JPH0619114A - Formation of fine pattern - Google Patents

Abstract

PURPOSE:To improve resolution and depth of focus by disposing phase shifters on a photomask to be used as an original plate and optically combining a deformed illumination method and a phase shift method. CONSTITUTION:The phase shifters are disposed in a part or the whole of the photomask to be used as the original plate at the time of exposing the photomask with an exposure device using the deformed illumination. The phase shifters preferably consist of a shifter thickness different from the shift thickness to apply the phase shift of 0.5 times the exposure wavelength. For example, the phase shift mask to be used is not the conventional phase shift mask of applying the phase shift of lambda/2 but is the phase shift mask of, for example, lambda/4 The phase shift quantity varies from lambda/2 when this phase shifters are imparted to the mask patterns 2 finer than the optimum line width/inter-line spacing and, therefore, the zero order diffracted light is not completely erased and is suppressed to the extent that the light is weakened. Further, the effect of weakening the intensity of the zero order diffracted light eventually makes up the defect of the low contrast of the projected image possessed by the deformed illumination exposure device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine pattern forming method, and more particularly, to an annular illumination, an oblique illumination, an exposure apparatus used in the manufacture of electronic components such as semiconductor integrated circuit devices, display circuit devices and printed circuit boards. A Levenson-type phase shifter or an auxiliary pattern-type phase shifter is provided on a part or all of a photomask that serves as an original plate when exposing with an exposure apparatus that uses modified illumination such as four-hole illumination, and the modified illumination method and the phase shift method are used. The present invention relates to a fine pattern forming method which is optically combined.

[0002]

2. Description of the Related Art In Japanese Patent Publication No. 62-50811 (Reference 1) and Japanese Patent Application Laid-Open No. 57-62052 (Reference 2), "projection masters for transmissive illumination" have one of adjacent openings. There is disclosed a so-called Levenson-type phase shift mask which realizes an improvement in resolution by providing a phase shift member. In addition, “Deformed illumination was adopted for i-line and doubled depth of focus was demonstrated at 0.35 μm” Nikkei Microdevices, PP
The 28-37, 1992, April issue (Reference 3) discloses the outline of the principle of modified illumination and its effect.

[0003]

As a result of examining the above-mentioned prior art, the present inventor has a problem that the modified illumination method causes a reduction in contrast.

Therefore, it is conceivable to combine the modified illumination method and the phase shift method, but it is described in p26 of Document 3 that "if the Levenson-type phase shift and modified illumination are combined in principle, resolution will not be achieved." As has been done
Traditionally, the combination of Levenson-type phase shift and modified illumination has been counterproductive.

An object of the present invention is to combine the Levenson-type phase shift method and the modified illumination method under predetermined conditions so that the Levenson-type phase shift method is used alone or the modified illumination method is used alone. It is to provide a technique capable of improving the resolution and the depth of focus as compared with the case of using it.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0007]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

That is, when exposure is performed by an exposure apparatus using modified illumination, a phase shifter is provided on a part or all of a photomask which is an original plate, and a modified illumination method and a phase shift method are optically combined. This is a pattern forming method.

The phase shifter of the photomask has a shifter thickness different from the shifter thickness that gives a phase shift of 0.5 times the exposure wavelength. For example, the phase shift mask used in the present invention is not a phase shift mask which gives a conventional phase shift of λ / 2, but a phase shift mask which gives a phase difference of λ / 4, for example.

[0010]

In the modified illumination exposure apparatus described above, there is an optimum line width / line spacing Ro depending on the arrangement method of the illumination system diaphragm.
In a fine pattern close to o, of the diffracted light generated by illuminating the mask, 0th-order diffracted light (center line light),
Only one of the + 1st order diffracted light (right side light) and the −1st order diffracted light (left side light), that is, two diffracted lights are involved in the image formation.

On the other hand, in a Levenson type phase shift mask which gives a phase shift of λ / 2 which is generally used,
Since the phase difference of λ / 2 causes destructive interference between the adjacent openings, the 0th-order diffracted light is completely eliminated. Therefore, conventionally, the combination of the modified illumination and the Levenson-type phase shift resolves the image. It has been said that it will not do.

However, if a phase shifter that gives a phase difference different from λ / 2 is added to a mask pattern finer than Ro, the resolution and the depth of focus can be improved in combination with modified illumination due to the operation described below.

Since the phase shift amount is different from λ / 2, 0
The second-order diffracted light is not completely erased, but can be suppressed to a degree such as "weakening", which enables a combination of a phase shift mask and modified illumination.

Further, the action of "weakening" the intensity of the 0th-order diffracted light compensates for the disadvantage that the modified illumination exposure apparatus originally has a low contrast of a projected image. In the modified illumination exposure apparatus, as described above, since only the 0th-order diffracted light and either the + 1st-order diffracted light or the -1st-order diffracted light are involved in the image formation, either the -1st-order diffracted light or the + 1st-order diffracted light forms an image. Do not get involved in. Therefore, it is relatively 0
This is because the intensity of the second-order diffracted light is increased, the intensity of the ± first-order diffracted light is decreased, and the contrast is low.

