JPH04155842A - Manufacture of charge transfer device - Google Patents

Abstract

PURPOSE:To contrive to effectively inhibit the extent that the regions of impurity layers spread up to the lower parts of first electrodes by a method wherein the first electrodes are formed at prescribed positions on a first insulating film and the impurity layers are selectively formed using the first electrodes and second insulating films, which are positioned on the sidewalls of the first electrodes, as masks. CONSTITUTION:A first oxide film layer 4 is formed on a semiconductor substrate, which is constituted of a P-type substrate 1 and an N-type buried layer 2, as a first insulating film and thereafter, first electrodes 5, 5... are formed at prescribed regions on the layer 4. Second oxide film layers 6 which are used as second insulating layers are formed in such a way as to cover the whole of the sidewalls and upper surfaces of the electrodes 5. A P-type impurity is implanted using the layers 6 as masks to form selectively P-type impurity layers 3 and second electrodes 7, 7... are formed between the layers 6. A high-temperature heat treatment is not applied to the P-type impurity and the diffusion and lateral spread of the layers 3 are inhibited. The extent of the layers 3 to the lower parts of the electrodes 5 is reduced. At the time of ion implantation of the P-type impurity, the P-type impurity layer 3 implanted regions are far off from the end parts of the electrodes 5 and the diffusion and intrusion of the layers 3 into the lower parts of the electrodes 5 are further inhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a charge transfer device applied to a solid-state image pickup device that can be used in an integrated video camera or the like.

(Prior Art) In recent years, charge transfer devices have been widely put into practical use in imaging units of integrated video cameras and the like. Among them, embedded channel CCD (charge coupled device)
e) has low noise characteristics and is therefore being actively developed.

A conventional charge transfer device will be described below with reference to the drawings.

FIGS. 5 and 6 are schematic diagrams showing the manufacturing process and structure of a conventional charge transfer device, respectively. In the configuration diagram of FIG. 6, 1 is a P-type substrate, 2 is an n-type buried layer, 3 is a P-type impurity layer, 4 is a first oxide film layer, 5 is a first electrode, 6 is a second oxide film layer, 7 is a second electrode. In addition, in the same figure (a),
G1 is a first input terminal that connects the odd numbered rows of the first electrodes 5 and the odd numbered rows of the second electrodes 7; G2 is the first input terminal that connects the even numbered rows of the first electrodes 5 and the second
This is a second input terminal connected to the even numbered rows of electrodes 7.

In the figure (b), φ1 is a pulse waveform applied to the first input terminal G1, and φ2 is a pulse waveform applied to the second input terminal G2. Each pulse waveform φ1. φ
2 are input terminals Gl and G2, respectively, which receive positive voltage when at high level.
to be applied.

The lower diagram of FIG. 6(a) is a diagram showing the potential distribution at time t in FIG. 6(b). QS is a signal charge, and QL is a residual charge generated due to transfer loss.

Regarding the conventional charge transfer device configured as described above,
The manufacturing method and operation thereof will be explained below.

FIG. 5 is a diagram showing the manufacturing process of the conventional charge transfer device. First, in the case of FIG. 5(a), the first oxide film layer 4 is formed, and then the first electrode 5 is formed.

Next, as shown in FIG. 4B, a P-type impurity layer 3 is implanted using the first electrode 5 as a mask. Subsequently, a second oxide film layer 6 is formed in the case shown in FIG. 5C, and a second electrode 7 is formed in the case shown in FIG.

(Problems to be Solved by the Invention) However, in the above-described conventional method for manufacturing a charge transfer device, due to the formation of the P-type impurity layer 3 or the second oxide film layer 6 or other heat treatment steps, The region of the impurity layer expands below the first electrode 5, and as a result, the depletion voltage of the buried channel formed below the first electrode 5 is partially lowered.

Further, there is a problem in that the portion where the depletion voltage has decreased acts as a barrier and residual charges are generated, which significantly deteriorates the characteristics of the charge transfer device.

The present invention has been made in view of this point, and its purpose is to effectively suppress the extent to which the region of the impurity layer extends below the first electrode.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes high-temperature heat treatment when manufacturing a charge transfer device having a plurality of transfer electrodes on a semiconductor region via an insulating film. After forming the second oxide film layer and the like, the impurity layer is formed.

