JP3087353B2 - Photomask and exposure method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask (also referred to as a reticle) used as a projection original in a lithography process for manufacturing a semiconductor device, and an exposure method using the same.

[0002]

2. Description of the Related Art In a lithography process for manufacturing a semiconductor device, a photomask used as a projection original generally has a structure in which a light-shielding pattern made of a metal such as chromium is formed on a transparent substrate. A desired circuit pattern is transferred to the wafer surface by transmitting and illuminating the photomask and forming an image of the light shielding pattern on the wafer surface by the projection optical system.

FIG. 3A shows a light transmitting portion (substrate bare surface portion) 10.
2 schematically shows a planar structure of a conventional photomask on which a line-and-space pattern in which light-shielding portions 2 and light-shielding portions (hatched portions are shaded in the figure) 101 are alternately repeated is shown. The transmittance is as shown in FIG. As shown in the figure, the amplitude transmittance is low (= 0) in the light-shielding portion 101 of the line and space pattern,
A pair of light-shielding portions 10 adjacent to each other,
1 and the light transmission portion 102 are the basic period P of the pattern of FIG.
Becomes

In recent years, in order to enhance the contrast of a projected image, various phase shift masks provided with a phase shift section for changing the phase of transmitted light at a specific portion of the light transmitting section have been proposed. For example, Japanese Patent Publication No. 62-50811 discloses a technique related to a spatial frequency modulation type phase shift mask.

FIG. 4A schematically shows a plane structure of a phase shift mask of a spatial period modulation type. A phase member is added to every other light transmitting portion 102b of the line and space pattern. The phase of the light transmitted through the adjacent light transmitting portions 102a and 102b via the light shielding portion 101 is shifted by π. FIG. 4 shows the amplitude transmittance of this phase shift mask.
This is shown in (b). As shown in the figure, since the amplitude of the light transmitted through the light transmitting portion 102b to which the phase member is added and the amplitude of the light transmitted through the light transmitting portion 102a to which the phase member is not added are inverted, the light transmitting portion 102a (without the phase member) ) -Shading part 101
-Light transmitting portion 102 (having a phase member)-The light shielding portion is the basic period P of the pattern.

[0006]

However, the conventional techniques as described above have a problem that they cannot cope with the miniaturization of circuit patterns accompanying the recent high integration of semiconductor elements. That is, although it has been recognized that the use of the above-described phase shift mask improves the imaging performance to some extent, the resolving power capable of resolving the required fine pattern has not yet been secured.

The present invention has been made in view of the above points, and provides a photomask and an exposure method that can obtain higher resolution by using third information other than the amplitude and phase of light. It is intended for.

[0008]

In order to achieve the above object, a photomask according to the present invention is a photomask in which a pattern to be projected and transferred is formed on a transparent substrate. At least two types of polarizing members that convert into respective polarization states orthogonal to each other are repeatedly formed, and the two types of polarizing members are configured to transmit light polarized in a direction inclined with respect to a side of the pattern. Is what is done. In this case, it is preferable that the two types of polarizing members are configured to transmit light polarized in a direction inclined at 45 degrees to the sides of the pattern. Further, a configuration may be adopted in which a phase member for changing the phase of the transmitted light is arranged in a part of the light transmitting section provided with the polarizing member. Further, in another photomask of the present invention, in a photomask in which a pattern to be projected and transferred is formed on a substrate, at least two types of polarized light that are converted into mutually orthogonal polarization states are provided on a light reflecting portion of the substrate. A member is provided. In this case, it is preferable that the two kinds of polarizing members are configured to convert light polarized in a direction inclined with respect to a side of the pattern. It is more preferable to convert to light polarized in a direction inclined at 45 degrees to the side of. The exposure method of the present invention includes a step of illuminating the photomask and a step of forming an image of a pattern of the photomask on a wafer surface by a projection optical system.

