JPH02211450A - Phase shift mask and its manufacture - Google Patents

Abstract

PURPOSE:To eliminate a change with the lapse of time in the membrane property of a shifter, to eliminate reflection on the boundary surface with a transparent substrate, and to facilitate film thickness control by forming a recessed part of specific depth as the shifter in the transparent substrate. CONSTITUTION:The shifter 13 consisting of the recessed part of the depth (D) satisfying an equation is formed in the glass substrate 11. Here, lambda is the wavelength of irradiating light and (n) is the refractive index of the shifter. Then a light shielding pattern 12 made of Cr, etc., is formed on, for example, the substrate 11, and a specific conductive film 14 and a positive resist film 15 are laminated in order by coating and then exposed by an electron beam exposing method and developed to remove the exposed part of the film 15. Then the film 14 is etched, and the substrate 11 is dry-etched to remove the films 15 and 14, thus forming the phase shifting mask.

Description

[Detailed Description of the Invention] [Summary] Regarding a phase shift mask among photomasks and its manufacturing method, the purpose of the phase shift mask is to obtain a high quality and stable phase shift mask. and a shifter that shifts the phase of light by 180°, and the depth D at which the shifter is provided on the transparent substrate.
=λ/2(n-1) concave portion.

Further, there are two methods for manufacturing a phase shift mask: a formation method (1) in which a shifter is formed after forming a light-shielding pattern by a normal mask formation method, and a formation method (n) in which a light-shielding pattern and a shifter are formed separately. There are three methods of formation (III), in which a second mask having a pattern in which only the shifter forming part is a light transmitting part is transferred to a first mask having only a light-shielding pattern, and the first mask is made into a phase shift mask. be.

[Industrial application field]

The present invention relates to a phase shift mask and a method of manufacturing the same, among photomasks and methods of manufacturing the same used in methods of manufacturing semiconductor devices and the like.

In the manufacturing method of semiconductor devices, photolithography technology is an essential step, and there is a demand for higher quality photomasks used in the photolithography technology.

[Conventional technology]

There are two types of photomasks used in photolithography technology: those that have a pattern with the same dimensions as the device pattern to be transferred onto a semiconductor wafer (hereinafter referred to as wafer), and are transferred to a 1:1 size. is called a mask (in a narrow sense), and the device pattern to be transferred is, for example, 5
A device that is magnified twice and projected on a wafer in a reduced size is called a reticle, and recently reticles have become more widely used. Although the present invention is mainly used for reticles, it can also be applied to masks.
Therefore, the reticle will be simply referred to as a mask (in a broad sense) and will be described below.

In recent years, due to the resolution limitations of ultraviolet exposure, electron beam exposure, which is suitable for miniaturization, has been increasingly used, but this electron beam exposure is necessary for exposure processing such as beam writing, making it difficult to improve throughput. There's a problem.

Therefore, photolithography techniques such as ultraviolet exposure method and deep ultraviolet exposure method have been reviewed, and an exposure method using a phase-shifting mask has been proposed.

Reference: IEEE Transaction On
Electron Devices, Vol, HD
-29+ No, 12. DECEMBER1982,
ρp, 1828-1836 The method involves making a predetermined pattern portion have a different optical path length than other pattern portions, and shifting the phase of the light on the wafer by 180° between both patterns. The aim is to improve contrast and significantly improve resolution using conventional photolithography equipment.

Figure 6 (a), ■) is a diagram explaining the principle of the phase shift, Figure 6 (a) is a diagram explaining the intensity distribution of light on a wafer by a normal mask, and Figure 6 (b) is a diagram explaining the phase shift principle. FIG. 3 is a diagram illustrating the intensity distribution of light on a wafer due to a shift mask. First, to explain Fig. 6(a), (a
-1) shows a cross section of a normal mask, in which a light-shielding pattern is provided on the glass substrate, and light is emitted from the back side (arrow).
FIG. (a-2) to (a-4) show the strength E of the electric field due to light irradiation on the wafer;
-5) indicates the intensity I of light on the wafer. That is,
The electric field strength E due to the light transmitting part on the left side of the mask is expressed as (
(a-2) shows the electric field strength E due to the light transmitting part on the right side, (a-3) shows the electric field strength E, and (a-4) shows the total electric field strength Σ
It is E. Since the intensity I of light is proportional to the square of the electric field intensity, it is shown in (a-5). As can be seen, in a normal mask, adjacent patterns are affected, and the light-shielding pattern in the adjacent exposure gap is affected by the diffracted light.

Therefore, the contrast deteriorates and this becomes the resolution limit.

