JPH10303212A - Bipolar transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve high frequency power gain by providing a shield electrode by setting a parasitic capacitance by a standardized shield at a specified value when a shield electrode is provided between a base pad electrode and a semiconductor board through an insulation film. SOLUTION: Shield electrodes 13AP, 13A cover a first insulation film 4 below base pad electrodes 11P, 11 selectively and are formed of a first conductive film connected to an emitter electrode 7 through emitter pad electrodes 12P, 12. The sum of capacitance between the base pad electrodes 11P, 11 and the shield electrodes 13AP, 13A and a capacitance between an emitter electrode 7 and a semiconductor board 1 is made one or more times to one and half or less times the capacitance between the base pad electrodes 11P, 11 and the semiconductor board 1 when the shield electrodes 13AP, 13A are not provided. The area of the shield electrodes 13AP, 13A and the thickness and permittivity of the first insulation film 4 and a second insulation film 8 are set.

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 a bipolar transistor for amplifying a high-frequency small signal.

[0002]

2. Description of the Related Art A conventional bipolar transistor is shown in FIG.
As shown in FIG. 1, a p-type base region 2 formed on the surface of the n-type silicon semiconductor substrate 1, an n-type emitter region 3 formed on the surface of the p-type base region 2, and an n-type silicon semiconductor substrate 1 A first insulating film 4 (silicon oxide film) covering the first insulating film 4 and a first conductive film (aluminum-based alloy film) selectively covering the first insulating film 4. Base electrodes 6 connected to regions 3 respectively
And a second insulating film 8 (silicon oxide film) that covers the first insulating film 4 on which the base electrode 6 and the emitter electrode 7 are formed, and selectively covers the second insulating film 8. Base electrode 1 made of a second conductive film (gold film) and connected to base electrode 6 and emitter electrode 7, respectively.
1P and an emitter pad electrode 12P.

Further, as shown in FIG. 4, a first insulating film under the base pad electrode 11P is coated to form a shield electrode 1P.
3 may be provided (JP-A-60-262462). The shield electrode 13 uses a metal film or a resistance film.

[0004]

The bipolar transistor shown in FIG. 3 has a problem that the high-frequency power gain is low because of the capacitance between the base pad electrode 11P-n type silicon semiconductor substrate 1 (collector region). This problem can be solved by providing the shield electrode 13 shown in FIG.

The shield electrode 13 reduces the base-collector parasitic capacitance and improves the high-frequency power gain. However, since the parasitic capacitance between the base and the emitter and the parasitic capacitance between the emitter and the collector are increased, it is affected by the method of providing the shield electrode. That is, merely providing the shield electrode is not sufficient.

An object of the present invention is to provide a bipolar transistor which can reliably achieve an improvement in high-frequency power gain by providing a shield electrode.

[0007]

A bipolar transistor according to the present invention has a second conductivity type base region formed on a surface of a first conductivity type semiconductor substrate and a surface portion of the second conductivity type base region. A first conductive type emitter region, a first insulating film covering the semiconductor substrate, and a first conductive film selectively covering the first insulating film. Select a base electrode and an emitter electrode respectively connected to the one conductivity type emitter region, a second insulating film covering the first insulating film on which the base electrode and the emitter electrode are formed, and the second insulating film. Selectively covering a base pad electrode and an emitter pad electrode which are made of a second conductive film to be covered and connected to the base electrode and the emitter electrode, respectively, and a first insulating film under the base pad electrode. A shield electrode made of a first conductive film connected to the emitter electrode via the emitter pad electrode, wherein a sum of a base pad electrode-shield electrode capacitance and an emitter electrode-semiconductor substrate capacitance forms the shield electrode. The area of the shield electrode, the thicknesses of the first insulating film and the second insulating film, and the relative permittivity are set so as to be 1 to 15 times the capacitance between the base pad electrode and the semiconductor substrate when not provided. That is.

[0008] The high-frequency power gain of a bipolar transistor is strongly affected by electrode wiring. Therefore, by changing the size of the shield electrode, the influence of the sum of the capacitance between the shield electrode and the semiconductor substrate and the capacitance between the base pad electrode and the shield electrode (parasitic capacitance due to the shield) on the high-frequency power gain can be reduced by general small signal amplification Using a high-frequency bipolar transistor equivalent circuit (common emitter). The result is shown in FIG. The vertical axis shows the relative gain (expressed in decibels based on the case where no shield electrode is provided), and the horizontal axis shows the parasitic capacitance due to the shield (standardized by the capacitance between the base pad electrode and the semiconductor substrate when no shield electrode is provided). However,
When a shield electrode is not provided, the capacitance between the base pad electrode and the semiconductor substrate is almost equal to the collector junction capacitance, and the frequency is 2
GHz, and the center of the base pad electrode coincides with the center of the shield electrode. As the size of the shield electrode is increased, the relative gain initially increases due to a decrease in the collector-base capacitance. However, when the standardized parasitic capacitance exceeds 5, the improvement in the relative gain decreases and becomes approximately 15 to 0. become.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a plan view showing a first embodiment of the present invention, and FIG.
It is an X-ray sectional view.

