JP3166812B2 - Halftone 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 photomask having a pattern mainly used in a projection exposure apparatus, and more particularly to a photomask having a high resolution by giving a phase difference to projection exposure light passing through the photomask. The present invention relates to a phase shift mask that enables pattern transfer. More particularly, the present invention relates to a halftone type phase shift mask formed by forming a halftone material film having a desired pattern on a transparent substrate.

[0002]

2. Description of the Related Art Various types of phase shift masks have been conventionally proposed. For example, a Levenson-type phase shift mask having a structure in which a transparent film is provided so as to invert the phase on one side adjacent to the opening on the mask, or a phase shifter having a resolution equal to or less than the resolution limit is formed around the pattern to be formed. There are a phase shift mask with an auxiliary pattern having a structure, a self-aligned phase shift mask having a structure in which a chromium pattern is formed on a substrate, and an overhang of a phase shifter is formed by overetching, or the like.

The phase shift mask of each of the above structures is provided with a chromium pattern and a shifter pattern on a substrate. Apart from this structure, a phase shift mask formed of only a shifter pattern is used as a transmission type phase shift mask. Shift masks and halftone phase shift masks are also known. A transmissive phase shift mask is a phase shift mask that separates patterns by utilizing the fact that light intensity becomes zero at a boundary between light transmitted through a transparent part and light transmitted through a phase shifter. Therefore, it is also called a shifter edge-based phase shift mask.

A halftone type phase shift mask is formed by forming a so-called semi-transparent phase shifter pattern having partial transparency with respect to projection exposure light on a substrate and forming the pattern at a boundary of the phase pattern. This is a phase shift mask that improves the resolution of a pattern in a portion where the light intensity is zero. Since the transmission type phase shift mask and the halftone type phase shift mask have a simple layer structure, the manufacturing steps are easy and the defects on the mask are few.

A halftone type phase shift mask is formed by laminating a halftone material film 2 on a transparent substrate 1 as shown in FIG. 7, for example. As shown in FIG. 6, a transparent substrate 1 surrounded by a halftone material film 2
The main pattern 3 is formed on the substrate. Then, a desired pattern, in this embodiment, the letter “A” is formed inside the main pattern 3.

Now, consider a case where a pattern is transferred to a resist provided on the surface of a silicon wafer by a stepper using such a halftone type phase shift mask. In this case, as shown in FIG. 6, the periphery of the main pattern 3 is surrounded by an aperture 4, and further, as shown in FIG. 7, the light R passing through the main pattern 3 is irradiated onto the wafer 5. Usually, for example, a 1/5 reduced image is formed on the wafer 5. At this time, the aperture 4 surrounding the main pattern 3 acts so that light does not shine on an area other than the predetermined exposure area of the wafer 5.

However, since a gap of 1 to 2 mm is formed between the main pattern 3 and the aperture 4,
The light that has hit the halftone material film 2 located on the outer peripheral edge of the main pattern 3 passes light of an amount corresponding to the light transmittance inherent to the halftone material film 2. Therefore, FIG.
For example, when a plurality of transfer images are sequentially formed on the wafer 5 by shifting the irradiation position of the exposure light as shown by an arrow A,
As shown in FIG. 8, two adjacent main patterns 3
Are exposed twice, and the portion Q surrounded by the four main patterns is exposed four times.

The outer peripheral portion of the main pattern 3 is a portion where the resist should not be exposed to light. For this reason, the halftone material film 2 is provided on that portion. If the resist is exposed or exposed four times, the resist is exposed.

In order to solve such a problem, as shown in FIG. 9, a phase shift mask in which a frame-shaped light-shielding band 6 is formed on a halftone material film located on the outer peripheral portion of a main pattern 3 is known. . As shown in FIG. 10, the light-shielding band 6 has a thickness of, for example, about 1 μm in a halftone material film.
It is formed by providing square opening portions 7 vertically and horizontally at a pitch of. These openings 7 are portions where the transparent substrate is directly exposed. The light-shielding band 6 is intended to block the passage of light by interference between light passing through the opening 7 and light having a phase inverted after passing through the halftone material film.

