JP3225074B2 - Method for manufacturing phase shift photomask - 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 for manufacturing a photomask used for manufacturing a high-density integrated circuit such as an LSI or a super LSI, and more particularly to a phase shift layer for forming a fine pattern with high precision. The present invention relates to a method for manufacturing a photomask having

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs, and VLSIs apply a resist on a substrate to be processed such as a Si wafer, expose a desired pattern by a stepper or the like, and then perform development and etching. It is manufactured by repeating a lithography process.

[0003] A photomask called a reticle used in such a lithography process tends to be required to have higher and higher precision as the performance and integration of a semiconductor integrated circuit become higher and higher. The line width of the device pattern formed using these photomasks is 1 Mbit D
1.2μm for RAM and 0.8μ for 4Mbit DRAM
In the case of m and 16 Mbit DRAMs, further miniaturization of 0.5 μm is required, and various exposure methods have been studied to meet such requirements.

However, for example, in the case of a 64 Mbit DRAM class device, a pattern having a line width of 0.35 μm is required, and the stepper exposure method using a reticle becomes the resolution limit of a resist pattern. For example, Japanese Patent Application Laid-Open No. 58-
A reticle based on a new concept called a phase shift photomask has been proposed, as disclosed in Japanese Patent Publication No. 173744 and Japanese Patent Publication No. 62-59296. Phase shift lithography using a phase shift reticle is a technique for improving the resolution and contrast of a projected image by manipulating the phase of light passing through the reticle.

[0005] Phase shift lithography will be briefly described with reference to the drawings. FIG. 2 is a diagram showing the principle of the phase shift method,
FIG. 3 is a diagram showing a conventional method, and FIG. 2 (a) and FIG.
(A) is a cross-sectional view of the reticle, FIG. 2 (b) and FIG. 3 (b)
2 (c) and 3 (c) show the light amplitude on the wafer, FIGS. 2 (d) and 3 (d) show the light intensity on the wafer, respectively, and 1 denotes the light intensity on the wafer. A substrate 2, a light shielding film 3, a phase shifter 3, and an incident light 4 are shown.

In the conventional method, as shown in FIG. 3A, only a light-shielding film 2 made of chrome or the like is formed on a substrate 1 made of glass or the like, and a light transmitting portion of a predetermined pattern is formed. However, in phase shift lithography,
As shown in FIG. 2A, a phase shifter 3 made of a transmission film for inverting the phase (a phase difference of 180 °) is provided on one of the adjacent light transmission portions on the reticle. Therefore, in the conventional method, the amplitude of light on the reticle is in phase as shown in FIG. 3 (b), and the amplitude of light on the wafer is also in phase as shown in FIG. 3 (c). While the pattern on the wafer cannot be separated as shown in FIG. 3D, in phase shift lithography, the light transmitted through the phase shifter
As shown in FIG. 2B, since the phases are made opposite to each other between the adjacent patterns, the light intensity becomes zero at the boundary of the patterns, and the adjacent patterns are clearly separated as shown in FIG. 2D. be able to. As described above, in the phase shift lithography, a pattern that cannot be separated conventionally can be separated and the resolution can be improved.

Next, an example of a conventional manufacturing process of a phase shift reticle will be described with reference to FIG. 5. FIG. 5 is a sectional view showing the manufacturing process of the phase shift reticle, as shown in FIG. Next, a chrome reticle completed by providing a chromium pattern 6 on a substrate 5 is prepared, and a transparent film 7 made of SiO ₂ or the like is formed on the chromium pattern 6 as shown in FIG. Form. Next, as shown in FIG. 3C, an ionizing radiation resist layer 8 such as chloromethylated polystyrene is formed on the transparent film 7, and as shown in FIG. Align,
A predetermined pattern is drawn by ionizing radiation 9 such as an electron beam exposure apparatus, developed and rinsed to form a resist pattern 10 as shown in FIG.

