JP3225673B2 - Method for manufacturing phase shift mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a phase shift mask used as a photomask (reticle) for photolithography in the field of manufacturing semiconductor devices, and more particularly to a method of manufacturing a so-called edge-enhancement type phase shift mask. The present invention relates to a method for improving the processing accuracy of a main pattern and an auxiliary pattern.

[0002]

2. Description of the Related Art In the field of semiconductor integrated circuits, submicron level processing has already been realized in mass production factories, and quarter micron level processing which will be indispensable in the future half micron level and further 64 Mbit DRAM class.
Research on level processing is underway.

The technology that has been the key to the advance of such fine processing is photolithography. Conventional advances have been made to shorten the exposure wavelength and increase the numerical aperture of a reduction projection lens of a stepper (reduction projection exposure apparatus). NA). Of these, regarding the shortening of the wavelength, KrF excimer
Although deep ultraviolet lithography using laser light (248 nm) is promising, development of a resist material having sufficient performance has been delayed, and it is difficult to immediately introduce it into a mass production site.

On the other hand, a so-called super-resolution technique for increasing the resolution by using a harmonic component of exposure light is used for g-line (436 nm) lithography using a conventional high-pressure mercury lamp as a light source or i-line (365 nm). Many attempts have been made to extend lithography life.

One of the super-resolution techniques that has been spotlighted is a phase shift method. This is a method for improving the resolution by giving a local phase difference to the exposure light transmitted through the photomask and utilizing the mutual interference of the transmitted light. In the phase shift method, in order to generate a phase difference, it is necessary to form a phase shifter having a predetermined pattern on a transparent substrate made of glass, quartz, or the like constituting the reticle. This phase difference is usually set to 180 °, and is given by a transparent film pattern made of SOG (spin-on-glass) or the like, or a groove formed by etching a transparent substrate to a predetermined depth.

The principle of resolution improvement by the phase shift method is as follows.
There are broadly divided into spatial frequency modulation and edge enhancement, and various types of phase shift masks have been proposed by combining these principles and mask structures. Among them, the latter edge enhancement has a great effect of improving the resolution of an isolated pattern such as a contact hole. A typical phase shift mask based on the principle of edge enhancement has an auxiliary pattern having a fine size equal to or smaller than the resolution limit around a main pattern. Here, when the phase difference is generated by carving a groove in the glass substrate, either the main pattern or the auxiliary pattern may be used as the groove.

In any case, since the phase of the transmitted light is inverted between the main pattern and the auxiliary pattern forming the light transmitting portion, the light intensity distribution of the transmitted light in the central main pattern becomes steep, and the resolution is increased. It improves.

[0008]

By the way, in the manufacturing process of the edge-enhancement type phase shift mask in which the auxiliary pattern is arranged around the main pattern as described above, when the main pattern forming region is defined and when the auxiliary pattern is formed. In defining the formation region, lithography must be performed twice, once each.

In general, lithography for forming a light-shielding film pattern on a reticle is performed by electron beam lithography. However, in a process in which an electrically isolated light-shielding film pattern is formed by the first electron beam lithography, when the second electron beam lithography is performed, the residual charge of the above-described isolated light-shielding film pattern is reduced. Due to the influence, the electron beam is deflected, and a desired pattern may not be obtained.

In order to solve this problem, for example, in Japanese Unexamined Patent Publication No. Hei 4-50942, after forming a groove serving as a main pattern or an auxiliary pattern in a transparent substrate by the first electron beam lithography and etching, the entire surface of the substrate is removed. After coating with a transparent conductive film, the second electron beam
A technique for performing lithography is disclosed. However, this transparent conductive film must be removed by etching in a later step under conditions that can ensure selectivity to the light-shielding film. For example, when MoSi _x (molybdenum silicide) is used as the transparent conductive film, it is removed using a fluorine-based gas such as CF ₄ .

However, since the light-shielding film serving as the etching base at this time is an extremely thin film, such selective etching is not easy. Moreover, since the transparent substrate is simultaneously etched by this etching,
The previously formed groove is further deepened. In order to offset the change in the amount of phase shift due to this, theoretically, the depth of the groove should be set small in advance in consideration of the increase in the depth at this time. It is technically difficult to always perform the control with good reproducibility.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method capable of producing an edge-enhancement type phase shift mask with high accuracy and high reproducibility without being affected by residual charges in an isolated light-shielding film pattern. I do.

