JPH08250407A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE: To form a resist pattern in accordance with designed values on a substrate surface having a stepped-height-difference by providing a mask part, whose. mask size is deviated from a designed value, on a reticle during an exposure step for a stepped surface which is not focused and by carrying out a plurality of exposures focused in accordance with the stepped surfaces and one development. CONSTITUTION: A first exposure is carried out with a stepped surface A from among at least two stepped surfaces A, B being focused. A reticle 20a used during this first exposure has a mask part 21a with a designed width value X on the part facing the stepped surface A. At that time, the part facing the stepped surface B not focused is provided with a mask part 22a having a width X+dX larger than the designed value X. A second exposure is carried out with the stepped surface B being focused. A second reticle 20b has a mask part 22b with the designed width value X. Further, a mask part 21b has a width X+dX larger than the designed value X.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device including a step of forming a resist pattern on a semiconductor substrate having a large height difference.

[0002]

2. Description of the Related Art An exposure process using a stepper having a focus adjusting function is usually used for pattern processing of a semiconductor integrated circuit or the like. In order to form a fine wiring pattern etc. as designed, there is a step inside each chip area of the semiconductor substrate, and even if the step is directly reflected in the resist applied to this, it is as designed regardless of the height difference. It is desired to form a resist pattern.

However, in a reduction projection exposure apparatus for processing a fine pattern, it is the primary purpose to increase the resolution, and there is a trade-off relationship between the resolution and the depth of focus, so it is difficult to obtain a sufficiently large depth of focus. Therefore, when focusing on a high step surface, defocus occurs on a low step surface, and conversely, when focusing on a low step surface, a defocus occurs on a high step surface.

In order to solve such a problem, several methods have been conventionally proposed. For example, a phase shifter is provided on the reticle to cut the 0th-order light, and the ± 1st-order diffracted light with the same optical path length is made incident on the reduction projection lens to cause two light beams to interfere with each other to improve the contrast of the optical image transferred on the wafer. To strengthen. Thereby, the resolution and the depth of focus can be improved. Alternatively, the illumination light is obliquely incident, the 0th-order light is inclined with respect to the optical axis to make the optical path lengths of the 0th-order light and the 1st-order light equal, and two-beam interference of the 0th-order light and the 1st-order light is taken. . This can also improve resolution and depth of focus.

As another method, a method has been proposed in which a plurality of reticles are prepared according to the stepped surface on the substrate, and the stepped surface that is out of focus is shielded from light to perform a plurality of exposures. Kaihei 4-5814, JP-A-5-80528). For example, as shown in FIG. 7, two step surfaces 1 having a height difference,
When there are two, first, as shown in (a), the entire step surface 1 is shielded from light, and the first reticle 71 having a predetermined mask pattern formed on the step surface 2 is used to focus on the step surface 2. Exposure, and then, as shown in FIG.
The second reticle 72, which is shielded from light and has a predetermined mask pattern formed on the step surface 1, exposes the step surface 1 in focus. Then develop.

Japanese Unexamined Patent Publication (Kokai) No. 5-80528 also discloses a method in which one reticle is used and exposure and development are repeated a plurality of times depending on the step surface. In the first exposure / development, a certain step surface is focused, and in the second exposure / development step, the step surface not sufficiently resolved in the previous exposure is focused and exposed / developed.

[0007]

However, the previously proposed methods still have problems to be solved.
For example, the method of arranging the phase shifter to improve the illumination light causes inconsistency in the arrangement of the phase shifter depending on the layout of the pattern, and the effect cannot be obtained. Moreover, the oblique incidence method of illumination light is not effective for an isolated pattern.

In the method of performing multiple exposure depending on the step, for example, in the method of FIG. 7 using two reticles, the resist pattern 73 obtained by development is often shown in FIG.
As shown in (c), a bridge 74 made of resist that cannot be removed occurs at the boundary between the step surfaces 1 and 2. In the method of performing multiple exposure / development using one reticle, the process is extremely complicated because the development is performed plural times.

The present invention has been made in view of the above points, and an object thereof is to provide a method of manufacturing a semiconductor device having a resist pattern forming step capable of forming a fine resist pattern on a stepped substrate surface as designed. I am trying.

