US 3112850 A
Description (OCR text may contain errors)
mca-a im SR Q /zwl 301120850 moss REFEREMQE Dec. 3, 1963 D. J. GARIBOTTI 01cm: OF MICRO-SEMICONDUCTORS Filed 001:. 31, 1962 Mb ED WWW 3112850 QR IN 225/2 United States Patent 3,112,850 DICING 8F MlCRO-SEMICONDUCTORS Domenick .l. Garihotti, Hazardville, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Oct. 31, 1962, Ser. No. 234,373 7 Claims. (Cl. 225-2) My invention relates to the fabrication of micro-semiconductor devices. More particularly, my invention is directed to the dicing of micro-semiconductor wafers or ribbons.
Historically it may be observed that the reproducibility and quality of semiconductor devices has been dependent upon developments and improvements in the materials from which they have been fabricated. For example, considerable development was required for the refinement of techniques for the product-ion of good germanium crystals and, even after these techniques for germanium were developed, it was again only after considerable effort that the silicon technology reached the same levels. After much experimentation, it was found that the best Si for most device purposes was produced by the floating zone technique rather than the Czochralsky method as used for Ge. Regardless of the single crystal processing technique utilized, the end product was essentially of cylindrical shape. The very nature of this geometry required that these cylindrical crystals be sawed into slices which in turn, were cut into dies of suitable sizes for device fabrication. Recently, controlled dendritic crystals in the form of thin ribbons have been produced in the laboratory. Commercial production of such ribbons of Si and Ge will drastically cut the cost of semiconductor devices since the ribbons have a vastly greater growth rate and since the wasteful and time consuming stop of sawing cylindrical crystals into slices may be eliminated.
Should production of semiconductor materials in ribbon form become economically practicable, it will still be necessary to perform the step of dicing the ribbon into chips of suitable size. In the prior art, dicing of semiconductor wafers was originally accomplished by means of thin diamond saws or cutting wheels charged with diamond particles. An example of this approach to dicing is shown in US. Patent 2,865,082, issued to P. E. Gates on December 23, 1958. The technique exempli'fied by the Gates patent is a relatively time consuming and costly procedure which produces a very low yield due to fracturing of the crystalline materials. Other prior art mechanical procedures for dicing include the use of a cutting tool in which a blade is vibrated vertically to the wafer at very high frequency rates by means of a magnetostrictive drive and the use of streams of abrasive particles directed against exposed portions of a masked wafer. These latter dicing methods suffer from the same disadvantages as the aforementioned procedures. is, they are slow, produce considerable waste because of cracks and chips, and they are expensive in the sense that the cuts made must be as wide as the abrasive stream or cutting tool and are thus wasteful of crystalline material which has itself been produced at considerable expense.
In an attempt to overcome the above-mentioned disadvantages of the prior art, manufacturers of semiconductor devices developed chemical dicing processes. U.S. Patent That Patented Dec. 3, 1963 3,046,176, issued to W. A. Bosenberg on July 24, 196-2, reveals several such chemical dicing processes. While an improvement over mechanical dicing, the chemical proccesses are still relatively time consuming and do not result in what can be termed a high yield of uniform quality. The latter deficiency may be due to the fact that since semiconductor materials are very susceptible to surface contamination by impurities, there may be undesirable reactions between any impurities in the coating and etching materials used in these chemical processes and the semiconductor material.
My invention overcomes the above-mentioned disadvantages of the prior art by providing a novel method of dicing semiconductor ribbons or wafers which is faster and produces a higher yield than previously obtainable.
It is therefore an object of my invention to provide an improved method of dicing semiconductor wafers.
It is another object of my invention to provide an improved method of fabrication of active devices from semiconductor wafers or ribbons.
These and other objects of my invention are accomplished by scribing the wafer or ribbon along lines where division of the components is desired with a highly energized, precisely focused beam. The scribed wafers or ribbons are then immersed in an ultrasonic cell and are broken along the scribed lines by ultrasonic energy produced in said cell. Alternatively, the fracturing may be accomplished by mechanically distorting the scribed slab of semiconductor material.
