JPH0992635A - Method for washing semiconductor wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a foreign object from adhering to a wafer surface by suppressing the electrification of a semiconductor wafer in running-water washing using ultra-pure water by using a wafer carrier with a high conductivity and grounding the wafer carrier during washing. SOLUTION: Since a wafer carrier is normally an insulator made of, for example, polypropyrene or fluororesin, a deposition resistivity can be reduced to 1×10<15> Ω/cm or less by blending, for example, carbon and metal filler to a plastic material for constituting the wafer carrier. A semiconductor wafer is set to this sort of conductive wafer carrier and running-water washing is performed by ultra-pure water while grounding the wafer carrier, thus preventing the wafer carrier the semiconductor wafer from being electrified and hence obtaining a semiconductor wafer with an extremely high degree of washing and forming a high-quality epitaxial layer using the semiconductor wafer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a semiconductor wafer with ultrapure water.

[0002]

2. Description of the Related Art Compound semiconductors are used in the fabrication of semiconductor elements such as Schottky gate field effect transistors (MESFETs), high mobility transistors (HEMTs), heterojunction bipolar transistors (HBTs), and various light emitting and receiving devices. . These semiconductor devices are manufactured by forming electrodes on the surface of a mirror-finished wafer by means of a molecular beam epitaxial growth (MBE) method, a metal organic vapor phase epitaxial growth (MOVPE) method or the like, and then forming electrodes.

Conventionally, a mirror-finished wafer is produced by the following procedure. First, a single crystal ingot is sliced to cut a wafer. This wafer is rough-polished with alumina abrasive grains or the like to improve its flatness, and then mirror finished by mechanochemical polishing. Next, the wafer is set on a polypropylene or fluororesin wafer carrier, and degreasing cleaning with an organic solvent, running water cleaning with a cleaning liquid having an extremely slight etching action, and running water cleaning with ultrapure water are sequentially performed. Finally, the wafer is dried by an isopropyl alcohol (IPA) drying method or a spin drying method.

[0004]

The ultrapure water and the wafer carrier are insulators, and the GaAs wafer is also a high resistance material. Therefore, during cleaning with running ultrapure water, the wafer carrier and the GaAs wafer are charged by friction with the ultrapure water. Minute foreign matter in ultrapure water electrostatically adheres to the charged wafer surface. When exposed to a thermal environment such as annealing or epitaxial growth, this foreign substance becomes an electrically active carrier and deteriorates the electrical characteristics of the device. In addition, it becomes a source of defects in the epitaxial crystal, which becomes a problem.

An object of the present invention is to suppress the electrostatic charge of a semiconductor wafer and to prevent the electrostatic adhesion of foreign matter to the surface of a wafer during flushing with ultrapure water.

[0006]

SUMMARY OF THE INVENTION An essential point of the present invention is to make a wafer carrier electrically conductive, and to ground the carrier to prevent the wafer carrier from being charged, and to prevent a semiconductor from coming into contact with the wafer carrier. This is to suppress the electrification of the wafer.

In order to instantly remove the electric charge from the charged polymer, the volume resistivity of the wafer carrier is set to 1 × 1.
It must be less than 0 ¹⁵ Ω / cm.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Since a wafer carrier is usually an insulating material such as polypropylene or fluororesin, the volume resistivity of 1 × can be obtained by blending carbon, metal filler, etc. in a plastic material forming the wafer carrier.
It can be 10 ¹⁵ Ω / cm or less. like this,
By setting the semiconductor wafer on the conductive wafer carrier and performing running water cleaning with ultrapure water while grounding the wafer carrier, it is possible to prevent the wafer carrier and the semiconductor wafer from being charged.

[0009]

【Example】

<Example 1> A polypropylene mixed with carbon was injection-molded to prepare a wafer carrier. At this time, the volume resistivity is changed from 1 × 10 ¹⁴ to 1 × by changing the amount of carbon mixed.
10 ¹⁶ Ω / cm. A semi-insulating GaAs wafer whose mirror surface was finished by the method described in the prior art was placed in the wafer carrier whose volume resistivity was changed, and washed with running ultrapure water for 10 minutes. At this time, two types of cleaning were performed, one with the ground wire connected to the carrier and the other without. Finally, the wafer was dried with a spin dryer. The number of foreign matters on the wafer surface was measured by a surf scan manufactured by Tencor. Next, the MOVPE method was performed to remove un-GaAs from 0.
After growing to 5 μm, the impurity concentration at the interface between the epitaxial layer and the GaAs substrate was examined by SIMS. The number of foreign matters on the wafer surface after cleaning with ultrapure water and drying is shown in FIG. In the cleaning with the ground wire connected, when the volume resistivity of the carrier was 1 × 10 ¹⁵ Ω / cm or less, almost no foreign matter adhered, but 1 ×
When it was higher than 10 ¹⁵ Ω / cm, the resistance of the carrier was increased and the number of foreign matters attached was increased. When the ground wire was not connected, a large number of foreign matters were observed. Table 1 shows the SIMS analysis results of the interface between the epitaxial layer and the GaAs substrate. Almost no impurities were found on the wafer having a volume resistivity of 1 × 10 ¹⁵ Ω / cm or less and washed with a carrier connected to the ground, but a large amount of impurities was found under other conditions.

[0010]

[Table 1]

Example 2 When the same experiment as in Example 1 was conducted on the InP wafer, the same result as in Example 1 was obtained.

[0012]

According to the cleaning method of the present invention, a semiconductor wafer having an extremely high degree of cleanliness can be obtained. By using this semiconductor wafer, a high-quality epitaxial layer can be formed thereon, and the yield of semiconductor devices manufactured from the epitaxial wafer can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the influence of the volume resistivity of a wafer carrier and the presence / absence of ground during wafer cleaning on the number of foreign matters on the wafer surface after cleaning.

Claims (2)

[Claims] 1. A method of cleaning a semiconductor wafer held on a wafer carrier with ultrapure water, wherein a conductive carrier is used as the wafer carrier, and the wafer carrier is grounded during cleaning. Semiconductor wafer cleaning method. 2. The volume resistivity of the wafer carrier is 1 × 1.
The method for cleaning a semiconductor wafer according to claim 1, wherein the resistance is 0 ¹⁵ Ω / cm or less.