Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
1999-05-20
2001-06-05
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S629000, C359S839000, C359S850000
Reexamination Certificate
active
06243209
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to optics and more specifically to an optical arrangement suitable for beam scanning lithography.
BACKGROUND
Beam scanning lithography is a well-known field, see for instance Allen, U.S. Pat. No. 5,255,051 and Allen et al., U.S. Pat. Nos. 5,327,338 and 5,386,221, describing systems which use an array of light beams (typically laser beams) and an optical system involving reflective optics for imaging a pattern onto a substrate. A typical application is for generating patterns for use in semiconductor lithography. The array of light beams is scanned across a substrate in a controlled fashion with the beams being turned on and off in order to expose a photosensitive resist on a surface of the substrate. The exposed areas are then developed, defining a pattern in the resist which is later used for other steps such as etching, etc. Such lithography machines typically use an array of laser beams often referred to as a “brush” with a number of very small diameter laser beams arranged in a line or an m×n array where m and n are integers each greater than or equal to one.
Typically the light beams are independently modulated, that is turned on or off or modulated between being on and off and so having a gray scale level of intensity. There are also known systems using light beams in which the light beams, instead of being incident on a semiconductor wafer, are incident on a semiconductor which is a photocathode. The incident light beams generate electrons ejected from the photocathode which in turn form an electron beam which in turn is used to define a pattern on, for instance, a sensitive substrate.
It is well known to provide a linear array of laser beams from a single laser; see Allen, U.S. Pat. No. 4,797,696, incorporated herein by reference in its entirety. For many types of pattern generating systems, rather than a single linear array of beams it is desirable to have a rectangular m×n array. This array is called rectangular because the beams are arranged in a shape which is rectangular in a plane perpendicular to the axis of the beams. Each individual beam in cross-section is typically circular, although this is of no particular importance to this disclosure.
It would be desirable therefore to find a simple and efficient (lossless) way to transform such an initial linear array of equal intensity light beams, for instance laser beams, into a rectangular shaped array of equal intensity beams. It is important that the transformation be essentially lossless so that the full intensity of each individual beam is preserved but it is moved, in terms of location, relative to other of the beams. It is also important that the pitch (the spacing between beam centers) be precise for accurate lithography.
SUMMARY
In accordance with this invention, a linear array of equal intensity optical beams is transformed into a rectangular array with the same number of optical beams, while keeping the intensity of each beam essentially constant. Thus an m×n array of beams is converted into an
m
2
×
2
n
array where m is an even integer and n is an integer, as described above. The basic optical component which performs this conversion is a body of material transmissive to the beams, for instance fused silica or glass, in the form of a plate having two principal parallel surfaces and a particular thickness. The front surface of the plate is partially coated with a reflective coating. The remainder of the front surface is not so coated but instead has an anti-reflective coating, thus making this portion of the front surface transmissive. The opposite surface of the plate has a reflective coating which covers that entire opposite surface.
The incident laser beams are directed from their source onto the front surface of the plate so that approximately half of them fall on the reflective portion and the remainder fall on the non-reflective portion. Obviously, the beams that fall on the reflective portion are reflected back at an angle of reflection equal to the angle of incidence. (It is to be understood that typically the angle of incidence is not 90° but it is a predetermined angle selected to achieve the purposes in accordance with this invention.) The remainder of the beams is transmitted through the anti-reflective coating and through the plate and reflects off the opposite (back) surface of the plate. These beams then are transmitted back through the plate and back out through another portion of the front surface anti-reflective coating to the exterior. The index of refraction of the plate, the thickness of the plate, and the angle of incidence of the beams on the plate are selected so that when these beams which reflect from the back surface return to the front surface they are shifted by exactly the right number of beam spacings laterally and by one beam spacing transversely. (Beam spacing refers to the center-to-center distance between adjacent beams in the array.) Thus the plate is positioned so that the beams which are incident on its back surface strike a region of the front surface that is anti-reflective coated and thereby exit the plate. After leaving the plate the two sets of beams are traveling in the same direction with the desired beam spacing and all beams are in parallel.
Several such optical elements (plates) may be arranged in series. By using for instance two such optical elements arranged in series and properly located, an initial array of, e.g., thirty-two beams by one beam is converted into a rectangular array of eight beams by four beams.
REFERENCES:
patent: 4528452 (1985-07-01), Livesay
patent: 4797696 (1989-01-01), Allen et al.
patent: 4871919 (1989-10-01), Donohue et al.
patent: 5646786 (1997-07-01), Kurtz et al.
patent: 5999320 (1999-12-01), Shirasaki
patent: 19830198 (1999-02-01), None
PCT International Search Report & Transmittal PCT/US00/13977 Sep. 6, 2000.
Epps Georgia
Etec Systems, Inc.
Leitich Greg
Spector David N.
LandOfFree
Method and apparatus for providing rectangular shape array... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for providing rectangular shape array..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for providing rectangular shape array... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2449364