Specifically, the at least two kinds of polarizing members used in the present invention are members that generate the following 1 to 3 polarized light, and the generated polarized light in any of the cases 1 to 3 is orthogonal to each other. Each polarization state. 1. Two linearly polarized lights whose vibration directions (the vibration direction referred to in the present specification are the vibration directions of the electric vector unless otherwise specified) are orthogonal to each other. 2. Right-handed circularly polarized light and left-handed circularly polarized light. 3. The direction of the long axis is orthogonal and the rotation direction is opposite 2
Elliptically polarized light.

[0010]

In a generally used exposure apparatus, when a photomask is transmitted and illuminated, diffracted light corresponding to a pattern formed on a photomask is generated, and the generated diffracted light is again projected onto an image plane by a projection optical system. Collected on top to form an image of the pattern. At this time, the higher the order of the diffracted light is taken into the projection optical system, the better the fidelity of the obtained image to the original drawing. Therefore, if the diffraction angle is small,
A pattern can be resolved even with an exposure apparatus having a small numerical aperture (NA). In other words, if an exposure apparatus having the same numerical aperture (NA) is used, a finer pattern can be resolved with a photomask having a smaller diffraction angle.

By the way, as is well known in the field of wave optics, assuming that the basic period of a pattern is P, the diffraction angle θ is Psin θ = nλ (n = 0, ± 1, ± 2,...) (1) Get out in the direction to meet. Here, λ represents the wavelength, and n represents the order of the diffracted light.

As is easily understood from equation (1), the diffraction angle θ decreases as the period P increases. 3 and 4 described above.
Is compared, the basic period P of the line-and-space pattern in the phase shift mask (FIG. 4) is twice as large as the basic period P of the conventional photomask without the phase member (FIG. 3). ing. For this reason, the diffraction angle of the diffracted light generated by the phase shift mask of FIG. 4 is smaller than that of the photomask of FIG. 3, and higher order diffracted light is taken into the projection optical system. This is one of the main reasons that the imaging performance is improved by using the phase shift mask.

Here, if the numerical aperture of the exposure apparatus is very large, it is possible to capture even a diffracted light beam having a large diffraction angle. However, the numerical aperture of the exposure apparatus cannot be increased arbitrarily. Is set in consideration of the overall imaging performance including the depth of focus of the exposure apparatus, and there is a limit in extending the resolution limit on the exposure apparatus side. If the period P becomes smaller than a certain value due to the progress of pattern miniaturization, even ± 1st-order diffracted light will not reach the image plane, making it impossible to resolve.

Therefore, in the present invention, the pattern period P
The resolution is improved by enlarging.
Hereinafter, the operation of the present invention will be specifically described with reference to an example in which the present invention is applied to the line and space pattern of FIG. 3 (see FIG. 1). In FIG. 1, a polarizing member that transmits light that vibrates in directions perpendicular to each other is added to the light transmitting portions 2a and 2b adjacent to each other via the light shielding portion 1. Arrows in the figure indicate the vibration directions of light that can pass through the light transmitting portions 2a and 2b, and here, two orthogonal polarization states are referred to as A and B, respectively.

In general, light can be represented by the sum of two orthogonal polarization states, so that the polarizations A and B are considered independently. First, focusing on the polarized light A, the light transmitting portion 2a can pass through as it is, but cannot transmit the light transmitting portion 2b, and the light transmitting portion 2b becomes a light non-transmitting portion for the polarized light A. Therefore, the amplitude transmittance of the pattern of FIG. 1A observed with the polarized light A is in the state indicated by A in FIG. 1B, and the transmittance is increased only in every other light transmitting portion 2a.

Similarly, considering the polarized light B, the light transmitting portion 2b can transmit light, but the light transmitting portion 2a becomes a light non-transmitting portion for the polarized light B. That is, the portion that can be transmitted through the polarized light A is reversed, and the amplitude transmittance of the pattern observed with the polarized light B is in the state indicated by B in FIG.

From these facts, two orthogonally polarized lights A, B
1 are separated from each other and pass through the photomask. The basic period P of the pattern in FIG. 1 is a light transmitting portion 2b (a light non-transmitting portion of polarized light A) -a light shielding portion 1-a light transmitting portion 2a (a light non-transmitting portion of polarized light B). -The light-shielding portion 1 and the basic period P of the pattern is twice as large as that in the case where the light in the average state of the polarized light A and the polarized light B passes through the conventional photomask (the case of FIG. 3 described above). I understand. This means that even if an exposure apparatus having the same numerical aperture is used, a higher resolution can be obtained by using the photomask of FIG. 1 to which a polarizing member through which two orthogonally polarized lights A and B are respectively transmitted is added. Is shown.

