JP2849249B2 - Infrared image sensor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared image sensor and a method of manufacturing the same, and more particularly to an infrared image sensor having an increased dynamic range.

[0002]

2. Description of the Related Art In recent years, infrared cameras have been used in various fields such as maritime security, volcano observation, and industrial security. The center of this infrared camera system is an infrared image sensor (solid-state image sensor), and an infrared image sensor using a silicon semiconductor has the highest resolution and high image quality. Here, an example of a conventional infrared image sensor using a silicon semiconductor will be described. FIG. 4 is a plan view showing the configuration of a conventional infrared image sensor, in which a PtSi Schottky barrier diode is used for an infrared light detector, and CSD (Charge Sweep) is used for charge transfer.
Device) PtSi type IRCSD using the method.
In FIG, 1 is PtSi Schottky barrier diode photodetector, 2 transfer over the gate (hereinafter TG) for sending the detected light charges the photodetector 1, the vertical charge delivered by the transfer gate 2 3 , A storage gate 7, a storage control gate 8, a horizontal CCD 9 for performing horizontal charge transfer,
Reference numeral 10 denotes an FDA (Floating Diffusion Ampli) serving as an output unit.
fier). Reference numeral 5 denotes a transfer gate scanner circuit, and reference numeral 6 denotes a CSD scanner circuit. Between these scanners, a gate electrode (not shown) of TG 2 on one horizontal line is electrically connected by a vertical scanning line 4. Scanner circuit 5 and CSD scanner circuit 6
Can be applied.

[0003] Next, the PtSi type IRCSD having the above configuration
The operation of will be briefly described. The incident infrared light is P
The light arrives at the tSi Schottky barrier diode photodetector 1, where it is photoelectrically converted to generate signal charges, which are accumulated in the Schottky junction. Then, only the TG 2 selected by the transfer gate scanner circuit 5 opens, and only the signal charges accumulated in the photodetector 1 connected to the opened TG 2 are read out into the CSD channel 3.
At this time, other photodetectors not selected by the transfer gate scanner circuit 5 continue to accumulate signal charges during this time, and there is no concern about mixing of signal charges between pixels in the CSD channel 3. Next, the signal charges read out into the CSD channel 3 and spatially expanded are transferred in the vertical direction by a sweeping operation using a potential wall formed by the CSD scanner circuit 6 and collected in the storage gate 7. The signal charges collected in the storage gate 7 are
Water by opening the storage control gate 8 Rights C CD
9 is transferred. The horizontal C the CD 9 in the transferred signal charges are read out to the outside is output as a video signal from the charge which is a detection unit FDA10. Then, a pulse is applied by shifting the line selected by the transfer gate scanner circuit 5 by one stage, and the same operation is repeated to thereby reset the line.
Get the screen video output. Thus, the PtSi type I
In the RCSD, a video signal corresponding to the amount of infrared light incident on the light detection unit can be obtained.

Next, a PtSi type IRCSD having the above configuration
The silicon process will be briefly described. The wafer process is roughly divided into five processes, (1) element isolation step, (2) CSD / horizontal CCD formation step, (3) transistor part (TG scanner circuit part, CSD scanner circuit part, FDA part, etc.) Forming process, (4) photodetector forming process, and (5) wiring process.

[0005] The LOCOS (Local Oxidation of Silicon) process is used as the main step (1) for element isolation. In this LOCOS process,
(a) The p-type silicon wafer 20 shown in FIG.
After forming a thin thermal oxide film (underlay oxide film) 21 (FIG. 5)
5 (c)), a nitride film 22 is deposited on the entire surface as shown in FIG. 5 (c), and then a resist 23 is formed on a region where an element is to be formed by lithography as shown in FIG. 5 (d). After removing the nitride film in the field portion by an etching technique, the resist 23 and the patterned nitride film 2 are left.
Using 2a as a mask, a p-type dopant impurity (for example, boron) is ion-implanted into the entire region to form a P ⁺ region 24 serving as a channel cut region. Then, after removing the resist, the wafer is thermally oxidized to selectively oxidize only the field portion, and finally, the nitride film 22a is removed to form the element isolation region 25.

[0006] In this way, the periphery of the photodetector 1, the CSD
The field isolation oxide films around the section 3, around the horizontal CCD section 9, around the transistor section, etc. are all formed simultaneously.
Further, p-type impurity was ion implanted before the field oxide
More, the lower field isolation oxide film 25 channel cut region 24 is formed. In this case, the channel cut region 24 of each element is formed simultaneously with all, thus also the impurity concentration are the same ones.

The CSD / horizontal CCD forming step of (2) includes ion implantation of an N-type impurity (for example, phosphorus) for forming a buried channel, and a CSD gate and a horizontal CCD gate for driving the CSD / horizontal CCD. Forming a step.

In the step (3) of forming a transistor portion, ion implantation is performed by self-alignment using the gate portion and the field oxide film as a mask in order to form a gate and a diffusion layer forming a source / drain portion. And forming a deep N-type region (eg, with arsenic).