[0013]

SUMMARY OF THE INVENTION A method of manufacturing a phase shift mask according to the present invention is proposed in view of the above-mentioned object, and a light transmitting portion opened in a light shielding film pattern on a transparent mask substrate is provided. A method of manufacturing a phase shift mask composed of a main pattern, and an auxiliary pattern arranged around the main pattern to shift the phase of exposure light, wherein the phase shift mask is formed on the entire surface of a transparent mask substrate. A resist layer is formed on the light-shielding film, and has an opening that follows the main pattern by charged particle beam irradiation and development.
Forming a pattern and selectively etching away the light-shielding film using the resist pattern as a mask,
Forming a groove-shaped main pattern by etching a part of the transparent mask substrate in a thickness direction; removing the resist pattern; forming a photoresist layer on the entire surface of the substrate; Forming a photoresist pattern having an opening following the light transmitting portion by a developing process, and etching and removing the light shielding film exposed in the opening using the photoresist pattern as a mask to form an auxiliary pattern. It has a step of forming.

According to the present invention, a resist layer is formed on a light-shielding film formed on the entire surface of a transparent mask substrate, and a resist pattern having an opening following an auxiliary pattern is formed by irradiation with a charged particle beam and a developing process. And selectively etching away the light-shielding film using the resist pattern as a mask, and further etching a part of the transparent mask substrate in a thickness direction to form a groove-shaped auxiliary pattern, Removing the resist pattern, forming a photoresist layer on the entire surface of the substrate, forming a photoresist pattern having an opening at least following the main pattern in the light transmitting portion by light irradiation and development processing, Using the photoresist pattern as a mask, the light shielding film exposed in the opening is removed by etching to form a main pattern. And it has a process.

Further, the present invention is characterized in that the resist layer is formed by using an electron beam resist material, and the charged particle beam is irradiated with an electron beam.

[0016]

The point of the present invention is that the first lithography is performed by lithography using a charged particle beam such as an electron beam as in the past, but the second lithography is performed by photolithography. These first two
Any of the first lithography may define the formation region of the main pattern or the auxiliary pattern. In any case, since pattern formation by photolithography is not affected by the residual charge on the substrate,
Each time, the pattern formation accuracy is significantly improved as compared with the case where electron beam lithography is performed.

Also, by adopting photolithography,
A series of processes related to the transparent conductive film as described in the above-mentioned publications, that is, the formation of the transparent conductive film and the selective etching of the light-shielding film become unnecessary. Further, by omitting the selective etching, the depth of the groove already formed in the transparent substrate does not change, thereby facilitating the process design. Thereby, the processing accuracy of the phase shift mask is improved, and the quality is uniform.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

Embodiment 1 This embodiment is an example of manufacturing an edge-emphasized phase shift mask in which a main pattern of a contact hole is formed by a groove. This process will be described with reference to FIGS. First, as shown in FIG. 1A, an electron beam (EB) irradiation was performed on a mask substrate on which a Cr light-shielding film 2 and a positive-type electron beam resist layer 3 were sequentially formed on a quartz substrate 1. . This electron beam irradiation was performed in a region following the main pattern of the contact hole.

Next, the electron beam resist layer 3 is developed to selectively dissolve and remove the electron beam irradiation area.
As shown in (b), the opening 4 was formed following the main pattern. Next, dry etching is performed, and FIG.
As shown in FIG. 5, the Cr light-shielding film 2 exposed inside the opening 4 was removed, and a groove 1a having a predetermined depth was formed in the quartz substrate 1. Thereafter, the electron beam resist layer 3 was removed. Thus, a main pattern corresponding to the actual contact hole pattern is formed.

The refractive index n of the quartz substrate 1 used here is
Is 1.45. In general, in a phase shift mask, the thickness (here, the depth of the groove) of the phase shifter d required to invert the phase by 180 ° is d = λ / 2 (n−
1) (1 is the refractive index of air) In this embodiment,
The phase shift mask to be manufactured is an i-line stepper (λ = 3
65 nm), the groove 1a is calculated from the above formula.
Was 405 nm in depth.

Next, an area for forming an auxiliary pattern is defined.
Photolithography was performed. That is, FIG.
As shown in (d), a positive type
Forming a photoresist layer 5;
Another photo mask PM ₁Through the wavelength λ₁Simply
Selective exposure was performed with colored light. Here, the photomask P
M₁Is a method in which a Cr light-shielding film 7 deposited on a quartz
Patterning by electron beam lithography
It is something that is done. The opening provided on the Cr light shielding film 7
The opening 8 is a region where a main pattern and an auxiliary pattern are formed.
That is, it follows the pattern of the light transmitting portion.

The above-mentioned selective exposure is the same-size exposure between the photomasks, and can be performed using an apparatus similar to an existing glass substrate exposure apparatus for a liquid crystal display. The mask substrate formed with the photomask PM ₁ and finally phase shift mask, positional accuracy equivalent accuracy by using the alignment marks (not shown) is applied to the current stepper (reduction projection exposure apparatus) Be matched. At this time, although a small amount of electric charge caused by the scattered electrons at the time of the previous electron beam irradiation remains on the surface of the quartz substrate 1, photolithography was not affected by the residual electric charge.