Next, after performing a heat treatment and a descum treatment as necessary, as shown in FIG. 1F, the transparent film 7 exposed from the opening of the resist pattern 10 is dried by the etching gas plasma 11. Etching is performed to form the phase shifter pattern 12. The phase shifter pattern 12 is formed by etching gas plasma 1
1 may be performed by wet etching instead of dry etching.

Next, the remaining resist is ashed and removed by oxygen plasma 13 as shown in FIG. Through the above steps, a phase shift photomask having the phase shifter 12 as shown in FIG.

[0010] In addition to the phase shift photomask of the phase shifter placing type in which such a phase shifter is located on the chrome pattern, as shown in a cross section in FIG. A phase shift photomask of a type where a phase shifter is placed underneath is also proposed. The feature of this photomask is that since the phase shifter layer can be formed on a flat substrate, the in-plane variation of the phase shifter film thickness can be reduced.

An example of a manufacturing process of such a phase shift reticle of the type under the phase shifter will be described with reference to FIG. FIG. 6 is a cross-sectional view showing a manufacturing process of the phase shift reticle. First, as shown in FIG. 1A, an alumina layer 1 serving as an etching stopper layer is formed on a quartz substrate 14.
5 is formed. Next, as shown in FIG. 2B, a transparent film 16 made of SiO ₂ is formed on the film 15. Next, as shown in FIG. 3C, a chromium film 17 serving as a light-shielding film is formed on the transparent film 16. Next, as shown in FIG. 2D, an ionizing radiation resist layer 18 such as chloromethylated polystyrene is formed on the chromium film 17, and a predetermined pattern is drawn by ionizing radiation 19 such as an electron beam exposure apparatus. After development and rinsing, a resist pattern 18 is formed as shown in FIG. Next, as shown in FIG. 3F, wet etching of the chromium layer 17 is performed using the resist pattern 18 as a mask. A cerium nitrate ammonium solution is used as an etchant. Next, as shown in FIG.
To remove the resist to obtain a chrome mask as shown in FIG.

Next, as shown in FIG. 1I, an ionizing radiation resist layer 21 such as chloromethylated polystyrene is formed on the transparent film 15 on which the chromium pattern 17 is formed.
Alignment is performed on the resist layer 21 in accordance with a conventional method, and a predetermined pattern is drawn by ionizing radiation 22 such as an electron beam exposure apparatus, developed and rinsed to form a resist pattern 21 as shown in FIG. .

Next, after performing a heat treatment and a descum treatment as required, the transparent film 16 exposed from the opening of the resist pattern 21 is dried by an etching gas plasma 23 as shown in FIG. Etching is performed to form the phase shifter pattern 16. As an etching gas, CF ₄ , C ₂ F ₆ , CHF ₃ , CHF ₃ +
O ₂ and a mixed gas thereof are used.

Next, the remaining resist is ashed and removed by oxygen plasma 24 as shown in FIG. Through the above steps, the phase shifter 16 as shown in FIG.

[0015]

By the way, in a phase shift reticle manufacturing process as shown in FIGS.
In order to perform high-precision dimensional control, dry etching is usually used for pattern processing of a phase shifter. In particular, in a phase shift reticle of the phase shifter lower type, wet etching cannot be used because an undercut is formed during phase shifter etching.

In the case where the phase shifter layer of the phase shifter lower type is formed by dry etching, even if the etching is performed under the same conditions as the phase shifter upper type, there is a problem that an etching residue is generated after the etching.

The residue during the dry etching is such that the surface of the phase shifter layer is damaged when the chromium layer is formed, and the surface is roughened, and a small amount of chromium remains on the surface of the phase shifter material during the chromium etching. It is considered that chromium serves as an etching mask and the above residue is generated.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a method of manufacturing a phase shift photomask in which the generation of etching residues during phase shift pattern dry etching is prevented. .

[0019]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention provides a method for removing a surface layer containing chromium slightly remaining on the surface of a phase shifter material after chromium etching by wet etching or plasma treatment. The present inventors have found that dry etching can be performed without generating an etching residue of the shifter layer, and have completed the present invention.