[0010]

According to the present invention, there is provided a semiconductor having a step of forming a resist pattern by applying a resist on a semiconductor substrate having at least first and second step surfaces having different heights and exposing and developing the resist. In the method of manufacturing the device,
In the step of forming the resist pattern, the mask portion of the portion facing the first step surface is dimensioned as designed, and the mask portion of the portion facing the second step surface is wider than the design value. A first exposure step of performing an exposure focused on the first step surface of the substrate coated with the resist, using a first reticle having a mask pattern;
A second reticle having a mask portion for the first step surface wider than a design value and a mask portion for the second step surface having dimensions as designed is used to focus on the second step surface. It is characterized by having a second exposure step of performing combined exposure and a development step of developing the resist that has undergone these exposure steps to form a resist pattern.

[0011]

According to the present invention, a desired resist pattern can be obtained by forming a reticle separately according to the step surface and performing a plurality of exposures and a single development in which focusing is performed according to the step surface. Unlike the method of shielding the entire stepped surface that is out of focus from light, in the present invention, the reticle in a certain exposure process is provided with a mask portion whose mask size is deviated from the design value even for a stepped surface that is out of focus. Since it is provided, unlike the conventional multiple exposure method in which the stepped surface that is out of focus is entirely shielded from light, no bridge is generated in the final resist pattern. Also, since the developing process is only once,
The process is simpler than the method of repeating exposure and development using one reticle.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a resist pattern forming process of one embodiment. The flow of the exposure process is shown in FIG. For illumination in the exposure process, an oblique incidence illumination method as shown in FIG. 6B is used. That is, the illumination light is obliquely incident on the reticle 61, only the 0th and 1st order diffracted light is extracted and introduced into the reduction projection system 63, and is collected on the wafer 64 coated with the resist by the two-beam interference method. Light up. Alternatively, FIG. 6 (a)
As shown in, a method of using 0th-order light and + 1st-order light (or -1st-order light) by utilizing a phase shift method may be used.

The exposure and development process of this embodiment will be described in detail. As shown in FIG. 5, the wafer is loaded on the stepper stage (S1), and the first reticle 20a is set (S2).・ Align (S3),
The first exposure is performed (S4). This first exposure process is shown in FIG.

In the semiconductor wafer 10, as illustrated in FIG. 1, a LOCOS oxide film 12 is formed on a silicon substrate 11, a first layer wiring 13, an insulating film 14, a second layer wiring 15, an insulating film 16 and a third layer. The layer wiring layer 17 is formed and has a large step. The surface of the wafer 10 is coated with a positive type resist 18 reflecting the steps. The first exposure is performed by focusing on the step surface A of at least two step surfaces A and B. The first reticle 20a used for the first exposure is the mask portion 21a of the portion facing the step surface A.
Is the width X according to the design value, and the mask portion 22a in the portion facing the stepped surface B that is out of focus at this time has a width X + dX wider than the design value X.

By this first exposure, the mask portion 21a is directly transferred onto the step surface A as shown by the broken line. A sharp image transfer cannot be performed on the stepped surface B where the focus is deviated, but since the mask portion 22a is formed wide, at least the range of the width X required as a resist pattern remains unexposed.

Subsequently, as shown in FIG. 5, the second reticle 20b is set (S5), wafer alignment is performed (S6), a second exposure is performed (S7), and the wafer is taken out ( S8). This second exposure process is shown in FIG.

This second exposure is carried out on the two step surfaces A and B.
Of these, the focus is on the step surface B. In the second reticle 20b used for the second exposure, the mask portion 22b in the portion facing the step surface B has the width X as designed,
At this time, the mask portion 21b in the portion facing the stepped surface A that is out of focus has a width X + wider than the design value X.
It is dX. Therefore, in the second exposure, as shown by the broken line, the mask portion 22b is directly transferred to the step surface B, and the step surface A defocused is at least in the range of the width X required as the resist pattern. Remains unexposed.

After passing through the above two exposure steps, the resist 18 is developed. By this development, as shown in FIG.
Resist patterns 18A and 18B having a width X as designed on both step surfaces A and B are obtained.

According to this embodiment, multiple exposure is carried out, but development is carried out once, and therefore the process is simple. Further, by using the multiple exposure method described above and the phase shift method or the oblique incident illumination method that can obtain high resolution, it is possible to substantially improve the depth of focus while maintaining the high resolution characteristics. . In particular, a deep depth of focus can be obtained when processing a large number of linear resist patterns with a predetermined space. Further, for the isolated line, the effect of increasing the depth of focus can be obtained by the same mechanism as the FLEX method.

