JPH08106151A - Phase shift mask and its production - Google Patents

Abstract

PURPOSE: To increase the depth of focus and to improve stability for resolution of a contact hole by forming a halftone phase shifter into a specified pattern on a transparent substrate and forming a pattern of a light-shielding material to decrease the transmittance for light near the border between the area where the halftone phase shifter is formed and the area where no phase shifter is formed. CONSTITUTION: This mask is obtd. by successively laminating a SOG film 4 as a transparent material layer and a thin Cr film 5 of low transmittance for a low transmittance film on a quartz substrate 1 to form a laminated body, forming an aperture 3 in this laminated body to form a halftone phase shifter 6, and forming a light-shielding Cr film pattern 2p as a light-shielding pattern around the bottom of the aperture 3. When light beams for exposure enters through the quartz substrate 1 to the mask, transmitted light beams having the same phase and the same intensity as those of the incident light exit through the aperture 3, while transmitted light beams with reduced intensity due to the low transmittance Cr film 5 and 180 deg. inversion of the phase due to the SOG film 4 are obtd. through the area where the halftone phase shifter 6 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase shift mask used as a mask (reticle) for photolithography in the field of manufacturing semiconductor devices, and more particularly to a so-called halftone type phase shift mask which emits light in the halftone region. The present invention relates to improvement of contrast and depth of focus by increasing transmittance. It also relates to a method for easily manufacturing such a phase shift mask.

[0002]

2. Description of the Related Art In the semiconductor industry, mass production of 64M DRAM, which is a next-generation LSI, is imminent, and stable microfabrication technology with a design rule of 0.35 μm level is required.

The technique that has become a key to such fine processing is photolithography, and the progress has been made to shorten the exposure wavelength and to increase the numerical aperture (NA) of the reduction projection lens of the stepper (reduction projection exposure apparatus). It has been supported. Of these, far-ultraviolet lithography using KrF excimer laser light (248 nm) is promising for shortening the wavelength, but the development of resist materials with sufficient performance has been delayed, and it will not be immediately introduced to mass production sites. difficult.

On the other hand, there is also an attempt to prolong the life of i-line (365 nm) lithography using a conventional high-pressure mercury lamp as a light source, by a so-called super-resolution technique in which a higher harmonic component of exposure light is used to increase the resolution. Many have been done.

The phase shift method is one of the technologies that are in the limelight as a super-resolution technology. This is the g-line (436
While the photolithography before (n.m.) mainly used the amplitude distribution information of light, it uses the phase information in addition to the amplitude distribution information. That is, on a substrate made of a transparent material such as glass or quartz, a phase shifter made of a material having a refractive index different from that of the substrate is formed to have a thickness that gives a phase difference of 180 °, and is locally applied to the transmitted light of a photomask. The phase difference is generated, and the mutual interference of transmitted light is utilized to improve the resolution.

The principle of resolution improvement by the phase shift method is as follows.
It is roughly classified into spatial frequency modulation and edge enhancement, and various types of phase shift masks have been proposed by combining these principles and mask structures. Of these, the latter edge enhancement has a great effect of improving the resolution for an isolated pattern such as a contact hole. Among these, the halftone type phase shift mask, which is a type of edge enhancement type, has a phase shifter with a low light transmittance formed on a substrate, is relatively easy to manufacture, and has no pattern shape dependence. . For this reason, it can be applied not only to memory devices but also to logic devices, and is considered most practical for practical use.

FIG. 1 shows an essential part of a halftone type phase shift mask conventionally used for contact hole exposure.
2 (a). This mask comprises a thin low-transmissivity Cr film 12 having a film thickness of about 20 nm on a transparent substrate 11 made of a transparent material such as quartz, and coated glass (SOG: spin on glass) having a refractive index different from that of the transparent substrate 11. 2) and the like are sequentially formed, and these are processed in a common pattern to form a halftone phase shifter 15 having an opening 13 corresponding to a contact hole.