Hereinafter, a method of manufacturing the phase shift reticle of the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing a manufacturing process of a phase shift reticle according to the present invention. First, an alumina layer 25 serving as an etching stopper layer is formed on a quartz substrate 24 as shown in FIG.
As the etching stopper layer 25, other than alumina, MgF ₂ , SiN, Cr ₂ O ₃ , ITO, SnO ₂
Etc. may be used. Next, as shown in FIG. 2B, SOG (spin-on-glass) is formed on the entire surface of the film 25.
The film 26 is formed with a film thickness d that satisfies d = λ / 2 (n−1). Here, λ is the wavelength used for this reticle, and n is SOG
Is the refractive index of

Instead of this SOG 26, a sputter Si
O ₂ , CVD (chemical vapor depo)
position) An SiO ₂ or SiN film may be used.

Next, as shown in FIG.
A chromium film 27 serving as a light shielding film is formed on 6. Light shielding film 2
Although the single-layer chromium 7 is shown, other materials used as a photomask light-shielding film such as chromium / low-reflection film chromium, chromium oxide film, chromium oxynitride film, tungsten, molybdenum silicide, or these Can be applied in the same manner. Further, as the substrate 24, high precision is required, and quartz glass having a small coefficient of thermal expansion is generally used. However, low-thermal-expansion glass, soda-lime glass, or the like can also be used.

Next, as shown in FIG. 2D, an ionizing radiation resist layer 28 such as chloromethylated polystyrene is formed on the chromium film 27, and a predetermined pattern is formed by ionizing radiation 29 such as an electron beam exposure apparatus. After drawing, development and rinsing, a resist pattern 28 is formed as shown in FIG. Next, as shown in FIG. 2F, wet etching of the chrome layer 27 is performed using the resist pattern 28 as a mask. A cerium nitrate ammonium solution is used as an etchant. Next, as shown in FIG. 3G, the resist is peeled off by the oxygen plasma 30, and a chrome mask as shown in FIG.

Next, as shown in FIG. 1I, an ionizing radiation resist layer 31 such as chloromethylated polystyrene is formed on the SOG film 26 on which the chromium pattern 27 is formed, and the resist layer 31 is formed on the resist layer 31 in accordance with a conventional method. Alignment is performed, a predetermined pattern is drawn by ionizing radiation 32 of an electron beam exposure apparatus or the like, developed, and rinsed to form a resist pattern 31 as shown in FIG.

Next, after performing a heat treatment and a descum treatment as necessary, the surface portion of the transparent film 26 exposed from the opening of the resist pattern 31 is buffered with hydrofluoric acid as shown in FIG. Etch slightly. As the buffered hydrofluoric acid, a mixed solution of hydrofluoric acid and an ammonium fluoride solution is used. Instead of buffered hydrofluoric acid, a low concentration of hydrofluoric acid may be used.

As a surface treatment method, instead of wet etching with buffered hydrofluoric acid, surface dry etching with plasma using an inert gas such as argon, helium, krypton, or xenon may be used.

Next, as shown in FIG. 1L, the SOG layer 26 is etched by dry etching using a reactive plasma 33 to form a phase shifter pattern 26.

Next, as shown in FIG. 2 (m), the remaining resist is ashed and removed by oxygen plasma 34 to complete a phase shift photomask as shown in FIG. 2 (n). Note that the resist can be removed by a wet method using a stripper or an acid for resist instead of dry etching using oxygen plasma.

As described above, by using the method for manufacturing a phase shift photomask of the present invention, particularly, in a phase shift photomask of a phase shifter lower type,
It is possible to prevent the generation of etching residues at the time of dry etching used for forming a phase shifter, and to suppress a decrease in transmittance in a portion where there is no phase shifter. For this reason, there is no difference in transmittance between the portion having the phase shifter and the portion having no phase shifter, and it is possible to prevent deterioration of the pattern transferred onto the wafer.

