JPH05291233A - Manufacture of compound semiconductor wafer - Google Patents

Abstract

PURPOSE:To reduce an irregularity in the characteristic of a device which is manufactured and to enhance the characteristic by a method wherein a compound semiconductor wafer is mirror-polished, cleaned and washed by water, it is immersed in a specific solvent immediately after that, stuck water is replaced with a solvent and a steam drying operation by means of isopropyl alcohol is performed. CONSTITUTION:A compound semiconductor wafer is mirror-polished, cleaned and washed by water; immediately after that, the wafer is immersed in a solvent which is soluble in both water and isopropyl alcohol(IPA) at an arbitrary ratio; stuck water on the surface is replaced with the solvent; after that, a steam drying operation by means of IPA is performed. It is preferable that the solvent for stuck-water substitution use is used while it is being filtered by using a circulation and filtration device. For example, a GaAs single crystal is cut off to a wafer; the surface of the wafer is polished; the wafer is cleaned organically; after that, the wafer is washed by ultrapure water. Immediately after that, the wafer is immersed, two times for five minutes each, in a tank in which IPA in a liquid state has been put; stuck water on the surface is replaced with the IPA; after that, the wafer is dried by means of an IPA steam drying device.

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 semiconductor wafer, and further to a method for drying a semiconductor wafer after mirror finishing, and more particularly to a technique suitable for drying a GaAs wafer.

[0002]

2. Description of the Related Art GaAs compound semiconductors have been attracting attention in recent years as materials for light emitting devices or microwave devices. GaAs wafers used as substrates for such devices and elements are GaAs single crystal ingots cut into thin plates, which are then mirror-polished by lapping and other processes and then used as wafers for electronic devices and optical elements through cleaning and drying processes. Provided. The GaAs wafer thus mirror-polished may have an epitaxial layer grown on its surface depending on the application. Therefore, the surface of such a wafer is required to have an extremely high degree of cleanliness without deposits or oxides.

Therefore, conventionally, a method of obtaining a clean surface by cleaning a mirror-polished GaAs wafer with a mixed solution of phosphoric acid-hydrogen peroxide-water or hydrofluoric acid-hydrogen peroxide-water. Have been proposed (JP-A-62-62)
-252140). Furthermore, in general, cleaning with ultrapure water and drying are performed after processing with an etching solution,
A steam drying method using IPA (isopropyl alcohol) is often used as a drying method. In this IPA vapor drying method, the water after washing is exposed to IPA vapor to condense on the surface of the wafer to remove moisture adhering to the IP.
It is replaced by A and removed, which is a suitable method for large-scale processing of wafers.

[0004]

However, the above-mentioned I
It has been clarified by the present inventor that the PA vapor drying method has the following problems when applied to a GaAs wafer. That is, the wafer after washing with water is IP
A little water adheres to the surface of the wafer during the process of transferring to the A vapor drying chamber and of course exposing to the IPA vapor, and carbon dioxide in the air is absorbed by the attached water to generate carbonic acid. , The concentration of carbonic acid increases with the drying of the adhered water on the surface and reacts with GaAs on the wafer to produce Ga ₂
Oxides such as O ₃ , As ₂ O ₃ and As ₂ O ₅ are generated. Moreover, in the above drying step, the water on the wafer surface does not dry uniformly, but it remains locally like spots on the surface of the wafer, and they gradually become smaller and disappear, so that they reach a dry state, so that they are locally dried. There are many oxides. Of these oxides, As ₂ O ₃ has a particularly high sublimation property (sublimation temperature = 80 ° C.), so it easily sublimes in the IPA vapor atmosphere (82.5 ° C. or higher) and volatilizes from the wafer surface. It ends up.

As described above, the wafer surface on which As ₂ O ₃ production and sublimation proceed at the same time is in a state of As deficiency because the produced As ₂ O ₃ volatilizes. The present inventors
When the wafer dried by PA vapor was analyzed by XPS (X-ray photoelectron spectroscopy), it was found that the surface state was high in Ga ₂ O ₃ and As ₂ O ₅ . A wafer having such a large amount of oxides and an excessive amount of Ga is difficult to obtain even if the etching is performed immediately before device fabrication.
It has been found that the ratio of a: As does not become 1: 1 and unevenness is generated on the wafer surface due to etching or the flatness is deteriorated, which causes variation and deterioration of device characteristics. The present invention has been made to solve the above problems, and an object of the present invention is to provide a wafer drying method capable of improving the characteristics with little variation in the characteristics of the manufactured device. To provide.

[0006]

The present inventor has studied a method of suppressing the oxidation of the surface of a GaAs wafer during IPA vapor drying. The reason why the oxidation of the GaAs wafer surface progresses during IPA vapor drying is that the adhered water remains on the wafer surface.
I got the idea that it should be replaced with a solvent that does not react with GaAs. However, since this solvent is further replaced with IPA vapor thereafter, it is required to be soluble in IPA. As a solvent having such properties, alcohols such as methanol and ethanol are suitable, and it has been concluded that IPA is particularly suitable.
On the other hand, when substituting the adhering water on the wafer surface with another solvent after cleaning with ultrapure water, minute foreign substances (hereinafter referred to as particles) in the solvent may adhere to the wafer surface. As a countermeasure against this, the present inventor has found that a tank for storing the replacement solvent may be equipped with a circulation filtration device to constantly filter the replacement solvent to maintain the cleanliness of ultrapure water. ..