The bipolar transistor of this embodiment has a p-type structure formed on the surface of n-type silicon semiconductor substrate 1.
-Type base region 2, n-type emitter region 3 formed on the surface of p-type base region 2, and n-type semiconductor silicon substrate 1.
A first insulating film 4 made of a silicon oxide film having a thickness of 1 μm and a first conductive film (aluminum alloy film) selectively covering the first insulating film 4 to form a p-type base region 2 and Base electrodes 6 connected to n-type emitter regions 3 respectively
And a second insulating film 8 (a silicon oxide film having a thickness of 500 nm) which covers the first insulating film 4 on which the base electrode 6 and the emitter electrode 7 are formed, and a second insulating film 8. A base pad electrode 11P, 11 and an emitter pad electrode 12P, 12 which are made of a second conductive film (aluminum alloy film) to be selectively covered and connected to the base electrode 6 and the emitter electrode 7, respectively;
P (circle with a radius of 40 μm), 11 (width 12 μm, length 2
0 μm) and a first conductive film connected selectively to the emitter electrode 7 via the emitter pad electrodes 12P and 12 by selectively covering the first insulating film 4 below the first insulating film 4 (a circle having a radius of 45 μm), 13A. (Width 12μm, length 20μ
m).

The calculated parasitic capacitance due to the shield, which is normalized by setting the relative dielectric constant of the first insulating film 4 and the second insulating film 8 to be the same, is 4.9.

From FIG. 2, the relative gain is 1.1 dB.
Similar results were obtained with the actual prototype.

As described above, when the shield electrode is provided, the parasitic capacitance due to the standardized shield is one or more and one or more.
It is effective to set the value to 5 or less, preferably 2.5 to 10 times, and especially to about 5.

When actually mounting on a package,
Although the base terminal of the package and the base pad electrode 11P are connected by ball bonding, it has been described that the tip of the bonding wire does not protrude from the base pad electrode. If it protrudes, the parasitic capacitance will increase accordingly, and will deviate from the curve of FIG.

Although the shield electrode is formed of an aluminum alloy film, a metal film such as a gold film can be used in addition to the shield electrode. Further, similar effects can be obtained not only in NPN-type bipolar transistors but also in PNP-type bipolar transistors.

[0016]

The first effect is that an improvement in high-frequency power gain when a bipolar transistor is operated with a common emitter can be reliably achieved.

The reason is that a shield electrode is inserted between the base pad electrode and the semiconductor substrate (collector region) via an insulating film to reduce the parasitic capacitance between the base pad electrode and the collector and to prevent the presence of the shield electrode. This is because the magnitude of the parasitic capacitance is a condition effective for improving the gain.

[Brief description of the drawings]

FIG. 1 is a plan view (FIG. 1) showing a first embodiment of the present invention;
(A)) and a cross-sectional view taken along line XX of FIG.
(B)).

FIG. 2 is a graph showing a relationship between a parasitic capacitance due to a shield electrode and a relative gain.

FIG. 3 is a plan view showing a conventional example (FIG. 3A) and FIG.
FIG. 3A is a sectional view taken along line XX (FIG. 3B).

FIG. 4 is a sectional view showing another conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 n-type silicon semiconductor substrate 2 p-type base region 3 n-type emitter region 4 first insulating film (field oxide film) 5 opening 6 base electrode 7 emitter electrode 8 second insulating film (interlayer insulating film) 9 opening DESCRIPTION OF SYMBOLS 10 Opening 11P, 11 Shield electrode 12P, 12 Emitter pad electrode 13, 13AP, 13A Base pad electrode 14 Opening 15 Shield electrode-emitter pad electrode connection wiring

Claims (2)

[Claims] A first conductive type base region formed on a surface portion of the first conductive type semiconductor substrate; a first conductive type emitter region formed on a surface portion of the second conductive type base region; A first insulating film covering the substrate, and a base electrode comprising a first conductive film selectively covering the first insulating film and connected to the first conductive type base region and the first conductive type emitter region, respectively. And an emitter electrode, a second insulating film covering the first insulating film on which the base electrode and the emitter electrode are formed, and a second conductive film selectively covering the second insulating film. A base pad electrode and an emitter pad electrode connected to the base electrode and the emitter electrode, respectively, and a first insulating film under the base pad electrode which is selectively covered and connected to the emitter electrode via the emitter pad electrode. And a base pad electrode-semiconductor substrate capacitance when the sum of the base pad electrode-shield electrode capacitance and the emitter electrode-semiconductor substrate capacitance is not provided with the shield electrode. A bipolar transistor, wherein the area of the shield electrode, the thicknesses of the first insulating film and the second insulating film, and the relative dielectric constant are set so as to be at least 1 and at most 15 times as large as the above. 2. The bipolar transistor according to claim 1, wherein the capacitance between the base pad electrode and the semiconductor substrate when no shield electrode is provided is substantially equal to the collector junction capacitance.