JPH0467147A - Photomask - Google Patents

Abstract

PURPOSE:To enable a resist pattern high in precision to be formed on wafers different in height by one time of exposure by providing some openings with a transparent material and giving to exposure light passing through these openings a light path difference longer than the exposure light passing through the other openings located not extremely near to these openings. CONSTITUTION:The exposure light transmitted through a transparent substrate 1 is partly shielded by a chromium pattern 2, and the light passing through the transparent material 3 is extended in light path than the light not passing through the material 3 among the light having passed through the pattern 2 by (1 - 1/n) X d/25, where (d) is the thickness of the material 3 and (n) is its refractive index, thus permitting the image-forming height to be lowered on the surface of the wafer 6 for the light passing through the material 3, and the best image to be formed on the height-lowered part 5, and on the other hand, the light not passing through the material 3 to form the best image on the part 8, and consequently the best image formation to be executed on the surface of the wafer having the height difference in only one time of exposure operation and the fine resist patterns high in precision to be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a photomask used in the manufacture of semiconductor devices, particularly in photolithography processes.

BACKGROUND OF THE INVENTION In recent years, high integration has progressed in the field of semiconductor device manufacturing, and the height difference due to miniaturization and multilayer wiring has become more and more noticeable. Along with this, it has become increasingly difficult to form a designed pattern in a photolithography process.

A method of forming a resist pattern using a conventional photomask will be described below.

FIG. 6 shows a cross section of the structure of a conventional photomask and a wafer substrate with a resist pattern. An upper step 59 and a lower step 55 are provided on the wafer substrate 56, and resist patterns 58 and 54 are formed on each by transferring the chrome patterns 52 and 53 of the photomask. The best imaging position of the photomask transfer pattern of the exposure device coincides with the upper part 59 of the step, and a sufficiently good resist pattern is formed at the upper part 59 of the step. On the other hand, since the imaging position is shifted in the lower part 55 of the step, a sufficiently good resist pattern cannot be formed. FIG. 7 shows the principle of automatic focusing of an exposure device, in which the surface 64 of a wafer substrate 68 on a stage 69 of the exposure device is reflected by the wafer surface 64 from the light emitting section 62, and The light receiving section 6
3, the stage of the exposure device is moved up and down to align with the imaging position 65. Find out the position of the silicon wafer surface. At this time, if the light reflecting surface 64 is aligned with the upper part 66 of the step, the focal point 65 is aligned with the upper part 66 of the step, and conversely, if the light reflecting surface 64 is aligned with the lower part 67 of the step, the focal point 65 is aligned with the lower part 67 of the step. That is, it is difficult to focus on the upper part of the step and the lower part of the step at the same time. Therefore, as shown in FIG. 8, it is necessary to expose the upper part of the step and the lower part of the step separately. 8th
In (a) of the figure, the upper part of the step is exposed, then in (b) of the same figure.
A second exposure is performed at the bottom of the step, and the entire surface is developed as shown in FIG.

Problems to be Solved by the Invention However, the conventional configuration described above requires two exposure steps and two photomasks, resulting in high cost and misalignment between the upper step and the lower step. In a single exposure process, the best image formation position shifts either at the top of the step or at the bottom of the step, making it difficult to form a fine resist pattern with high precision.

The present invention solves the above-mentioned conventional difficulties, and aims to form highly accurate and fine resist patterns on each wafer surface having different heights in a single exposure process.

Means for Solving the Problems In order to achieve the above-mentioned object, a first means of the present invention provides exposure light that passes through openings in villas that are not adjacent to each other in addition to exposure light that passes through some openings of a photomask. Some openings are provided with a transparent material sufficient to provide light and an optical path difference. A second means is to provide transparent materials with different thicknesses or refractive indexes at the opening of the section and the opening of the annex, respectively.

A third method is to make the transparent substrate of some of the openings thinner.

Effect: With this configuration, there is a partial optical path difference in the light that passes through the photomask, and the image formation positions on the wafer surface are at different heights.Therefore, even on a wafer surface with steps, the focus can be adjusted to each step. It is possible to form fine resist patterns with high precision.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the cross-sectional structure of a photomask and a resist pattern on a wafer substrate in this example. In the figure, 1 is a transparent glass substrate, 2 is a thin chrome material pattern for blocking light, and has a large number of openings. 3 is a transparent material having a thickness d and a refractive index n sufficient to change the imaging position of the transfer pattern on the wafer surface. The end of the transparent material 3 is provided in a light shielding part. The above is the configuration of the photomask section. 6 is the wafer substrate, 5 is the bottom of the step, 8
is the upper part of the step, and 4 and 7 are cross sections of the positive photoresist pattern. For example, a 115 reduction projection exposure device is used as the exposure device.

In the photomask configured as described above, light transmitted through the transparent glass substrate 1 is partially blocked by the chrome material pattern 2. Of the light that has passed through the chromium material pattern 2, the light that has passed through the transparent material 3 is shifted downward in position by (1-1/n)d/25, where the thickness of the transparent material is d1 and the refractive index is n. This can be easily determined because, as shown in Figure 5, the displacement due to the parallel plane plate is (1-1/n)d, and in the case of reduced projection, there is the relationship x'/x = (y'/y)2. .

However, in this formula, X: Distance between the photomask and the lens focal point on the photomask side Two Longitudinal Magnifications By shifting the image formation position on the wafer substrate surface downward in this way, it is possible to have the best image formation position with respect to the lower part of the step. On the other hand, the light that does not pass through the transparent material 3 has its best imaging position at the top of the step without shifting its imaging position.