The photodetector forming step of (4) is a step of forming a dense N-type impurity region around the region to be the photodetector, that is, at the end of the field oxide film, and providing a guard ring for preventing an increase in dark current. And forming a PtSi layer on the photodetector section.

Further, in the wiring step (5), wiring is made of Al.

[0011]

Since the conventional infrared image sensor is configured as described above, the impurity concentration in the channel cut region around the photodetector is formed by implanting impurities before forming the field oxide film. Therefore, the impurity concentration was the same in other regions, for example, in the peripheral channel cut regions such as the transfer gate scanner circuit portion and the CSD scanner circuit portion.

Considering the dynamic range of an infrared image sensor, it is necessary to increase the saturation charge to increase the dynamic range.
In the i-type IRCSD, the capacitance is determined by the capacitance of the photodetector, and this capacitance depends on the capacitance of the pn junction formed by the guard ring region (N ⁺ type) and the channel cut region (p type) around the photodetector. The pn junction capacitance is proportional to the p-type impurity concentration in the channel cut region. That is, in order to increase the saturation charge of the PtSi type IRCSD, it is sufficient to increase the p-type impurity concentration in the channel cut region around the photodetector.

However, as described above, if the p-type impurity is increased at the time of forming the channel cut region around the photodetector portion, the concentration of the channel cut region around the transistor portion is also increased at each location, thereby increasing the source / source voltage of the field transistor. The drain breakdown voltage is reduced. However, compared to the voltage applied to the pixel section including the photodetector section,
Since a large voltage (approximately 10 V) is applied to the transistors in other portions in the other regions, the withstand voltage of the transistors in each portion cannot be reduced so much (requires 10 V or more). Therefore, in the conventional IRCSD, since the impurity concentration in all the channel cut regions in the device is formed to be the same, there is a limit in increasing the saturation charge.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an infrared image sensor capable of increasing the amount of saturated charges without lowering the breakdown voltage of a transistor region other than a pixel portion. With the goal.

[0015]

According to the infrared image sensor and the method of manufacturing the same according to the present invention, at the time of forming an element isolation region, an impurity is implanted into a pixel region and a peripheral circuit region by using a first resist. By covering the peripheral circuit region with a second resist and additionally implanting impurities using the first and second resists as masks, the impurity concentration of the channel cut region of the pixel region is reduced to the channel cut region of the region other than the pixel portion. The impurity concentration is higher than the impurity concentration.

[0016]

According to the present invention, when forming the element isolation region,
Impurity implantation is performed on the pixel region and the peripheral circuit portion using a first resist, and at least the peripheral circuit region is covered with a second resist, and additional impurities are implanted using the first and second resists as a mask. Therefore, the impurity concentration of the channel cut region of the pixel region can be made higher than the impurity concentration of the channel cut region of the peripheral circuit region, and the breakdown voltage of the photodetector can be reduced without lowering the withstand voltage of the peripheral circuit region other than the pixel region. The saturation charge can be increased.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An infrared image sensor according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a PtSi type IRCSD according to one embodiment of the present invention, and shows a region 11 in which the impurity concentration of a channel cut region of a pixel portion region is higher than the impurity concentration of a channel cut region of a region other than the pixel portion. The configuration other than that of the conventional P shown in FIG.
Since the configuration is the same as that of the tSi type IRCSD, its description is omitted. Further, the operation principle is completely the same as that of the conventional one, and the description thereof is omitted.

Next, the manufacturing process will be briefly described. This wafer process is roughly divided into the same as the conventional PtSi type IRCSD wafer process, (1) an element isolation step, (2) a CSD / horizontal CCD formation step, and (3) a transistor section (TG scanner circuit section / CSD section). Scanner circuit section, FDA section, etc.) formation process, (4) photodetector formation process,
(5) It consists of a wiring process. In the present invention, the conventional PtSi
The only difference from the wafer process of the type IRCSD is the element isolation step (1), and only this step will be described below.

In the element isolation step (1), the conventional PtSi
The LOCOS process is used as in the case of the type IRCSD. First, after forming a thin thermal oxide film on the p-type silicon wafer 20 shown in FIG. 2A (see FIG. 2B), a nitride film 22 is deposited on the entire surface (FIG. 2C). Next, as shown in FIG. 2D, a resist 23 is left on a region where an element is to be formed by a lithography technique, and a nitride film in a field portion is removed by an etching technique. P-type impurities (for example, boron) are ion-implanted into the entire region using 22 a as a mask to form a P ⁺ region on the surface of the substrate 20, and a channel cut region 24 is provided. Then, in order to make the channel cut impurity concentration of the pixel portion region higher than the channel cut impurity concentration of the peripheral transistor region other than the pixel portion, on the resist 23 used for patterning the nitride film 22, the lithography technique is again applied. A resist pattern 26 that opens only the pixel area is formed. Thereafter, when a p-type impurity (for example, boron) is ion-implanted again, the p-type impurity is additionally implanted only into the field portion of the pixel region, and the concentration is increased (FIG. 2E). Finally, as shown in FIG. 2 (f), after the two layers of resist are removed, when the wafer is oxidized, only the field portion is oxidized, and when the nitride film 22a is removed, an element isolation region 25 is formed. As described above, the channel cut region 27 in the pixel portion region can be configured to have a higher impurity concentration than the channel cut region 24 in the peripheral transistor region.

