JP2861776B2 - Semiconductor wafer with protective film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer having a protective film, and more particularly to a semiconductor wafer having an LB film and a polymer film for protecting the surface of the wafer.

[0002]

2. Description of the Related Art Compound semiconductors are used in the manufacture of various light emitting and receiving devices, such as a Schottky gate field effect transistor (MESFET), a high mobility transistor (HEMT), a heterojunction bipolar transistor (HBT), and the like. In these devices, an active layer is formed on a mirror-finished wafer surface by a molecular beam epitaxial growth (MBE) method, a metal organic vapor phase epitaxial growth (MOVPE) method, an ion implantation method, or the like. A mirror wafer is created by the following procedure.

[0003] An ingot is sliced and a wafer is cut out. This wafer is roughly polished to improve its flatness, and then mirror-finished by mechanochemical polishing. Next, degreasing cleaning, cleaning with a cleaning liquid having an extremely slight etching effect, and ultrapure water cleaning are performed. Finally, the wafer is dried by an IPA (isopropyl alcohol) drying method or a spin drying method.

The wafer is individually mounted on a wafer tray filled with an inert gas and stored. When this stored wafer is used for epitaxial growth or ion implantation, pretreatment such as organic cleaning and etching is always performed to remove organic substances and oxides on the wafer surface.

[0005]

Since active dangling bonds are present on the wafer surface, the stored wafer surface is deteriorated by impurity contamination such as organic substances and the formation of oxides. Therefore, prior to the epitaxial growth of the crystal or ion implantation, a pretreatment such as cleaning or etching must be performed to remove impurities and oxides. However, this pretreatment is a complicated operation and is not a stable treatment, but rather has the problem of contaminating the surface and deteriorating the flatness of the surface.

Specifically, for example, when epitaxial growth is performed by MBE, it is necessary to etch the wafer surface by about several μm before growth and then clean the wafer surface by heat treatment in an MBE furnace. In addition, thermal cleaning in the furnace cannot be completely performed, cleaning takes time, and the time is not stable.In addition, oxides on the wafer surface remain, which is good in subsequent epitaxial growth. In many cases, crystal growth was not possible.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art by coating the wafer surface with a protective film having good protective properties and peeling properties, without performing pretreatment such as cleaning and etching. It is an object of the present invention to provide a novel semiconductor wafer with a protective film capable of obtaining a high-quality epitaxial crystal and an ion-implanted layer.

[0008]

The semiconductor wafer with a protective film according to the present invention is obtained by forming an LB film on the surface of a molecular layer on the surface and coating the polymer film on the LB film. L for surface protective film
The reason why the two layers of the B film and the polymer film are used is that the LB film alone is too thin, and the polymer film alone is too strong in bonding, so that it is difficult to peel off both from the wafer surface.

[0009] The molecular layer level means one molecular layer or two or more molecular layers. As the LB film, polyimide,
There are various things such as stearic acid and tricosenoic acid. There is no particular limitation as long as the thin film can be controlled at the molecular level. In addition, there are various polymer films such as vinyl chloride, cellophane, and polypropylene. There is no particular limitation as long as the film has a thickness of several tens μm to several mm.

The semiconductor is Si or a compound semiconductor, the compound semiconductor is a group III-V compound semiconductor, and the group III-V compound semiconductor is GaAs or Indium.
P and the like.

[0011]

The operation will be described with reference to FIG. Active dangling bonds 1 are present on the surface 3 of the wafer 2 after polishing, cleaning and drying (FIG. 1A). By forming one molecular layer of the LB film 4 on the wafer surface 3, the dangling bonds 1 on the wafer surface 3 are inactivated (FIG. 1B).

When the polymer film 5 is further pressed onto the LB film 4, the molecular ends of the LB film 4 and the polymer film 5 are bonded to form a surface protective film (FIG. 1C). As a result, adhesion of impurities to the wafer surface 3 during storage and surface oxidation by oxygen and moisture are suppressed.

The connection between the LB film 4 and the polymer film 5
Is significantly stronger than the bond between the wafer surface 3 and the wafer surface 3.
, And a clean wafer surface 3 is obtained.
(D)).

Therefore, before the epitaxial growth or ion implantation, the protective film composed of the LB film 4 and the polymer film 5 is peeled off, so that a clean wafer surface 3 can be easily obtained. A good epitaxial crystal or ion-implanted layer can be obtained without any treatment.

The LB film can be attached by any method such as a wet treatment such as a vertical immersion method, a horizontal attachment method, a moving wall method, and a dry treatment by a vapor deposition method.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, GaAs is used as the semiconductor wafer.
A crystal wafer will be described, but is common to Si, InP, and the like.

