JPH08203801A - Projection aligner - Google Patents

Abstract

PURPOSE: To achieve an optimum illumination condition corresponding any pattern cycle. CONSTITUTION: In a projection aligner having a light source 1, an illuminating optical system 2 for focusing the light emitted from the light source on a reticle 5, a projecting optical system 6 for projecting the pattern of the reticle on a substrate 7, the illuminating optical system has a first illuminating optical system 21 and a second illuminating optical system 22, and the first illuminating optical system 21 focuses the light emitted from the light source on an auxiliary mask 3, and the second illuminating optical system 22 is disposed at the position making the auxiliary mask and the reticle 5 conjugate. An element of incoherent 4, for screening the 0th order diffraction light, is disposed at the center part of the second illuminating optical system, and the pattern of the auxiliary mask has a period twice that of a pattern of a reticle image formed by the second illuminating optical system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus for projecting and exposing a circuit pattern on a substrate to manufacture semiconductors, liquid crystal display devices and the like.

[0002]

2. Description of the Related Art Conventionally, there is a modified illumination method (so-called SHRINC method) shown in FIG. 4 as a method for improving the resolution and depth of focus of a projection optical system of a projection exposure apparatus. A brief description will be given with reference to FIG. First, the light α emitted from the light source 1 is transmitted through the transmissive plate 8 having a transmissive portion in the peripheral portion.

The light α enters the illumination optical system 2, and the illumination optical system 2 forms an angle θ with the optical axis of the reticle 5.
Incident on. At this time, since the 0th-order diffracted light β emitted from the reticle 5 is incident on the peripheral portion of the projection optical system 6, the 1st-order diffracted light γ is incident on the peripheral portion on the opposite side of the projection optical system 6. When the first-order diffracted light γ enters the projection optical system 6, it becomes possible to form a fine pattern. At this time, the angle θ formed by the optical axis is determined so that the pattern period C on the reticle 5 has a relationship of sin θ = λ / 2P (1) with the direction cosine sin θ of the illumination light α.
Here, λ is a wavelength used for projection exposure.

Under such a condition, the 0th-order diffracted light β and the 1st-order diffracted light γ emitted from the reticle 5 form symmetric angles with respect to the optical axis. Here, the exit angle of the 0th-order diffracted light β and the exit angle of the 1st-order diffracted light γ are both θ. By doing so, since the 0th-order diffracted light β and the 1st-order diffracted light γ form a symmetrical angle on the wafer 7, not only a fine image is formed on the wafer 7, but also the depth of focus becomes deep.

[0005]

However, in the conventional method as described above, all pattern periods P on the reticle 5 are
There was a drawback that it was not optimal for.
For example, when the pattern period P on the reticle 5 is changed by the optical system shown in FIG. 4, the 0th-order diffracted light β is emitted from the reticle 5 while keeping the angle θ as it is, but the 1st-order diffracted light γ is the diffraction of the reticle 5. Under the influence, the reticle 5 is ejected at an angle different from the angle θ. If the angle of the 0th-order diffracted light β and the angle of the 1st-order diffracted light γ emitted from the reticle 5 are different, the position of the image due to the illumination from the different transmissive portions on the transmissive plate 8 shifts with respect to the focus shift, and thus the wafer
There is a problem that the depth of focus becomes shallower and the contrast of an image formed on the wafer 7 becomes lower.

The present invention has been made in view of such conventional problems, and an object thereof is to provide an optimum illumination condition corresponding to any pattern period.

[0007]

In order to solve the above problems, in the present invention, a light source, an illumination optical system for condensing light emitted from the light source onto a reticle, and a pattern of the reticle are provided on a substrate. In a projection exposure apparatus having a projection optical system for projecting onto the above, the illumination optical system has a first illumination optical system and a second illumination optical system, and the first illumination optical system outputs the light emitted from the light source. The second illumination optical system is arranged at a position where the auxiliary mask and the reticle are conjugate with each other, and the light is condensed on the auxiliary mask.
An incoherence element provided with a light shielding portion for shielding the second-order diffracted light is arranged, and the pattern of the auxiliary mask is the pattern of the image of the reticle by the second illumination optical system.
Provided is a projection exposure apparatus having a double cycle.

[0008]

The operation will be described below with reference to FIG. 1 showing an embodiment. The light of the light source 1 is condensed on the auxiliary mask 3 by the first illumination optical system 21 of the illumination optical system 2. At this time, since the auxiliary mask 3 has the same effect as that of the diffraction grating,
The 0th-order diffracted light and the ± 1st-order diffracted lights are generated. Then these 0
The second-order diffracted light and the ± first-order diffracted lights enter the second illumination optical system 22 of the illumination optical system 2.

