JP3207913B2 - 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 photomask used for manufacturing high-density integrated circuits such as LSIs and VLSIs and a method for manufacturing the same, and more particularly, to a phase shift when a fine pattern is formed with high precision. The present invention relates to a method for manufacturing a photomask having a layer.

[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.

A photomask called a reticle used in such a lithography process tends to be required to have higher and higher accuracy as the performance and integration of a semiconductor integrated circuit become higher. DRA which is LSI
Taking M as an example, the dimensional deviation in a 5-fold reticle for a 1-Mbit DRAM, that is, a reticle having a size five times as large as the pattern to be exposed, takes an average value ± 3σ (σ is a standard deviation). Also, a precision of 0.15 μm is required. Similarly, a 5 × reticle for a 4 Mbit DRAM has a dimensional accuracy of 0.1 to 0.15 μm, and a 5 × reticle for a 16 Mbit DRAM has a dimensional accuracy of 0.05 to 0.1 μm. Dimensional accuracy is required.

Furthermore, the line width of a device pattern formed using these reticles is 1 Mbit DRAM.
1.2 μm, 0.8 μm for 4 Mbit DRAM, 1 μm
6-Mbit DRAMs are required to be further miniaturized to 0.6 μm, and various exposure methods are being studied to meet such requirements.

However, in the case of the next-generation device pattern of the 64MDRAM class, for example, the resolution of a resist pattern is limited by the conventional stepper exposure method using a reticle.
For example, JP-A-58-173744, JP-B-62
A reticle based on a new concept of a phase shift mask, as disclosed in, for example, JP-A-59296, has been proposed. 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.

[0006] 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 the drawings. FIG. 4 is a cross-sectional view showing a manufacturing process of the phase shift reticle. In the figure, 10 is a substrate, 11 is a conductive layer, 12 is a chromium film, 13 is a resist layer, 14 is ionizing radiation, 15 is a resist pattern, 16
Is an etching gas plasma, 17 is a chromium pattern, 1
8 is oxygen plasma, 19 is a transparent film, 20 is a resist layer,
21 is ionizing radiation, 22 is a resist pattern, 23 is an etching gas plasma, 24 is a phase shift pattern, 2
Reference numeral 5 denotes oxygen plasma.

First, as shown in FIG. 4A, a conductive layer 11 made of a tantalum thin film layer or the like is formed on an optically polished substrate 10 in order to prevent a charge-up phenomenon due to an exposure beam when drawing a phase shifter pattern. Is formed thereon, and a chromium film 12 is formed thereon. Further, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied by a conventional method such as spin coating, and is subjected to a heat drying treatment to have a thickness of 0.1 mm. A resist layer 13 having a thickness of about 2.0 μm is formed. The heating and drying treatment is usually performed at 80 to 150 ° C. for about 20 to 60 minutes, depending on the type of resist used.

Next, as shown in FIG. 1B, a pattern is drawn on the resist layer 13 with an ionizing radiation 14 using an exposure device such as an electron beam drawing device according to a conventional method, and an organic solvent such as ethyl cellosolve or ester is drawn. After development with a developer as a main component, rinsing with alcohol is performed to form a resist pattern 15 as shown in FIG.

Next, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as resist dust and whiskers remaining on the edge portion of the resist pattern 15, and the like, as shown in FIG. As shown, the resist pattern 1
The chromium layer 12 is dry-etched with the etching gas plasma 16 to form a chromium pattern 17. It is obvious to those skilled in the art that the chromium pattern 17 may be formed by wet etching instead of dry etching by the etching gas plasma 16.

After etching as described above, the resist pattern 15, ie, the remaining resist is ashed and removed by oxygen plasma 18 as shown in FIG. Complete the mask. This process can be performed by solvent stripping instead of the ashing process using the oxygen plasma 18.

Subsequently, the photomask is inspected, a pattern is corrected if necessary, and the photomask is washed. Then, as shown in FIG.
A transparent film 19 made of (spin-on-glass) SiO ₂ or the like is formed. Next, as shown in FIG. 6H, an ionizing radiation resist layer 20 of chloromethylated polystyrene or the like is formed on the transparent film 19 in the same manner as described above, and as shown in FIG. The resist layer 20 is aligned according to a conventional method, and ionized radiation 21 such as an electron beam exposure device is used.
Draw a predetermined pattern, develop, rinse,
As shown in FIG. 1J, a resist pattern 22 is formed.

Next, if necessary, a heating process and a descum process are performed, and as shown in FIG. 1K, the transparent film 19 exposed from the opening of the resist pattern 22 is etched with an etching gas plasma. Dry etching is performed by using 23 to form a phase shifter pattern 24. Note that the phase shifter pattern 24 may be formed by wet etching instead of dry etching by the etching gas plasma 23.

