JPH09197679A - Projecting optical device and projecting optical method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely align a substrate with an imaging surface of an projecting optical system. SOLUTION: A height position of a predetermined area in a wafer W is obtained by an oblique incident AF system. A mark locate at a position different from the predetermined area is observed by a television camera 56 through a projecting lens 18, and a focusing position (the position of a substrate) is obtained from a signal with which the contract becomes highest while an imaging optical path is change. A resist on the mark is removed so that the height position of the mark area is different from that of the predetermined area. This difference in height caused by the difference in structure, is used as an offset which is added to the oblique incident AF system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, an exposure apparatus used for manufacturing an integrated circuit, and more particularly, to an optical system including a resist-coated wafer and a mask or reticle on which a pattern to be exposed is formed. The present invention relates to a projection optical device and a projection optical method for adjusting a physical positional relationship.

[0002]

2. Description of the Related Art In an alignment focusing apparatus used in a conventional exposure apparatus and the like, illumination light for alignment is applied from above a resist layer formed on a semiconductor substrate.

That is, alignment marks are formed on the semiconductor substrate as surface irregularities. And
Furthermore, a resist layer is formed on it. The illumination light for alignment is applied to the mark for alignment via the resist layer.

In this way, the alignment mark on the substrate is illuminated through the resist layer, and its position is detected to perform predetermined alignment, for example, alignment between the reticle and the substrate.

[0005]

However, in the above-mentioned conventional system, interference fringes may occur in the illuminated portion due to the influence of the resist. For this reason, it is difficult to determine the optimal alignment position and focusing position, and alignment and focusing cannot be performed satisfactorily, and the reproducibility of alignment and the like deteriorates.

The present invention has been made in view of the above points, and an object of the present invention is to provide a projection optical apparatus and a projection optical method which can detect the in-focus position satisfactorily and have good reproducibility.

[0007]

A projection optical system according to a first aspect of the invention is a projection optical system for projecting a pattern formed on a mask by illumination light onto a substrate coated with a photosensitizer. By detecting the substrate via the projection optical system by the detection light having the same wavelength as the illumination light,
In a projection optical device including a focus detection system that detects a focus position of the projection optical system, the focus detection system performs the focus in a region where at least three of the photosensitive agents are removed from the substrate. Based on the detection result of the position and the thickness information of the photosensitive agent, the table on which the substrate is placed,
It is characterized by further comprising drive control means for driving the projection optical system so as to move in an optical axis direction or incline with respect to the optical axis direction.

According to the projection optical method of the invention described in claim 2, the pattern formed on the mask by the illumination light is projected onto the substrate coated with the photosensitizing agent through a projection optical system.
In the projection optical method for detecting the focus position of the projection optical system by detecting the substrate with detection light having the same wavelength as the illumination light, the focus position is the substrate from which the photosensitive agent has been removed. Detecting the in-focus position with respect to the upper region, and determining the in-focus position of the region on the substrate coated with the photosensitive agent based on the detection result and the thickness information of the photosensitive agent. It is a feature.

According to the present invention, in observing a mark or a mark image, the observation is performed under various conditions in which the optical path length of the detection light is changed. A change in the optical path length changes the focus position in the detection means. For this reason, the contrast of the observed image changes. The amount of defocus between the reticle and the wafer can be obtained from the difference in the optical path length of the detection light that provides good image contrast.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the configuration of this example will be described with reference to FIG. In FIG. 1, a wafer W having a resist layer formed on its surface is mounted on a leveling stage 10 that can rotate around the X and Y axes and move in the Z axis direction. This leveling stage 10
Is driven by a motor 12.

Next, the leveling stage 10 is constructed on an XY stage 14 that can move in the XY directions.
The XY stage 14 is driven by a motor 16. A projection lens 18 is disposed above the wafer W, and a reticle R is disposed above the wafer W while being held by a reticle holder 20.

Next, on the side of the projection lens 18, an oblique incidence AF slit light transmission system (hereinafter simply referred to as "AF light transmission system").
22 and an oblique incidence leveling sensor light transmission system (hereinafter simply referred to as “leveling light transmission system”) 24 are provided. The light transmitted from the AF light transmission system 22 and the leveling light transmission system 24 are both incident on the light transmission system side objective lens system 28 by the action of the beam splitter 26.

Next, the light transmitted through the light transmitting system side objective lens system 28 is obliquely incident on the wafer W, is reflected there and is incident on the light receiving system side objective lens system 30, and is transmitted therethrough to form a beam. It is configured to be separated by a splitter 32. A
The light transmitted from the F light transmission system 22 is obliquely incident AF light receiving system (hereinafter referred to as “AF light receiving system”) 3 as shown by a solid line.
4, the light output from the leveling light transmission system 24 is incident on a leveling sensor light receiving system (hereinafter, referred to as “leveling light receiving system”) 36 as shown by a broken line.

