Patent Description:
Heretofore, in a CMOS type solid-state imaging element (CMOS image sensor), in order to increase an amount of charges which can be accumulated in a photodiode which performs photoelectric conversion in a pixel section, a potential such that the charges can be accumulated to a deep region has been formed in some cases. In such a case, a normal transfer gate is not used, but a vertical gate electrode which is inserted into silicon is used, resulting in that to a deep region is modulated to perform the reading operation with a generated electric field. In addition, in order to increase a modulation power, a structure is also proposed in which a plurality of vertical gate electrodes is adopted (e.g., refer to PTL <NUM> to PTL <NUM>). The document <CIT> is a relevant prior art.

In the related art described above, the vertical gate electrode is used in the transfer gate, resulting in that the reading operation with the generated electric field is performed. However, since the vertical gate electrode itself is at the same potential, the extension of a length of the vertical gate electrode results in that it becomes difficult to generate the electric field in a depth direction. On the other hand, the related art described above also proposes that a semiconductor region is divided into a plurality of regions, and in a position closer to a substrate surface, an impurity concentration becomes high. In this case, however, there is a problem that the number of processes is increased.

The present technology has been created in the light of such a situation, and it is therefore desirable to enhance charge transfer efficiency in a transfer gate having a vertical gate electrode.

The present technology is created in order to solve the problem described above, and a first aspect thereof is a solid-state imaging element, and an electronic apparatus including the solid-state imaging element. In this case, the solid-state imaging element is as recited in claim <NUM>. Further advantageous embodiments are recited in the dependent claims.

In addition, in the first aspect, the plurality of vertical gate electrodes may have a shape whose diameter is not changed to a given depth of the semiconductor substrate, and the diameter becomes small in the depth direction from the given depth. In addition, the plurality of vertical gate electrodes may have a shape whose diameter becomes small in the depth direction to the given depth of the semiconductor substrate, and the diameter may not be changed from the given depth.

In addition, in the first aspect, the plurality of vertical gate electrodes may have a shape in which a central portion in the depth direction of the semiconductor substrate swells, and a shallow portion and a deep portion may be thin.

In addition, in the first aspect, the plurality of vertical gate electrodes may have a shape in which the diameter becomes small in steps in the depth direction of the semiconductor substrate.

In addition, in the first aspect, the plurality of vertical gate electrodes may have a shape in which lengths thereof in the depth direction of the semiconductor substrate are different from one another.

In addition, in the first aspect, the plurality of vertical gate electrodes may have a shape in which a cross section along a diameter has a polygonal shape.

In addition, in the first aspect, a gate electrode of the transfer gate may be electrically separated from one another so as to correspond to the plurality of vertical gate electrodes, respectively.

In addition, in the first aspect, the plurality of vertical gate electrodes may have a shape whose parts are connected to one another to have a squared U-shape in cross section, and in which a cross-sectional area thereof becomes small in the depth direction of the semiconductor substrate.

In addition, in the first aspect, the plurality of vertical gate electrodes may form a donut cylindrical shape, and may have a shape whose cross-sectional area becomes small in the depth direction of the semiconductor substrate.

According to the present technology, an excellent effect can be offered in which in the transfer gate having the vertical gate electrode, the charge transfer efficiency can be enhanced. It should be noted that the effect described here is by no means necessarily limited, and any of the effects described in the present disclosure may also be offered.

Hereinafter, a mode for carrying out the present technology (hereinafter, referred to as an embodiment) will be described. A description is given in accordance with the following order.

<FIG> is a block diagram depicting an example of a configuration of an electronic apparatus as an example of a semiconductor apparatus having an imaging element in an embodiment of the present technology. The electronic apparatus includes an imaging element <NUM> and a peripheral circuit section. The peripheral circuit section includes a vertical drive circuit <NUM>, a horizontal drive circuit <NUM>, a control circuit <NUM>, a column signal processing circuit <NUM>, and an output circuit <NUM>.

The imaging element <NUM> is a pixel array in which a plurality of pixels <NUM> each including a photoelectric conversion section is arranged in the two-dimensional array. The pixel <NUM> includes, for example, a photodiode becoming the photoelectric conversion section, and a plurality of pixel transistors. Here, a plurality of pixel transistors, for example, can include three transistors: a transfer transistor; a reset transistor; and an amplification transistor.

