JPH09180992A - Pattern formation method - Google Patents

Abstract

(57) Abstract: A pattern having an exposure light source wavelength or less is formed by a photolithography technique using a phase shifter. SOLUTION: A photoresist layer 2 and a photobleaching material layer 3 are successively formed on a substrate 1 to be processed, and a first exposure mask 5 composed of a phase shifter 4 is used for a first exposure. ,
Exposure with an exposure amount 6 that makes only the photobleachable material layer 3 transparent,
Forming an unphotobleached pattern latent image 7 on the photobleachable material layer 3,
Next, a second exposure mask 9 composed of the phase shifter 4 is used to perform a second exposure to expose the photoresist layer 2 and a dark portion 10 formed by the unphotobleached pattern latent image 7.
The dark portion 11 is formed by the light shielding effect of the phase shifter edge,
Unnecessary parts are removed by development processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical lithography technique used for manufacturing ULSI, and more particularly to a pattern forming method for easily forming a fine pattern having a wavelength equal to or shorter than a wavelength of an exposure source.

[0002]

2. Description of the Related Art The progress of semiconductor devices is remarkable, and DRA
Taking high integration technology of M (dynamic random access memory) as an example, high integration has been achieved at a rate of 4 times almost every 3 to 4 years. This highly integrated technology has been achieved by the progress of miniaturization technology of each element pattern size that constitutes an element, and the lithography technology which is an element pattern formation technology has played a leading role in the microfabrication technology. Among them, optical lithography for forming a pattern by using light has been used for mass production of semiconductor devices as a lithography technique having both high mass productivity and fine processability.

However, in recent years, the minimum required processing size of a pattern is the i-line (0.36) of a mercury lamp used for normal exposure.
Due to the fact that the wavelength has become equal to or less than the wavelength of 5 μm), microfabrication by conventional optical lithography has become increasingly difficult. In order to improve this situation, in optical lithography, the lithography performance has been improved by using methods such as the development of an exposure apparatus that further shortens the wavelength of the exposure light source and the improvement of the exposure mask that is the original image of the pattern. ing. Among them, the exposure mask is relatively positively studied by each research institute because high resolution can be obtained relatively easily without modifying the exposure apparatus itself.

A method of improving this exposure mask will be briefly described below. This method is a method in which the phase of light passing through the mask pattern is changed by manipulating the mask structure to enhance the fine workability.
Here, the operation of the phase information is performed by disposing a transparent film called a phase shifter on the mask. Such an exposure mask is generally called a phase shift mask or a phase shift reticle.

By the way, it has been known that when this phase shifter is independently formed on a transparent mask substrate and exposed using this mask, a fine pattern reflecting the shape of the phase shifter can be easily formed. For example, Japanese Journal of Applied Physics (Jpn.
J. Appl. Phys.) Vol. 30, No. 5, May, 1991, p.
p. 1131 to 1136 have a pattern size width of approximately 0. 0 when exposed by a normal mercury lamp i-line (0.365 μm) using a phase shift mask composed only of an optically transparent phase shifter film. It is described that a 1 μm isolated pattern can be easily formed at a pattern transfer position corresponding to a shifter edge of a phase shifter.

Further, a method of forming a periodic pattern applying this pattern forming method has also been proposed. For example,
In the method described in JP-A-6-112119, a positive resist film, a water-soluble PVA (polyvinyl alcohol) film, and then a negative resist film having a predetermined thickness are sequentially formed on a substrate to be processed. A phase shift layer is formed by patterning the upper negative resist, and then,
It has been proposed as a pattern forming method in which a fine periodic pattern is formed in a region below an edge of a negative resist pattern by exposing the entire surface.

