JPH02246231A - Charge coupled type device - Google Patents

Abstract

PURPOSE:To improve transfer efficiency and a dynamic range by forming each pixel for transferring signal charge in a groove shape, and elongating the effective length of each electrode in the signal-charge transfer direction. CONSTITUTION:An interval l between groove parts is specified in the transfer direction of signal charge at the surface part of a semiconductor substrate 3. N<-> type impurity layers D1-D5 and the like are formed at the end surface of the groove parts by a means such as ion implantation and the like. The neighboring impurity layers D1-D5 and the like are separated with barrier layers IS1-IS6 comprising P<+> type impurity layers. Gate electrodes G1-G5 and the like facing the impurity layers D1-D5 are laminated through oxide layers Si which are laminated on the surface of the semiconductor substrate. Since the transfer pixels for transferring the signal charge are formed in the groove shape and the effective length of each gate electrode in the signal transfer direction is made long, the quantity of the signal charge that can be transferred, i.e., the transfer efficiency, and a dynamic range can be improved even if integration density is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a charge-coupled device (CCD), and in particular:
This invention relates to a charge-coupled device with increased integration in the direction of signal charge transfer.

[Conventional technology]

A conventional charge-coupled device has a structure shown in FIG. That is, this is a built-in CCD (BCO
D), a different type of impurity layer (N- impurity layer) 2 is formed on the surface of the semiconductor substrate 1 by ion implantation, and a plurality of gate electrodes g, ~g8, etc. are formed on the upper surface in the signal charge transfer direction X. For example, four-phase driving force type drive signals φ1 to φ as shown in FIG.
4 is applied to generate a potential profile as shown by the dotted line in FIG. 4, thereby transferring signal charges.

[Problem to be solved by the invention]

However, in such a charge-coupled device, since each gate electrode is formed substantially horizontally to the surface of the semiconductor substrate, there is a problem that the degree of integration cannot be increased.

In other words, in order to design a charge-coupled device with consideration to signal charge transfer efficiency and dynamic range, it is necessary to make the area of each gate electrode relatively large. In order to prevent charges from mixing during transfer, a potential barrier is generated so that the side edges of adjacent gate electrodes overlap (for example, in FIG. 4, the side edges of gate electrode g2 overlap gate electrode g3). (overlapping with the side edges of the signal charge transfer direction), it was not possible to increase the degree of integration in the signal charge transfer direction X.

In addition, the limitations in improving the degree of integration due to these reasons hinder the increase in pixel density when applied as a signal charge transfer path of a solid-state imaging device using COD, for example.

That is, as in a field interline transfer solid-state imaging device (FIT-COD) or an interline surface imaging device (IL-COD), a signal charge transfer path is formed adjacent to a light-receiving element corresponding to a pixel. However, if the structure is such that the signal charges generated in these light-receiving elements are read out via a signal charge transfer path,
Even if we try to improve the pixel density by forming the light-receiving element as finely as possible, it is not possible to perform micromanufacturing of the transfer element due to the design limitations of the gate electrode mentioned above, so in the end, a gate with a low density is used. Pixels are manufactured according to the size of the electrode.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a charge-coupled device that can improve the degree of integration in the signal charge transfer direction.

[Means to solve the problem]

In order to achieve such an object, the present invention provides a plurality of gate electrodes on the upper surface of a semiconductor substrate in the direction of signal charge transfer, and applies drive signals to these gate electrodes to transfer signal charges to the signal charge. In a charge-coupled device that transfers charges in the signal charge transfer direction, a plurality of grooves are formed on the surface of the semiconductor substrate in the direction of signal charge transfer, and the inner end faces of these grooves are coated with a predetermined concentration and a concentration corresponding to charge transfer pixels. diffusing different types of impurity layers, forming a barrier layer made of a predetermined impurity between each impurity layer, stacking the gate electrode on the upper surface of these impurity layers, and applying the drive signal to the gate electrode. The structure is such that signal charges are transferred in the signal charge transfer direction.

In a charge-coupled device having such a structure, a potential gradient is generated by designing each impurity layer formed on the end face of the groove to have a high concentration distribution in the signal charge transfer direction. It may also be a structure.

[Effect]

In the charge-coupled device of the present invention having such a structure, each transfer pixel for transferring signal charges is formed in the shape of a groove to lengthen the effective length of each gate electrode in the signal charge transfer direction. Therefore, even if the degree of integration is increased, the amount of signal charge that can be transferred, in other words, the transfer efficiency and dynamic range can be improved.

Note that the impurity layers that are adjacent to each other are separated by the barrier layer, but when a drive signal is applied to the gate electrode, charges move in the lower layer of these barrier layers due to a change in potential, so that the impurity layers are separated by the barrier layer. The signal charge transfer operation is realized.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

First, the structure will be explained based on FIG. 1. In the figure, 7-shaped charge transfer pixels are formed on the surface of a P-type semiconductor substrate 3. For example, these charge transfer pixels are transferred from the left side to the right side of the figure. The structure is such that signal charges are transferred through pixels.