The manufacturing method according to the present invention is not limited to the phase shift photomask as shown in FIGS. 2 to 4, but may be a phase shift photomask having another principle or configuration, such as a halftone phase shift photomask. Also applicable to

As described above, the method of manufacturing a phase shift photomask according to the present invention includes at least a method of manufacturing a phase shift photomask for forming a phase shifter pattern for giving a phase difference between predetermined regions by dry etching. A step of removing the transparent layer surface portion including the etching obstacle attached to the surface of the phase shifter pattern transparent layer before etching, and a step of subsequently etching the transparent layer into a predetermined pattern by dry etching. The removing step is a surface etching using buffered hydrofluoric acid or a hydrofluoric acid solution. Another method for manufacturing a phase shift photomask of the present invention is a method for manufacturing a phase shift photomask in which a phase shifter pattern for providing a phase difference between predetermined regions is formed by dry etching, wherein at least reactive plasma etching is used. A step of removing the surface portion of the transparent layer including the etching obstacle attached to the surface of the phase shifter pattern transparent layer before dry etching, and a step of subsequently etching the transparent layer into a predetermined pattern by dry etching. Wherein the removing step is a surface etching by plasma using an inert gas such as argon, helium, krypton, or xenon.

In this case, a transparent layer for a phase shifter pattern is formed on a substrate, a light-shielding pattern is formed thereon, and then a predetermined pattern portion of the transparent layer exposed from the light-shielding pattern is covered to remove the light. After that, the present invention can be applied to a case where a phase shift photomask having a phase shifter pattern between a light shielding pattern and a substrate is manufactured.

As the transparent layer, spin-on-glass or the like can be used.

[0034]

In the present invention, at least a removing step of removing the transparent layer surface portion including an etching obstacle adhered to the surface of the phase shifter pattern transparent layer prior to dry etching, and thereafter, the transparent etching by dry etching. And the step of etching the layer into a predetermined pattern, in particular, in a phase shift photomask of the phase shifter lower type, it is possible to reliably prevent the generation of etching residues during dry etching used to form the phase shifter pattern, It is possible to suppress a decrease in transmittance in a portion where there is no phase shifter. For this reason, there is no difference in transmittance between the portion having the phase shifter and the portion having no phase shifter, and it is possible to prevent deterioration of the pattern transferred onto the wafer.

[0035]

An embodiment of the present invention will be described below.
An alumina layer serving as an etching stopper layer is formed on a quartz substrate. Next, an SOG having a refractive index of 1.41 was formed on this film.
A film is formed to a thickness satisfying 445 nm.

Next, a chromium film serving as a light-shielding film is formed on the SOG film to a thickness of 80 nm. Next, a SAL603 (manufactured by Shipley) having a thickness of 5 was formed as a resist film on the chrome film.
Spin-code to be 00 nm. next,
Drawing of SAL 603 is performed by an electron beam exposure apparatus. Develop and rinse to form a SAL603 resist pattern. Using the resist pattern as a mask, wet etching of the chromium layer is performed. As an etchant,
Cerium ammonium nitrate solution is used.

Next, the SOG on which the chromium pattern is formed
SAL603 (manufactured by Shipley) is spin-coated as a resist film on the film to a thickness of 500 nm. Next, alignment is performed according to a conventional method, and writing on the SAL 603 is performed using an electron beam exposure apparatus. Develop and rinse to form a SAL603 resist pattern.

Next, after performing a heat treatment and a descum treatment as required, the surface portion of the SOG film exposed from the opening of the resist pattern is immersed in 0.5% hydrofluoric acid for 1 minute.
Etch. Next, the SOG layer is etched by reactive ion etching using C ₂ F ₆ gas to form a phase shifter pattern.

Next, the remaining resist was ashed and removed by oxygen plasma to complete a phase shift photomask. Note that the removal of the resist can be performed by a wet method using a stripping solution dedicated to the resist, an acid, or the like, instead of dry etching using oxygen plasma.