In this manner, exposure can be performed on the surface of a wafer substrate having steps with the best imaging position corresponding to each step in one exposure process, and a fine resist pattern with high precision can be formed. Note that the distance between the light passing through the transparent material 3 and the light not passing through the transparent material 3 is set to be at least twice the resolution limit dimension so as not to interfere with each other.

When a positive resist pattern is formed as in this embodiment, the boundary edge of the transparent material is usually used as a light-shielding part because a shadow occurs. In the drawing, the transparent material fits into the opening, but it may not fit into the opening.

FIG. 2 is a cross-sectional view for explaining a photomask and its mode of use in a second embodiment of the present invention. In the figure, 11 is a transparent glass substrate, 12 is a pattern formed by depositing chromium, and 13, 17 and 18 are transparent materials, which have different film thicknesses. 16 is a wafer substrate, 15, 19.20 are the lower part of the step, and the upper part of the same.

The middle part is shown. 14 is a positive type photoresist pattern.

This embodiment is characterized in that the thicknesses of the plurality of transparent materials are made to correspond to the height differences of the plurality of wafer substrates. A similar effect can be obtained by selectively changing the refractive index of the transparent material.

FIG. 3 is a cross-sectional view for explaining a photomask and its usage pattern in a third embodiment of the present invention. In the figure, 21 is a transparent glass substrate, 22 is a chrome pattern,
Reference numeral 23 denotes a thinly etched portion of the glass substrate 21 from the chromium-coated surface.

Reference numeral 26 indicates a wafer substrate, 25.27 indicates the lower part of the step, and the upper part thereof. 24 is a positive photoresist pattern.

This embodiment is characterized in that the photomask is turned upside down and the glass substrate is etched from the chromium-coated surface side in a part of the mask opening to provide an optical path difference.

FIG. 4 is a sectional view for explaining a photomask and its usage pattern in a fourth embodiment of the present invention. In the figure, 31 is a transparent glass substrate, 32 is a pattern formed by depositing chromium, and 36 is a thinly etched portion of the glass substrate surface opposite to the surface to which the pattern is deposited. Reference numeral 35 indicates a wafer substrate, 34.37 indicates the lower part of the step, and the upper part thereof.

33 is a positive type photoresist pattern.

This embodiment is characterized in that an optical path difference is provided by inverting the photomask and etching the glass substrate from the surface opposite to the surface on which the pattern is deposited.

In these embodiments, the third. In the fourth embodiment, since only a portion of the glass substrate needs to be processed, the formation process is simplified.

Incidentally, in the present invention, the photomask is not limited to one for one-to-one transfer, but also naturally includes a reticle used for reduction projection for five-to-one or ten-to-one transfer. Naturally, negative types of resists are also included.

Effects of the Invention As described above, the present invention provides an optical path difference in some openings of the photomask, thereby obtaining the best imaging position in accordance with the step difference in the wafer substrate, and creating a fine and highly accurate resist pattern. There can be

[Brief explanation of drawings]

Figures 1 to 4 are cross-sectional views showing a photomask in an embodiment of the present invention and its mode of use, respectively, and Figure 5(a) is an optical path diagram showing a vertical shift in the imaging position due to the presence of a transparent material. , FIG. 5(b) is a diagram showing the relationship between vertical magnification and lateral magnification of imaging due to the presence of a lens, FIG. 6 and FIG. 8(a) to (
C) is a sectional view of a photomask and resist pattern in a conventional example, and FIG. 7 is a diagram showing the principle of automatic focusing of an exposure apparatus. 1.11, 21.31...Light-transmissive glass substrate, 2.12, 22.32...Pattern, 3...
...Transparent material, 4,7.14.24.33...
・Photoresistor pattern, 5, 15, 25.34.6
7... Wafer substrate, 8, 19, 27, 37.
66...Top of wafer step, 10...
・Transparent material end, 13, 17° 18... Transparent material with different film thickness, 20... Wafer step middle part, 2
3, 36...Glass substrate etching part, 61
... Lens, 62 ... Light emitting section, 63
. . . Light receiving section, 64 . . . Wafer substrate surface, 65 . . . Imaging position, 69 . . . Stage of exposure device. Name of agent: Patent attorney Shigetaka Awano and one other person Figure 1 Figure 2 Figure 3 1 ruri entrance] beast 2 ri DI, ha 1 coon 5L Moe Lane! 7 Tousu Kuzu 4th return! 27Ω Muhaan bz large, ttep t7 wafer number ヱ lower tank P Fig. l j'Last stem handling quahar k11 lower 1p 5chi, 53 Kushito Munst 8? of

Claims (3)

[Claims] (1) In a photomask in which a light-shielding film is provided on a transparent substrate and a large number of opening patterns are formed by partially removing the light-shielding film, exposure light that passes through some of the openings is exposed to separate parts that are not extremely close to each other. 1. A photomask comprising a transparent material in some of the openings in order to provide an optical path difference from the exposure light that passes through the openings. (2) In a photomask in which a light-shielding film is provided on a transparent substrate and a large number of opening patterns are formed by partially removing the light-shielding film, the exposure light that passes through some of the openings is exposed to separate parts that are not extremely close to each other. A photomask characterized in that transparent materials having different film thicknesses or different refractive indexes are provided in some of the openings and in the other openings to provide an optical path difference with respect to the exposure light that passes through the openings. . (3) In a photomask in which a light-shielding film is provided on a transparent substrate and a large number of opening patterns are formed by partially removing the light-shielding film, the exposure light that passes through some of the openings is exposed to separate parts that are not extremely close to each other. 1. A photomask characterized in that the transparent substrate in some of the openings is formed thin in order to provide an optical path difference with the exposure light that passes through the openings.