JPH07307268A - Optical device for illumination - Google Patents

Abstract

PURPOSE:To reduce reflected light from a substrate through a simple method by forming a part or the whole illumination light in inclined light to a specified region and forming the polarized light of inclined light in linearly polarized light contained in the plane of incidence of inclined light. CONSTITUTION:Beams emitted from a KrF excimer laser beam source 81 changed into a narrow zone are linearly polarized. The beams are projected to a fly's eye lens 83 through a collimator lens 82. A mask 85 is irradiated with polarized and rotated beams in the plane of incidence by a spatial filter 11 placed at the rear of the fly's eye lens 83 through a condenser lens 84. The colarized light of illumination light is formed in p-polarized light to the plane of incidence. Accordingly, reflected light from a substrate can be reduced remarkably and simply without using an antireflection film and a die-containing resist.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical device which is a part of an exposure device used for transferring a circuit pattern in a manufacturing process of a semiconductor integrated circuit or a liquid crystal display device.

[0002]

2. Description of the Related Art In a step of exposing a semiconductor integrated circuit or a liquid crystal display device, a circuit pattern on a mask is transferred to a resist coated on a substrate by using an exposure device. Since semiconductor elements and the like have a three-dimensional structure, there are often steps on the substrate. Since the light incident on the stepped portion of the substrate is reflected in an oblique direction, there arises a problem that even the portion shielded by the mask is exposed. Further, even when the substrate is flat, if the reflectance of the substrate is large, the resist shape is deteriorated due to the influence of standing waves. Conventionally, in order to solve these problems, a method of forming an antireflection film on a substrate is known. Also known is a method of reducing the light reaching the substrate by using a resist with a die.

[0003]

The method using the antireflection film cannot be used in some cases because the substrate is contaminated depending on the process. There is also a problem that the number of steps for forming the antireflection film increases. In order to greatly reduce the light reaching the substrate by using the die-containing resist, it is necessary to increase the absorptance of the resist. As a result, there arises a problem that the resist profile disappears vertically.

An object of the present invention is to solve the above problems and to provide an illumination optical apparatus used in an exposure apparatus that reduces the reflected light from a substrate by a simple method.

[0005]

The present invention provides an illumination optical device for uniformly illuminating a predetermined area on an object with illumination light from an illumination optical system, wherein a part or the whole of the illumination light is applied to the predetermined area. It is an illumination optical device comprising: a means for making the inclined light and a means for making the polarized light of the inclined light a linearly polarized light included in the incident surface of the inclined light.

[0006]

The illumination light is diffracted by the pattern on the mask. The finer the mask pattern, the larger the diffraction angle. Therefore, as shown in FIG.
In the case of 1, only the 0th order light 25 passes through the projection optical system 27, so that an image is not formed on the wafer 28. In contrast, Figure 2
In the case of the obliquely incident illumination light 29 as shown in FIG.
In addition, the + 1st order light 26 or the −1st order light 24 passes through the projection optical system, so that an image is formed on the wafer 28.

Therefore, the secondary light source of the illumination optical system is shown in FIG.
Consider the two types shown in (a) and (b).

Since the openings 31 and 32 are separated from the center of the secondary light source 30, the illumination light enters the mask in an oblique direction. The position of the opening corresponds to a portion of σ = 0.5 to 0.6 when expressed by a coherent factor σ that is normally used. The difference between FIG. 3A and FIG. 3B lies in the polarization direction of the illumination light. In FIG. 3A, the light passing through the opening 31 is P-polarized with respect to the incident plane, but FIG.
Then, the light passing through the opening 32 is S-polarized with respect to the incident plane.

FIG. 5 shows the electric field intensity distribution 51 when the mask of FIG. 4 is irradiated with such illumination light and an image is formed on the resist film 52 on the Si substrate 53 having a step by the projection optical system.
And shown in FIG. The step direction is arranged in a direction orthogonal to the plane of incidence of the illumination light so that the influence of reflection is greatest. FIG. 5 corresponds to P-polarized light, and FIG. 6 corresponds to S-polarized light. The width of the light shielding portion 23 and the transparent portion 41 on the mask in FIG. 4 is 0.2 μm when projected on the wafer. Also, the illumination light is a KrF excimer laser light (wavelength 248n
m), the numerical aperture of the projection optical system is 0.6. It is known that the resist reacts to an electric field and the magnetic field does not contribute to the exposure of the resist. Looking at the electric field intensity distribution in the resist, the reflected light penetrates to the light-shielded portion in the S-polarized light, but does not penetrate in the P-polarized light. Therefore, in FIG.
If the illumination optical system of (a) is used, the influence of substrate reflection can be reduced.

