JPH10293948A - Production of recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a recording medium which may be formed with a thinner second Si oxide layer of the recording medium surface, may be improved in the smoothness of the surface and allows writing of recording bits by and for a low impressed voltage and short voltage impression time. SOLUTION: In the process for producing the recording medium with which the accumulation of charges by implantation of the charges from a probe is possible, an SOI substrate consisting of a single crystalline Si substrate 1, a first Si oxide layer 2 formed on the single crystalline Si substrate and a single crystalline Si layer 3 formed on the first Si oxide layer is manufactured. The single crystalline Si layer 3 on the first Si oxide layer 2 is nitrided to form an Si nitride layer 4 and thereafter, part of the Si nitride layer 4 is oxidized to form the second Si oxide layer 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a recording medium used for recording information using the principle of a scanning probe microscope.

[0002]

2. Description of the Related Art A scanning tunneling microscope (hereinafter referred to as STM) or a scanning atomic force microscope (hereinafter referred to as AFM) has been put into practical use as a surface microscope having a spatial resolution of an atomic scale (these are scanning). Type probe microscope (hereinafter referred to as SPM). In these SPMs, an information recording / reproducing device that writes recorded information in a local region by applying the fact that a tip can access a sample surface at an atomic level has been considered. The STM detects the tunnel current that flows when the distance between the biased conductive tip and the conductive sample is reduced to less than several angstroms, and controls the distance between the tip and the sample so that the tunnel current becomes constant. While scanning the tip while imaging the tunnel current or the feedback control signal, a surface image is formed. As a recording method applying STM, a voltage is applied between the tip and the recording medium,
There are a method of locally changing the surface morphology of the recording medium, a method of changing the conductivity of the recording medium, and the like.

On the other hand, the AFM detects an atomic force acting on the tip and the sample surface when the tip approaches the sample by several angstroms or less, scans the tip in a two-dimensional plane, and scans the surface including irregularity information. Make up the image. As a means for detecting an atomic force, an elastic cantilever having one end fixed and a tip held near a free end is used. As a multifunctional microscope for observing AFM and STM with the same apparatus, there is a combined scanning atomic force / tunneling microscope (AFM / STM). According to this, a probe used in the AFM includes a cantilever and a tip held by the cantilever, and by making the tip conductive, a current flowing between the tip and the sample can be detected. In a normal usage, a current is detected by applying a bias between the tip and the sample during the AFM operation, and a surface unevenness image and a tunnel current distribution image by the same tip can be simultaneously obtained. Also in this multifunction device, an information recording / reproducing device that writes recording information in a local area by applying the fact that a tip can access a sample surface at an atomic level has been considered.

[0004] In many cases, information is recorded in a local area by applying a voltage between the tip and the medium. The method is as follows:-A method in which holes are made by melting the medium surface. A method of changing the conductivity of the medium by changing the crystal-non-crystal of the medium. -A method of making the tip material fly on the medium to make it uneven-A method of changing the conductivity of the medium. -A method of accumulating charges in a medium. Etc. Among them, the method of accumulating electric charge in a medium has a clear mechanism and is easy to write and erase, and therefore, is one of the most practical classes among the information recording and reproducing methods using the SPM technology. There are mainly two types of media used, one is a Si nitride layer / Si oxide layer / Si substrate (NO
S) type, and the other is a Si oxide layer / Si nitride layer / Si oxide layer / Si substrate (ONOS) type. Both are the same in that charges are stored near the interface between the co-oxidized Si layer and the Si nitride layer. However, the ONOS type can store the charges more near the surface, so that the bit diameter can be reduced, which is advantageous for higher density. become. ONOS type media is n-type S
After oxidizing the surface of the i-substrate, a silicon nitride layer is formed by LP-CVD,
(Ichiro F)
ujiwara, et al. , Jan. J. App
l. Phys. Vol. 35, (1996) pp. 27
64-2769 Part 1, No. 5A, May
1996).