<Example 1> GaAs after polishing, washing and drying
A single molecular layer LB film made of oleic acid was formed on the surface of the s-crystal wafer by a vertical immersion method. Next, a vinyl chloride sheet having a thickness of 100 μm was pressed thereon. The wafer was left in the atmosphere for 1 to 12 months. After being left for each period, the sheet on the wafer surface was mechanically peeled off, and Auger electron spectroscopic analysis of the surface was performed.

As a comparative sample, a sample which was individually polished, washed, dried and mounted individually on a wafer tray filled with nitrogen was also prepared. After being left for the same period, Auger electron spectroscopic analysis of O and C on the surface was performed. The Auger analysis results are shown in FIGS. After polishing and cleaning, those stored in nitrogen increased both O and C, and organic contamination and surface oxidation were observed. However, those with the protective layer of this example showed almost all increase in O and C. And kept a clean surface.

Example 2 GaAs after polishing, cleaning and drying
Oleic acid was vertically immersed on the surface of the
A molecular layer was formed. Next, a vinyl chloride sheet having a thickness of 100 μm was pressed. Place this wafer in air for one month to 12
Left for months. After being left for each period, the sheet on the wafer surface is peeled off, and H is grown by molecular beam epitaxy (MBE).
EMT was grown. The electrical characteristics were evaluated at 77K.

For comparison, a similar experiment was carried out for wafers individually polished, washed, dried, and mounted on a wafer tray sealed with nitrogen. Note that the comparative example was not pre-processed. FIG. 4 shows the results. After polishing and cleaning, the mobility of the two-dimensional electron gas of the wafer stored in nitrogen decreases as the storage period increases, but the one provided with the protective layer of the present invention includes:
No decrease was observed.

<Example 3> GaAs after polishing, washing and drying
Oleic acid was formed in one molecular layer on the s-crystal wafer by a vertical dipping method. Next, a vinyl chloride sheet having a thickness of 100 μm was pressed. The wafer was left in the atmosphere for 1 to 12 months. After being left for each period, the sheet on the wafer surface was peeled off and ion implantation was performed. Implant Si ions,
After annealing in an arsine atmosphere, the sheet resistance was examined by the eddy current method.

For comparison, a similar experiment was carried out for wafers individually polished, washed, dried, and mounted on a wafer tray sealed with nitrogen. Note that the comparative example was not pre-processed. FIG. 5 shows the relationship between the storage period and the sheet resistance. The sheet resistance of the wafer stored in nitrogen increased with the storage period, and the activation rate decreased. The sheet resistance of the wafer provided with the protective layer of the present invention hardly changed.

[0023]

【The invention's effect】

(1) According to the first and second aspects of the present invention, the surface of the wafer is covered with the surface protective film composed of the LB film and the polymer film. Can be. In use, since the polymer film is coated on the LB film, a clean surface can be obtained simply and in a very short time only by peeling the polymer film. Therefore, no special packing is required for storing the wafer, which is economically advantageous.

Further, even for a wafer stored for a long period of time, a high-quality epitaxial crystal and ion-implanted layer can be stably obtained without any special pretreatment, so that the process time can be shortened and the yield can be improved. .

Further, the formation of the LB film and the coating of the polymer film are both simple methods and do not require expensive equipment.
Economically advantageous.

(2) According to the third to sixth aspects of the present invention, particularly, the compound semiconductor wafer having an unstable surface can be protected, so that the quality of the compound semiconductor product can be improved.

[Brief description of the drawings]

FIG. 1 is a process diagram of a protective film forming method for explaining an embodiment of a semiconductor wafer with a protective film according to the present invention.

FIG. 2 is a comparative characteristic diagram showing a change over time of O on the wafer surface between the first embodiment having a protective film and a comparative example.

FIG. 3 is a comparative characteristic diagram showing a change over time of C on a wafer surface between the first embodiment having a protective film and a comparative example.

FIG. 4 is a comparison characteristic diagram showing a change over time in two-dimensional electron gas mobility in a second embodiment in which HEMT is grown on a wafer surface and a comparative example.

FIG. 5 is a comparison characteristic diagram showing a change over time in sheet resistance between the third example in which ions are implanted into the wafer surface and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Unbonded hand 2 Wafer 3 Wafer surface 4 LB (Langmuir-Blodgett) film 5 Polymer film

Claims (6)

(57) [Claims] 1. A semiconductor wafer provided with a protective film in which a Langmuir-Projet (LB) film at the molecular layer level is formed on the surface and a polymer film is coated thereon. 2. The semiconductor wafer with a protective film according to claim 1, wherein said semiconductor is Si. 3. The semiconductor device according to claim 1, wherein said semiconductor is a compound semiconductor.
4. The semiconductor wafer with a protective film according to 1. 4. The semiconductor wafer with a protective film according to claim 3, wherein said compound semiconductor is a III-V group compound semiconductor. 5. The semiconductor wafer with a protective film according to claim 4, wherein said III-V compound semiconductor is GaAs. 6. The semiconductor wafer with a protective film according to claim 1, wherein said III-V compound semiconductor is InP.