An oblique incidence AF system mainly composed of an AF light transmitting system 22 and an AF light receiving system 34 is disclosed in, for example,
It is disclosed in Japanese Patent No. 42205 and detects a focus position with respect to the projection lens 18.

A leveling sensor system mainly comprising a leveling light transmitting system 24 and a leveling light receiving system 36 is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-113706, in which a wafer surface is rotated around XY axes. This is to detect the state.

Next, from above the reticle R,
Illumination light having the same wavelength as the exposure light guided by the fiber 38 is incident by the action of the lens 40, beam splitter 42, objective lens system 44 and mirror 46. The illumination light passes through the alignment mark portion of the reticle R, then passes through the projection lens 18, and further enters the wafer W.

Further, the illumination light reflected by the wafer W passes through the projection lens 18 and the reticle R, and enters the transparent rotary plate 50 by the action of the mirror 46, the objective lens 44, the beam splitter 42, and the relay lens system 48. It is supposed to.

As shown in FIG. 7, the transparent rotary plate 50 has a plurality of glass plates 5 having different thicknesses TA to TG.
0A to 50G are provided. These thicknesses TA to TG are set, for example, in the following relationship. TA <TB <TC <TD <TE <TF <TG (1)

When the transparent rotating plate 50 rotates, the glass plate 5
0A to 50G are sequentially inserted into the optical path. By inserting the glass plates 50A to 50G, the optical path length changes little by little. In this example, a glass plate 50 is used for the pattern on the reticle R.
D is set to give a standard optical path length.

Next, the rotational position of the transparent rotary plate 50 as described above is detected by the encoder 52, and the light transmitted through the transparent rotary plate 50 is reflected by the mirror 54 and enters the television camera 56. It has become.

The signal output sides of the encoder 52 and the television camera 56 are both connected to a TTL focus detection processing circuit (hereinafter, referred to as "focus detection circuit") 58. The focus detection circuit 58 detects a focus shift based on an input signal and outputs a TTL focus shift signal TFS to the main control system 60, as will be described later with reference to FIGS. Has functions.

Next, the main control system 60 includes, in addition to the focus detection circuit 58, the AF light receiving system 34 and the leveling light receiving system 3.
6 are connected to each other, and an oblique incidence AF system detection signal GPS
And leveling detection signal LV by leveling sensor system
S is input to the main control system 60.

The output side of the main control system 60 is connected to the motors 12, 1
Drive signals θyS and θxS for leveling and a drive signal ZS in the Z direction are respectively output to the motor 12, and the drive signal XS in the X and Y directions is output to the motor 16.
YS is output respectively.

Next, the reticle R will be described in detail with reference to FIGS. FIG. 2 shows a reticle R
FIG. 3 is an enlarged view of a step Y mark area which is a part of the reticle R.

In FIGS. 2 and 3, reticle R
Is a pattern area RPA to be exposed and projected, and a suitable area around this area is indicated by X in FIG.
A step X mark area RSX and a step Y mark area RSY are provided respectively corresponding to the Y direction.
Further, reticle alignment marks Rθ and Rxy are respectively provided in appropriate regions other than the pattern region RPA, and a boundary portion between this region and the pattern region RPA is
A shading band RSR is formed.

In the above-described step Y mark area RSY, as shown in FIG. 3, a mark of a line-and-space grid pattern (hereinafter referred to as a "grid mark") FY
R and rectangular step Y marks RYA and RYB are respectively formed. A shading band RSR is also formed around the step Y mark area RSY, and the distance from the center in the arrangement direction of the lattice marks FYR to the pattern area RPA is Dr.

Next, the wafer W will be described in detail with reference to FIGS. FIG. 4 shows a part of the surface of the wafer W, FIG. 5 shows an enlarged view of the wafer mark area, and FIG. 6 shows a view along the line VI-VI in FIG. A cross section of the wafer W is shown.

In FIGS. 4 to 6, the wafer W
There are many shot areas or chip areas S1, S2,... Corresponding to the pattern area RPA of the reticle R above. Then, these shot areas S1, S
2, S3, On street line between ... and each corresponding to the XY direction, the wafer mark region Sy _1, Sy _2,
.., Sx ₁ , Sx ₂ ,. These wafer mark areas Sy ₁ , Sy ₂ ,... Sx ₁ , Sx ₂ ,.
Are Dx _C and Dy _C from the center SC of the shot areas S1, S2,.