The vertical drive circuit <NUM> drives the pixels <NUM> in units of a row. The vertical drive circuit <NUM>, for example, includes a shift register. The vertical drive circuit <NUM> selects a pixel drive wiring, and supplies a pulse for driving the pixels <NUM> to the selected pixel drive wiring. As a result, the vertical drive circuit <NUM> successively selectively scans the pixels <NUM> of the imaging element <NUM> in a vertical direction in units of a row, and supplies pixel signals based on signal charges generated in response to a quantity of received light in the photoelectric conversion sections of the pixels <NUM> to the column signal processing circuit <NUM>.

The horizontal drive circuit <NUM> drives the column signal processing circuit <NUM> in units of a column. The horizontal drive circuit <NUM>, for example, includes a shift register. The horizontal drive circuit <NUM> successively outputs a horizontal scanning pulse, thereby selecting the column signal processing circuits <NUM> to cause the pixel signals to be outputted from the column signal processing circuits <NUM> to a horizontal signal line <NUM>.

The control circuit <NUM> controls the whole of the solid-state imaging apparatus. The control circuit <NUM> receives an input clock and data used to instruct an operation mode or the like, and outputs data such as internal information in the solid-state imaging apparatus. That is, the control circuit <NUM> generates a clock signal and a control signal each becoming a reference of operations of the vertical drive circuit <NUM>, the column signal processing circuit <NUM>, the horizontal drive circuit <NUM>, and the like on the basis of a vertical synchronous signal, a horizontal synchronous signal, and a master clock. Then, the control circuit <NUM> inputs these signals to the vertical drive circuit <NUM>, the column signal processing circuit <NUM>, the horizontal drive circuit <NUM>, and the like.

The column signal processing circuit <NUM>, for example, is arranged every column of the pixels <NUM>, and executes signal processing such as noise removal every pixel column for the signals outputted from the pixels <NUM> for one row. That is, the column signal processing circuit <NUM> executes the signal processing such as CDS, signal amplification, or AD conversion for removing a fixed pattern noise peculiar to the pixel <NUM>. A horizontal selection switch (not depicted) is connected between an output stage of the column signal processing circuit <NUM>, and the horizontal signal line <NUM>.

The output circuit <NUM> executes signal processing for the signals which are successively supplied from the column signal processing circuits <NUM> through the horizontal signal line <NUM>, and outputs the resulting signals. In this case, the output circuit <NUM> buffers the signals from the column signal processing circuits <NUM>. In addition, the output circuit <NUM> may execute black level adjustment, column dispersion correction, various kinds of digital signal processing, and the like for the signals from the column signal processing circuits <NUM>.

<FIG> is a cross-sectional view depicting an example of a cross section of the imaging element <NUM> in the embodiment of the present technology. In the figure, a depth direction of a semiconductor substrate <NUM> is depicted downward (Z-coordinate). It is supposed that the semiconductor substrate <NUM> is composed of a p-type silicon substrate.

A photodiode (PD) <NUM> includes an n-type impurity region (n-type region) <NUM>, an n-type high-concentration impurity region (n+-type region) <NUM>, and a p-type high-concentration impurity region (p+-type region) <NUM> which are formed from a back surface side to a front surface side of the semiconductor substrate <NUM> in order in the inside of the semiconductor substrate <NUM>. The photodiode <NUM> mainly includes a pn junction as a bonding surface between the p+-type region <NUM> and the n+-type region <NUM>. A p-type low-impurity concentration region (p--type region) <NUM> which is lower in impurity concentration than the p+-type region <NUM> is formed between the n+-type region <NUM> constituting the photodiode <NUM>, and a gate insulating film <NUM>. The photodiode <NUM> is a photoelectric conversion section which is formed in a depth direction of the semiconductor substrate <NUM>, and generates the charges corresponding to the quantity of received light.

A floating diffusion (FD) <NUM> is formed in a region as an n-type high-concentration impurity region (n+-type region) on a surface side of the semiconductor substrate <NUM> over the outside of the photodiode <NUM>. The floating diffusion <NUM> is a charge accumulating section which accumulates the charges generated by the photodiode <NUM>.

A transfer gate (TG) <NUM> is a gate of the transfer transistor <NUM> which is arranged between the photodiode <NUM> and the floating diffusion <NUM>, and transfers the charges in the photodiode <NUM> to the floating diffusion <NUM>. The transfer gate <NUM> is formed within the semiconductor substrate <NUM> via a gate insulating film <NUM>.

<FIG> is a view depicting an example of a cross section, when viewed from another angle, of the imaging element <NUM> in the embodiment of the present technology. a in the figure is a cross-sectional view in the case where viewed from the back surface side of the semiconductor substrate <NUM>. b in the figure is a cross-sectional view in the case where viewing the floating diffusion <NUM> from the vertical gate <NUM>.

