JP3247428B2 - Projection exposure mask and projection exposure method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure technique , and more particularly, to a projection exposure mask utilizing a phase shift method .
The present invention relates to a projection exposure method using the mask .

[0002]

2. Description of the Related Art In recent years, semiconductor integrated circuits have continued to be highly integrated and miniaturized. In manufacturing such semiconductor integrated circuits, lithography technology is important as a key to processing. As a lithography technique, a projection exposure apparatus for reducing and exposing a mask pattern onto a wafer is widely used.

[0003] In this type of projection exposure apparatus, a phase shift method was proposed by IBM in 1980 for mask manufacturing technology, and various phase shift methods have been proposed since then. 8 to 10 show conceptual diagrams of the phase shift method of the Levenson type, the self-alignment type, and the shifter edge utilizing type, respectively. Here, a Levenson-type phase shift mask means that a phase difference between light passing through a phase shifter formed on a light-transmitting substrate and light passing through a light-transmitting substrate is 180 × (2n + 1) ± 30 (degrees). : N satisfies the following relationship:

A self-alignment type phase shift mask is a pattern in which a pattern is formed on a light-transmitting substrate by a light-shielding film, and a light-transmitting film is provided around the pattern formed by the light-shielding film or at a portion other than the periphery. The phase difference of the light passing through the light-transmitting substrate with respect to the light passing through the light-transmitting substrate is 180 × (2n + 1) ± 30 (degrees): n is an integer.

A shifter-edge type phase shift mask is
A pattern is formed at least in part on the light-transmitting substrate by the light-transmitting film, and a phase difference between light passing through the pattern by the light-transmitting film and light passing through the light-transmitting substrate is 180 × (2n + 1) ± 30. (Degree): n satisfies the following relationship:

FIG. 11 shows a comparison of the effect of improving the resolving power by simulation of each phase shift method, and FIG. 12 shows a comparison of the focus margin. According to these figures, it can be said that the Levenson type and the shifter edge type have a greater resolution improving effect and a larger focus margin than the self-alignment type, and the Levenson type and the shifter edge type are used for devices having a design rule of 0.40 μm or less. Can be said to be effective. However, since the shifter edge type can be applied only to a pattern limited to a single-stroke pattern, the Levenson type phase shift method is promising for a fine wiring pattern such as an actual DRAM.

In the Levenson-type phase shift method, conventionally, unless shifters are alternately arranged in a repetitive pattern such as line and space as shown in FIG.
It was thought that a sufficient effect as the phase shift method could not be obtained. That is, when the Levenson-type phase shift method is used, the pattern must be designed so that the phase shifters are alternately arranged, and the Levenson-type phase shift method has a large design limitation in terms of resolution.

[0008]

As described above, in the conventional Levenson-type phase shift method, a sufficient effect as the phase shift method cannot be obtained unless the shifters are alternately arranged in a repetitive pattern such as line and space. It has been considered that the Levenson-type phase shift method has a great limitation in designing a mask pattern.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the design constraints of a mask while maintaining sufficient resolution in the Levenson-type phase shift method. Projection exposure mask
And a projection exposure method .

[0010]

According to the gist of the present invention, a sufficient effect can be obtained even if the shifters are not alternately arranged in a repetitive pattern in order to reduce design constraints in the Levenson type phase shift mask. It is to realize such a shifter arrangement.

That is, the present invention relates to a projection exposure mask used for projecting and exposing a fine pattern on a wafer, comprising: a light-transmitting substrate; a light-shielding layer formed in a predetermined pattern on the substrate; in selectively formed projection exposure mask and the phase shifter layer is formed to shift approximately 180 degrees out of phase with respect to lithography light transmitted through the substrate into the opening region which is not covered with the light shielding layer, the opening region When the area where the phase shifter is not formed is φ1 and the area where the phase shifter is formed is φ2, basically,
Alternately arranges φ1 and φ2, and partially φ1 or φ2
Without making at least one of φ2 consecutive three or more
It is characterized in that up to two are continuously arranged . Further, according to the present invention, in a projection exposure method for exposing a pattern of a mask onto a wafer by an exposure apparatus using the projection exposure mask having the above configuration, the coherence factor of the exposure apparatus when exposing the pattern of the mask is 0.5. It is characterized by having been set to less than.