In the wafer mark area Sy ₁ described above, as shown in FIG. 5, marks of a line-and-space grid-like concavo-convex pattern (hereinafter referred to as “grid-like marks”) FYW.
And a rectangular step Y mark WYA are respectively formed. The distance from the center of the lattice mark FYW in the arrangement direction to the shot area S1 is Dw.

As shown in FIG. 6, a resist layer PR having a thickness ΔZr is formed on the wafer W as described above, but the wafer mark areas Sy ₁ , Sy ₂ ,... Sx ₁ , Sx
_{In 2} ..., The resist layer PR has been removed in advance by means such as an excimer laser. The excimer laser light is a high-energy pulse laser having an oscillation wavelength in the ultraviolet region. When a spot of the excimer laser light is irradiated on the resist layer, the irradiated portion of the resist is vaporized and removed.

Next, the operation of the system having the above configuration will be described with reference to FIGS. The detection method shown in these figures is disclosed in, for example, JP-A-60-10154.
It is publicly known from the publication No. 0.

First, a leveling measurement is performed on any of the shot areas on the wafer W, for example, S1, by a leveling sensor. In this leveling measurement, the leveling light transmission system 2 is used at the center SC portion of the shot area S1.
4. This is performed using the leveling light receiving system 36. In the main control system 60, the detection signal L from the leveling light receiving system 36
Based on the VS, the inclinations θ _x and θ _y of the wafer W with respect to the X and Y axes are respectively obtained, and the leveling drive signals θ _x S and θ _y S are input to the motor 12, respectively.

Next, focusing is performed by the oblique incidence AF system. This focusing is performed by the AF light transmission system 22, AF
This is performed using the light receiving system 34. In the main control system 60,
Based on the detection signal GPS from the AF light receiving system 34, a focus shift amount in the Z direction is obtained, and a drive signal ZS for focusing is input to the motor 12.

After the above operation, illumination light for correcting the in-focus position is irradiated via the fiber 38. As a result, the television camera 56 observes the lattice mark FYW on the wafer W and the lattice mark FYR on the reticle R.

FIG. 8 shows the scanning direction of the video signal, and the images IR and IW of the lattice marks FYR and FYW are scanned in the SL ₁ and SL ₂ directions, respectively. FIGS. 9A to 9C show examples of the waveform of the video signal when scanned in this manner. FIG. 7A shows a case where a glass plate 50B is used, and FIG.
(C) shows the case where the glass plates 50D and 50F are used, respectively.

These waveform examples will be described in detail below.
As described with reference to, the glass plates 50A to 50G sequentially inserted into the illumination light path each have a slightly different thickness. For this reason, the optical path length also changes little by little, and consequently the in-focus position changes around the imaging surface position of the television camera 56.

When the in-focus position is on the imaging surface, the grid marks FYR and FYW are most clearly observed by the television camera 56. Therefore, the unevenness of the video signal corresponding to the lattice mark arrangement is the largest. On the other hand, when the focus position is shifted from the imaging surface, the grid marks FYR and FYW are blurred and observed by the television camera 56. Therefore, the unevenness of the video signal corresponding to the grid-like mark arrangement becomes smaller in inverse proportion to the degree of the shift of the focus position.

On the other hand, the optical path length fluctuation amount by the glass plates 50A to 50G can be obtained in advance. Therefore, based on the video signal amplitudes Va, Vb, Vc... (Corresponding to contrast) when the glass plates 50A to 50G are inserted in the optical path, and the optical path length variation amounts of the respective glass plates 50A to 50G, FIG. A graph as shown can be obtained. This operation involves the output of the encoder 52,
This is performed by the focus detection circuit 58 based on the output of the television camera 56.

Graphs of the amplitude of the video signal and the amount of variation in the optical path length are obtained for each of the lattice mark FYR of the reticle R and the lattice mark FYW of the wafer W, and are shown as graphs GA and GB in FIG. It is shown.

Here, if the reticle R and the wafer W are at the in-focus position with respect to the projection lens 18, the peak points of the graphs GA and GB coincide. However, when both are not at the in-focus position, the peak points of the graphs GA and GB are shifted in accordance with the amount of defocus. That is, the shift between the peak points of the graphs GA and GB corresponds to the focus shift amount ΔZ between the reticle R and the wafer W.

The focus shift amount ΔZ between the reticle R and the wafer W, which is well determined without being affected by the resist as described above, is obtained from the focus detection circuit 58.
It is input to the main control system 60 as a TTL defocus signal TFS.