When a mask pattern finer than Ro is exposed, the opening angle between the 0th order / ± 1st order diffracted light increases, and
There is a possibility that the first-order diffracted light does not fall within the projection lens pupil, but in a Levenson-type phase shift mask that gives a phase shift to adjacent apertures on the mask, the opening angle is made smaller than when no phase shift is used. Because of the effect, even in a pattern finer than Ro, the combination of the modified illumination exposure device and the phase shift mask can improve the resolution and the depth of focus.

As described above, the phase shift mask different from λ / 2 has the effect of "weakening" the 0th-order light, which compensates the weaknesses of the modified illumination light source exposure apparatus even for patterns of Ro or higher. Have.

[0017]

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

FIG. 1 is a principle explanatory view for explaining an embodiment of a fine pattern forming method of the present invention, and FIG. 2 is a principle explanatory view for explaining a fine pattern forming method by an oblique illumination method. Is. In addition, in FIG. 1 and FIG.
Is a reticle substrate (glass substrate), and 2 is a light shielding film (Cr pattern).

In FIG. 2, θ ₀ is the oblique illumination tilt angle = 0
Next light direction, θ ₁ is inclination angle of first order diffracted light, p is pattern pitch (line width + line spacing), d ₀ is optical path difference caused by oblique illumination, and d ₁ is because first order diffracted light is generated in θ ₁ direction. This is the required optical path difference.

D ₀ = psin θ ₀ , d ₁ = psin θ ₁ , d ₁ + d ₂
= Λ, in order to optimize at Ro = 0.35 μm, θ ₀
= Θ ₁ , p = 0.35 × 2 × 5 (μm), sin θ
₀ = λ / 2p = λ / 7, and the wavelength of the irradiation light λ = 0.36
If 5 (μm) is used, θ ₀ = sin ~ ¹ (0.35 / 7) ≈3
It becomes ゜.

By setting θ ₀ = θ ₁ in FIG. 2, even if the wafer is vertically displaced on the side on which the image of the reticle, which is an object, is projected, that is, the focal position is displaced. Even if occurs, an optical path difference does not occur between the two light fluxes (0th order and + 1st order diffracted light or −1st order diffracted light) involved in image formation, and it is possible to obtain a large depth of focus.

In the fine pattern forming method of this embodiment, an Hg lamp i-line ⅕ reduction projection exposure apparatus was used, and the optimum width of the modified illumination / line interval Ro = 0.35 μm. Moreover, the illumination inclined about 3 degrees was used.

An example of a Levenson type phase shift which gives a phase shift different from λ / 2 to a line width / line spacing of 0.25 μm using the above-mentioned oblique illumination system will be described.

This is because if the modified illumination exposure apparatus optimized for 0.35 μm is for 64 M [bit] DRAM,
A 64 M [bit] DRAM exposure apparatus and a phase shift mask are combined to exemplify a 256 M [bit] DRAM class fine pattern forming method.

In order to obtain the maximum depth of focus with a line width / line spacing pattern of 0.25 μm, the method of forming a fine pattern of the present embodiment uses the oblique illumination having the inclination of 3 ° as shown in FIG.
As shown in, d ₀ '= p'sin θ ₀ , d ₁ ' = S + p'sin θ ₀
And the optical path difference given by the phase shifter is S
And

Using d ₁ '+ d ₂ ' = λ, S = λ-2
It becomes p'sin θ ₀ . In addition, λ = 0.365 μm, p ′ =
0.25 μm × 2 × 5 = 2.5 μm, sin θ ₀ = λ / 2p =
Substituting λ / 7 and obtaining S / λ,

[0027]

## EQU1 ## S / λ = 1-2p'sin θ ₀ /λ=1-2×2.5×0.36/7/0.365≈0.2857, and a phase shifter that gives a phase shift of 0.2857 times the exposure wavelength λ is 0.2. It may be applied to a 25 μm pattern.

In this embodiment, in order to arrange the numbers and simplify the calculation, a shifter which gives a phase shift of 0.25 times λ is used. As a result, the angle of the first-order diffracted light slightly expands, but does not deviate from the projection optical system pupil.

The function of "weakening" the 0th order light by the λ / 4 shifter will be described below.

When the relative intensity of the 0th-order light when a normal mask is used (when a phase shift mask is not used) is simplified and calculated,

[0031]

[Equation 2] Becomes

On the other hand, in the case of the λ / 4 shifter,

[0033]

[Equation 3] Therefore, the introduction of the λ / 4 shifter can reduce the 0th-order light intensity by half.

This is because not only a fine pattern of Ro or less is required for a modified illumination exposure apparatus which originally has only one of 0th-order light and ± 1st-order diffracted light for forming an image and originally has a low contrast of a projected image. It also has a great effect on improving the contrast of a large pattern.

As described above, in the present embodiment, the combination of the phase shift mask different from λ / 2 and the modified illumination exposure apparatus is described only for the pattern finer than Ro. However, the effect of "weakening" the 0th order light is expected, The phase shifter may be applied to patterns of Ro or higher.