The 0th-order diffracted light and the ± 1st-order diffracted lights that have entered the second illumination optical system 22 are provided in the second illumination optical system 22 with a light-shielding portion for shielding the 0th-order diffracted light in the central portion. And reaches the incoherence element 4. The incoherence element 4 has a function of blocking the 0th-order diffracted light and transmitting the ± 1st-order diffracted light by the light-shielding portion at the center. At this time, the incoherent element 4 is
There is a function of causing an optical path length difference between the first-order diffracted light and the -1st-order diffracted light. Since the optical path length difference generated at this time is made larger than the coherence length, the + 1st order diffracted light and the −1st order diffracted light do not interfere on the reticle 5.

± 1 transmitted through the incoherent element 4
The secondary diffracted light is emitted from the second illumination optical system 22 and focused on the reticle 5. At this time, the auxiliary mask 3 and the reticle 5 have a conjugate positional relationship. Here, if the + 1st-order diffracted light and the -1st-order diffracted light focused on the reticle 5 are coherent, an interference fringe is generated on the reticle 5. In this case, part of the pattern of the reticle 5 is not illuminated by the dark portion of the interference fringes, and as a result, the correct pattern is not projected on the wafer 7. However, in the present invention, the + 1st-order diffracted light and −1 which are focused on the reticle 5 by the incoherence element.
Since an optical path length difference larger than the coherence length is provided for the next-order diffracted light, interference fringes do not occur.

By the way, the incoherence element 4 is
A light-shielding portion for shielding 0th-order diffracted light is provided in the central portion. The size of the light-shielding portion may always remain constant, and it is not necessary to replace the reticle 5 at the same time. This is because the 0th-order diffracted light refers to light that has passed through without being affected by diffraction. Therefore,
As long as the size of the light source 1 or the first illumination optical system 21 does not change, the size of the 0th-order diffracted light that reaches the light shielding part at the center of the incoherent element 4 does not change.

Further, in the present invention, the cycle of the pattern of the auxiliary mask 3 is twice as long as the cycle of the image pattern of the second illumination optical system of the reticle 5. Looking at the optical system from the opposite side, it can be said that the image of the reticle 5 is formed on the auxiliary mask 2. Here, considering the light in the original illumination direction, the angle formed by the 0th-order diffracted light newly generated by the reticle 5 and the optical axis and the angle formed by the 1st-order diffracted light newly generated by the reticle 5 and the optical axis are , And both are θ, optimum illumination can be obtained. The angle formed by the new 0th-order diffracted light and the 1st-order diffracted light is 2θ. That is, the second illumination optical system 22
Therefore, if the angle between the first-order diffracted light incident on the reticle 5 and the optical axis is θ, it can be said that the illumination is optimum. Since the pattern cycle of the auxiliary mask 3 is twice the cycle of the image on the pattern of the auxiliary mask 3 of the reticle 5, this condition is satisfied.

Furthermore, since the reticle 5 and the auxiliary mask 3 are in a conjugate positional relationship, there is a pair between the angle of the first-order diffracted light condensed on the reticle 5 and the angle of the light flux of the first-order diffracted light emitted from the auxiliary mask 3. Since there is one relationship, the lighting is optimal at all locations on the reticle 5. As described above, when the auxiliary mask 3 having a period twice that of the projected image of the second illumination optical system of the reticle 5 is used, it is possible to satisfy the formula (1).

[0014]

EXAMPLE A first example will be described below with reference to FIG. FIG. 1 is a diagram showing an embodiment of the present invention. The light emitted from the light source 1 illuminates the auxiliary mask 3 by the first illumination optical system 21 of the illumination optical system 2. Here, a mercury lamp, a krypton fluoride laser, an argon fluoride laser, or the like can be considered as the light source. The auxiliary mask 3 generates 0th-order diffracted light and ± 1st-order diffracted light. These diffracted lights are collimated by the first optical group 221 of the second illumination optical system 22 of the illumination optical system 2. The 0th-order diffracted light and the ± 1st-order diffracted lights that have become parallel light reach the incoherence element 4. The 0th-order diffracted light is blocked by the incoherence element 4, and the ± 1st-order diffracted light is transmitted through the incoherence element 4. The ± first-order diffracted light that has passed through the incoherence element 4 is condensed on the reticle 5 by the second optical group 222 of the second illumination optical system 22. The ± first-order diffracted light focused on the reticle 5 causes the reticle 5 to generate new zero-order diffracted light and new first-order diffracted light. The new 0th-order diffracted light and the 1st-order diffracted light are imaged on the wafer 7 by the projection optical system 6.