That is, in the surface portion of the semiconductor substrate 3, the interval l between the grooves in the signal charge transfer direction is determined according to the following formula, and in this embodiment, the interval is about 2×1 μm! It is formed every time.

Note that ε represents the dielectric constant of the semiconductor substrate, K represents the absolute temperature, NA represents the impurity concentration of the semiconductor substrate, and nl represents the number of electrons in the genuine semiconductor. Further, N- type impurity layers D1 to D5, etc. are formed on the inner end face of each groove by means such as ion implantation, and furthermore, P is formed between the mutually adjacent impurity layers DI-D5, etc.
They are separated by a barrier layer 15I-136 made of a type impurity layer. Then, a gate electrode GI-G!1, etc., which faces the impurity layer DI''Ds, is laminated via an oxide film layer S1 laminated on the surface of the semiconductor substrate, for example, the four layers shown in FIG. Wiring is performed to apply drive signals φ1 to φ4 of the drive method.

Next, the operation of the embodiment having such a structure will be explained.
The drive signal φ! of the four-layer drive system as shown in FIG. ~φ4
When is sequentially applied to each gate electrode G1-G5, etc., the impurity layer under the gate electrode, the potential profile of ~D3, etc. changes, and the signal charges are sequentially transferred in a predetermined transfer direction X.

During this transfer, the amplitude of the drive signals φ1 to φ4 is set to approximately 5
When set to volts, the interval i between each of the barrier layers IS+ to IS6 is about 1 μm, so the signal charge passes through the semiconductor substrate under the barrier layer and is transferred from the upstream transfer pixel to the downstream transfer pixel. Signal charges will be transferred to. Further, to describe signal charge transfer between transfer pixels provided with gate electrodes G+ and G2 as a representative example, the drive signal φ1 is “L” level and the drive signal φ4 is “H1 level” as shown in FIG.
When reaching the 1st level, the impurity JifD+ Fermi
Since the Fermi level of the impurity ND2 becomes lower than the Fermi level of the impurity ND2, the signal charge moves as shown by Q in the figure due to the difference in the Fermi level between the barriers ISz. Such Fermi level differences also occur in other transfer pixels according to changes in the levels of the drive signals φ1 to φ4, and signal charges are transferred one after another.

As described above, according to this embodiment, each transfer pixel for transferring signal charges is formed in the shape of a groove, and the length of each gate electrode in the signal charge transfer direction is lengthened, thereby increasing the degree of integration. Also, the amount of signal charge that can be transferred, in other words, the transfer efficiency and dynamic range can be improved.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 2, the same or corresponding parts as in FIG. 1 are indicated by the same reference numerals, and the differences from the previous embodiment shown in FIG. The impurity concentrations of the impurity layers D1 to D5, etc., are lower on the upstream side of the signal charge transfer direction X and higher on the downstream side. In FIG. 2, the low concentration region is indicated by N-1, and the low concentration region is indicated by N'.

In this way, by creating a concentration gradient in each impurity layer, a potential well that descends from upstream to downstream is potentially formed, which improves problems such as signal charges remaining during transfer and improves charge transfer efficiency. You can improve your performance. Also, the third
The drive signals of the so-called two-phase drive system as shown in the figure φ, φ
It becomes possible to perform signal charge transfer by applying B, and it becomes possible to increase the transfer pitch, so it is possible to realize a substantial improvement in the degree of integration.

〔Effect of the invention〕

As explained above, according to the present invention, each transfer pixel for transferring signal charges is formed in a groove shape, and the effective length of each gate electrode in the signal charge transfer direction is lengthened.
The amount of signal charge that can be transferred, in other words, the transfer efficiency and dynamic range can be improved, and the degree of integration can be improved.

[Brief explanation of drawings]

Fig. 1 is a vertical sectional view showing the structure of one embodiment of the present invention; Fig. 2 is a longitudinal sectional view showing the structure of another embodiment;
Timing chart of phase drive signals; FIG. 4 is a longitudinal sectional view showing the structure of a conventional example; FIG. 5 is a timing chart of four-phase drive signals. Codes in the figure: D1 to D5; Impurity layer Si; Oxide film layer Is-IS6; Barrier layer Gi ""Gs; Gate electrode agent Patent attorney (8107) Kiyoshi Sasaki (3 others)

Claims (2)

[Claims] (1) A charge-coupled device in which a plurality of gate electrodes are provided on the top surface of a semiconductor substrate in the direction of signal charge transfer, and signal charges are transferred in the direction of signal charge transfer by applying a drive signal to these gate electrodes. A plurality of grooves are formed on the surface of the semiconductor substrate in the direction of signal charge transfer, and an impurity layer of a predetermined concentration and type corresponding to a charge transfer pixel is diffused on the inner end surface of these grooves, and A barrier layer made of predetermined impurities is formed between each impurity layer, the gate electrode is stacked on the upper surface of these impurity layers, and the signal charge is transferred in the signal charge transfer direction by applying the drive signal to the gate electrode. A charge-coupled device with a transfer structure. (2) In the charge-coupled device according to claim (1), each impurity layer formed on the end face of the groove has a high concentration distribution in the signal charge transfer direction.