However, in this method, it is very difficult to form the opening portion 7 accurately in a square shape, and in many cases, a desired sufficient light-shielding property cannot be obtained. In order to improve the light-shielding property, it is conceivable to correct the opening 7 having an incorrect shape. However, it is very difficult to correct the opening 7, and it is more difficult to find the opening having the incorrect shape. .

[0011]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and has a light-shielding device capable of reliably blocking exposure light around a main pattern of a halftone type phase shift mask. The purpose is to provide a belt.

[0012]

In order to achieve the above object, a halftone type phase shift mask according to the present invention comprises:
In a halftone type phase shift mask formed by laminating a halftone material film on a transparent substrate, a metal film having a light-shielding property that can be selectively etched over the entire thickness direction of the halftone material film is formed by half. An upper layer of the tone material film, provided in a frame shape on the outer periphery of the main pattern, an edge of the metal film provided on the outer periphery of the main pattern,
It is provided outside the edge of the halftone material film provided on the outer peripheral portion of the main pattern.

As a halftone material film, for example, Mo
Si-based materials, more specifically, for example, the chemical symbol Mo
A material represented by SiO _X N _X (X and Y are integers) can be used.

The phrase "selective etching is possible" with respect to the metal film means that the metal film has a property that only the metal film can be removed by etching without removing the halftone material film by etching. As a metal capable of such selective etching, for example, if a halftone material film is formed of a Mo.Si-based material, Cr (chromium), CrO (chromium oxide),
CrN (chromium nitride), CrON (chromium nitride oxide), or a composite film in which these are laminated can be employed. When a composite film is employed, a two-layer structure as shown in FIGS. 11 and 12 or a three-layer structure as shown in FIG. 13 can be used.

The thickness of the metal film is, for example, 300 to 150.
Set to about 0 °. However, it is desirable that the metal film be formed to have a relatively small thickness. If the metal film is too thick, when the metal film itself is patterned by etching, it may not be possible to finish the metal film itself into an accurate shape due to the influence of so-called side etching. If the metal film is thin, the influence of side etching can be suppressed to a small degree, so that precise patterning can be performed.

With respect to the positional relationship between the frame-shaped metal film and the halftone material film, for example, the following two cases can be considered.
One is, as shown in FIGS. 1, 3 (i) and 5 (i), the inner peripheral edge of the metal film 8 on the outer peripheral portion of the main pattern 3 and the halftone material film on the outer peripheral portion of the main pattern 3. 2
Are set so that the inner peripheral edge of the main pattern 3 coincides with the direction perpendicular to the main pattern 3 (the direction perpendicular to the paper surface of FIG. 1 and the vertical direction of FIGS. 3 and 5). The other one is, as shown in FIGS. 2 and 4 (i ′), the inner peripheral edge of the metal film 8 on the outer peripheral portion of the main pattern 3 is formed inside the halftone material film 2 on the outer peripheral portion of the main pattern 3. The positional relationship between the two is set so as to be provided outside the peripheral edge.
In this case, the shift amount δ between both edges is, for example, 0.05 μ
m. The width of the metal film 8 is, for example,
It is set to 1.5 mm to 3 mm.

[0017]

In the halftone type phase shift mask according to the present invention, the passage of light is reliably blocked by the metal film formed in a frame shape. Therefore, when a transfer image is continuously formed on an exposure target such as a wafer using the phase shift mask, the area around the transfer image is not erroneously exposed. Further, since the metal film itself is formed of a material having a light-shielding property, compared with a case where a light-shielding band is formed by a combination of a halftone material film and an opening portion,
A light-shielding band having high light-shielding properties can be formed. In addition, since the metal film is made of a material that can be selectively etched with respect to the halftone material film, the metal film and the halftone material film are individually etched. Since the other film is not etched when one of the films is etched, the shapes of both the metal film and the halftone material film can be accurately formed in a desired shape.

[0018]

EXAMPLES (Comparative Example 1) As a comparative example, an example of a method of manufacturing the halftone type phase shift mask shown in FIG. 1 will be described. As shown in FIG. 3A, on a transparent substrate 1 formed of quartz, a Mo / Si-based halftone material film 2, a Cr film 18 as a metal film, and a known film forming method. Resist film 13
Was formed. The thickness of each film is one halftone material film 2
200 to 2000 °, Cr film 18 is 300 to 1500
Å, and the thickness of the resist film 13 was 3000 to 6000Å.