FIG. 2 is a schematic view showing the principle of charge storage type information recording / reproducing. The recording medium has an ONOS structure in which a first Si oxide layer 22, a Si nitride layer 23, and a second Si oxide layer 24 are formed on an n-type single crystal Si substrate 21. An electrode layer 25 for applying a voltage is formed on the back surface of the single crystal Si substrate 21. The recording on the medium (FIG. 2-a) is first performed in the AFM mode, that is, by applying a voltage between the electrode layer 25 on the back surface of the substrate and the probe 26 with the tip of the probe 26 in contact with the medium surface. As the probe 26, a probe in which conductivity is imparted by coating a metal on a cantilever made of Si nitride or the like is usually used. By this voltage application, the Si nitride layer 23 and the second Si oxide
Charges are injected and accumulated near the interface of the layer 24 to generate the recording bit 2.
7 is formed. Reproduction is performed in a scanning Maxwell stress microscope (SMM) mode (FIG. 2B). When the surface is scanned in a non-contact manner with the medium in a state in which a voltage is applied to the probe 26, a stress acts on the probe 26 due to the accumulated charge in the vicinity of the recording bit 27 where the charge is accumulated. Is displaced. By detecting this displacement, the recording bit 27 is recognized. The displacement of the probe 26 is normally detected by irradiating the back surface of the probe with laser light 27 and detecting the reflected light by a heterodyne interferometer 28.

[0006]

In such a charge storage type recording medium, the most important is the thickness of the second Si oxide layer. It is more preferable that this film thickness is originally thin.
By making it thinner, at a lower voltage and in a shorter time,
Then, smaller bits can be recorded, and the recorded bits can be detected with high resolution even during reproduction. However, the conventional manufacturing method has a problem that if the thickness is too small, the interface between the Si nitride layer and the second Si oxide layer is not formed well, and a portion where no charge is accumulated occurs, causing an error. Was. That is, conventionally, the second Si oxide layer has been manufactured by oxidizing a Si nitride layer formed by the LP-CVD method. However, since a film formed by vapor deposition such as the LP-CVD method is formed by randomly gathering polycrystals, the crystal grain size and the orientation are not uniform. When the second silicon oxide layer is formed by oxidizing such a silicon nitride film, the oxidation rate also varies, and the most important uniformity of the oxide film thickness for the charge storage type is impaired. . Therefore, the film thickness of the second Si oxide layer is a film thickness in consideration of them, and is set to about 4 to 5 nm.
It was difficult to make the film thickness smaller than that. Then, in order to form a good recording bit on the recording medium having the second Si oxide layer having such a thickness, an applied voltage of 10 V or more and an application time of 10 msec or more were required. .

Therefore, the present invention solves the above-mentioned problems in the conventional art, and can reduce the thickness of the second Si oxide layer on the surface of the recording medium and improve the smoothness of the surface. It is another object of the present invention to provide a method of manufacturing a recording medium on which recording bits can be written by using a low applied voltage and a short voltage application time.

[0008]

In order to solve the above-mentioned problems, the present invention is characterized in that a method for manufacturing a recording medium is constituted as follows. That is, the method for manufacturing a recording medium of the present invention is a method for manufacturing a recording medium capable of accumulating charges by injecting charges from a probe. The formed first silicon oxide layer, and the first silicon oxide layer
Forming an SOI substrate composed of a single crystal Si layer formed on the layer, nitriding the single crystal Si layer on the first Si oxide layer to form a Si nitride layer, and then forming a part of the Si nitride layer; Is oxidized to form a second Si oxide layer.
Further, the method of manufacturing a recording medium according to the present invention, wherein
The layer is a film formed by epitaxial growth.

