JP2569640B2 - Focusing correction method for projection exposure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] A projection optical system for projecting a pattern of a photomask onto a substrate to be exposed, a substrate stage for moving the substrate to be exposed in an XY direction parallel to the exposure surface and a Z direction perpendicular to the exposure surface, A luminous flux is incident on the exposure surface of the substrate to be exposed, and the reflected light is detected,
And the adjusting mechanism provided in the detecting means is the Z of the substrate stage.
With a focusing optical system interlocked with the directional movement, the Z-direction movement of the substrate stage is changed to determine the state of the substrate stage where the focusing is optimal from the exposed substrate exposed.
In this state, the adjustment point of the adjustment mechanism is set as a first reference, and during the exposure operation, the adjustment point of the adjustment mechanism is adjusted to the first reference to adjust the focus of the projection exposure in the projection exposure apparatus. A method for correcting a focusing error of a focusing mechanism caused by a change over time in environmental conditions after the first standard is set, and using a focus detection plate having a small light-transmitting window for a substrate to be exposed. A light-shielding pattern having a minute light-transmitting region is provided on a photomask, and the light-shielding pattern is provided on the substrate stage in parallel with the exposure surface.
Around the time when the reference is set, the light beam from the small light transmission area by the projection optical system passes through the small light transmission window due to the movement of the focus detection plate by the substrate stage and the movement of the photomask parallel to the pattern surface of the photomask. Position of the focus detection plate so that the intensity becomes maximum and the incident light beam of the focusing optical system irradiates the vicinity of the minute light transmitting window, and the adjustment point of the adjustment mechanism in that state is set to the second position. During the exposure operation, the position of the focus detection plate is timely adjusted, and the amount of deviation of the adjustment point of the adjustment mechanism from the second reference in that state is determined. It is configured to correct the first reference.

[Industrial applications]

The present invention includes a focusing optical system that causes a light beam to be incident on an exposure surface of a substrate to be exposed, detects reflected light thereof, and an adjustment mechanism provided in the detection unit is interlocked with Z-direction movement of a substrate stage. The present invention relates to a method for correcting the focus of projection exposure in a projection exposure apparatus.

The projection exposure apparatus is used, for example, for exposure by photolithography technology in the manufacture of semiconductor devices, and it is important to accurately perform focusing.

[Conventional technology]

FIG. 2 is a schematic side view of a projection exposure apparatus having the above-described focusing optical system.

In FIG. 2, reference numeral 1 denotes a substrate to be exposed such as a wafer;
Is a photomask (or reticle), 10 is a projection optical system, 20
Is a substrate stage, and 30 is a focusing optical system.

The projection optical system 10 is configured such that the light flux 12 from the light source 11 is
And the light flux 13 having passed through the mask pattern 4 provided on the photomask 3 is focused by the lens system 14,
An image of the mask pattern 4 is formed on the focal plane 15. Therefore, by aligning the exposure surface 2 of the substrate 1 with the focal plane 15, the mask pattern 4 can be clearly projected and exposed on the exposure surface 2.

The substrate stage 20 includes a substrate chuck 22 for holding the substrate 1 in parallel with the focal plane 15 of the exposure surface 2 of the substrate 1 and an XY table.
The XY table 21 can move the substrate 1 in the XY direction parallel to the exposure surface 2, and the substrate chuck 22 can move the substrate 1 in the Z direction perpendicular to the exposure surface 2. The exposure plane 2 is made to coincide with the focal plane 15 in an appropriate state.

The focusing optical system 30 detects that the incident light beam 32 from the light source 31 irradiates the exposure surface 2 and detects the reflected light 33, and the adjusting mechanism 35 provided in the detecting means 34 moves the substrate stage 20 in the Z direction. Linked. By changing the adjustment point of the adjustment mechanism 35, the position of the exposure surface 15 in the Z direction can be set to a position corresponding to the change of the adjustment point. Used for focusing to 15. The incident light beam 32 has such a long wavelength that the photosensitive agent on the exposure surface 2 is not exposed to light, so that the substrate 1 is not exposed during focusing.

That is, while exposing the substrate 1 by changing the Z-direction movement of the substrate stage 20 in steps, the adjusting mechanism 35 is provided for each step.
Check the adjustment point of. Next, a step for obtaining the sharpest exposure image and optimal focusing from the developed substrate 1 is determined, and the adjustment point in the step is set as a reference A for focusing. Do the above before the exposure work,
During the exposure operation, focusing can be performed by adjusting the adjustment point of the adjustment mechanism 35 to the reference A.

[Problems to be solved by the invention]

However, the projection exposure apparatus uses a projection optical system due to temporal changes in environmental conditions such as temperature, pressure, and humidity.
A change occurs in the refractive index of the optical path of the light beam 13 at 10, and the position of the focal plane 15 moves in the Z direction over time.

It is only necessary that the focusing by the focusing optical system 30 follow this movement, but desired tracking cannot be performed because the optical path of the focusing optical system 30 is different from the optical path of the projection optical system 10.

