JPH0541386A - Method for manufacturing semiconductor device - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] Good ohmic contact with the metal electrode formed on the back surface when an epitaxial wafer having a substrate with a restricted impurity concentration for epitaxial growth is used. Provided is a method for manufacturing a semiconductor device capable of obtaining the above. [Structure] By implanting ions into the back surface of the substrate 11 having a high resistivity of the epitaxial wafer 1, the impurity concentration of the surface layer at a depth of about 1 μm on the back surface of the substrate is set to about 10 ²⁰ cm ⁻³ , whereby the metal electrode is formed. A good ohmic contact with can be formed, improving the on-voltage of the device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device using an epitaxial wafer in which a semiconductor layer of a second conductivity type is epitaxially grown on a semiconductor substrate of a first conductivity type.

[0002]

2. Description of the Related Art If an epitaxial method is used, a semiconductor layer of an arbitrary conductivity type and an arbitrary thickness can be formed on a semiconductor substrate, and a crystal layer with few internal defects can be obtained. Epitaxial wafers are often used for manufacturing semiconductor devices.

[0003]

However, when a layer of a conductivity type different from that of the substrate is epitaxially grown, if the impurity concentration of the substrate is high, the impurity concentration of the epitaxial layer varies due to diffusion of impurities during growth, and the conductivity Since it is difficult to set the mold or the impurity concentration to a desired level, it may not be possible to sufficiently increase the impurity concentration of the substrate. For this reason, there arises a problem that the specific resistance of the substrate cannot be low enough to make ohmic contact with the metal electrode formed on the back surface of the substrate. Therefore, it becomes impossible to reduce the voltage drop between the device electrodes when the manufactured semiconductor device is conductive, that is, the on-voltage.

An object of the present invention is to provide a semiconductor device which can obtain good ohmic contact with a metal electrode formed on the back surface when an epitaxial wafer having a substrate with a restricted impurity concentration is used for epitaxial growth. It is to provide a manufacturing method of.

[0005]

In order to achieve the above object, the present invention provides a semiconductor device using an epitaxial wafer in which a semiconductor layer of the second conductivity type is grown on one surface of a semiconductor substrate of the first conductivity type. In the manufacturing method of 1., the step of performing ion implantation from the other surface of the substrate is included. And
The impurity concentration of the epitaxial wafer substrate is 1 × 10 ¹⁹ cm
^-3 or less, and it is effective that the impurity concentration of the ion-implanted surface layer is 8 × 10 ¹⁹ cm ^-3 or more. In addition, the semiconductor element is an insulated gate bipolar transistor (hereinafter referred to as I
(Referred to as GBT) is effective.

[0006]

[Operation] By implanting ions into the back surface of the epitaxial wafer on the side opposite to the semiconductor substrate epitaxial layer,
Even if the resistance of the semiconductor substrate is high, good ohmic contact can be made with the metal electrode on the back surface of the substrate.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an I manufactured according to an embodiment of the present invention.
Shows GBT. For manufacturing this IGBT, the impurity concentration is 10
A silicon epitaxial wafer 1 having an n ⁻ layer 12 grown on a p-type substrate 11 of about ¹⁹ cm ⁻³ is used. A pattern of the gate electrode 2 made of polycrystalline silicon is formed on the n ⁻ layer 12 of this wafer through an insulating film.
Is used as a mask for ion implantation and thermal diffusion.
The well 3 and the n ⁺ source region 4 in the surface layer thereof are formed. The p-well 3 and the n ⁺ region 4 have a surface impurity concentration of about 1 × 10 ²⁰ cm ⁻³ or more in order to make ohmic contact with a source electrode (not shown). On the other hand, on the back surface of the p-substrate 11 which is in contact with the drain electrode (not shown), boron ions 5 are accelerated at a accelerating voltage of 50 to 100 keV and a dose amount of 1 × 10 ¹⁵ to 1 × 10 ¹⁶ cm ^-2 depending on the impurity concentration of the substrate. And the impurity concentration of the surface layer having a depth of about 1 μm from the surface is set to about 1 × 10 ²⁰ cm ⁻³ , at least 8 × 10 ¹⁹ cm ⁻³ or more.

FIG. 2 shows the relationship between the dose amount of boron ion implantation and the ON voltage of the completed IGBT of rated 600 V and 50 A. According to this, compared with the IGBT manufactured using the conventional epitaxial wafer, the voltage decreased by about 40% to 1.7V. Further, the variation of the ON voltage was about 40% of the average value in the conventional IGBT, but could be suppressed to 20% in the IGBT according to the embodiment of the present invention. In addition, although an n-channel IGBT is manufactured in the above-described embodiment, a p-channel IGBT can be similarly implemented, and in that case, phosphorus ions are implanted at a similar dose amount.

[0009]

According to the present invention, in order to prevent impurities from being mixed into epitaxial layers of different conductivity types, ions are implanted into the surface layer on the back surface of the substrate of an epitaxial wafer having a substrate with a reduced impurity concentration, so that the back surface of the substrate is Good ohmic contact of the metal electrode to the can be obtained. As a result, it has become possible to manufacture a semiconductor element having a low on-voltage and a small variation in the on-voltage using conventional equipment.

[Brief description of drawings]

FIG. 1 is an IGBT manufactured according to an embodiment of the present invention.
Cross section

FIG. 2 is a diagram showing the relationship between the dose of ion implantation on the back surface of an epitaxial wafer and the on-voltage of a manufactured IGBT.

[Explanation of symbols]

1 Epitaxial Wafer 11 p Substrate 12 n ^- Epitaxial Layer 2 Gate Electrode 3 p Well 4 n ⁺ Source Region 5 Boron Ion

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H01L 29/784 9168-4M H01L 29/78 321 J

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor device using an epitaxial wafer in which a semiconductor layer of a second conductivity type is grown on one surface of a semiconductor substrate of a first conductivity type, including a step of implanting ions from the other surface of the substrate. A method of manufacturing a semiconductor device, comprising: 2. The semiconductor device according to claim 1, wherein the epitaxial wafer substrate has an impurity concentration of 1 × 10 ¹⁹ cm ⁻³ or less, and the ion-implanted surface layer has an impurity concentration of 8 × 10 ¹⁹ cm ⁻³ or more. Manufacturing method. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is an insulated gate bipolar transistor.