JPH05249649A - Photomask and its production - Google Patents

Abstract

PURPOSE:To facilitate formation of a fine contact hole pattern with good reproducibility. CONSTITUTION:This photomask is constituted of four regions divided by two pieces of boundary lines intersecting at one point on a transparent mask substrate which allows the transmission of exposing light. Phase shifters in which the phases of the exposing light transmitted through the four regions anticlockwise, substantially and respectively have relations 0, pi/2, pi, (3/2)pi, are provided in the region 1, the region 2, the region 3 and the region 4. The light intensity on the A-A' plane and the light intensity on the B-B' plane are zero at the intersected point of the four regions. As a result, the formation of the fine contact hole pattern at the intersected of the four regions is enabled by using a negative type resist.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask and its manufacturing method, and more particularly to a photomask using a phase shift method and its manufacturing method.

[0002]

2. Description of the Related Art FIG. 16 is a diagram showing a conventional example, and is a diagram showing a method for forming a fine contact hole pattern using the phase shift method, which was previously proposed by the present inventors (Patent application No. 2-283372).

In FIG. 16, 31 is a first exposure mask, 32 is a transparent substrate, 33 is a phase shift layer, 34 is a second exposure mask, 35 is a transparent substrate, 36 is a phase shift layer, 37.
Reference numerals 38 and 38 denote linear regions in which the intensity of transmitted light is small, and 39 denotes a point in which the intensity of transmitted light is weak.

A method of forming a fine contact hole pattern using the conventional phase shift method will be described below. [First exposure] FIG. 10A shows two phase inversion layers 33 having a rectangular shape including an end portion extending in the vertical direction on the transparent substrate 32.
The 1st exposure mask 31 which formed is shown.

FIG. 1B shows the transparent substrate 32 and the phase inversion layer 3 when exposed by using the first exposure mask 31.
3 shows a state in which the exposure light transmitted through 3 and 3 interfere with each other to generate a linear region 37 in which the intensity of the transmitted light is small.

[Second exposure] FIG. 3C shows a second exposure mask 34 in which two rectangular phase inversion layers 36 including edges extending in a lateral direction are formed on a transparent substrate 35. Shows.

FIG. 3D shows the transparent substrate 35 and the phase inversion layer 3 when exposed by using the second exposure mask 34.
6 shows a state in which the exposure lights that have passed through 6 and 6 interfere with each other to generate a linear region 38 in which the intensity of the transmitted light is low.

[Results of First and Second Exposures] FIG. 6E shows the results of the first and second exposures. As shown in the figure, as a result of the first exposure and the second exposure, the intensity of the transmitted light at 14 points 39 where the ends of the phase inversion layer intersect is higher than that of other portions. It is left in a weak state.

As described above, when the first exposure mask 31 and the second exposure mask 34 are used to perform two exposures, both ends of the phase inversion layer (long sides of the rectangular phase inversion layer) are exposed. Since the intensity of the transmitted light is almost the same, the interference of the transmitted light is effectively performed along this edge portion, and a linear region where the intensity of the transmitted light is weak is generated, so that the first exposure and the second exposure are performed. The second exposure leaves a small region of weak transmitted light intensity at the intersection.

Therefore, the subject of the above-mentioned exposure is the negative resist coated on the insulating film, and after the first exposure by the first mask and the second exposure by the second mask, the negative resist is applied. By developing the resist, a fine contact hole pattern can be formed in the negative resist.

[0011]

The conventional method of forming a fine contact hole pattern using the phase shift method requires two photomasks and two exposures, which is complicated. , There was a problem.

Further, since the exposure process is required twice, it is difficult to align the positions, and it is impossible to form a fine contact hole pattern with good reproducibility.
The present invention solves the above problems and provides a photomask and a method for manufacturing the same, which makes it possible to form a fine contact hole pattern easily and with good reproducibility. The purpose is to provide.

[0013]

In order to achieve the above object, the present invention is configured as follows. (1) A photomask using a phase shift method, which intersects at one point on a transparent mask substrate that transmits exposure light.
Divided by the boundary line of the book, four regions consisting of a first region, a second region, a third region, and a fourth region are formed counterclockwise around the intersection point. The phases of the exposure light transmitted through the four regions are substantially 0, π / 2, π, (counterclockwise or clockwise) in the second region, the third region, and the fourth region, respectively. 3/2)
A phase shifter having a relationship of π is provided.

