JPH09259428A - Surface roughening method for silicon substrate for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface roughening method to produce a substrate having a texturing pattern with excellent CSS characteristics by applying ultrasonic waves on a silicon substrate while subjecting the substrate to wet etching so as to form a specified rugged pattern on the substrate surface. SOLUTION: Ultrasonic waves are applied on a silicon substrate while the substrate is subjected to wet etching to form a rugged pattern having the depth between 5nm and 100nm on the substrate surface. By this method, a uniform rugged pattern can be formed on the surface, which makes a grinding process to compensate the fluctuation in the roughness height unnecessary. Therefore, the process of surface roughening can be simplified. A uniform texturing pattern can be formed on the surface of the silicon substrate and the CSS characteristics can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for roughening the surface of a silicon substrate for a magnetic recording medium, which is useful for an external recording device of a computer, particularly for a magnetic hard disk.

[0002]

2. Description of the Related Art With the progress of the information society, a large-capacity recording medium is required. Especially, a magnetic disk, which plays a central role as an external memory of a computer, has a recording capacity and a recording density both increasing year by year. However, development is in progress for higher density recording. In particular, due to the development of notebook type personal computers and palmtop personal computers, small discs are required, and higher density recording is desired.

In such a magnetic disk, most of the characteristics of the magnetic medium, such as strength, surface smoothness, warpage and weight, are attributed to the substrate. Conventionally, NiP is used for the substrate
However, since the aluminum alloy is soft, it has a problem that the thickness of the substrate cannot be reduced, it is easily scratched during handling, or it is dented by impact. Therefore, it has been proposed to use single crystal silicon for the substrate (Japanese Patent Publication No. 1-42048, Japanese Patent Publication No. 2-41089, and Japanese Patent Publication No.
59523, Japanese Patent Publication No. 1-45140, JP-A-6-68463
Japanese Patent Laid-Open No. 6-28655 and Japanese Patent Laid-Open No. 4-259908). In particular, in Japanese Examined Patent Publication No. 2-41089, a silicon substrate used for semiconductors is used as a silicon substrate, and a base layer is formed on the silicon substrate, and then a recording film made of a magnetic material such as an iron alloy or a cobalt alloy is formed. It is disclosed. Japanese Patent Publication No. 2-59523 discloses a method of forming unevenness on a silicon substrate in a coating type recording medium. However, as the recording density increases, the recording film becomes thinner and information is recorded and reproduced. The distance (flying height) between the magnetic head and the recording medium is 0.1 μm or less, but the flying height cannot be lowered by forming a large protrusion as in this document. Also, Japanese Patent Laid-Open No. 4-259908
The publication discloses that concentric circular texturing is applied because the surface of silicon is too smooth and the CSS characteristics (start / stop characteristics when contacting the magnetic head of the recording medium) are deteriorated.

[0004]

When the surface irregularities of the substrate are as small as possible, the distance (flying height) between the magnetic head and the recording medium during recording / reproducing information can be reduced, and higher density can be achieved. Becomes On the other hand, when a silicon substrate is used as the recording medium, the flying height can be lowered as described above, but there is a problem that the surface is too smooth and the CSS characteristics are not sufficient. There is an etching treatment as one of the methods for roughening the surface of a silicon substrate, but there are various documents (JAP Vol.40, No11, No.
4569, latest LSI process technology (Industrial Research Association, 1983)
See). However, the surface cannot be roughened even if a mixture of hydrofluoric acid and nitric acid having a concentration ratio for mirror etching, which is generally known as an etching solution for silicon, is used,
Further, even if the treatment is performed by changing the concentration ratio of the mixed acid, the surface of the substrate can be roughened only to the extent that a large undulation occurs at most, which is not suitable for forming a texturing pattern on the substrate for a magnetic recording medium. A method for uniformly roughening the surface is a method for forming a quadrangular pyramid-shaped depression, which is performed in the field of silicon substrates for solar cells. It is not suitable for forming a texturing pattern on a silicon substrate for a magnetic recording medium because the substrate surface is too rough.

When the etching solution is anisotropic and alkaline and contains sodium hydroxide and / or potassium hydroxide, particularly sodium hydroxide solution or potassium hydroxide solution, the alkali concentration is If it is high, there is a problem that large depressions are likely to be formed, and if the alkali concentration is low, there is a problem that unevenness cannot be formed at all. Further, only by immersing the silicon substrate in the alkaline etching solution, the surface distribution of the generated irregularities is nonuniform, and even if a stirrer such as a stirrer is used, the etching uniformity is not sufficient. For this reason, when the flying height of the flying head is lowered, an attempt to reduce the unevenness of the surface causes a part where there is no unevenness, and there is a problem that the CSS characteristics are not sufficient. The present invention intends to solve the above problems and provide a surface roughening method for a silicon substrate for a magnetic recording medium having a textured pattern with excellent CSS characteristics.

