METHOD FOR RECORDING AND REPRODUCING INFORMATION

Abstract: Material easily vaporized by electron beams are regularly arranged longitudinally and laterally in the form of fine grains on a substrate. An array of the fine grains is scanned by electron beam to turn ON and OFF the electron beam in accordance with signals, thereby selectively vaporizing the fine grains. The substrate on which information is recorded is scanned by electron beam to detect the presence or absence of the fine grains thereby reading information. According to this system, recording density of approximately 10¹² bits/cm² can be realized.

Description: The present invention relates to a method for recording and reproducing information, and more particularly to a method for recording and reproducing information which is capable of recording information with high density. Methods for recording and reproducing information heretofore known include a magnetic recording and reproduc­ ing method which uses a ferromagnetic medium such as a magnetic disc, a magnetic tape or the like, a laser-beam recording and reproducing method which makes use of a laser beam, or a semiconductor memory, etc. However, the recording density of these prior arts is 10⁸ to 10⁹ bits/cm² at the best, and a recording and reproducing system capable of recording information with higher density than that just mentioned has been required. It is an object of the present invention to provide a new recording and reproducing method capable of recording with higher density. This invention provides a method which comprises regularly arranged fine grains on a substrate previously, the fine grains consisting of material that may be vaporized by electron beam, irradiation then irradiating electron beam is modulated according to information to be recorded on the thus regularly arranged fine grains to selectively vaporize the fine grains thereby recording of information, and irradiating the electron beam on the substrate with information recorded thereon to detect the presence and absence of the fine grains, thereby reproduc­ ing the recorded information. According to this method, the possible recording density is determined by the size of fine grains previously regularly arranged and the diameter of the electron beam to be irradiated. If the present electron optics technology is utilized, the recording density of 10¹² bits/cm² or more may be obtained. Forms of embodying the present invention include a method for regularly arranging fine grains on a substrate, specific examples of materials forming fine grains, a method for reducing the irradition of electron beams for recording, a method for preventing the vaporization of fine grains by electron beam irradition for reproduction, a method for detecting the presence or absence of fine grains, etc. The method according to the present invention will be described in detail with reference to the drawings. According to the present invention, first, fine grains of material capable of vaporizing by electron beam, irradiation are regularly arranged on the substrate. As a method for preparing said fine grains, various lithography techniques used for producing integrated circuits may be used. However, the following method using a phenomenon which has been recently discovered is preferable. (See Japanese Patent Application No. 163, 881/1984). According to this method, finely drawn electron beam is irradiated in a stripe-like pattern on a substrate having a very smooth surface while being scanned. Subsequently the electron beam is likewise irradiated in a stripe-­ like pattern on the same place in a scanning direction at right angles to that of the former. Thereafter, material forming fine grains having a means thickness of 10 to 100Å is deposited on the substrate by vacuum evaporation method. Then, the fine grains of the deposited material are regularly in accordance with the locus of the election beam irradiation. Alternatively, the order of preparation is reversed to that of the above-described method. That is, material forming fine grains having a film thickness of 10 to 100 Å is uniformly deposited on the substrate, and then the electron beam is scanned in a stripe-like pattern crossed with each other so that the material is vaporized in the unrequired area, thereby regularly arranging the fine grains longitudinally and laterally. FIG. 1 shows a system of fine grains obtained according to the aforementioned method. When the finely drawn electron beam is scanned along the rows of fine grains aligned in a two-dimensional pattern and at the same time the electron beam is turned ON and OFF according to a digitally-converted signal (0 or 1), the electron beam impinged upon a fine grain corresponding to "0" signal (indicated at black circles in FIG. 1) , and electron beam is not irradiated on a fine grain corresponding to "1" signal (indicated at white circles in FIG. 1). In the present invention, since the fine grains consist of material which are vaporized by electron beam irradiation, the fine grains are present or absent according to the digital signal, and then the signal is recorded. Material forming fine grains that may be used in the present invention can be of any material if they are vaporized by electron beam irradiation. These materials include halides, for example, such as LiF, LidCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbF, RbCl, RabBr, RbI, CsF. CsCl, CsBr, CsI, CuCl, CuBr, CuI, AgF, AgCl, AgBr, AgI, AℓF₃, and