Next, the remaining resist is ashed and removed by oxygen plasma 25 as shown in FIG. Through the above steps, a phase shift mask having the phase shifter 24 as shown in FIG.

[0016]

However, in the conventional phase shift photomask manufacturing process, there are many steps after forming a transparent film to be a phase shifter, and the SOG formed as the phase shifter is subjected to the plate making and cleaning steps. In some cases, the properties such as silanol (Si-OH) conversion are caused, and as a result, the film quality such as the refractive index may be changed. For this reason,
It cannot guarantee the phase of the phase shifter, and also involves many problems such as a prolonged manufacturing period and high cost due to an increase in yield.

The present invention has been made in view of such a situation, and an object of the present invention is to change the phase of a phase shifter by adding a simple step when a change in the refractive index is detected and a change in the refractive index is detected. An object of the present invention is to provide a method of manufacturing a phase shift photomask which is more practical, improves the yield rate, lowers the cost, and shortens the manufacturing period by restoring the shifter.

[0018]

SUMMARY OF THE INVENTION In view of the above problems, the present invention aims to develop a method for improving the yield rate and reducing the cost, and for stably producing a high-precision phase shift photomask. As a result of the research, in the phase shift photomask manufacturing process, a phase shift photomask having a high resolution is obtained by restoring the phase shifter layer (SOG) that has undergone deterioration such as silanolation by post-processing such as heating.
The present inventors have found that the phase shifter layer can be stably manufactured at low cost while guaranteeing the phase difference of the phase shifter layer, and have completed the present invention based on such knowledge.

Hereinafter, a method for manufacturing a phase shift photomask of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing each step of a method for manufacturing a phase shift photomask according to the present invention, in which 30 is a substrate, 31 is a conductive layer,
2 is a light shielding layer, 33 is a phase shift layer, 34 is an ionizing radiation resist, 35 is a phase shifter pattern, 36 is an ionizing radiation, 37 is an ionizing radiation resist pattern, 38 is an etching gas plasma, 39 is an oxygen plasma, 40 is a heating or heating This represents an annealing process using laser light.

First, as shown in FIG. 1B, a phase shift layer 33 is applied to a chromium mask formed and subjected to a defect inspection according to a conventional method as shown in FIG.
It is formed with a film thickness suitable for.

D = λ / {2 (n−1)} (nm) (1) where, n: refractive index of phase shift layer material, λ: exposure wavelength (nm), d ... The thickness (nm) of the phase shift layer.

The phase shift layer 33 is made of SOG
(Spin-on-glass).

On this, an ionizing radiation resist layer 34 is formed as shown in FIG. 3C, alignment is performed according to a conventional method, and as shown in FIG. A pattern is drawn with an electron beam 36 so that the resist pattern remains in the phase shifter pattern portion, and the resist layer 34 is subjected to plate making after exposure, thereby forming an ionizing radiation resist pattern 37 as shown in FIG.

Next, as shown in FIG. 1F, using the ionizing radiation resist pattern 37 as a mask, the SOG layer 33 as a phase shift layer is etched with an etching gas plasma 38.
To pattern the phase shift layer 33.

Thereafter, as shown in FIG. 2G, the ionizing radiation resist pattern 37 is peeled off by an oxygen plasma 39 and ashing is performed.

Thereafter, when a change in the film quality / refractive index of the phase shifter 35 layer is detected in the defect inspection step through a cleaning step, as shown in FIG.
The phase shifter material is restored to the original film quality and refractive index by ultraviolet light or heat treatment 40, and after the defect inspection again, a phase shift photomask as shown in FIG.

In the conventional method, since the annealing step as shown in FIG. 1 (h) was not performed, there is no way to cope with the case where the phase shifter layer is deteriorated in the manufacturing process. According to the present invention, the phase shift photomask is completed, the phase difference is assured, the yield rate is improved, and the cost is increased only by increasing the number of simple steps such as laser irradiation, ultraviolet irradiation, or heating the photomask. It is also possible to reduce.

That is, in the method for manufacturing a phase shift photomask of the present invention, a method for manufacturing a phase shift photomask in which a transparent layer is formed and the transparent layer is patterned to form a phase shifter pattern is provided. An inspection step of detecting a change in the refractive index of at least a part of the transparent layer due to a reaction of silanolation in the step; and, when a change in the refractive index is detected in the inspection step, an original refractive index is obtained by heating after patterning. And a step of restoring the image. In this case, the heat treatment is desirably performed in a nitrogen atmosphere. Another method for manufacturing a phase shift photomask of the present invention is as follows.
In a method for manufacturing a phase shift photomask in which a transparent layer is formed and the transparent layer is patterned to form a phase shifter pattern, at least a part of the refractive index of the transparent layer due to a silanolation reaction in a step after forming the transparent layer An inspection step of detecting a change in the refractive index, and, when a change in the refractive index is detected in the inspection step, a step of restoring the original refractive index by annealing treatment with laser light or ultraviolet light after patterning. Characteristic method.