My invention may be better understood and its numerous advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals apply to like elements in the various figures and in which:
FIGURE 1 is a schematic view of an electron beam machine which is utilized to generate a high energy, precisely focused beam for scribing the semiconductor wafer or ribbon.
FIGURE 2 is a view of a scribed micro-semiconductor wafer.
FIGURE 3 is a schematic view of an ultrasonic cell in which the scribed wafer of FIGURE 2 is diced.
Referring now to FIGURE 1, an electron beam machine is indicated generally as 10. While the scribing step of my novel process may be performed with any device, such as a Laser, which generate a highly energized and extremely finely focused beam, I have found the electron beam 21 most advantageous tool. Electron beam machines, as they are generally known, are devices which use the kinetic energy of an electron beam to work a material. US. Patent No. 2,987,610, issued June 6, 1961, to K. H. Steigerwald, discloses such a machine. These machines operate by generating a highly focused beam of electrons. The electron beam is a welding, cutting and machining tool which has practically no mass but has high kinetic energy because of the extremely high velocity imparted to the electrons. Transfer of this kinetic energy to the lattice electrons of the workpiece generates higher lattice vibrations which cause an increase in the temperature within the impingement area sufficient to accomplish work. In fact, the temperature becomes so high that the material impinged upon melts and evaporates. Present state of the art electron beam machines, as a result of recently developed refinements in electron optics, can provide a beam focused to produce power densities on the order of ten billion watts per square inch. With such high power density the beam can locally heat, fuse, or vaporize materials and the desired type of work can be accomplished in such a short time that material adjacent to the beam impingement point is not affected by heat transfer from the work region. The electrons, which are accelerated through a potential of approximately 100 kv. or to a velocity 0.55 that of the velocity of light, may be focused into a beam which has a diameter of less than 0.0005 inch at the point of impingement on the work by means of electromagnetic focusing.
Machine comprises an evacuated chamber 12 containing the micro-semiconductor wafer or ribbon 14 to be diced positioned on a movable table 1.6. This wafer or ribbon may be Si, Ge, GaAs, InSb, SiC, AlP etc. The machine also comprises an electron beam column 18 which is in communication with chamber 12 and which contains a source of electrons, beam forming means and beam focusing means. The sources of electrons comprises a directly heated cathode or filament 20 which is supplied with heating current from a filament supply, not shown, and which has a high negative acceleration volage applied thereto from a high voltage source, not shown. An apertured anode 22 is positioned in the electron beam column 18 between the cathode and the material to be worked. The anode is connected to the case of the machine which is grounded at 24. The difference in potential between the cathode 20 and anode 22 causes the electrons emitted from the cathode to be accelerated down column 18. The electrons are focused into a beam indicatcd genenally as 26 by an electron optical system com prising adjustment coils 23 and 30, and a magnetic lens assembly 32.
Under operating conditions, the beam impinges on the wafer or ribbon 14 where it gives up its kinetic energy in the form of heat. This heating causes local evaporation of the semiconductor material and thus grooves, hereinafter referred to as lines, are scribed in the surface of the wafer or ribbon. The scribing or etching is preferably done along cleavage planes when possible. The width of these scribed lines can be maintained less than 0.001 inch. This, of course, is a much smaller area of waste or erosion than obtainable by any of the prior art dicing methods. The wafer or ribbon may be precisely scribed along lines where division of components is desired by causing deflection of beam 26 across the surface of the wafer by means of varying the current to deflection coils 34. This deflection may be controlled manually by an operator observing the wafer through an optical system comprising a penta-mirror assembly consisting of mirrors 36 and 38, a protective glass 40, a viewing light 42 for illuminating the work area and a viewing system 44 which includes means for magnifying the image of the piece being worked which is reflected thereto by the mirrors. However, for quantity production, the deflection and pulsing of beam 26 will be controlled automatically by programming means such as a computer or a flying spot scanner which is scanning a negative of the pattern to be scribed. Also, the motion of table 16 may be programmed so as to cause scribing of the desired pattern by a fixed electron beam or the scribing can be accomplished by a combination of table movement and beam deflection both of which are programmed by means well known in the art.
