VLSI-based system for durable high-density information storage

The invention relates to using VLSI techniques to store information on a substrate. One embodiment of a die with text deposited upon the die uses semiconductor processing techniques during fabrication. Included in the die are a substrate, a first paragraph and a second paragraph. The first and second paragraphs are in contact with the substrate. The second paragraph is aligned with the first paragraph in a column.

BACKGROUND OF THE INVENTION

This invention relates in general to VLSI fabrication techniques and, more specifically, to using these techniques to store information.

Any unnecessary traces of a metal, an oxide or a polysemiconductor are avoided in semiconductor processing. Adding unnecessary traces makes the mask and fabrication more complex. This added complexity can increase the likelihood of defects in the finished semiconductor circuit. Consequently, semiconductor circuits avoid use of unnecessary traces.

Progress in VLSI technology over the past few decades has been phenomenal. Packing densities have increased by several orders of magnitude. However, to date, VLSI technology has been used largely for creating electronic circuits, micro-machines or sensors. Other uses for the VLSI technology are needed.

SUMMARY OF THE INVENTION

The invention relates to using VLSI techniques to store information on a substrate. One embodiment of a die with text deposited upon the die uses semiconductor processing techniques during fabrication. Included in the die are a substrate, a first paragraph and a second paragraph. The first and second paragraphs are in contact with the substrate. The second paragraph is aligned with the first paragraph in a column.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The present invention includes a novel use of Very Large Scale Integration (VLSI) technology for creating very durable and long-term repositories of textual and graphical information. The invention allows converting the information to be stored into an input form suitable for VLSI fabrication systems, allows fabricating the information repositories and allows accessing the stored information. The invention creates features representing textual and/or graphical information on a semiconductor (or other) wafer. These features may be created on the wafer surface itself or on a layer of material deposited on the wafer surface. Such materials can include, but are not limited to, metals, oxides and photoresists. In this way, large amounts of text are archived using VLSI technology.

Referring first toFIG. 1, a depiction of an embodiment of a wafer100having multiple die104is shown. The die104are generally aligned in a grid across the wafer100. Typically, all die104on the wafer100are the same. Although the die104in this embodiment is rectangular, other embodiments could have die of different shapes. For example, the die could be shaped as star or cross.

With reference toFIG. 2, a depiction of an embodiment of a die104from the wafer100is shown. Approximately eleven columns204of text appear on the die104. Each column204includes a number of paragraphs. Each paragraph is separated by a hard return and a tab. In some cases the first character of a section or chapter is enlarged and/or ornately decorated to signify changing sections or chapters. A dark silhouette pattern208against a lighter background overlays the columns204of text. The silhouette pattern208is darker than the background in this embodiment, but other embodiments could reverse this. Although this embodiment shows an English character set, other embodiments could include character sets in any language as well as symbol character sets.

The features, once created on the wafer, can be overlaid with an optically clear protective coating using materials such as a resin, an optically clear overcoat (e.g., EXP980024 available from Brewer Science™ of Missouri), a thin and clear nitrite film, a spin-on glass film, or an aluminum oxide layer. Additionally, the back surface of the wafer can be metallized to add durability to the typically fragile wafer100.

Referring next toFIG. 3, an illustration of an embodiment of a portion212of a column204from the die104is shown. The portion212is a magnification of a part ofFIG. 2that shows a test sample of text308. The portion212shows the dividing line316between the silhouette208and the background312. To allow for contrast, the text308on the silhouette208is a light color and the text308on the background312is a dark color.

With reference toFIG. 4, an illustration of an embodiment of a word400having diffraction grating subpattern is shown. By adjusting the spacing of the diffraction gratings, the word400or character appears in different colors. The minimum size of the features is limited only by the capabilities of the VLSI fabrication technology used. For example, one-hundred and thirty nanometer features are being used today. In addition to colors, other embodiments could use bolding, underlining, italics, strikeout, subscripts, superscripts, shadows, small caps and other effects with the text308. Further, the diffraction lines the produce the different colors could be oriented at any angle with respect to the text308and not just horizontally as depicted in this embodiment.

Referring next toFIG. 5, a flow diagram of an embodiment of a process for converting text and graphics into an electronic mask file is shown. The process begins in step515where a text file505and graphics file510are chosen and loaded into page layout software. The text505is in a file format such ASCII text or rich text. Included in the text file505are hard returns between paragraphs and markers for the beginning of a section or chapter. The graphics file510is preferably a two color silhouette.

Page layout software such as Adobe PageMaker™ or Quark Xpress™ is used to create and lay-out the text and graphics in a space proportional in size to the dimensions of the desired die104. The resolution of the drawing in the page layout software is chosen such that it corresponds to the feature size of the semiconductor process. The number of columns needed and font size for adequate resolution is chosen with the page layout software. A page layout file520is produced from the software in step515.