Next, the photoresist layer 5 was developed to selectively dissolve and remove the exposed area, thereby forming an opening 9 covering up to the auxiliary pattern area as shown in FIG. 2 (e). Next, as shown in FIG. 2F, the Cr light-shielding film 2 exposed inside the opening 4 was removed by dry etching to form an auxiliary pattern 1b. After this,
The photoresist layer 5 was removed to complete the phase shift mask.

When this phase shift mask is exposed from the non-formed surface side of the Cr light shielding film 2 with exposure light having a wavelength of λ ₂ , the phase of the transmitted light of the groove 1 a, which is the main pattern, of the auxiliary pattern 1 b orbiting around the groove 1 a It is inverted with respect to the phase of the transmitted light.
Thereby, the contrast is enhanced at the edge portion of the main pattern, and a fine contact hole pattern can be resolved.

Embodiment 2 This embodiment is an example of manufacturing an edge-emphasized phase shift mask in which an auxiliary pattern around a contact hole is formed by a groove. This process will be described with reference to FIGS. First, as shown in FIG. 3A, an electron beam was applied to a mask substrate on which a Cr light-shielding film 12 and a positive-type electron beam resist layer 13 were sequentially formed on a quartz substrate 11. This electron beam irradiation was performed in a region following the auxiliary pattern around the contact hole.

Next, the electron beam resist layer 13 was developed to selectively dissolve and remove the electron beam irradiation region, thereby forming an opening 14 following the auxiliary pattern as shown in FIG. 3B. . Next, dry etching is performed, and FIG.
As shown in (c), the Cr light-shielding film 12 exposed inside the opening 14 was removed, and a groove 411 having a depth of 405 nm was formed in the quartz substrate 11. The island region surrounded by the groove 11a is the main pattern 11b corresponding to the actual contact hole pattern. Thereafter, the electron beam resist layer 13 was removed.

Next, the Cr light shielding film 1 on the main pattern 11b
2 to selectively remove 2
Photolithography for forming a pattern was performed. That is, as shown in FIG. 4D, a positive photoresist layer 15 is formed on the entire surface of the mask substrate, and another photoresist mask PM is formed on this photoresist layer 15.
2, selective exposure was performed with monochromatic light of wavelength λ1. The exposure energy at this time was set to such a value that only the thickness of the photoresist layer 15 on the Cr light shielding film 12 could be exposed.

Here, the photomask PM ₂ is formed by patterning the Cr light shielding film 17 deposited on the quartz substrate 16 by ordinary electron beam lithography. Now, the width of the groove 11a is c, the main pattern 1
Assuming that the width of 1b is b, the width a of the opening 18 provided in the Cr light shielding film 17 is determined so as to satisfy the relationship of ab ≦ 2c. The idea of forming the groove-shaped auxiliary pattern first and removing the light-shielding film on the central main pattern later to prevent the main pattern and the auxiliary pattern from being displaced is disclosed in, for example, Japanese Patent Application Laid-Open No. HEI 4-1992. −51
151 or the like.

In particular, in the example shown in FIG.
When the relationship of b = c is satisfied, the photomask P
Alignment margin of the M ₂ and the mask substrate is the largest. In other words, when both are accurately aligned, the region up to the center of the groove 11a is exposed by the exposure light transmitted through the opening 18. A deviation from this state to the left and right of a size of c / 2 is allowed.

This photolithography was not affected by the residual charges due to the previous electron beam irradiation.

Next, the photoresist layer 15 is developed to selectively dissolve and remove the exposed area, thereby forming an opening 19 covering up to half of the auxiliary pattern 11a as shown in FIG. 4 (e). . The depth of the opening 19 is a depth at which the Cr light shielding film 12 is just exposed.

Next, dry etching is performed, and FIG.
As shown in (f), the Cr light-shielding film 12 on the main pattern 11b exposed inside the opening 4 was removed. Thereafter, the photoresist layer 15 was removed to complete a phase shift mask. When this phase shift mask is exposed with exposure light of wavelength λ ₂ from the non-formed surface side of the Cr light-shielding film 2, the phase of the light transmitted through the groove 11a, which is the auxiliary pattern, is transmitted through the main pattern 11b located at the center thereof. Is inverted with respect to the phase of Thereby, the contrast is enhanced at the edge portion of the main pattern 11b, and the fine contact hole
The pattern can be resolved.

Although the present invention has been described based on two embodiments, the present invention is not limited to these embodiments. For example, the materials constituting the mask substrate are not limited to those described above, and a glass substrate may be used instead of the quartz substrate, or a negative resist material may be used instead of the positive electron beam resist material or the photoresist material. It doesn't matter.

The first lithography can be performed by ion beam irradiation instead of the electron beam irradiation described above. In addition, it goes without saying that the exposure wavelength in photolithography, the depth of the groove formed as the main pattern or the auxiliary pattern, and the like can be appropriately changed.

