Device for detecting chemical/physical phenomenon having a diffusion layer formed between an input charge control region and a sensing region on a substrate

Provided is a charge-transfer-type sensor suitable for high integration while eliminating a potential barrier. A sensor provided with a semiconductor substrate 10 partitioned into a sensing region 5 in which a potential varies in corresponding fashion to a variation in the external environment, a charge input region 2 for supplying charges to the sensing region 5, an input charge control region 3 interposed between the sensing region 5 and the charge input region 2, and a charge accumulation region 7 for accumulating electric charges transported from the sensing region 5, the sensor for detecting the amount of electric charges accumulated in the charge accumulation region 7, wherein a diffusion layer 4 is formed between the input charge control region 3 and the sensing region 5 of the substrate 10, and dopants for producing charges having the same polarity as the charges supplied from the charge input region 2 are diffused in the diffusion layer 4.

TECHNICAL FIELD

The present invention relates to an improvement of a chemical/physical phenomenon detecting device.

BACKGROUND ART

As a chemical/physical phenomenon detecting device, a cumulative chemical/physical phenomenon detecting device disclosed in Patent Document 1 is known.

This detection device is used as, for example, a pH sensor, and removes the influence of remaining charges due to a potential barrier (so-called “bump” of potential). The remaining charges can be a factor in generating a false signal so that the charges should be removed to perform high-sensitivity detection.

In a prior chemical/physical phenomenon detection device, this potential barrier is formed at a position adjacent to the first charge control electrode which defines the potential of an Input Charge Control (ICG) region. That is, a silicon nitride film defining the sensing region on the substrate inherently covers the first charge control electrode according to the manufacturing process of the device, so that the silicon nitride film becomes thick on the side surface of the first charge control electrode. Hence, the external environment is not sufficiently reflected in the potential change of the substrate.

As a method for removing the influence of the remaining charges due to the potential barrier, a charge removal well is provided between the input charge control region and the sensing region. By controlling the potential of this removal well, the remaining charges in the sensing region are forcedly attracted to this removal well, thereby preventing the generation of the false signal.

PRIOR ART DOCUMENT

Patent Document

Patent Document 2: Published Japanese Translation No. 2010-525360

SUMMARY OF THE INVENTION

Problems to be Solved by the Present Invention

A second charge control electrode is disposed at a position corresponding to the removal well in addition to the first charge control electrode for controlling the potential of the removal well formed between the sensing region and the input charge control region.

On the other hand, techniques for two-dimensionally measuring changes in the external environment such as pH by integrating the chemical/physical phenomena detection devices are being developed, and in this development, a higher density of integration of the devices is required.

A chemical/physical phenomenon detection device disclosed in Patent Document 1 adopting a structure in which a second charge control electrode and a wiring for driving the second charge control electrode are added is not preferable from the viewpoint of high integration thereof.

Of course, it is needless to say that a higher sensitivity is required for a chemical/physical phenomenon detection device, so the influence of the false signal caused by the potential barrier must be eliminated.

In view of the above, it is an object of the present invention to provide a chemical/physical phenomenon detecting device suitable for high integration while eliminating a potential barrier.

Means to Solve the Problems

As a result of intensive studies to achieve such object, the present inventors have conceived the chemical/physical phenomenon detecting device of the first aspect. That is,

A chemical/physical phenomenon detection device comprising;

a sensing region in which the potential of the sensing region changes in accordance with a change in an external environment,

a charge input region for supplying charges to the sensing region,

an input charge control region interposed between the sensing region and the charge input region, and

a charge accumulation region for accumulating charges transferred from the sensing region, wherein a diffusion layer is formed between the input charge control region and the sensing region on a substrate, and dopants for generating charges having the same polarity as that of the charges supplied from the charge input region are diffused in the diffusion layer.

According to the chemical/physical phenomenon detecting device of the first aspect defined as above, in the diffusion layer formed between the input charge control region and the sensing region, the potential in a neutral state of the diffusion layer is supplied from the potential of the sensing region. Here, the neutral state means a state in which no charge is present in the diffusion layer, and in this state, the potential of the sensing region is different from the potential of the diffusion layer. That is, when electrons are adopted as the charges to be input, the potential of the diffusion layer is always higher than the potential of the sensing region. As a result of the doped diffusion layer, no potential barrier is formed between the charge supply control region and the sensing region.

According to the chemical/physical phenomenon detecting device defined in the first aspect, the electrode for controlling the potential of the charge removal well and wiring therefor are not required so that it is suitable for the requirement of high density integration in comparison with the conventional chemical/physical phenomena detecting device in which a charge removal well is formed to remove the potential barrier.

