JPS6239057A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To decrease the transfer loss in the junction between a transfer gate and a transfer channel, by providing an impurity layer on the surface of a substrate in the transfer channel provided by a buried channel, the impurity layer having a type of conductivity opposite to that of the buried channel. CONSTITUTION:In the region where a transfer gate 36 is connected with a transfer channel 3, an impurity layer 11 having a type of conductivity different from that of the transfer channel 3 is provided on the surface of the transfer channel (buried channel) 3. By appropriately controlling the impurity concentration of the impurity layer 11, any potential well produced by the narrow channel effect in the transfer channel can be eliminated completely. The channel potential is thereby rendered flat along the charge transfer direction, and the transfer loss in the charge transfer can be decreased.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to solid 11! This invention relates to an old improvement of a charge transfer unit for reducing transfer errors in a charge transfer unit of an image device.

[Prior Art] In recent years, solid-state imaging devices have become highly integrated, and as a result, pixel sizes have also become smaller, and accordingly, higher sensitivity has been required. As one of the improvement measures to satisfy this demand for higher sensitivity, Tatoeva M, Kimata
I5SCC (International
Solid State Circuit Conference February 1985 Digest of Technical Papers (DIGEST OF TEC) (NIC
A charge sweeping type solid state 111 as disclosed on page 100 of AL PAPER 8)! A II device has been developed.

FIG. 3 is a diagram showing the planar arrangement of the charge conversion region and the vertical charge transfer section of this charge sweeping type solid-state imaging device. In FIG. 3, the solid-state imaging device includes a photoelectric conversion element 32 composed of a photodiode, for example, for converting an applied optical signal into signal charges, and a system for selectively reading out signal charges from the photoelectric conversion element 32. Transfer game-1-36 with surface channels for transfer game-1
-36, and a transfer channel 3 formed of a buried channel serving as a path for transferring signal charges from -36.

1-Charge transfer operation 1 of transfer channel 1-36 and transfer channel 3; & Scan the contact bottle area 35! 31 Kara'7'-to'lRm (Transfer 1 pole) 33
, 34A.

III II ,i depending on the applied signal voltage level
I do it. In other words, the control voltages to the 1-transfer gate 1.36 and the transfer channel 3 are the same transfer/l'-to-N
It is given by the balance 33°34. This electric 1j? iM1 solid type l#! The movement of the statue is the same as the preceding technique tl mentioned above.
Although it is disclosed in detail in the I literature or in the Television Society technical report TEBS101-6ED841 by Honsetsu et al., page 31, it will be briefly explained below. The signal charge from the photoelectric conversion element 32 connected to the 1st column (1st horizontal line) is transferred to the transfer channel (for vertically transferring the charge via the transfer gate 36) by the signal@voltage from the running i-keyaki 31.
horizontal COD (not shown) in one horizontal period.
eViCe) is gathered (transferred) to the horizontal COD during the horizontal retrace period, and is sequentially transferred in series (
, will be released twice in a row. According to this charge sweeping method, signal charges from only one photoelectric conversion element 32 within one vertical line are read out to the transfer channel 3 and transferred in the vertical direction. In this case, the length of the potential well in the transfer channel 3 corresponds to the first power straight line, so the area of the potential well becomes large, and even if the width of the transfer channel 3 is made sufficiently small, sufficient sensitivity cannot be obtained. In real life, it is possible to maintain the same level of dog δ゛. ,, L'4N makes the area occupied by the photoelectric conversion element 32 thicker! 2, and the frontage ratio (ratio of the area occupied by the b photoelectric conversion element to the area of the pixel) can be increased.