(2) A method of manufacturing a photomask having the above structure (1), wherein a first transparent film is formed on a transparent substrate,
A step of sequentially depositing a second transparent film and a third transparent film,
A step of selectively covering the first region and the second region with a first mask material; a step of completely removing the third transparent film on the third region and the fourth region using the first mask material as a mask; Using the first mask material as a mask, the third region and the fourth region
Removing the second transparent film on the region to a predetermined depth,
After removing the first mask material, selectively covering the first region and the fourth region with the second mask material, and using the second mask material and the third transparent film on the second region as a mask,
A step of completely removing the second transparent film on the third region, and a step of completely removing the third transparent film on the second region and the first transparent film on the third region using the second mask material as a mask. Configure to include.

(3) A method of manufacturing a photomask having the structure of (1) above, which comprises depositing a transparent film on a transparent substrate and selecting the first region and the second region with a first mask material. Step of removing the transparent film on the third region and the fourth region by using the first mask material as a mask, and transparent of the third region and the fourth region by using the first mask material as a mask. A step of removing the substrate to a predetermined depth; a step of removing the first mask material and then selectively covering the first region and the fourth area with a second mask material;
Using the mask material and the transparent film on the second region as a mask,
Removing the transparent substrate in the third region to a predetermined depth,
The second mask material is used as a mask to remove all the transparent film on the second region and simultaneously remove the transparent substrate in the third region to a predetermined depth.

[0016]

FIG. 1 is a diagram showing the principle of the present invention.
Is a top view of the photomask according to the present invention, and FIG. 6B shows the light intensity on the AA ′ plane and the light intensity on the BB ′ plane of FIG.

As shown in FIG. 1 (a), the photomask according to the present invention comprises a transparent mask substrate that transmits exposure light,
It is composed of four regions divided by two boundary lines intersecting at one point.

Counterclockwise around the intersection, the region 1,
When referred to as region 2, region 3, and region 4, the phase of the exposure light transmitted through these four regions is substantially counterclockwise in region 1, region 2, region 3, and region 4. Are provided with phase shifters having a relationship of 0, π / 2, π, (3/2) π, respectively.

A- of the photomask having the above structure
The light intensity on the A ′ plane and the light intensity on the BB ′ plane are illustrated in FIG. From Figure (b), Region 1,
It can be seen that the light intensity is zero at the intersection of the two boundary lines that partition the regions 2, 3, and 4. From this result, it is possible to form a fine contact hole pattern at the intersection of the four regions by using the negative resist.

From the curve showing the light intensity on the plane AA 'in FIG. 2 (b), the light intensity of the region where the adjacent regions are in contact is 1
Although it has fallen to about / 2, the light intensity ratio with the intersection is sufficiently large, so it does not pose a problem.

[0021]

【Example】

[Embodiment 1] Hereinafter, a first method of manufacturing a photomask according to the present invention will be described in the order of steps.

[Step 1, FIG. 2] A silicon nitride film 12, a silicon oxide film 13, and a silicon nitride film 14 are sequentially deposited on a quartz substrate 11 by CVD method CVD or sputtering method.

At this time, the respective film thicknesses are converted into the phase of the exposure light, and the phase conversion thickness of the silicon nitride film 12 = π / 2 The phase conversion thickness of the silicon oxide film 13 = 2π The silicon nitride film 14 The phase conversion thickness is set to be π / 2.

Between the phase and the physical film thickness, the film thickness (nm) at which the phase difference is π = λ (nm) / (2 ×
(N-1)) However, there is a relation of λ: wavelength of exposure light and n: refractive index.

As a specific example, when the i-line is used as the exposure light, the silicon nitride film (π / 2) = (365 nm / (2 ×
(2.05-1))) / 2 = 87 nm, and the silicon oxide film (2π) = (365 nm / (2 × (1.
46-1))) × 2 = 793 nm.

[Step 2, FIG. 3] After the first resist is applied on the entire surface, as shown in the left side of FIG. 3, a first EB (electron beam) drawing method is performed so as to cover only the regions 1 and 2.
Pattern the resist.

Using the first resist as a mask, the silicon nitride film in the region 3 and the silicon nitride film in the region 4 are removed by CF ₄
It is removed by the RIE method using + O ₂ . Using the first resist as a mask, the silicon oxide film in the region 3 and the region 4
The silicon oxide film of is removed by the RIE method using CHF ₃ by the thickness of π in phase conversion (396 nm).

The phase of each region at this stage is as follows. Region 1: 0 Region 2: 0 Region 3: (3/2) π Region 4: (3/2) π [Step 3, FIG. 4] After stripping the first resist, a second resist is applied over the entire surface.

