JPH06151280A - Forming method for hole pattern - Google Patents

Abstract

PURPOSE:To prevent a hole pattern forming device from decreasing in throughput due to the replacement of a light source modulation filter and to restrain a hole pattern from deteriorating in quality at transfer due to the deviation of a filter in alignment by a method wherein a negative resist is used when a hole pattern is formed. CONSTITUTION:Negative resist is applied onto the surface of a substrate 9 where a pattern is formed to form a mask pattern 6 used for forming a hole pattern. On the other hand, the g ray of a mercury lamp is made to serve as a light source 1 and turned to parallel rays of light through a collimator 2, which are turned uniform by a fly eye lens 3, this image forming point is made to serve as a secondary light source, a ring band filter is installed at the image forming point, rays of light are condensed by a condenser lens 5 and then directed to the surface of a resist film formed on a wafer 9 through the mask 6, a pupil 7, and a projecting lens. By this setup, a light source modulation filter such as a ring band filter is not required to be replaced corresponding to the type of a mask pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hole pattern forming method, and more particularly, to a hole pattern forming method for transferring a hole pattern on a mask onto a wafer in the hole forming using a negative resist.

[0002]

2. Description of the Related Art With the progress of semiconductor technology, the speed and integration of semiconductor devices, and thus semiconductor elements, are being advanced.
Along with this, the need for miniaturization of patterns is increasing more and more, and the pattern dimensions are also required to be miniaturized and highly accurate.

As shown in FIG. 7, the conventional exposure apparatus uses a mercury lamp as a light source lamp such as g-line 436 nm and h-line 405.
nm, i-line 365 nm, etc., excimer laser (Kr
F) is used. Then, an optical system including an optical integrator (fly's-eye lens) or the like in order to improve irradiation uniformity obtains uniformized light 100, which is passed through a diaphragm 104 and a two-dimensional illumination optical system 105. The projection optical system 1 including the diaphragm 107
It is configured to guide light from 08 onto the wafer 109 to perform pattern exposure.

In such a reduction projection exposure apparatus,
Once the exposure wavelength is determined, the pattern formation characteristics such as resolution and depth of focus are determined by the numerical aperture (NA) of the projection optical system 108.
= Sin θ) and the coherency of illumination light (σ = sin φ)
/ Sin δ). In such a conventional apparatus, since the property of the light illuminating the reticle 106 is determined only by the coherency σ value, a fine pattern can be obtained while satisfying various conditions such as depth of focus, uniformity within a region, and line width controllability. However, there was a limit determined by NA and σ. Therefore, the numerical aperture NA of the projection optical system 108
When the size of the secondary light source 100 is determined, the pattern forming characteristic is automatically determined, and there is a problem that the resolution performance cannot be further improved.

Therefore, for the purpose of solving this problem as much as possible, light having a short wavelength such as far-ultraviolet light has been used as an exposure light source. However, although the process using the 248 nm oscillation line of the KrF excimer laser, which is about to be used in the next-generation exposure light source, is being developed as a chemically amplified resist as a resist material, it is still in the research stage and is not yet commercialized at this time. Have difficulty. When the wavelength of the exposure light source is changed in this way, it takes a considerable period of time from the material development to the practical use because it is necessary from the material development.

In recent years, attempts have been made to miniaturize the exposure light source without changing it. One of the methods is a phase shift method. This phase shift method is a technique for improving the resolution and contrast of a projected image by manipulating the phase of light passing through a mask. That is, in this method, the phase inversion layer is partially provided in the light transmitting portion, the influence of the diffraction of light from the adjacent pattern is removed, and the pattern accuracy is improved.

There are several types of this phase shift method,
A Levenson type is known in which two adjacent light transmitting portions are alternately provided with a phase difference of 180 degrees.

However, it is difficult for this method to exert its effect when three or more patterns are adjacent to each other. That is, when the optical phase difference between the two patterns is 180 degrees, the other pattern has the same phase as one of the previous two patterns, and as a result, the patterns having the phase difference of 180 degrees are resolved, but the phase difference is 180 degrees. There is a problem in that 0-degree patterns are unresolved.