In <FIG> and <FIG>, a voltage is applied to the transfer gate <NUM>, resulting in that the charges in the photodiode <NUM> are transferred in a direction indicated by an arrow of a chain line to the floating diffusion <NUM> via the vertical gate <NUM>.

<FIG> is a view depicting an example of appearance of the transfer gate <NUM> in the embodiment of the present technology. The transfer gate <NUM> includes the transfer gate electrode <NUM> as a planner electrode, and two vertical gate electrodes <NUM> which are formed in the depth direction. Charges <NUM> in the photodiode <NUM> pass between the two vertical gate electrodes <NUM> to be transferred to the floating diffusion <NUM>.

Each of the vertical gate electrodes <NUM> in the embodiment is formed in such a way that a diameter thereof is changed so as to become small in the depth direction of the semiconductor substrate <NUM>. This shape of the diameter results in that with respect to the potential between the two vertical gate electrodes <NUM>, the modulation becomes small in a deep portion, and the modulation becomes large in a shallow portion. Then, a distribution of the potentials causes an electric field to be generated in a depth direction of the vertical gate electrode <NUM> to enable the satisfactory charge transfer to be performed. That is, in the range in which the modulation powers between the two vertical gate electrodes <NUM> overlap each other to exert an influence, the charges can be efficiently transferred.

<FIG> is a view depicting an example of a cross-sectional view of the transfer gate <NUM> in the embodiment of the present technology. When a distance between the vertical gate electrodes <NUM> is short, the modulation power increases, so that the potential becomes deep. On the other hand, when the distance between the vertical gate electrodes <NUM> is long, the modulation power decreases, so that the potential becomes shallow. With this structure, the degree of the modification can be controlled depending on the distance between the two vertical gate electrodes <NUM>, and the shape thereof. That is, in a design of the potential in the vicinity of the vertical gate electrode <NUM>, the distance between the vertical gate electrodes <NUM>, and the shape thereof can be used as parameters used to adjust the way of giving the distribution of the electric fields.

<FIG> is a view of assistance in comparing in shape the transfer gate <NUM> in the embodiment of the present technology, and the existing transfer gate with each other. In a and b of the figure, a downward arrow indicates the depth direction in the semiconductor substrate.

In order to suck up the charges from the deep region to the shallow region of the photodiode, heretofore, the vertical gate electrode has been used. The existing vertical gate electrode, as depicted in b of the figure, has a vertical shape.

In the vertical gate electrode, since when a length thereof becomes long, the electric field near the vertical direction along the vertical gate electrode is hard to generate, the charges become difficult to transfer. In addition, since the modulation range is wider in the structure using two vertical gate electrodes than in the structure using one vertical gate electrode, the charges can be sucked up from the photodiode in the deeper and wider range. However, it is not changed that the electric field in the depth direction is hard to generate.

Then, in the embodiment of the present technology, as depicted in a of the figure, two tapered vertical gate electrodes are used, resulting in that the electric field in the vertical direction is strengthened to enhance the transfer efficiency to facilitate the transfer design.

<FIG> is a graph of assistance in comparing a potential distribution of the transfer gate <NUM> in the embodiment of the present technology, and that in the existing transfer gate with each other. In the figure, a right-hand direction indicates the depth direction in the semiconductor substrate, and a downward direction indicates the potential.

The potential of the existing vertical gate electrode having the vertical shape is indicated by a dotted line, and the potential of the vertical gate electrode <NUM> having the tapered shape in the embodiment is indicated by a solid line. It should be noted that in this case, one-dimensional potential in the depth direction in an intermediate point between the two vertical gate electrodes is plotted.

As indicated in this case, in the existing vertical shape, the potential in the vicinity of the vertical gate electrode generates the power source voltage, and the electric field is hardly generated. On the other hand, in the structure having the tapered shape like the embodiment, it is understood that instead of decreasing the modulation in a lower portion of the vertical gate electrode <NUM>, the electric field in the vicinity of the vertical gate electrode <NUM> is generated.

<FIG> is a view depicting an example of a size of the transfer gate <NUM> in the embodiment of the present technology. Let us consider a structure in which the two vertical gate electrodes <NUM> are arranged at a distance VGD, and conduct through a pad type gate electrode <NUM>. However, it is supposed that a length of each of the vertical gate electrodes <NUM> is VGL, and a shape thereof tapers off along the depth direction. It is also supposed that a thickness of each of the vertical gate electrodes <NUM> is VGR1 in the thickest portion, and is VGR2 in the thinnest portion.

As the distance VGD between the vertical gate electrodes is shorter, an electric field ratio, in the vicinity of the vertical gate electrode, between the vertical shape and the tapered shape becomes larger. In addition, as the angle of the taper in the vertical gate electrode <NUM> is larger, the electric field ratio, in the vicinity of the vertical gate electrode, between the vertical shape and the tapered shape becomes larger.