In other words, the specific solution of the present invention is to form a first insulating film on a semiconductor substrate, then form a first electrode in a predetermined region of the first insulating film, and then After forming the second insulating film that covers at least the side walls of the electrode, the first
The impurity layer is selectively formed using the electrode and the second insulating film located on the side wall of the first electrode as a mask.

Furthermore, the formation of the impurity layer is 10° in the direction of charge transfer.
The structure is such that it is formed by ion implantation with an inclination angle of 45" to 45".

(Function) With the above structure, the impurity layer is formed after the second insulating film is formed, which is subjected to high-temperature heat treatment. This eliminates the need for a high-temperature heat treatment step after forming the impurity layer, reducing the extent to which the impurity layer spreads below the first electrode, thereby significantly improving transfer loss.

Moreover, when the impurity layer is implanted at an inclined angle, the impurity layer is formed at a distance from the first electrode, so even if the impurity layer spreads laterally, the first electrode It can be sufficiently prevented from spreading below the electrode.

(Example) Hereinafter, a first example of the present invention will be described with reference to the drawings.

FIGS. 1 and 2 are schematic diagrams showing the manufacturing process and structure of the charge transfer device of the present invention. In the configuration diagram of Figure 2, 1
is a P-type substrate, 2 is an n-type buried layer, 3 is a P-type impurity layer,
4 is a first oxide film layer, 5 is a first electrode, 6 is a second oxide film layer,
7 is a second electrode.

In addition, in the same figure (a), G1 is the first input terminal connecting the odd numbered rows of the first electrodes 5 and the odd numbered rows of the second electrodes 7;
is a second input terminal connecting the even numbered columns of the first electrodes 5 and the even numbered columns of the second electrodes 7. In the same figure (b), φ1 is a pulse waveform applied to the first input terminal G1, φ2 is a pulse waveform applied to the second input terminal G2,
When each pulse is at a high level, a positive voltage is applied to each input terminal Gl.
.

Apply to G2.

The lower diagram of FIG. 2(a) is a diagram showing the potential distribution at time t in FIG. 2(b), where QS is a signal charge.

The manufacturing method and operation of the charge transfer device of the present invention configured as described above will be described below.

FIG. 1 is a diagram showing the manufacturing process of the charge transfer device shown in FIG. 2. First, in the case of FIG. After forming the first oxide film layer 4 as a first insulating film on the buried layer 2,
First electrodes 5.5 are formed in a predetermined area. Next, in FIG. 5B, a second oxide film layer 6 is formed as a second insulating film so as to cover the entire sidewall and top surface of the first electrode 5.

The heat treatment at this time requires 20 minutes or more at 1000°C. Subsequently, in the case of (c) in the same figure, a P-type impurity layer 3 is selectively implanted using the second oxide film layer 6 as a mask, and in the case of Cd) in the same figure, a P-type impurity layer 3 is formed between the second oxide film layers 6. Second electrode 7
．． Form 7.

As described above, in this embodiment, the second oxide film layer 6 is
After being formed by heat treatment at temperatures above .degree. C., the P-type impurity layer 3 is implanted using the second oxide film layer 6 as a mask, so that the P-type impurity is not subjected to the high-temperature heat treatment as in the prior art. This suppresses the diffusion and lateral spread of the P-type impurity layer 3, which makes it possible to reduce the spread of the P-type impurity layer 3 below the first electrode 5, thereby significantly improving transfer loss. I can do it.

Furthermore, since the second oxide film layer 6, which serves as a mask when ion-implanting the P-type impurity layer 3, is usually 1,500 to 3,000 thick, the implanted region of the P-type impurity layer 3 is Since it is far away from the end of the first electrode 5, diffusion and penetration of the P-type impurity layer 3 downward into the first electrode 5 can be further suppressed.

Next, a second embodiment of the present invention will be described with reference to the drawings.

FIGS. 3 and 4 are schematic diagrams showing the manufacturing process and structure of the charge transfer device of the present invention. The difference from the structure shown in FIG. 2 of the first embodiment is that in the structure shown in FIG. 4, impurity implantation is performed at an inclined angle.

