist film thickness above and below the step. Therefore, in an actual semiconductor device, dimensional variation due to the standing wave effect becomes a problem.

Secondly, there are problems of dimensional variation and deterioration of pattern shape due to irregular reflection from the substrate. In particular,
The influence of irregular reflection at the stepped portion of a highly reflective substrate such as an Al substrate is large, and when the base is a concave portion, overexposure results, and the size tends to be thin with a positive resist.

As described above, in the conventional process, the transmittance of the resist is high, the exposure light reaches the substrate, is easily affected by the reflection at the interface between the resist and the substrate, and the dimensional accuracy of the pattern is poor. Had.

An object of the present invention is to solve the above problems and to provide a pattern forming method with high dimensional accuracy, which is a surface resolution process using an acid catalyst.

[0010]

A pattern forming method of the present invention comprises a step of applying a resist containing a substance which generates an acid by irradiating a semiconductor substrate with a radiation and a compound whose solubility is changed by the acid. The method comprises the steps of exposing the resist, applying an electric field perpendicularly to the resist so that the electric potential of the resist surface is positive with respect to the semiconductor substrate, and developing the resist. It consists of

Further, preferably, the above-mentioned pattern forming method is characterized in that the resist transmits radiation only near the surface of the resist. The above pattern forming method is characterized in that the step of applying an electric field perpendicularly to the resist is performed while heating. Further, in the step of applying the resist, firstly, a resist containing a compound whose solubility is changed by an acid and absorbing radiation is applied, and secondly, by a substance and an acid which generate an acid by irradiation with radiation. There is provided the above-mentioned pattern forming method, which comprises applying a resist containing a compound whose solubility is changed.

Further, in the pattern forming method of the present invention, a step of applying a resist containing a substance which generates an acid upon irradiation of a radiation on the semiconductor substrate and a compound whose solubility is changed by the acid, and exposing the resist. A step of applying an electric field perpendicular to the resist and applying a magnetic field to the semiconductor substrate so that the electric potential of the resist surface becomes a positive potential, and applying a magnetic field perpendicular to the resist; And a developing step.

Further preferably, the resist is provided with the above-mentioned pattern forming method, wherein the radiation transmits only in the vicinity of the surface of the resist. The above-mentioned pattern forming method is characterized in that the step of applying an electric field and a magnetic field perpendicular to the resist is performed while heating. Further, in the step of applying the resist, firstly, a resist containing a compound whose solubility is changed by an acid and absorbing radiation is applied, and secondly, by a substance and an acid which generate an acid by irradiation with radiation. There is provided the above-mentioned pattern forming method, which comprises applying a resist containing a compound whose solubility is changed.

[0014]

In the present invention, a resist containing a substance having a low transmittance for exposure light and a polymer whose acid is generated by irradiation of exposure light on the semiconductor substrate and a polymer whose solubility is changed by the attack of the acid is applied. When is exposed to light, acid is generated near the resist surface. Next, by applying an electric field perpendicularly to the resist film and so that the electric potential of the resist surface becomes positive with respect to the semiconductor substrate, the acid (H ⁺ ) generated near the resist surface becomes anisotropic. Sex spread. During acid diffusion, the polymer is attacked by the acid, changing the solubility of the polymer in the developer. The acid finally reaches the interface between the substrate and the resist, but since it moves vertically, the acid can be moved to the lower surface of the resist without destroying the distribution of the acid near the surface generated immediately after exposure. After that, when development is performed with a developing solution, a vertical pattern is formed although the transmittance of the resist material is low and light is transmitted only near the surface. That is, the image formed on the resist surface can be vertically transferred to the resist lower surface,
It is not necessary to form an image even in the resist as in the conventional method, and a pattern is formed even if the exposure light is not transmitted to the substrate. Therefore, since the exposure light does not pass through to the substrate, it is not affected by the reflection at the interface between the resist and the substrate, which has been a problem in the past. Can be prevented. Moreover, it is sufficient to form an image only on the surface, and it has the advantages that the depth of focus is deep and the resolution is high as compared with the conventional method of forming an image on the entire resist bulk. In particular, when the resist is heated when an electric field is applied perpendicularly to the resist, the sensitivity is increased because the reaction of the change in the solubility of the polymer due to the attack of the acid is promoted. Further, the lower layer resist is a resist that contains a polymer whose solubility is changed by an acid and absorbs exposure light, and the upper layer resist contains a substance that generates an acid when exposed to exposure light and a polymer whose solubility is changed by an acid. Also in the case of a resist having a two-layer structure, the same effect can be obtained by exposing, vertically applying an electric field, and developing, as in the case of the single-layer resist having a low transmittance described above. That is, when exposed, an acid is generated in the upper layer resist, and when an electric field is applied, the acid moves vertically in the lower layer resist, and the acid changes the solubility of the polymer in the upper and lower layer resists. Is obtained. Since light is absorbed in the lower layer resist, it is not affected by reflection from the substrate as well.