[0006]

The present invention relates to a method for surface roughening a silicon substrate for a magnetic recording medium, in which ultrasonic waves are applied while performing wet etching on the silicon substrate,
The gist is a method for roughening the surface of a silicon substrate for a magnetic recording medium, which comprises forming irregularities of 5 nm or more and 100 nm or less on the substrate surface. That is, according to the present invention, since uniform unevenness is formed in the surface of the silicon surface by applying ultrasonic waves when the surface of the silicon substrate is wet-etched, the grinding for compensating the difference in height of the unevenness is performed. Is unnecessary, and the steps of the surface roughening method can be simplified. Further, by using an alkaline solution as the etching solution, the alkali concentration is lowered to reduce the generation of large depressions, and the solution temperature is raised, whereby the irregularities can be formed in a short time. The result is a uniform texturing pattern on the surface of the silicon substrate, which improves CSS properties.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a texturing pattern on the surface of a magnetic recording medium using a silicon substrate is formed by applying ultrasonic waves with an alkaline etching solution to control the solution temperature and the alkali concentration. By this, unevenness optimal as a texturing pattern is uniformly formed on the surface of the silicon substrate of the magnetic recording medium. The details will be described below. The silicon substrate used in the present invention only needs to have a silicon layer on the surface of the substrate, and for example, a non-magnetic substrate such as single crystal silicon, polycrystalline silicon or a glass substrate on which a silicon thin film is formed may be used. Silicon substrates are preferred. When single crystal silicon is used for the silicon substrate, the single crystal resistivity, p-type, n-type, and manufacturing method are not particularly limited. The etching of the present invention forms unevenness on the substrate surface by an oxidation-reduction (oxidation-dissolution) reaction by the etching liquid on the surface of the silicon substrate, and the etching liquid is more preferable than the acidic solution because the amount of silicon removed from the substrate is small. Also, an alkaline solution is preferable.
Silicon surface etching with an alkaline solution forms inverted pyramid-shaped irregularities on the substrate surface in (100) -oriented single crystal silicon. If the height of the unevenness is as small as possible, the distance (flying height) between the magnetic head and the recording medium during recording / reproducing information can be reduced, and higher density recording can be performed. Rmax 5 nm or more 100
The thickness is required to be not more than nm, preferably not more than 30 nm, and more preferably not more than 20 nm. CS on the surface of the silicon substrate
The conditions for applying ultrasonic waves to form the most suitable unevenness in the surface as a texturing pattern with excellent S characteristics are that the transmission frequency is 10 kHz or more and 100 kHz or less, and preferably 20 kHz or less.
Greater than or equal to kHz and less than or equal to 50 kHz is recommended. If the alkali concentration of the alkali solution exceeds 0.5% by weight, there is a problem that the silicon substrate is likely to have pits. If the alkali concentration is less than 0.0001% by weight, it takes a long processing time to form irregularities. % And 0.5% by weight or less. The higher the alkali concentration, the shorter the processing time. As the alkali, sodium hydroxide, potassium hydroxide or a mixture thereof is preferable. Examples of the solvent include water, alcohols such as methanol, ethanol, isopropanol, n-propanol, butanol (various isomers) and pyrocatechol, and mixtures thereof. The solution temperature may be 20 ° C. or higher and 95 ° C. or lower, and preferably 40 ° C. or higher and 90 ° C. or lower, in order to obtain an appropriate etching rate.

[0008]

【Example】

Example 1 Single crystal silicon outer diameter 48 mm, inner diameter 12 mm, thickness 0.38
The silicon substrate for magnetic recording medium of 0.2 mm in weight is etched with a 0.2 wt% concentration of sodium hydroxide solution at a solution temperature of 50 ° C. under the conditions of ultrasonic frequency of 47 kHz and ultrasonic input of 300 W for 5 minutes. I did. The surface roughness of the substrate after etching was measured with a stylus surface roughness meter. As a result, the average height of the irregularities was 15 nm at Rmax, and the in-plane variation was within ± 3 nm.

Then, an underlayer Cr was formed on this substrate by a sputtering method.
Thickness 1000 Å, recording layer Co _62.5 Ni ₃₀ Cr _7.5 thickness 500 Å,
For a silicon disk substrate for magnetic media with a protective layer C deposited to a thickness of 300Å, place this on a spindle motor, set the magnetic head so that it touches the substrate, raise the spindle from the stationary state to 3600 rpm, and leave it for 15 seconds. The cycle until the spindle motor is stopped is 1 cycle,
After performing a CSS test for 10,000 cycles, the magnetic head was left on the disk substrate and the adsorbability of the magnetic head to the disk substrate was examined one day later. The results are shown in Table 1.

