Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-10-20
2002-11-19
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S067000, C355S071000, C356S399000
Reexamination Certificate
active
06483571
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an exposure apparatus and an exposure method, and more particularly, to an exposure apparatus and an exposure method used in a lithography process for fabricating semiconductor integrated circuits, liquid crystal display device, thin film magnetic heads, or the like.
To fabricate devices, such as a semiconductor integrated circuit, a liquid crystal display device, and a thin film magnetic head, optical lithography is generally employed to form a circuit pattern on a substrate. During optical lithography, a exposure operation is performed, for example, in the following manner. A mask (original plate), on which a circuit pattern is formed, is arranged in an exposure apparatus and illuminated by an exposure light from a light source. The illuminated pattern is projected and the pattern of the mask is transferred onto the substrate, to which the photoresist has been applied, via an optical projection system.
A step and repeat (one-shot exposure) process is an example of such projection transcription. In the step and repeat process, shot areas, defined on the substrate, are moved in a stepped manner (stepping) and the circuit pattern is repeatedly exposed and transferred onto each of the shot areas. A step and scan (scanning exposure) process, in which the mask is moved together with the substrate while repeatedly exposing and transferring the circuit pattern onto the each of the shot areas, is also known.
An exposure apparatus, which projects and transfers a circuit pattern of a reticle onto a wafer, to fabricate a semiconductor integrated circuit will now be discussed.
In the exposure apparatus, the reticle and the wafer are arranged respectively on a reticle stage and a wafer stage. To properly project a pattern image from the reticle to the wafer or onto a circuit pattern already formed on the wafer, fine adjustments to the relative position and direction (rotation) of the reticle and the wafer must be made. In this case, the required position measurement, and subsequently performed position correction, or the required positioning, which includes both position measurement and position correction, are referred to as alignment.
The alignment includes reticle alignment and wafer alignment. The exposure apparatus has a reticle alignment sensor for measuring the position of a reticle alignment mark, which is formed together with the circuit pattern on the surface of the reticle. A wafer alignment sensor, which measures the position of a wafer alignment mark formed together with a circuit pattern on the surface of the wafer, is also provided. An alignment reference plate used to measure the relative position between the projected image of the reticle pattern and each of the shot areas on the wafer (including a base line amount of the wafer alignment sensor) is provided on the wafer stage. The reference plate has a reference mark that is used to perform position measurement with the two alignment sensors.
During reticle alignment, for example, the reticle alignment mark on the reticle surface is projected onto the reference plate, and the positional relationship between the reference mark and the reticle alignment mark is measured by a reticle alignment sensor. During wafer alignment, for example, the position of the reference mark and the position of the wafer alignment mark of at least three, for example, five to ten, shot areas, are measured using the wafer alignment sensor. The base line amount is then determined from the detection result of the reticle alignment sensor and the reference mark detection result of the wafer alignment sensor. Further, based on the wafer alignment detection result of the wafer alignment sensor, the position of each shot area on the wafer to which the reticle pattern is to be transferred is calculated as described in Japanese Unexamined Patent Publication No. 61-44429 and the corresponding U.S. Pat. No. 4,780,617. The information of the relative position between the reticle pattern projection image and each shot area obtained in this manner is used to move the reticle stage and the wafer stage so that the positions of the reticle and the wafer are matched in a two dimensional manner. When each wafer undergoes exposure for the first time, a circuit pattern and a wafer alignment mark are not yet formed on the wafer surface. Thus, the above wafer alignment is not performed. Further, when performing a TTR (Trough The Reticle) process, during which the wafer alignment sensor detects the reticle alignment mark and the wafer alignment mark, the detection of the reference mark, that is, the calculation of the base line amount is not necessary.
In a one shot exposure type exposure apparatus, at least one set of symmetrical reticle alignment marks are provided. In a scanning exposure type exposure apparatus, to reduce the influence of mark writing errors and compensate for mark measurement errors, multiple sets of the symmetrical marks are arranged and the positions of the multiple marks are measured.
Normally, an integrated circuit is formed from plural layers. The fabrication process includes the formation of a field oxide film, the dispersion of impurities, the formation of a gate oxide film, the formation of an insulating layer, and the formation of a wiring layer. The optical lithography process is repeatedly performed especially during the oxide layer formation process and the wiring layer formation process.
Since the pattern formed on the reticle differs for each process, the reticle must be changed when different processes are performed with the same exposure apparatus. After the reticle is changed and prior to exposure, reticle alignment must be performed to position the reticle at its predetermined position. Whenever exposure of the entire surface of a single wafer is completed, the wafer is exchanged with the next wafer, and prior to exposure, the new wafer must undergo wafer alignment to be positioned at its predetermined position.
Especially, during reticle alignment in the scanning exposure type exposure apparatus, the time for measuring the multiple sets of the reticle alignment marks is long. This results in a shortcoming in which the throughput of the exposure apparatus decreases significantly as the frequency of reticle exchanges increases.
Further, in recent years, to finely narrow the line widths of the circuit pattern in accordance with further integration of integrated circuits, for example, double exposure is performed to synthesize two types of patterns formed respectively on two reticles and form a pattern for a single layer of the wafer. Such double exposure inevitably increases the number of times the reticle is exchanged and further decreases the throughput of the exposure apparatus.
As described below, there are multiple types of double exposure.
(A) Exposure is performed by setting different optimal illumination conditions for a first reticle having, for example, an isolated line pattern, and for a second reticle having, for example, an L/S (line and space) pattern.
(B) Exposure is performed by arranging a first reticle and a second reticle, each having only an isolated line pattern, so that the isolated lines of the first reticle and the isolated lines of the second reticle are lined alternately to form an L/S pattern.
(C) A first reticle having an L/S pattern is first exposed, and then, a second reticle having a protection pattern and a thinning pattern is exposed. As a result, the L/S pattern corresponding to the protection pattern remains, and the L/S pattern corresponding to the thinning pattern is thinned thereby forming the isolated pattern.
(D) A first reticle having a phase shifter is first exposed, and then the residual areas at the peripheral portion of the phase shifter is exposed by a reticle and eliminated.
In types (A) and (B), the order of using the first and second reticles can be changed. However, in types (C) and (D), the second reticle must be exposed after the first reticle.
In this manner, during double exposure, the reticle must be exchanged at leas
Adams Russell
Kim Peter B.
Nikon Corporation
Synnestvedt & Lechner LLP
LandOfFree
Exposure apparatus and method for transferring a pattern... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exposure apparatus and method for transferring a pattern..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exposure apparatus and method for transferring a pattern... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2963016