In step525, the page layout file520is converted into a binary image file530. This can be done using a screen capture program and an image manipulation program such as Hijaak Pro™ or Adobe PhotoShop™. Alternatively, custom software could perform this conversion to the binary image file530. In this embodiment, each pixel in the binary image corresponds to a rectangle in the die layout.

In step535, the text and graphical regions of binary image file530are represented as a collection of simple geometric primitives in a geometric primitives file540that can be fabricated with the available fabrication technology. Primitives such as rectangles are used in this embodiment to represent each pixel, but in other embodiments can also include general polygons, triangles, lines, curves, and circles. In alternative embodiments, several like and adjacent pixels can be grouped into larger primitives.

In addition to a binary image file, diffraction patterns and color materials, for example, could be used to change the color of a graphical image. Some embodiments could change the processing materials to suit the desired colors of the graphical image. Alternatively, colors in the graphical image could signify a different shaped primitive (e.g., a circle) or signify a different style.

In step545, each geometric primitive in the file540is translated into a basic chip layout command such as a “Box” command (corresponding to rectangles) in the CIF language to produce a CIF or GDS file550. In addition to the CIF and GIF format, any other chip layout format could be used. The complete collection of primitives corresponding to the whole binary file would, by this process, result in a list of “Box”-like commands. It is noted, we use the phrase ‘box command’ to mean any of a variety of commands corresponding to simple geometric primitives in the rest of this document. This list constitutes the chip layout file, which can be used by a VLSI fabrication facility to create the patterns for the masks used in lithographing the die104.

With reference toFIG. 6, a flow diagram of another embodiment of a process for converting text and graphics into an electronic mask file is shown. The process begins in step610where for each of the elements (e.g. letters of the alphabet, punctuation marks, numerals, and graphic characters) a binary pattern that represents that character is generated for a particular font in a font/style file600. All these binary patterns are collected into one or more ‘font/style files’. For each element of the font/style files600, a list of primitives that make the element is generated. This yields a “subroutine” for generating that element.

The list of primitives that make up an element can be generated in a variety of ways. In one embodiment, each pixel of the element is treated as a separate rectangular primitive. The primitives generated from the font/style file600are stored in a character subroutine file630. Some embodiments may include special features in the character subroutine file630such as printing a special character at the beginning of a chapter or section. At this point in the process, the text can be processed to produce characters in the desired font.

A text file620, the character subroutines file630and a binary image file640are loaded into the chip layout generator in step650to produce a chip layout file660. In this embodiment, the text file is an ASCII file and the binary image file is a TIFF file. If only a text file620is specified without a binary image file640, each element in the text file620is read and corresponding subroutine from the character subroutine file630is looked-up. The sequence of elements is translated into the corresponding sequence of subroutine calls and a chip layout file is created. The set of subroutine calls may be appended to the subroutines.

If only a binary image or graphics file640is specified without a text file620, each pixel in the graphics file640is read and translated into an appropriate ‘box’ command. These ‘box’ commands form a chip layout file660.

In some instances, a graphics file640may be combined with a text file620to create a chip layout file660. There are several options for accomplishing this. One option is to have the text wrap around the graphics. The graphic itself is represented as a collection of geometric primitives like rectangles. By knowing the position of the graphics, the text can be wrapped around the graphics.

Another option is to have the text overlay the graphic, but to have the text change polarity (normal or reverse contrast) depending on whether it is inside or outside the graphic element. The text may change features other than polarity. For instance, it could change style (normal or bold), change fonts (e.g. Geneva to Helvetica), or change from one type of element to another. Once the style or type of element is determined from both the graphics and text file, the appropriate subroutine is looked up from set of subroutines generated in the character subroutine file630and outputted to the chip layout file660.

The mask corresponding to the chip layout file660described above (e.g., CIF or GDS format) can be created using E-Beam Lithography, X-Ray Lithography, or any of a variety of techniques commonly used now or in the future for VLSI. The input to the process is the chip layout file660and the polarity of the mask. The mask can be a 1-to-1 contact mask or a minification mask suitable for use in a stepper configuration.

Referring next toFIG. 7, a depiction of an embodiment of an upper case “A” element700is shown. The element700approximates the font Helvetica using a number of rectangles. Other embodiments could use other fonts. The black regions denote “pixels” of the element. Similarly,FIG. 9shows a depiction of an embodiment of a lower case “a” element900.

With reference toFIG. 8, a depiction of the embodiment of the upper case “A” element700showing constituent rectangle primitives800is shown. The primitives800are rectangles of different sizes positioned to approximate the element700. Each primitive is comprised of “box” commands each being a square defined by the feature size of the process. Some embodiments are not limited by the feature size of the process. Since the die is not a functional circuit, the only limitation on size and shape is defined by the state of the art in mask fabrication. Although this embodiment uses rectangular primitives, other embodiments could have primitives of any geometric shape.

Referring next toFIGS. 10 and 11, shown are depictions of embodiments of an upper case “A” and a lower case “a” elements1000,1100with reverse contrast. Reverse contrast provides contrast for text overlaying a dark background or a dark silhouette.

With reference toFIG. 12, a flow diagram of an embodiment of a process for lithographing text and/or graphics onto a semiconductor substrate is shown. A variety of methods can be used for fabricating chips104based on mask described above. The process begins in step1200by depositing photoresist directly on the wafer or on a layer of some other material that has first been deposited on the wafer. Next, expose the photoresist to electromagnetic radiation of the appropriate wavelength through the mask in step1210. Etch away the exposed or unexposed photoresist to leave a positive or negative impression and bake the photoresist to increase its durability in step1220. Optionally, the wafer is coated with an optically clear protective material.

Referring next toFIG. 13, a side elevational view of an embodiment of a semiconductor wafer1300with text and/or graphics lithographed thereon is shown. To produce the semiconductor wafer1300depicted; the process ofFIG. 12was employed. The bottommost portion is a substrate1304. An optional intermediate layer(s)1308may be deposited upon the substrate1304. A photoresist pattern1312is on the optional intermediate layer(s)1308. A clear protective coating1316envelopes the photoresist1312.

With reference toFIG. 14, a flow diagram of another embodiment of a process for lithographing text and/or graphics onto a semiconductor substrate is shown. The process begins in step1400where one or more layers of materials such as metals or polysilicons are deposited on the substrate. Next, photoresist is deposited in step1410. In step1420, the photoresist is exposed to electromagnetic radiation of the appropriate wavelength through the mask.

Etch away the exposed or unexposed photoresist to leave a positive or negative impression in step1430. The layer below the photoresist is etched through the cavities created in the photoresist layer in step1440. Any photoresist left behind is removed to reveal the patterned layer of material in step1450. Optionally, coat the wafer with an optically clear protective material in step1460.

Referring next toFIG. 15, a side elevational view of another embodiment of a semiconductor wafer1500with text and/or graphics lithographed thereon is shown. To produce the semiconductor wafer1500depicted, the process ofFIG. 14was employed. The bottommost portion is a substrate1504. An optional intermediate layer(s)1508may be deposited upon the substrate1504. A metal pattern1512is on the optional intermediate layer(s)1508. A clear protective coating1516envelopes the metal pattern1512.

With reference toFIG. 16, a flow diagram of yet another embodiment of a process for lithographing text and/or graphics onto a semiconductor substrate is shown. The process begins in step1600where photoresist is deposited directly on the substrate or on a layer of some other material that has first been deposited on the substrate. In step1610, the photoresist is exposed to electromagnetic radiation of the appropriate wavelength through the mask. The exposed or unexposed photoresist is etched away in step1620to leave a positive or negative impression. Next, a material such as a metal or a polysilicon is deposited on the patterned photoresist in step1630. The photoresist is lifted off in step1640leaving behind the material from step1630in the cavities of the photoresist pattern. Optionally, the wafer is coated with an optically clear protective material in step1650.

Referring next toFIG. 17, is a side elevational view of yet another embodiment of a semiconductor wafer with text and/or graphics lithographed thereon is shown. To produce the semiconductor wafer1700depicted, the process ofFIG. 16was employed. The bottommost portion is a substrate1704. An optional intermediate layer(s)1708may be deposited upon the substrate1704. A metal pattern1712is on the optional intermediate layer(s)1708. A clear protective coating1716envelopes the metal pattern1712.

The information stored in text and graphics may be accessed. A magnification device equipped with an illuminator that can cast light on the chip from above can be used to aid the human eye to see the fine details of the information on the chip. The chip can be mounted on a stage capable of precise movements under the magnifying device. The magnification device may be coupled to an electronic or photographic capture device, such as a film camera or an electronic camera.

If the chip is imaged by the magnification device and captured by an electronic capture device, the resulting electronic image may be processed. For instance, one could compare the electronic images of two chips to see if they are identical. This capability could be used for access control or security applications. One could also perform automated character recognition. The output could be printed, searched for specific items or translated into an audio signal and transmitted so that the chip could be “read out loud” to a human or a listening device.

In light of the above description, a number of advantages of the present invention are readily apparent. First, the density of information storage can be very high. This is due to the very small features that can be fabricated with modern VLSI technology. Second, the information storage is very durable against disruptive influences such as radioactivity, strong electromagnetic fields, high temperatures, moisture, chemicals and mechanical strain. Existing means of information storage, such as magnetic discs, tapes and CDs tend to fall prey to one or more of these factors. In fact, even electronic memories fabricated using VLSI technology can not robustly tolerate these influences. Third, information access from our devices is straightforward. Finally, this means of information storage is very cost effective and easy to manufacture in large quantities.

A number of variations and modifications of the invention can also be used. For example, the substrates used could be an insulator. The layers could be formed over the insulator using VLSI techniques.

Although the invention is described with reference to specific embodiments thereof, the embodiments are merely illustrative, and not limiting, of the invention, the scope of which is to be determined solely by the appended claims.