In order to solve this problem, it is necessary to fundamentally rethink the device design, and it is quite difficult to put it into practical use.

Therefore, there is a halftone method as a method which does not require a device design change. In this method, a semi-transmissive film is used for the light-shielding portion, so that a sharp image intensity is obtained at the edge portion due to the optical phase inversion effect at the pattern edge portion.

However, in this method, since the semi-transparent film is used instead of the light-shielding film, there is a problem that the residual film rate becomes high.

Further, in this method, a semitransparent film is used in the light-shielding portion of the pattern, and a sharp image intensity can be obtained at the edge portion due to the optical phase inversion effect at the edge portion of the pattern. Regarding the hole formation, when a positive resist is used, a DOF improving effect can be obtained by using a halftone mask.

Further, as another attempt to achieve miniaturization without changing the exposure wavelength, as a method for devising the shape of the light source of the exposure apparatus, for example, as shown in Japanese Patent Laid-Open No. 61-91662, conventional exposure is used. An attempt has been made to perform exposure by only the peripheral light without using the central light of the secondary light source by mounting the light source modulation filter in place of the circular diaphragm that determines the size of the secondary light source used in the apparatus. It has been confirmed that the resolution is improved and the depth of focus is increased with respect to the L / S pattern.

However, as indicated above, L / S
Although it has the effect of improving resolution and DOF for patterns, it has a D effect compared to normal illumination for hole patterns.
OF is reduced. Here, the hole pattern means an isolated punching pattern such as a pattern having a hole such as a contact hole. That is, as shown in FIG. 8, which shows the result of the defocus dependence of the contrast in the hole pattern (positive) of the normal Cr mask having the pattern size of 0.7 μm (pitch 4.2 μm), the coherency σ in the hole pattern is It can be seen that the lower the better, the better the normal lighting. That is, the use of annular illumination reduces the focus margin.

In the present situation where the need for light source modulation is increasing due to the demand for miniaturization of L / S patterns, it becomes necessary to replace the light source modulation filter depending on the pattern to be transferred due to the pattern type dependency due to the above light source modulation. For,
There is a problem that the throughput is lowered and a new filter automatic mounting function is required.

[0016]

As described above, when an isolated punching pattern including a hole pattern is formed, the use of annular illumination reduces the focus margin. Therefore, the optical modulation filter should be replaced or There was a problem of whether to accept the reduction of the focus margin.

The present invention has been made in view of the above circumstances, and in the formation of the hole pattern, it is not necessary to replace the light source modulation filter due to the dependency of the pattern type. It is an object of the present invention to provide a hole pattern forming method that prevents deterioration during transfer.

[0018]

Therefore, the method of the present invention is characterized in that a negative resist is used when forming a hole pattern. That is, a negative resist is applied to the surface of the substrate on which a pattern is to be formed, and the exposure mask is provided with a mask pattern for forming a hole pattern, at a uniform light source surface or at a position conjugate with the light source surface, A ring filter having a dark part in the center or 4 which is symmetrical with respect to the optical axis four times and which is off the optical axis.
An exposure step of forming a hole pattern by forming a filter image having a high intensity in one area or a filter having a composite shape thereof and forming a pattern image of the exposure mask on the surface of the substrate on which a pattern is to be formed. It is characterized by including.

Preferably, the mask pattern has a phase difference of "180 × (2n + 1) ± 30" between the exposure light transmitted through the portion where the hole pattern is to be formed and the exposure light transmitted through the peripheral portion or the boundary portion thereof. : N = integer ", which is a semitransparent material or a transparent material.

[0020]

According to the present invention, it is not necessary to replace the light source modulation filter such as the ring filter depending on the type of mask pattern, and it is possible to improve the throughput and the focus margin in the line and space pattern.

Preferably, this mask has a phase difference of "180 ×" between the exposure light transmitted through the portion where the hole pattern is to be formed and the exposure light transmitted through the peripheral portion or the boundary portion thereof.
If a halftone mask made of a semitransparent material that satisfies the relationship of (2n + 1) ± 30: n = integer ”, a phase shift mask using a shifter edge, or the like is used, reduction of the defocus amount can be prevented. .

