Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-02-09
2002-07-16
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S005000, C430S322000, C430S396000
Reexamination Certificate
active
06420094
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photolithography which is applied for precise processing when semiconductor devices are produced, and more particularly relates to an optical exposure method used for photolithography.
When semiconductor devices such as ultra-LSIs are highly integrated and precise processing is required, manufacturers greatly rely on improvements in lithographic technology. Photolithography using light is suitable for mass production. Therefore, it is adopted for economical reasons.
2. Description of the Related Art
In order to improve resolution in optical exposure technology, it is important to increase the numerical aperture (NA) and to reduce the wavelength of light generated by a light source. On the other hand, the focal depth is reduced as NA is increased. Recently, attention has been given to a deformation illumination method (an oblique incident illumination method) which improves the critical resolution and focal depth (for example, shown in pages 28-37 of “Nikkei Micro Device” No. 82, April, 1992).
For holes in the diaphragm (the apertures) in the deformation illumination method, zonal holes and four holes symmetrical with respect to a point are well known. In a conventional illumination method, a ray of illumination light sent from a circular hole, coinciding with an optical axis, to a photomask (reticule) is vertically incident and an image is formed by three beams of light of 0, +1, and −1. However, with this deformation illumination method, the position of the diaphragm is shifted from the optical axis, so that illumination light sent from the hole is obliquely incident on the photomask, and image formation is conducted by two beams of light of 0 and +1 sent from the photomask. In a focal position, higher contrast can be provided by the conventional illumination method, however, in a defocal position, higher contrast can be provided by the deformation illumination method, so that the focal depth and resolution can be considerably improved.
In the conventional deformation illumination method, i.e., only for a simple line and space pattern, a pattern of the photomask is projected and exposed on a register with a diaphragm having the aforementioned general type of diaphragm holes. Accordingly, the illumination system does not meet the requirement of each pattern, so that the effect of oblique incidence of the deformation illumination method is not sufficient.
Also, recently, attention has been given a lithographic technology using a phase shift mask, and the following pattern forming method has been reported to be an effective technology: an unexposed portion (pattern) is used that is accompanied by a sharp decrease of optical intensity generated by a step portion (the phase of exposure light is changed by 180° by this step portion) of a phase shifter of a phase shift mask.
However, when a pattern is formed by this technology, the unexposed portion (pattern) is formed in all step portions of the phase shifter. Therefore, in many applicable fields, it is necessary to provide a process to inhibit the formation of a pattern generated by the unexposed portion generated by an unnecessary step portion of the phase shifter.
Therefore, the following techniques have been conventionally proposed to ease the sharp decrease of optical intensity: another exposure mask is put on the unnecessary unexposed portion so as to conduct an exposure operation (double exposure); and a multi-shifter (step of 90°) is provided stepwise in a step portion of the phase shifter, the pattern formation of which is not necessary.
However, in the double exposure method that has been conventionally proposed as a method to remove an unnecessary unexposed portion, it is necessary to manufacture a plurality of masks so as to conduct multi-exposures. Accordingly, it is necessary to increase the number of the mask manufacturing processes. On the other hand, it is also necessary to ensure an alignment of the double exposure, so that the throughput is lowered.
Moreover, when a multi-shifter is manufactured, a complicated and difficult process technique is required in order to provide an optically accurate multi-shifter, and further a big problem is caused when a manufactured phase shift is inspected and corrected.
In order to meet the demand of forming minute patterns, for example, attention is given to an oblique incidence illumination method disclosed in the official gazette of Japanese Unexamined Patent Publication No. 2-142111 (1990). According to this method, a ray of light that is vertically incident on a lens is incident being oblique at a predetermined angle, so that focusing is conducted using interference of light.
However, in the aforementioned conventional method, the-same light source is used for any device patterns without giving attention to the profile of the light source. Accordingly, problems are caused.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a projection exposure method with a deformation illumination system optimal for a device pattern (photomask pattern).
It is another object of the present invention to provide a method by which an unnecessary unexposed portion can be easily removed without using the aforementioned multi-exposure method or relying on the technique in which the phase shift mask having a multi-shifter is used, in the case where a pattern is formed using the unexposed portion accompanied by a sharp decrease of optical intensity caused by a step portion of the phase shifter.
It is another object of the present invention to provide an optimization method for a light source profile to obtain an optimal light source profile in accordance with a device pattern.
It is another object of the present invention to realize an optical projection exposure in which resolving power can be provided that is higher than that of the conventional phase shift mask or oblique incidence illumination.
The aforementioned object can be accomplished by an optical exposure method by which a pattern on a photomask is projected and exposed on a register on a base plate with an exposure device including a deformation illumination system composed of a light source, a diaphragm and a condenser lens, and also including a photomask and a projection lens, wherein the optical exposure method uses a ray of linear light for illumination that is parallel with a photomask pattern in a position separate from an optical axis of the exposure device (or the optical exposure method uses two rays of linear light for illumination that are symmetrical with respect to the optical axis) when the photomask pattern is a line and space pattern.
The aforementioned object can be accomplished by an optical exposure method, wherein the optical exposure method uses a ray of first linear light for illumination that is parallel with a first pattern portion in a position separate from the optical axis of the exposure system (or the optical exposure method uses two rays of first linear light for illumination that are parallel with the first pattern portion symmetrical with respect to the optical axis), the optical exposure method also uses a ray of second linear light for illumination that is parallel with a second pattern portion in a position separate from the optical axis of the exposure system (or the optical exposure method also uses two rays of second linear light for illumination that are parallel with the second pattern, two rays of second linear light being symmetrical with respect to the optical axis), when the first pattern portion of line and space, and the second pattern portion of similar line and space make a right angle with each other in the photomask pattern.
Moreover, it is preferable to use an optical exposure method in which the first linear light and the second linear light are oblique by an angle &phgr; with respect to the optical axis in a position on the photomask, and an equation 2p·sin &phgr;=&lgr; is satisfied (where p is a setting pitch of the line and space pattern on the pro
Asai Satoru
Hanyu Isamu
Haruki Tamae
Nakagawa Kenji
Arent Fox Kintner & Plotkin & Kahn, PLLC
Barreca Nicole
Fujitsu Limited
Huff Mark F.
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