[0007]

However, in the pattern forming method for obtaining the periodic pattern, the processing steps are more complicated than the ordinary photolithography processing steps, so that there arises a problem that the throughput of the lithography steps is reduced. Furthermore, an increase in the number of processing steps may lead to an increase in the probability of occurrence of defects such as pattern resolution defects. There are also technical difficulties. For example, since the resist pattern formed in the upper layer is used as a phase shifter, it is necessary to make the resist film thickness of the upper layer resist uniform. However, in the actual device structure, since there is not a little step on the surface of the substrate to be processed, it is difficult to form the upper layer resist with a uniform film thickness due to this. That is, the phase shift effect becomes weak due to the film thickness distribution of the upper layer resist, and there arises a problem that a desired fine pattern cannot be formed in a desired exposure region. On the other hand, when the problem caused by the step is alleviated by increasing the film thickness of the lower layer resist, the aspect ratio of the resist pattern formed on the lower layer resist becomes too large,
The desired pattern may not be formed due to another problem such as pattern collapse. For the above reasons, it is considered difficult to form a desired fine pattern in the exposed sample plane of the actual device structure by the conventional method. Moreover, even if these conventional techniques are used for forming a periodic pattern,
A pattern of 2 or less could not be formed.

An object of the present invention is to provide a pattern forming method which reduces the number of processing steps, is less susceptible to a step of a substrate to be processed, and easily forms a pattern of 1/2 or less of an exposure wavelength. Especially.

[0009]

The object of the present invention is to form a material, which causes a photobleaching reaction by irradiation of light, on a photoresist in place of a phase shifter formed on a substrate to be processed, and to provide a phase difference in transmitted light. Using a first exposure mask composed of a phase shifter for giving a first exposure with a desired exposure amount or exposure light, and then using a second exposure mask similarly composed of a phase shifter, The object of the present invention is achieved by performing a second exposure with a desired exposure amount or exposure light and performing a development process.

The means of the present invention will be described in detail with reference to FIG. 1 by taking the case of using a positive resist as an example.

First, as shown in FIG. 1A, a positive photoresist layer 2 and a photobleaching material layer 3 are successively formed on a substrate 1 to be processed. Next, the first exposure is performed using the desired first exposure mask 5 composed of the phase shifter 4. At this time, the first exposure is performed with an exposure amount 6 that makes only the photobleachable material layer 2 transparent. However, since the shifter edge portion of the phase shifter 4 becomes a dark portion due to the phase shifter effect, a fine unphotobleached pattern latent image 7 is formed on the photobleachable material layer 3 as shown in FIG. 1B. Next, using the desired second exposure mask 8 composed of the phase shifter 4,
A second exposure is performed. At this time, the second exposure is performed with an exposure amount 9 that the photoresist layer 2 exposes. However, in the photoresist layer 2, the dark portion 10 formed by the light shielding effect of the unphotofading pattern latent image formed by the first exposure,
The dark portion 11 of the second exposure mask 8 due to the phase shifter effect forms a latent image as shown in FIG. Then, an unnecessary portion is removed by development processing or the like, whereby a fine pattern as shown in FIG. 1D can be obtained. The first and second exposures are usually performed via a projection lens (not shown). However, similar results can be obtained even if the exposure mask and the substrate to be processed shown in the drawing are brought close to each other or brought into close contact with each other.

If a negative resist whose solubility in a developing solution is lowered by irradiation of light is used instead of the positive resist, a black-and-white inverted pattern opposite to the above can be obtained. Also, the consistency between the first exposure and the second exposure is
Satisfaction can be satisfied by forming alignment marks and the like on the substrate to be processed in advance to obtain conformity and using the alignment marks.
Further, a material that becomes light black by irradiation with light can be used as in the above.

[0013]

Embodiment 1 of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing a method of patterning a positive resist according to the present invention. First, an antireflection film 14 for reducing the influence of reflected light from the substrate 13 is formed on a substrate 13 to be processed having a step of 0.2 to 0.3 μm as shown in FIG. A positive photoresist film 2 and a photobleaching material film 3 were formed by coating. For the photobleaching material, we tried to use a water-soluble contrast enhancer which is generally used for improving the resolution of resist.