organic compounds, for example, such as palmitic acid, stearic acid, acrylic acid, methacrylic acid, methallophtacyanine, merocyanine, napthalene, anthracen, pyrene, etc. Particularly, KI, RbI or CsI is preferred. According to the method of the present invention recording can be made at a room temperature in substrate temperature. However, the substrate temperature is pre­ ferably from 100°C to 1000°C at which the intensity of electron beam irradiation required to vaporize the fine grains is reduced so that quicker recording is possible. On the other hand, the smaller the size of fine grains, the lower the intensity of electron beam irradiation required to vaporize one fine grain, and therefore quicker recording is possible. Particularly, the size of fine grains smaller than 0.1µm is preferred. In the present invention, signals recorded by the presence or absence of fine grain are reproduced by scanning electron beam irradiation in a manner similar to that of recording along the rows of recorded fine grains to detect the presence or absence of grain. Means for detecting the presence or absence of grain include methods for detecting the quantity of secondary electrons, reflected electrons, specimen absorbing current, cathode luminescense, or etc. However, the method for detecting the number of secondary electrons is preferred which can obtain the highest ratio of signal to noise. According to the present invention, since reproduction is also carried out by electron beam irradiation. If electron beam if irradiated under the same conditions as those of electron beam used for recording, fine grains are vaporized during reproducing to lose the recording, which is not preferable. To avoid this, the present invention is possible to provide the methods of: (1) decreasing the strength of electron beams used when reproducing as compared with that when recording, (2) increasing a substrate temperature when recording as compared with that when reproducing, and (3) coating recorded fine grains with material which is not vaporized by reproducing electron beam irradiation. Among these methods, the methods (2) and (3) are preferable because signals are less deteriorated. In the method (3), when a large amount of coating is used, the ratio of signal to noise is low whilst when a small amount of coating is used, signal is unavoidably deteriorated when reproducing is repeated, which are not preferable. After all the thickness of 5 to 50Å is preferred. It is noted that these three methods may be combined for use. Materials used for the coating in the method (3) above can be any material if the latter is not evaporated by electron beam irradiation and can easily form a thin film. These materials include, for example, metals such as Be, Mg, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Ca, Mn, Fe, Co, Ni, Cu, Zn, etc.; semiconductors such as Si, Ge, etc.; oxided such as BeO, CaO, Fe₂O₃, MgO, NiO, SiO₂ ZnO, ZrO₂, Aℓ₂O₃, Cr₂O₃, TiO₂, CoO, etc.; nitrides such as TiN, Zr₃N₂, AℓN, CrN, Si₃N₄, ZrN, Mg₃N₂, FeN, BN, etc.; and organic compounds such as polyethylene, polyimide, polyacrylonitrile, polycarbonate, etc. The easiest method comprises introduc­ ing a recorded system of fine grains into the vacuum atmosphere evacuated by a diffusion pump and irradiating electron beam on the surface therein. According to this method, it is possible to thinly coat hydrocarbon, which is induced by electron beam irradiation, on said system of fine grains. This can be considered that oil vapor from the diffusion pump is changed in properties by the electron beam and adsorbed. The recording density obtained by the method of the present invention is determined according to the size of fine grains and the diameter of electron beams irradiated. The diameter of electron beam may be drawn to 20 Å or less even in the present electro-optics, and the recording density is almost determined by the size of the fine grains. Since the size of fine grains on the substrate may be made to be as small as 100 Å or less, the recording density possibly used is above 10¹² bits/cm². BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view schematically showing the state of the surface of a substrate on which information is recorded according to the present invention; and FIG. 2 shows waveforms of reproducing signals by secondary electrons detected from the substrate according to an embodiment. EXAMPLE The method of the present invention will be described in detail by way of a few examples. However, the scope of the present invention is not limited by these examples. Example 1 An area of 20 µm x 20 µm on a silicon wafer was irradiated for three minutes scanning in a stripe-like pattern at intervals of 200 Å with electron beam having a diameter of approximately 50 Å, accelerating voltage of 30 KV and current of 10 µµA. At this time, when the electron beam is transferred to another scanning line, the beam undergoes blanking to prevent irradiation. The, the same area was irradiated under the same condition as described above with the scanning direction set at right angles to that of the former. Subsequently, potassium iodide was deposited in a weight thickness of 40 Å on the silicon wafer. When the portion of the wafer on which electron beam was irradiated is observed by an electron microscope, fine grains of potassium iodide having a diameter of approximately 150 Å orderly arranged in a two-dimensional square