JPS63173357A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce a junction capacitance between a buried layer and a substrate, and improve high frequency characteristics of a transistor, by forming an oxide layer in contact with the buried layer on the rear of a semiconductor substrate. CONSTITUTION:Silicon oxide layers 2 and 3 are formed, by oxidizing a P-type silicon substrate 1 in the manner in which the thickness of an unoxidized part is made to correspond to a buried layer. Through an aperture formed by patterning the silicon oxide film 2, high concentration N-type impurity is introduced on the surface of the silicon substrate 1, and the buried layer is formed so as to reach a silicon oxide film 3. After that, the silicon oxide film is eliminated, and a low concentration N-type epitaxial layer 5 is grown. During this process, the high concentration N-type impurity in the buried layer 4 diffuses also into the epitaxial layer 6, and the thickness of the buried layer 4 increases. As a process is contained wherein the silicon oxide film 3 in contact with the bottom surface of the buried layer 4 is formed on the rear of the silicon substrate 1, the junction capacitance between the silicon substrate 1 and the buried layer 4 can be remarkably decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION r Industrial Application Field The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for manufacturing a semiconductor device including a step of forming a buried layer on a semiconductor substrate.

[Conventional technology]

In bipolar ICs, in order to lower the collector series resistance,
A buried layer is provided.

FIGS. 3(a) to 3(c) are cross-sectional views of a semiconductor chip shown in order of steps for explaining a conventional method of manufacturing a semiconductor device.

As shown in FIG. 3 (a), N-type high-concentration impurities are introduced into the surface of the silicon substrate 1 using the silicon oxide film 1o selectively formed on the surface of the P-type silicon substrate 1 as a mask. Form layer 4.

Next, as shown in FIG. 3(b), the silicon oxide film 10 is removed, and an epitaxial layer 5 containing low concentration N-type impurities is formed on the surface of the P-type silicon substrate 1.

Next, as shown in FIG. 3(c), an epitaxial layer 5 is formed.
A high-concentration P-type impurity is selectively introduced into the surface of the silicon substrate to form an isolation region 6 that reaches the silicon substrate 1.
A P type base region 7, an N type emitter region 8, and an N type collector/contact region 9 are formed on the surface of the epitaxial layer 5 surrounded by the isolation region 6 to form a vertical NPN transistor.

[Problem that the invention seeks to solve]

In the conventional semiconductor device manufacturing method described above, since the contact surface between the silicon substrate 1 and the buried layer 3 is a PN junction, for example, in the case of an NPN transistor shown in FIG. The junction capacitance between
There is a problem in that the high frequency characteristics of the transistor, especially the signal rise characteristics, are deteriorated.

An object of the present invention is to provide a method for manufacturing a semiconductor device with less parasitic capacitance in the collector and excellent high frequency characteristics.

[Means for solving problems]

The semiconductor manufacturing method of the present invention includes a step of forming an oxide film on the entire surface of a conductive type semiconductor substrate with a thickness equivalent to a buried layer left in the center, and selectively etching the oxide film on the surface to form an opening. forming a buried layer that reaches the oxide film on the back surface by introducing impurities of opposite conductivity type into the semiconductor substrate using the oxide film as a mask; and forming an epitaxial layer of opposite conductivity type.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1(a) to 1(d) are cross-sectional views of a semiconductor chip shown in order of steps for explaining a first embodiment of the present invention.

As shown in FIG. 1(a), a P-type silicon substrate 1 is oxidized with high-temperature steam at about 1000°C, and the oxidation time is increased so that the non-oxidized part becomes 5 to 10 μm thick, which corresponds to the buried layer. Then, a silicon oxide film 2.3 is formed.

Next, as shown in FIG. 1(b), high concentration N-type impurities are introduced into the surface of the silicon substrate 1 through the openings formed by patterning the silicon oxide film 2 using lithography technology. After forming the buried layer 4 that reaches the film 3, the silicon oxide film 2 is removed.

Next, as shown in FIG. 1(c), a lightly doped N-type epitaxial layer 5 is grown. At this time, the buried layer 4 has a high concentration of N
The type impurity also diffuses into the epitaxial layer 5, and the buried layer 4
The thickness increases.

Next, as shown in FIG. 1(d), an epitaxial layer 5 is formed.
A P-type high concentration impurity is selectively introduced into the surface of the epitaxial layer 5 to form an isolation region reaching the silicon substrate 1, and a P-type base region 7, An N-type emitter region 8 and an N-type collector contact region 9 are formed to form a vertical NPN? - form a transistor;

In this way, by forming the silicon oxide film 3 in contact with the bottom surface of the buried layer 4 on the back surface of the silicon substrate 1, the silicon substrate 1
The junction capacitance between the capacitor and the buried layer 4 can be significantly reduced, and can be reduced to 1/2 or less of the conventional value.

FIGS. 2A and 2B are cross-sectional views of a semiconductor chip shown in the order of steps for explaining a second embodiment of the present invention.

As shown in FIG. 2(a), a highly doped P-type buried layer 10 having a larger diffusion coefficient than the impurity of the buried layer 4 was formed inside the buried layer 4 formed in the first embodiment. After that, an N-type epitaxial layer 5 is formed.

Next, as shown in FIG. 2(b), a P-type collector region 1 reaching the buried layer 10 is formed on the surface of the epitaxial layer, and an epitaxial layer 5 surrounded by the buried layer 10 and the collector region 11 is formed. An N-type base region 12 and a P-type emitter region 13 are formed on the surface of the vertical PNP in a floating state).
form a transistor.

〔Effect of the invention〕

As explained above, the present invention has the effect of reducing the junction capacitance between the buried layer and the substrate and improving the high frequency characteristics of the transistor by forming an oxide layer in contact with the buried layer on the back surface of the semiconductor substrate. There is.

[Brief explanation of the drawing]

FIGS. 1(a) to (d) are cross-sectional views of a semiconductor chip shown in the order of steps for explaining the first embodiment of the present invention, and FIGS. FIG. 3(a) is a cross-sectional view of a semiconductor chip shown in the order of steps for explaining an embodiment of the present invention.
-(C) are cross-sectional views of a semiconductor chip shown in the order of steps for explaining a conventional method of manufacturing a semiconductor device. 1... Silicon substrate, 2, 3... Silicon oxide film, 4.
...Buried layer, 5.Epitaxial layer, 6.Isolation region, 7.Base region, 8.Emitter region, 9.
...Collector contact region, 10...Buried layer, 1
1...Collector area, 12...Base area, 13...
emitter area. 17 = Tob Tsushin) Figure 1 α Ribo Figure 3

Claims (1)

[Claims] A process of forming an oxide film on the entire surface of a semiconductor substrate of one conductivity type, leaving a thickness equivalent to a buried layer in the center, and selectively etching the oxide film on the surface to form an opening, using the oxide film as a mask. Introducing impurities of opposite conductivity type into the semiconductor substrate to form a buried layer reaching the oxide film on the back surface, and removing the oxide film on the front surface to form an epitaxial layer of opposite conductivity type on the surface of the semiconductor substrate. 1. A method of manufacturing a semiconductor device, the method comprising: forming a semiconductor device.