JPS62204510A - Liquid phase epitaxial growth method - Google Patents

Abstract

PURPOSE:To obtain an epitaxial crystal of high quality having less film thickness distribution by reversing the rotating direction of a substrate holder for holding a substrate at a special time interval in heated solution at the time of growing the crystal. CONSTITUTION:A crucible base 3 is disposed in a core tube 2 on which a heater 1 is wound, and a crucible 4 is placed on the base. Solution 8 which contains a material solute to be grown and solvent is filled in the crucible 4, and heated by the heater 1 to approx. 1,000 deg.C. A substrate 7 is held in a substrate holder 6 mounted at the lower end of a supporting shaft 5. The shaft 5 is rotatably driven by a growing apparatus to rotate the holder 6 and the substrate 7, thereby growing a thin film on the substrate 7. At this time, the rotating direction of the substrate is reversed at a time interval of 18sec or shorter.

Description

[Detailed Description of the Invention] [Summary] When growing a crystal on the substrate by the liquid phase epitaxial growth method by rotating the substrate in a heated solution, by inverting the substrate holder at time intervals of 18 seconds or less, Aim to make the film thickness uniform.

[Industrial application field]

The present invention relates to a liquid phase epitaxial growth method for growing crystals on a substrate by rotating the substrate in a heated solution.

[Conventional technology]

Bubble memories with a storage capacity of 4M bits are currently being mass-produced, but research is underway to achieve even higher density and lower costs. To achieve this, the bubble magnetic domain, which is the storage medium, must be made smaller, and along with this the crystal film thickness must also be made thinner. However, the thinner the film thickness, the greater the influence of film thickness variations. In particular, since the film thickness and the collapse magnetic field H0 are in a proportional relationship, the thinner the film thickness is, the more uniform the film thickness distribution becomes.

In the conventional garnet film growth method, a substrate holder is rotated in one direction or reversed in a solution during growth, but the time interval between reversals has not been considered a particular problem.

[Problem that the invention seeks to solve]

That is, in conventional bubble crystals, the film thickness is as thick as 1 μm or more, so the film thickness distribution did not pose much of a problem. However, with high-density bubble crystals, the film thickness is extremely thin, approximately 0.5 μm, and a more uniform film thickness is now required.

A technical object of the present invention is to eliminate such problems in conventional liquid phase epitaxial growth methods and to obtain higher quality epitaxial crystals with less film thickness distribution.

[Means for solving problems]

The liquid phase epitaxial growth method is a method in which a substrate is immersed in a heated solution containing a raw material solute and a solvent, and a crystal is grown on the substrate homoepitaxially or heteroepitaxially from the solution. In the present invention, when growing a crystal by this liquid phase epitaxial growth method, the direction of rotation of a substrate holder holding a substrate is reversed at time intervals of 18 seconds or less in a heated solution.

[Effect]

Thus, according to the present invention, the direction of rotation of the substrate is reversed at time intervals of 18 seconds or less. Since the contact conditions between each position on the substrate surface and the solution are not constant, if the substrate continues to rotate in the same direction for a long time, the film thickness will also not be constant. However, if the rotation direction is reversed at a time interval of 18 seconds or less, the liquid surface in contact with the substrate surface at the time of reversal is agitated, changing the contact conditions between each surface of the substrate and the liquid. By renewing the contact conditions at short intervals of 18 seconds or less in this way, the entire surface of the substrate will eventually have a uniform film thickness. As a result of experiments, it was confirmed that when the reversal period exceeds 18 seconds, the variation in film thickness becomes large and the film cannot be put to practical use.

〔Example〕

Next, examples will be used to explain how the liquid phase epitaxial growth method according to the present invention is actually implemented. FIG. 1 is a sectional view of an apparatus for carrying out the method of the invention. Heater 1
A crucible stand 3 is disposed in a furnace core tube 2 wound with a crucible, and a crucible 4 is placed on it. The crucible 4 contains a melt t&8 consisting of a raw material solute to be grown and a solvent, and is heated to about 1000°C in a heat 1. A substrate 7 is held in a substrate holder 6 attached to the lower end of the support shaft 5 .