In these cases, the transparent layer is typically formed by spin-on-glass.

[0030]

[Function] With the recent high integration of LSIs and super LSIs, high integration of photomasks is required, and the mask configuration is also complicated. Accordingly, the number of processes is increased, and the occurrence of defects due to dust and the like becomes a problem. ing. In addition, the cost is inevitably high.

In the present invention, a change in the refractive index of at least a portion of the transparent layer due to a silanolation reaction in a step after the formation of the phase shifter transparent layer is detected, and when the change in the refractive index is detected, Since the original refractive index is restored by heat treatment after patterning or by annealing treatment with laser light or ultraviolet light, the yield rate is improved and the production cost is improved without increasing the number of steps for the phase shift photomask production. It can be kept low, and also the phase difference can be guaranteed.

[0032]

EXAMPLES Examples of the production method of the present invention will be described below. Example 1 After inspecting the quality of a photomask manufactured according to an ordinary method, SGO (spin-on-glass; refractive index: 1.45) is spin-coated on the mask so that the thickness of the phase shifter layer becomes 406 nm. The film is formed by a method. Thereafter, the mask on which the SOG is formed is heated at 300 ° C. in a nitrogen atmosphere, and the SOG is baked. After confirming that there is no defect in the phase shifter layer, a resist pattern serving as an etching mask is prepared using an ionizing radiation resist or the like, and then the entire surface of the mask is exposed to an etching gas plasma to form an SOG phase shifter pattern. I do. After that, the resist pattern is peeled off by oxygen plasma and ashed.

In the subsequent inspection process, if any change in the SOG phase shifter or a change in the refractive index is found, this SOG phase shifter
The phase shift photomask in which the alteration defect was found was heat-treated at 300 ° C. in a nitrogen atmosphere, and after defect inspection and correction again,
Complete the phase shift photomask.

The deviation of the amount of phase shift of the phase shift photomask manufactured by such a process is an average value ± 3σ.
When (σ is a standard deviation), a value of ± 2.0 ° was obtained, and it was confirmed that a highly accurate phase shift photomask was obtained. In addition, no deviation in the phase shift amount other than the above was observed at the periphery of the mask.

[0035]

With the recent high integration of LSIs and VLSIs, high integration of photomasks is required, and the mask configuration is also complicated. Accordingly, the number of steps is increased, and the number of defects due to dust is frequent. It has become. In addition, the cost is inevitably high.

According to the method for manufacturing a phase shift photomask of the present invention, a change in the refractive index of at least a part of the transparent layer due to a silanolation reaction in the step after the formation of the phase shifter transparent layer is detected, and the refractive index of the transparent layer is detected. If a change is detected,
Since the original refractive index is restored by heat treatment after patterning or by annealing treatment with laser light or ultraviolet light, the yield rate is improved and the production cost is improved without increasing the number of steps for the phase shift photomask production. It can be kept low, and also the phase difference can be guaranteed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing steps of a method for manufacturing a photomask having a phase shift layer according to the present invention.

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

FIG. 3 is a diagram showing a conventional method.

FIG. 4 is a cross-sectional view showing a manufacturing process of a conventional phase shift photomask.

[Explanation of symbols]

 REFERENCE SIGNS LIST 30 substrate 31 conductive layer 32 light shielding layer 33 phase shift layer 34 ionizing radiation resist 35 phase shifter pattern 36 ionizing radiation 37 ionizing radiation resist pattern 38 etching gas plasma 39 oxygen plasma 40 heating or laser Annealing treatment by light

Claims (4)

(57) [Claims] 1. A forming the transparent layer, the method of manufacturing a phase shift photomask to form a phase shifter pattern by patterning the transparent layer, at least the transparent layer by the reaction of a silanol of at after the transparent layer forming step An inspection step for detecting a change in a part of the refractive index;
And when a change in the refractive index is detected, a step of restoring the original refractive index by a heat treatment after patterning.
A method for manufacturing a phase shift photomask. 2. A method for forming a transparent layer, comprising the steps of:
Phase shifter to form a phase shifter pattern
In the photomask manufacturing method, in the process after forming the transparent layer,
At least a part of the transparent layer by the silanolation reaction of
An inspection step for detecting a change in the refractive index; and
If a change in the refractive index is detected
Laser light or ultraviolet light annealing
And a step of restoring the refractive index to
Manufacturing method of a phase shift photomask. 3. The heat treatment is performed in a nitrogen atmosphere.
The phase shift photomask according to claim 1, wherein
Production method. 4. The method according to claim 1, wherein the transparent layer is formed by spin-on-glass .
2. The method for manufacturing a phase shift photomask according to claim 1 .