JPH07263653A - Solid-state imaging device - Google Patents

Abstract

PURPOSE:To provide a solid-state imaging device which provides a high-quality picture with less noise even when electric charge accumulation is performed for an extended period with a CCD image sensor with a built-in temperature sensor. CONSTITUTION:On a p<+>-type semiconductor substrate 5 of about 490mum thickness where impurities are highly concentrated a p<->-type semiconductor area 6 of about 10mum thickness where its concentration is less than the p<+>-type semiconductor substrate 5 is formed, and further a frame part 1 (photo-detecting surface), a horizontal transportation part 2 and an output part 3 are formed, and on the p<+>-type semiconductor substrate 5. a temperature sensor 4 is farmed, a semiconductor substrate SB thus constituted. Figure (b) shows a cross section at B-B' of figure (a). As shown in figure (b), between a frame part 1 and a temperature sensor 4, a light-shielding groove 20 which acts optical shielding is formed as far as the p<+>-type semiconductor substrate 5, and in the light- shielding groove 20, a silicon group resin of non-transparent material 21 is imbedded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device such as a CCD image sensor.

[0002]

2. Description of the Related Art A dark current is one of the factors that determine the performance of a solid-state image pickup device such as a CCD image sensor. It is known that the dark current has a temperature dependency and decreases with a decrease in temperature. ing. As one of the means for reducing the dark current, there is a method of reducing the dark current by disposing the solid-state imaging device on an electronic cooling element such as a Peltier element and cooling the solid-state imaging device. Must always be operated at a constant temperature.
Therefore, a temperature sensor for monitoring the temperature is generally used. A CCD image sensor equipped with such a temperature sensor is disclosed in, for example, "Japanese Patent Laid-Open No. 2-1872".
No. 44872). The CCD image sensor has an optical portion that shields the light-receiving photodiode, and shields light incident from the outside of the light-receiving photodiode so that the light-receiving photodiode can be used only for temperature detection. It is a thing.

In a solid-state image pickup device capable of such temperature monitoring, a temperature sensor having a pn junction diode structure is formed on the same substrate. Therefore, since the chip temperature can be easily detected, this solid-state imaging device can be constantly operated at a constant temperature.

[0004]

Therefore, the inventors have
Attempts have been made to install such a temperature sensor and a light-shielding film on a CCD for faint light detection that is currently manufactured. 3 to 5 show the structure and characteristics of the CCD image sensor manufactured by the inventors.

FIG. 3 is a configuration diagram of a full frame transfer type CCD image sensor. As shown in FIG. 3A, the full frame transfer type CCD has a plurality of light receiving element portions arranged in a horizontal row and a vertical row on a semiconductor substrate and a plurality of light receiving element sections arranged along the vertical row. A frame unit 1 including a vertical transfer unit formed of a CCD group, a horizontal transfer unit 2 coupled to the frame unit 1, and an output unit for converting charges transferred by the horizontal transfer unit 2 into a voltage and outputting the voltage. 3 and a temperature sensor 4 having a diode structure for simply detecting the chip temperature.

The full frame transfer type CCD has a frame section 1 and a horizontal transfer section 2 when an image pickup operation is performed.
By applying a predetermined drive pulse to each,
The charge transfer operation is performed. In that case, photoelectric conversion is performed in the frame portion 1 by light reception within one frame period to generate signal charges, and the generated signal charges are vertically transferred to the horizontal transfer unit 2 during a closed period such as a shutter. The signal charges are sequentially transferred to the horizontal transfer unit 2 for each signal charge obtained in one horizontal column of the frame unit 1, and are horizontally transferred in each horizontal blanking period by the charge transfer operation of the horizontal transfer unit 2. Then, the imaging output signal is obtained from the output unit 3.

The temperature sensor 4 is provided as a temperature monitor for operating the solid-state image pickup device at a constant temperature all the time, and has a pn junction diode structure.