[Problems that the invention attempts to solve] Figure 4 is similar to Figure 3.1. FIG. 4 is a diagram showing a cross-sectional structure of a solid-state imager (not shown); FIG. A cross-sectional structure taken along line B-8 is shown. FIG. 4 1=': 111?iI on the semiconductor substrate 1 of the first conductivity type ((xp type in the figure)
A second conductive type (n-type in the figure) impurity region 43 is provided to form a buried channel serving as a transfer path. In addition, in order to electrically isolate adjacent elements, an element isolation oxide film 41 formed using, for example, a selective country method, and a first conductivity type (in the figure) formed using, for example, an ion implantation method, are used. 1)' type) impurity diffusion layer 42 having a high impurity concentration for element isolation is provided. Further, the impurity diffusion layer (buried channel 7 channel) 43 connected to the transfer gate 36 is in contact with the impurity diffusion layer 42 only on one side (Fig. 4 (b)), but the area of
In the fourth section (a), the impurity diffusion @B43 is sandwiched between the impurity diffusion layers 42.

In the above configuration, impurity diffusion! I! The lateral diffusion of impurities from 42 begins to affect the impurity diffusion layer 43 that becomes the buried channel, and as the width of the transfer channel 3 (impurity diffusion m43) becomes narrower as shown in FIG. A so-called narrow channel effect occurs in which the potential formed there becomes lower in response to the applied voltage.
As can be seen from the figure, the effect of non-Ni diffusion, which becomes the transfer channel for isolation, is only on one side in the 1-link connected to the 1-transfer gate 36. On the other hand, in areas outside of JR, it comes from both sides, and the degree of influence is different.

FIG. 6 is a diagram schematically showing the cross-sectional structure along the line c-c'' in FIG. 3 and the bottle formed there; FIG. Figure <b> shows the potential formed there. Normally, the transfer gate region is formed near the center of the transfer electrodes 33, 34, so the falloff that occurs in the transfer channel 3 in that region +, +:' As a result, as can be seen from FIG. 6(1)), a so-called built-in potential well 44 is formed near the center of the transfer electrodes 33, 34, and the There is a problem in that the signal N'F4 is captured and a residual charge Q is generated, which deteriorates the signal charge transfer rate.

Therefore, the purpose of this illumination is to eliminate problems such as (a) di and to reduce transfer losses by eliminating the so-called built-in potential wells formed in the direction of signal charge transfer. Please provide the imaging device (+i).

[Means for solving the problem] The solid-state 1iri image device according to the present invention includes a buried channel formed at the connection portion between the i-transfer gate and the transfer channel portion that transfer signal charges from the photoelectric conversion element. An impurity layer of a conductivity type opposite to that of the buried channel is provided on the substrate surface of the transfer channel.

[Function] The impurity layer formed on the substrate surface of the transfer channel portion in this invention has the effect of reducing the ditonel potential of the buried channel, so when a narrow transfer channel is used, the narrow channel effect causes l - Potential wells generated at the connection between the transfer gate and the transfer channel section can be canceled out, and transfer loss can be reduced.

[Embodiment of the invention] Figure 1 shows the light 1 of the solid enclosure U, which is an example of this light emission.
FIG. 4 is a diagram showing a planar arrangement of a variable recovery area J5 and a vertical transfer point, and corresponds to the conventional solid-state imaging device shown in FIG. 3. Here, the same reference F number is given to the part I:6 which corresponds to the solid-state imaging device of FIG. In FIG. 1, as a feature of this invention, transfer gate 3
6 and the transfer channel 3 [1] An impurity layer 11 of a conductivity type (Jp type in the figure) that is connected to the transfer channel 3 is provided on the surface of the transfer channel (buried channel) 3.

Figure 2 1 shows the cross-sectional structure of the solid-state imaging device in Figure 1.
Figure 2(a) shows the cross section 4 [(structure) taken along line A-A- in Figure 1; Figure 2 (C) shows the cross-sectional structure after the line has healed.
1 shows a cross-sectional structure taken along line CC- in FIG. Figures 2(a) and (b) are Figure 4(a).

(1)), and Figure 2 (C) corresponds to Figure 6.
Figure 2 (h) corresponds to Figure <a>.

As seen from (C), the transfer channel is
An inorganic material @11 is formed on the surface of the region connected to the 1-ransf 1-gate 1- of the i-material diffusion [43]. Next, the function of this impurity layer 11 will be explained.

A load without a signal from the charging converter 32 is
1-36 to the forwarding tunnel 3.

In the transfer channel 3, the signal charge is transferred within the n-type drain hole 43 which becomes a buried channel.