For this reason, if the environmental condition changes after the reference A is set, the exposure surface 2 positioned by the above-mentioned focusing is shifted from the focusing surface 15 and the focusing is not accurately performed. There is.

As a measure to solve this problem, it is conceivable to set the reference A frequently. However, setting the reference A takes a lot of time as described above to reduce the operation rate of the projection exposure apparatus. Therefore, this measure is not practical.

[Means for solving the problem]

The above problems are caused by a projection optical system for projecting the pattern of the photomask onto the substrate to be exposed, a substrate stage for moving the substrate to be exposed in the XY direction parallel to the exposure surface and the Z direction perpendicular to the exposure surface, and the exposure surface of the exposure substrate. And an adjusting mechanism provided in the detecting means is provided with a focusing optical system interlocked with the Z-direction movement of the substrate stage to change the Z-direction movement of the substrate stage. The state of the substrate stage at which the focusing is optimal is determined from the exposed substrate, and the adjustment point of the adjustment mechanism in that state is set as a first reference. During the exposure operation, the adjustment point of the adjustment mechanism is determined as the first point. In a projection exposure apparatus that performs focusing by adjusting to a reference 1, a focus detection plate having a fine light transmitting window is provided on a substrate stage in parallel with an exposure surface of a substrate to be exposed, and a fine light transmitting area is provided. A light-shielding pattern having the following pattern is provided on the photomask. Around the setting of the first reference, the movement of the focus detection plate by the substrate stage and the movement of the photomask parallel to the pattern surface of the photomask cause minute light transmission by the projection optical system. The position of the focus detection plate is adjusted so that the light flux from the region passes through the small light-transmitting window and its intensity is maximized, and the incident light beam of the focusing optical system irradiates the vicinity of the small light-transmitting window, In this state, the adjustment point of the adjustment mechanism is set as a second reference. During the exposure operation, the position of the focus detection plate is timely adjusted, and the second reference of the adjustment point of the adjustment mechanism in the state is set. Is solved by the focusing correction method of the present invention in which a shift amount is obtained from the first reference and the first reference is corrected based on the shift amount.

[Action]

 The first criterion is the criterion A described above.

In addition, if the position of the focus detection plate is adjusted, the focus detection plate matches the focal plane of the projection exposure system. Therefore, the second criterion is that when the focus detection plate is regarded as the exposure surface of the substrate to be exposed. It is an adjustment point of the adjustment mechanism that optimizes focusing,
At the time when the first reference is set.

Since the above-mentioned shift amount is a shift amount of the second reference in accordance with a change in environmental conditions that occurs after the first reference is set, if the first reference is corrected with this shift amount, the second shift This is equivalent to resetting the standard of 1.

Needless to say, since the above-mentioned deviation amount can be obtained in a very short time by adjusting the position of the focus detection plate, the operation rate of the projection exposure apparatus hardly decreases even if it is performed frequently.

Thus, the focusing by the focusing optics can follow the changes and is accurate.

〔Example〕

Hereinafter, an embodiment of focus adjustment according to the present invention will be described with reference to the side view of FIG. The same reference numerals indicate the same objects throughout the drawings.

In FIG. 1, first, a focus detection plate 42 having a small light transmitting window 41 having a size of, for example, about 1 μm is connected to the exposure surface 2 of the substrate 1.
To the side of the substrate chuck 22 in parallel with
A photodetector 43 composed of, for example, a photomultiplier is provided so that the intensity of a light beam that has passed through the minute light transmitting window 41 from the projection exposure system 10 side can be detected. In the embodiment, a reflecting mirror 44 is arranged between the light detecting window 43 and the minute light transmitting window 41 for convenience of arrangement of the light detector 43. The focus detection plate 42 moves in the Z direction with the movement of the substrate stage 20 in the Z direction, and always keeps a constant distance from the exposure surface 2 in the Z direction.

The minute light-transmitting window 41 is formed by forming a light-shielding film on a transparent substrate or a light-shielding thin plate as a main body of the focus detection plate 42, and forming a minute opening in the light-shielding film or the thin plate.

The photomask 3 is provided with a light-shielding pattern 6 having a small light-transmitting region 5 having a size of about 1 μm, for example, beside the mask pattern 4.

Then, the movement of the substrate stage 20 in the XYZ directions causes the position of the focus detection plate 42 in the Z direction to be in the vicinity of the focal plane 15 of the projection optical system 10, and the incident light beam 32 of the focusing optical system 30 causes the minute light transmitting window to move. The focus detection plate 42 is positioned so as to irradiate the vicinity of 41, and the center of the light flux 13a from the small light transmitting region 5 by the projection optical system 10 is moved by the movement parallel to the mask pattern 4 surface of the photomask 3. With the photomask 3 positioned so as to pass through the center of the light window 41, the focus detection plate 42 is moved so that the intensity of the light beam 13a passing through the minute light transmitting window 41 is maximized by the Z-direction movement of the substrate stage 20. Can be located.
In this state, the focus detection plate 42 matches the focal plane 15. Here, the above state is referred to as “positioning of the focus detection plate 42”.

