JPH0350818A - Exposing apparatus - Google Patents

Abstract

PURPOSE:To make it possible to monitor the amount of exposure of a wafer accurately and thereby to execute accurate control of the amount of exposure at all times by a method wherein a change in the retardation of an exposure light generated by an image rotating prism is reduced so that the state of polarization of the exposure light entering a beam splitter may not change so much when the image rotating prism rotates during exposure. CONSTITUTION:A linearly polarized laser light emitted from a laser 1 passes through a 1/4 wave plate 2 and an image rotating prism 3 and enters an illuminating optical system 4. Since the 1/4 wave plate 2 is provided so that the plane of polarization of the laser light be changed from that of linear polarization to that of circular polarization, the state of polarization of the laser light entering a half mirror 5 dose not change so much in accordance with the rotation of the image rotating prism 3 and illuminance on the light-sensing surface of a light-sensing element of an integrating exposure meter 6 is fixed substantially. Accordingly, the ratio between the illuminance on the light sensing surface and that on a water 11 is always fixed, the quantity of the laser light reaching the wafer 11 can be monitored accurately by the integrating exposure meter 6, and the amount of exposure can always be controlled accurately on the occasion when each pattern region arranged on the wafer 11 is exposed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an exposure apparatus, and particularly relates to (1) an exposure apparatus using a laser such as an excimer laser as an exposure light source.

[Prior art] In recent years, with the increase in the degree of integration of integrated circuits such as LSI, lpm
An exposure apparatus is used that can accurately form the following fine patterns on a wafer F-.

Further, in order to further increase the resolution line width of the equipment, development of exposure apparatuses equipped with an excimer laser that emits high-intensity light in the far ultraviolet region as an exposure light source is being actively conducted.

In such an exposure apparatus, it is necessary to expose the wafer with a predetermined exposure amount, and technology related to this exposure amount control is an important technology. Normally, in order to control the exposure amount, a half mirror is provided in the optical path of the exposure light, and the reflected light reflected by the half mirror or
One of the transmitted lights is received by a light receiving element for monitoring the exposure amount, and a shutter installed in the optical path of the exposure light is controlled to open or close in accordance with an output signal from the light receiving element.

The reflectance (transmittance) of a half mirror provided in the optical path of the exposure light normally exhibits different values for the P-polarized light component and the S-polarized light component of the exposure light. Therefore, if the polarization state of the exposure light incident on the half mirror changes from moment to moment, the ratio between the amount of light incident on the light receiving element and the amount of exposure light incident on the wafer will fluctuate. It is not possible to monitor the exposure amount accurately using the element.

-4. When using the above-mentioned excimer laser as a light source for exposure, if the cross-sectional intensity distribution of the light emitted from the light source is uneven, brightness unevenness will occur between multiple secondary light sources formed by optical inch craters. As a result, the mask pattern cannot be accurately transferred onto the wafer. Therefore, is it possible to consider a method in which an image rotation prism (image rotation prism) is provided in the optical path of the exposure light from the light source, and by rotating this prism during exposure, the cross-sectional intensity distribution of the exposure light is made uniform? The exposure light that has passed through the image rotation prism produces a phase difference between mutually orthogonal polarization components, that is, the P polarization component and the S polarization component.

FIG. 2 is an explanatory diagram for explaining the function of the image rotation prism 20. Light incident on the surface A of the image rotation prism 20 is refracted by the surface A, and then totally reflected by the rear surface H and directed toward the surface B. Then, it is refracted by surface B and exits from surface B. Therefore, arrow 21
, 22, the light incident on the image rotation prism 20 is reversed by the image rotation prism 20, and by rotating this prism 20 in the θ direction, the incident light is rotated. This makes the cross-sectional intensity of the incident light uniform. On the other hand, since the incident light is totally reflected on the surface H of the image rotation prism 20, the mutually orthogonal polarization components of the incident light, that is, P
A phase difference δ occurs between the polarized light component and the S-polarized light component.