As shown on the left side of FIG. 4, area 1 and area 4
The second resist is patterned by the EB drawing method so as to cover only this. Using the second resist and the silicon nitride film remaining on the surface of the region 2 as a mask, the silicon oxide film in the region 3 is removed by the RIE method using CHF ₃ .
(In RIE using CHF ₃ , the etching rate of the silicon nitride film is sufficiently slower than that of the silicon oxide film.) The phase of each region at this stage is as follows.

Region 1: 0 Region 2: 0 Region 3: (3/2) π + π = (5/2) π Region 4: (3/2) π [Step 4, FIG. 5] Using the second resist as a mask Area 2
And the silicon nitride film in the region 3 are replaced by C
It is removed by the RIE method using F ₄ + O ₂ . (Note that
In RIE using CF ₄ + O ₂ , the etching rate of the silicon oxide film is sufficiently slower than that of the silicon nitride film. ) The phase of each region at this stage is as follows.

Region 1: 0 Region 2: π / 2 Region 3: (5/2) π + π / 2 = 3π Region 4: (3/2) π The photomask according to this embodiment is completed through the above steps. .. The finished photomask is shown in FIG. Phase 2π
Is equivalent to the phase 0, the phase 3π of the region 3 is equivalent to π, and the phase of each region is as follows.

Region 1: 0 Region 2: π / 2 Region 3: π Region 4: (3/2) π [Embodiment 2] A second method of manufacturing a photomask according to the present invention will be described below in the order of steps. ..

[Step 1, FIG. 7] An alumina film 22 is deposited on a quartz substrate 21 by a CVD method or a sputtering method to have a thickness of π / 2 in terms of phase.

The phase conversion film thickness in the case of the alumina film is as follows when the i-line is used as the exposure light. Alumina film (π / 2) = (365 nm / (2 × (1.6
2-1)) / 2 = 147 nm [Step 2, FIG. 8] After applying the first resist on the entire surface, as shown in the left part of FIG. 8, a first EB drawing method is performed so as to cover only the regions 1 and 2. 1 Pattern resist.

Using the first resist as a mask, the alumina film in region 3 and the alumina film in region 4 are removed by sputtering. Using the first resist as a mask, the quartz substrate in the region 3 and the quartz substrate in the region 4 are subjected to R using CHF _3.
By the IE method, the thickness of π (396 nm) in terms of phase is removed.

The phase of each region at this stage is as follows. Region 1: 0 Region 2: 0 Region 3: (3/2) π Region 4: (3/2) π [Step 3, FIG. 9] After stripping the first resist, a second resist is applied over the entire surface.

As shown in the left side of FIG. 9, area 1 and area 4
The second resist is patterned by the EB drawing method so as to cover only this. Using the second resist and the alumina film remaining on the surface of the region 2 as a mask, the quartz substrate in the region 3 is phase-converted (3/2) by the RIE method using CHF _3.
π− (thickness of alumina film) = 396 × 1.5 (nm) −
Only 147 (nm) is removed.

The phase of each region at this stage is as follows. Area 1: 0 Area 2: 0 Area 3: (3/2) π + ((3/2) π−α) = 3π−
α region 4: (3/2) π where α is the phase difference corresponding to 147 nm.

[Step 4, FIG. 10] Using the second resist as a mask, the entire surface is etched at a substantially uniform etching rate by the sputtering method. Since the sputtering method is a physical etching method, the etching rate hardly depends on the material. In this way, etching is performed until the alumina film in the region 2 is lost. (Note that the second resist remains in regions 1 and 2 even if sputter etching is performed.
The film thickness is set in advance. ) The phase of each region at this stage is as follows.

Region 1: 0 Region 2: π / 2 Region 3: 3π−α + α = 3π Region 4: (3/2) π The photomask according to this embodiment is completed through the above steps. The completed photomask is shown in FIG. Phase 2
Since π is equivalent to phase 0, the phase 3π of region 3 is equivalent to π, and the phase of each region is as follows.

Region 1: 0 Region 2: π / 2 Region 3: π Region 4: (3/2) π [Example of forming contact hole pattern of DRAM using photomask according to the present invention] FIG. For example: The positions of the contact holes of the bit line contact and the storage contact of this memory cell are as shown in FIG.

Below, examples of a photomask for forming a bit line contact hole pattern and an example of a photomask for forming a storage contact hole pattern, to which the present invention is applied, will be shown.