FIG. 12 (b) is a sectional view taken along line BB of FIG. 12 (a) (however, it is made smaller than FIG. 12 (a) and is inverted. ]. When the exposure light hν is incident on the mask from the transparent substrate 11 side, transmitted light is emitted from the opening 13 in the same phase as the incident light but with substantially the same intensity, but low transparency from the formation region of the halftone phase shifter 15. The transmitted light whose intensity is attenuated by the Cr film 12 and whose phase is inverted by 180 ° by the transparent material layer 14 is obtained.

The light amplitude distribution on the wafer obtained by this mask is as shown in FIG. 12 (c), and the light intensity distribution on the wafer is as shown in FIG. 12 (d).
However, a commonly used reduction projection exposure device (stepper)
Since the reduction ratio is, for example, 1/5, the scale of these drawings is not equal to that of FIG. The area where the photoresist film on the wafer is actually resolved is an area in which the transmitted light intensity exceeds the exposure threshold value indicated by the dotted line in FIG. 3D, and is mainly due to the contribution of the primary peak to the fine contact. It can be seen that holes can be formed with excellent contrast.

[0010]

By the way, in the above-mentioned halftone type phase shift mask, the low transparency Cr film 1 is used.
When the light transmittance of 2 is changed, the intensity of the primary peak that contributes to image formation changes. Here, the above mask is an i-line stepper (exposure wavelength 365 nm, numerical aperture NA = 0.
57, coherency factor σ = 0.30), and a result of simulating how the variation of the contact hole diameter due to defocus depends on the light transmittance T of the Cr film 12 is shown in FIG. The light transmittance T of the low transparency Cr film 12 was controlled by the film thickness. From this figure, it can be seen that when the variation of the contact hole diameter is the smallest, that is, when the depth of focus is large and the contact hole can be resolved most stably, the light transmittance T = 15%.

However, the increase in the intensity of the primary peak is
At the same time, an increase in the intensity of unnecessary secondary peaks caused by diffraction at the edge of the phase shifter is also caused. This state is shown in FIG. In this figure, the secondary peak of the curve showing the light transmittance T = 15% exceeds the exposure threshold value and may be erroneously resolved. In order to avoid such a resolution of the secondary peak, the light transmittance of the shifter forming region of a general halftone type phase shift mask is set to about 10%. In other words, under the present circumstances, the accuracy of resolution is given priority and the depth of focus is sacrificed.

For the halftone type phase shift mask,
In addition to the one using the low-transmissivity Cr film and the transparent material layer (SOG) as described above, there is also known one using a single material film such as an amorphous carbon film, a Cr-containing SiO _x film, a MoSiO film or a MoSiON film. Has been. But,
All material films are still in the research stage, and existing technologies cannot support them.

Therefore, the present invention provides a halftone type phase shift mask capable of expanding the depth of focus while maintaining excellent resolution and, for example, improving the stability of contact hole resolution, and its practical manufacture. The purpose is to provide a method.

[0014]

DISCLOSURE OF THE INVENTION The phase shift mask of the present invention is proposed in view of the above-mentioned object, and is a transparent substrate and a halftone phase formed on the transparent substrate with a predetermined pattern. It comprises a shifter and a light shielding material pattern for reducing the light transmittance in the vicinity of the boundary between the formation region and the non-formation region of the halftone phase shifter on the transparent substrate.

Here, the non-formation area of the halftone phase shifter is an opening corresponding to the connection hole pattern, and the light shielding material pattern is formed along the edge of the opening in the thickness direction of the halftone phase shifter. It is preferable that it is formed so as to occupy at least a part thereof. The optimum width of the light shielding material pattern is determined in relation to the opening width of the opening. The absolute value cannot be unconditionally quantified because it depends on the design rule, but it is a necessary condition that the site where the secondary peak occurs can be shielded. Generally, it may be selected to be about 35% of the opening width. If the width of the light shielding material pattern is too narrow, the generation of the secondary peak cannot be suppressed, and if it is unnecessarily wide, the mask does not substantially function as a halftone type.