The principle of a phase shift mask will be explained with reference to FIG. 6(b). (b-1) shows a cross section of the phase shift mask, in which a light shielding pattern and a shifter are formed on a glass substrate.
This is a diagram in which light (arrow) is irradiated from the back surface. The following (b-2) to (b-4) show the electric field strength E due to light irradiation on the wafer, (b-5) shows the light intensity I on the wafer, and (b-2) shows the mask The electric field strength E due to the left light transmitting part provided in , (b-3) shows the electric field strength E due to the right light transmitting part, and (b-4) is the total electric field strength ΣE. be. In addition, (a-5) is a diagram showing the light intensity I which is proportional to the square of the electric field strength. In this way, when the shifter is provided, the phase is shifted by 180 degrees, and the influence of the electric field due to the diffracted light is canceled out in the narrow gap shielding pattern, improving the contrast and improving the resolution limit.

FIG. 7 shows a cross-sectional view of a conventional phase shift mask, in which 1 is a glass substrate, 2 is a light shielding pattern 23 made of chromium (Cr), which is a shifter, and 4 is a transparent conductive film. This shifter is made of a resist film such as PMMA (polymethyl methacrylate) or Sin.

(silicon oxide) film is used, and its thickness D D-λ/2(n-1) Here, λ is the wavelength of the irradiated light, and n is the refractive index of the shifter. The condition is to match the formula.

If such a phase shift mask is used, for example, a light-shielding pattern with a minimum width of 2.5 μm can be provided on a reticle with a reduction ratio of 115, and a pattern with a width of 0.5 μm can be provided. If you use 0.2
It is said that it is possible to fabricate patterns with a width of μm.

Next, an overview of the conventional method of forming a phase shift mask is given in Section 8.
This will be explained with reference to step-by-step sectional views shown in FIGS. (a) to (d).

Refer to FIG. 8(a); this figure is a cross-sectional view of a normal mask produced by a conventional forming method, in which a light-shielding pattern 2 made of Cr is provided on a glass substrate 1.

Refer to FIG. 8(b); Next, a transparent conductive film 4 (for example, an ITO film) is formed on the above-mentioned ordinary mask to prevent charge-up during the next step of electron beam exposure.

See FIG. 8(C); Next, a PMMA film (positive resist) 3 serving as a shifter is coated to the above-mentioned thickness, prebaked if necessary, and then exposed using an electron beam exposure method.

See FIG. 8(d); next, by developing and removing the exposed portion, the phase shift mask is completed.

Although Figures 6, 7, and 8 are shown in reverse, when the mask is used, light is irradiated from the back side, so it is in the state shown in Figure 6, and it is difficult to make the mask. In some cases, the shielding pattern is fabricated with the shielding pattern facing upward, so that the state shown in FIGS. 7 and 8 is illustrated.

[Problem to be solved by the invention]

By the way, in the conventional phase shift mask described above, since the shifter 3 is made of a material different from that of the glass substrate, such as a resist film, it is difficult to control the material including the refractive index and the film thickness in accordance with the above formula. In particular, since the resist film is an organic substance, the quality of the film changes over time, resulting in a change in Schiff) I, which is difficult to control.

In addition, there is a problem that the irradiated light is reflected at the boundary between the shifter 3 and the glass substrate, so in order to reduce the effect,
There is a problem in that the material for the shifter is required to have a refractive index close to that of glass, and it is very difficult to select the material.

Furthermore, in the configuration of a conventional phase shift mask coated with a transparent conductive film, for example, an ITO film, there is a problem in that the light transmittance decreases.

The present invention proposes a phase shift mask and a method for manufacturing the same, with the aim of reducing such problems and obtaining a high quality and stable phase shift mask.

[Means for solving the problem] The problem is to increase the depth D=λ/of the shifter provided on the transparent substrate.
This problem is solved by a phase shift mask having 2(n-1) concave portions.

In addition, the formation method includes a formation method (1) in which a shifter is formed after forming a light-shielding pattern by a normal mask formation method, a formation method (II) in which a light-shielding pattern and a shifter are formed separately, and a light-shielding method (II) in which a light-shielding pattern and a shifter are formed separately. There are three forming methods (I[I) in which a second mask having a pattern in which only the shifter forming part is a light transmitting part is transferred to a first mask having only a pattern to make the first mask a phase shift mask. be.

[For production]

In the present invention, a shifter in a phase shift mask is formed into a concave portion having a depth of D=λ/2(n-1) by etching a transparent substrate.

In this way, the problem of the material of the shifter will be resolved, there will be no reflection at the interface between the shifter and the transparent substrate, and the film thickness of the shifter can be easily controlled, resulting in a high-quality and stable phase shift mask. It will be done.

〔Example〕

Examples will be described in detail below with reference to the drawings.