This phase difference δ (retardation) is determined by the image rotating prism 2
When the refractive index of 0 is n and the angle of incidence of the incident light on the surface H is 11, it can be expressed as follows. Therefore, when linearly polarized laser light enters the image rotation prism 20, the laser light emitted from the prism 20 becomes elongated elliptically polarized light, and when the image rotation prism 20 is rotated around the optical axis (the center of the light flux of the incident light) as the rotation axis. In synchronization with the rotation of the image rotation prism 20, the polarization plane of the emitted laser beam also changes periodically.

In this way, if you try to make the cross-sectional intensity distribution of the exposure light uniform by rotating the image rotation prism, the polarization state of the exposure light emitted from the prism will become elongated elliptically polarized light, which changes from moment to moment. For the reason mentioned above, it is difficult to accurately monitor the amount of exposure using the light receiving element in the case where an image rotating prism is installed between the light source and the half mirror that guides the light to the light receiving element for monitoring the amount of light. Therefore, accurate exposure control cannot be performed when exposing a wafer.

[Summary of the Invention] The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to provide an exposure apparatus that can always accurately control the exposure amount.

In order to achieve the above object, the present exposure apparatus includes a light source that supplies exposure light that is linearly polarized in a predetermined direction for exposing a wafer with a pattern on a mask, and an image rotation system that rotates an image in response to the exposure light from the light source. a prism; a beam splitter provided in the optical path of the exposure light that has passed through the image rotation prism;
a light receiving means for receiving the light transmitted through the beam splitter or the light reflected by the beam splitter; and a control means for controlling the exposure amount when exposing the wafer in response to the output from the light receiving means. , a wavelength plate disposed between the light source and the image rotation prism to convert the exposure light into circularly polarized light.

Since the present exposure apparatus is configured in this manner, even when the image rotation prism is rotated, the polarization plane of the exposure light emitted from the image rotation prism changes only slightly. Therefore, since the ratio of the illuminance on the wafer to the illuminance on the light-receiving surface of the light-receiving means can be made almost constant, it is necessary to constantly and accurately control the exposure amount. In addition, since the cross-sectional intensity distribution of the exposure light can be made uniform by rotating the image rotating prism, for example, the brightness distribution of the secondary light source surface formed by the optical inch grater that receives the exposure light from the light source can be made uniform, and the pattern of the mask can be made uniform. It becomes possible to accurately transfer images onto a wafer.

Hereinafter, the present invention will be described in detail based on Examples.

Embodiment FIGS. 1(A) and CB) are schematic diagrams showing an embodiment of the present exposure apparatus. In Figure 1 (A), l is the wavelength (in)
Kr emits a linearly polarized laser beam of 248.4n@
F excimer laser 12 is a wavelength plate provided to convert linearly polarized laser light into circularly polarized light, and 3 is quartz (SiO□).
An image rotating prism (image rotary prism) consisting of 4
5 is the illumination optical system, and 5 is the half mirror (beam splitter).
), 6 is a planted exposure meter, 7 is an exposure amount control circuit (control means)
, 8 is a total reflection mirror, 9 is a reticle, IO is a projection lens, 11 is a wafer, 12 is a support member that supports the image rotation prism 3, and 13 is a driver (driver) that rotates the support member 12 about the optical axis AX. 14 is a controller for controlling the rotation of the support member 12 by the driver 13, that is, the rotation of the image rotating prism 3.

The illumination optical system 4 includes a beam expander (not shown), an incoherent optical system, an optical increment condenser lens, etc. arranged in order from the laser l side. After splitting the wavefront of a laser beam into multiple mutually incoherent beams, each of these beams is incident on each lens element that makes up the optical integrator, and the optical integrator forms multiple secondary light sources. do. and,
By superimposing the laser beams from these secondary light sources on the reticle 9 through the action of a condenser lens, the circuit pattern on the reticle 9 is illuminated with uniform illuminance.

Further, the projection lens 10 is used to reduce the circuit pattern of the reticle 9 illuminated by the optical system 4 to 115 and project it onto the wafer.
Quartz (Si) has a high transmittance of 4ii for laser light.
n2).