[Example of Photomask for Forming Bit Line Contact Hole Pattern, FIG. 14] FIG. 14 shows an example of a photomask for forming a bit line contact hole pattern to which the present invention is applied.

As shown in FIG. 14, a bit line contact hole pattern is formed at an intersection of four regions having a relationship of 0, π / 2, π, (3/2) π in a counterclockwise direction. It

When the i-line (λ = 365 nm) is used as the exposure light and the negative resist is used, a fine bit line contact hole pattern having a diameter of about 0.2 μm can be formed.

[Example of Photomask for Forming Storage Contact Hole Pattern, FIG. 15] FIG. 15 shows an example of a photomask for forming storage contact hole pattern to which the present invention is applied.

As shown in FIG. 15, the phase is clockwise.
0, π / 2, π, (3/2) π, the intersections of the four regions having a relation of 0, π /
An accumulation contact hole pattern is formed at an intersection of four regions having a relationship of 2, π, (3/2) π.

When the i-line (λ = 365 nm) is used as the exposure light and the negative resist is used, a fine accumulation contact hole pattern having a diameter of about 0.2 μm can be formed.

[0049]

According to the present invention, it is possible to realize a photomask using the phase shift method, which can easily and finely form a fine contact hole pattern.

Therefore, it greatly contributes to high integration of the semiconductor integrated circuit device. Further, since no special method is used for the manufacturing method, a photomask suitable for high integration can be manufactured at low cost, which greatly contributes to the reduction of manufacturing cost of the semiconductor integrated circuit device.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is a diagram showing a process 1 of Example 1.

FIG. 3 is a diagram showing a process 2 of Example 1.

FIG. 4 is a diagram showing a process 3 of Example 1.

5 is a diagram showing a process 4 of Example 1. FIG.

FIG. 6 is a diagram showing a finished photomask of Example 1;

FIG. 7 is a diagram showing a process 1 of Example 2.

FIG. 8 is a diagram showing a process 2 of Example 2.

FIG. 9 is a diagram showing a process 3 of Example 2.

FIG. 10 is a diagram showing a process 4 of Example 2.

FIG. 11 is a diagram showing a finished photomask of Example 2;

FIG. 12 is a diagram showing an example of a DRAM cell.

FIG. 13 is a diagram showing positions of contact holes of a memory cell.

FIG. 14 is a diagram showing an example of a photomask for forming a bit line contact hole pattern.

FIG. 15 is a diagram showing an example of a photomask for forming a storage contact hole pattern.

FIG. 16 is a diagram showing a conventional example.

Claims (3)

[Claims] 1. A photomask using a phase shift method, which is divided by two boundary lines intersecting at one point on a transparent mask substrate that transmits exposure light, and is counterclockwise about the intersection point. A first area, a second area, a third area, and a fourth area
Four regions are formed, and the phases of the exposure light transmitted through the four regions are counterclockwise in the first region, the second region, the third region, and the fourth region.
Or clockwise, substantially 0, π / 2, respectively
A photomask provided with a phase shifter having a relationship of π, (3/2) π. 2. The method of manufacturing a photomask according to claim 1, wherein a step of sequentially depositing a first transparent film, a second transparent film, and a third transparent film on a transparent substrate, and a first region. And a step of selectively covering the second region with the first mask material, a step of completely removing the third transparent film on the third region and the fourth region by using the first mask material as a mask, and a first mask material Is used as a mask to remove the second transparent film on the third region and the fourth region by a predetermined depth. After removing the first mask material, the first region and the fourth region are removed by the second mask material. A step of selectively covering, a step of using the second mask material and the third transparent film on the second area as a mask, a step of completely removing the second transparent film on the third area, and a step of using the second mask material as a mask , The third transparent film on the second area and the first transparent film on the third area Manufacturing method of a photomask which comprises a step of removing. 3. The method of manufacturing a photomask according to claim 1, wherein the step of depositing a transparent film on the transparent substrate, and the first region and the second region are selectively covered with the first mask material. And a step of removing all the transparent film on the third region and the fourth region by using the first mask material as a mask, and by using the first mask material as a mask, the transparent substrates in the third region and the fourth region are predetermined. Of removing the first mask material, and then selectively covering the first region and the fourth region with the second mask material after removing the first mask material, and the second mask material and the second area on the second area. Using the transparent film as a mask, a step of removing the transparent substrate in the third region to a predetermined depth, and using the second mask material as a mask, removing all the transparent film on the second region and simultaneously removing the transparent substrate in the third region. Including a step of removing a predetermined depth Manufacturing method of a photomask according to claim.