JPS6038869A - Two-dimensional charge coupled device image sensor - Google Patents

Abstract

PURPOSE:To eliminate the deterioration of a pulse shape by forming contact holes on transfer electrodes having the same phase on each transfer channel at every phase number and connecting the transfer electrodes having the same phase in common by a low resistance electrode. CONSTITUTION:Contact holes 34-42 are bored to first layer or second layer polysilicon electrodes. Vertical transfer pulses are transmitted from aluminum wirings in the vertical direction. Accordingly, spaces among bus lines are brought to approximately several dozen mum because the bus lines are wired by aluminum at every four picture elements regarding one horizontal line such as 21 in vertical transfer electrodes, and the deterioration of a pulse shape can be ignored approximately.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-dimensional COD image sensor, particularly an interline type two-dimensional COD image sensor with a low resistance vertical transfer electrode.
Regarding D image sensor. Currently, a wide variety of devices are being developed as solid-state two-dimensional image sensors, such as frame transfer CCDs, interline CODs, MOS types, and CID types. Among these, interline C
Two-dimensional image sensors using OD are currently being actively developed as devices with excellent performance due to their good S/N and sensitivity.

By the way, such a two-dimensional image sensor is designed to have a large number of pixels and a high density in order to improve the sharpness of the image. For this reason, in the interline type COD image sensor, the vertical transfer channels are increasingly miniaturized, and the amount of signal charge that can be handled is reduced. In general, the amount of signal charge depends on the COD channel capacitance and dynamic voltage, and the channel capacitance depends on the device shape,
Determined by process conditions. On the other hand, the driving voltage is determined by a pulse voltage applied from the outside. Therefore, in order to ensure a sufficient amount of signal, it is necessary to increase the channel capacity and to accurately supply the externally applied pulse voltage to the device. By the way, since the transfer electrode of COD is generally formed of polysilicon, its resistance is not necessarily small. The vertical transfer electrode of this two-dimensional COD image sensor using polysilicon acts not only as a capacitive load but also as a high resistance load for external pulses. Therefore, the vertical transfer electrode viewed from the external pulse becomes a distributed constant circuit load of resistance and capacitance, and the applied pulse is not accurately supplied to the internal vertical transfer electrode. This does not mean that the drive voltage applied from the outside is not directly transmitted to the transfer electrode, but it also means that it is difficult to control the cross-point voltage between each pulse in the double clocking method that is generally used to drive the vertical COD. do. Therefore the vertical COD
A sufficient amount of signal charge will not be ensured.

FIG. 1 shows a unit pixel plan view of a conventional interline type CCD two-dimensional image sensor. In the figure, l is a channel stopper, 2 is a photodiode region, and 3 is a vertical COD.
4 is a first layer polysilicon electrode, and 5 is a second layer polysilicon electrode 10, which is an original shield electrode made of aluminum. The polysilicon electrodes of the first and second layers are 6 to 9
The pixels are commonly connected to adjacent pixels on a horizontally elongated region.

A two-dimensional image sensor is formed by arranging such unit pixels in a matrix.

Further, vertical transfer pulses are applied from both left and right sides of the first layer and second layer polysilicon electrodes constituting the vertical transfer electrodes. The polysilicon electrodes constituting the unit pixel shown in FIG.
It consists of areas 4 and 5 that cover the OD transfer channel 3 and have a large capacitance like eaves plates. That is, two-dimensional CC
The vertical transfer positive electrode made of polysilicon in the D image sensor can be regarded as a kind of distributed constant circuit of resistance and capacitance. Therefore, the direct transfer pulse waveforms applied from the left and right sides are distorted by this distributed constant circuit, and the original voltage or rising and falling waveforms are no longer reproduced on the electrodes inside the CCD. Therefore, first of all, the effective applied voltage decreases and H
Second, it becomes difficult to control the cross-point voltage of the double clocking pulse. This directly leads to a reduction in the amount of signal charge that can be handled by the vertical COD.

The purpose of the present invention is to provide a two-dimensional COD that eliminates the above-mentioned conventional drawbacks.
Our goal is to provide image sensors.

According to Fuinenane, the COD has a matrix, a plurality of photodiodes arranged in a box shape, and a COD transfer channel arranged between each photodiode column arranged in the vertical direction.
In an interline CCD two-dimensional image sensor configured with transfer electrodes having a constant number of vertical transfer channels, contact holes are provided on the transfer electrodes in the same phase on each of the transfer channels for each of the number of phases, A two-dimensional CCD image sensor characterized in that the in-phase transfer electrodes are commonly connected by a low resistance electrode is obtained.

The present invention will be described in detail below with reference to the drawings. Second
The figure shows an embodiment of the two-dimensional COD image sensor according to the present invention, and 1 shows a plan view of the main part.
1 to 14 are first layer polysilicon electrodes, 15 to 17 are second layer polysilicon electrodes, and 15 to 17 are second layer polysilicon electrodes.
Layer polysilicon/electrode, 18 to 33 are photodiode regions, 34 to 42 are contact holes made in the first or second layer polysilicon electrodes, and 43 to 47 are vertically in-phase polysilicon electrodes in common. This is an aluminum electrode for connection. In this embodiment, four-phase drive is assumed, and transfer electrodes of the same phase are commonly connected for every four transfer channels. Furthermore, while the vertical transfer pulses were conventionally supplied from the left and right sides, in this embodiment they are supplied from the aluminum wiring in the vertical direction. For this reason, for one horizontal line of the vertical transfer electrode, for example 12, conventionally it was necessary to apply a pulse to a polysilicon electrode with a length of about 10 pixels, but in this embodiment, it is necessary to apply a pulse to 4 pixels. Since the pass lines are wired with aluminum in each case, the interval between them is approximately several tens of μm at most, and the deterioration of the pulse waveform can be almost ignored. Of course, the Fulmi bus line may be wired not every 41 iji pixels but every integral multiple of the pixels. The present invention not only prevents such deterioration of the pulse waveform, but also helps prevent defects due to polysilicon wire breakage in the relatively long and narrow portions 6 to 9 in FIG. Furthermore, the aluminum pass lines 43 to 47 of this embodiment not only serve as the original shield electrode like the conventional original shield electrode 10 made of aluminum, but are also compatible with conventional processes.

As described above, according to the present invention, it is possible to realize an interline COD two-dimensional image sensor that prevents deterioration of pulse waveforms.

[Brief explanation of drawings]

FIG. 1 is a plan view of a unit pixel of a conventional interline type COD two-dimensional image sensor, and FIG. 2 shows an embodiment according to the present invention. In the figure, 4, 11-14 are first layer polysilicon electrodes, 5.15-17 are second layer polysilicon electrodes, 3
4 to 42 are contact holes, and 43 to 47 are pass lines made of aluminum. Ivl Figure 0 [. -I J rIl 7

Claims (1)

[Claims] It has a plurality of photodiodes arranged in a matrix and a CCD vertical transfer channel arranged between each vertically aligned photodiode row, and the CCD vertical transfer channel is composed of transfer electrodes having a fixed number of phases. In the interline type CCD two-dimensional image sensor,
A two-dimensional CO characterized in that contact holes are provided on the transfer electrodes of the same phase on each of the transfer channels for each of the number of phases, and the transfer electrodes of the same phase are commonly connected by a low resistance electrode.
D image sensor.