The planted exposure meter 6 has a light-receiving element (light-receiving means) installed at a position to receive the light from the half mirror 5, and sequentially integrates the output signals from this light-receiving element, and controls the exposure amount using the integrated value. input to the circuit. Reticle 9 is reticle stage 9
0 and the wafer 11 is placed on the wafer stage 110! held. Reticle stage 90 and wafer stage 1
10 are both movable in translation within a plane orthogonal to the optical axis of the projection lens 90, and are rotatable about the optical axis of the projection lens 90 as a rotation axis. Therefore, the circuit pattern on the reticle 9 and a predetermined pattern area (shot) on the wafer 11 must be aligned by moving the stages 90 and 110, and after the alignment is completed, the reticle 9 is Project the circuit pattern on lens 1o
Projection exposure onto the wafer through the wafer.

FIG. 1(B) is a schematic diagram showing the structure of KrF excimer laser 1, in which 101 and 102 are used to select the wavelength of the laser beam to be emitted from the laser 1 and narrow the wavelength width to about 0.005 nm. 101 is a reflective type ink, and 102 is two prisms. 103 is a pair of windows, 104 is an aperture.
, 105 is a pair of discharge electrodes, 106 is an output mirror, 10
Reference numeral 7 indicates a gas chamber, in which released, 'If M and KrF gases are stored, and the inside of the gas chamber is isolated from the outside by a window 103.

When a pressure of 1 is applied to the pair of discharge electrodes 105, a claw discharge is generated between these electrodes, and a laser beam is oscillated between the grete ink 101 and the output mirror 106. Since the pair of prisms 102 and the grating 101 have wavelength selectivity, the grating 101 and the output mirror 101
The laser beam oscillated between 6 and 6 has a center wavelength of 248.4nn.
, is specified as a laser beam with a wavelength width of 0.005 nm. Furthermore, the pair of prisms 102 are each provided such that the incident angle of the laser light incident thereon coincides with the Brewster angle. Therefore, the laser light oscillated between the crating 101 and the output mirror 106 becomes linearly polarized light consisting of P polarized light.

Hereinafter, the exposure operation by the present exposure apparatus will be explained based on FIG. 1(A).

A linearly polarized laser beam emitted from a laser 1 passes through an image rotation prism 3 supported by an h-wavelength plate 2 and a support member 12, and enters an illumination optical system 4. The driver 13 moves the support member 1 based on the command signal from the controller 14.
2 is rotated at a predetermined number of rotations, thereby rotating the image rotation prism 3 with the light 1Fil+AX as the rotation axis.

As mentioned above, the wavelength plate 2 is installed to convert the polarization plane of the laser beam from linear polarization to circular polarization, so
The change in retardation that occurs in the laser beam as the image rotation prism 3 rotates is small. Therefore, even if the image rotation prism 3 is rotated, the polarization state of the laser light incident on the illumination optical system 4 does not change much. Also, by rotating the image rotating prism 3, the cross-sectional intensity distribution of the laser beam (optical axis AX
(intensity distribution in a plane substantially perpendicular to the plane) is also made uniform.

The number of rotations of the support member 13 by the driver 13 is, for example, set at several times during one exposure time so that the cross-sectional intensity molecule i of the laser beam is sufficiently averaged during one exposure time for the pattern area on the wafer 11. Set it to rotate a thousand times.

The laser beam from the illumination optical system 4 enters the half mirror 5 which is installed obliquely with respect to the optical path (optical axis AX) of the laser beam, a part of which is reflected by the half mirror 5, and most of the remaining laser beam is reflected by the half mirror 5. Light passes through the half mirror 5. half mirror
The laser beam transmitted through the laser beam 5 is reflected by the mirror 8 and illuminates the reticle 9, and the wafer 11 is exposed in accordance with the circuit pattern of the reticle 9 as described above.

On the other hand, the laser light reflected by the half mirror 5 enters the light receiving element of the integrating exposure meter 6, and the light receiving element outputs a signal corresponding to the intensity (light amount) of the incident laser light. During exposure, the integrated value input from the integrated exposure meter 6 to the exposure amount control circuit 7 is compared with a reference value (value corresponding to a default exposure amount) set in advance in the circuit 7, and the integrated value and the reference value are compared. It is compared. When the integrated value matches the reference value, a predetermined control signal is input from the circuit 7 to a driver (not shown) of the laser I, and the driving of the laser I (emission of laser light) is stopped. This completes the exposure of the predetermined pattern area on the wafer 11.