The halftone phase shifter can be composed of a laminate of a transparent material layer having an optical constant different from that of the substrate and a low transmittance film having a lower light transmittance.
A coated glass layer can be used as the transparent material layer, and a Cr thin film having a thickness capable of exhibiting a predetermined light transmittance can be used as the low transmittance film. Further, the light shielding material pattern may be composed of a Cr thin film having a thickness capable of exhibiting a light shielding property. It is known that the linear relationship shown in the graph of FIG. 4 is established between the film thickness of the Cr thin film and the light transmittance when, for example, i-line (365 nm) is used as the exposure light, and the film thickness is 40 nm. It becomes a nearly perfect light-shielding film. The film thickness capable of exhibiting a predetermined light transmittance can be obtained from this graph.

On the other hand, the manufacturing method of the present invention for manufacturing such a phase shift mask comprises a step of forming a light shielding material pattern on a transparent substrate, and a transparent material layer having an optical constant different from that of the substrate on the entire surface of the substrate. A step of sequentially forming a low-transmittance film having a lower light transmittance, and patterning the low-transmittance film and the transparent material layer in accordance with one edge of the light-shielding material pattern to form a halftone phase And a step of forming a shifter. Alternatively, the order of stacking the transparent material layer and the low transmittance film may be reversed.

A Cr thin film having a thickness capable of exhibiting a predetermined light transmittance can be used as the low transmittance film, and coated glass can be used as the transparent material layer. Further, as the light shielding material pattern, a Cr thin film having a thickness capable of exhibiting a light shielding property can be used.

[0019]

Since the phase shift mask of the present invention has the light shielding material pattern for reducing the light transmittance in the vicinity of the boundary between the formation region and the non-formation region of the halftone phase shifter, the phase shift mask in the edge portion of the phase shifter is 2 due to diffraction of exposure light
The occurrence of the next peak is prevented. Therefore, the light transmittance of the shifter formation region is increased from the current mainstream value to increase the intensity of the primary peak that contributes to image formation, thereby making the slope of the primary peak steep and improving the contrast. . Further, since the margin for optimizing the light transmittance is widened, it is possible to select, for example, a condition in which there is little variation in the hole diameter with respect to a focus shift when exposing a contact hole without being restricted by the secondary peak. . That is, the depth of focus can be increased.

The phase shift mask has a thick Cr film as a light shielding material pattern, a thin Cr film as a low transmittance film,
By using the coated glass as the transparent material layer, it is provided as a mask suitable for i-line lithography or excimer laser lithography. When manufacturing this mask, a thick Cr film (light-shielding material pattern) is first formed on the transparent substrate.
Is formed, and a coated glass layer (transparent material layer) and a thin Cr film (low transmittance film) are laminated thereon in this order or in the reverse order, and this laminated body is formed into the light shielding material pattern. Since patterning is performed according to one of the edges, a phase shift mask whose surface is flattened by the coated glass layer can be easily and accurately manufactured by applying existing technology.

[0021]

EXAMPLES Specific examples of the present invention will be described below.

Example 1 This example is a structural example of a halftone type phase shift mask in which a light shielding material pattern is arranged around the opening end of a contact hole pattern.