Next, in the main control system 60, a necessary offset is applied to the detected focus position of the AF light receiving system 34 based on the focus shift amount ΔZ, and the focus drive signal ZS is output to the motor 12. To be done. That is, since the focus shift of ΔZ exists with respect to the focus position of the wafer W detected by the oblique incidence AF system, the offset amount is corrected.

At this time, the thickness ΔZr of the resist layer PR on the wafer W is also taken into consideration when determining the offset amount. This is because the focus shift amount ΔZ was measured using a grid-like mark without the resist layer PR, whereas the focus measurement by the oblique incidence AF system was performed on the resist layer surface. That is, by adding the offset, the projected image of the reticle pattern can be focused on the position (the position in the thickness direction) where the true focusing is desired in the thickness of the resist layer PR.

In the above example, the XY alignment can be favorably performed without being affected by the resist. As the alignment system, a detection system for the amount of defocus ΔZ can be used. That is, with the TV camera 56, the step mark W of the wafer W is
The YA and the step marks RYA and RYB of the reticle R are observed at the same time, and the drive signals XS and YS are output from the main control system 60 to the motor 16 so that the step mark WYA is located at the center between the step marks RYA and RYB. It

The present invention is not limited to the above-mentioned example, and, for example, when focus detection via a projection lens is applied to three marks located in directions orthogonal to each other in the XY plane, In addition to focus, calibration and alignment during leveling can be performed, and one device can perform three functions.

Further, in the above embodiment, since the mark on the wafer is provided on the street line, the use of the illumination light having the exposure wavelength does not affect the resist in the circuit pattern portion. This is particularly effective when the thickness is large. Incidentally, even when the illumination light for mark detection is different from the wavelength of the exposure light, the same effect can be obtained by using, for example, an optical element for correcting chromatic aberration of the projection lens.

Further, as a focus detection system of the TTR (through the reticle) system, light from the reticle and light from the wafer are separated on the pupil plane of the projection lens, and the image of the reticle mark is formed on the wafer. And a so-called pupil division system for detecting the state of superposition of the reticle mark itself and the reflected image of the reticle mark.

[0048]

As described above, according to the present invention, since the mark portion is removed from the photoresist on the wafer to detect the mark, the focus position of the illumination light can be favorably detected. . Further, since the height position can be accurately set in consideration of the thickness of the photosensitizer applied on the substrate, in submicron lithography, the numerical aperture (NA) of the projection lens is set to be large and the depth of focus is shallow. Even if it becomes, it can respond sufficiently.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a projection optical apparatus of the present invention.

FIG. 2 is a plan view showing an example of a reticle R of FIG.

FIG. 3 is an enlarged plan view showing a mark portion of a reticle R in FIG. 2;

FIG. 4 is a plan view showing an example of a wafer W of FIG.

FIG. 5 is an enlarged plan view showing a mark portion of the wafer W in FIG. 4;

FIG. 6 is a cross-sectional view of a portion of a lattice mark on the wafer W of FIG.

FIG. 7 is an explanatory diagram illustrating an example of a transparent rotating plate that changes an optical path length.

FIG. 8 is an explanatory diagram showing a scanning direction of a video signal and a mark arrangement direction.

FIG. 9 is a diagram showing a relationship between a video signal and an optical path length.

FIG. 10 is a diagram showing a focus shift amount.

[Explanation of symbols]

 Reference Signs List 10 Z stage 12 Motor 14 XY stage 16 Motor 18 Projection lens 22 AF light transmission system 24 Leveling light transmission system

Claims (2)

[Claims] 1. A projection optical system for projecting a pattern formed on a mask by illumination light onto a substrate coated with a photosensitizer, and detection light having the same wavelength as the illumination light, through the projection optical system. In a projection optical device including a focus detection system that detects a focus position of the projection optical system by detecting the substrate, at least three of the photosensitive agents on the substrate by the focus detection system are provided. Based on the detection result of the in-focus position in the removed region and the thickness information of the photosensitive agent, the table on which the substrate is placed is moved in the optical axis direction of the projection optical system or with respect to the direction. A projection optical device comprising drive control means for driving so as to tilt. 2. The substrate is detected by detection light having the same wavelength as the illumination light through a projection optical system that projects the pattern formed on the mask by the illumination light onto the substrate coated with the photosensitive agent. Thus, in the projection optical method for detecting the in-focus position of the projection optical system, the in-focus position is detected by detecting the in-focus position with respect to a region on the substrate from which the photosensitive agent has been removed. A projection optical method, comprising: determining a focus position of an area on the substrate coated with the photosensitizer based on a result and thickness information of the photosensitizer.