JPH0192941A - Large capacity readout only memory - Google Patents

Abstract

PURPOSE:To attain the increased capacity by arranging an area having at least two kinds of secondary electron emission rates onto a recording medium substrate so as to form a read only memory and radiating a charged particle ray onto the area so as to detect the area. CONSTITUTION:A secondary electron ray radiated by radiating a focused charged particle ray 4 onto a recording medium provided with a high secondary electron radiation area 2 and a low secondary electron radiation area 3 on a substrate 1 is detected by a secondary electron detector 6 and the information is read by the intensity. Since the minimum area required to record information is reduced to an area of (50nm)<2> or the like, it is possible to increase the capacity considerably. For example, in case of the minimum recording area of (50nm)<2>, the information of ultra-large capacity of 4,000 Gbits is recorded on the recording medium substrate of 10cm<2>. That is, the recording capacity of the read only memory is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a read-only memory, and more particularly to a read-only memory that can easily be increased in capacity using a charged particle beam.

[Conventional technology]

Conventionally, large-capacity read-only memories have been widely used in the form of floppy disks, compact disks, etc., using magnetic thin films, laser light reflecting films, or the like as recording media. These conventional large-capacity read-only memories use a method that records the direction and magnitude of magnetization or the reflected intensity of laser light as information within a magnetic thin film.

There were the following problems.

[Problem that the invention seeks to solve]

In other words, in the case of a magnetic thin film, the minimum area required for recording information cannot be smaller than the size of the magnetic domain, which is determined by the type of magnetic material.Currently, the size of the magnetic domain is 0.2~
It is 0.3 μm. Therefore, since this magnetic domain size becomes the minimum recordable area size, the maximum memory capacity is theoretically limited.

Furthermore, when using a laser beam reflective film, the minimum recordable area is determined by the beam diameter of the laser beam.

Since the focusing limit of laser light is approximately 1/2 of the wavelength, the physical limit is 0.1 to 0.2 μm. Therefore, the minimum beam diameter of the laser beam determines the maximum capacity of the memory.

As mentioned above, the current large capacity read-only memory is
Considering the recording method, we are approaching the theoretical limit of increasing the capacity, and it is impossible to increase the capacity any further. For example, in the case of magnetic compact disks, the limited capacity is 5 to 10 Gbytes, which poses an obstacle to future increases in capacity.

An object of the present invention is to provide an information recording and reading method that enables an innovative increase in the capacity of the above-mentioned large-capacity read-only memory.

[Means for solving problems]

The above object is to provide a read-only memory comprising areas having at least two types of secondary electron emission rates arranged on a recording medium substrate, and to charge the areas having at least two types of secondary electron emission rates. This is achieved by using a read-only memory that is characterized by irradiating and detecting particle beams.

FIG. 1 is a diagram for explaining the present invention in detail, and shows a charged particle beam focused on a recording medium having a high secondary electron emission region 2 and a low secondary electron emission region 3 on a substrate 1. This is a read-only memory in which a secondary electron detector 6 detects a secondary electron beam 5 emitted by irradiating the electron beam 4, and reads information based on the intensity of the detected secondary electron beam 5.

[Effect]

As is well known, the beam diameter of the charged particle beam 4 is, for example, 1 nm or less for electron beams and 50 nm for ion beams.
It can be focused on: Furthermore, according to microfabrication techniques such as electron beam exposure method or Since the structure can be formed, it can be processed to be as small as the beam diameter of a charged particle beam using the above-mentioned high or low secondary electron emission region. Therefore, in the read-only memory according to the present invention, the minimum area on which information must be recorded can be reduced to approximately (50 nm), making it possible to dramatically increase the capacity.For example, the minimum recording area (50 nm)'', an extremely large amount of information of 4000 Gbits can be recorded on a 10 aJ recording medium substrate.

As described above, according to the present invention, the recording capacity of a read-only memory can be innovatively increased.

Its technological, industrial, and social effects are significant.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 2 to 6.

Example 1 In this example, an ultra-large capacity read-only memory using grooves on a substrate having different secondary electron emission rates as information recording areas of the present invention and an electron beam as a charged particle beam will be described. FIG. 2 and FIG. 3 are diagrams for explaining this embodiment.

First, FIG. 2(a) explains the information recording system of this embodiment, in which groove diameters (r) are formed on a conductive information recording medium substrate 1 by electron beam exposure and dry etching. ) 0.1 μm, interval between grooves 0.1 μm, groove depth (
d) This shows the formation of secondary electron emission grooves 7 of 0.1 to 0.5 μm.

FIG. 2(b) shows the groove depth (d) of the secondary electron emission groove 7.
These are the results of an experimental investigation of the relationship between the ratio (d/r) of the groove diameter (r) and the secondary electron emission rate.

The experimental results showed that as d/r increases, the secondary electron emission rate decreases, and when d/r is 3 or more, almost no secondary electrons are emitted. Therefore, the groove depth is 0.1
The secondary electron emission rates of the .mu.m and 0.4 .mu.m grooves were used as a high secondary electron emission region and a low secondary electron emission region, respectively, and a difference in the secondary electron emission rates of 1150 was obtained.

FIG. 3 is a block diagram for explaining a reading method of a read-only memory using the disc-shaped recording medium having the above-mentioned secondary electron emission grooves.

A Si disc-shaped substrate 1 with a thickness of 500 μm on which a secondary electron emission groove 7 is formed is mounted on a rotary table 11, and a rotation drive device! 12, and the position detection device 14 are connected to the rotation control device 1.
3 to control the position of the substrate 1.