A perspective view of a main part of the halftone type phase shift mask constructed in this embodiment is shown in FIG. 1 (a) and a sectional view taken along the line AA in FIG. 1 (b). However, the scale of the figure (b) is smaller than that of the figure (a), and the top and bottom are reversed. This mask is for resolving a 0.35 μm diameter contact hole pattern on the wafer using an i-line stepper with a reduction ratio of 1/5. The structure is, for example, a quartz substrate 1 (refractive index n = 1.4
7, extinction coefficient k = 0.000) and a SOG film 4 (n = 1.44, k =) having a thickness of about 183 nm as a transparent material layer.
0.003) and a thin low-permeability Cr film 5 as a low-transmittance film.
Are sequentially laminated to form a laminated body, and the length of one side of the laminated body is d ₁ = 2.1 μm (the dimension on the wafer is 0.42 μm).
The square opening 3 is formed as a halftone phase shifter 6, and a film thickness of about 40 nm and a width d ₂ = 0.75 μm (the size on the wafer is 0 as a light shielding material pattern around the bottom surface of the opening 3). 0.15 μm) light-shielding Cr film pattern 2p is arranged. Here, the light transmittance of the low transparency Cr film 5 is 5 to 20% based on the data shown in FIG.
It was set in the range of (33 to 15 nm in terms of Cr film thickness conversion).
The width d ₂ of the light-shielding Cr film pattern 2p described above corresponds to slightly less than 36% of the length d ₁ of one side of the opening.

Exposure light hν is applied to this mask from the quartz substrate 1 side.
Is transmitted, the transmitted light having the same phase as the incident light and substantially the same intensity is emitted from the opening 3, and the halftone phase shifter 6
From the region where the Cr is formed, the transmitted light whose intensity is attenuated by the low-transmissivity Cr film 5 and whose phase is inverted by 180 ° by the SOG film 4 is obtained. However, the exposure light that has entered the light-shielding Cr film pattern 2p is not emitted to the opposite side of the quartz substrate 1.

The light amplitude distribution on the wafer obtained by this mask is shown in FIG. 1 (c), and the light intensity distribution on the wafer is shown in FIG. 1 (d). However, since the reduction ratio of a commonly used reduction projection exposure apparatus (stepper) is 1/5, the scale of these drawings is not equal to that of FIG. The above-mentioned light amplitude distribution is the conventional distribution [see FIG. 12 (c)]. ], The amplitude of the light is plus (+)
This means that the portion where the light-shielding Cr film pattern 2p is present is discontinuous at the portion where it is switched to minus (-). Therefore, the secondary peak does not appear in the light intensity distribution curve of FIG.

Next, this halftone type phase shift mask is mounted on an i-line stepper (NA = 0.57, σ = 0.3), and the contact hole diameter transferred onto the photoresist film is out of focus. On the other hand, the degree of fluctuation was simulated while changing the light transmittance of the low-transmissivity Cr film 5. The light transmittance of the low-transmissivity Cr film 5 is T = 5%
(Cr film thickness 33 nm), T = 10% (27 nm), T
= 15% (at 21 nm) and T = 20% (at 15 nm). The results are shown in Figure 2. From this figure,
It was found that the case where T = 15% had the least influence on the focus shift of 0.75 μm.

In FIG. 4, T = 10%, T = 15%, T =
The light intensity distribution on the wafer obtained for each case of 20% is shown. From this figure, it is understood that the light intensity is suppressed to the exposure threshold value or less in the region other than the opening 3 not only when T = 15% but also when the light transmittance is increased to 20%. On the other hand, conventionally, even if it is desired to use the condition of T = 15%, since the secondary peak exceeds the exposure threshold value, the fluctuation of the contact hole diameter T = is large.
I had no choice but to use the 10% condition.

Transferring the contact hole pattern is the most difficult process of securing the depth of focus in any photolithography. However, it is apparent that the use of the phase shift mask of the present invention makes it possible to form a contact hole pattern having a small dimensional variation with excellent resolution even if the light transmittance T of the formation region of the halftone phase shifter is 15%. .

Example 2 In this example, a method of manufacturing the halftone phase shift mask described in Example 1 will be described with reference to FIGS.

First, as shown in FIG. 5, the quartz substrate 1
40 nm thick light-shielding Cr by sputtering
Film 2 was blanket deposited. Next, this was patterned using an electron beam resist (not shown) to form a square frame light-shielding Cr film pattern 2p as shown in FIG.