Details of the structure of the frame portion 1, the temperature sensor 4 and its surroundings are shown in FIG. 3 (b). On the p ⁺ type semiconductor substrate 5 which impurities are heavily doped with a thickness of about 490Myuemu, lower concentration than the p ⁺ -type semiconductor substrate 5 having a thickness of about 10 [mu] m, p ^- -type semiconductor layer 6 is formed, Further, each element region is formed on it. An n ⁻ type semiconductor region 7 for receiving incident light and performing photoelectric conversion is formed in the frame portion 1, and transfer electrodes 9 and 10 are formed thereon via an insulating layer 8. Then, an n ⁺ type semiconductor region 12 is formed in the temperature sensor 4 in order to form a pn junction diode for detecting temperature, and a wiring electrode 13 for taking out an electrode is formed on both sides of the adjacent channel stop region. Has been formed. Further, the portions other than the frame portion 1 are covered with a light shielding material 14 so that incident light does not enter.

FIG. 4 shows the circuit configuration of the temperature sensor. As shown in FIG. 4, the anode terminal of the pn junction diode used for the temperature monitor has an SS terminal (C
Since it is commonly connected to the CD ground level),
This terminal can only be used for the ground terminal. By connecting the other cathode terminal (Tsens) to the current sink and monitoring the voltage change between it and the SS terminal, the temperature can be known with rough accuracy. Here, when a constant current is applied to the diode, dV / dT = (qV-Eg) / qT (Equation 1) where q: electron charge amount V: applied voltage T: measurement temperature dV: voltage change amount dT : Amount of change in temperature Eg: Energy band gap is used, and dV / dT is about −
It changes almost linearly at a ratio of 2 to 3 mV / deg C. Monitor voltage is about 0.3-0.6V at room temperature
The current sink (I
Adjusting _bias ) is appropriate.

FIG. 5 shows the IV characteristic of this temperature sensor. The temperature sensor can monitor the temperature by utilizing the fact that the current increases as the temperature rises.

When the diode is used to monitor the temperature, if it is operated in a large current region, the current flowing in the diode partially heats the CCD chip.

The effect of the series resistance of the diode appears.

The temperature coefficient (amount of change per degree) becomes small, which makes detection difficult.

Problems such as the above occur. Therefore, it is desirable to operate the temperature sensor within the range of the arrow shown in FIG. 5 (current value 100 pA to 10 μA).

However, even when operated within such a current value range, the CCD image sensor for weak light detection manufactured by the inventors of the present application observes a large noise component in the image signal obtained by imaging. Was done. That is, since the CCD image sensor for detecting faint light is manufactured so that the charge accumulation time during image pickup is long and the detection sensitivity is high, the installation of such a temperature sensor greatly affects the CCD image sensor. It is thought that

The cause of this adverse effect is considered to be the use of a pn junction diode for the temperature sensor. That is, it is considered that this diode functions as a light emitting diode due to the radiative recombination of minority carriers injected when a forward voltage is applied to this diode. In other words, in the commonly manufactured CCD, the charge accumulation time was as short as 1/30 second, so no problem occurred because the temperature sensor emitted light was weak light, but a measurement CCD image for weak light detection. The sensor requires long-time charge accumulation (ranging from a few seconds to about 2 hours per pixel in astronomical observation) in its light-receiving area, and when the temperature sensor formed on the same semiconductor substrate emits light, the solid-state imaging device is Due to its sensitivity, it is considered that the emitted light is mixed in the frame portion of the solid-state imaging device and causes deterioration of the image. In particular, when the temperature sensor is used in an operating range of several μA, it was confirmed that the light emission of the temperature sensor deteriorates the image in a charge accumulation time of several tens of seconds.

The present invention has been made in view of the above problems that have occurred in the process of product development by the inventors. Since the temperature can be measured using a temperature sensor and weak light is measured. It is an object of the present invention to provide a solid-state imaging device that can obtain a good quality image even when performing imaging for a relatively long time.

[0018]

In order to achieve the above object, the present invention provides a solid-state image pickup device (CCD image sensor, MOS image sensor, etc.) having a light receiving surface for photoelectrically converting incident light on a semiconductor substrate. In the above, the semiconductor substrate has a semiconductor temperature sensor formed on the semiconductor substrate and a groove formed on the semiconductor substrate between the light receiving surface and the semiconductor temperature sensor.