In the phase shift reticle of the phase shifter lower type obtained as described above, no etching residue is observed in the portion without the phase shifter, and the transmittance in the mask plane is constant. No deterioration occurred in the pattern transferred above.

[0041]

As is apparent from the above description, according to the method for manufacturing a phase shift photomask of the present invention, at least the etching obstacles attached to the surface of the transparent layer for phase shifter patterns before dry etching are included. Since the method includes a step of removing the transparent layer surface portion and a step of subsequently etching the transparent layer into a predetermined pattern by dry etching, particularly, in a phase shift photomask of a phase shifter lowering type, a phase shifter pattern is formed. It is possible to reliably prevent the generation of an etching residue at the time of dry etching used for the above, and to suppress a decrease in transmittance in a portion where there is no phase shifter. For this reason, there is no difference in transmittance between the portion having the phase shifter and the portion having no phase shifter, and it is possible to prevent deterioration of the pattern transferred onto the wafer.

When the transparent layer surface including the etching obstacle is removed by dipping in buffered hydrofluoric acid or a hydrofluoric acid solution before dry etching, a special device such as a vacuum device is not required, and a photomask is not required. The cost required for fabrication does not increase much.

[Brief description of the drawings]

FIG. 1 is a sectional view of each step of an embodiment of a method for manufacturing a phase shift photomask according to the present invention.

FIG. 2 is a diagram illustrating the principle of a phase shift photomask.

FIG. 3 is a diagram showing the principle of a conventional photomask.

FIG. 4 is a sectional view of a phase shift photomask of a phase shifter lower type.

FIG. 5 is a cross-sectional view showing an example of a manufacturing process of a conventional phase shift photomask of a phase shifter-mounted type.

FIG. 6 is a cross-sectional view showing an example of a manufacturing process of a conventional phase shift photomask of a phase shifter lower type.

[Explanation of symbols]

 Reference Signs List 24 substrate 25 etching stopper layer 26 transparent film (phase shifter pattern) 27 light-shielding film 28 ionizing radiation resist layer (resist pattern) 29 ionizing radiation 30 oxygen plasma 31 ionizing radiation resist layer (resist pattern) 32 ... Ionizing radiation 33 ... Reactive plasma 34 ... Oxygen plasma

Claims (4)

(57) [Claims] 1. A method of manufacturing a phase shift photomask for forming a phase shifter pattern for providing a phase difference between predetermined regions by dry etching, wherein at least an etching obstruction attached to a surface of the phase shifter pattern transparent layer before dry etching. possess a removal step of removing the transparent layer surface portion including an object, followed by a step of etching the transparent layer in a predetermined pattern by dry etching, the removing step, buffered hydrofluoric acid or hydrofluoric acid solution
A method for producing a phase shift photomask, characterized in that the surface is etched by a method. 2. A phase shifter for providing a phase difference between predetermined regions.
Phase pattern formed by dry etching
In the method for manufacturing a vertical photomask, at least
Before dry etching using reactive plasma etching
Etch attached to the surface of the phase shifter pattern transparent layer
For removing the surface portion of the transparent layer including the blocking obstacle
After that, the transparent layer is specified by dry etching.
Etching the pattern, the removing step
But not argon, helium, krypton, xenon, etc.
Surface etching by plasma using active gas
A method for manufacturing a phase shift photomask. 3. A transparent layer for a phase shifter pattern is formed on a substrate, a light-shielding pattern is formed thereon, and the predetermined pattern portion of the transparent layer exposed from the light-shielding pattern is covered. 3. The method for manufacturing a phase shift photomask according to claim 1, wherein a phase shift photomask having a phase shifter pattern between the light shielding pattern and the substrate is manufactured. 4. A method of manufacturing a phase shift photomask according to any one of claims 1 to 3, characterized in that the transparent layer is made of spin-on-glass.