On the other hand, an electron beam 4 focused to a beam diameter of 10 nm is formed in a focusing lens barrel 9 while being controlled by a charged particle beam control device 10, and 2 Next, the electron emission groove 7 is irradiated. The secondary electron beam 5 emitted at this time is detected by a secondary electron detector 6,
Furthermore, from the intensity signal and the substrate position signal from the rotation control device 13, using the information readout control device 15, "
1" and at O" information is read.

Since the disk-shaped substrate 1 described above has a diameter of 10 mm and the area required for recording information is (0.2 μm)z, a recording capacity of approximately 200 Gbit was achieved.

In this example, an electron beam was used as the charged particle beam 4, but
Ga+, In+ with a beat diameter of 1100n.

Even when an ion beam of Sn 10 or the like was used, information could be read out in a similar manner.

Embodiment 2 In this embodiment, a superhuman capacity read-only memory using a concave-convex structure on a substrate having different secondary electron emission rates as an information recording area of the present invention will be described. FIG. 4 is a diagram for explaining this example, in which an aluminum film with a thickness of 1 μm is vacuum-deposited on a Si substrate 1 for a recording medium, and then etched by an electron beam exposure method and a dry etching method. An aluminum cylinder 16 with a diameter of 0.1 μm is formed as a high secondary electron emission region, and an aluminum cylinder 16 with a depth of 50 μm is formed as a low secondary electron emission region.
2 shows a cross section of a disk-shaped substrate in which a secondary electron emission groove 7 with a diameter of 0.1 μm is formed. Above aluminum cylinder 1
The ratio of the secondary electron emission rate of 6 and the secondary electron emission groove is 200:
1, and a high secondary electron intensity difference was obtained. When the information on this disc-shaped substrate was read using the same readout method as described in Example 1, all 200G bits of information could be read out without any errors during readout, and this recording method The effectiveness was confirmed.

Embodiment 3 In this embodiment, an ultra-large-capacity read-only memory that utilizes a difference in secondary electron emission rate caused by a difference in impurity concentration as an information recording area will be described. FIG. 5 is a diagram for explaining this example, in which a focused Ga beam with an acceleration voltage of 100 KeV and a beam diameter of 0.05 μm is placed on the Si substrate 1.
+ Implantation amount I x 10”8 by ion beam implantation
/d low concentration impurity layer 17 and implantation amount I x 1
0"'/cd high concentration impurity layer 18 is formed in a circular shape with a diameter of 0.1 μm. The above-mentioned low concentration impurity layer 17 and high concentration impurity layer 18 are There is a difference of about 10:1 in the electron emission rate, and even in this example where the high concentration impurity layer 18 was used as a low secondary electron emission region, reading was performed using the readout method used in Example 1. As a result, it was found that all bits of 200 Gbits could be detected, confirming the effectiveness of this recording method.

Embodiment 4 In this embodiment, an ultra-large capacity spill-only memory that utilizes the difference in secondary electron emission rate caused by different crystal structures as the information recording area of the present invention will be described. FIG. 6 is a diagram for explaining this example, in which a 200 nm thick A substrate is placed on a semi-insulating Ga As substrate 1.
Epitaxial growth layer 19 of Q o, aGaAso, 7
is formed by the molecular beam epitaxy method, a GaAs epitaxial layer 20 with a thickness of 1100 nm is formed thereon by the same method, and then processed into a 50 nm opening by the electron beam exposure method and dry etching method. ing.

The secondary electron emission rate of the AQ GaAs layer 19 is about 10 times higher than that of the GaAs epi layer 20, so six layers using the GaAs layer 20 as a low secondary electron emission region In this example as well, when information was read using the read method used in Example 1, all bits of 200 Gbits could be detected, confirming the effectiveness of this recording method.

〔Effect of the invention〕

According to the present invention, 2
Since this is a read-only memory that uses an information read-out method that detects the intensity of the electron beam, a microscopic area with dimensions similar to the beam diameter of the charged particle beam is sufficient as the information storage area, and therefore, it is different from the conventional read-only memory. It has now become possible to realize ultra-large capacity read-only memory with a capacity of 100 Gbit or more, which was previously impossible to achieve, and its technological and industrial effects are significant.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a memory device for explaining the basic configuration of the present invention, and FIG. 2(a) and FIGS. 4 to 6 are sectional views of essential parts of a memory according to an embodiment of the present invention , FIG. 2(b) is a correlation diagram between groove depth and secondary electron emission rate, and FIG. 3 is a schematic block diagram of a memory device according to an embodiment of the present invention. 1... Substrate, 2... High secondary electron emission region, 3...
Low secondary electron emission region, 4...Charged particle beam, 5...2
Next electron beam. 6... Secondary electron detector, 7... Secondary electron emission groove, 8
...Evacuation device, 9...Focusing lens barrel, 10...Charged particle beam control device, 11...Rotary table, 12...
- Rotation drive device, 13... Rotation control device, 14...
Position detection device, 15... Reading control device, 16...
・Aluminum cylinder, 17...Low concentration impurity layer, 18
...High concentration impurity layer, 19- A Q G a A
s layer, 2O-GaAs[.

Claims (1)

[Claims] 1. A large-capacity read-only memory comprising regions having at least two types of secondary electron emission rates arranged on a substrate. 2. Claim 1, wherein the regions having at least two types of secondary electron emission rates have different compositions, crystal structures, or geometrical shapes of the constituent materials of the substrate. High-capacity read-only memory as described. 3. A large-capacity read-only memory characterized by detecting regions having at least two types of secondary electron emission rates by irradiating them with a charged particle beam.