JP2000344549A - Method for tempering glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the warp of a glass substrate subjected to tempering treatment by subjecting the glass substrate to ion exchange tempering by dipping the glass substrate into a molten salt liquid at a temp. higher than a prescribed temp. and re-heating the glass substrate in a prescribed temp. range lower than the strain temp. of the glass substrate. SOLUTION: A glass substrate is tempered by gradually raising the temp. of the glass substrate to a temp. close to the temp. of the molten salt solution T1 (T1 is equal to or lower by 50 to 110 deg.C than strain temp. of the substrate) over a time t1 (t1=10 to 60 min) in order to avoid the formation of cracks by rapid temp. rising in a heating furnace, then after taking out (t2=1 to 2 min) and dipping the glass substrate into a solution tank at the temp. T1 for the prescribed time t3 (t3=15 min to 5 h) to subject the glass substrate to ion- exchange. Thereafter, the substrate is taken out of the solution tank and cooled to about 200 deg.C under the atmosphere over the time t5 (t5=5 min), and the substrate is reheated in the heating furnace at a temp. T2 (T2 is equal to or lower by 150 to 200 deg.C than the strain temp. of the substrate) for the prescribed time t6 (t6=10 min) and, after taking the glass substrate out of the furnace, the substrate is cooled over the time t4 (t4=10 min) under the atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a method for chemically strengthening a glass substrate.

[0002]

2. Description of the Related Art As a substrate for an information recording medium of an HDD (hard disk drive), instead of a conventional aluminum substrate,
Glass substrates with excellent smoothness and durability have attracted attention.
Among them, the glass substrate is 38
It is immersed in a molten salt solution such as nitrate at about 0 ° C. to 500 ° C. to improve the strength of the substrate surface by an ion exchange method. FIG. 3 shows an example of the change over time of the substrate temperature in this case.

In FIG. 3, prior to immersing a glass substrate in a molten salt solution, the temperature T1 of the molten salt solution (T1 = T1 =
The temperature is gradually raised over a period of time (t1 = 10 to 60 minutes) to near the strain point temperature of the substrate below 50 ° C. to 100 ° C., and after being taken out of the heating furnace (t2 = 1).
Minutes to 2 minutes) and immersed in the solution tank for a predetermined time (t3 = 15 minutes to 5 hours) to strengthen the substrate by ion exchange.
(Low temperature ion exchange method). The tempered glass substrate is taken out of the solution tank and allowed to cool in the air (t4 = 10 minutes).
Note that the strain point temperature is a temperature at which the glass has a viscosity of 4 × 10 ¹⁴ poises. At this temperature, viscous flow cannot practically occur. Temperature.

[0004]

However, in the above-mentioned conventional processing method, there is a problem that the glass substrate after the tempering treatment is warped. That is, FIG. 4 shows a contour map of the surface of the glass substrate S, where FIG. 4 (A) is before the strengthening process and FIG. 4 (B) is after the strengthening process. As is clear from this, when the strengthening process is performed, during subsequent cooling,
Since the inner peripheral portion of the glass substrate S has a lower heat radiation than the outer peripheral portion, a temperature difference occurs between the two portions, and a concentric warpage occurs in the glass substrate S due to the difference in thermal contraction. This is remarkable when the above-mentioned tempering treatment is performed using a holder in which a large number of glass substrates are closely arranged in a vertical position in order to improve production efficiency. For example, a 3.5-inch glass substrate is used before the tempering treatment. 2 μm
The warpage of the glass substrate may be about 6 to 10 μm after the strengthening process, and in order to stably guarantee the flying height of the recording / reproducing head in the HDD at about 25 nm, the warpage of the glass substrate must be reduced. It is necessary to suppress it to 5 μm or less. Conventionally, in glass, the strain at or below the strain point temperature was considered to be almost negligible. Even if there is, warpage occurs.

The present invention has been made in view of such a demand, and an object of the present invention is to provide a glass substrate strengthening method capable of minimizing the warpage of a glass substrate after the strengthening process.