[0009]

Next, a manufacturing method of the present invention will be described with reference to the drawings. As the substrate, an SOI substrate in which a single-crystal Si layer 3 is formed on a single-crystal Si substrate 1 via a first Si oxide layer 2 (FIG. 1A). SOI substrate is S
a method of implanting oxygen ions into an i-wafer and then performing a heat treatment to form a silicon oxide layer (commonly called SIMOX);
It is manufactured by a method in which a wafer is bonded to another Si wafer on which an Si oxide film is formed, and then one of the Si wafers is ground and thinned. Also, recently, a method of dissolving and removing porous Si after laminating a single-crystal Si layer epitaxially grown on porous Si with another Si wafer on which a Si oxide film is formed (Japanese Unexamined Patent Publication No.
No. -021338) has been proposed. The SOI substrate manufactured by this method is extremely excellent in terms of film thickness uniformity, crystallinity, processability, and the like, as compared with others. Further, since the substrate can be formed to have a desired thickness with respect to the single crystal Si layer or the first Si oxide layer, it is most preferable as the substrate used in the present invention.

The substrate is subjected to a heat treatment in a nitrogen gas or an ammonia gas containing hydrogen to nitride the single crystal Si layer to form a Si nitride layer 4 (FIG. 1B). The heat treatment is performed at 1100 to 1300 ° C. Subsequently, a second Si oxide layer 5 is formed on the outermost surface of the nitrided single crystal Si layer, that is, the nitrided Si layer 4 by oxidizing the substrate (FIG. 1C). The oxidation is performed at 1000 to 1300 ° C. in a mixed gas of oxygen and hydrogen. By this processing, a uniform 2-3 nm thick Si oxide
Layers can be formed. Finally, the electrode layer 6 is formed on the back surface of the SOI substrate to obtain an ONOS charge storage type recording medium (FIG. 1-d). The surface of the medium obtained by this method has better smoothness than the conventional method. This is because a smooth single crystal Si layer is used as a starting layer. Information recording on the medium is performed in the AFM mode, and is performed by applying a voltage between the medium and a probe provided with conductivity while in contact with the medium. The voltage application is usually performed at 5 to 8 V for several tens μsec to several hundred μsec. Information is reproduced in the SMM mode by scanning the medium with a probe and detecting a change in surface charge.

When information is recorded / reproduced using a recording medium produced by the production method of the present invention, the following characteristic effects can be obtained. -Since the second Si oxide layer can be made thinner, the applied voltage during recording can be reduced and the time can be shortened.・ Because it is possible to lower the applied voltage and shorten the recording time,
Since the load on the probe can be reduced, the durability of the probe can be improved. Since the smoothness of the medium surface is good, the wear of the tip of the probe performing the contact scanning during recording can be reduced, and the durability of the probe can be improved.

[0012]

Embodiments of the present invention will be described below. [Example 1] In Example 1, first,
According to the method described in JP-A-021338, SOI
A substrate was prepared. The single-crystal Si substrate 1 was n-type, the thickness of the first Si oxide layer 2 was 2 nm, and the thickness of the single-crystal Si layer 3 was 6 nm. This substrate is placed in an ammonia gas atmosphere at 1250 ° C.
The single crystal Si layer is nitrided by heating at
Layer 4 was formed. Subsequently, the substrate was oxidized in an atmosphere of oxygen and hydrogen at 1200 ° C. to oxidize the surface of the Si nitride layer, thereby forming a second Si oxide layer 5. Next, the single crystal S
The Si oxide layer and the Si nitride layer formed on the back surface of the i-substrate were removed by dry etching. T
The electrode layer 6 was formed by depositing i: 5 nm and Au: 50 nm.

By these treatments, the outermost surface of the silicon oxide layer 5 is 2.5 nm thick / the silicon nitride layer 4 is 8 nm thick / the silicon oxide layer 2
A recording medium having a thickness of 2 nm / single-crystal Si substrate 1 / electrode layer 6 was produced. When the surface of this medium was measured by AFM, the maximum surface roughness within a square of 5 μm was 1.0 nm. Next, information was recorded and reproduced on this medium. As the probe, a tungsten-coated Si nitride probe was used. The recording conditions were a rectangular pulse having an applied voltage of 8 V and an application time of 100 μsec. Under these conditions, pulse application was performed 10,000 times. Subsequently, when reproduction was performed in the SMM mode, the bit diameter was about 60 nm, and recording and reproduction could be performed satisfactorily without error.
Next, the tip of the used probe was scanned with a scanning electron microscope (FE).
-SEM). As a result, no change such as abrasion was observed in the tungsten layer at the tip of the probe.

