Photocopying – Projection printing and copying cameras – Image transferred to or from curved surface
Reexamination Certificate
1999-06-28
2001-07-17
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Image transferred to or from curved surface
C355S055000, C355S077000, C716S030000, C359S853000
Reexamination Certificate
active
06262791
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to photo imaging on nonplanar substrates, and more particularly, to an imaging system using a corrective diffractive optical element with an ellipsoidal mirror for focusing a two dimensional image onto a three dimensional substrate.
Conventional integrated circuits, or “chips,” are formed from two dimensional or flat surface semiconductor wafers. The semiconductor wafer is first manufactured in a semiconductor material manufacturing facility and is then provided to a fabrication facility. At the latter facility, several layers are processed onto the semiconductor wafer surface, including various circuit design images, to create a very large scale integrated (“VLSI”) design. Although the processed chip includes several layers fabricated thereon, the chip remains relatively flat.
A fabrication facility is relatively expensive due to the enormous effort and expense required to create flat silicon wafers and chips. Moreover, the wafers produced by the above processes typically have many defects which are to the above cutting, grinding and cleaning processes as well as due to the impurities, including oxygen, associated with containers used in forming the crystals. These defects become more and more detrimental as the integrated circuits formed on these wafers become smaller.
Another major problem associated with modern fabrication facilities for flat chips is that they require extensive and expensive equipment. For example, dust-free clean rooms and temperature-controlled manufacturing and storage areas are necessary to prevent the wafers and chips from defecting and warping. Also, these types of fabrication facilities suffer from a relatively inefficient throughput as well as an inefficient use of the silicon. For example, facilities using in-batch manufacturing, where the wafers are processed by lots, must maintain huge inventories to efficiently utilize all the equipment of the facility. Also, because the wafers are round, and the completed chips are rectangular, the peripheral portion of each wafer cannot be used.
Still another problem associated with modern fabrication facilities is that they do not produce chips that are ready to use. Instead, there are many additional steps that must be completed, including cutting and separating the chip from the wafer; assembling the chip to a lead frame which includes wire bonding, plastic or ceramic molding and cutting and forming the leads, positioning the assembled chip onto a printed circuit board; and mounting the assembled chip to the printed circuit board. The cutting and assembly steps introduce many errors and defects due to the precise requirements of such operations. Additionally, the positioning and mounting steps are naturally two-dimensional in character, and therefore do not support curved or three-dimensional areas.
U.S. patent Ser. No. 08/858,004 entitled S
PHERICAL
S
URFACE
S
EMICONDUCTOR
I
NTEGRATED
C
IRCUIT
, herein incorporated by reference as if produced in its entirety, describes a three dimensional, sphere-shaped substrate for receiving various circuits. Of the many process disclosed in the above-referenced application, several are related to imaging a circuit design onto the three dimensional substrate. Often, the circuit design to be imaged may be two dimensional in nature.
One solution for imaging a two-dimensional circuit design to a three-dimensional object, such as a sphere, is to use an elliptical mirror system. However, there are numerous problems associated with the elliptical mirror system for reflecting the image onto the sphere's surface. Referring to
FIG. 1
, a collimated beam
10
is shown reflecting off of an elliptical mirror
12
. The elliptical mirror
12
has two focus points and an image emerging from one focus point is reflected by the elliptical mirror and refocus at the second focus point. As the beam
10
passes through the first focus point of the elliptical mirror
12
at various angles, the beam
10
is reflected toward the second focus point, and towards a spherical semiconductor device
14
located near the second focus point.
In actuality, the beam
12
focuses at a point
16
, which is one of an infinite number of points on a best focus surface
18
that emerges between the surface of the elliptical mirror
12
and the device
14
. The best focus surface
18
is not spherical. Instead it is aspheric in shape and not compatible with projecting and focusing images on the surface of a spherical semiconductor. As a result, the image on at least some portions of the spherical surface is out of focus.
Therefore, what is needed is an apparatus and a method for reshaping the best focus surface to more closely match the surface geometry of a sphere.
SUMMARY OF THE INVENTION
The present invention, accordingly, provides an apparatus and a method for reshaping the best focus surface of an elliptical mirror to more closely match the surface geometry of a nonplanar substrate. To this end, one embodiment of the apparatus includes a complex phase plate located between a mask for generating the image and the elliptical mirror. The mirror has a unique wavefront error and an aspheric image focus surface which is corrected by the complex phase plate, thereby shifting the focus surface to correspond to the substrate's surface.
The apparatus may be used for various shaped substrates, such as a spherical shaped semiconductor device.
In one embodiment, the complex phase plate includes a variable focal length optical element. The variable focal length optical element may include a diffractive optical element with a plurality of complex phase grating sections repeated over a surface thereof, located in immediate proximity to the mask.
In one embodiment, the method of the present invention corrects the projected image of the mask for the surface of the nonplanar substrate. Wavefront errors are ascertained for the elliptical mirror by projecting an image of the mask onto the substrate. Phase differentials for correcting the wavefront errors for each section of the mask are determined and an optical element generated to introduce the phase differentials, thereby correcting the projected image to a modified best focus surface.
An advantage of the present invention is that a two-dimensional mask design can be projected and focused on to a spherical surface using an elliptical mirror by altering the best focus surface of the elliptical mirror.
REFERENCES:
U.S. Serial No. 08/858,004, filed on May 16, 1997, Spherical Shaped Semiconductor Integrated Circuit, Akira Ishikawa, Abstract and fifteen (15) sheets of drawings.
U.S. Serial No. 09/094,761, filed on Jun. 15, 1998, Total Internal Reflection Holography Method and Apparatus for Lithography on a 3-D Spherical Shaped Integrated Circuit, Karlton Powell, Abstract and six (6) sheets of drawings.
U.S. Serial No. 09/107,875, filed on Jun. 30, 1998, Spherical Cell Design for VLSI Circuit Design on a Spherical Semiconductor, Eiji Matsunaga and Nobuo Takeda, Abstract and seven (7) sheets of drawings.
Adams Russell
Ball Semiconductor Inc.
Haynes and Boone LLP
Kim Peter B.
LandOfFree
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