[0006]

In order to achieve the above object, in the method of the present invention, a glass substrate is immersed in a molten salt solution at a predetermined temperature or higher to strengthen the substrate by ion exchange. Is characterized in that the glass substrate is reheated in a predetermined temperature range lower than the strain point temperature.
In this case, the predetermined temperature range is desirably set to a temperature range of 150 ° C. to 200 ° C. or lower than the strain point temperature of the glass substrate.

In the method of the present invention, when the glass substrate is reheated within the above-mentioned temperature range, the warpage caused at the time of cooling after the tempering treatment is eliminated, and a new warpage occurs at the time of cooling after the reheating. Nonetheless, as a result, the warpage of the glass substrate after the tempering treatment can be minimized.

[0008]

FIG. 1 shows a change with time of a substrate temperature in a processing method of the present invention. Prior to immersing the glass substrate in the molten salt solution, the temperature T1 of the molten salt solution (T1 = 50% or less of the strain point temperature of the substrate) is previously set in a heating furnace in order to prevent breakage due to a rapid rise in temperature, as in the prior art. ° C-10
Time (t1 = 10 minutes to 60)
), And after being taken out of the heating furnace (t2 = 1 minute to 2 minutes), immersed in the solution tank for a predetermined time (t3 = 15 minutes to 5 hours) to reach the temperature T1. The substrate is strengthened by ion exchange (low-temperature ion exchange method).

After being taken out of the solution tank, time t5 (t5
= 5 minutes) and allowed to cool to about 200 ° C. in the air, and then the glass substrate was put into a heating furnace again and the temperature T2 (T2
= Temperature = 150 ° C. to 200 ° C. below the strain point temperature of the substrate) for a predetermined time (t6 = 10 minutes). Thereafter, the glass substrate is taken out of the heating furnace and allowed to cool in the atmosphere (t4 = 10 minutes).

As described above, the glass substrate after the tempering treatment is reheated in the heating furnace at the above temperature T2, so that the warpage of the glass substrate is reduced to about 2 μm before the tempering treatment as shown in FIG. In this case, as is apparent from FIG. 2, when the temperature T2 is lower than 200 ° C. below the strain point temperature of the substrate, the lower the temperature T2, the more the warpage that occurs at the time of cooling (t5) after the strengthening treatment is not eliminated. By
The warpage of the substrate increases. Further, if the temperature T2 is higher than the strain point temperature of the substrate and is higher than 150 ° C., a new warp occurs at the time of cooling to the atmosphere after reheating (t4),
As the temperature T2 increases, the warpage of the substrate also increases. As a result, the temperature T2 is set to 150 ° C. or lower than the strain point temperature of the substrate.
By selecting the temperature in the range of 200 ° C. to 200 ° C., the warpage of the glass substrate can be minimized.

Note that the range of the temperature T2 at which the warpage of the glass substrate can be minimized is about 50 ° C. (see FIG. 2).
A certain degree of unevenness in the temperature distribution in the heating furnace is allowed, and the temperature control of the heating furnace can be simplified. Further, since the reheating time (t6) is about 10 minutes, the entire processing time is not so long as compared with the conventional case.

[0012]

As described above, according to the glass substrate strengthening treatment method of the present invention, the warpage of the glass substrate after the strengthening treatment can be reduced as much as possible. When used as a medium substrate, the flying height of the recording / reproducing head can be stably guaranteed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change over time of a glass substrate temperature in a processing method of the present invention.

FIG. 2 is a diagram showing a relationship between a reheating temperature and a warpage of a glass substrate.

FIG. 3 is a diagram showing a temporal change of a glass substrate temperature in a conventional processing method.

FIG. 4 is a contour diagram showing warpage of a glass substrate.

Claims (2)

[Claims] After immersing a glass substrate in a molten salt solution at a predetermined temperature or higher to strengthen the substrate by ion exchange,
A glass substrate strengthening method, wherein the glass substrate is reheated in a predetermined temperature range lower than a strain point temperature of the glass substrate. 2. The temperature range is equal to or lower than the strain point temperature.
The glass substrate strengthening method according to claim 1, wherein the temperature is in a temperature range of 50C to 200C.