For exposure, an i-line stepper (wavelength 0.365μ
m, the numerical aperture of the lens is 0.52), and the photofading property is applied to the sample thus produced through the first exposure mask 5 in which the phase shifter 4 is arranged on the optically transparent glass substrate. The first exposure was performed with an exposure amount of light 6 that changes only the material film 3. As a result, the photobleachable material film 3 is shown in FIG.
A non-light fading pattern latent image 7 was formed by shielding the phase shifter as shown in FIG.

Then, a second exposure was similarly performed by the light 9 through the second exposure mask 8 on which the phase shifter 4 was arranged. However, in the photoresist layer 2, the dark portion 10 formed by the light blocking effect of the unphotobleached pattern latent image 7 formed by the first exposure and the dark portion 11 by the phase shifter effect of the second exposure mask 8 are formed. A latent image as shown in (c) was formed. Next, the photobleachable material film 3 was previously removed by washing with water. After that, development was performed using an alkaline developer of photoresist, and as shown in FIG. 2D, a fine pattern 12 was obtained without being affected by the step difference of the substrate to be processed.

Although the antireflection film 14 is formed as the lower layer of the photoresist 2 in the first embodiment, it is not always necessary if the resist 2 is a material that is not easily affected by the reflection from the substrate. Further, when the antireflection film 14 is formed as in Example 1, it is necessary to make the film thickness as thin as possible so as not to hinder the etching of the next substrate to be processed.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing a method of patterning a negative resist according to the present invention.

First, in FIG. 3A, a so-called light-shielding portion 15 made of Cr or MoSi, an optically transparent light-transmitting portion 16, and a phase shifter for giving a phase difference to the phase of incident light are formed. It is a figure which shows a part of top view of the exposure mask 18 comprised from the phase shifter part 17 which was opened. The transparent portion 16 and the phase shifter portion 17 of the mask are formed with a width of approximately 0.4 μm in terms of the size on the substrate to be processed.

Using this mask, the sample is exposed by the i-line stepper as in the first embodiment. Sample is substrate 1
A sample was used in which a negative photoresist layer 2 was formed thereon, and then a photobleaching material layer 3 that exhibited a photobleaching reaction by irradiation with light was formed. For the photobleachable material layer 3, an attempt was made to use a water-soluble contrast enhancer generally used for improving the resolution of a resist.

FIG. 3B is a diagram showing a cross section of a sample as a result of exposure with the mask shown in FIG. 3A at an exposure amount that changes only the photobleaching material layer 3. Similar to the first embodiment, an unphotofading pattern latent image 7 is formed on the photofading material film 3 by shielding the phase shifter.

FIG. 3C shows a so-called light-shielding portion 15 made of Cr or MoSi, a light-transmitting portion 19, and a phase shifter portion 20 having a phase shifter for giving a phase difference to the phase of incident light. It is a top view of the exposure mask 21 comprised. However, the light transmitting portion 19 and the phase shifter portion 20 are formed of a conductive film ITO or the like so that the light transmittance is lower than that of the light transmitting portion 16 and the phase shifter portion 17 of FIG. The transmittance is reduced by the desired value. Exposure of the exposed portion of the sample shown in FIG. 3B was performed using the mask of FIG. As a result, as in the case of Example 1, the dark portion 10 formed in the photoresist layer 2 by the light blocking effect of the unphotofading pattern latent image 7 formed by exposure, and FIG.
The dark portion 11 formed by the exposure mask 21 of (c) formed a latent image as shown in FIG. Next, the photobleachable material film 3 was previously removed by washing with water. After that, development was performed using an alkaline developer of photoresist, and it was found that a fine line & space pattern 22 having a pattern line width of about 0.1 μm was obtained as shown in FIG. 3 (e). .

Further, according to the method of the second embodiment, as shown in the plan view of FIG. 3 (f), it is possible to form a pattern 22 having open pattern ends. This is achieved by arranging the pattern so that the light-transmitting portion and the phase shifter portion of the exposure mask are covered with the light-shielding portion.