Next, a resist film 13 'having a desired pattern was formed by electron beam exposure and development (step b). Further, using the resist film 13 ′ as a mask, a conventional method of wet etching using an etching solution prepared by adding perchloric acid to ceric ammonium nitrate or dry etching using a chlorine-based gas is used to form the Cr metal. The film 18 was patterned into a Cr metal film 18 'having a desired pattern (step c). At this time, the halftone material film 2 is not etched by each of the above-mentioned etching agents.

Thereafter, the halftone material film 2 is subjected to dry etching using a fluorine gas such as CF ₄ , C ₂ F ₆ or the like.
Was patterned into a halftone material film 2 ′ having a desired pattern (step d). Thus, a desired main pattern 3 is formed on the phase shift mask. At this time, since the Cr metal film 18 'serving as a mask was not etched, the pattern of the halftone material film 2' was obtained with extremely high dimensional accuracy.

Next, the resist film 13 'is peeled off using oxygen plasma or sulfuric acid (step e), a resist 23 is applied again (step f), and the metal film shown in FIG. A resist film 23 ′ having a frame pattern corresponding to the frame shape of No. 8 was formed (g). Then, using the resist film 23 'as a mask, the Cr metal film 18' is patterned into the Cr metal film 8 having a desired frame shape pattern by ordinary wet etching or dry etching using a chlorine-based gas (step h). ). Also at this time, the halftone material film 2 'is not etched.

Thereafter, the resist film 23 'is peeled off using oxygen plasma or sulfuric acid, thereby forming a halftone type phase shift mask provided with a halftone material film 2' having a desired pattern and a metal film 8 having a frame shape. Obtained (step i). In this phase shift mask, the inner peripheral edge of the metal film 8 on the outer peripheral portion of the main pattern 3 and the inner peripheral edge of the halftone material film 2 ′ on the outer peripheral portion of the main pattern 3 The direction coincides with the direction at right angles (the vertical direction in FIG. 3).

The pattern of the halftone material film 2 'of the halftone phase shift mask thus obtained has been finished with extremely high dimensional accuracy. Further, in the manufacturing process from the step (a) to the step (i) in FIG. 3, a cleaning process using an acid, an alkali, or the like is performed in an appropriate step. At the time of this cleaning, the presence of the Cr metal film 18 prevents the halftone material film 2 from being changed in characteristics due to the influence of an acid, an alkali, or the like.

Embodiment 1 The halftone phase shift mask shown in FIG. 2 will be described with reference to an example of a method of manufacturing the same. FIG. 4 shows an example of the manufacturing method. This manufacturing method is basically
This is the same as the manufacturing method shown in FIG. The difference is that the resist 23 is used from the step (f) to the step (g ′).
Is formed on the resist 23 ′ having a desired frame-shaped pattern such that the inner peripheral edge of the resist 23 ′ is located outside the edge of the halftone material film 2 ′ on the outer peripheral portion of the main pattern 3. It is to be. Thereby, in the phase shift mask finally obtained in the step (i ′), the inner peripheral surface edge of the frame-shaped metal film 8 on the outer peripheral portion of the main pattern 3 is It is located outside the inner peripheral edge of the film 2 '.

According to this phase shift mask, the phase of light passing through the halftone material film 2 ′ located between the main pattern 3 and the frame-shaped metal film 8 is different from the phase of light passing through the main pattern 3. The light amplitude becomes 0 (zero) at the edge of the halftone material film 2 ′ at the outer peripheral portion of the main pattern 3 due to the inherent effect of the halftone material film that the halftone material film is inverted. Therefore, an effect is obtained that the boundary line between the main pattern 3 and the outer peripheral portion is more clearly transferred onto the exposure object, for example, a silicon wafer.

Comparative Example 2 FIG. 5 shows another manufacturing method for manufacturing the phase shift mask shown in FIG. In this manufacturing method, the same processing as in the previous embodiment shown in FIG. 3 is performed from step (a) to step (c), and a metal film 18 ′ having a desired pattern is formed on the transparent substrate 1.