In the case where the taper ratio of <NUM> or more in the depth direction is applied to a structure in which the distance VGD between the vertical gate electrodes is <NUM> or less, and the diameter VGR1 of the vertical gate electrode is <NUM> or more, the effect in which the electric field in the depth direction is strengthened is recognized. Here, the wording "the taper ratio is <NUM>" means that, at a depth of <NUM> in the depth direction, the diameter of the vertical gate electrode decreases by <NUM>. In addition, in the case where an applied voltage to the transfer gate <NUM> is smaller, the strengthening degree of the electric field is increased.

In order to form such a shape, the condition such that at the time of dry etching, gaseous species or a partial pressure is adjusted to generate the taper is used.

As described above, according to the embodiment of the present technology, the electric field is applied to the vicinity of the vertical gate electrode, so that the charges in the photodiode can be efficiently transferred to the floating diffusion.

<FIG> is a view depicting an example of a structure of a first modified change of the vertical gate electrode in the embodiment of the present technology. In the first modified change, in a vertical gate electrode <NUM>, a diameter is not changed to a given depth of the semiconductor substrate, and is decreased toward the lower side below the given depth in the depth direction. That is, the vertical gate electrode <NUM> has a structure in which an upper portion has a normal columnar shape, and a lower portion has a tapered shape. The tapered portion causes the vertical electric field due to the structure to be generated, and the columnar portion causes the electric field due to multistage implantation to be generated. As a result, the charges can be taken out from the deep portion.

<FIG> is a view depicting an example of a structure of a second modified change of the vertical gate electrode in the embodiment of the present technology. In the second modified change, in a vertical gate electrode <NUM>, a diameter is decreased in the depth direction to a given depth of the semiconductor substrate, and is not changed from the given depth. That is, the vertical gate electrode <NUM> has a structure such that the shallow portion has a tapered shape, and the deep portion has a vertical shape. When the end of the vertical gate electrode is thinned, the case where the modulation range becomes small, and thus it may be impossible to read out the charges from the photodiode may be generated. On the other hand, in this second modified change, the end of the vertical gate electrode is formed into the vertical shape, resulting in that in the shallow portion, the electric field in the depth direction can be generated while the modulation power is maintained.

<FIG> is a view depicting an example of a structure of a third modified change of the vertical gate electrode in the embodiment of the present technology. In the third modified change, a vertical gate electrode <NUM> has a shape in which a central portion swells. That is, the vertical gate electrode <NUM> has the structure in which the central portion swells, and a shallow portion and a deep portion are each thinned. In this structure, the modulation is strengthened in a region in which the central portion of the vertical gate electrode swells. Therefore, a transfer route of the charges does not reach the vicinity of the surface of the vertical gate electrode, but stops at the central portion, resulting in that the charges can be transferred without being influenced by defects in the vicinity of the interface.

<FIG> is a view depicting an example of a structure of a fourth modified change of the vertical gate electrode in the embodiment of the present technology. In the fourth modified change, a vertical gate electrode <NUM> has a shape in which a diameter is decreased in steps. That is, the vertical gate electrode <NUM> has a structure in which the diameter is changed step by step. A hole having different diameters is dug in several times, thereby enabling the structure to be realized.

<FIG> is a view depicting an example of a structure of a fifth modified change of the vertical gate electrode in the embodiment of the present technology. In the fifth modified change, in two vertical gate electrodes <NUM> and <NUM>, lengths thereof in the depth direction of the semiconductor substrate are different from each other. This state is such that after the length of one of them is changed to adjust the transfer route of the charges, the electric field in the vertical direction can also be applied.

<FIG> is a view depicting an example of a structure of a sixth modified change of the vertical gate electrode in the embodiment of the present technology. Although in the embodiment described above, the cross section along the diameter has the circular shape, in the sixth modified change, in the vertical gate electrode <NUM>, a cross section along a diameter has a rectangular shape. That is, the cross section has a columnar shape which differs in diameter in the depth direction. In this case, although the example in which the cross section has the rectangular shape, the cross section along the diameter may have a polygonal shape.