In the chemical/physical phenomenon detection device defined in the first aspect, the charge input (ID) region is also doped to be the same semiconductor type as the diffusion layer. For example, when the charges supplied from the charge input region are electrons, the charge input region and the diffusion layer are doped n-type to the semiconductor substrate. Therefore, in order to simplify the manufacturing process of the chemical/physical phenomenon detection device, it is preferable to dope the charge input region, the diffusion layer, and the charge accumulation region also using the same mask.

As a result, the chemistry/physical phenomenon detection device according to the second aspect of the present invention is defined as follows.

The chemical/physical phenomenon detection device according to claim1, wherein the same dopant is diffused into the diffusion layer and the charge input region.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

FIG. 1shows the principle configuration of the chemical/physical phenomenon detection device1according to the first embodiment of the present invention.

The chemical/physical phenomenon detection device1is comprised of a silicon substrate10and a structure stacked on the silicon substrate10.

On the silicon substrate10, a charge input (ID) region2from which charges are input or supplied, an input charge control (ICG) region3, a diffusion layer4, a sensing region5, a charge transfer control (TG) region6, and a charge accumulation (FD) region7are partitioned in series. In the example ofFIG. 3, a rectangular sensing region is adopted and a diffusion layer4—input charge control region3—charge input region2are formed in order from a side of the sensing region as well as the charge transfer control region6and the charge accumulation region7are formed in order from another side of the sensing region5. All of regions can be aligned linearly. The section of each region is defined by the difference in semiconductor type on the surface of the semiconductor substrate10. For example, when electrons are used as charges, the charge input (ID) region2, the diffusion layer4and the charge accumulation (FD) region7are n+ type regions, and the input charge control (ICG) region3and the sensing region5are p-type regions.

In the charge accumulation region7, a reset unit8for discharging the charges accumulated in the charge accumulation region7and a charge amount detection unit9for detecting an amount of charges in the charge accumulation region. A well-known conventional circuit is adopted for the reset unit8and the charge amount detection unit9.

A silicon oxide insulating layer11is stacked on the surface of the substrate10, and on the layer11, an ICG electrode15is mounted at a position opposed to the input charge control region3and the potential of the input charge control region3is controlled by the ICG electrode15. A TG electrode16for controlling the potential of the charge transfer control region6is formed as well at a position opposed to the region6. In a portion corresponding to the sensing region5, a silicon nitride layer13is stacked as a sensitive layer. Since the silicon nitride layer13is formed after the ICG electrode15and the TG electrode16, the silicon nitride layer13also covers these electrodes.

An area and planar shape of each region, the amount of dopant introduced, and the material of the sensitive film can be arbitrarily designed in consideration of the object to be measured, measurement conditions, required sensitivity and the like.

Both the charge input region2, the diffusion layer4, and the charge accumulation region7are doped with an n-type dopant. Before forming the insulating layer11, the doping is performed by masking the surface of the substrate10and implanting an n-type dopant. From the viewpoint of minimizing the number of times of mask processing, it is preferable to make the doping conditions be the same for the charge input region2, the diffusion layer4, and the charge accumulation region7. As a result, the same dopant is introduced into these three regions at the same concentration by one doping treatment.

According to the chemical/physical phenomenon detecting device1shown inFIG. 1, even if the silicon nitride layer13exists on the side surface of the ICG electrode15, the region of the substrate opposed thereto exists as the diffusion layer4. Since the dopant for increasing the potential of the diffusion layer4is diffused therein, the formation of the potential barrier is prevented.

FIG. 2shows the potential of each region when the diffusion layer4is omitted. InFIG. 2, reference numeral20denotes a potential barrier. In the example ofFIG. 1, since the diffusion layer4having a potential higher than that of the sensing region5is formed at the position where the potential barrier20is formed, the potential barrier20is buried therein and disappears.

When holes are used as charges, the diffusion layer4has a potential lower than that of the sensing region5. In other words, the potential of the diffusion layer4is far from the potential of the sensing region5when viewed from the neutral state of the diffusion layer4.

As to the diffusion layer4, when the silicon nitride layer13covering the side surface of the ICG electrode15on the side of the sensing region5is projected onto the diffusion layer4below inFIG. 1, the projected silicon nitride layer13is contained in the diffusion layer4.

FIG. 3shows the plan structure of the chemical/physical phenomenon detection device1. As shown inFIG. 3, the diffusion layer4is formed between the ICG region3and the sensing region5. Note thatFIG. 1is a cross-sectional structure taken along line I-I inFIG. 3.