Then, in the focusing optical system 30, the adjustment point of the adjustment mechanism 35 at the time when the position of the focus detection plate 42 is adjusted can be confirmed.

Under the above circumstances, the standard A mentioned above (first standard)
The correction of the focusing with respect to the time-dependent change of the environmental condition after setting is performed as follows.

That is, when the reference A of the adjustment point of the adjustment mechanism 35 is set,
At about the same time, the position of the focus detection plate 42 is adjusted, and the adjustment point of the adjustment mechanism 35 in that state is set as a reference B (second reference).

During the exposure operation, the position of the focus detection plate 42 is adjusted in a timely manner, the deviation amount α of the adjustment point of the adjustment mechanism 35 from the reference B in that state is obtained, and the adjustment mechanism 35 is used for focusing.
When the adjustment point is adjusted to the reference A, the adjustment point is shifted from the reference A by the shift amount α. This deviation α is based on the reference A
Corresponds to the amount of movement of the focal plane 15 in the Z direction due to a change in the environmental condition after the setting of the focus condition. Thus, the focusing as described above corrects the change in the environmental condition and shifts the exposure surface 2 to the focal plane 15.
To match.

Needless to say, since the deviation amount α can be obtained in a very short time by adjusting the position of the focus detection plate 42, the operation rate of the projection exposure apparatus hardly decreases even if it is performed frequently.

In the above-described embodiment, the light beam transmitted through the minute light transmitting window 41 is guided to the light detector 43 by the reflecting mirror 44. However, if possible, the reflecting mirror 44 is removed and the light The photodetector 43 may be disposed at any position by using an optical fiber instead of the reflecting mirror 44.

〔The invention's effect〕

As described above, according to the configuration of the present invention, a projection optical system that projects a pattern of a photomask onto a substrate to be exposed, and a substrate stage that moves the substrate to be exposed in the XY direction parallel to the exposure surface and the Z direction perpendicular to the exposure surface And a focusing optical system that causes a light beam to be incident on the exposure surface of the substrate to be exposed and detects the reflected light thereof, and an adjusting mechanism provided in the detection means is interlocked with the Z direction of the substrate stage. The state of the substrate stage at which focusing is optimal is determined from the substrate to be exposed which has been exposed by changing the Z direction movement, and the adjustment point of the adjustment mechanism in that state is set as the first reference. In a projection exposure apparatus that performs focusing by adjusting an adjustment point of an adjustment mechanism to a first reference, a focus adjustment mechanism generated with a change over time in environmental conditions after the first reference is set. It is possible to easily correct the misalignment, almost without lowering the operating rate of the projection exposure apparatus, there is an effect which makes it possible to maintain accurate focusing.

[Brief description of the drawings]

 FIG. 1 is a side view illustrating an embodiment, and FIG. 2 is a schematic side view of a projection exposure apparatus. In the figure, 1 is a substrate to be exposed, 2 is an exposure surface, 3 is a photomask, 4 is a mask pattern, 5 is a small light transmitting area, 6 is a light shielding pattern, 10 is a projection optical system, 13 and 13a are light beams, and 14 is a lens. System, 15 is the focal plane, 20 is the substrate stage, 21 is the XY table, 22 is the substrate chuck, 30 is the focusing optical system, 32 is the incident light beam, 33 is the reflected light, 34 is the detecting means, 35 is the adjusting mechanism, 41 Is a small light transmitting window, 42 is a focus detection plate, 43 is a light detector, and 44 is a reflecting mirror.

Claims (1)

(57) [Claims] 1. A projection optical system for projecting a pattern of a photomask onto a substrate to be exposed, and a substrate to be exposed being parallel to the exposure surface.
A substrate stage that moves in the XY direction and a Z direction that is perpendicular to the substrate stage, and a reflection mechanism that irradiates a light beam on the exposure surface of the substrate to be exposed and detects the reflected light, and an adjustment mechanism provided in the detection means moves the substrate stage in the Z direction. An interlocking focusing optical system is provided to determine a state of the substrate stage at which the focusing is optimal from a substrate to be exposed which has been exposed by changing the movement of the substrate stage in the Z direction. A projection exposure apparatus that performs focusing by adjusting the adjustment point of the adjustment mechanism to the first reference during the exposure operation, wherein a focus detection plate having a small light-transmitting window is provided on the substrate to be exposed. Provided on the substrate stage in parallel with the exposure surface, and provided on the photomask with a light-shielding pattern having a small light-transmitting region, and before and after the setting of the first reference, focus detection by the substrate stage By the movement of the plate and the movement of the photomask parallel to the pattern surface of the photomask, the luminous flux from the small light-transmitting region by the projection optical system passes through the small light-transmitting window to maximize its intensity, and is incident on the focusing optical system. The position of the focus detection plate is adjusted so that the light beam irradiates the vicinity of the minute light transmitting window, and the adjustment point of the adjustment mechanism in that state is set to the second position.
During the exposure operation, the position of the focus detection plate is timely adjusted, and the second adjustment point of the adjustment mechanism in that state is adjusted.
A deviation amount from the reference, and correcting the first reference based on the deviation amount.