As described above, according to the present embodiment, when the channel cut region is formed in the element isolation step, P-type impurities are implanted into the pixel region and the peripheral transistor region using the nitride film 22a and the resist 23 as a mask. Further, a resist 2 which opens the pixel area and covers the peripheral transistor area
Since the P-type impurity is implanted again by using No. 6,
Alternatively, the impurity concentration of the channel cut region in the pixel portion region can be made higher than the impurity concentration of the channel cut region in the region other than the pixel portion. Dependent PtSi
The saturation charge of the type IRCSD can be increased, while the impurity concentration in the region other than the pixel portion is not different from that of the conventional product, so that the breakdown voltage of the transistor in the region other than the pixel portion is not reduced. Therefore, the dynamic range of the infrared image sensor can be increased without lowering the withstand voltage of the field transistor in a region other than the pixel portion.

In the above embodiment, the impurity concentration of the channel cut region in the entire region within the pixel is set higher than the impurity concentration of the channel cut region in the region other than the pixel portion. As shown in the example, the present invention can be applied to a case where only the impurity concentration of the channel cut region around the photodetector 1 is higher than the impurity concentration of the channel cut region in the other regions. That is, as shown by the region 12 in FIG. 3 , the impurity concentration of the channel cut region around the photodetector 1 is higher than the impurity concentration of the channel cut region around the CSD portion 3 and the region other than the pixel portion. The same effect as described above may be obtained. In this case, in the manufacturing process shown in FIG. 2E, the resist 2 is also applied to a portion which becomes a channel cut region around the CSD portion 3 in the pixel portion region.
6 can be easily formed.

In the above embodiment, the charge transfer in the vertical direction is described using the CSD method as an example.
Another charge transfer element such as a CD method may be used. In this case, the same effect as described above can be obtained.

In the above embodiment, PtSi is used for the photodetector.
Although a Schottky barrier diode was used, IrSi or P
A Schottky barrier diode made of another silicide such as d ₂ Si may be used.

Further, in the above embodiment, the case where the channel cut region is formed by ion implantation has been described. However, the channel cut region may be formed by a thermal diffusion technique.

[0025]

As described above, according to the present invention, the impurity concentration of the channel cut region of the pixel region is configured to be higher than the impurity concentration of the channel cut region of the peripheral circuit region other than the pixel region. Further, there is an effect that the saturation charge amount of the photodetector can be increased without lowering the breakdown voltage of the transistor region other than the pixel portion, and an infrared image sensor having an increased dynamic range can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an infrared image sensor (PtSi type IRCSD) according to an embodiment of the present invention.

FIG. 2 is a diagram showing a device isolation process of an infrared image sensor (PtSi type IRCSD) according to one embodiment of the present invention.

FIG. 3 shows a PtSi type IRC showing another embodiment of the present invention.
It is a block diagram of SD.

FIG. 4 is a configuration diagram of a conventional PtSi type IRCSD.

FIG. 5 is a view showing a device isolation process of a conventional PtSi type IRCSD.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photodetector 2 Transfer gate 3 CSD part 4 Vertical scanning line 5 Transfer gate scanner circuit 6 CSD scanner circuit 7 Storage gate 8 Storage control gate 9 Horizontal CCD part 10 FDA part 11,12 High-concentration channel cut area 20 Substrate 21 Underlay Oxide film 22 Nitride film 23 Resist 24 P ⁺ region 25 Element isolation region 26 Resist having an opening in pixel portion 27 High concentration P ⁺ region

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/339 H01L 21/76 H01L 27/14-27/148 H01L 29/762-29/768

Claims (2)

(57) [Claims] 1. A pixel region in which a plurality of pixel units each including a photoelectric converter and a charge readout unit are formed on a substrate, and a peripheral circuit region for reading out charges in the pixel region to the outside are respectively formed by element isolation regions. In the infrared image sensor formed so as to be divided and provided with a channel cut region below the element isolation region, at least a channel cut region below the element isolation region around the photoelectric converter in the pixel portion is formed in the peripheral circuit region. Than the channel cut region below the element isolation region
An infrared image sensor having a high concentration and a uniform impurity concentration . 2. An infrared image sensor in which an impurity is implanted into a portion to be a channel cut region of a substrate, an element isolation region is formed thereon by a selective oxidation method, and a pixel region and a peripheral circuit region are divided. In the manufacturing method, a step of sequentially forming an underlying oxide film and a nitride film on a substrate, and removing a nitride film in a portion forming an element isolation region of the pixel region and the peripheral circuit region using a first resist; Impurity implantation is performed using the first resist as a mask,
Forming an impurity-implanted layer in a portion to be an element isolation region of the substrate; and removing a first resist covering at least the peripheral circuit region without removing the first resist.
A method of manufacturing an infrared image sensor, comprising: a step of laminating and forming an upper layer; and a step of additionally implanting an impurity of the same conductivity type as the impurity using the first and second resists as a mask.