Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-07-01
2002-07-30
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C356S399000, C355S053000
Reexamination Certificate
active
06426508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface-position detection device and a scanning projection exposure apparatus using the device. More particularly, the invention precisely and easily adjusts each exposure region of a semiconductor wafer (substrate) mounted on a wafer stage to a focal plane of a projection lens system (projection optical system) in a step-and-repeat or step-and-scan projection exposure apparatus for manufacturing semiconductor devices.
2. Description of the Related Art
At present, circuit patterns are becoming finer as the degree of integration of super LSIs (large-scale integrated circuits) increases, so that projection lens systems used in respective projection exposure apparatuses tend to have larger NAs (numerical apertures). As a result, allowable focal depths of respective lens systems in a circuit-pattern transfer process are becoming smaller. In addition, the sizes of areas to be exposed by projection lens systems are becoming larger.
Accordingly, in order to realize excellent transfer of a circuit pattern over the entire large-size region to be exposed, it is necessary to accurately position the entire region (shot) to be exposed of a wafer within the allowable focal depth of the projection lens system.
For that purpose, it is important to precisely detect the position and inclination of the surface of a wafer with respect to the focal plane, i.e., the plane where the image of a circuit, pattern on a reticle is focused, of a projection lens system, and adjust the position and inclination of the surface of the wafer.
Recently, there is an increasing demand for a scanning projection exposure apparatus which can increase an exposure region and an NA while using a projection lens equivalent to that used in a stepper.
In such a scanning exposure apparatus, in order to realize excellent transfer of a circuit pattern of a reticle over the entire region to be exposed, the position and inclination of the surface of a wafer, on which the circuit pattern is to be transferred, with respect to the image of the circuit pattern (the focal plane of the projection optical system) are precisely detected in synchronization with a scanning operation, and the surface of the wafer is sequentially adjusted to the optimum imaging surface of the projection optical system by continuously performing correction driving of auto-focus/auto-leveling during scanning exposure.
For example, a method using a detection optical system in which a light beam is projected from an oblique direction onto the surface of a wafer, and deviation in a reflection point of reflected light from the surface of the wafer is detected as deviation of reflected light on a sensor, and a method in which a plurality of positions on the surface of the wafer are detected using a gap sensor, such as an air microsensor, an electrostatic capacity sensor, or the like, and the surface position of the wafer is obtained based on the result of the detection are known as methods for detecting the height and the position of the surface of the wafer in the above-described exposure apparatus.
In a surface-position detection method in a scanning projection exposure apparatus in which the height of a wafer is continuously detected by performing relative scanning, in consideration of ease of control, positions to be measured are arranged, taking a point of start of exposure as a reference point, by (1) obtaining the minimum control frequency in the entire surface-position detection system from (a) the detection region of a measuring sensor, (b) a sampling period corresponding to the synchronizing scanning speed during exposure and the residual vibration mode of the structure of the apparatus, and (c) the control frequency of a control system, and (2) setting a constant sampling period based on the minimum control frequency.
In actual production facilities, however, chips having various sizes are produced using shrinked plates, cut-down plates, and the like, because various finer chips are demanded. Hence, in the above-described arrangement of sampling points to be measured depending on the control system, surface-position information is uncertain at peripheral portions, particularly at a portion near the position of an end of exposure by an amount within a fixed sampling interval, resulting in the generation of local defocus.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a surface-position detection device which can precisely adjust a wafer or a photosensitive substrate to a focal plane of a projection optical system even when the size of a shot changes, a projection exposure apparatus using the device, and a device manufacturing method using the apparatus.
According to one aspect of the present invention, a surface-position detection device for detecting surface-position information of a photosensitive plate disposed near an imaging surface of a projection optical system when performing projection exposure of a pattern on a surface of an object onto the photosensitive substrate via the projection optical system by performing relative scanning between the photosensitive substrate and the object includes detection means for detecting the surface-position information within a shot region of the photosensitive substrate in a direction of an optical axis of the projection optical system, and means for causing the detection means to detect the surface-position information at a plurality of points arranged so that a first end of the plurality of points coincides with a position to start a scanning exposure and a second end of the plurality of points coincides with a position to end the scanning exposure in accordance with a size of the shot region.
In one embodiment, an interval between adjacent points of the plurality of points is variable in accordance with a length of the scanning exposure in each shot region of the photosensitive substrate.
In another embodiment, the plurality of points are arranged with a substantially equal interval making the position to start a scanning exposure substantially equivalent to the first end and the position to end the scanning exposure substantially equivalent to the second end.
In still another embodiment, the size of the shot region is individually obtained in advance for each shot region from layout information of a region to be exposed on the photosensitive substrate.
According to another aspect of the present invention, a surface-position detection device for detecting surface-position information of a wafer when performing projection exposure of a pattern on a surface of a reticle onto the wafer via a projection optical system by performing relative scanning between the wafer and the reticle includes detection means for continuously detecting the surface-position information within a shot region of the wafer in a direction of an optical axis of the projection optical system, and means for causing the detection means to detect the surface-position information at a plurality of points arranged so that a first end of the plurality of points coincides with a position to start a scanning exposure and a second end of the plurality of points coincides with a position to end the scanning exposure in accordance with a size of the shot region.
In one embodiment, the surface-position information comprises inclination of the wafer with respect to a plane perpendicular to the direction of the optical axis of the projection optical axis.
In another embodiment, an interval between adjacent points of the plurality of points is variable in accordance with a length of the scanning exposure in each shot region within the wafer.
In still another embodiment, the plurality of points are arranged with a substantially equal interval making the position to start a scanning exposure substantially equivalent to the first end and the position to end the scanning exposure substantially equivalent to the second end.
In yet another embodiment, the size of the shot region is individually obtained in advance for each shot region from
Kosugi Yuji
Yamada Yuichi
Allen Stephone B.
Fitzpatrick ,Cella, Harper & Scinto
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