The photobleaching material used in the present invention is a material containing at least one material whose transparency to incident light changes upon irradiation with light, such as a nitrone compound or a diazonium salt compound. Any material other than the materials described in this embodiment can be used in the present invention as long as the material does not deteriorate the quality of the photoresist film during the formation of the conductive material film. In addition, even if the material causes deterioration of the quality of the photoresist film when the photobleaching material film is formed,
By forming a film that does not mix with each other between the lower resist film and the photobleaching material film, it can be used in the present invention.

Further, the relationship between the exposure sensitivity of the photoresist used in Examples 1 and 2 and the exposure sensitivity of the photobleaching material film is equal to each other, or better, the exposure amount of the photoresist is smaller. It is desirable that the so-called high sensitivity, that is, the reaction at. Further, in this embodiment, the photobleachable material film was previously removed before the resist development processing, but it may be removed simultaneously with the development processing. Further, as the diaphragm (called δ) during exposure has a larger diaphragm amount, that is, a smaller value of δ, it is possible to perform exposure with light (coherent light) having a uniform phase, so that a good pattern can be formed. Further, the method of changing the transmittance of the exposure mask is not limited to the embodiment, and a method of changing the light transmittance by forming another metal film or another material having a higher light absorption on a desired portion thinly is also possible. Can be used.

FIG. 4 shows, as a third embodiment, an example of an exposure mask which can be used in the present invention and a pattern formed by using the mask. In the same figure (a), the phase shifter 23 and the phase shifter 24 are arranged so as to be shifted by half the dimension x of one phase shifter pattern, and the phase shifter pattern having a length y is surrounded by the light shielding portion 27. It is a figure of the exposure mask 28 arrange | positioned at. Further, the phase shifter 24 has a transmittance lower than that of the phase shifter 23, and the light transmitting portion 26 has a lower transmittance with respect to the incident light than the light transmitting portion 25. Using an exposure stepper that reduces and projects the pattern on the exposure mask to ⅕ (1/5) on the exposure sample, the feed pitch amount of the exposure sample at the time of exposure is set to y / 5 (⅕) on the sample. The sample having the substrate structure of Example 2 was exposed to light by setting the feed pitch amount to (y). At this time, the exposure was performed in one direction indicated by an arrow in FIG. As a result, it was possible to form a continuous fine pattern 29 as shown in FIG. Further, not limited to the embodiment of the present invention,
A wide variety of patterns can be supported by combining the light-shielding portion, the light-transmitting portion, the phase shifter portion, and the negative or positive photoresist. By using the present invention, it has become possible to manufacture ULSI devices and the like that require fine dimensions.

[0026]

According to the present invention, the treatment process is simple as compared with the method of forming a phase shifter on the photoresist, and the conventional exposure wavelength is shorter than the exposure light source wavelength, and further, the exposure wavelength is 1 or less. A fine pattern of / 2 or less can be obtained relatively easily. The concept of the present invention is i
Not only the line, but also the g-line, and if the wavelength of the exposure source is shortened, it is possible to form a finer pattern. Therefore, for example, it can be applied to so-called excimer laser lithography. Therefore, the present invention can further promote the photolithography technology in which finer patterns are required, and contribute to high integration and high performance of semiconductor elements such as ULSI, and development of ultrafine devices.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an outline of the present invention.

FIG. 2 is an explanatory diagram of the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory view of Embodiment 3 of the present invention.