The width of the diffusion layer4can be arbitrarily set in consideration of etching conversion difference and mask shift. In this embodiment, the width of the diffusion layer4is set to 1.20 μm in the 2.0 μm process (that is, the minimum channel length is 2.0 μm).

Next, the operation of the chemical/physical phenomenon detection device1will be described with reference toFIG. 4.

FIG. 4(a)shows a reset step. In this reset step, the reset gate RG of the reset unit8is at a high potential, and the charges in the charge accumulation (FD) region (hereinafter may be simply referred to as “FD region”)7are discharged to the outside of the device.

FIG. 4(b)shows a standby step. In this standby step, the reset gate RG of the reset section8becomes a low potential, so that charges can be accumulated in the FD region7.

FIGS. 4(c) and (d)show the measurement step. As a premise of this step, the potential of the sensing region5varies depending on the external environment (the pH of the measurement object). First, as shown inFIG. 4(c), charges (in this case, electrons) are injected from the charge input (ID) region (hereinafter sometimes simply referred to as “ID region”)2and then charges go over an input charge control (hereinafter simply referred to “ICG region”)3and arrive or get into the sensing region5. After that, as shown inFIG. 4(d), when the charge supply from the ID region2is stopped, charges above the sensing region5are leveled by the ICG region3. At this time, the potential deference between the ICG region3and the sensing region5depends on the pH of the object to be measured, and an amount of charge corresponding to the potential difference remains on the sensing region5.

Since the potential of the diffusion layer4is set to be sufficiently higher than the potential of the sensing region5, no potential barrier is formed between the ICG region3and the sensing region5.

In the measurement step shown inFIG. 4(d), charges also exist in the diffusion layer4, and the input charges remain on the layer4. An amount of charges, including the remaining charges on the diffusion layer, depending on the potential difference between the ICG region3and the sensing region5defines the pH value of the object to be measured. In other words, the charges existing in the charge well due to the diffusion layer4has no influence on the amount of charges that can define the pH value.

FIGS. 4(e) and 4(f)show the charge transfer step. The potential of the charge transfer control (TG) region6is raised and the charges remaining in the step ofFIG. 4(d)are transferred to and in the charge accumulation (FD) region7. Hereinafter the charge transfer (TG) region may be simply referred as TG region, and the charge accumulation (FD) region may be simply referred as FD region.

By repeating the steps inFIGS. 4(c) to 4(f), a small change in pH can be converted to a large change in charge amount.

InFIG. 4(g), the amount of charges in the FD region7is converted to an electric signal by the charge detection section9. This makes it possible to specify the pH value.

FIG. 5shows an extended type chemical/physical phenomenon detecting device101. The same elements as those inFIG. 1are denoted by the same reference numerals, and a description thereof will be partially omitted.

The chemical/physical phenomenon detection device1of the direct type inFIG. 1and the chemical/physical phenomenon detection device101inFIG. 5adopt the same configuration in the substrate10, and they are different in structure with regard to stacked layers formed on the silicon oxide insulating layer11on the substrate.

In the chemical/physical phenomenon detecting device101shown inFIG. 5, a silicon oxide layer102is stacked on the entire surface of the insulating layer11, and a silicon nitride layer113as a sensitive layer is stacked on the surface of the silicon oxide layer102. The potential change of the silicon nitride layer113is transmitted to the sensing region defining electrode123via the conductive layers115,116, and117made of a metal material or the like buried in the silicon oxide layer102.

As a result, the potential of the silicon nitride layer113corresponding to the pH of the measurement object is reflected on the potential of the sensing region5.

It is to be noted that the extended type chemical/physical phenomenon detecting device101shown inFIG. 5can be made by a conventional process and, of course, the silicon oxide layer can be formed in multiple layers (see Published Japanese Translation No. 2010-535360, (he description of this literature is incorporated as part of this specification by reference).

Even with the chemical/physical phenomenon detecting device101shown inFIG. 5, unless the diffusion layer4is formed between the ICG region3and the sensing region5in the substrate10, as shown inFIG. 6, the potential barrier120is formed to retain the charges on the sensing region and the charges thus retained may cause a false signal.

On the other hand, as shown inFIG. 5, by forming the diffusion layer4between the ICG layer3and the sensing region5, the potential barrier120is not formed.

The chemical/physical phenomenon detecting device101also operates in the same manner as the chemistry/physical phenomenon detecting device inFIG. 1(seeFIG. 4).

The present invention is not limited to the description of the embodiment and examples of the invention at all. Various modifications are also included in the present invention as long as they can be easily conceived by those skilled in the art without departing from the spirit of the scope of claims.

EXPLANATION OF NUMERAL NUMBERS IN FIGS