JP2996567B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a manufacturing method of a solid-state imaging device <br/> is that used in a video camera or the like.

[0002]

2. Description of the Related Art CCD solid-state image sensors, which have been widely used in consumer and commercial video cameras, have been required to have higher resolution and higher performance, and picture elements have been increasingly miniaturized. . FIG. 3 is a schematic diagram of a cross-sectional structure of one pixel portion of the CCD image sensor. In the figure, 1 indicates an n-type silicon substrate, 2 indicates a low-concentration first P well, and 3 indicates a high-concentration second P well. 4 indicates an n-type region of the photodiode,
Reference numeral 5 denotes a p + region which is a surface dark current suppressing layer of the photodiode. Reference numeral 6 denotes an n-type region serving as a transfer channel of the CCD, 7 denotes a p + region for separating the photodiode and the CCD channel, and 8 denotes a p- region for separating and reading the photodiode and the CCD channel. 9,
Reference numeral 10 denotes a silicon oxide film and a silicon nitride film as a gate insulating film. 11 is a gate electrode, 12 is an interlayer insulating film between itself and the light shielding film 13, and 14 is a protective film. In the above-mentioned CCD solid-state imaging device, the transfer capacity of the CCD channel is reduced due to the miniaturization of the picture element, and the reduction of the dynamic range and the transfer efficiency are becoming problems. In order to improve the transfer capacity, it is necessary to increase the concentration of the CCD channel, and by lowering the temperature of the heat treatment, electrical separation between the photodiode and the CCD is enabled even if the concentration is increased. In addition, it is becoming difficult to secure a transfer efficiency of 95% or more, which is necessary to the extent that an image is not disturbed, due to a narrow CCD channel width. This is because when the width of the CCD channel is reduced, the potential of the channel becomes shallow due to the fixed potential (usually GND) on both sides of the channel, and a desired potential cannot be obtained.
That is, the narrow channel effect becomes stronger.
FIG. 4 shows a schematic cross-sectional view of one pixel of the CCD solid-state imaging device and the potential in the driving state. For this reason, the effective channel width becomes narrow, and the transfer capacity and transfer efficiency deteriorate. To ensure transfer capacity and transfer efficiency, it is necessary to form the CCD channel straight and wide in the transfer direction. The separation pattern is designed to have a layout that does not affect the CCD channel, or the temperature of the heat treatment is reduced so that the p-type impurity in the separation region does not diffuse to the CCD channel region. In addition, ONO (Ox) is required for the gate insulating film in order to prevent potential dip in the CCD transfer gate due to the necessity of low voltage driving.
A flat CCD channel is formed using an ide-Nitride-Oxide) film.

[0003]

By the way, only the lowering of the heat treatment temperature and the contrivance of the layout as described above require the CCD.
Deterioration of transfer capacity and transfer efficiency due to miniaturization of the channel are inevitable.

[0004] The present invention noted the above-described conventional problems, expanding the transfer capacity, and an object thereof is to <br/> provide a method for producing a good solid-state image pickup element of transfer efficiency.

[0005]

According to the present invention, in order to achieve the above object, a thick gate oxide film region is formed around a CCD channel so that the potential around the CCD channel becomes deeper.

[0006]

[Action] Solid-state imaging device having the above configuration, the area of the flat potential of the channel center with the potential around the CCD channel becomes deeper spread, the channel effective width is increased.

As a result, the effective width of the CCD channel is increased from 1.3 times to 1.6 times, the transfer capacity is similarly increased, and good characteristics with a transfer efficiency of 99% or more are obtained. .

[0008]

FIG. 1 shows a CCD having an embodiment of the present invention.
That shows a schematic diagram of a cross-sectional structure of a pixel portion of a solid-state IMAGING element.
The components denoted by reference numerals 1 to 14 in the figure are the same as those of the above-described conventional example, and have the same functions, so that the description thereof will be omitted.