Next, as shown in FIG. 7, S is formed on the substrate.
The OG film 4 was spin-coated to flatten its surface, and a low-transmissivity Cr film 5 having a thickness of 21 nm was formed by sputtering. Further, the low-transmissivity Cr film 5 and the SOG film 4 are dry-etched using an electron beam resist mask (not shown) to form a light-shielding Cr film pattern 2p.
The opening 3 was formed to match the inner edge of the.

The stacking order of the SOG film and the low-permeability Cr film may be reversed from the above order. The process in this case is as shown in FIGS. That is, as shown in FIG. 9, the light-shielding Cr film pattern 2p is formed.
To form a low-permeability Cr film 7, and then the surface of the substrate is flattened with the SOG film 4 as shown in FIG. After that, as shown in FIG. 11, the SOG film 4 and the low-transmissivity Cr film 7 are etched in accordance with the openings 3 of the light-shielding Cr film pattern 2p to form a halftone phase shifter 8. In addition, this etching is a resist
Although the optimum conditions are set for each film by using a mask, since the film in contact with the underlying quartz substrate 1 is the low-permeability Cr film 7, it is easy to determine the etching end point and easily secure the selection ratio. There are merits. The optical performance of this mask is almost the same as that of the mask shown in FIG.

The present invention has been described above based on the two embodiments, but the present invention is not limited to these embodiments.

For example, as the mask substrate, a glass substrate may be used instead of a quartz substrate. Further, although the above-mentioned embodiments have been described on the premise of the i-line exposure mask, an excimer laser exposure mask using a light source such as KrF can be similarly configured. In addition, the design rule, the thickness of each film constituting the mask, the optical constants, and the film forming method can be appropriately changed.

[0035]

As is apparent from the above description, according to the phase shift mask of the present invention, unnecessary secondary peaks are suppressed, and for example, the condition that the depth of focus can be expanded in contact hole exposure is restricted by the secondary peaks. It becomes possible to select it without receiving. As a result, the light transmittance of 10% in the shifter formation region of the conventional general halftone type phase shift mask is increased to 15% or more, and the intensity of the primary peak contributing to image formation is increased to increase its inclination. Can be made sharp, and as a result, the contrast can be improved. Further, the phase shift mask of the present invention can be manufactured by applying existing technology, and in this sense, it is extremely practical.

The present invention is extremely promising as a life prolonging measure for i-line lithography, and requires a highly integrated memory device such as next-generation 64M DRAM, 16MS RAM or a logic device, which requires a design rule of 0.35 μm. It becomes possible to manufacture with high reliability. Of course, it is also effective for manufacturing highly integrated devices of the next and subsequent generations to which excimer laser lithography is applied.

[Brief description of drawings]

1A and 1B are diagrams illustrating the configuration and optical performance of a halftone phase shift mask for contact hole exposure to which the present invention is applied, in which FIG. 1A is a perspective view of a main part, and FIG. 1B is a main part. A sectional view, (c) is a light amplitude distribution on the wafer when this mask is used, and (d) is a light intensity distribution on the wafer.

FIG. 2 is a characteristic diagram showing a simulation result of a change in contact hole diameter with respect to defocus in contact hole exposure using the halftone type phase shift mask of the present invention.

FIG. 3 is a characteristic diagram showing a simulation result of a light intensity distribution on a wafer in contact hole exposure using the halftone type phase shift mask of the present invention.

FIG. 4 is a characteristic diagram showing the relationship between the film thickness of a Cr thin film and i-line transmittance.

5 is a schematic cross-sectional view showing a state in which a light-shielding Cr film is formed on a quartz substrate in the manufacturing process of the halftone type phase shift mask shown in FIG.

6 is a schematic cross-sectional view showing a state in which the light-shielding Cr film of FIG. 5 is patterned.

7 is a schematic cross-sectional view showing a state in which the substrate of FIG. 6 is flattened with an SOG film and a low-transmissivity Cr film is further formed.