[0019]

According to the present invention, the semiconductor temperature sensor is composed of a device such as a photodiode or a phototransistor. By applying a forward voltage to these devices, the temperature of the solid-state imaging device can be detected from the temperature dependence of the current. Since the semiconductor substrate is provided with a groove between the light-receiving surface and the semiconductor sensor, even when the semiconductor temperature sensor emits light due to light emission recombination of the injected minority carriers, this light emission or light emission causes Carrier is not introduced into the light receiving surface. However, if the width of such a groove is sufficiently narrow, the light-shielding effect is reduced. Therefore, it is assumed that the semiconductor substrate further includes an opaque material embedded in the groove. It was decided to reliably block the light emitted from. It is effective that such an opaque material contains a silicon resin.
Here, the silicon-based resin is selected for the following reason.

When the solid-state image pickup device of the present invention is actually used, since a very high detection limit is required, it is cooled to a low temperature before use. In other words, the temperature of the semiconductor substrate rises and falls, so a silicon-based resin that can withstand thermal changes is desirable.
Also, considering the workability in manufacturing the solid-state imaging device, when the silicone resin, which has a relatively lower viscosity than the epoxy resin, flows into the light-shielding groove, air enters the groove and the resin floats. There are advantages such as less risk of becoming a state.

Further, the depth of the groove is the first in the semiconductor substrate.
A high-concentration semiconductor substrate having an impurity concentration and a low-concentration semiconductor substrate formed on the high-concentration semiconductor substrate and having a second impurity concentration lower than the first impurity concentration are provided, and the semiconductor temperature sensor is formed on the low-concentration semiconductor substrate. In this case, if the thickness of the low-concentration semiconductor substrate is equal to or larger than the thickness of the low-concentration semiconductor substrate, the carrier generated by the light emission from the temperature sensor easily disappears by the carrier complementary to the propagating carrier when propagating in the high-concentration semiconductor substrate. However, when propagating through the low-concentration semiconductor substrate, the groove always hits, so that it is possible to more reliably prevent light emission on the light-receiving surface and incidence of carriers due to this light emission.

As such a solid-state image pickup device, CC
When the D image sensor is used, a temperature sensor provided so that the chip temperature can be easily monitored, has a width of 150 μm and a depth of 15 μm (light-shielding) in a channel stop region formed around the temperature sensor. ) It is desirable to form a groove and to embed a silicon-based resin, which is an opaque material, in the groove. With such a configuration, when a forward voltage is applied to the temperature sensor having the pn junction diode structure, even if the temperature sensor functions as a light emitting diode due to radiative recombination of the injected minority carriers, the temperature sensor is embedded in the groove. The opaque material does not enter the frame portion of the solid-state imaging device. Therefore, even if the measurement region is a weak light region and charge accumulation is required for a long time, light emission from the temperature sensor does not mix as unnecessary charges, and a high-quality image can be obtained.

[0023]

First, a first embodiment of the solid-state image pickup device according to the present invention will be described.

FIG. 1 is a schematic configuration diagram in the case where the solid-state image pickup device according to the present invention is a temperature sensor built-in type full frame transfer type CCD. In this embodiment, for example, a P ⁺ type semiconductor substrate (high-concentration semiconductor substrate) 5 having a high concentration (first impurity concentration) of approximately 490 μm and doped with impurities is used.
A P ⁻ -type semiconductor region (low-concentration semiconductor substrate) 6 having a concentration lower than that of the P ⁺ -type semiconductor substrate 5 (having a second impurity concentration) and having a thickness of about 10 μm is formed thereon, and further shown in FIG. Like the CCD, a frame portion 1 (light receiving surface), a horizontal transfer portion 2 and an output portion 3 are formed, and a temperature sensor 4 is formed on the P ⁺ type semiconductor substrate 5 to form a semiconductor substrate SB. is doing. FIG. 1B shows a cross-sectional view of BB ′ in FIG. As shown in FIG. (B), between the frame portion 1 and the temperature sensor 4, the light-shielding grooves 20 so as to block these optically (grooves) P ⁺
The light-shielding groove 20 is formed until it reaches the type semiconductor substrate 5.
A silicon resin, which is an opaque material 21, is embedded in the.