Further, in this embodiment, the exposure process is performed twice.
The non-focused area is not completely shielded from light as in the conventional example of FIG. 7, but a certain amount of light is emitted. As a result, the bridge due to the resist left behind at the boundary of the step does not occur as described in FIG. In order to clarify this point, FIG.
Corresponding to, the step of processing a resist pattern having a constant width X so as to cross the step boundary is shown.

In the first exposure shown in FIG. 3A, the step surface A is focused. First reticle 2 used at this time
0a has a mask portion having a width X + dX that is wider than the specified width X in a portion facing the stepped surface B that is out of focus. FIG. 3 (b)
In the second exposure of, the step surface B is focused. The second reticle 20b used at this time is the step surface A that does not focus.
Has a mask portion having a width of X + dX. Two
When the development is performed after the exposure is repeated, as shown in FIGS. 3C and 3D, resist patterns 31 and 32 having a width X continuous over the step surfaces A and B are obtained. As in the example of FIG. 7, since the non-focus step surface is not completely shielded from light, the adjacent resist patterns 31 and 32 are reliably separated.

FIG. 4 shows the exposure process of the embodiment when a negative resist is used, corresponding to FIG. The wafer structure is the same as that of FIG. 1 except that the resist 19 is a negative type. As shown in FIG. 4A, the first exposure is performed by focusing on the step surface A of the two step surfaces A and B. The first reticle 3 used for this first exposure
0a is the width X of the opening 31a in the portion facing the step surface A as designed, and at this time the step surface B is out of focus.
The opening 32a of the portion opposed to is set to X-dX having a width narrower than the design value X. Focusing on the mask portion 33 that blocks light, the relationship is the same as in the embodiment of FIG.
By this first exposure, the opening 31a is directly transferred to the step surface A as shown by the broken line. The exposure width is small for the stepped surface B where the focus is deviated.

The second exposure is performed by focusing on the step surface B, as shown in FIG. 4 (b). In the second reticle 30b used for the second exposure, the opening 32b in the portion facing the step surface B has the width X as designed and the opening 31b in the portion facing the step surface A out of focus. Is X-dX, which is narrower than the design value X. This relationship is also the same as in the embodiment of FIG. In the second exposure, as shown by the broken line, the opening 32b is directly transferred to the step surface B, and the step surface A is exposed in a narrow range. Since the range of width X is sharply exposed on both step surfaces A and B in the above-described two exposure steps, when they are developed, step surfaces A and B are formed similarly to FIG. 2 of the previous embodiment. In both cases, a resist pattern having a width X as designed is formed.

[0024]

As described above, according to the present invention, a reticle is separately formed according to a step surface, and a desired resist pattern is formed by a plurality of exposures and a single development in which focusing is performed according to the step surface. Can be obtained. According to the present invention, the reticle in a certain exposure process is not entirely shielded from light even on a stepped surface that is out of focus, but a mask portion whose size is deviated from the design value is provided for exposure. There is no possibility that a bridge or the like will occur in a simple resist pattern. Further, since the development is performed once, the process is simple.

[Brief description of drawings]

FIG. 1 shows an exposure process according to an embodiment of the present invention.

FIG. 2 shows a state of resist pattern processing according to the embodiment.

FIG. 3 shows a resist pattern forming system straddling a step portion according to the embodiment.

FIG. 4 shows an exposure process according to another embodiment.

FIG. 5 shows a flow of an exposure process of an example.

FIG. 6 shows a configuration of an exposure optical system of an example.

FIG. 7 shows an example of a conventional exposure method.

[Explanation of symbols]

10 ... Semiconductor wafer, 18 ... Positive resist, A, B ...
Step surface, 20a ... First reticle, 20b ... Second reticle, 21a, 21b, 22a, 22b ... Mask portion, 1
9 ... Negative resist, 31a, 31b, 32a, 32b
... Opening part, 33 ... Mask part.

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device, comprising: a step of applying a resist on a semiconductor substrate having at least first and second step surfaces having different heights, exposing and developing the resist pattern to form a resist pattern. The step of forming a pattern is a mask pattern in which the mask portion of the portion facing the first step surface has a size according to the design value and the mask portion of the portion facing the second step surface is wider than the design value. Having 1st
Using the reticle described above, a first exposure step of performing an exposure focused on the first step surface of the substrate coated with the resist, and a mask portion for the first step surface is made wider than a design value. A second exposure step of performing an exposure focused on the second step surface by using a second reticle having a mask portion for the second step surface having a dimension as designed. And a developing step of forming a resist pattern by developing the resist that has gone through the steps.