Next, the manufacturing method and operation of the charge transfer device shown in FIG. 4 will be explained based on the process diagram shown in FIG. 3. First, in FIG. 3(a), the first oxide film layer 4 is formed, and then the first electrode 5 is formed. Next, as shown in FIG. 5B, a second oxide film layer 6 covering the first electrode 5 is formed. The heat treatment at this time was 100
It requires at least 20 minutes at 0°C. Next, the same figure (C)
At this time, using the second oxide film layer 6 as a mask, the P-type impurity layer 3 is implanted at an inclination angle of 10 to 45 degrees with respect to the charge transfer direction. The reason for this is that the thickness of the first electrode 5 is 0.5 μm.
Therefore, if the implantation angle is set to an inclination angle of 10 to 45 degrees, even if the P-type impurity layer 3 diffuses and spreads laterally during heat treatment in the post-process, the spread will be 0.1 to 0.5 μm.
This is because the influence on the lower part of the first electrode 5 can be ignored. Subsequently, the second electrode 7 is formed as shown in FIG. 3(d).

As described above, in this embodiment, the P-type impurity layer 3 is implanted at an inclined angle using the second oxide film layer 6 as a mask.
The potential barrier on the side where transfer loss occurs due to lateral diffusion of the type impurity layer 3 can be eliminated.

In addition, although the above explanation shows the case where a P-type impurity layer is formed in an N-type buried layer, the following can be similarly applied to the case where an N-type impurity layer is additionally formed in a P-type buried layer. Needless to say.

(Effects of the Invention) As explained above, according to the method for manufacturing a charge transfer device of the present invention, it is possible to suppress the lateral diffusion of the impurity layer below the electrodes and reduce the transfer loss. It becomes possible to create a high-performance charge transfer device with extremely little amount of charge transfer, and it is possible to exhibit remarkable practical effects.

Moreover, if the impurity layer is implanted at an angle with respect to the charge transfer direction, the impurity layer can be formed at a distance from the electrode and can be sufficiently prevented from spreading below the electrode. Therefore, it is possible to create a high-performance charge transfer device.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the manufacturing process of the charge transfer device in the first embodiment, Fig. 2 is a diagram showing the cross-sectional configuration, potential distribution, and pulse waveform of the charge transfer device, and Fig. 3 is a diagram showing the charge transfer device in the second embodiment. FIG. 4 is a diagram showing the cross-sectional structure, potential distribution, and pulse waveform of the charge transfer device. FIG. 5 is a diagram showing the manufacturing process of a conventional charge transfer device. FIG. 2 is a diagram showing a cross-sectional configuration, potential distribution, and pulse waveform of a conventional charge transfer device. 1...P-type substrate, 2...n-type buried layer, 3...
P-type impurity layer, 4... first oxide film layer, 5... first electrode, 6... second oxide film layer, 7... second electrode, G1...
First input terminal, G2...Second input terminal, φ1...G
1 manual waveform, φ2...G2 manual waveform, QS...signal charge, GL...residual charge. 1...P type substrate 2,...N type buried layer 3, P type impurity layer 4, first oxide film layer 5, first electrode 6...second oxide film layer 7, second electrode G1... 1st input terminal G2・2nd input terminal φ1・・G1 manual waveform φ2・・G2 manual waveform QS・・Signal charge GL・Residual charge Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Claims (3)

[Claims] (1) After forming a first insulating film on a semiconductor substrate, a first electrode is formed in a predetermined region of the first insulating film, and then,
After forming a second insulating film that covers at least a side wall of the first electrode, selectively add an impurity layer using the first electrode and the second insulating film located on the side wall of the first electrode as a mask. 1. A method of manufacturing a charge transfer device, comprising: forming a charge transfer device. (2) The method for manufacturing a charge transfer device according to claim (1), wherein the impurity layer is formed by ion implantation having a predetermined inclination angle with respect to the charge transfer direction. (3) After forming a first insulating film on the semiconductor substrate, forming a first electrode in a predetermined region of the first insulating film, and then
After forming a second insulating film that covers at least a side wall of the first electrode, the second insulating film is formed using the first electrode and the second insulating film located on the side wall of the first electrode as a mask. 1. A method for manufacturing a charge transfer device, comprising implanting impurities so as to selectively form an impurity layer at a distance of 0.1 μm to 0.5 μm from a side surface of a film on a substrate surface.