[Explanation of symbols]

1 ... Substrate to be processed, 2 ... Positive photoresist layer, 3 ... Photobleaching material layer, 4 ... Phase shifter, 5, 8 ... Exposure mask,
6, 9 ... exposure, 7 ... unphotofading pattern latent image.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 21/30 574

Claims (9)

[Claims] 1. A pattern forming method comprising forming a photosensitive resist layer on a substrate to be processed and exposing the desired pattern, and then developing the desired pattern to form a desired pattern, wherein the photosensitive resist layer is formed on the substrate to be processed. And a step of forming at least one material layer containing a photobleaching material whose light transmittance changes by light irradiation, and a desired first pattern for imparting a phase difference to transmitted light was formed. A step of exposing the first pattern with an exposure amount or exposure light that changes only the layer made of the photobleaching material through a first exposure mask or reticle, and then imparting a phase difference to the transmitted light. A step of performing a second exposure through a second exposure mask or reticle on which a desired second pattern is formed, and then a step of forming a desired pattern by a developing process. Pattern forming method characterized by comprising the. 2. In a pattern forming method, wherein a photosensitive resist layer is formed on a substrate to be processed, and a desired pattern is formed by exposure to a desired pattern and then development processing, the photosensitive resist layer is formed on the substrate to be processed. And then forming at least one material layer containing a photobleaching material whose light transmittance changes by irradiation with light, for the first exposure in which a desired pattern for imparting a phase difference to the transmitted light is formed. Through the mask or reticle, the first exposure is performed with an exposure amount or exposure light that changes only the photobleachable material layer, and then a second exposure is performed on the exposure position on the formation surface of the first pattern. The exposure position of the pattern is moved by a desired distance to expose the pattern of the mask or the reticle, and then a desired pattern is formed by a developing process. Pattern forming method characterized by comprising the extent. 3. A pattern forming method comprising forming a photosensitive resist layer on a substrate to be processed, exposing the desired pattern, and then developing the desired pattern to form a desired pattern, wherein the photosensitive resist layer is formed on the substrate to be processed. And then forming at least one material layer containing a photobleaching material whose light transmittance changes by irradiation with light, an exposure mask or reticle having a plurality of types of patterns that impart a phase difference to the transmitted light. Select the desired exposure area above and perform the first exposure with an exposure amount or exposure light that changes only the photobleachable material layer, and then select the desired exposure area on the mask or the reticle. And a second exposure step, and then a development step to form a desired pattern. 4. A pattern forming method comprising forming a photosensitive resist layer on a substrate to be processed, exposing the desired pattern, and then developing the desired pattern to form the desired pattern, wherein the photosensitive resist layer is formed on the substrate to be processed. And then forming at least one material layer containing a photobleaching material whose light transmittance changes by irradiation with light, having a plurality of types of patterns that impart a phase difference to the transmitted light, and the patterns are Pattern formation, which comprises a step of performing desired multiple exposure using an exposure mask or reticle composed of patterns having different transmittances for incident light, and then a step of forming a desired pattern by development processing. Method. 5. The pattern according to claim 4, wherein the masks for exposure or the patterns having different transmittances constituting the reticle expose the photosensitive resist with an exposure amount that changes only the photobleachable material layer. A pattern forming method, which is a pattern set to obtain an exposure amount. 6. The selection of the exposure area according to claim 3,
A desired pattern is selected and exposed by covering unnecessary patterns on the exposure mask or the reticle at each exposure, or only a desired exposure area of the mask or the reticle is exposed by scanning type exposure. A pattern forming method in which a desired pattern is selected and exposed by. 7. The laminated type phase shifter according to claim 1, 2, 3 or 4, wherein the mask is formed of a phase shifter layer for imparting a phase difference to transmitted light, and the phase shifter is a laminated type phase shifter made of coating type glass. A pattern forming method, comprising a recessed phase shifter in which an uneven shape is formed on the mask substrate, and forming a pattern by using a shifter edge of the phase shifter. 8. The pattern forming method according to claim 1, 2, 3, or 4, wherein the minimum dimension and the minimum inter-arrangement dimension of the phase shifter are dimensions that give phase difference information to the phase of incident light. 9. The pattern according to claim 1, 2, 3, or 4, wherein the photobleaching material includes at least one material such as a nitrone compound or a diazonium salt compound whose transparency to incident light is changed by irradiation with light. Forming method.