The present invention can also be applied to a phase shift mask, and it is possible to further increase the pattern period by combining a polarizing member and a phase member and adding them to a light transmitting portion (details will be described later). .

[0019]

【Example】

Embodiment 1 A first embodiment of the present invention will be described with reference to FIG. In the figure, light shielding portions 1 made of chrome or the like are arranged at a predetermined pitch on a substrate transparent to exposure light, and a line and space pattern is formed. Two straight lines whose vibration directions are orthogonal to each other and whose vibration directions are inclined at 45 degrees with respect to the sides of the pattern (the reason will be described later) are provided on the light transmitting parts 2a and 2b adjacent to each other via the light shielding part 1. Polarizing members for transmitting the polarized lights A and B are provided. The polarizing member may be provided on the light-shielding pattern forming surface side, or may be provided on the side opposite to the light-shielding pattern.

In this photomask, the light transmitting portion 2b becomes a light non-transmitting portion for the polarized light A, the light transmitting portion 2a becomes a light non-transmitting portion for the polarized light B, and the amplitude transmission of the polarized light of A and B respectively. The rate is as shown in Fig. 1 (b). That is,
The basic period P of the pattern in this embodiment is twice as large as that in the case where the polarizing member is not added, and the diffraction angle of the transmitted light is reduced by that amount, as described in the section of the operation. As a result, even if the same exposure apparatus is used, the resolution is improved as compared with the conventional photomask.

Now, the reason why the oscillation directions of the polarized light A and the polarized light B in the present embodiment are inclined at 45 degrees with respect to the sides of the pattern will be described. For linearly polarized light, TE (tr
ansverse electric) polarization state and TM (transverse magnetic) polarization state in which the vibration direction of the magnetic vector is perpendicular to the plane of incidence, that is, the vibration direction of the electric vector is in the plane of incidence. TE polarization and T
It is in the average state of M polarized light. For example, a polarizing member that transmits only TE polarized light (an electric vector vibrates in a direction parallel to the pattern of FIG. 1A) is provided in the light transmitting portion 2a, and TM polarized light (FIG. 1A) is provided in the light transmitting portion 2b. If a polarizing member that transmits only the electric vector vibrates in the pattern arrangement direction is provided, the following problem occurs.

That is, when the photomask is illuminated by transmission,
Diffracted light of each order is generated from the photomask, and light having different diffraction orders reaches the imaging plane through different optical paths in the incident surface. The direction of vibration of the vehicle is always aligned with the direction perpendicular to the plane of incidence, and the interference effect between diffracted light beams is maximized. On the other hand, in the case of TM polarized light, the direction of oscillation of the electric vector of the diffracted light of a different order is shifted in accordance with the difference in the diffraction angle, and the interference effect of the diffracted light is reduced.

Therefore, on the image plane, the light intensity of the portion corresponding to the light transmitting portion 2a through which the TE polarized light is transmitted is large, and the light intensity of the portion corresponding to the light transmitting portion 2b through which the TM polarized light is transmitted is low. That is, the brightness of the bright portion differs in a series of line and space patterns. In the present embodiment, in order to avoid such a difference in brightness, the vibration direction of light transmitted through the light transmitting portions 2a and 2b is inclined by 45 degrees with respect to the sides of the pattern, and In the bright part, an intermediate light intensity between the case of the TE polarized light and the case of the TM polarized light is obtained. In the case where the light intensity of the bright part of the pattern image does not need to be uniform, it goes without saying that the vibration direction itself is not particularly limited as long as the vibration directions of the polarized lights A and B are orthogonal to each other.

Further, in the example of FIG. 1, only two types of polarizing members for providing the orthogonal polarized lights A and B are used, but three or more types of polarizing members may be used for the photomask of the present invention. It is a matter of course that three or more types of polarizing members may be used in a series of patterns, not to mention using a polarizing member suitable for each pattern at a place where the arrangement direction of the patterns is different.