According to this exposure apparatus, the polarization state jE of the laser beam incident on the half mirror 5 does not change much depending on the rotation of the image rotating prism 3 due to the action of the wavelength plate 2. The illuminance on the light-receiving surface of the light-receiving element of the integrating exposure meter 6 is approximately constant. Therefore, the illuminance on the light receiving surface and the wafer 11
The illuminance on the wafer 11 is always at a constant ratio, and the amount of laser light that reaches the wafer 11 is accurately monitored by the integrating exposure meter 6. When exposing each pattern area arranged on the wafer 11, It becomes possible to accurately control the exposure amount.

Regarding illumination of the reticle 9, since the image rotating prism 3 can be rotated to temporally uniformize the cross-sectional intensity distribution of the laser beam, a plurality of optical inclators in the illumination optical system 4 are used to illuminate the reticle 9. It becomes possible to make the luminance distribution of the secondary light source uniform (approximately equal), and the circuit pattern on the reticle 9 can be illuminated in a good condition. In the projection type exposure apparatus shown in FIG. 1, the secondary light source surface formed in the illumination optical system 4 and the pupil surface of the projection lens 10 are set in an optically conjugate relationship. If the luminance 1 (i) of the plurality of secondary light sources is made uniform, the luminance 7ij on the pupil plane of the projection lens IO will also be made uniform.

Therefore, it becomes possible to accurately transfer the circuit pattern of the reticle 9 onto the wafer 11 via the projection lens 10.

In the exposure apparatus shown in FIG.
It is also possible to configure a reflective storm wave plate by attaching it to a mirror and to reflect the laser beam.

In addition to controlling the drive of laser 1, as shown in Figure 1, a shutter mechanism is provided in the optical path of the laser light from laser 1 to control the opening and closing of the shutter. It may be configured to control.

The embodiments described above relate to a projection type exposure apparatus that projects a circuit pattern on a reticle using a projection lens, but the present invention is not limited to this projection type exposure apparatus. Therefore, it is possible to apply the present invention to exposure apparatuses of contact type and proximity type. The present invention can also be applied to an exposure apparatus that uses a light source that emits linearly polarized light other than a laser as an exposure light source.

Effects of IJI from U] As explained above, according to the present invention, changes in the exposure light turbulence that occur in the image rotation prism that rotates the exposure light linearly polarized in a predetermined direction are suppressed, and the rotation during exposure is suppressed. The polarization state of the exposure light incident on the beam splitter does not change much even when the prism rotates, so the light receiving element that receives the light that has passed through the beam splitter or the light that has been reflected by the beam splitter can accurately The amount of exposure to the wafer can be monitored. Therefore, it is possible to provide an exposure apparatus that allows accurate exposure control at all times.

In addition, by installing an image rotating prism in the optical path of the exposure light and rotating it, the cross-sectional intensity of the exposure light can be increased! Since the opening can be made uniform, the brightness 4j on the secondary light source surface in the illumination optical system can be made uniform, and the pattern transfer performance can be improved.

[Brief explanation of drawings]

FIGS. 1(A) and 1(R) are schematic diagrams of 1,21° showing an example of an exposure apparatus for unexploded II+. FIG. 2 is an explanatory view for explaining the action of an image rotating prism. ■... Excimer laser 2... Sait wave plate 3... Image rotation prism 5... Half mirror 6... Integrating exposure meter 7... Exposure amount control circuit 12... Support member 13... ...Driver 14...Controller

Claims (1)

[Scope of Claims] A light source that supplies exposure light linearly polarized in a predetermined direction for exposing a wafer with a pattern on a mask, an image rotation prism that receives and rotates the exposure light from the light source, and the image rotation prism a beam splitter provided in the optical path of the exposure light that has passed through the beam splitter; a light receiving means for receiving the light transmitted through the beam splitter or the light reflected by the beam splitter; An exposure apparatus comprising: a control means for controlling an exposure amount during exposure; and a quarter wavelength plate disposed between the light source and the image rotation prism so as to convert the exposure light into circularly polarized light.