[0022]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is an explanatory diagram showing the basic structure of an optical system of a reduction exposure apparatus used for pattern formation of a first embodiment of the present invention.

This exposure apparatus is characterized in that, when performing pattern exposure, the light rays homogenized by the fly-eye lens are guided to the phase shift mask via the ring filter.

That is, in this exposure apparatus, the g-line of the mercury lamp is used as the light source 1, the collimator 2 collimates the parallel rays, and the fly-eye lens 3 homogenizes the rays, and the image forming position is used as the secondary light source 4. An annular filter is installed here, and after being condensed by the condenser lens 5, it is guided to the resist film surface on the wafer 9 from the mask 6 via the pupil 7 and the projection lens 8.

The mask used here is shown in FIGS.
As shown in (c), the diameter is 0.35 on the silicon oxide substrate.
The light-shielding pattern is made of Cr and has a pitch of 0.7 μm and a pitch of 0.7 μm.

Further, the numerical aperture NA = 0.5 and the coherence factor σ = 0.
3 and, as shown in FIG. 2 (a), an annular filter was used in which the radius r ₂ = 0.9r ₁ was shielded from the center with respect to the diameter r ₁ of the opening. Here, the transmittance of the shielding portion of the filter is 0, and the transmittance of the opening portion (transmission portion) is 1. The exposure wavelength is λ
= 0.248 μm and numerical aperture NA = 0.45. Figure 2
(c) shows the light intensity profile on the wafer when the mask is transferred by this exposure apparatus. Where I
_e represents the light intensity for obtaining a desired pattern size (0.35 μm), and Imin represents the minimum light intensity value.
The contrast defined as below was used as the evaluation amount.

Contrast = (I _e −I _min ) / (I _e + I _min ). FIG. 3 is a result showing the defocus dependence of the contrast in the above mask. Note that black circles are normal σ
= 0.3, the result with a σ stop is shown, and the white circle shows the result with the ring filter. As is clear from this graph, by using the ring filter, it is possible to improve the focus margin with the hole pattern by maintaining the high contrast even when the defocus increases.

Therefore, in addition to the line and space pattern, when a hole pattern is formed by one exposure apparatus, if only the resist process is changed without changing the shape of the light source, focus can be obtained even in the annular exposure. It is possible to improve the margin.

Second Embodiment Next, a second embodiment of the present invention will be described.

Although an example using a Cr mask has been described in the above embodiment, an example using a phase shift mask will be described here.

The phase shift mask used here is formed by forming a semitransparent film pattern.
The phase difference with respect to the light transmitting part is 180 degrees, and the amplitude transmittance is 15%.
As. The pattern was a 0.4 μm hole pattern (pitch 1.6 μm). As the exposure apparatus, a numerical aperture NA = 0.5, the coherence factor sigma = 0.6, annular filter used was shielded radius r ₂ = 0.67r ₁ from the center with respect to the radius r _1.

Here, FIG. 4A shows a case where a normal mask is used as a mask for comparison, and FIG. 4A shows a case where the above phase shift mask is used. Note that the black circles are the above-mentioned normal illumination, and the white circles are the results when the ring filter is used.

Here, in order to compare the above results, the contrast is shown as 1 in each non-defocused state, and is shown as 1 in total. In both FIGS. 4 (a) and 4 (b), an improvement in focus margin can be expected by using a ring filter. 4 (a) and 4 (b), the contrast required for the resolution of the pattern is 0.8, and the combination with the above phase shift mask (halftone mask) is more effective when using the ring filter. It is as large as about 50% (normally about 30% with a Cr mask), and the focus margin is further improved.

This effect can be obtained also when a shifter edge-use type mask which is composed of only a shifter and forms a dark portion at the edge portion of the shifter is used.

It should be noted that the phase shifter layer does not necessarily have to perform a phase shift of 180 degrees, and if it is a degree that sharply lowers the light intensity distribution of the pattern edge in the vicinity of 180 degrees, some 180 degrees ( It may be off (about 30 degrees).