Thereafter, the resist 13 'is peeled off (step d''), and a new resist 23 is applied (step e''). Then, a resist 23 ′ having a frame-shaped pattern is formed by electron beam exposure and development (step f ″), and the halftone material film 2 is formed into a desired pattern using the resist 23 ′ and the metal film 18 ′ as a mask. It is etched into the film 2 '. Then
The metal film 18 'is etched into the frame-shaped metal film 8 using the frame-shaped pattern resist 23' as a mask (step h ''), and the resist 23 'is peeled off to obtain a halftone phase shift mask required. (Step i).

[0028]

According to the halftone type phase shift mask of the present invention, the passage of light is reliably blocked by the light-shielding metal film formed in a frame shape. Therefore, when a transferred image is continuously formed on an exposure target such as a wafer using the halftone type phase shift mask, the area around the transferred image is not erroneously exposed. Also, since the metal film itself is formed of a material having a light shielding property,
A light-shielding band having a higher light-shielding property can be formed than a conventional light-shielding band in which a light-shielding band is formed by a combination of a halftone material film and an opening.

Further, since the metal film is made of a material that can be selectively etched with respect to the halftone material film, the metal film and the halftone material film are individually etched. When one of the metal film and the halftone material film is etched, the other film is not etched, so that the shapes of both the metal film and the halftone material film can be accurately formed into desired shapes.

Further, the phase of the light passing through the halftone material film located between the main pattern and the frame-shaped metal film is inverted with respect to the phase of the light passing through the main pattern. By virtue of this action, the light amplitude becomes 0 (zero) at the edge of the inner peripheral surface of the halftone material film forming the main pattern. Therefore, the boundary line between the main pattern and the peripheral portion around the main pattern is more clearly transferred onto the exposure object, for example, a silicon wafer.

[Brief description of the drawings]

FIG. 1 is a plan view showing a comparative example of a halftone phase shift mask according to the present invention.

FIG. 2 is a plan view showing one embodiment of a halftone type phase shift mask according to the present invention.

FIG. 3 is a diagram showing an example of a manufacturing method for manufacturing the comparative example shown in FIG.

FIG. 4 is a diagram showing an example of a manufacturing method for manufacturing the embodiment shown in FIG.

FIG. 5 is a diagram showing another example of a manufacturing method for manufacturing the comparative example shown in FIG.

FIG. 6 is a plan view showing a conventional phase shift mask and a state in which an aperture is put on the mask.

FIG. 7 is a side sectional view showing an example of an exposure system using a halftone type phase shift mask.

FIG. 8 is a schematic diagram showing a state where a main pattern is transferred onto an exposure target using a conventional halftone type phase shift mask.

FIG. 9 is a plan view showing an example of a conventional halftone type phase shift mask.

FIG. 10 is an enlarged view showing a light shielding zone of the conventional halftone type phase shift mask shown in FIG.

FIG. 11 is a diagram showing a partial cross-sectional structure of one embodiment of a metal film.

FIG. 12 is a view showing a partial cross-sectional structure of another embodiment of the metal film.

FIG. 13 is a diagram showing a partial cross-sectional structure of still another embodiment of the metal film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Halftone material film 2 'Patterned halftone material film 3 Main pattern 4 Light-shielding aperture used at the time of exposure 5 Wafer (exposure target) 8 Frame-shaped metal film 13 Resist film 13' Resist film (halftone material) 18 Cr metal film 18 'Cr metal film (for patterning halftone material film) 23 Resist film 23' Resist film (for patterning light shielding metal film)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-223464 (JP, A) JP-A-6-83034 (JP, A) JP-A-6-282063 (JP, A) JP-A-6-230 289589 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (1)

(57) [Claims] 1. A halftone type phase shift mask comprising a halftone material film laminated on a transparent substrate,
A metal film having a light-shielding property that can be selectively etched over the entire region in the thickness direction of the halftone material film is provided on the halftone material film in a frame shape on an outer peripheral portion of the main pattern, Edge of the metal film provided on the outer periphery of
The half is provided on the outer periphery of the main pattern.
A halftone type phase shift mask provided outside an edge of a tone material film .