JPS6281753A - Signal charge detection device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a signal charge detection device.

[Conventional technology]

Recently, 'fc charge transfer devices using CCD or the like have been widely used. For example, semiconductor image pickup devices are already rapidly encroaching on the field of use for conventional electronic image pickup tubes. However, since the amount of signal charge in the charge transfer device is extremely small, the quality of the function of the signal charge detection device for detecting this signal charge greatly influences the characteristics of the electronic device using the charge transfer device ii.

FIG. 3 is a plan view of an example of a MOS transistor used in a conventional signal charge detection device.

2 in FIG. 3, a MOS transistor 10 has a function as a reset transistor, and its source region 1 is
It is generally called a floating diffusion region. This source region l is held at the reset drain voltage VRD applied to the gate electrode 3, but its potential changes when charge is injected by the output gate OG of the charge transfer device. This potential change in the source region 1 is detected by, for example, a source follower circuit connected to the source region 1. Note that TG 2 in FIG. 3 is a transfer gate to which a transfer lock signal φ is applied.

The detected signal voltage Vout can be expressed by the following equation (1,) where Q is the charge injected into the source region 1 and G is the gain of the source follower circuit.

However, CL is the capacitance due to the wiring from the source region 1 to the source follower circuit, CR is the gate-source capacitance of the MOS transistor 10, Cpj is the junction capacitance of the source region 1,
CM is the capacitance of the first MOS transistor of the source follower circuit connected to the source region 1.

Since G is normally as low as about 0.9, the detection sensitivity of the signal charge detection device is i1. RAYO iCt, CR, CFj-CM
It depends on the dog.

4 and 5 are cross-sectional views taken along lines A'-A' and B-B' of the MOS transistor shown in FIG.

In FIGS. 4 and 5, there is N on the P-type semiconductor substrate 4.
Source region 1 and drain region 2 consisting of a type impurity diffusion layer
A gate electrode 3 is formed in the upper part between the source region 1 and the drain region 2 through a gate oxide film 6a.
is formed.

A P<0> type channel stopper region 5 is formed below the field oxide film 6 and is in contact with the source region 1 and drain region 2 .

When the MOS transistor 10 operates, a reverse bias is applied to the source region 1 and the P-type semiconductor substrate 4, so that the junction capacitance C! is increased as shown in FIG. exists. Also, there is a junction capacitance C between the source region 1 and the channel tip (region 5).
2 exists. That is, the junction capacitance -4Crj in equation (1) is formed by this Ct and C2.

[Problem that the invention seeks to solve]

In the conventional signal charge detection device described above, the source region 1 of the MOS transistor 10 is connected to the channel stopper region 5.
Since the junction capacitance C2 is in contact with , the junction capacitance C2 is large, which poses a problem of lowering the detection sensitivity of the signal charge detection device.

That is, since the channel stopper region 5U is generally formed of a material having an acceptor concentration N^ that is two orders of magnitude higher than that of the P-type semiconductor substrate 4, most of Crj is formed by this C2.
It is no exaggeration to say that it consists of

If you want to raise the specific value, Pm semiconductor substrate 4 (7)
7 Habit 7” Tar af, Np, 1= 1.0×
10 pieces/cgl, acceptor concentration Naz in channel stopper region 5 = 1. OXl 017 pieces/cI! , donor 1 degree ND1 in source region l = 1-OX 10''
pieces/ci, the junction surface fR8l between the source region 1 and the P-type semiconductor substrate 4 is 10 μm×10 μm, and the junction surface S2 between the source region 1 and the channel stop region 1 is 13 m×20
μm, reverse bias voltage VB is IOV, and to simplify the calculation, we use a step junction, then the junction capacitance f4 C] and Cz
is determined by the following equation (2+, (3)).

≧0.002PF ・・・・・・(2) ≧0.0053pF ・・・・・・(3) Here esi
is the dielectric constant of the semiconductor substrate, ε0 is the dielectric constant of vacuum, φ1.
φ2 is the diffusion potential of each junction. From this, the junction capacitance 1crj (C1+ Cz =0.OO
81 pP), approximately 65% is the junction capacitance C2 with the channel stopper region 5.

An object of the present invention is to provide a signal charge detection device with improved detection sensitivity.

[Means for solving problems]

The signal charge detection device of the present invention includes a source region and a drain region of opposite conductivity formed on a conductivity type semiconductor substrate, and a gate electrode formed on the upper part between the source region and the drain region with an insulating film interposed therebetween. A signal charge detection device using a MOS transistor having a MOS transistor as a reset transistor, which is formed apart from the source region (one channel stopper region).

〔Example〕

Next, a practical example of the present invention will be described with reference to the south side.

FIG. 1 is a plan view of a MOS transistor used in an embodiment of the present invention, and FIG. 2 is a plan view of the MOS transistor shown in FIG.

In FIGS. 1 and 2, a MOS transistor 20 is composed of a source region 1, a drain region 2, a gate electrode i3, etc., and is used in the conventional signal charge detection device shown in FIGS. For the MOS transistor 10 and 'A', in order for the source region 1 to be closer to the edge 5a of the channel stopper region 5, it is only necessary to partially change the shape of the mask when forming the channel stopper region 5. No problem.

By separating the source region 1 from the channel stopper region 5 in this way, the conventional junction capacitance C2 shown in FIG. Although C3 is added, the junction capacitance Cpj formed by the source region 1 itself is significantly reduced.

If we increase the specific numerical value, C4 can be obtained as shown in equation (4).

≧0.00056pF (4) Therefore, the junction capacitance of the source region that can be used in this embodiment is Crj=Ct+
C4=0.00336pF, which is the junction capacitance C of the conventional source region in contact with the channel stopper region 5.
This is reduced to 1/2.4 compared to rj=0.0081 pF.

Although the above embodiment describes the case where a P-type semiconductor substrate is used, similar effects can be obtained when an N-type semiconductor substrate is used.

〔Effect of the invention〕

As explained above, the present invention has the effect of significantly reducing the value of the junction capacitance 1tcrj formed by the source region by separating the channel stopper region and the source region.

Therefore, a signal charge detection device having a highly sensitive detection ability can be obtained.

[Brief explanation of drawings]

FIG. 1 is a plan view of a MOS transistor used in an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line c-c' of the MOS transistor in FIG. The plan views of the MOS transistors used in FIGS. 4 and 5 are the MOS transistors h-A' line and B in FIG.
It is a sectional view taken along the -B' line. DESCRIPTION OF SYMBOLS 1... Source region, 2... Drain region, 3... Gate electrode, 4... P-type semiconductor substrate, 5... Channel Stopper area, 6.
・・・−・Field oxide film. 10.20---MOS transistor. Agent: Patent Attorney Shinko Uchihara / Graduated from Tokyo 2, Tetsu

Claims (1)

[Claims] An M having a source region and a drain region of opposite conductivity type formed on a semiconductor substrate of one conductivity type, and a gate electrode formed on an upper part between the source region and the drain region with an insulating film interposed therebetween.
A signal charge detection device using an OS transistor as a reset transistor, wherein the source region is formed apart from a channel stopper region.