Embodiment 2 Next, an embodiment in which the present invention is combined with a phase shift mask will be described with reference to FIG. In FIG. 2A, a light-shielding portion 1 made of chrome or the like is arranged at a predetermined pitch on a transparent substrate to form a line-and-space pattern. 2
At d, polarizing members are provided, each transmitting two linearly polarized lights A and B whose vibration directions are orthogonal to each other and whose vibration directions are inclined at 45 degrees to the sides of the pattern. In the present embodiment, two light transmitting portions 2c and 2d adjacent to each other via the light shielding portion 1 and to which a polarizing member for transmitting two orthogonally polarized light beams A and B are added are set as one set. , A phase member for changing the phase of transmitted light by π is added.

The amplitude transmittance of the photomask having such a structure is as shown in FIG. 2 (b). First, polarization A
The light transmitting portion 2c can pass through only the light transmitting portion 2c, the light transmitting portion 2d becomes a light opaque portion for the polarized light A, and the amplitude of the closest light transmitting portion 2c among the light transmitting portions 2c to which the same polarizing member is added is inverted. Will be. As for the polarized light B, the light transmitting portion 2c through which the polarized light A can be transmitted becomes the light non-transmitting portion, and the amplitude of the closest light transmitting portion 2d is inverted as in the case of the polarized light A.

Therefore, the basic period P of the pattern in FIG. 2 is the light transmitting portion 2d (without the phase member), the light shielding portion 1-the light transmitting portion 2c (with the phase member), the light shielding portion 1 and the light transmitting portion 2d.
(With phase member) -light-shielding portion 1-light transmitting portion 2c (without phase member) -light-shielding portion 1, and the basic period P of the pattern is four times that of the conventional example of FIG. Therefore, if the photomask of FIG. 2 is used, even if the same exposure apparatus is used, FIG.
It is possible to resolve a much finer pattern than the photomask described above.

Here, it is needless to say that the method of combining the phase member and the polarizing member is not limited to the example shown in FIG. 2, but light beams having orthogonal vibration directions do not interfere with each other. It is desirable to dispose each member. In FIG. 2A, the polarized light A and the polarized light B do not interfere with each other, and the polarized light A and the polarized light B interfere with each other. Therefore, it is assumed that a phase member is added only to the light transmitting portion 2c or only the light transmitting portion 2d. Then, since the phases of the light beams oscillating in the same direction do not change, the same is obtained with or without the addition of the phase member.

When a polarizing member that transmits polarized light C that vibrates in the third direction is added to a polarizing member that transmits two orthogonal polarized lights A and B, the polarized light A and the polarized light C In the case where three or more types of polarizing members are provided in the adjacent light transmitting portion, it is desired to pay attention to the interference of each polarized light.

As for the phase shift mask, a spatial frequency modulation method in which a phase shift member is added to one of the adjacent light transmitting portions via a light shielding portion (see the photomask described with reference to FIG. 4 and the photomask disclosed in Japanese Patent Publication No. Sho 62-50811). Mask), a multi-stage method in which phase members having different thicknesses are provided, an auxiliary pattern method in which an auxiliary pattern made of a phase shift member is provided around the periphery of the light shielding pattern, an edge in which a phase shift member is provided at the boundary between the light shielding portion and the light transmitting portion Although various methods such as an emphasis method have been proposed, the present invention can be applied to any type of phase shift mask. In addition to adding a phase member and a polarizing member in combination as in the example of FIG. 2, depending on a circuit pattern, only a phase member may be added in a certain region and only a polarizing member may be added in another region. Further, it is not always necessary to provide a light-shielding film at a portion corresponding to a dark portion of a pattern image to be transferred, and a pattern may be formed only by a phase shift member. For example, by disposing the phase shift members in a checkerboard pattern, a dark portion can be obtained without using a light-shielding film.

