JPH0590278A - Semiconductor device - Google Patents

Abstract

PURPOSE:To provide a bipolar transistor which is higher in current amplification factor and equal to a conventional one in breakdown strength between a collector and an emitter. CONSTITUTION:A carbon fluoride thin film layer 112 is provided to an interface between a polycrystalline silicon and a single-crystal silicon of an emitter to prevent holes from flowing into a polycrystalline silicon layer 108 to lessen a base current. Therefore, a base current is lessened, whereby a semiconductor device of this design is enhanced in current amplification factor. This semiconductor device is the same as a conventional one in base impurity profile, so that it is hardly lessened in breakdown strength between an emitter and a collector.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bipolar transistor, and more particularly to the structure of a bipolar transistor having a high current amplification factor.

[0002]

2. Description of the Related Art Bipolar transistors are widely used in both digital, IC and linear ICs because of their high speed and high driving capability. In particular, a bipolar transistor using a polycrystalline semiconductor layer as an emitter can form a shallow junction and is excellent in high speed.

FIG. 2 shows a conventional NPN type bipolar transistor having a polycrystalline silicon emitter. 201 is a P ⁻ type silicon substrate, 202 is an N ⁺ type buried layer, 203 is an N ⁻ type epitaxial layer, 204 is a P ⁺ type insulating diffusion layer,
Reference numeral 205 is an element isolation oxide film, 206 is an N ⁺ type collector diffusion layer, 207 is a P type base region, 208 is an N ⁺ type polycrystalline silicon emitter, 209 is an N ⁺ type emitter region, 21
Reference numeral 0 is an interlayer insulating film, and 211 is a metal wiring.

In this conventional bipolar transistor, a natural oxide film 212 of silicon having a thickness of about 20Å exists at the interface between single crystal silicon and polycrystalline silicon, and acts as a barrier against the injection of holes into polycrystalline silicon. For this reason,
The base current is limited, and a higher current amplification factor (hereinafter abbreviated as h _FE ) can be obtained compared to a double diffusion type transistor (reference: PATTON et al. Physics, Technolog).
y, and Modeling of Polysilicon Emitter Contacts fo
r VLSI Bipolar Transistors ； IEEE TRANSACTIONS ON
ELECTRON DEVICES, VOL. ED-33 No. 11 p.1754-1768 No
v. 1986).

[0005]

However, in this conventional bipolar transistor, it is necessary to increase the impurity concentration of the base region in order to make the collector-emitter breakdown voltage and the Early voltage above a certain value. , High h _FE cannot be obtained. For example, using an epitaxial layer with an impurity concentration of 1 × 10 ¹⁶ cm ⁻³ ,
When the breakdown voltage between the emitters is 7 V or higher and the Early voltage is 50 V or higher, h _FE can be obtained only about 50.

An object of the present invention is to provide a bipolar transistor which has the same collector-emitter breakdown voltage and early voltage as the conventional one and has a higher h _FE .

[0007]

The semiconductor device of the present invention comprises:
A bipolar transistor having a polycrystalline semiconductor emitter layer doped with impurities at a high concentration is provided with a very thin fluorocarbon compound thin film at the interface between a single crystal semiconductor and a polycrystalline semiconductor.

[0008]

The present invention will be described below with reference to the drawings. FIG. 1 is a vertical cross-sectional view of a bipolar transistor of the present invention. Although the basic structure is the same as that of a conventional bipolar transistor, the polycrystal silicon layer 108 is in contact with a single crystal silicon layer 109, and a polyhedral inside of a diffusion window is formed. It has a thin film of several Å to several tens of Å fluorocarbon compounds at the crystal-single crystal interface. This thin film prevents holes from being injected into the polycrystalline silicon 108, resulting in a decrease in base current and an improvement in h _FE . This effect is similarly observed in the natural oxide film of silicon as described above, but the barrier property against holes is more prominent in the fluorocarbon thin film.

As a method of forming a fluorocarbon thin film, there is a method of performing plasma treatment in a mixed gas atmosphere of CF ₄ 65%, H ₂ 35% and a pressure of 5 Pa.

[0010]

The characteristics of the present invention and the conventional transistor are shown in FIGS. 3 and 4 for comparison. FIG. 3 shows h _FE -I _C (collector current) characteristics when the collector-emitter breakdown voltage is almost the same. The size of the transistor of the present invention is 121, which is larger than that of the conventional transistor h _FE 76. 4A and 4B show I _C − when h _FE is equal.
It is a V _CE (collector-emitter voltage) characteristic. If h _FE is equal, the Early voltage is 191V according to the invention,
The conventional transistor is 83 V, which is larger than that of the transistor of the present invention.

As described above, according to the present invention, by providing the fluorocarbon compound thin film at the interface between the single crystal semiconductor layer and the polycrystalline semiconductor layer of the emitter portion of the bipolar transistor, the current can be increased as compared with the conventional bipolar transistor. This has the effect of increasing the amplification factor. Moreover, the collector-emitter breakdown voltage and the early voltage are the same as before.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a bipolar transistor according to an embodiment of the present invention,

FIG. 2 is a vertical cross-sectional view of a bipolar transistor using a conventional polycrystalline silicon layer as an emitter,

FIG. 3 is a comparison of h _FE −I _C characteristics of a transistor of the present invention and a conventional transistor,

4 (a) and (b) show I _C -V _CE characteristics of a transistor of the present invention and a conventional transistor, respectively.

[Explanation of symbols]

101, 201 P ⁻ type silicon substrate 102, 202 N ⁺ type buried layer 103, 203 N ⁻ type epitaxial layer 104, 204 P ⁺ type insulating diffusion layer 105, 205 Element isolation oxide film 106, 206 N ⁺ type collector diffusion layers 107 and 207 P-type base region 108, 208 N ⁺ -type polycrystalline silicon layer 109, 209 N ⁺ -type diffusion layer 110, 210 interlayer insulating film 111, 211 a metal wiring 112 fluorocarbon compound thin 212 natural oxide film

Claims (1)

[Claims] 1. A bipolar transistor having, as an emitter layer, a polycrystalline semiconductor layer doped with a high concentration of impurities, comprising a very thin fluorocarbon compound thin film at the interface between the single crystal semiconductor layer and the polycrystalline semiconductor layer. Semiconductor device.