FIG. 1 shows a cross-sectional view of a phase shift mask according to the present invention, in which 11 is a glass substrate (transparent substrate) with a thickness of 2 to 3 cm;
2 is a light-shielding pattern made of Cr with a film thickness of 600 to 1,000 thick, and 13 is a shifter made of a recessed portion having a depth of D=λ/2(n-1). Note that this phase shift mask is advantageous in terms of manufacturing because the conductive film can be easily removed.

The following FIGS. 2(a) to 2(e) show step-by-step sectional views of the method (1) for forming a phase shift mask according to the present invention.

Refer to FIG. 2(a); this figure is a cross-sectional view of a normal mask manufactured by a conventional forming method, in which a light-shielding pattern 12 made of Cr is provided on a glass substrate 11.

Refer to Figure 2 (with); Next, after applying a conductive film 14 to prevent charge-up during the next step of electron beam exposure, a positive resist film 15 is applied to a thickness of about 1 μm, and as required. If so, it is prebaked and exposed using an electron beam exposure method. Here, the electron beam exposure method is used.
Of course, this is because fine patterns can be drawn and the positive electron beam resist film has excellent dry etching resistance. Note that in this case, the conductive film 14 does not need to be transparent; for example, opaque molybdenum silicide (MoSit) can be used.

Refer to FIG. 2(C); Next, the exposed portion of the resist film is removed by development, and then the conductive film 14 is etched (for example, a Mo5iz film is etched with CC1a + O! gas), and the shifter forming portion is removed. is exposed.

Refer to FIG. 2(d); Next, using the resist film 15 as a mask, the glass substrate 11 is vertically dry-etched using a CF4 + O
form 3. Etching can be carried out in a few minutes, and since the refractive index of the quartz glass substrate is about 1.5, the amount of etching is about the wavelength of the irradiated light.
When using wA light, the etching amount is approximately 0.36μ
It becomes m. Note that this etching may be performed by wet etching using hydrofluoric acid, or by adding wet etching to the above-mentioned dry etching.

See FIG. 2(e); Next, the resist film 15 and the conductive film 1
4 completes the phase shift mask.

Next, FIGS. 3(a) to 3(6) are step-by-step cross-sectional views of the phase shift mask forming method (II) according to the present invention, the essence of which is an efficient exposure process in which each pattern portion is processed only once. There are characteristics.

Refer to FIG. 3(a); First, a light-shielding film 12 made of Cr is deposited on the glass substrate 11 by sputtering, and a positive-type Lujist film 16 is applied thereon. The transparent part is exposed using a light exposure method.

Refer to FIG. 3 et al.; Next, after developing and patterning the first resist film 16 to open a window in a light transmitting part, the light shielding film 12 in the exposed light transmitting part is removed by etching.

Refer to FIG. 3(C); next, a conductive film 14 is deposited to prevent charge-up during electron beam exposure in the next step. This conductive film 14 does not need to be transparent; for example, M
Use o5iz.

Refer to FIG. 3(d); Next, the positive type second resist film 1
After coating No. 7 (film thickness: 1 μm), the shifter forming portion is exposed using an electron beam exposure method.

See FIG. 3(e); Next, the second resist film 1 is developed.
After patterning 7 and opening a window in the shifter forming portion, the conductive film 14 in the window portion 0 (shifter forming portion) is removed, and furthermore, the light shielding film in the window portion is removed by etching.

Refer to FIG. 3(f); Next, the glass substrate 11 of the shifter forming portion is coated with CFa +O! A concave shifter 13 is formed by dry etching to a predetermined thickness using a mixed gas.

Refer to FIG. 3 (8); Finally, resist film 17 and conductive film 1
4 is removed to complete the phase shift mask.

Formation method (II) according to the step shown in FIG. 3 is a processing method in which the shifter forming portion is patterned at one time, so the shifter forming portion is patterned during normal mask formation in the step shown in FIG. Next, this is a more efficient formation method than the formation method H) of double patterning in which the same pattern is patterned once when forming the shifter.

Next, FIG. 4(a), ■) shows an application pattern of a phase shift mask, and this figure shows an application pattern in which the effect of applying a phase shift mask is particularly large and allows highly accurate patterning. . Among them, FIG. 4(a) is an example of a pattern in which a large number of wiring lines are formed in parallel, such as bit lines in a memory device, and a shifter 13 is installed at every other light transmitting part in the gap between linear light shielding patterns 12. We have established
If a phase shift mask provided with such a shifter is used, the resolution can be approximately doubled.

In addition, Fig. 4 (■) is an example of a window pattern, in which shifters 13 are provided on all sides of a rectangular window shape.If a phase shift mask with this shape is used, the contrast will be improved, and if a conventional normal mask is used, the shifter 13 will be Even minute window patterns that could not be etched can be opened.

Next, FIGS. 5(a) to 5(-) show step-by-step cross-sectional views of the phase shift mask forming method (III) according to the present invention, in which a phase shift mask is formed using two masks. A method of forming a phase shift mask having a rectangular window pattern as shown in FIG. 4(b) will be explained.

