Semiconductor device manufacturing: process – Forming bipolar transistor by formation or alteration of... – Including diode
Reexamination Certificate
1997-06-13
2001-02-06
Saadat, Mahshid (Department: 2815)
Semiconductor device manufacturing: process
Forming bipolar transistor by formation or alteration of...
Including diode
C438S326000, C438S357000, C438S358000, C438S057000, C257S187000, C257S463000, C257S446000
Reexamination Certificate
active
06184100
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the construction of a light receiving element and a manufacturing method of the semiconductor device including the light receiving elements.
2. Description of the Related Art
FIG. 1
shows the construction of a related art of a photodiode and a bipolar transistor which are light receiving elements and formed on the same substrate. In
FIG. 1
, the left area shows an example of the construction of the photodiode, and the right area shows an example of the construction of the bipolar transistor. An N type deposit layer
14
and a P type deposit layer P
+
15
are formed on an n type semiconductor substrate
11
, respectively. Then a P type semiconductor element isolation region
17
is formed by growing an N type epitaxial layer
16
.
A base region
18
of a P type semiconductor is formed at the right area on the epitaxial layer
16
and an N
+
type diffusion layer
19
are formed in the left area and emitter and collector regions in the right area.
Nextly, an electrode layer of photodiode
22
and electrode layers of a base, an emitter and a collector of bipolar transistor
22
are formed in pattern. Then an insulation film is formed thereon. The thickness of the N
−
type epitaxial layer
16
is determined by the characteristic of bipolar element, and generally in the bipolar IC having approximately 10 [V] resisting power, the film thickness of 3-4 [&mgr;m] was necessary.
According to the construction described above, the light receiving sensitivity of the photodiode is determined by the number of carriers generated in a vacant layer
100
and the number of carriers reached to the vacant layer
100
by diffusion out of carriers generated in the area interior to the vacant layer. Accordingly, in order to improve the light receiving sensitivity it was necessary to widen the vacant layer
100
and to increase the number of carriers to be brought in the vacant layer by providing semiconductor layer having long diffusion length at the upper and lower parts of the vacant layer
100
. These two processes, to enlarge the width of vacant layer
100
and to provide the semiconductor layer having long diffusion length lead to control the impurity concentration.
On the other hand, the frequency characteristic of the photodiode is determined by the parasitic capacitance and parasitic resistance of the diode. Accordingly, in order to improve the frequency characteristic, it is necessary to decrease the parasitic capacitance and the parasitic resistance. In order to decrease the parasitic capacitance it is effective to enlarge the vacant layer
1000
and this means the decreasing of the impurity concentration of the junction. Furthermore, to decrease the parasitic resistance means to increase the impurity concentration of the semiconductor layer except the vacant layer. For example, referring to
FIG. 1
, the P type deposit layer
15
is provided to decrease the parasitic resistance of anode. Since the P type deposit layer
15
has high impurity concentration, the lengths of diffusion of a small number of carriers are short and the carriers which contribute to the light receiving sensitivity of the photodiode are almost all carriers generated at the upper part of this P type deposit layer
15
.
These photodiodes are widely used to read information recorded on such as the compact disc (CD) and mini disc (MD). However, the wavelength of the semiconductor laser used in this type of optical disc is 780 [nm] and since the absorption length in Si of the laser with 780 [nm] wavelength is 9 [&mgr;m], it created a problem that sufficient light receiving sensitivity could not be obtained due to the existence of P type deposit layer
15
positioned at 3-4 [&mgr;m] from the surface in the conventional composition shown in FIG.
1
.
SUMMARY OF THE INVENTION
In view of the foregoing, the first object of this invention is to improve the light receiving sensitivity of photodiodes.
The second object is to improve the frequency characteristics of photodiodes.
The third object is to achieve said first and second objects and provide a method of manufacturing a semiconductor device which is capable of easily isolating photodiodes from bipolar elements.
The foregoing objects and other objects of the present invention have been achieved by the provision of a light receiving element in which the impurity density of the first and second conductive types in the parts to be vacated when impressing the reverse voltage are both kept less than 1E16 [cm
−3
]. Thus, since in the case of impressing the reverse voltage to the light receiving elements, the impurity densities of the first and second conductive types vacancies to be formed can be kept both less than 1E16 [cm
−3
], the vacant layer can be sufficiently enlarged, and both the improvement in the light receiving sensitivity and the decrease of parasitic capacitance can be achieved. Thus, the construction of light receiving element having fairly good frequency characteristics can be obtained.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.
REFERENCES:
patent: 4458158 (1984-07-01), Maryland
patent: 5023195 (1991-06-01), Sekikawa et al.
patent: 5245203 (1993-09-01), Morishita et al.
patent: 5252851 (1993-10-01), Mita et al.
patent: 5283460 (1994-02-01), Mita
patent: 5382824 (1995-01-01), Popovic
patent: 5418396 (1995-05-01), Mita
patent: 5500550 (1996-03-01), Morishita
Richards N. Drew
Saadat Mahshid
Sony Corporation
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