JPS62172720A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve the ohmic characteristics by a method wherein a silicon wafer etched with KOH is temporarily washed and after neutralizing the etched part with acid base chemical and ultrasonic washing the same, an electrode layer is formed by evaporating process. CONSTITUTION:An N<-> type epitaxial layer 2 is grown on an N-type silicon wafer 1 and then a P-type impurity region 3 is buried in the epitaxial layer 2. The surface of epitaxial layer 2 is coated with a silicon oxide film 4 while a part of the silicon oxide film 4 on the surface of region 3 is opened to be coated with a P-type surface electrode layer 5. A thin natural oxide film 6 is formed by mechanically grinding the backside of wafer 1. The natural oxide film 6 on the ground surface is removed by immersing the wafer 1 in KOH contained in an etching vessel at constant temperature of around 40-60 deg.C for slightly etching the ground surface. next, the wafer 1 is temporarily washed and after cleansing with acid base chemical to be ultrasonic washed. Finally, after centrifugal drying process, a backside electrode layer 7 is formed on the ground surface by evaporating process. Through these procedures, the electrode layer 7 is provided with excellent ohmic characteristics to the silicon wafer 1 while improving the bonding strength.

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing a semiconductor device, and in particular improves a pre-evaporation treatment process for an electrode layer to improve ohmic contact with a wafer when depositing an electrode layer. This is what I did.

Traditionally, two techniques have been used: For example, the back side of elements such as diodes and transistors (
When forming a back electrode layer on the surface on which no devices are formed, after forming the above-mentioned device on the front side of the silicon wafer, mechanically polish the back side of the silicon wafer to make it thinner. , a desired electrode layer is deposited on this polished surface. However, since a very thin native oxide film is formed on the polished surface, it is known that the ohmic properties of the electrode layer and the adhesion strength of the electrode layer to silicon wafer λ are not very good.

In such a case, it is appropriate to perform a treatment such as lightly quenching the polished surface with an HF-based chemical solution and then performing ultrasonic water washing to remove the natural oxide film formed on the polished surface. It is believed that

O <I'll do it. However, if the HF-based chemical solution mentioned above is used, the silicon oxide film formed on the surface of the silicon wafer (the side on which devices are formed) will be etched, so to prevent this, In addition, it is necessary to add the troublesome work of covering the surface side of the silicone wafer with a resist or the like before etching. Moreover, it is inevitable that the etched surface will be contaminated by the process of removing the resist and the like after etching.

For this reason, at present, the ohmic properties and adhesion strength of the electrode layer to the silicon wafer have to be sacrificed to some extent without performing etching with an HF-based chemical as described above.

The present invention was devised in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a semiconductor device that can improve the ohmic characteristics of an electrode layer to a silicon wafer and improve the adhesion strength with simple and effective operations. There is.

In the method for manufacturing a semiconductor device according to the present invention, a silicon wafer on which an electrode layer is to be deposited is chemically etched with KOH and then temporarily washed with water, and the etched portion of the silicon wafer is etched with an acid-based chemical solution. After neutralization treatment and ultrasonic water washing, a desired electrode layer is deposited thereon.

(2) Since KOH is used, the reaction with the silicon wafer during etching is relatively slow, and areas other than the exposed portion of the silicon wafer are not unnecessarily etched. Although KOH is alkaline, the etching surface of the silicon wafer is thought to be contaminated by positive ions, but this can be prevented by neutralizing it with an acid-based chemical solution and performing ultrasonic water cleaning. , the etched surface is activated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Here, a case is described in which a back electrode layer of a diode is formed, focusing on one element on a silicon wafer.

In FIG. 1(a), an N-type silicon wafer 1 includes:
An N-type epitaxial layer 2 is grown, and a P-type impurity region 3 is embedded in the surface side of the epitaxial layer 2. A silicon oxide film 4 is deposited on the upper surface of the epitaxial layer 2 .

A window is opened in the silicon oxide film 4 on the surface of the P-type impurity region 3, and a P-type front electrode layer 5 is deposited thereon.

For example, the back side of the silicon wafer 1 on which such devices are formed (the side on which no devices are formed) is
Mechanically polished to a thickness of about 5 to 150 μm. This polished surface is uneven, which is preferable because it increases the deposition area of the back electrode layer that will be deposited later, but it cannot prevent the formation of a very thin native oxide film 6 on this surface (see Figure 1). (see (b)).

Therefore, the following process is performed on this polished surface.

First, the KOH placed in the etching tank was heated at about 4d~60℃.
The polished surface of the silicon wafer 1 is lightly chemically etched by keeping the temperature at a constant temperature and immersing the silicon wafer 1 therein for about 1 to 3 minutes. In KOH, only the exposed surface of the silicon wafer 1, that is, the polished surface, is lightly etched without etching the silicon oxide film 4, so the natural oxide film 6 on the surface of the polished surface is removed (see FIG. 1). See C). However, although KOH is an alkaline type, there is a possibility of passivation contamination of the polished surface due to + ions, so the etched polished surface is cleaned as follows. First, the silicon wafer 1 is temporarily rinsed with ultrapure water (about 10 to 15 seconds), then cleaned with a dilute acidic chemical such as acetic acid, and then immersed in ultrapure water and subjected to ultrasonic waves. Perform ultrasonic water washing for about 20 minutes.

Next, after performing centrifugal drying using so-called acetone dipping, a desired back electrode layer 7 is formed on the polished surface of the silicon wafer 1 by an appropriate electrode deposition method (see FIG. 1(d)). Since this back electrode layer 7 tends to have a multilayer structure, for example, it has a Cr-Ni-Ag structure here.

Incidentally, FIG. 2 shows the relationship between the Cr film thickness of each back electrode layer and the forward voltage in the diode in the above embodiment and in the conventional diode. As can be seen from the figure, it has been confirmed that the diode according to the embodiment of the present invention has improved ohmic properties compared to the conventional diode.

The present invention provides a simple and easy processing method that does not require the additional troublesome work of covering areas other than the areas where electrode layers are to be formed (other than the exposed areas of the silicon wafer) with resist, as in the case of processing using an HF system. Since the area on which the electrode layer is to be deposited can be treated well with effective operations, the electrode layer deposited on this area can have good ohmic characteristics and high adhesion strength to the silicon wafer.

[Brief explanation of drawings]

Figures 1(a) to (dl are process diagrams for explaining one embodiment of the present invention; Figure 2 is a diode to which the present invention is applied and the Cr film thickness and forward voltage of the back electrode layer of the conventional diode) 1...Silicon wafer 5...Top electrode layer 7...Back electrode layer. Patent applicant: ROHM Co., Ltd. Agent, patent attorney Takaharu Ohnishi Figure 1

Claims (1)

[Claims] (1) The silicon wafer on which the electrode layer is to be deposited is chemically etched with KOH and then temporarily washed with water, and the etched portion of the silicon wafer is neutralized with an acid-based chemical and washed with ultrasonic water. 1. A method for manufacturing a semiconductor device, comprising depositing a desired electrode layer on a semiconductor device.