Further, particularly in the present invention, a resist containing a substance having a low transmittance for exposure light and a polymer capable of generating an acid by irradiation with radiation and a polymer whose solubility is changed by an attack of the acid is applied, When the resist is exposed to light, acid is generated near the surface of the resist. Next, an acid (H ⁺⁾ generated near the resist surface is applied perpendicularly to the resist film and by applying a magnetic field perpendicularly to the semiconductor substrate so that the potential of the resist surface becomes positive. ) Has a vertical cyclotron motion and is anisotropically diffused. During acid diffusion, the polymer is attacked by the acid, changing the solubility of the polymer in the developer. Acid (H ⁺ ) absorbs energy from electric and magnetic fields,
High-energy H ⁺ attacks the acid generator, and a new acid is induced. The acid finally reaches the interface between the substrate and the resist, but since it moves vertically, the acid can be moved to the lower surface of the resist without destroying the distribution of the acid near the surface generated immediately after exposure. After that, when development is performed with a developing solution, a vertical pattern is formed although the transmittance of the resist material is low and light is transmitted only near the surface. As an effect, the effect of reflection from the substrate can be prevented as in the case where only the electric field is applied, and since the acid is generated in an amplified manner by applying the electric field and the magnetic field at the same time, the sensitivity can be further increased. it can.

Therefore, by using the present invention, it is possible to prevent the influence of the reflection of exposure light from the substrate in photolithography, and it is effective in forming a fine pattern with high dimensional accuracy.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A pattern forming method according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a process sectional view of a pattern forming method in a first embodiment of the present invention.

In FIG. 1A, a chemically amplified resist 13 having a thickness of 1.2 μm is applied on a Si substrate 14. The chemically amplified resist 13 is composed of two components, an acid generator and a polymer. The acid generator used was an onium salt, and the polymer used was a polyvinylphenol with hydroxyl groups protected by tBOC. Further, a dye was added to the resist 13 so that the transmittance was 10% or less with respect to the KrF excimer laser light as the exposure light. By exposing with the KrF excimer laser 11, the pattern on the mask 12 was transferred to the resist 13, and an acid was generated near the resist surface.

In FIG. 1B, after the exposure, the cathode electrode 19 is brought into close contact with the back surface of the Si substrate 14, and the anode electrode 18 is placed horizontally with a distance of 3 μm from the resist 13 surface. A DC voltage of + 10V was applied to 18. Further, the Si substrate 14 was placed on the hot plate 20 and heated to 100 ° C. At this time, the acid generated near the resist surface during exposure vertically moved to the lower part of the resist by the electric field 17. Further, during the transfer of acid, the attack of acid cleaved the bond of tBOC group attached as a protective group of polyvinylphenol to form a phenolic hydroxyl group, which changed into alkali-soluble. It was developed with an alkaline developer to form a pattern (FIG. 1 (c)).

As described above, according to this embodiment, acid is generated on the resist surface and the acid is vertically diffused by the electric field. Therefore, only the resist surface portion needs to be exposed. That is, the pattern is formed even if the transmittance of the resist is lowered and the exposure light does not reach the substrate. Therefore, the influence of the reflection of the exposure light from the substrate can be prevented, and there is no dimensional variation due to the standing wave effect. Fine pattern formation was realized.

In this embodiment, the exposure light used is KrF.
An excimer laser was used, but light of other wavelengths such as i-line,
Alternatively, X-ray, electron beam or ion beam may be used. The resist used was an onium salt as an acid generator and a polyvinylphenol hydroxyl group protected with tBOC as a polymer. However, the acid generator may be another type such as sulfonic acid. Any material that changes solubility may be used. Further, the distance between the anode electrode for generating an electric field and the resist surface and the applied voltage may be under the condition that the acid moves.

FIG. 2 is a sectional view showing the steps of a pattern forming method according to the second embodiment of the present invention.

In FIG. 2A, the lower layer resist 22 is applied on the Si substrate 14 in a film thickness of 1 μm, and the upper layer resist 21 is applied in a film thickness of 0.2 μm. The lower layer resist 22 is a polymer in which hydroxyl groups of polyvinylphenol are protected by tBOC,
Further, a dye was added, and the transmittance was adjusted to 10% or less with respect to the KrF excimer laser light as the exposure light. The upper layer resist 21 is composed of two components, an acid generator and a polymer. The acid generator used was an onium salt, and the polymer used was a polyvinylphenol with hydroxyl groups protected by tBOC. The mask 12 is exposed by the KrF excimer laser 11.
The upper pattern was transferred to a resist, and an acid was generated in the upper layer resist.