[0012]

When the shifters are arranged at the openings of the Levenson-type phase shift mask, the shifters are originally arranged so that the continuous patterns do not have the same phase. The shifters were arranged so as to satisfy the following conditions, and the respective limit resolution and depth of focus were examined. As a result, it has been found that even if two consecutive patterns have the same phase, the reduction in the resolving power is extremely small, and if three or more consecutive patterns have the same phase, a large reduction in the resolving power appears.

Therefore, when the shifters are arranged in the openings as in the present invention, the shifters are arranged so that three consecutive patterns do not have the same phase, so that the Levenson type in which the shifters are not alternately arranged in a repeated pattern is provided. Also in the phase shift mask, a sufficient effect as the phase shift method can be obtained. In other words, conventionally, the shifters were alternately arranged in a repetitive pattern such as line & space in order to enhance the effect of the Levenson-type phase shift method, so that design restrictions were great. Even if they are not alternately arranged, a sufficient effect as the phase shift method can be obtained, and a degree of freedom in design can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. (Example 1)

FIG. 1 is a diagram showing a main configuration of a projection exposure apparatus according to an embodiment of the present invention. Light from the light source side is applied to a Levenson-type phase shift mask 3 by a condenser lens 2 through an aperture stop 1. This mask 3
A light-shielding layer is formed in a predetermined pattern on a light-transmitting substrate substrate, and a phase shifter layer for shifting a phase with respect to lithography light transmitted through the substrate is selectively formed in an opening region not covered by the light-shielding layer. It is something.

Here, the opening region of the mask 3 is basically formed such that the phase shifter layers are alternately formed and partially formed with two portions where the phase shifter layer is formed or two portions where the phase shifter layer is not formed. I have. Specifically, when arranging the phase shifter layer in the opening region of the mask 3, the phase shifter layer is placed in a part that cannot be arranged alternately by a pattern.
In this case, the phase shifter layers are alternately arranged. That is, as described later, a shifter arrangement is used in which three consecutive patterns do not have the same phase.

The light transmitted through the mask 3 is reduced and projected on a wafer 5 by a projection lens 4. Thereby, the mask 3
Is reduced and transferred onto the wafer 5.

FIG. 2 shows examples of the arrangement of the phase shifters (types A to G), and FIG. 3 shows the value of the depth of focus (DOF) in each example of the arrangement of the shifters. In FIG. 2, q indicates a normal pattern of the Cr opening, s indicates a pattern of the Cr opening in which the shifter is arranged, and the numerals indicate the arrangement relationship between the pattern and other patterns. That is, 0 is the same phase of the light transmitted through the openings of all the patterns, 1 is the phase of the light transmitted through the adjacent openings of 180 ° opposite phase, and 2 is the phase of the light transmitted through the adjacent openings. In relation to the above, one is in phase, the other is 180 degrees out of phase, and 3 indicates that the phases of the light transmitted through the adjacent openings are in phase.

Type A is a normal mask, type B is a Levenson-type regular shifter arrangement, and types C to G are a Levenson-type irregular shifter arrangement. The irregular shifter arrangement indicates an arrangement in which up to three consecutive patterns have the same phase.

As shown in FIG. 3, a shifter arrangement (type A
To G), for example, 0.30 to 0.4
For 0 μm device prototypes, the shifters of types A, D, F, and G have poor resolution. In these shifter arrangements, three consecutive patterns have the same phase. That is, it can be said that a shifter arrangement in which three consecutive patterns have the same phase should be avoided. Shifter arrangements (types B, C, and E) in which three consecutive patterns in the shifter arrangement do not have the same phase are type A,
It can be said that device resolution of 0.30 to 0.40 μm is possible by disposing shifters as in types B, C, and E compared with D, F, and G.

In other words, conventionally, shifters were alternately arranged in a repetitive pattern such as line & space in order to enhance the effect of the Levenson-type phase shift method, so that design restrictions were great. By avoiding a shifter arrangement having the same phase, a sufficient effect can be obtained even if the shifters are not alternately arranged in a repetitive pattern, so that a degree of freedom in design is generated.

