Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2002-06-05
2004-09-07
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000
Reexamination Certificate
active
06788391
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an illumination device used in a scanning projection exposure apparatus, an exposure apparatus to which this illumination device is applied, and an exposure method for manufacturing semiconductor chips such as ICs and LSI circuits and devices such as liquid crystal elements, magnetic heads and CCDs, etc.
BACKGROUND OF THE INVENTION
The packing density of semiconductor devices such as ICs and LSI circuits is ever increasing and this has been accompanied by marked progress in techniques for micromachining semiconductor wafers. Examples of projection exposure apparatus at the center of such micromachining technology are a one to one (magnification I) projection exposure apparatus (mirror projection aligner), which performs exposure while scanning a mask and a photosensitive substrate with respect to a one to one magnification mirror having an arcuate exposure area, and a demagnifying projection exposure apparatus (stepper), which forms the pattern image of a mask on a photosensitive substrate by refraction optics and exposes the photosensitive substrate by a step-and-repeat method.
A step-and-scan scanning projection apparatus that provides a high resolving power and is capable of enlarging image size has recently been proposed. This scanning exposure apparatus uses short-wavelength light as the light source and emits the light in pulses. Various examples of these apparatus that seek to raise resolving power by using an excimer laser, for instance, have been proposed. In a scanning exposure apparatus that uses a pulsed light source to emit light in pulsed form, illumination is carried out uniformly so as to avoid non-uniform exposure while holding constant the amount of exposure on the illuminated surface. In order to achieve this, it is vital to establish an appropriate relationship between the pulsed light-emission timing or pulsed light-emission interval of the pulsed light source and the traveling velocity of the illuminated surface.
When scanning exposure is performed in the conventional scanning exposure apparatus, an acceleration period, which is the time required for a stage to reach a constant velocity starting from rest, and a deceleration period, which is the time required for the stage to come to rest starting from the constant velocity, are not used for the pulsed-light emission, and therefore these time periods represent wasted time as far as the overall time needed for the pulsed emission is concerned. As a consequence, the efficiency of the operation is poor and throughput declines. Further, in addition to a distance needed for a reticle stage and wafer stage to traverse the illumination area, distance for acceleration and deceleration also must be assured beforehand in the scanning zone. A problem which arises is a longer stroke necessary for the reticle and wafer stages. For this reason, the specification of Japanese Patent Application Laid-Open No. 9-223662 discloses a method of improving throughput. Specifically, when the surface to be illuminated is illuminated with pulsed light from a light source, the light source is made to emit pulsed light at a frequency proportional to the traveling velocity of the illuminated surface by emission control means, and exposure is carried out even during acceleration and deceleration of the stages, thereby improving throughput.
With a slit-scan exposure method, the reticle and substrate are scanned and therefore the phase at which a spectrum pattern appears varies with time. The direction in which the reticle and substrate are scanned, therefore, becomes a first problem. In a case where joint use is made of a rotating prism employed when a full-wafer exposure method is carried out, a second problem which arises is how to exercise control so as to rotate the prism in conformity with the scanning direction as well as the scanning velocities of the reticle and substrate. With the slit-scan exposure method, however, the phase at which a spectrum pattern appears varies with time owing to the scanning of the reticle and substrate. In order to avoid this, the specification of Japanese Patent Application Laid-Open No. 6-349701 discloses an example in which phase varying means is provided for varying, on a per-light-pulse basis, the phase of the spectrum pattern of pulsed light in the illumination area in accordance with the relative scanning velocity of the illumination area and mask and the relative pitch, in the scanning direction, of the spectrum of the pulsed light in the illumination area. In a case where exposure is carried out during stage acceleration and deceleration, as mentioned above, it is required that the rotating speed of the rotating prism be varied in conformity with the stage acceleration/deceleration pattern. However, since the rotating prism has a large inertia and is placed in the illuminating optical system, a small-size or hollow motor is used to drive the prism and this results in major space-related limitations. As a consequence, it is difficult to adjust angle of rotation in conformity with the stage acceleration/deceleration pattern.
SUMMARY OF THE INVENTION
The present invention has been proposed to solve the aforementioned problems of the prior art and its object is to provide an illumination device and a scanning exposure apparatus so adapted that when a surface to be illuminated is illuminated with pulsed light from a pulsed light source that emits the pulsed light, suitably sets pulse conditions, such as the pulsed light-emission timing or pulsed light-emission interval of pulses emitted from the pulsed light source, rotational speed of the rotating prism and travel conditions such as the traveling velocity and traveling distance of the illuminated surface, whereby the illuminated surface can be scanned and illuminated highly precisely without illumination non-uniformity (exposure non-uniformity) even in exposure during acceleration and deceleration, thus making it possible to manufacture semiconductor devices at a high throughput.
According to a first aspect of the present invention, the foregoing object is attained by providing an illumination device for a scanning exposure apparatus for carrying out exposure even when a movable stage is being accelerated and decelerated, comprising illumination-distribution varying means for temporarily varying the illumination distribution of an illumination unit that is for performing the exposure,
wherein the illumination-distribution varying means has a function for varying the temporary change of the illumination distribution for conformity with a pattern for driving the movable stage.
As a result, a surface to be illuminated can be scanned and illuminated highly precisely without illumination non-uniformity (exposure non-uniformity) even in exposure during acceleration and deceleration. This makes it possible to manufacture semiconductor devices at a high throughput.
According to a second aspect of the present invention, the foregoing object is attained by providing an illumination device for a scanning exposure apparatus for carrying out exposure even when a movable stage is being accelerated and decelerated, comprising:
an optical member for temporarily varying the illumination distribution of an illumination unit that is for performing the exposure; and
means for driving the optical member,
wherein a pattern for driving the optical member is decided based upon results of measuring an illumination distribution that conforms to an acceleration/deceleration pattern of the stage.
As a result, a change in illumination distribution with time can be optimized in simple fashion.
According to a third aspect of the present invention, the driving pattern of the optical member may be fixed within a shot.
According to a fourth aspect of the present invention, the foregoing object is attained by providing an illumination device for a scanning exposure apparatus for carrying out exposure even when a movable stage is being accelerated and decelerated, comprising illumination-distribution varying means for temporarily var
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Henry Hung
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