In FIG. 2B, after the exposure, the cathode electrode 19 is brought into close contact with the back surface of the Si substrate 14, and the upper layer resist 21 is formed.
The anode electrode 18 is installed horizontally with a distance of 3 μm from the surface of the
A DC voltage of 0V was applied. Further, the Si substrate 14 was placed on the hot plate 20 and heated to 100 ° C. At this time, the acid generated in the upper layer resist 21 during exposure moved vertically to the lower layer resist 22 by the electric field. Also, the upper layer,
In the lower layer resist, tBO attached as a protecting group for polyvinylphenol by acid attack during acid transfer
The bond of the C group is cleaved to form a phenolic hydroxyl group,
It became soluble in alkali. The upper layer resist 21 and the lower layer resist 22 were developed with an alkaline developer to form a pattern (FIG. 2 (c)).

As described above, according to the present embodiment, the acid is generated in the upper layer resist and the acid is vertically diffused into the lower layer resist by the electric field, so that the transmittance of the lower layer resist is lowered and the exposure light reaches the substrate. The upper resist and the lower resist are patterned at one time even if the light is not transmitted. Therefore, the influence of the reflection of the exposure light from the substrate can be prevented, and there is no dimensional variation due to the standing wave effect. Fine pattern formation was realized.

In this embodiment, KrF is used as the exposure light.
An excimer laser was used, but light of other wavelengths such as i-line,
Alternatively, X-ray, electron beam or ion beam may be used. As the upper layer resist, an onium salt was used as an acid generator and a polyvinylphenol hydroxyl group was protected with tBOC as a polymer, but the acid generator may be another type such as sulfonic acid. Any material that changes its solubility in As the lower layer resist, a polymer in which hydroxyl groups of polyvinylphenol are protected with tBOC was used, but any polymer whose solubility in an alkali developing solution is changed by an acid may be used and may contain an acid generator. Further, the distance between the anode electrode for generating an electric field and the resist surface and the applied voltage may be under the condition that the acid moves.

FIG. 3 is a sectional view showing the steps of a pattern forming method according to the third embodiment of the present invention.

In FIG. 3A, a chemically amplified resist 13 having a thickness of 1.2 μm is applied on a Si substrate 14. The chemically amplified resist 13 is composed of two components, an acid generator and a polymer. The acid generator used was an onium salt, and the polymer used was a polyvinylphenol with hydroxyl groups protected by tBOC. Further, a dye was added to the resist 13 so that the transmittance was 10% or less with respect to the KrF excimer laser light as the exposure light. By exposing with the KrF excimer laser 11, the pattern on the mask 12 was transferred to the resist 13, and an acid was generated near the resist surface.

In FIG. 3B, after the exposure, the Si substrate 14
The cathode electrode 19 is adhered to the back surface, and the resist 13 surface
Place the anode electrode 18 horizontally with a distance of 3 μm from
The anode electrode 18 is + 10V with respect to the sword electrode 19.
DC voltage was applied. In addition, an electromagnetic coil around the board
The magnetic field is evenly generated perpendicularly to the substrate by arranging
1 and place the Si substrate 14 on the hot plate 20.
Heated to 00 ° C. At this time, when exposing,
The acid generated by the side squeezes to the bottom of the resist due to the electric and magnetic fields.
It moved vertically while doing crotron movement. Also of acid
Protecting group of polyvinylphenol by acid attack during transfer
The bond of the tBOC group attached as
A hydroxyl group was formed and it became soluble in alkali. simultaneous
Acid (H ⁺) Absorbs energy from electric and magnetic fields,
H that has absorbed energy⁺Attacks the acid generator,
Acid is induced, and the reaction of cleaving tBOC group by a new acid
Be promoted. Develop with an alkaline developer to form a pattern
It carried out (FIG.3 (c)).

The acid amplification reaction will be described in detail with reference to FIG. Consider a thin layer obtained by dividing the resist into n equal parts in the film thickness direction. If an acid is generated in the A ₁ layer after exposure, H ⁺ moves to the A ₂ layer, A ₃ layer ... A _n layer due to the electric field and the magnetic field (Fig. 4).
(A)). If H ⁺ moves to the k-th layer A _k , H
⁺ Because incident to A _k layer to absorb high energy from the electric field and the magnetic field, and thus is equivalent to an ion beam exposure of H ⁺ in the thin resist film of A _k layer. Therefore, an acid is generated from the acid generator in the A _k layer by the high energy H ^+, and an acid amplification reaction occurs (FIG. 4 (b)).