In this embodiment, the light source 1, the incoherence element 4 and the entrance pupil of the projection optical system 6 are in a conjugate positional relationship, and the auxiliary mask 2, the reticle 5 and the wafer 7 are conjugated. It is in a positional relationship. In the present embodiment, the magnification of the second illumination optical system 22 of the illumination optical system 2 is set to 1x. As a result, when the pattern of the reticle 5 is as shown in FIG. 2A and the openings 52 and the light shielding portions 51 are arranged at the same interval with the period P, the period of the auxiliary mask 3 is as shown in FIG. The pattern of the auxiliary mask 3 as shown in b) is used, in which the openings 32 and the light shields 31 have the same interval and the pattern period 2P. By doing so, the direction cosine diffracted by the auxiliary mask 3 is sin θ.
Is sin θ = λ / 2P and the magnification of the second illumination optical system 22 is 1 ×, so that the reticle 5 is optimally illuminated.

Here, the size of the area in which the pattern of the auxiliary mask 2 is drawn is the same as the size of the area in which the pattern of the reticle 5 is drawn, and the edge portion of the reticle 5 is affected by diffraction. It may be expected that the illuminance of the illumination light is different from the central part. In such a case, as shown in FIG. 2, it is effective to make the size of the area where the pattern of the auxiliary mask 2 is drawn a little larger than the size of the area where the pattern of the reticle 5 is drawn. But,
Auxiliary mask 2 if uneven illumination distribution of illumination light does not occur
The size of the area in which the pattern is drawn and the size of the area in which the pattern of the reticle 5 is drawn may be the same.

Further, the incoherent element 4 used in this embodiment has the structure shown in FIG. Here, FIG. 3A is a sectional view of the incoherent element 4.
FIG. 3B is a front view of the incoherent element 4. The entire incoherence element 4 is made of a transmissive member having a refractive index n, and a region where 0th-order diffracted light reaches around the position where the optical axis passes is provided with a light shielding member 42. Further, the transmission region 41 is divided into two parts so that the ± 1st-order diffracted light reaches a region symmetrical about the optical axis. FIG.
As shown in (a), the transmissive member is thicker in one of the bisected transmissive regions 41 than in the other of the transmissive regions 41. It should be noted that the shape is not limited to the shape shown in FIG. 3 and may be symmetric so that the ± first-order diffracted lights become incoherent.

Then, in this embodiment, as shown in FIG. 3A, the difference in thickness in the direction along the optical axis between one of the transmissive regions 41 and the other of the transmissive regions 41 is d. When, the following conditions are satisfied. L = (n−1) d> L _c Here, L is the optical path length difference, and L _c is the coherence length. As described above, in the present embodiment, by using the incoherent element having such a structure, interference fringes do not occur even if the ± first-order diffracted light is condensed on the reticle 5.

In the present embodiment, the diffracted light incident on the incoherent element 4 is parallel light, but if the above-mentioned conjugate relationship is satisfied, it need not be parallel light. Then, if the auxiliary masks 3 having different pattern shapes are prepared in accordance with the corresponding patterns on the reticle 5, optimum illumination can be obtained at all positions on the reticle.
Further, for low frequency patterns, it is effective to make the pitch of the auxiliary mask pattern fine so that the 0th-order diffracted light is not cut by the light shielding portion of the incoherent element 4.

Further, as the auxiliary mask 3, strictly speaking, the one having a cycle twice as long as the projected image of the second illumination optical system of the reticle 5 is not used, but the one having a cycle almost twice may be used. Absent.

[0021]

As described above, according to the present invention, the illumination light can be optimized by exchanging the auxiliary mask in accordance with the cycle of the reticle pattern, and as a result, a deep depth of focus can be achieved. It is possible to obtain a high contrast image.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a conceptual diagram of a reticle and an auxiliary mask.

FIG. 3 is a diagram showing an incoherent element.

FIG. 4 is a diagram showing a conventional modified illumination method.

[Brief description of reference numerals]

 1 ... Light source 2 ... Illumination optical system 3 ... Auxiliary mask 4 ... Incoherent element 5 ... Reticle 6 ... ... Projection optical system 7 ... Wafer 21 ... First illumination optical system 22 ... Second illumination optical system

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G03F 7/20 521

Claims (1)

[Claims] 1. A projection exposure apparatus comprising a light source, an illumination optical system for condensing light emitted from the light source onto a reticle, and a projection optical system for projecting the pattern of the reticle onto a substrate. The illumination optical system includes a first illumination optical system and a second illumination optical system.
An illumination optical system, the first illumination optical system focuses the light emitted from the light source onto an auxiliary mask, and the second illumination optical system is located at a position where the auxiliary mask and the reticle are conjugated. And an incoherent element having a light-shielding portion for shielding 0th-order diffracted light in the central portion of the second illumination optical system, wherein the pattern of the auxiliary mask is the second
A projection exposure apparatus having a cycle twice as long as the pattern of the image of the reticle by an illumination optical system.