As described above, according to this embodiment, in the Levenson-type phase shift mask, up to two phase shifter layers are allowed to be continuous, and by avoiding a shifter arrangement in which three continuous patterns have the same phase, The design constraint of the mask can be reduced while maintaining the effect (sufficient resolution, sufficient DOF) as the phase shift method. Therefore, it is possible to easily and accurately create various patterns of the LSI by the projection exposure, and the effect is great. (Embodiment 2) Next, another embodiment of the present invention will be described.

As described above, in the Levenson-type phase shift method, unless the shifters are alternately arranged in a repetitive pattern such as line and space, a sufficient effect as the phase shift method cannot be obtained, and design constraints are imposed. Is big. Further, in order to obtain a sufficient effect using the shifter edge type phase shift mask, the edge portion of the shifter must be as close as possible to a vertical shape, which is difficult in many cases in manufacturing a mask. That is, in the Levenson-type phase shift mask, an exposure method that can obtain a sufficient effect even if the shifters are not alternately arranged in a repeated pattern is required. Also, in the shifter edge-based phase shift mask, an exposure method that can obtain a sufficient effect even when the edge portion of the shifter is tapered is required.

Therefore, in this embodiment, a sufficient effect can be obtained even in a Levenson-type phase shift mask in which the shifters are not alternately arranged in a repetitive pattern, and the shifter edge-based phase shift type in which the edges of the shifters are tapered. Provided is a technique capable of obtaining a sufficient effect even in a mask.

As means for this, the coherence factor (σ) of the projection exposure apparatus is set to a conventional value (0.5 to 0.6).
And 0.3 to 0.4. The σ value is σ = NA / N, where NA is the numerical aperture of the condenser lens 2 and NA ′ is the numerical aperture of the projection lens 4 in FIG.
A '.

The coherence factor (.sigma.) Of the exposure apparatus is set lower than the conventional value (0.5 to 0.6), and 0.3 to 0.
By setting to 4, a sufficient effect can be obtained even in a Levenson-type phase shift mask in which shifters are not alternately arranged in a repetitive pattern. In other words, conventionally, the shifters were alternately arranged in a repetitive pattern such as line & space in order to enhance the effect of the Levenson-type phase shift method, so that design restrictions were great. Even if they are not alternately arranged in a repetitive pattern, a sufficient effect can be obtained and a degree of freedom in design can be obtained.

The coherence factor (.sigma.) Of the exposure apparatus is set lower than the conventional value (0.5), and is set to 0.3 to 0.1.
By setting it to 4, a sufficient effect can be obtained even in a shifter edge-based phase shift mask in which the edge portion of the shifter is tapered. In other words, conventionally, the edge of the shifter had to be formed in a vertical shape in order to enhance the effect of the phase shift method using the shifter edge, and a process technique for this was required. A sufficient effect can be obtained even if the portion is not formed in a vertical shape, and a difficult process technique for forming the edge portion of the shifter in a vertical shape becomes unnecessary.

FIG. 4 shows the design dimension dependence (dimension linearity) of the finished dimension in this embodiment. The shifter arrangement is a Levenson-type phase shift mask in which the shifters are not alternately arranged in a repeated pattern as shown in FIG. From FIG. 4, it can be seen that the limit resolution is improved when σ = 0.3 than when σ = 0.5.

The following Table 1 shows the limit resolution in various shifter arrangements in which no shifters are alternately arranged in a repetitive pattern. The shifter arrangements of types A to G in Table 1 are as shown in FIG. (Table 1) Various shifter arrangements in which shifters are not alternately arranged in a repetitive pattern, especially B, which can be applied to an actual device.
It can be seen that for the types C and E, the limit resolution is improved when σ <0.4 than when σ = 0.5.

[0030]

[Table 1]

As described above, in the present embodiment, the coherence factor (σ) of the exposure apparatus is set to be lower than the conventional value (0.5) and 0.4 or less, so that the shifters are alternately arranged in a repetitive pattern. Sufficient effects can be obtained with the Levenson-type phase shift mask not disposed. In other words, conventionally, the shifters were alternately arranged in a repetitive pattern such as line & space in order to enhance the effect of the Levenson-type phase shift method, so that design restrictions were great. Even if they are not alternately arranged in a repetitive pattern, a sufficient effect can be obtained and a degree of freedom in design can be obtained.