In the above embodiments, i-line exposure (exposure wavelength 0.365 μm) was used for explanation, but it goes without saying that the same concept can be applied to an exposure apparatus using a light source such as g-line or excimer laser. Yes. Further, although the Levenson type phase shifter has been taken as an example, it goes without saying that the invention can also be applied to an auxiliary pattern system in which a shifter is provided on one side of openings adjacent to each other on a mask.

The method of manufacturing the phase shift reticle used in the present invention will be briefly described below.
As a typical example of the shifter thickness different from the shifter thickness that gives a phase shift of 2 times, the shifter thickness that gives a phase shift of 1/4 times the exposure wavelength is used.

In this embodiment, S is used as the shifter material.
OG (S pin O n G lass ) or a glass substrate. The refractive index for both i lines is n≈1.45, and the refractive index of the exposure atmosphere, air, is n ₀ = 1.0, and λ / 4 = t
(n−n ₀ ), and the shifter thickness t was set to about 0.20 μm.

FIG. 3 is a sectional view of a phase shift reticle in the phase shift reticle manufacturing process when the shifter material of this embodiment is SOG. In FIG. 3, 1 is a glass substrate, 2 is a Cr pattern of a light shielding film, 3 is a shifter made of SOG, and 4 is an EB resist.

On the Cr pattern 2 shown in FIG. 3 (a), as shown in FIG. 3 (b), a shifter 3 made of SOG of about 0.
After 20 μm spin coating, baking is performed, EB resist 4 is applied thereon, and as shown in FIG. 3C, a resist pattern for a phase shifter is formed by EB drawing and development, and an exposure wavelength is set by etching / resist removal. The reticle that gives a phase shift of 1/4 times that of the above is completed (FIG. 3 (d)).

FIG. 4 is a sectional view of a phase shift reticle in the phase shift reticle manufacturing process when the glass substrate of this embodiment is made of a shifter material. In FIG. 4, 1 is a glass substrate, 2 is a Cr pattern of a light shielding film, 5 is a resist for Cr patterning, and 6 is a resist for shifter patterning.

A resist pattern 6 for phase shift is formed by further applying a resist, drawing and developing on the pattern in which the resist after the Cr pattern etching shown in FIG. 4A is not removed (FIG. 4). (b)). After this,
By etching the glass substrate 1 by 0.2 μm and removing the resist, a phase shift reticle having the cross section shown in FIG. 4C can be obtained.

In this embodiment, although not shown, a thin film such as a silicon nitride film (Si ₃ N ₄ ) is provided as an etching stopper layer on the glass substrate 1, and SOG coating, baking and etching are performed thereon. After that, the manufacturing process shown in FIG. 4 may be taken.

In this embodiment, the phase shifter used for the 0.25 μmL / S pattern has been described. However, when a pattern of 0.25 μm and a larger pattern are mixed in one reticle, the phase shifter is 0.2. The above shifter may be used only for a pattern of 25 μm, and in the expectation of a 0th-order light amount reduction effect, λ can be applied to a pattern larger than 0.25 μm.
A shifter that gives a phase shift different from / 2 may be used.

As described above, the invention made by the present inventor is
Although the specific description has been given based on the above-described embodiments, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the invention.

[0046]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

Due to the effect of weakening the 0th-order light, it is possible to prevent a reduction in contrast when a modified illumination exposure apparatus is used.

By introducing a phase shift mask different from the λ / 2 phase shift in the resolution capability and the depth of focus of the modified illumination exposure apparatus, it is possible to significantly extend to a fine pattern, and the same apparatus achieves high integration and economy. It is possible to improve the property.

[Brief description of drawings]

FIG. 1 is a principle explanatory view for explaining an embodiment of a fine pattern forming method of the present invention,

FIG. 2 is a principle explanatory view for explaining a fine pattern forming method by an oblique illumination method according to the present invention,

FIG. 3 is a sectional view of a phase shift reticle in a phase shift reticle manufacturing process when the shifter material of the present embodiment is SOG.

FIG. 4 is a sectional view of a phase shift reticle in a phase shift reticle manufacturing process when the glass substrate of this embodiment is a shifter material.

[Explanation of symbols]

1 ... Glass substrate, 2 ... Cr pattern, 3 ... Shifter, 4 ...
EB resist, 5 ... Cr patterning resist, 6
… Shifter patterning resist.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuichi Soda 2-6-2, Otemachi, Chiyoda-ku, Tokyo Hirtitsu Electronics Engineering Co., Ltd.

Claims (2)

[Claims] 1. A phase shifter is provided in a part or all of a photomask which is an original plate when exposed by an exposure apparatus using modified illumination, and the modified illumination method and the phase shift method are optically combined. A characteristic fine pattern forming method. 2. The method for forming a fine pattern, wherein the phase shifter of the photomask has a shifter thickness different from a shifter thickness that gives a phase shift of 0.5 times an exposure wavelength.