Further, the filters shown in FIGS. 5 (a) to 5 (d) are used.
You may use what is shown in. In the first and second embodiments, the same effect can be obtained not only with the hole pattern but also with the isolated pattern, especially with the isolated pattern. Although not shown here, the phase difference between the exposure light that passes through the portion forming the hole pattern as a mask and the exposure light that passes through the boundary between the patterns is “180 × (2n + 1) ± 30: n =
The same effect as described above can be obtained also in a self-aligned phase shift mask having a negative mask structure that is changed to an "integer". Further, in the first and second embodiments, the annular illumination is used. Although the case where it is used has been described, a similar effect can be obtained by a fourth illumination using a fourth filter which is four-fold symmetrical with respect to the optical axis and has four apertures off the optical axis as shown in FIG. Similarly, a similar effect can be obtained by using a combination of a fourth filter and an annular filter or a fifth filter.

[0038]

As described above, according to the method of the present invention, it is not necessary to replace the light source modulation filter depending on the pattern type in forming the hole pattern.
It prevents the deterioration of the transfer characteristics due to the decrease of the throughput for replacement and the misalignment of the filter, and it is not the optimum illumination condition of the low coherence factor in the positive resist in forming the hole pattern, but the focus margin of the annular illumination exposure It is possible to obtain an improvement, and it is possible to significantly improve the throughput by only slightly changing the exposure sequence.

[Brief description of drawings]

FIG. 1 is a diagram showing an exposure apparatus used in a method according to an embodiment of the present invention.

FIG. 2 is a diagram showing an annular filter, a mask pattern and an image intensity profile on a wafer used in the method of the third embodiment of the present invention.

FIG. 3 is a diagram showing the defocus amount dependency of contrast by the same method.

FIG. 4 is a diagram showing a comparison result of focus margins between the method of the embodiment of the present invention and the case of using normal illumination.

FIG. 5 is a diagram showing a filter used in the same method.

FIG. 6 is a diagram showing a filter used in the same method.

FIG. 7 is a diagram showing a conventional exposure apparatus.

FIG. 8 is a diagram showing the defocus amount dependency of contrast when a contact hole is formed by using the method of the conventional example.

[Explanation of symbols]

 1 Light Source 2 Collimator 3 Fly's Eye Lens 4 Secondary Light Source 5 Condenser Lens 6 Halftone Mask 7 Pupil (Aperture) 8 Projection Lens 9 Wafer 11 Silicon Oxide Substrate 12 Mask Pattern, 100 Exposure Light 104 Aperture 105 Two-dimensional Lighting Engineering System 106 Reticle 107 Aperture 108 Projection system 109 Wafer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03F 7/20 521 9122-2H

Claims (2)

[Claims] 1. A step of applying a negative resist on the surface of a substrate on which a pattern is to be formed, and a step of applying a uniform pattern to an exposure mask on which a mask pattern for forming a hole pattern is formed on a transparent substrate. A light source surface or a position conjugate with the light source surface,
A ring-shaped filter having a dark portion in the center, a filter that is four-fold symmetric with respect to the optical axis and that has high intensity in four regions off the optical axis, or a filter having a composite shape thereof is installed to form a pattern. An exposure step of forming a hole pattern by forming a pattern image of the exposure mask on the surface of the substrate to be formed. 2. A step of applying a negative resist to the surface of a substrate on which a hole pattern is to be formed, exposure light transmitted through a portion on which a hole pattern is to be formed on a transparent substrate, and its peripheral portion or boundary. The phase difference of the exposure light passing through the area is “180 × (2n + 1) ± 3
For an exposure mask provided with a mask pattern for forming a hole pattern, which is made of a semitransparent material or a transparent material satisfying the relationship of 0: n = integer ”, a uniform light source surface or a conjugate surface with the light source surface is provided. position,
A ring-shaped filter having a dark portion in the center, a filter that is four-fold symmetric with respect to the optical axis and that has high intensity in four regions off the optical axis, or a filter having a composite shape thereof is installed to form a pattern. An exposure step of forming a hole pattern by forming a pattern image of the exposure mask on the surface of the substrate to be formed.