The present invention was made on the basis of the above idea. Immediately after mirror-polishing, cleaning, and washing a GaAs wafer, the wafer is immersed in a solvent soluble in both water and isopropyl alcohol at an arbitrary ratio. It is proposed that after immersing and substituting the adhering water on the surface with the above solvent, vapor drying with isopropyl alcohol is performed. In the above case, it is preferable to use the solvent for replacing the adhering water while being filtered by a circulation filtration device.

[0008]

According to the above-mentioned means, since the adhering water on the surface of the GaAs wafer is quickly replaced with the solvent that does not react with GaAs after cleaning, As and Ga constituting the wafer react with water to generate an oxide. Can be prevented
It is possible to reduce variations in the characteristics of manufactured devices and improve the characteristics, and when used as a substrate for epitaxial growth, reduce defects on the surface of the epitaxial layer and yield devices with excellent characteristics. It is possible to manufacture well.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. First, a non-doped GaAs single crystal with a diameter of 2 inches pulled by the liquid sealed Czochralski method is set to 1 mm.
After slicing into a wafer having a thickness of 1, the surface was polished by lapping and polishing, organic cleaning was performed using trichlene, acetone, and methanol, and then water cleaning was performed with ultrapure water (steps S1 to S3). After that, the above-mentioned wafer was dipped twice in a tank containing IPA in a liquid state for 5 minutes each time to replace the adhering water on the surface with IPA, and then dried by an IPA vapor dryer (steps S4 and S5). The tank containing the IPA for replacement was equipped with a circulation filter equipped with a filter having a pore diameter of 0.1 μm, and IPA was continuously filtered during the replacement process (step S4).

For comparison, the wafer after drying by the conventional IPA vapor drying method, that is, the wafers after the above steps S1 to S3 are immediately subjected to I without being replaced with the attached water by IPA.
An experiment of drying with PA steam was also conducted. As a result of analyzing the surfaces of these wafers by XPS (X-ray photoelectron spectroscopy), the wafers dried by the conventional IPA vapor drying method have a Ga / As composition ratio of 1.91 and Ga in excess. On the other hand, it was found that the composition ratio of Ga to As on the surface of the wafer dried by the method of the present invention was 1.06, which was close to stoichiometry.

When the number of particles having a particle size of 0.2 μm or more attached to the wafer surface after drying was measured, the average number of particles on the wafer surface dried by the method of the present invention was 20. Average number of particles (18) on wafer dried by IPA vapor drying method
Was almost equal to. Furthermore, the method of the present invention and the conventional IP
An epitaxial layer having a HEMT structure was grown on the surface of the wafer dried by the A vapor drying method by the MBE method, and the density and mobility of oval defects (oval defects) and the carrier concentration were measured. The results are shown in Table 1.

[Table 1] In the table, (A) is the method of the present invention and (B) is the conventional method.
The measurement result about the wafer dried by the PA vapor drying method is shown. Further, (C) in the table is a conventional IP.
A After drying by steam drying method, the wafer surface, sulfuric acid (H
₂ SO ₄ —H ₂ O ₂ —H ₂ O) etchant 2-3 μm
After etching, an epitaxial layer having a HEMT structure was grown, and the results of measuring the density and mobility of the oval defect and the carrier concentration are shown.

From Table 1, it can be seen that the wafer dried by the conventional IPA vapor drying method has a higher oval defect density of the epitaxial layer and a lower surface morphology than the wafer treated by the sulfuric acid-based etchant, and the mobility and It is also inferior in terms of carrier concentration. On the other hand, the wafer dried by the method of the present invention is not processed by the sulfuric acid-based etchant, but is compared with the wafer processed by the sulfuric acid-based etchant after being dried by the conventional IPA vapor drying method. It can be seen that the oval defect density, the mobility and the carrier concentration of the epitaxial layer are almost the same. Although the method of drying a GaAs wafer has been described in the above embodiment, the present invention is not limited to this and can be applied to InP wafers and other compound semiconductor wafers in general.

[0013]

As described above, the present invention is based on GaAs
Immediately after the wafer is mirror-polished, washed, and rinsed with water, the wafer is immersed in a solvent that is soluble in both water and isopropyl alcohol at an arbitrary ratio to replace surface water with the solvent, and then isopropyl alcohol. Since vapor drying is performed by means of the method described above, the action that the adhering water on the GaAs wafer surface is quickly replaced with a solvent that does not react with GaAs causes As and Ga constituting the wafer to react with water to generate oxides. Can be prevented, it is possible to reduce the variation in the characteristics of the device to be manufactured and improve the characteristics, and when used as a substrate for epitaxial growth, reduce the defects on the surface of the epitaxial layer, There is an effect that a device having excellent characteristics can be manufactured with high yield.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of a procedure of a wafer drying method according to the present invention.

Claims (3)

[Claims] 1. A compound semiconductor wafer is mirror-polished, washed, and washed with water, and immediately thereafter, the wafer is immersed in a solvent soluble in both water and isopropyl alcohol at an arbitrary ratio to remove water adhering to the surface from the solvent. The method for producing a compound semiconductor wafer is characterized in that vapor substitution with isopropyl alcohol is carried out after replacement with. 2. The solvent for displacing attached water is used while being filtered by a circulation filtration device.
A method for producing a compound semiconductor wafer according to claim 1. 3. The solvent for replacing the attached water is isopropyl alcohol.
A method for producing a compound semiconductor wafer according to claim 1.