With such a growth apparatus, by rotationally driving the spindle 5, the substrate holder 6 and the substrate 7 are rotated, and a thin film 71 is grown on the GGG substrate 7 as shown in FIG. At this time, Y is formed on the GGG substrate 7 by heteroepitaxial
, Fe, O,, to grow the crystal 71 of the system, Y2O2, Smz03, Luzos, C
aCO3, Pez02, Ge01, etc. are used, and PbO, 8203, etc. are used as the solvent. In the case of homoepitaxial growth, the substrate 7 and the thin film 71 have the same crystal structure and composition, so G is used as the raw material solute.
azOx, Gd2O2, etc. are used.

When the substrate holder 6 and the substrate 7 are now rotated by rotationally driving the support shaft 5, the substrate 7 is rotated at, for example, 70 rpm.
Rotate at a certain speed. This substrate rotation speed determines the crystal growth rate. That is, it is known that when the substrate rotation speed is high, the crystal growth rate is high, and when the rotation speed is low, the growth rate is slow.

FIG. 3(a) shows the film thickness uniformity with respect to the reversal time interval T when the substrate rotation speed is 7 Orpm, where the horizontal axis is the reversal time interval and the vertical axis is the standard deviation. In addition, as shown in Figure 3, the film thickness was measured at 21 points on the wafer, and the standard deviation σ of this distribution was found. Repeat alternately for 230 seconds. From the results of the experiments conducted in this manner, it was found that the shorter the inversion period T, the better the uniformity of the film thickness, as shown in FIG. 3(a). It is considered that the uniformity of the film thickness that can withstand a high-density device with a small bubble diameter is as long as σ is 0.025 μm or less, so it can be seen that T is preferably 18 seconds or less.

FIG. 4 shows the results of an experiment comparing the characteristics of the conventional unidirectional rotation and the reversal method using a period of 18 seconds or less according to the present invention. The characteristic line marked with Δ is the conventional method, and is an example of rotation in one direction at 120 rpm. The characteristic line marked O is the method of the present invention, and what is the rotation speed? Orpm is an example of reversal at a 5-second period. As is clear from this, when the inversion occurs every 5 seconds, the slope of the characteristic line is steep, the standard deviation is small, and there is little variation in film thickness.

Figure 5 shows the experimental results when the rotational speed was the same but the reversal period was changed. The characteristic line marked O is an example where the reversal period is 5 seconds, Δ
The characteristic line marked with a mark is an example of a reversal period of 15 seconds, and the characteristic line of a mouth seal is an example of a reversal period of 30 seconds.

As is clear from these results, the shorter the inversion period, the steeper the slope of the characteristic line and the smaller the standard deviation.

Although the case of growing a garnet film for bubbles has been described, it goes without saying that the present invention can be applied to the case of growing other thin films.

〔Effect of the invention〕

As described above, by reversing the substrate holder at a cycle of 18 seconds or less, it is possible to grow a high-quality thin film with a small thickness distribution, which is extremely effective when growing garnet films for microbubbles. be.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view explaining the basic principle of the liquid phase epitaxial growth method according to the present invention, FIG. 2 is a cross-sectional view showing a bubble substrate produced by the method of the present invention, and FIG. Figure 4 is a characteristic diagram showing the relationship between film thickness measurement points on the substrate, Figure 4 is a characteristic diagram showing the experimental results of the conventional method and the method of the present invention, and Figure 5 is a diagram showing the reversal period at a constant rotation speed. It is a figure which shows the characteristic when changing. In the figure, 4 is a crucible, 5 is a support shaft, 6 is a substrate holder, 7 is a substrate, 71 is a grown thin film, and 8 is a solution. Patent applicant Fujitsu Ltd. agent Patent attorney Aoyagi Cross-section f of the fertility water system

Claims (1)

[Claims] The substrate is immersed in a heated solution containing a raw solute and a solvent.
A liquid phase epitaxial growth method characterized by reversing the rotational direction of the substrate holder at time intervals of 18 seconds or less when growing a crystal from a solution by homoepitaxial or heteroepitaxial growth on a substrate held in a substrate holder.