In this embodiment, the description has been made mainly on the resolution performance, but it is necessary to consider not only the actual resolution but also the uneven illuminance. FIG. 6 shows the illuminance unevenness according to the σ value. Dimensional fluctuation ±
When considering 10%, illuminance unevenness of 4% or less is acceptable,
In this embodiment, σ> 0.2 is required. Thus σ
The lower limit of the value is constrained by illumination variability. Illumination unevenness can be improved to some extent by improving the optical system, but a lower σ is acceptable in this case. (Example 3)

FIG. 7 shows the angle dependence of a shifter edge portion of a dimension patterned using a shifter edge utilizing type phase shift mask according to a third embodiment of the present invention. FIG. 7 shows that σ =
It can be seen that the limit resolution is improved when σ = 0.3 than when 0.5.

As described above, the coherence factor (σ) of the exposure apparatus is set lower than the conventional value (0.5),
By setting the value to 0.4, a sufficient effect can be obtained even in a shifter edge-based phase shift mask in which the edge portion of the shifter is tapered. That is,
In the past, it was necessary to make the edge portion of the shifter a vertical shape in order to enhance the effect of the phase shift method using the shifter edge, and this required an advanced process technology. A sufficient effect can be obtained even if the portion is not formed in a vertical shape, and a process technology for forming the edge portion of the shifter in a vertical shape becomes unnecessary. Note that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the scope of the invention.

[0035]

As described above, conventionally, shifters are alternately arranged in a repetitive pattern such as line & space in order to enhance the effect of the Levenson-type phase shift method. By avoiding the shifter arrangement where three consecutive patterns are in phase,
Even if the shifters are not alternately arranged in a repetitive pattern, a sufficient effect can be obtained, and a degree of freedom in design can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main configuration of a projection exposure apparatus according to a first embodiment of the present invention;

FIG. 2 is an example of a shifter arrangement in the first embodiment (type A
To G).

FIG. 3 is a depth of focus (DOF) in the shifter arrangement of FIG. 2;
Characteristic diagram showing the value of

FIG. 4 is a characteristic diagram showing a design dimension dependency of a finished dimension in the second embodiment;

FIG. 5 is a diagram showing an example of a shifter arrangement in the second embodiment;

FIG. 6 is a characteristic diagram showing a change in illuminance unevenness with respect to a σ value;

FIG. 7 is a view showing the shifter edge angle dependency of a finished dimension in the third embodiment;

FIG. 8 is a schematic diagram for explaining the principle of the Levenson-type phase shift method,

FIG. 9 is a schematic diagram for explaining the principle of the self-alignment type phase shift method.

FIG. 10 is a schematic diagram for explaining the principle of a phase shift method using a shifter edge;

FIG. 11 is a diagram showing simulation results comparing focus margins when three types of phase shift methods are used;

FIG. 12 is a diagram illustrating the concept of a Levenson-type phase shift mask.

[Explanation of symbols]

 Reference numeral 1 denotes an aperture stop, 2 denotes a condenser lens, 3 denotes a phase shift mask, 4 denotes a projection lens, and 5 denotes a wafer.

Claims (2)

(57) [Claims] 1. A projection exposure mask used for projecting and exposing a fine pattern on a wafer, comprising: a translucent substrate; a light-shielding layer formed in a predetermined pattern on the substrate; For lithography light selectively formed in the uncovered opening area and passing through the substrate
In a projection exposure mask in which a phase shifter layer that shifts the phase by about 180 degrees is formed, a region where the phase shifter is not formed among the opening regions is φ1, and a region where the phase shifter is formed is φ2. Basically, φ1 and φ2 are alternately arranged, and
Typically, at least one of φ1 and φ2 is continuous for three or more
A mask for projection exposure, wherein up to two masks are continuously arranged without causing the mask to be exposed. 2. A projection exposure method for exposing a pattern of a mask onto a wafer using an exposure apparatus using the mask for projection exposure according to claim 1, wherein the coherence of the exposure apparatus when exposing the pattern of the mask is provided. A projection exposure method, wherein the factor is set to less than 0.5.