The reason why such a phenomenon occurs will be described below. It is known that the reflectance of light varies greatly depending on the polarization state. For example, when light is incident on a medium that does not have absorption at the Brewster angle, the reflectance of P-polarized light becomes zero. Since the semiconductor substrate generally absorbs light, there is no Brewster angle, but when light is incident obliquely, the reflectance of P-polarized light is much smaller than that of S-polarized light. Specifically, resist (refractive index n = 1.76, absorption coefficient k = 0.01
FIG. 7 shows the result of calculating the reflectance at the interface between 2) and Si (n = 1.41, k = 3.35). The refractive index used for the calculation is a value at the wavelength λ = 248 nm of the KrF excimer laser. When the incident angle is around 60 degrees, the reflectance of P-polarized light is about half that of S-polarized light. As a physical explanation, in the case of S-polarized light, the direction of the induced current generated at the boundary surface and the direction of the electric field are the same, so that a large induced current is generated and the reflectance is large. It becomes difficult to generate an electric current and the reflectance decreases. The calculation of the reflectance in FIG. 7 corresponds to the case where light is incident on the planar substrate from an oblique direction, but the same phenomenon occurs also in the case of a substrate having a step in consideration of the direction of the induced current.

[0011]

EXAMPLE FIG. 8 shows a first example of the illumination optical apparatus of the present invention.
Shown in. The light emitted from the narrow band KrF excimer laser light source 81 is linearly polarized. This light passes through the collimator lens 82 and enters the fly-eye lens 83. The light polarized and rotated in the incident plane by the spatial filter 11 placed behind the fly-eye lens 83 is condensed by the condenser lens 84.
And illuminates the mask 85. A top view of the spatial filter 11 is shown in FIG. 1 / 2.lamda. Plates 12, 13, and 14 are fitted in the small openings corresponding to the fly-eye lens 83 so that the polarization direction becomes linearly polarized in each incident plane. When the spatial filter 91 shown in FIG. 9 is used instead of the spatial filter 11, the resolution is improved due to the effect of annular illumination. 92 to 95 in the figure are 1/2 λ plates.

FIG. 10 shows a second embodiment of the illumination optical apparatus of the present invention. A narrow band KrF excimer laser light source 8
The light emitted from 1 is linearly polarized. This light passes through the polarization rotator 101, so that the plane of polarization is rotated. The polarization rotation amount is controlled by the polarization rotation control unit 102. At the same time, the reflecting mirrors 103 and 105 are rotated by rotating mechanisms 104 and 106.
The laser light scans the entire surface of the fly-eye lens 83 or a part thereof by rotating in the orthogonal directions. By adjusting the timings of the polarization rotation control unit 102 and the rotation mechanisms 104 and 106, the illumination light from the fly-eye lens 83 is controlled so as to be always linearly polarized in the incident plane. As a combination of the polarization rotation element 101 and the control unit 102, for example, a 1 / 2λ plate and a rotation mechanism can be used.

In the above embodiment, KrF is used as the light source.
Although an excimer laser was used, an ArF excimer laser, i-line, g-line, or X-ray of a high-pressure mercury lamp can be used instead. When the light source is not polarized, a polarizing element such as a polarizing plate may be inserted between the light source and the polarization rotating element. The substrate is not limited to Si, but Al, SiO ₂
It can be applied to everything.

[0014]

As described in detail above, according to the illumination optical device of the present invention, the reflected light from the substrate can be significantly and easily reduced without using an antireflection film or a die-containing resist.

[Brief description of drawings]

FIG. 1 is a diagram showing a first example of a spatial filter used in an illumination optical device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing traveling directions of diffracted light by direct incidence illumination and oblique incidence illumination.

FIG. 3 is a diagram showing the shape and polarization direction of a secondary light source in oblique incidence illumination.

FIG. 4 is a mask including a light shielding portion and a transparent portion.

FIG. 5 is an electric field intensity distribution diagram in a resist when oblique incidence illumination is performed by P-polarized light.

FIG. 6 is an electric field intensity distribution diagram in a resist when oblique incidence illumination by S-polarized light is performed.

FIG. 7 is a diagram showing polarization dependence of reflected light.

FIG. 8 is a diagram for explaining an illumination optical device that is a first embodiment of the present invention.

FIG. 9 is a diagram showing a second example of the spatial filter used in the illumination optical device according to the first embodiment of the present invention.

FIG. 10 is a diagram for explaining an illumination optical device that is a second embodiment of the present invention.

[Explanation of symbols]

 11 Spatial Filters 12, 13, 14 1/2 λ Plate 21 Direct Incident Illumination Light 22 Glass Substrate 23 Light-shielding Part 24 -1st Order Light 25 0th Order Light 26 + 1st Order Light 27 Projection Optical System 28 Wafer 29 Oblique Incident Illumination Light 30 2nd Order Light source 31, 32 Opening portion 41 Transparent portion 51 Electric field intensity distribution 52 Resist film 53 Si substrate 81 Laser light source 82 Collimator lens 83 Fly eye lens 84 Condenser lens 85 Mask 91 Spatial filter 92, 93, 94, 95 1 / 2λ plate 101 Polarized light Rotation element 102 Polarization rotation control section 103, 105 Reflecting mirror 104, 106 Rotation mechanism

Claims (2)

[Claims] 1. An illumination optical device for uniformly illuminating a predetermined area on an object with illumination light from an illumination optical system, and means for making a part or the whole of the illumination light oblique to the predetermined area. An illumination optical device comprising: a means for converting the polarized light of the inclined light into a linearly polarized light included in the incident surface of the inclined light. 2. The illumination optical device according to claim 1, wherein the polarization of the illumination light is P-polarized with respect to the plane of incidence.