In the embodiments shown in FIGS. 1 and 2, an example is described in which a polarizing member is used which converts linearly polarized light whose vibration direction is orthogonal. However, the polarizing member of the present invention is a circular member whose vibration direction rotates with time. A polarizing member that generates polarized light or elliptically polarized light may be used. When using circularly polarized light, see Figure 1
A polarizing member transmitting right-handed circularly polarized light is added to one of the adjacent light transmitting portions via the light-shielding portion in FIG. 2, and a polarizing member transmitting left-handed circularly polarized light is added to the other light transmitting portion. good. When using elliptically polarized light, the major axis directions are orthogonal,
What is necessary is just to add a polarizing member that transmits elliptically polarized light having the opposite rotation direction.

In the above description, the transmission type photomask has been described. However, in the case of a reflection type mask in which a reflection member (reflection film) is provided on a transparent substrate, a polarization member is added to the reflection portion. Thus, the resolving power can be increased similarly to the transmission type photomask. A reflective photomask is an apparatus that forms an image by illuminating the photomask with incident light and collecting light reflected from a reflective film by an imaging optical system. The light transmitting portion is a dark portion of the image, and the reflecting portion is a bright image. Because it corresponds to the department,
The light transmitting portion of the above-mentioned transmission type photomask may be replaced with a reflecting portion and the light shielding portion may be replaced with a light transmitting portion.

[0033]

As described above, in the photomask of the present invention, since at least two types of polarizing members for transmitting the lights of the respective polarization states orthogonal to each other are provided in the light transmitting portion, the basic period of the pattern is changed. Can be increased.
As the period of the pattern increases, the diffraction angle of the diffracted light generated by the photomask decreases accordingly, and the resolution can be improved even when an exposure apparatus having the same numerical aperture is used. Further, the photomask of the present invention can be combined with a phase shift mask developed in recent years, and can realize the resolution of a fine pattern which has been impossible in the past.

[Brief description of the drawings]

1 (a) is a schematic plan view of a photomask according to a first embodiment of the present invention, and FIG. 1 (b) is an explanatory diagram showing the amplitude transmittance of the photomask of FIG. 1 (a).

FIG. 2 (a) is a schematic plan view of a photomask according to a second embodiment of the present invention, and FIG. 2 (b) is an explanatory diagram showing the amplitude transmittance of the photomask of FIG. 2 (a).

3 (a) is a schematic plan view of a conventional general photomask, and FIG. 3 (b) is an explanatory diagram showing the amplitude transmittance of the photomask of FIG. 3 (a).

4 (a) is a schematic plan view of a conventional phase shift mask, and FIG. 4 (b) is an explanatory diagram showing an amplitude transmittance of the phase shift mask of FIG. 4 (a).

[Explanation of symbols]

 1 light-shielding part 2a, 2b, 2c, 2d light-transmitting part with added polarizing member

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03F 1/00-1/16

Claims (7)

(57) [Claims] 1. A photomask in which a pattern to be projected and transferred is formed on a transparent substrate, wherein at least two types of polarizing members for converting into mutually orthogonal polarization states are repeatedly formed in a light transmitting portion of the transparent substrate. A photomask, wherein the two types of polarizing members are configured to transmit light polarized in a direction inclined with respect to sides of the pattern. 2. The photo of claim 1, wherein the two types of polarizing members are configured to transmit light polarized in a direction inclined at 45 degrees with respect to a side of the pattern. mask. 3. The photomask according to claim 1, wherein a phase member for changing the phase of the transmitted light is disposed at a part of the light transmitting portion provided with the polarizing member. . 4. A photomask in which a pattern to be projected and transferred is formed on a substrate, wherein:
A photomask, comprising: at least two types of polarizing members for converting into mutually orthogonal polarization states. 5. The photomask according to claim 4, wherein the two kinds of polarizing members are configured to convert the polarized light into light polarized in a direction inclined with respect to a side of the pattern. 6. The photo of claim 5, wherein the two types of polarizing members are configured to convert the polarized light into light polarized in a direction inclined at 45 degrees to the sides of the pattern. mask. 7. A step of illuminating the photomask according to claim 1, 2, 3, 4, 5, or 6, and a step of forming an image of a pattern of the photomask on a wafer surface by a projection optical system. An exposure method comprising: