KR100462532B1 - Products obtained from ultra-high vacuum concentrated ion beam micromills - Google Patents

Abstract

Ultrahigh pressure vacuum concentrated ion beam micromilling devices and processes have been disclosed that can achieve high aspect ratios in chemical-free environments. The ultra-high pressure vacuum chamber 10 includes a plurality of ports for viewing the counter substrate, thinning the target substrate, inserting or adjusting the target substrate, and performing various analyzes on the target substrate. The port 12 uses the port 14 used for a camera port as a viewing port. Also disclosed is a permanent metric storage medium using a micromilling process, which can store digital or alphanumeric characters, graphic forms and even characters, for example.

Description

Ultra-high vacuum concentrated ion beam micromills and products obtained therefrom

(Field of invention)

The present invention relates to a method for micromilling a material at high aspect ratios and to articles provided by such methods, such as high density durable data storage media. This invention shows the result of contracting with the US Department of Energy (contract No. W-7405-ENG-36).

(Background of invention)

At present, ion milling is performed under a medium vacuum of about 10 ⁻⁶ Torr. The aspect ratio, ie the ratio of milling depth to horizontal cut, is generally limited to about 10 due to the redeposition of sputtered material generated by scattering from residual gas in the system. There is a need for a method of milling with increased aspect ratio.

The technology of storing information or data has changed drastically over the past hundreds of years, and long-term storage and interpretation of such data are becoming important issues.

Rothenberg, Scientific American, 42-47 pp, l995 describes the problem of long-term storage of documents.

Information or data storage is generally related to magnetic or optical record carriers. Recently, Scanning Tunnel Microscopes (STM's) have been used to examine the recording and reading of stored information by changing the terrain to flatten metal surfaces. Wiesendanger, J. Vac, Sci. technol B, v. 12, no. 2, pp. 515-529 (1994) discloses the use of similar scanning probe microscopes made of STM and nanometer size structures and the unresolved problem of limited transient stability of the nanometer size structure. For other similar citations, see Adamchuk et al., Ultramicroscopy v, 45, pp. 1-4 (1992) describe the use of STM to micro process a 10 nm deep and about 50 nanometer (nm) diameter hole in a gold thin film on a flat silicon substrate. Li et al., Appl. Phys. Lett., V. 54, no. 15, pp. 1424-1426 (1989) describe the electronic etching of nanometer-sized holes of depth up to 1 nm and a diameter of about 2 nm on a flat gold substrate in STM operation in the atmosphere, described in Silver et al., Appl. phys. Lett., V. 51, no. 4, pp. 247-249 (1987) describe the direct recording of metal properties in submicron units by the deposition of new materials (cadmium from organic metal gases) on surfaces with STM, Abraham et al., IBM J, Res. DEVELOP v. 30, no. 5, pp. 492-499 (1986) discuss the possibility of surface deformation and high density memory storage with STM through surface diffusion. Current data storage systems each have one or more problems, including long term stability or durability of the media.

It is an object of the present invention to provide a method of milling with an increased aspect ratio of at least about 10 and preferably greater than about 50.

It is another object of the present invention to provide a product comprising, for example, a durable data storage medium which is formed and manufactured by the milling method.

(Summary of invention)

In order to achieve the above object according to the present invention, as described in the embodiments of the present specification, the present invention locates a target substrate in an ultra-high vacuum environment, and computer control during formation of a milled microstructure on the target substrate. A method is provided for machining a high aspect ratio microstructure in a target substrate, the method comprising producing a computer data file configured for operation of the concentrated ion beam and exposing the target substrate to a computer controlled concentrated ion beam. The computer controlled focused ion beam is controlled by software using a computer data file to form a high aspect ratio milled microstructure on the target substrate.

The present invention also provides a durable data storage medium composed of a substrate having milling properties therein, wherein the milling properties have a depth aspect ratio from about l to 50 in width. Storage media include milling properties selected from the group consisting of digital characters, alphanumeric characters, glyphical and 3-D graphic characters, and halftones and grayscale images.

(Short description of the drawing)

Figure ll is a plan view of a chamber using an ultra-high vacuum concentrated ion beam system according to the present invention.

2 shows a grid line rotated 85 degrees to show detailed resolution showing how ion mill version 2.5 mills the pattern.

3 shows a Raw I (x, y) file for generating alphanumeric milling.

4 shows an example of a mathematically generated form used for 3-D ion milling in fourth generation software routines operating inside Mathcad.

FIG. 5 shows an image of an atomic force microscope with a milled structure in 3-D ion milling of FIG.

6 shows a bandpass filter that can be formed by the method of the present invention.

(Detailed explanation)

The present invention relates to a micromilling process for miniaturization reduced to nano size and to a product produced by the method. In the process of the present invention, micromilling is carried out under ultra-high vacuum, for example in a vacuum of less than about 10 ^-9 Torr, preferably in the range of about 50-120 picoTorr (6.3 x 10 ^-11 to 1.6 x 10 ^-10 millibar). Is carried out in ultra-high vacuum.

The micromilling method of the present invention can achieve a high aspect ratio, that is, a milling depth for horizontal cutting (width) of 10 or more and generally up to 50. With this aspect ratio, the method of the present invention is used as a very advantageous mechanism for making sub-micron transverse cross sections and depth-profiling. This is due to, for example, rapid failure of submicron size in an integrated circuit, which is fundamental by the use of a suitable auger analyzer or a second ion mass spectrometer associated with the apparatus used in the method. Have a check to track contaminants.

The micromilling method of the present invention can be used to fabricate beams, levers, capacitors, lenses, diffraction gratings, waveguides, bandpass filters, antennas and fasteners, for example, for microchemical, electronic and mechanical sensors. Each has a high aspect ratio.

This micromilling method can also be used to record data on a suitable substrate. The data at this time is, for example, characters on the substrate using digital or numeric characters, alphabet or alphanumeric characters, and characters in the form of graphics or hieroglyphs, ie three-dimensional (3-D) graphics or images. Can be recorded. 'Character' generally refers to any symbol of a recording or communication system, and in the present method of recording data has certain characteristics that can be distinguished from the surface background of the substrate. Binary systems for recording data are used to represent binary data characters without a single surface depression on the substrate and without a single surface depression on the substrate. The analog data system is also configured to convert a grayscale or halftone image into a milling control file whose residence time of each pixel is proportional to its source grayscale value. When read back with a phase sensitive optical microscope, such as a Mirau or a suitable interferometer, grayscale images are observed. Thus, the spatial position and grayscale value of each interferometer video pixel are color processed by being grabbed on a CCD camera with a frame grabber and colorizing. For example, assign it as the only color value in a bitmap in a lookup table that contains grayscale values.

1 shows a chamber used in an embodiment of the present invention or an ultra-high vacuum concentrated ion beam system that can be used to form a data storage medium. In FIG. 1, the ultrahigh vacuum chamber 10 includes a plurality of ports for viewing the target substrate, thinning the target substrate, inserting or adjusting the target substrate, and performing various analyzes of the target substrate such as secondary electron emission. do. Port 12 is port 14, which is used as a camera port. Other observation ports 16 and 18 are coarse pump ports 20 as shown. Another port 22 includes an ion beam gun driven by suitable software. Multiple ion beam guns can be used if you wish to add a rate to be pushed.

Compared with previous milling systems, the method achieves a high aspect ratio in an environment without chemical aid. That is, the absence of chemical assistance needs to be added to the system to achieve an aspect ratio between 10 and at least about 50. By "chemical-assist" is generally meant that a reactive gas such as chlorine is added to react with the sputtered material to reduce any redeposition. Materials that can be milled by the micromilling method of the present invention include refractory metals such as iridium, tantalum, tungsten, molybdenum and niobium and periodic rates such as scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper The elements of the first row transition metal of the table and vacuum compatible semiconductors such as silicon and gallium arsenide are included. Other materials may also include high temperature insulators such as alumina, ruby, sapphire, silica or quartz, as long as any additional charge can be compensated by a secondary electron gun or other suitable means in the mill.

In one embodiment of the micromilling method of the present invention, the transmission diffraction grating is manufactured for use as an infrared bandpass filter. One lattice material used pulsates the gas alumina to make a conductive film about 2-5 microns thick. The diffractive elements milled through the thin film were positioned in a regular array so that the diffraction intensity through the array could be modeled by conventional Rayleigh optical calculations. As a result, the grating with the shape and specification shown in FIG. 6 produces the main band at 11-12 microns (infrared) as desired. The use of this method is known as conventional Synchrotron X-ray lithography and as described by Mircroparts Gesellschaft fur Mikrostructurtechnik, karlsruhe, Germany, in that the diffraction element is smaller than that reported by or in May 1993 by Microparts. as an alternative to electroforming.

Since the spot size of the ion beam can be made extremely small (less than 50 nm in diameter), the use of ultra-high vacuum condensed ion micromilling can be significantly extended to produce transmission diffraction gratings that bandpass ultraviolet or visible light at typical high speed transmissions. It is expected to be.

In another embodiment of the present invention, the micromilling method is used for storing data on metal and semiconductor materials, for example. The storage of such data should be high density and high durability. "High Density" means that a small nail-shaped medium of approximately l / l6 inches in diameter and approximately one inch in length will accommodate approximately one gigabyte of ASCII information, assuming each Latin character is eight bits or one byte. About 1 cubic micron of milled characters. Equivalent binary notation allows comparison to write four gigabytes of information in the same space.

The data storage medium of the present invention is a medium in which electromagnetic pulses, radio frequencies, interferences, magnetic fields, solvents not limited to water, alcohol, and acetone, exposure to heat, increase and decrease of heat, and general regeneration of the fire can be obtained. Provide an extremely durable medium for storage. The data storage medium at this time reduces the need to replace the backup data by providing an advantage of high reliability compared to the magnetic / magneto-optical medium, and can be provided at low cost as the storage data on the actual substrate. For example, steel nail pins may be used as the actual storage material for milling data. Another advantage of such a data storage medium is that the character etch milling starts with an environmentally dry process, there is no breakage of the medium over time, and the medium can be recycled and used or, if desired, crushed and polished to It can be used.

In one embodiment of the data storage application of the milling method of the present invention, a suitable substrate comprises a binary character representing a series of individual surface depressions, one form of 1 or 0, on a preformatted medium by pre-milling. Is formed. In one way to promote processing of the following data storage systems, the pre-milled substrate is easier and faster to remove than the substrate material itself, but is durable and resistant to unintended degradation of the overcoat material. It can be backfilled with an overcoat material. Thus, the overcoat material at this time can be removed only for the characters necessary to change the binary character representation. In another method, one form of binary character, i.e. pre-casting of a series of individual bumps representing one or zero, can be formed on a suitable substrate. Such pre-casting may use polyvinyl alcohol, polystyrene, and spin-on glass, for example up to about 75 microns thick.

Then, the necessary bumps in the pre-cast material can be removed only for the characters needed to change the binary character representation.

One problem typically associated with long-term storage of data relates to the method that will be used to read out data after hundreds of millennia of data have been written. The advantage of this micromilling method for data storage is that it is possible to store data in multiple formats and densities on the same medium. For example, the protocol used to store data can be recorded at a single data density (size) that can be read by humans with a simple tool or by simple vision or small magnification. Thus, this protocol can be used to read residual data that has been recorded at higher densities (small sizes) and in other formats. Thus, in fact, the "Rosetta Stone" type makes it possible to provide the keys needed to be used to read stored data far into the future, reducing the coupling of information from storage and retrieval methods. Can lose. In contrast to the original "Rosetta Stone", this data storage medium uses several sizes of information rather than just one, and this data storage medium does not repeat the actual data, but rather to read the remaining data. Simply provide the key.

The data storage system of the present invention allows for the storage of various types of information in a single storage medium, i.e., milling alphanumeric characters and graphic or graphic characters into a single substrate, thereby retrieving both types of information. have. Alternatively, characters of different sizes can be milled into a single substrate. Among the various sizes, not only the large size targeted for human visual observation but also the small size targeted for effectively storing huge amounts of data can be included. In this way, huge amounts of data can be stored on a substrate, but after some time, even in the future, the fact that there is information stored on the substrate will be evident in the individual view of the data storage system. In addition, large size instructions on how to read small size characters can be included directly on the substrate. Thus, small sized characters may be included in the remaining area of the substrate around the large sized structure, or may be included in the milled area of larger sized characters.

In another embodiment of the present invention, the micromilling method can be used to form an antenna. Since a basic monopole antenna is a resonant structure that acts as a bandpass filter, if the relevant frequency is in the band of the antenna, the signal will appear at the antenna output. Radio waves (RF signals) are typically detected using differential displacement field detectors, which are antennas. The advantages gained by using antenna arrays to improve signal-to-noise are often to improve the performance of the antenna system. By using this micromilling method, very small antennas and antenna arrays can be made, and such small antennas and antenna arrays can increase the potential associated frequencies. One application of this approach is to use a small antenna connected to a Capacitively-Charged-Coupled Device (CCCD) to create a "picture" that uses an RF signal as a light source.

In micromilling methods for data storage, three separate procedures can be used to produce digital, alphanumeric, and three-dimensional image data. As a result, all procedures produce a file called a millstream file that can be read and processed quickly by a commercial digital-to-analog converter. The file has the following format:

s = three-dimensional mode designator: nf = number of frame repetitions: np = total number of data lines; t [i] x [i] y [i] to t [i] = beam stop at nanoseconds dwell time; x [i] = horizontal position in digital-to-analog converter unit 0-4095, y [i] = vertical horizontal position in digital-to-analog converter unit 0-4095. The entries s, nf and np are collectively known as millstream headers. The digital and alphanumeric data modes used are actually a limited case of three-dimensional image milling. Separate software is used for simple line and box milling, which is useful as FEI's 2.5-million edition.

Processing of the digital data for ion milling control is as follows. Digital data can be first derived mathematically or read by Mathcad 4.0, a commercial number and graphics package using the following software that has been developed to work within Masscad. For example, the next array of alternating 1s and 0s was used to create a digital array of corresponding ion beam stop times.

Test patterns are made for continuous use in ion milling. For example, the above mentioned digital array can be made in the software example below.

The change in the above example is obtained by adjusting the values or parameters of n, m, D, T and E. These intermediate files (eg NGRATE2. Prn) are proven on the left and only a single space separates the t, x and y values. This is the file structure obtained by a commercial ionmill software package from FEI. Subsequent file processing requires removal of the minus sign, shifting the left registry, and adding appropriate headers. This proves very convenient for writing the conversion routines in BASIC to make the last mill file from the intermediate xxx.prn file. An example of a preferred file conversion routine is shown below.

Also, any text editor package can be used to convert files for this purpose. An easy-to-use package includes the "Find and Replace" feature of version 2.0 of Microsoft Word for Windows. Typically, the "find" operation can locate the "-", for example, and the "replace all" operation can be used to convert to "". Therefore, the left registry shift can be achieved automatically. Then, the processed file is xxx. txt, and finally, the millstream header is xxx. txt file to add FEI Co. Ionmill software Version 2.5 compatible files, xxx. stored as str

Alphanumeric data, such as human-readable characters, exposure masks, business card logos, or any item that can be placed on a flatbed scanner to produce grayscale images, or any video frame grabber The output falls within this category. In general, this processing scheme is to (1) scan the item (e.g., textbook page) to expose the electronically related image area, and (2) improve contrast in the selected area. (3) convert the image into a black and white image, (4) save the converted image as a PostScript file, for example, and (5) remove the header and footer from the PostScript file, Save as a defined Mathcad file, (6) assign dwell time to dark areas (e.g. black printed text), (7) vectorize the file (i.e. remove data from unnecessary white areas) And (8) create the last millstream file as shown in Figure 3, using the method described above for digital data.

Operations (1)-(4) can be performed in a commercial scanner package called ColorlabVersion 4.0 With an Epson Es-300-C Flatbed Scanner with an IBM-PC adapter using the menu function. (5) The operation can be performed in Microsoft Word for Windows Version 2.0 using the Delete function. Operations (5)-(6) can be done using additional software developed to operate inside Mathcad, as in the examples below.

This'software is designed to read a file which was generated in Colorlab by scanning a printed logo and rendering a black and white Postscript file. Then in Microsoft WinWord, the Postscript header and footer are removed, the grayscale text 0-F (hex) is replaced with 0-9 (dec) (we have chosen the simplest case of 0-1 (dec).), And every other character was replaced by a space so that single digits could be recognized (Set a very large page size in WinWord) .There is no loss of resolution, but the number of columns in WinWord doubles (this example was executed at 72 1pi.) . The file was stored as lanlblk.pm. a structured Mathcad file of 239 lines by 78/2 = 39 columns. The Los Alamos logo is rendered below.

Then, operation (7) can be performed as described above with respect to digital data.

Also, (3)-(5) operations can be skipped and the grayscale image can be TIFF (a few flavors xxx. Tif), Windows bitmap (xxx. Bmp), Windows paintbrush (xxx.pcx). ), TARGA (xxx. Tga) or Grayscale Postscript (xxx.eps). Thereafter, the software package Mocha Version 1.1 can be commanded using a menu, and the pixel intensity can be extracted from the array format, and stored as a comma or space delimiting an ASCII string file (+ xxx.dat). have. Then, operation (6) can still be accomplished by another software routine to operate inside Mathcad as in the example below.

This program will extract pixel intensity data from a Mocha Vl, 1 worksheet and produce an Ionmill xxx.prn precursor file for subsequent conversion to an Ionmill xxx. str file.

N = # of x elements: M = # of y elements: P = # of pixels = rows (Mt). Initial read file is lanllog. dat. Change as necessary for other file reads, Other changes: WRITEPRN (lanlmoc). We also incorporate a vectorizing routine which reduces the size of the mill files to only the essential pixels.

The structure of a PostScript file for use in constructing an ion mill precursor file is xxx. Which contains "j" depending on the characterization of the character "i". Requires an eps header. Therefore, space is added between characters in the text editor so that its corresponding file size is twice as large, for example 78 × 70, which is useful for 156 × 70 but without resolution.

Therefore, these files up to the acceptance limit of ion mill software can be processed. However, the scanned text image must be rotated +90 degrees in trigonometry sense, ie counterclockwise: otherwise, a very slow matrix transformation function is required to create the correct orientation for the ion mill file. .

3-D image data is actually stored as a 3-D structure ion-milled in the substrate material. All structures within this category can be described mathematically as form-dependent variable functions.

z = t (X, y)

A further restriction is that for a given set of x and y values, only one value of t is allowed. Physically, this determines that all milling positions are violated in the line where the ion beam is not visible. However, the following structural milling from other orientations will remove a single evaluated limit of z.

Single orientation 3-D milling computes array z [i, j], makes its graph for normal inspection purposes, and ion mills of the same type as already described for digital case and alphanumeric data. This is done by creating a precursor file. Continuous processing to form a millstream file is as described previously.