The configuration of the portion other than the light-shielding groove 20 and the opaque material 21 and the operation at the time of image pickup are the same as those of the normal CCD shown in FIG. 3, and a drive pulse is applied to the transfer electrodes 9 and 10. As a result, the signal charges generated by the incidence of light on the frame portion 1 are transferred. Here, the light shielding groove 20 has a width of about 150 μm and a depth of about 15 μm in the channel stop region 11 between the frame portion 1 and the temperature sensor 4 until it reaches the P ⁺ type semiconductor substrate 5 by using directional etching. It is dug and formed. Further, as is clear from FIG.
Are provided so as to surround the temperature sensor 4 on the semiconductor substrate SB. The temperature sensor 4 includes an n ⁺ type semiconductor layer 12 and a p
^In this CCD, a carrier is generated by light generated by applying a forward voltage to the temperature sensor 4, which is a photodiode including a ⁻ type semiconductor layer 6. The carriers are mainly generated in the P ⁻ type semiconductor region 6 around the temperature sensor 4, and the generated carriers are generated in the P ⁺ type semiconductor substrate 5 and the P ⁻ type semiconductor region 6.
It diffuses inside and enters the frame portion 1 of the solid-state imaging device (CCD). Carrier which has entered into the P ⁺ -type semiconductor substrate 5 Among them, the disappear recombine to P ⁺ -type semiconductor substrate 5 are high concentration. Therefore, P ⁺ -type semiconductor substrate 5 P ^- comprise a type semiconductor region 6, the P ^- in the case of forming a semiconductor region frame part 1 and the temperature sensor 4 on the 6, the depth of the light-shielding grooves 20, P ^{It is} sufficient to dig up to a depth (about 15 μm) to reach the ⁺ type semiconductor substrate 5.
The light-shielding groove 20 is filled with a silicon-based resin which is an opaque material 21 after oxidizing the surface of the P ⁻ type semiconductor region 6.

The silicon resin is selected for the following reason. In fact, when using the solid-state imaging device of the present invention, a very high detection limit is required, and therefore, the solid-state imaging device is cooled to a low temperature before use. That is, since the temperature of the P ⁺ type semiconductor substrate 5 rises and falls, it is desirable to use a silicon-based resin that can withstand thermal changes. Also, from the viewpoint of workability, there is a risk that the silicone resin, which has a relatively lower viscosity than the epoxy resin, will enter air into the light shielding groove and float when the resin enters the light shielding groove. There are advantages such as less. Further, since the light-shielding groove 20 is dug in the vertical direction with respect to the P-type semiconductor region of the same conductivity type, it can be said that digging the light-shielding groove 20 does not affect the device.

As described above, if the light-shielding groove 20 is formed around the temperature sensor 4 and the light-shielding groove 20 is filled with the opaque material 21 such as a silicon-based resin, when the forward voltage is applied to the temperature sensor 4, the injection is performed. Even if the temperature sensor 4 functions as a light emitting diode by light emission recombination of the minority carriers generated, light emitted from the temperature sensor 4 and carriers generated by this light emission are shielded by the light shielding groove 20 and the opaque material filled in the light shielding groove 20. The silicone resin 21 does not enter the frame portion 1. Therefore, even when the measurement region is a weak light region and charge accumulation is required for a long time, it is possible to suppress the influence of light emission of the temperature sensor and prevent image deterioration.

Next, a second solid-state image pickup device according to the present invention will be described.
Examples will be described.

