Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2002-07-31
2004-03-30
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S548000
Reexamination Certificate
active
06713747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light exposure apparatus and method such as a light exposure apparatus and method used for manufacturing semiconductors, liquid crystal display elements or the like by means of a photolithographic process, and more particularly to a so-called slit-scanning type light exposure apparatus for successively exposing the pattern of a mask on light-sensitive substrates by scanning the mask and the photosensitive substrates in synchronism in a slit-like illuminating area.
2. Related Background Art
Upon manufacturing semiconductors or liquid crystal display elements by means of a photolithographic process, a projection light exposure apparatus is used which exposes the pattern of photomask or a reticle (hereinafter generally referred to as the “reticle”) on substrates (wafers, glass plates or the like) coated with photosensitive material through a projecting optical system. Conventionally, a stepper is mainly used as a projection light exposure apparatus to manufacture semiconductors. The stepper is a projection light exposure apparatus which successively totally transcribes the pattern image of a reticle pattern images in shot areas in a step and repeat way.
However, a so-called slit-scanning type projection light exposure apparatus has come to be developed, which will be described briefly.
In the slit scanning type projection light exposure apparatus, a reticle is scanned at a speed V in a predetermined scanning direction in an illuminating area having an elongated rectangular shape, a circular shape or a hexagonal shape (hereinafter generally referred to as a “slit shape”), wafers are scanned at a speed &bgr;·V (where &bgr; is the projection magnification of a projection optical system) in a direction conjugate with the scanning direction of the reticle in a light exposure area conjugate with the illuminating area and the projection optical system, and thus pattern images of the reticle are successively exposed and transcribed in exposure fields (shot areas) on the wafers.
The reasons why attention is paid to the slit scanning type light exposure apparatus are as follows:
First, as patterns of semiconductor devices have recently become finer and finer and the size of the devices have become larger and larger, much larger projection optical systems have been required. Thus, the manufacturing cost of the apparatus has become much higher and the size of the apparatus has also become much larger, reducing applicability of the apparatus to manufacture of semiconductors.
Secondly, as the device pattern has become finer and finer, distortions, flatness and astigmatism of the projection image of the projection optical system have come to be very near to their limits, and thus high operational performance required for the stepper cannot be obtained.
With the slit scanning light exposure method, light exposure is performed by the use of only a slit-like light exposure area in the projection optical system. When, therefore, the same projection optical system is used, the field size of the slit scanning type projection light exposure apparatus can be made larger by 2
1/2
times than that of the stepper. In other words, with the same field size as the stepper, the slit scanning type projection light exposure apparatus can employ an optical system ½
1/2
times smaller than the stepper, improving a lens characteristic more than the stepper.
Thirdly, in a case where a reflecting and refracting optical system having a concave reflecting mirror is used as a projection optical system, areas in the light exposure field in which good optical characteristics can be obtained are limited to narrow circular arc portions. Thus, a slit scanning light exposure system is required for exposing the whole pattern of the reticle on wafers.
In the general projection light exposure apparatus, a suitable amount of exposure light (exposure light energy) is selected depending on light sensitivity of photoresists coated on wafers. Under the condition where continuous light is used as exposure light in the stepper, the amount of exposure light is controlled in accordance with the illuminating time length of the exposure light. When pulse light is used, on the other hand, the amount of the exposure light is controlled by the number of pulses of the illuminating light.
SUMMARY OF THE INVENTION
The control of the amount of exposure light is also necessary in the slit scanning type projection light exposure apparatus. When, for example, continuous light is used as exposure light in this type of prior apparatus, the width of the slit-shaped illuminating area in its scanning direction is made constant, and the amount of exposure light on every wafer is controlled to a moderate value by adjusting the scanning speeds of the reticle and the wafers and the exposure light reduction rate.
When, however, a pulse light source
is used for providing pulse light e.g., an excimer laser or the like in a slit scanning type projection light exposure apparatus, energy variations of exposure light pulses are large. In consequence, it is difficult in the prior slit scanning type light exposure apparatus to set the accumulated values of the energies for respective pulses to a value within the allowed value.
It is accordingly an object of the present invention to obtain a required control accuracy for the amount of exposure light in spite of a small number of measurements of the generation of the pulse light when a pulse light source which produces light pulses having large energy variations is used.
In order to achieve this object of the present invention, a light exposure apparatus according to one aspect of the present invention including an illuminating optical system for projecting light pulses from a light source on a mask formed with a pattern, a mask stage for carrying the mask, a substrate stage for carrying a photosensitive substrate and a driving system for scanning the mask stage and the substrate stage in synchronism with each other so that the pattern is exposed on the photosensitive substrate, comprises:
a stop having two edges for limiting the shape of an illuminating area on the mask in the illuminating system to a predetermined shape;
an edge adjusting portion for adjusting position or positions of one or both of the two edges with respect to a scanning direction of the mask;
an exposure light energy detecting portion for detecting exposing energy per light pulse;
a calculating portion for calculating, in response to information from the exposure light energy detecting portion, accumulated amount of exposure light per each of accumulated exposure light calculating zones formed by dividing the light exposure area on the photosensitive substrate at predetermined intervals in a scanning direction of the photosensitive substrate; and
a control portion for controlling the edge
adjusting portion in response to a difference between a predetermined accumulated amount of exposure light and a calculated amount of exposure light.
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Miles & Stockbridge P.C.
Nikon Corporation
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