A feature of this embodiment is that a thick silicon oxide film region 15 for controlling potential is formed at an end of an n-type region 6 serving as a transfer channel of a CCD.
In order to form the thick silicon oxide film region 15, after forming p and n type regions in the silicon substrate shown in FIGS. 1 to 7, a silicon oxide film as a gate insulating film and silicon nitride films 9 and 10 are formed. Form. Thereafter, in order to form the gate insulating film of the MOS transistor of the peripheral circuit with a low-noise silicon oxide film, the silicon nitride film 10 of the peripheral circuit is removed by photoetching. At this time, the CCD
The silicon nitride film in the silicon oxide film region 15 at the end of the n region 6 serving as the transfer channel of the above is also removed. Thereafter, in a step of thermally oxidizing the silicon nitride film 10, a thick silicon oxide film region 15 is formed.

FIG. 2 is a sectional view showing the structure of a CCD channel section of one pixel section of a CCD image pickup device according to an embodiment of the present invention and the potential of the CCD channel in a driving state. C
The potential of the CD channel is proportional to the thickness of the silicon oxide film and the silicon nitride films 9 and 10 as the gate insulating films. An end of an n-type region 6 serving as a transfer channel of the CCD;
That is, in the silicon oxide film region 15, since the thickness of the silicon oxide film is thicker than the central portion of the channel, the potential of the insulating film is deeper than in the normal case. In the case of the present embodiment, the thickness of the silicon oxide film 9 and the silicon nitride film 10 as the gate insulating film is 80 nm in effective film thickness, and the thickness of the silicon oxide film region 15 as the peripheral portion of the channel is 120 nm. In this case, the transfer capacity is increased by about 20% as compared with the conventional case, and the transfer efficiency is 98%.
% To 99% or more. As a result of the analysis by the device simulation, the width of the maximum potential region in the CCD channel was increased by 18% as compared with the conventional case, and as a result, the transfer capacity was increased and the transfer efficiency was improved.

The thickness of each film used in the present embodiment is not uniquely determined. From the experimental results by the inventor, the gate insulating film at the center (normally, from 40 nm to 15 nm) is used.
The thickness of the silicon oxide film region 15 at the end of the channel is in the range of 40% to 130% as compared with that of the channel without using side effects such as dielectric breakdown and dark current increase. The capacity was increased and the transfer efficiency was improved.

[0012]

According to the manufacturing method of the apparent to the <br/> onset light of the solid-state imaging device from the description of the embodiments according to the present invention, the CCD transfer
A silicon oxide film and a silicon nitride film are deposited on the channel.
Layering and before the end of the transfer channel
Removing the silicon nitride film;
Forming a silicon oxide film on the
An ONO gate insulating film at the center of the transfer channel,
At the end of the transfer channel, a thick silicon oxide film
20% lower than before by forming a gate insulating film
With the expanded CCD channel transfer capacity, 99
Solid-state image pickup device that have a percent high transfer efficiency can be formed.

[Brief description of the drawings]

Schematic cross-sectional view of one pixel of the solid-state imaging device of an embodiment of the present invention; FIG

Figure 2 a is a potential diagram of the driving state of the cross-sectional schematic view b is the solid-state imaging device of one pixel of an embodiment der Ru solid-state imaging device of the present invention

FIG. 3 is a cross-sectional schematic view of one pixel of the solid-state imaging device of conventional example

[4] a is potential diagram of the driving state of the cross-sectional schematic view b is the solid-state imaging device of one pixel of the solid-state image pickup element

[Explanation of symbols]

 Reference Signs List 1 n-type silicon substrate 2 first P-well 3 second P-well 4 photodiode n-type region 5 photodiode surface p + region 6 n-type region serving as CCD transfer channel 7 p + isolation 8 p-isolation 9 silicon oxide film 10 silicon nitride film DESCRIPTION OF SYMBOLS 11 Gate electrode 12 Interlayer insulating film 13 Light shielding film 14 Protective film 15 Thick silicon oxide film region

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 27/148 H04N 5/335

Claims (1)

(57) [Claims] 1. Silicon oxide on a transfer channel of a CCD
Forming a film by stacking a film and a silicon nitride film, and removing the silicon nitride film at an end of the transfer channel.
A step of, to form a further silicon oxide layer on the transfer channel
The ONO gate insulating film at the center of the transfer channel,
At the end of the transfer channel, a thick silicon oxide film
Method for manufacturing a solid-state imaging device characterized by forming an over gate insulating film.