lattice-like pattern at intervals of 200 Å were observed. Electron beams having a diameter of 40 Å, accelerating voltage of 10 KV and current of 1 µµA were irradiated along the thus arrayed rows of fine grains while scanning at a speed of 2 cm/sec, and secondary electrons at that time was detected. When this signal is processed by a comparator, a signal as indicated in FIG. 2 (1) was obtained. Next, electron beams having a diameter of 100 Å, accelerating voltage 40 KV and current 100 µµA were irradi­ ated on the thus arranged fine grains scanned along the rows thereof at a speed of 2 cm/sec. At that time, the electron beam was turned ON/OFF every other fine grain. Electron beam having a diameter of 40 Å, accelerating voltage 10 KV, current 1 µµA were irradiated scanning at a speed of 2 cm/sc along the rows of fine grains on the wafer after being subjected to the aforementioned step and the quantity of secondary electron at that time was detected. When this signal is processed by a comparator, a signal as shown in FIG. 2 (2) was obtained. This shows that the recorded signal was reproduced without modification. Embodiment 2 An area of 20µm x 20µm on a silicon wafer was irradiated for three minutes scanning in a stripe-like pattern at intervals of 200 Å with electron beam having the diameter of approximately 50 Å, accelerating voltage 30 KV, current 10µµA. At this time, when the electron beam is transferred to another scanning line, the beam undergoes blanking to prevent irradiation. Then, the same area was irradiated under the same condition as that described above with the scanning direction set at right angles to that of the former. Subsequently, NaCl was deposited in a weight thickness of 40 Å by vacuum evaporation on the silicon wafer. When the portion of the water on which electron beam was irradiated is observed by an electron microscope, fine grains of NaCl having a diameter of approx. 150 Å arranged in a two-dimensional square lattice-like pattern at an interval of 200 Å were observed. Electron beam having a beam diameter of 40 Å, accelerating voltage of 10 KV and current of 1 µµ A were irradiated while scanning at a speed of 2 cm/sec along the thus arrayed rows of fine grains and the intensity of secondary electrons at that time was detected. When this signal is processed by a comparator, a signal as indicated in FIG. 2(3) was obtained. The wafer was heated and maintained at 300°C, and electron beams having a diameter of 50 Å, accelerating voltage of 30 KV and current of 10 µµA were irradiated while scanning at a speed of 2 cm/sec along the thus arrayed rows of fine grains. At that time, the electron beam was turned ON/OFF every other fine grain. Next, the temperature of the wafer is returned to room temperature, and electron beam having a diameter of 50 Å, accelerating voltage of 30 KV and current of 10 µµA were irradiated while scanning at a speed of 2 cm/sec along the rows of fine grains on the wafer and the intensity of secondary electrons at that time was detected. When this signal is processed by a comparator, a signal as indicated in FIG. 2 (4) was obtained. This shows that the recorded signal was reproduced without modification. Embodiment 3 An area of 20 µm x 20 µm on a silicon wafer was irradiated for three minutes while scanning in a stripe-­ like pattern at an interval of 200 Å with electron beams having a diameter of approximately 50 Å, accelerating voltage of 30 KV and current 10 µµA. At this time, when the electron beam is transferred to another scanning line, the beam undergoes blanking to prevent irradiation. Then, the same area was irradiated under the same condition as that described above with the scanning direction set at right angles to that of the former. Subsequently, pyrene was deposited in a weight thickness of 30 Å on the silicon wafer. When the portion of the wafer on which electron beam was irradiated is observed by an electron microscope, fine grains of pyrene having a diameter of approx. 150 Å arranged in a two-dimensional square lattice-like pattern at an interval of 200 Å were observed. Electron beams having a diameter of 100 Å, accelerating voltage of 40 KV and current of 100µµA were irradiated while scanning at a speed of 2 cm/sec along the the rows of fine grains. At that time, an electron beam was turned ON/OFF. every other fine grain. Next, carbon of approximately 20 Å was vacuum deposited on the fine grain. Electron beams having a diameter of 40 Å, accelerating voltage of 10 KV and current of 1 µµÅ were irradiated while scanning at a speed of 2 cm/sec, along the rows of fine grains after being subjected to said step and the intensity of secondary electrons at that time was detected. When this signal is processed by a comparator, a signal as shown in FIG. 2(5) was obtained. This shows that the recording signal was reproduced without modification. According to the present invention, there is provided a new information recording and reproducing method on the basis of a principle which is fundamentally different from that of conventional various information recording and reproducing methods. The recording density is above 10¹² bits/cm², which is far above 10⁹ bits/cm², the upper limit of that of prior art. The device of the present invention is considered to be widely used in future in the field of video information recording and reproducing apparatus, memories of electronic computers, etc. which would require higher density recording.