As described above, according to the present embodiment, the acid is generated on the resist surface, and the acid is vertically diffused while the cyclotron motion is caused by the electric field and the magnetic field. Therefore, only the resist surface portion needs to be exposed. That is, the pattern is formed even if the transmittance of the resist is lowered and the exposure light does not reach the substrate. Therefore, the influence of the reflection of the exposure light from the substrate can be prevented, and there is no dimensional variation due to the standing wave effect. Fine pattern formation was realized. In addition, high energy is given to the acid by the electric field and the magnetic field, and the amplification reaction of acid generation occurs as the high energy acid moves vertically,
The sensitivity became higher.

In this embodiment, the exposure light used is KrF.
An excimer laser was used, but light of other wavelengths such as i-line,
Alternatively, X-ray, electron beam or ion beam may be used. The resist used was an onium salt as an acid generator and a polyvinylphenol hydroxyl group protected with tBOC as a polymer. However, the acid generator may be another type such as sulfonic acid. Any material that changes solubility may be used. Further, the distance between the anode electrode for generating an electric field and the resist surface and the applied voltage may be under the condition that the acid moves.

[0033]

As described above, according to the pattern forming method of the present invention, the surface of the resist is exposed to generate an acid, and an electric field is applied perpendicularly to the substrate to vertically apply the acid to the lower part of the resist. Since the light is diffused, it is only necessary to form an image of the pattern on the resist surface, and it is not necessary to transmit light to the substrate, so that the influence of reflection from the substrate is not exerted. Therefore, it is possible to prevent the dimensional variation of the resist pattern due to the standing wave effect, the dimensional variation due to irregular reflection at the stepped portion of the high reflection substrate, and the pattern shape deterioration, which have been problems in the past. Further, since an image is formed only on the resist surface, a higher resolution and a higher depth of focus can be obtained as compared with the conventional method of forming an image on the resist bulk.

Further, in particular, by simultaneously applying an electric field and a magnetic field to the substrate after exposure to give high energy to the generated acid, the generated acid attacks the acid generator to generate new acid. In this way, acid proliferation occurs, resulting in higher sensitivity. Therefore, by using the present invention, a resist process which is not affected by the reflection from the substrate is realized, which effectively works for forming an extremely fine and highly precise pattern, and therefore, for manufacturing an ultra-high-density integrated circuit. It can make a big contribution.

[Brief description of drawings]

FIG. 1 is a process sectional view of a pattern forming method according to a first embodiment of the present invention.

FIG. 2 is a process sectional view of a pattern forming method according to a second embodiment of the present invention.

FIG. 3 is a process sectional view of a pattern forming method according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of acid proliferation occurrence in the same example.

FIG. 5 is a process sectional view of a conventional pattern forming method.

FIG. 6 is an explanatory diagram of a multiple interference effect.

FIG. 7 is an explanatory diagram of dimensional variation due to the standing wave effect.

[Explanation of symbols]

 11 KrF excimer laser 12 mask 13 resist 14 Si substrate 15 acid generation 16 acid transfer 17 electric field 18 anode 19 cathode 20 hot plate 21 upper layer resist 22 lower layer resist 31 magnetic field 32 electromagnetic coil

Claims (7)

[Claims] 1. A step of applying a resist containing a substance which generates an acid by irradiation of a radiation onto a semiconductor substrate and a compound whose solubility is changed by the acid, a step of exposing the resist, and a step of exposing the resist to the resist. And a step of applying an electric field vertically to the semiconductor substrate so that the potential of the resist surface becomes a positive potential, and a step of developing the resist. 2. The pattern forming method according to claim 1, wherein the resist transmits radiation only near the surface of the resist. 3. The pattern forming method according to claim 1, wherein the step of applying an electric field perpendicularly to the resist is performed while heating. 4. A step of applying a resist containing a substance which generates an acid by irradiating a semiconductor substrate with a radiation and a compound whose solubility is changed by the acid, a step of exposing the resist, and a step of exposing the resist to the resist. Vertically and vertically to the semiconductor substrate, an electric field is applied so that the potential of the resist surface becomes a positive potential, and a magnetic field is vertically applied to the resist; and a step of developing the resist. Pattern formation method. 5. The pattern forming method according to claim 4, wherein the resist transmits radiation only near the surface of the resist. 6. The pattern forming method according to claim 4, wherein the step of applying an electric field and a magnetic field perpendicular to the resist is performed while heating. 7. The step of applying the resist comprises firstly applying a resist containing a compound whose solubility is changed by an acid and absorbing radiation, and secondly producing a acid by irradiating with the radiation. 5. The pattern forming method according to claim 1, wherein a resist containing a compound whose solubility is changed by an acid is applied.