<FIG> is a view depicting an example of a structure of a seventh modified change of the vertical gate electrode in the embodiment of the present technology. In the seventh modified change, transfer gate electrodes <NUM> are separately provided so as to correspond to the vertical gate electrodes <NUM>, respectively. That is, the transfer gate electrodes <NUM> have structures which are independently of each other so as to correspond to a plurality of the vertical gate electrodes <NUM>. Since in this structure, the transfer gate electrodes <NUM> are electrically separated from each other so as to correspond to a plurality of the vertical gate electrodes <NUM>, respectively, different voltages can be applied to the respective vertical gate electrodes <NUM>. As a result, the transfer route can be changed or adjusted by a timing of the voltage application. For example, a first state in which the right transfer gate is turned ON and the left transfer gate is turned OFF, and a second state in which the left transfer gate is turned ON and the right transfer gate is turned OFF are repeated, thereby enabling the charges to be transferred by the reverse transfer. Naturally, in this structure as well, the same voltage may also be applied to both of them.

<FIG> is a view depicting an example of a structure of an eighth modified change of the vertical gate electrode in the embodiment of the present technology. Although in the embodiment described above, the two vertical gate electrodes <NUM> are provided, in the eighth modified change, three vertical gate electrodes <NUM> are provided. That is, there is no restriction in the number of vertical gate electrodes <NUM>, and three or more vertical gate electrodes <NUM> may be provided if necessary. As a result, the central potential is made deeper, resulting in that the electric field can be further generated in the depth direction.

<FIG> is a view depicting an example of a structure of a ninth modified change of the vertical gate electrode in the embodiment of the present technology. Although in the embodiment described above, the example in which a plurality of vertical gate electrodes <NUM> is separately arranged has been described, in the ninth modified change, parts of vertical gate electrodes <NUM> are connected to each other, and a shape is such that a cross section has a squared U-shape and becomes small in the depth direction of the semiconductor substrate. That is, the electrode structure is such that the thickness of the squared U-shape becomes thicker from a lower portion to an upper portion, and a silicon portion between them becomes narrower from the lower portion to the upper portion. In this case as well, since the electric field is generated in the depth direction in the principle similar to that of the embodiment described above, the charges can be transferred.

<FIG> is a view depicting an example of a structure of a tenth modified change of the vertical gate electrode in the embodiment of the present technique. In the tenth modified change, a vertical gate electrode <NUM> forms a donut cylindrical shape, and thus has a shape in which a cross-sectional area becomes smaller in the depth direction of the semiconductor substrate. In a lower portion, the modulation becomes weak because an inter-electrode distance is long, and in an upper portion, the modulation becomes strong because the inter-electrode distance is short. As a result, the electric field can be generated in the vertical direction. For forming this structure, the etching is performed in such a way that the diameter is changed from the lower portion to the upper portion.

As described above, according to the embodiment and modified changes of the present technology, the vertical gate electrode structure tapered in the depth direction is used, resulting in that the transfer electric field can be generated in the depth direction and the charges can be read out from the deep portion. As a result, even in the structure in which the vertical gate electrode is lengthened, the charges are easy to read out, and an amount of saturated charges can be generated in the deep portion of the photodiode. In addition, the parameters with respect to the tapered shape are adjusted, resulting in that the modulation amount and electric field in the vicinity of the vertical gate electrode can be controlled. For this reason, the potential at the time of the transfer can be adjusted by the shape of the vertical gate electrode without revising the potential design using the implantation.

It should be noted that the embodiment described above depicts the example for embodying the present technology, and the matters in the embodiment and the invention specific matters in CLAIMS have a correspondence relationship. Likewise, the invention specific matters in CLAIMS, and the matters in the embodiment of the present technology to which the same names as those in the invention specific matters in CLAIMS are added have a correspondence relationship. However, the present technology is by no means limited to the embodiment, and various changes are made for the embodiment without departing from the subject matters, thereby enabling the present technology to be embodied.

Claim 1:
A solid-state imaging element (<NUM>), comprising:
a photoelectric conversion section (<NUM>) formed in a depth direction of a semiconductor substrate (<NUM>) and generating charges corresponding to a quantity of received light;
a charge accumulating section (<NUM>) accumulating the charges generated by the photoelectric conversion section; and
a transfer gate (<NUM>) transferring the charges generated by the photoelectric conversion section (<NUM>) to the charge accumulating section (<NUM>),
wherein the transfer gate (<NUM>) includes a plurality of vertical gate electrodes (<NUM>) which is filled to a predetermined depth from an interface of the semiconductor substrate (<NUM>), and at least a part of a diameter is different in the depth direction of the semiconductor substrate (<NUM>),
wherein the vertical gate electrodes (<NUM>) are laterally separated from each other by the semiconductor substrate (<NUM>) and characterised in that the plurality of vertical gate electrodes (<NUM>) having a shape whose diameter becomes smaller at a taper ratio of <NUM> or more in the depth direction of the semiconductor substrate (<NUM>).