As mentioned above, in the conventional award system 1, transfer channel 3
As the width of the transfer 'f-1-net 3 (layer 43 in the impurity layer 43) becomes narrower, the tunnel bodential well 7″f formed in the buried chitnel becomes shallower. - The part connected to the transfer channel 1-36 is less likely to be affected by this narrow channel effect, so the channel potential is deeper than other parts of the transfer channel 3, and a built-in potential well 44 is formed there. However,
In the invention, the transfer channel 3 (impurity diffusion layer 4
3) where p is connected to the transfer gate 30.
Since the type impurity 1!11 is formed on the surface of the transfer channel 3, the channel potential of the n-type buried channel impurity diffusion layer 43 is low (the potential well is shallow).
The potential well that was conventionally formed near the center of the transfer gate l-N poles 33 and 34 can be removed.

′! j', that is, the impurity il of the three-component layer 11 under this p-type
By appropriately controlling the angle of 1 degree (2 degrees), it becomes possible to completely cancel out the bottleneck caused by the narrow channel effect in the transfer tunnel 3.

In the above embodiments, the impurity diffusion layer serving as the buried channel is described as being of n'' type, but it goes without saying that the conductivity type is not limited to this case.

In addition, in the above embodiment, the charge transfer region is of the M load sweeping type, but the charge transfer region may also be formed of a commonly used charge coupled device (COD). In the case where the width of the transfer channel is made so narrow that the narrow channel effect becomes noticeable, the same effects as in the above embodiment can be obtained by applying the present invention.

[Effects of the Invention] As described above, according to the present invention, an impurity layer having a conductivity type opposite to that of the buried channel forming the transfer channel is provided on the substrate surface in the transfer channel portion in contact with the transfer gate. Therefore, the channel potential well caused by the narrow channel effect of the buried channel can be canceled out, the channel potential becomes flat along the charge transfer direction, and transfer loss in charge transfer can be reduced.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a planar arrangement of a photoelectric conversion section and a charge transfer section of a solid-state +St device which is an embodiment of the present invention. FIG. 2 is a diagram showing the cross-sectional structure of the solid-state imaging device shown in FIG. 1, and FIG. Figure (b) is B- in Figure 1.
8" line, and FIG. 2(C) shows the cross-sectional structure along c-c-m in FIG. 1. FIG. 3 shows the charging conversion part and FIG. 4 is a diagram showing a planar arrangement of a charge transfer section. FIG. 4 is a diagram showing a cross-sectional structure of the solid-state device shown in FIG. 3, and FIG. Figure 4(b) shows the cross-sectional structure of Figure 3.
FIG. 5 is a diagram showing the cross-sectional structure along line 8". FIG. 5 is a diagram showing the relationship between the transfer channel width and the channel potential formed there. FIG. 6 is a diagram showing the solid state shown in FIG. 6A and 6B are diagrams showing the cross-sectional structure of the III imaging device and the channel potential formed therein, with FIG. 6(a) showing the cross-sectional structure along the line C-C- of FIG. is a diagram schematically showing the channel potential formed in the cross-sectional structure of FIG. 6(a). In the figure, 3 is a transfer channel, 11 is a second conductivity type impurity layer, and 32 is a photoelectric conversion element photoelectric conversion section), 33.3
4 is a transfer gate electrode, 43 is a first conductivity type impurity diffusion layer that becomes a buried channel, and 42 is a channel cut impurity diffusion layer. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Figure 33.34 - Transfer voltage rating 35; Koshitaft Toto Figure 6 (a) C' (b)

Claims (1)

[Scope of Claims] A plurality of photoelectric conversion elements, a transfer gate provided for each of the plurality of photoelectric conversion elements and selectively reading signal charges from the photoelectric conversion element, and the transfer gate. A solid-state imaging device includes a transfer means for receiving and transferring signal charges from a charge transfer element, the transfer means comprising a charge transfer element having a buried channel of a first conductivity type serving as a path for the signal charges, In a connection region of the buried channel of the charge transfer element with the transfer gate, an impurity layer of a second conductivity type is provided in a surface region of the buried channel.
Solid-state imaging device.