Claims: 1. A method for recording and reproducing information comprising regularly arranging on a substrate fine grains which consist of material that may be evaporated by irradiat­ ion of electron beams, irradiating electron beam modulated according to information to be recorded on the thus regularly arranged fine grains to selectively evaporate the fine grains thereby recording information, and irradiating electron beam on the substrate on which information is recorded to detect the presence or absence of fine grains thereby reproducing the recorded information. 2. The method for recording and reproducing inform­ ation according to claim 1, wherein the material that may be evaporated by irradiation of electron beam is selected from LiF, LiCl, LiBr, LiI, NaF, NaCℓ, NaBr, NaI, KF, KCl, KBr. KI, RbF, RbCl, RbBr. RbI, CsF, CsCl, CsBr, CsI, CuCl, CuBr, CuI, AgF, AgCl, AgBr, AgI, AℓF₃, palmitic acid, stearic acid, crylic acid, methacrylic acid, methallophtacyanine, merocyanine, napthalene, anthracen, and pyrene. 3. The method for recording and reproducing inform­ ation according to claim 1, wherein in order to regularly arraying fine grains on the substrate, the electron beam is scanned in a stripe-like pattern crossed each other in two different directions and then the material that may be evaporated by electron beam irradiation is deposited thereon. 4. The method for recording and reproducing information according to claim 1, wherein the material that may be evaporated by electron beam irradiation is first deposited on the substrate and then the electron beam is scanned in a stripe-like pattern crossed each other on the deposited film, thereby regularly arranging fine grains on the substrate. 5. The method for recording and reproducing information according to claim 1, wherein a temperature of the substrate when recording is heated to 100°C or above. 6. The method for recording and reproducing information according to claim 1, wherein a temperature of the substrate when reproducing is lower than a temperature of the substrate when recording. 7. The method for recording and reproducing information according to claim 1, wherein the intensity of electron beam used for reproducing is decreased as compared with that of electron beam used for recording. 8. The method for recording and reproducing information according to claim 1, wherein the fine grains on the substrate which has already been recorded are coated with material which is not evaporated by electron beam irradiation of used for reproducing. 9. The method for recording and reproducing information according to claim 8, wherein the coating material is selected from metals such as Be, Mg, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Ca, Mn, Fe, Co, Ni, Cu, Zn, ; semiconductors such as Si, Ge, ; oxides such as BeO, CaO, Fe₂O₃, MgO, NiO, SiO₂, ZnO, ZrO₂,Aℓ₂O₃, Cr₂O₃, TiO₂, CoO, ; nitrides such as TiN, Zr₃N₂, AℓN, CrN, Si₃N₄, ZrN, Mg₃N₂, FeN, BN, ; and organic compounds such as polyethylene, polyimide, polyacrylonitrile, polycarbonate. 10. The method for recording and reproducing information according to claim 8, wherein the coating is performed by electron beam irradiating in the vacuum atmosphere evacuated by a diffusion pump. 11. The method for recording and reproducing information according to claim 1, wherein the fine grains are detected by either detection of quantity of secondary electrons reflecting electrons, cathode luminescense, or specimen absorbing current when electron beam is irradiated.

Inventors: UMEMURA, SHIZUO
Applicants: FUJI PHOTO FILM CO., LTD., RESEARCH DEVELOPMENT CORPORATION OF JAPAN
Application year: 1986
Main classification: G11B9
IPC codes: G11B9, G11B7