Example 2 Single-crystal silicon outer diameter 48 mm, inner diameter 12 mm, thickness 0.38
mm of silicon substrate for magnetic recording medium is applied with a 0.2 wt% concentration of sodium hydroxide solution at a solution temperature of 40 ° C. under the conditions of ultrasonic frequency of 47 kHz and ultrasonic input of 300 W.
Etching was performed for 10 minutes. The surface roughness of the substrate after etching was measured with a stylus surface roughness meter. As a result, the average height of the irregularities was Rmax = 17 nm, and the in-plane variation was within ± 3 nm. In addition, a CSS test was performed on the silicon disk substrate for magnetic media formed under the same conditions as in Example 1, and the adsorbability of the magnetic head to the disk substrate was examined. The results are shown in Table 1.

Example 3 Single-crystal silicon outer diameter 48 mm, inner diameter 12 mm, thickness 0.38
Etching a silicon substrate for magnetic recording medium (mm) with a 0.02 wt% concentration sodium hydroxide solution at a solution temperature of 60 ° C. under the conditions of ultrasonic frequency of 47 kHz and ultrasonic input of 300 W for 6 minutes. I did. The surface roughness of the substrate after etching was measured by a stylus type surface roughness meter. As a result, the average height of the irregularities was Rmax = 18 nm, and the in-plane variation was within ± 5 nm. A CSS test was performed on the silicon disk substrate for magnetic media formed under the same conditions as in Example 1 to examine the adsorptivity of the magnetic head to the disk substrate. The results are shown in Table 1.

EXAMPLE 4 Outer diameter 48 mm, inner diameter 12 mm, thickness 0.38 using single crystal silicon
mm of silicon substrate for magnetic recording medium, 0.2 wt% concentration of potassium hydroxide solution, solution temperature 50 ℃, ultrasonic frequency
Apply ultrasonic waves under the conditions of 47kHz and ultrasonic wave input of 300 W. 3
Etching was performed for a minute. The surface roughness of the substrate after etching was measured with a stylus surface roughness meter. As a result, the average height of the irregularities was Rmax = 20 nm, and the in-plane variation was within ± 5 nm. A CSS test was performed on the silicon disk substrate for magnetic media formed under the same conditions as in Example 1 to examine the adsorptivity of the magnetic head to the disk substrate. The results are shown in Table 1.

Comparative Example 1 A silicon substrate was etched under the same conditions as in Example 1 except that the solution temperature was 10 ° C., but the surface Rmax was 7 nm ± 2.
nm and unevenness were not formed. Table 1 shows the results of the adsorptivity of the magnetic head to the disk substrate after the CSS test for the silicon disk substrate for magnetic media formed under the same conditions as in Example 1.

Comparative Example 2 Using a single crystal silicon, the outer diameter is 48 mm, the inner diameter is 12 mm, and the thickness is 0.38.
A silicon substrate for a magnetic recording medium having a size of 0.2 mm was etched using a sodium hydroxide solution having a concentration of 0.2 wt% at a solution temperature of 40 ° C. for 8 minutes without applying ultrasonic waves. The surface of the substrate after etching was only visually confirmed to have a mottled pattern, and no irregularities were formed. Table 1 shows the results of the adsorptivity of the magnetic head to the disk substrate after the CSS test for the silicon disk substrate for magnetic media formed under the same conditions as in Example 1.

[0015]

[Table 1]

[0016]

According to the present invention, since the in-plane uniform unevenness can be easily formed on the silicon substrate, the silicon substrate is used.
A magnetic recording medium with good CSS characteristics can be obtained.

Claims (4)

[Claims] 1. A method for roughening a surface of a silicon substrate for a magnetic recording medium, wherein ultrasonic waves are applied while wet etching the silicon substrate to form irregularities of 5 nm or more and 100 nm or less on the substrate surface. Surface roughening method of silicon substrate for magnetic recording medium. 2. The wet etching etching solution is an alkaline solution, and the alkaline concentration of the solution is 0.0001% by weight.
The method for roughening the surface of a silicon substrate for a magnetic recording medium according to claim 1, wherein the amount is 0.5% by weight or more. 3. The temperature of the alkaline solution of the etching solution is 20 ° C.
The method for roughening the surface of a silicon substrate for a magnetic recording medium according to claim 1 or 2, which is not lower than 95 ° C. 4. The method for roughening a silicon substrate of a magnetic recording medium according to claim 1, wherein the etching solution is a solution containing sodium hydroxide and / or potassium hydroxide.