Example 2 In Example 2, an SOI substrate was manufactured in the same manner as in Example 1. The single-crystal Si substrate 1 is n-type, the thickness of the first Si oxide layer 2 is 3 nm, and the single-crystal Si
The thickness of the layer 3 was 5 nm. The substrate is heated and maintained at 1300 ° C. in an ammonia gas atmosphere to form single crystal Si.
The layer was nitrided to form a Si nitride layer 4. Subsequently, the surface of the substrate was oxidized at 1200 ° C. in an atmosphere of oxygen and hydrogen to oxidize the surface of the Si nitride layer 4 to form a second Si oxide layer 5. Next, the silicon oxide layer and the silicon nitride layer formed on the back surface of the single crystal Si substrate 1 were removed by dry etching. The electrode layer 6 was formed by forming a film of Ti: 5 nm and Au: 50 nm on the removed surface.

By these treatments, a recording medium composed of the first surface of the first Si oxide layer 5 having a thickness of 2 nm / Si nitride layer 4 having a thickness of 7 nm / Si oxide layer 2 having a thickness of 2 nm / single crystal Si substrate 1 / electrode layer 6 is produced. did it. Next, information was recorded and reproduced on this medium. Probe is platinum coated nitrided S
An i-probe was used. The recording conditions were a rectangular pulse having an applied voltage of 7 V and an application time of 80 μsec. Under these conditions, pulse application was performed 20,000 times. Subsequently, when reproduction was performed in the SMM mode, the bit diameter was about 50 nm.
Recording and reproduction could be performed satisfactorily with no error in diameter. Next, the tip of the used probe was observed with a scanning electron microscope (FE-SEM). As a result, no change such as abrasion was observed in the platinum layer at the tip of the probe.

[0016]

According to the present invention, as described above, the SO
By manufacturing the recording medium by nitriding and oxidizing the single crystal Si layer of the I substrate, the thickness of the second Si oxide layer on the surface of the recording medium can be made thinner than before, and the surface smoothness can be improved. This makes it possible to write a recording bit with a low applied voltage and a short voltage application time, thereby improving the durability of the probe.
Further, according to the present invention, since the smoothness of the medium surface can be improved, it is possible to reduce the abrasion of the tip of the probe performing the contact scanning during recording and to improve the durability of the probe. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a manufacturing method of the present invention.

FIG. 2 is a schematic diagram showing the principle of charge storage type information recording and reproduction.

[Explanation of symbols]

 1, 21: single crystal Si substrate 2, 22: first Si oxide layer 3: single crystal Si layer 4, 23: Si nitride layer 5, 24: second Si oxide layer 6, 25: electrode layer 26: probe 27: Laser light 28: Heterodyne interferometer

Claims (2)

[Claims] 1. Injecting a charge from a probe,
A method of manufacturing a recording medium capable of storing electric charges, comprising: a single-crystal Si substrate; a first Si oxide layer formed on the single-crystal Si substrate; and a first Si oxide layer formed on the first Si oxide layer. An SOI substrate made of the single-crystal Si layer thus formed, and nitriding the single-crystal Si layer on the first Si oxide layer to form a nitrided S
After forming the i-layer, a part of the Si nitride layer is oxidized to form a second
A method for manufacturing a recording medium, comprising forming an Si oxide layer of 2. The semiconductor device according to claim 1, wherein said single-crystal Si layer is a film formed by epitaxial growth.
3. The method for manufacturing a recording medium according to item 1.