Separate software routines have been recorded for each such distant milled 3-D shape.

There is only one equation for each shape, but the techniques for indexing arrays, formatting data, writing files, and converting are the same for all shapes in this category.

The example below shows the typical software required to create a 3-D feature (in this case, a screw thread).

FIG. 4 shows a plot of the generated 3-D structure, and FIG. 5 shows an atomic force microscope image of the actual milled structure.

Using the techniques described above, one can extend the method of milling 3-D shapes according to grayscale or color pixel values extracted from video-generated TIFF, bitmap, TARGA, or other graphics files. Data from that shape can be recovered from depth information available from scanning probe techniques such as atomic force microscopy and scanning tunneling microscopy.

In particular, since various changes and modifications will become apparent to those skilled in the art, the present invention is further illustrated in the following examples, which are intended only as examples.

Example 1

All 52 alphanumeric characters were typed, including all upper and lower case letters of the alphabet. Therefore, these typed alphabetic characters were scanned into data files and converted into recognition millstream files by the software of the FEI ion mill machine, which was placed on high carbon steel (HCS) dowel pins. Etched or micromilled text. The letters were 10 microns in size and occupied the entire space on the dowel pins of 520 square microns. Four additional characters were recorded on the same HCS dowel at a size of one square micron per character. In order to retrieve the milled data, a scanned video print of the actual milled surface 500 times magnified was supplied to a commercial character recognition software application. The results of this test showed that the character recognition program can recognize most milled characters, even at the unlearned level. The milled text at this time had an aspect ratio of depth to at least 15 widths, as determined by the measurement limits of the atomic force microscope.

While the invention has been described in detail, the description is illustrative in all respects and not restrictive. Various modifications and variations can be devised without departing from the scope of the present invention. In addition, the Example disclosed this time is only an example and it is intended that various Example is obtained within the range of the equivalent of invention described in the claim.

Claims (14)

Arranging the target substrate inside the ultra-high vacuum environment; Generating a computer data file configured for operation of a computer controlled focused ion beam to form a milled microstructure on the target substrate; Exposing the target substrate with the computer controlled concentrated ion beam, and controlling the computer controlled concentrated ion beam by software using the computer data file to form a high aspect ratio milled microstructure on the target substrate; , Wherein said microstructure has a milled depth: milled width aspect ratio of greater than 10: 1. The method of claim 1, Said process being chemical-assist free. The method of claim 1, The microstructure is a bandpass filter. The method of claim 1, The microstructure is a data storage medium. With a substrate having milled characters therein, And the milled character has an aspect ratio of depth to width from about 1 to about 50. The method of claim 5, And said milled character is a character selected from the group consisting of digital characters, alphanumeric characters, hieroglyphs and graphic characters. The method of claim 5, The substrate is a material selected from the group consisting of iridium, tantalum, tungsten, molybdenum, niobium, titanium, vanadium, chromium, manganese, iron, copper, nickel, cobalt, silicon, gold, scandium, and pulsed gas aluminum. Durable data storage medium. The method of claim 5, And the milled characters each occupy about one square micron. The method of claim 5, And the milled characters are digital characters each occupying space with a minimum diameter of about 150 nanometers. The method of claim 5, Durable data storage medium, characterized in that each milled character is a single depression The method of claim 10, And wherein the milled text is filled with overcoat material at a sufficient level to form an essentially smooth surface that does not contain distinguishable milled text. The method of claim 11, At least a portion of the milled character is filled with an overcoat material at a sufficient level such that the at least part of the milled character forms an essentially smooth surface on the substrate that is indistinguishable as a character. . The method of claim 11, At least a portion of the milled characters filled with overcoat material is such that the overcoat material has been removed such that the milled characters are distinguishable as one character. The method of claim 5, And said milling represents data stored as pixels having variable depth and aspect ratio, said data being recoverable as an image selected from the group consisting of a halftone image, a grayscale image and a color image.