[0036]

As is apparent from the above description, according to the present invention, two out of two lithography steps for forming either the main pattern or the auxiliary pattern in the manufacturing process of the edge-enhancement type phase shift mask. The second lithography is performed by photolithography. Thus, even if residual charges exist on the mask substrate by the first lithography using the charged particle beam, a precise main pattern or auxiliary pattern can be formed without being affected by the residual charges.

The present invention is extremely promising as a life-extending measure for i-line lithography, and
64Mbit DRAM where m is the main pattern rule
Alternatively, a semiconductor device such as a 16 Mbit SRAM can be manufactured with high reliability.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a process for manufacturing an edge-enhancement type phase shift mask for forming a contact hole pattern having a groove-shaped main pattern in the order of steps, and FIG. A mask substrate on which a Cr light-shielding film and an electron beam resist layer are formed; (b) shows a state in which the electron beam resist layer is developed to form an opening; (c)
Represents a state in which the Cr light-shielding film exposed in the opening is removed, the quartz substrate is etched to a predetermined depth to form a groove-shaped main pattern, and the electron beam resist layer is removed.

FIG. 2 is a schematic cross-sectional view showing a continuation of the process example of FIG. 1; FIG. Area to be selected and exposed,
(E) is a state in which the photoresist layer is developed to form an opening, and (f) is a state in which the Cr light-shielding film exposed in the opening is removed to form an auxiliary pattern, and the photoresist layer is removed. The state in which the phase shift mask is completed is shown.

FIG. 3 is a schematic cross-sectional view showing an example of a process for manufacturing an edge-enhancement type phase shift mask for forming a contact hole pattern having a groove-shaped auxiliary pattern in the order of steps, and FIG. A mask substrate on which a Cr light-shielding film and an electron beam resist layer are formed; and (b) a state in which an opening is formed by developing the electron beam resist layer.
(C) removes the Cr light-shielding film exposed in the opening,
A state in which a quartz substrate is etched to a predetermined depth to form a groove-shaped auxiliary pattern and an electron beam resist layer is removed is shown.

FIG. 4 is a schematic cross-sectional view showing a continuation of the process example of FIG. 3; (E) is a state in which an opening is formed by developing the photoresist layer, and (f) is a state in which a Cr light-shielding film exposed in the opening is removed. The phase shift mask is completed by forming the main pattern and removing the photoresist layer, respectively.

[Explanation of symbols]

1,11: quartz substrate 1a: groove (main pattern) 1b: auxiliary pattern 2,12: Cr light-shielding film 3,13 (positive type) electron beam resist layer 5,15 ... (positive) photoresist layer 11a ... groove (auxiliary patterns) 11b ... main pattern PM _1, PM ₂ ... photomask

Claims (3)

(57) [Claims] 1. A light-transmitting portion opened in a light-shielding film pattern on a transparent mask substrate is constituted by a main pattern and an auxiliary pattern arranged around the main pattern to shift the phase of exposure light. In the method for manufacturing a phase shift mask, a resist layer is formed on a light-shielding film formed on the entire surface of a transparent mask substrate, and a resist pattern having an opening portion following a main pattern is formed by irradiation with a charged particle beam and development processing. Forming, and selectively etching away the light-shielding film using the resist pattern as a mask, and further forming a groove-shaped main pattern by etching a part of the transparent mask substrate in a thickness direction, Removing the resist pattern, forming a photoresist layer on the entire surface of the base, and irradiating and developing the opening to follow the light transmitting portion. Forming a photoresist pattern having a phase shift, and forming an auxiliary pattern by etching and removing the light-shielding film exposed in the opening using the photoresist pattern as a mask. Manufacturing method of mask. 2. A light-transmitting portion opened in a light-shielding film pattern on a transparent mask substrate is composed of a main pattern and an auxiliary pattern disposed around the main pattern to shift the phase of exposure light. In the method for manufacturing a phase shift mask, a resist layer is formed on a light-shielding film formed on the entire surface of a transparent mask substrate, and a resist pattern having an opening following an auxiliary pattern is formed by irradiation with a charged particle beam and a developing process. Forming, and selectively etching away the light-shielding film using the resist pattern as a mask, and further forming a groove-shaped auxiliary pattern by etching a part of the transparent mask substrate in a thickness direction, Removing the resist pattern, forming a photoresist layer on the entire surface of the substrate, and irradiating with light and developing to reduce the amount of light in the light transmitting portion. Forming a photoresist pattern having an opening also following the main pattern, and forming a main pattern by etching and removing the light shielding film exposed in the opening using the photoresist pattern as a mask. A method for manufacturing a phase shift mask. 3. The method according to claim 1, wherein the resist layer is made of an electron beam resist material, and the charged particle beam irradiation is an electron beam irradiation. .