See FIG. 5(a); this figure shows an ordinary mask made by a conventional forming method, with a rectangular light transmitting window 1 placed on a glass substrate 11.
8 shows a first mask A provided with a light-shielding pattern 12 having a pattern of 8.

Refer to FIG. 5(b); this figure also shows a second mask B, which is a normal mask and is provided with a light-shielding pattern 12 in which the shifter forming portions around the four peripheries of the window are opened.

Refer to FIG. 5(C); Next, after coating the mask A with a positive resist film 19 (thickness 1 to 2 μm), the mask B is aligned with the mask A and exposed, and the resist film 19 is exposed to light. This example uses a light exposure method to transfer and expose the shifter forming area, and there is no need to apply a conductive film. Alignment marks are required.

See FIG. 5(d); next, the exposed portion of the resist film is removed by development to expose the shifter forming portion.

Refer to FIG. 5(e); Next, using the resist film 19 as a mask and dry etching the glass substrate 11 using a CF4+O□ mixed gas as a reaction gas, a concave shifter 13 of a predetermined thickness is formed.

See FIG. 5(f); next, the resist film 19 is removed to complete the phase shift mask.

The formation method (■) using such two masks is a manufacturing method with high mass productivity, and does not necessarily require the application of electron beam exposure.

Note that since the above-described method for forming a phase shift mask according to the present invention is a processing method that etches the glass surface, some unevenness may occur on the bottom surface of the recessed part of the shifter 13, but the degree of unevenness is about λ. There is no effect up to an unevenness of /10, and for example, if the thickness of the recess is 360 nm when using I gland irradiation light, there is no problem up to an unevenness of 30 nm. Moreover, flatness to this extent can be easily formed by the above-mentioned etching method.

〔Effect of the invention〕

As is clear from the above description, the phase shift mask according to the present invention has higher quality and stable properties than conventional phase shift masks, and therefore is extremely useful for improving the quality and performance of semiconductor devices such as LSI. It is something that contributes.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a phase shift mask according to the present invention, FIGS. 2(a) to (e) are cross-sectional views in the order of steps of the method (1) for forming a phase shift mask according to the present invention, and FIG. ) to (barrels are step-by-step cross-sectional views of the phase shift mask forming method (n) according to the present invention, FIGS. 4(a) and (9) are diagrams showing application patterns of the phase shift mask, and FIG. 5(a) ) to (f) are step-by-step sectional views of the phase shift mask forming method (III) according to the present invention, FIG. 6 is a diagram explaining the principle of the phase shift mask, and FIG. 7 is a cross section of a conventional phase shift mask. 8(a) to (→ are cross-sectional views in the order of steps of a conventional phase shift mask forming method. In the figures, 1.11 is a glass substrate, 2.12 is a light-shielding pattern or a light-shielding film, 3 is PMM
A film or shifter 4 is a transparent conductive film, 13 is a shifter (concave shifter), 14 is a conductive film, 15, 16, 17, and 19 are resist films, 18 is a rectangular light transmission window, A is a first mask, B indicates the second mask. Half 4FJM+=rrja#shift 7s 7s#61! ! 1
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Claims (4)

[Claims] (1) A light shielding pattern that blocks light and a shifter that shifts the phase of light by 180° are provided on a transparent substrate, and the depth D = λ/2 (n-1
) (where λ is the wavelength of irradiation light and n is the refractive index of the shifter). (2) patterning a resist film on a transparent substrate provided with a light-shielding pattern to expose a shifter forming portion of the transparent substrate; and then etching the transparent substrate in the shifter forming portion to a depth D A method for manufacturing a phase shift mask, comprising the step of forming a shifter having a concave portion of =λ/2(n-1). (3) Patterning a first resist film on the transparent substrate covered with the light-shielding film, and etching the light-shielding film using the first resist film pattern as a mask to remove the light-transmitting portion excluding the shifter forming portion. a step of removing the light shielding film; a step of patterning a second resist film and etching away the light shielding film in the shifter formation portion using the second resist film pattern as a mask; and then forming the shifter. A method for manufacturing a phase shift mask, comprising the step of etching a portion of the transparent substrate to form a shifter consisting of a recess with a depth of D=λ/2(n-1). (4) Align a second mask having a pattern with only the shifter forming part as a light transmitting part to the first mask coated with a resist film and having only a light-shielding pattern, and transfer the pattern of the second mask to the resist film. to expose the shifter forming portion, and then etching the transparent substrate of the shifter forming portion of the first mask to a depth D=λ.
A method for manufacturing a phase shift mask, comprising the step of forming a shifter having a recess of /2(n-1) to make the first mask a phase shift mask.