Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-09-01
2003-03-04
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S055000, C324S765010, C250S491100, C356S400000
Reexamination Certificate
active
06529263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a position detection apparatus for detecting the surface position of an object, an exposure apparatus having the position detection apparatus, a control method therefor, and a device manufacturing method.
The position detection apparatus of the present invention can be applied to, e.g., a surface position measuring apparatus for measuring a small distance by an electrostatic scheme. The exposure apparatus of the present invention can be applied to, e.g., a slit-scan exposure apparatus.
2. Description of the Related Art
As surface position detection apparatuses for semiconductor exposure apparatuses, position detection apparatuses which obliquely irradiate a semiconductor wafer, placed at a position where a mask pattern is to be transferred through a projecting lens, with light from a projector, and detect light obliquely reflected by the surface of the semiconductor wafer to detect the surface position are widely used.
FIG. 9
is a schematic view of such a conventional surface position detection apparatus.
As shown in
FIG. 9
, illumination light emitted from the output end of an optical fiber
9
illuminates a pattern forming plate
11
through a condenser lens
10
. The illumination light passing through the pattern forming plate
11
is projected onto the exposure surface of a wafer
5
through a lens
12
, mirror
13
, and projection objective lens
14
, so the image of the pattern on the pattern forming plate
11
is formed on the exposure surface of the wafer
5
from an oblique direction with respect to an optical axis EX. The illumination light reflected by the wafer
5
is reprojected onto the light-receiving surface of a light-receiving device
18
through a condenser objective lens
15
, mirror
16
, and imaging lens
17
. The image of the pattern on the pattern forming plate
11
is formed on the light-receiving surface of the light-receiving device
18
. When the wafer
5
moves in the vertical direction, the image of the pattern moves to the left or right on the light-receiving surface
18
. When an arithmetic circuit
19
calculates the position of the pattern, the surface position of the wafer
5
can be detected.
In the exposure apparatus, such a focus detection system has a plurality of measurement points in one shot (area to be exposed) of a wafer. A surface position z and tilt component (tilt) of the measurement shot are calculated by comparing the measurement results at the plurality of measurement points within the X-Y plane. Highly accurate focus position control is achieved by controlling a Z·tilt stage
8
.
In recent years, a slit-scan exposure apparatus which exposes while holding a reticle and wafer conjugate with a projecting lens and scanning both the reticle and wafer to increase the exposure area has received a great deal of attention. In this exposure apparatus, a focus detection signal is directly used as a closed loop signal for controlling the posture of the stage. As the signal, a signal as smooth as possible, i.e., a signal averaged for an exposure area is necessary.
However, since the slit light projection scheme cannot measure position while uniformly illuminating a measurement surface of interest, the measurement areas always become discrete. In addition, experiments conducted by the present inventors have revealed that when a thin slit-like light beam irradiates the edge portion of a step, the reflected light is scattered to generate a large focus detection error.
This problem can be solved by using an electrostatic sensor as a focus detection sensor. An electrostatic sensor is more advantageous as a focus detection sensor of a slit-scan exposure apparatus than an optical sensor because it can almost uniformly average within the detection area, does not generate any focus detection error at an edge portion, and has a high response speed.
FIG. 10
is a view showing the principle of distance measurement by an electrostatic sensor. Referring to
FIG. 10
, a flat electrode
30
used for measurement is arranged near an object
31
to be measured. A high-frequency voltage is applied from an oscillator OS to the flat electrode
30
. An ammeter AM is connected between the flat electrode
30
and oscillator OS. The ammeter AM and a measurement device
32
connected to the ammeter AM measure the magnitude of an AC current flowing to the flat electrode
30
. The current measurement result is input to an arithmetic circuit
33
. A distance d between the flat electrode
30
and the object
31
to be measured is measured by arithmetic processing by the arithmetic circuit
33
.
Although the above-described surface position detection apparatus can obtain high accuracy in detecting the surface position of a substrate having a chip layout (pattern of a chip) compatible with the apparatus, no high accuracy can be obtained in detecting the surface position of a substrate having a chip layout incompatible with the apparatus.
In addition, when the shape of the wafer surface changes to a shape incompatible with the apparatus because of the repeated lithography process, the above-described surface position detection apparatus cannot accurately detect the surface position of the substrate.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has as its object to accurately detect the surface position of an object to be measured independently of the surface state of the object.
According to the first aspect of the present invention, there is provided a position detection apparatus for detecting a position of an object surface in a direction normal thereto, comprising at least two detection sections, a selection section for selecting at least one detection section from the at least two detection sections, and a measurement device for measuring the position of the object surface in the direction normal thereto using the detection section selected by the selection section.
In the position detection apparatus according to the first aspect, preferably, for example, each of the at least two detection sections has an electrode, and the measurement device applies an electrical signal containing an AC component to the electrode of the selected detection section to measure a distance between the electrode and the object surface.
In the position detection apparatus according to the first aspect, for example, the electrodes of the at least two detection sections preferably oppose different portions of the object surface.
In the position detection apparatus according to the first aspect, for example, the electrodes of the at least two detection sections are preferably in one plane.
In the position detection apparatus according to the first aspect, for example, the electrodes of the at least two detection sections are preferably concentric with each other.
In the position detection apparatus according to the first aspect, for example, the selection section preferably alternatively selects one detection section from the at least two detection sections.
In the position detection apparatus according to the first aspect, for example, the selection section determines the number of detection sections to be used for measurement.
In the position detection apparatus according to the first aspect, for example, the selection section preferably selects at least one detection section in accordance with a shape of the object surface.
In the position detection apparatus according to the first aspect, for example, preferably, the apparatus comprises at least two sets of the at least two detection sections, the selection sections, and the measurement devices, and further comprises an arithmetic section for calculating a tilt of the object surface on the basis of a measurement result by the at least two measurement devices.
According to the second aspect of the present invention, there is provided an exposure apparatus having a projecting lens for projecting a pattern onto a substrate, a stage which moves while supporting the substrate, a position detect
Hasegawa Masanobu
Oguri Hisaaki
Sasaki Toyoshige
Brown Khaled
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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