It should be noted that it is impossible for the surface of the semiconductor material to become contaminated during this scribing step, which produces a wafer such as is shown in FIGURE 2, since the process is carried out in a vacuum and since electrons, the cutting tool, have no material properties and thus are extremely pure in a chemical sense.
After the wafer or segment of ribbon has been scribed, it is removed from the evacuated work chamber 16 and is placed in an ultrasonic cell. Such a cell is depicted in the ultrasonic energy.
FIGURE 3 and comprises a tank 50 vibrated by a transducer 52. The frequency of vibration of transducer 52 is controlled by a frequency generator 54-. Tank *50 holds a liquid 56 such as acetone or distilled water which will not react with or otherwise contaminate the semiconductor material. The scribed wafer or ribbon 14 is suspended in the bath 56 and is broken along the scribed lines by I have also found it to be pos sible to fnacture the semiconductor material along the scribed lines mechanically by causing distortion of the wafer or ribbon by passing it between rubber balls of different diameter and hardness.
While a preferred embodiment of my invention has been shown and described, various modifications and sub stitutions may be made without deviating from the spirit and scope of my invention. Thus, while I have discussed my invention in terms of dicing chips of semiconductor material which are then used in the fabrication of microsemiconductor devices, such devices may be fabricated by first attaching contacts to the semiconductor material by welding with the electron beam after which the completed devices are scribed and diced. In either event, my invention provides a unique method of separating micro-semiconductors at low cost and with a greater than yield of useful components. Also, my invention is applicable in the cutting or forming of desired shapes, regular or irregular, from any material which is notch sensitive. That is, materials such as alumina, beryllia, cermets and metals such as tungsten and molybdenum which, when scribed or indented, show propensity upon loading to fracture in a brittle fashion without plastic flow and thus yield sharply defined interfaces may be formed into desired shapes by my invention. Such materials, and particularly the ceramics, may not readily be shaped by other techniques such as machining or chemical milling. Thus, my invention is described by way of illustration rather than limitation and accordingly, it is understood that my invention is to be limited only by the appended claims taken in view of the prior art.
1. The method of fabricating micro-semiconductor devices from a slab of semiconductor material including the steps of scribing the slab of semiconductor material with a high energy beam,
and then fracturing said slab in accordance with the pat tern of scribing.
2. The method of fabricating micro-semiconductor devices from a slab of semiconductor material including the steps of scribing the slab of semiconductor material with a high energy beam,
and then fracturing said slab in accordance with the pattern of scribing by vibrating said slab with ultrasonic energy.
3. The method as in claim 2 wherein the step of fracturing the slab includes immersing the scribed slab in the fluid medium of an ultrasonic cell and passing ultrasonic energy through the fluid medium.
4. The method as in claim 2 wherein the step of scribing the slab of semiconductor material includes passing the working beam of an electron beam machine over said slab to locally evaporate part of the slab and produce lines therein.
5. The method of fabricating micro-semiconductor devices from a slab of semiconductor material including the steps of placing said slab of semiconductor material in the vacuum chamber of an electron beam machine, focusing the working beam of the electron beam machine on said slab,
deflecting said working beam in a predetermined pattern to scribe said slab,
immersing said scribed slab in the fluid medium of an ultrasonic cell,
and passing ultrasonic energy through said fluid medium to vibrate said slab and fracture said slab in accordance with the scribed pattern. 6. The method of dicing notch sensitive materials including the steps of scribing a pattern of grooves in a slab of notch sensitive material with a high energy beam, and then fracturing said slab in accordance with the pattern of scribing. 7. The method of claim 6 wherein the step of scribing includes placing the slab in the work chamber of an apparatus which generates and utilizes an intense beam of charged particles,
evacuating the chamber,
activating the charged particle generator,
and directing the beam of charged particles across the slab in accordance with a desired pattern thereby producing grooves in the slab through the local evaporation of the material.
References Cited in the file of this patent UNITED STATES PATENTS Pietschack Dec. 28, 1943 2,778,926 Schneider Jan. 22, 1957 2,970,730 Schwarz Feb. 7, 1961 3,061,739 Stone Oct. 30, 1962