8 is a schematic cross-sectional view showing a state where a halftone phase shifter is formed by patterning the SOG film and the low transparency Cr film of FIG.

FIG. 9 is a process of manufacturing another configuration example of a halftone phase shift mask for contact hole exposure to which the present invention is applied, in which a light-shielding Cr film patterned on a quartz substrate is replaced with a low-transmission Cr film. It is a typical sectional view showing the state where it was covered.

10 is a schematic cross-sectional view showing a state in which the surface of the base body of FIG. 9 is flattened with an SOG film.

11 is a schematic cross-sectional view showing a state in which a halftone phase shifter is formed by patterning the SOG film and the low transparency Cr film of FIG.

12A and 12B are views for explaining the configuration and optical performance of a conventional halftone type phase shift mask for contact hole exposure, wherein FIG. 12A is a perspective view of a main part, FIG. FIG. 7C shows the light amplitude distribution on the wafer when this mask is used, and FIG. 8D shows the light intensity distribution on the wafer.

FIG. 13 is a characteristic diagram showing a simulation result of a change in contact hole diameter with respect to defocus in contact hole exposure using the halftone type phase shift mask of the present invention.

FIG. 14 is a characteristic diagram showing a simulation result of a light intensity distribution on a wafer in contact hole exposure using a conventional halftone type phase shift mask.

[Explanation of symbols]

 1 Quartz substrate 2 Light-shielding Cr film 2p Light-shielding Cr film pattern 3 Opening 4 SOG film 5,7 Low transparency Cr film 6,8 Halftone phase shifter

Claims (11)

[Claims] 1. A transparent substrate, a halftone phase shifter formed in a predetermined pattern on the transparent substrate, and light near a boundary between a formation region and a non-formation region of the halftone phase shifter on the transparent substrate. Phase shift mask consisting of a light blocking material pattern that reduces the transmittance. 2. The non-formation region of the halftone phase shifter is an opening corresponding to the connection hole pattern, and the light shielding material pattern is at least along the edge of the opening in the thickness direction of the halftone phase shifter. 2. The phase shift mask according to claim 1, which is formed so as to occupy a part. 3. The halftone phase shifter comprises a laminated body of a transparent material layer having an optical constant different from that of the substrate and a low transmittance film having a lower light transmittance than the transparent material layer. Phase shift mask described in. 4. The phase shift mask according to claim 3, wherein the transparent material layer is a coated glass layer. 5. The phase shift mask according to claim 3, wherein the low transmittance film is made of a Cr thin film having a thickness capable of exhibiting a predetermined light transmittance. 6. The light shielding material pattern is composed of a Cr thin film having a thickness capable of exhibiting a light shielding property.
The phase shift mask according to any one of 1. 7. A step of forming a light shielding material pattern on a transparent substrate, and a transparent material layer having an optical constant different from that of the substrate and a low transmittance film having a light transmittance lower than that of the substrate are sequentially formed on the entire surface of the substrate. And a step of forming a halftone phase shifter by patterning the low transmittance film and the transparent material layer in accordance with one edge of the light shielding material pattern. . 8. A step of forming a light shielding material pattern on a transparent substrate, and a low transmittance film and a transparent material layer having a higher light transmittance and a different optical constant than that of the substrate are sequentially formed on the entire surface of the substrate. A method of manufacturing a phase shift mask, comprising the steps of: forming a halftone phase shifter by patterning the transparent material layer and the low transmittance film in accordance with one edge of the light shielding material pattern. 9. The method of manufacturing a phase shift mask according to claim 7, wherein a Cr thin film having a thickness capable of exhibiting a predetermined light transmittance is used as the low transmittance film. 10. The method for manufacturing a phase shift mask according to claim 7, wherein a coated glass layer is used as the transparent material layer. 11. The method of manufacturing a phase shift mask according to claim 7, wherein the light shielding material pattern is composed of a Cr thin film having a thickness capable of exhibiting a light shielding property.