In this embodiment, the light shielding groove 20 is formed by dicing, not by etching. Dicing is used as a step of cutting a large number of chips formed on one wafer. FIG. 2A is a schematic configuration diagram showing a second embodiment of the solid-state imaging device according to the present invention. Shading groove 20 by dicing
When digging, it is difficult to form the light shielding groove 20 so as to surround the temperature sensor 4 as in the first embodiment. Therefore, the region where the light shielding groove 20 is bored is dug from end to end of the chip between the bonding pad 22 and the temperature sensor 4 in the length and width directions as shown in FIG. As shown in FIG. 3B, the trench is dug to have a width of 100 μm and a depth of 15 μm.

A feature of this embodiment is that the temperature sensor 4 is arranged outside the bonding pad 22. This is because when the light-shielding groove 20 is formed by dicing, as described above, since the chip is cut in the lengthwise direction of the CCD, the bonding pad 22 must be located inside the light-shielding groove 20. This is because the light shielding groove 20 cannot be dug due to the influence of the connected wiring.

As described above, if the light shielding groove 20 is formed between the bonding pad 22 and the temperature sensor 4 by dicing, the light shielding groove 20 can be formed by a method other than etching. It should be noted that the solid-state imaging device according to the present invention is not limited to the type of semiconductor and the conductivity type of each portion or semiconductor region of the solid-state imaging device described above.

[0032]

As is apparent from the above description, according to the solid-state image pickup device of the present invention, even if the temperature sensor having the pn junction diode structure functions as a light emitting diode, the light emitted from the temperature sensor is generated by the groove. The opaque material embedded in the groove prevents the light from entering the light-receiving surface of the solid-state imaging device. Therefore, even if a weak light is received by the light-receiving surface, even if charge is stored for a long time, It is possible to obtain a good quality image with little noise.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram when the solid-state imaging device according to the present invention is a full-frame transfer CCD with a built-in temperature sensor (FIG. 1A) and line BB ′ in FIG. 1A. It is sectional drawing (the same figure (b)).

FIG. 2 is a schematic configuration diagram (FIG. 2A) showing a second embodiment of the solid-state imaging device according to the present invention and a line segment C in FIG. 2A.
FIG. 6B is a cross-sectional view taken along line C ′ (the same figure (b)).

[Figure 3] Full frame transfer CCD with built-in temperature sensor
(A) in the figure and a line segment A in (a) in the figure
FIG. 6B is a cross-sectional view taken along line A-A '(FIG. 7B).

FIG. 4 is a circuit configuration diagram of a temperature sensor.

FIG. 5 is a graph showing an IV characteristic of a temperature sensor.

[Explanation of symbols]

1 ... frame portion, 2 ... horizontal transfer unit, 3 ... output unit, 4 ... temperature sensor, 5 ... p ⁺ -type semiconductor substrate, 6 ... p ^- -type semiconductor layer, 7 ... n ^- -type semiconductor regions, 8: insulating layer, 9, 10 ... Transfer electrodes, 11 ... Channel stop region, 12 ... n ⁺
-Type semiconductor layer, 13 ... Wiring electrode, 14 ... Shading material, 20 ...
Light-shielding groove, 21 ... Opaque material, 22 ... Bonding pad, SB ... Semiconductor substrate.

Claims (4)

[Claims] 1. A solid-state imaging device having a light receiving surface for photoelectrically converting incident light on a semiconductor substrate, wherein the semiconductor substrate is a semiconductor temperature sensor formed on the semiconductor substrate, the light receiving surface and the semiconductor temperature sensor. And a groove formed on the semiconductor substrate, the solid-state imaging device. 2. The solid-state imaging device according to claim 1, wherein the semiconductor substrate further includes an opaque material embedded in the groove. 3. The solid-state imaging device according to claim 2, wherein the opaque material contains a silicon-based resin. 4. The high-concentration semiconductor substrate having a first impurity concentration, and the low-concentration semiconductor substrate having a second impurity concentration lower than the first impurity concentration, formed on the high-concentration semiconductor substrate. The solid-state imaging device according to claim 1, wherein the semiconductor temperature sensor is formed on the low-concentration semiconductor substrate, and the depth of the groove is equal to or larger than the thickness of the low-concentration semiconductor substrate. .