JP2007201267A - Solid state imaging element and its fabrication process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit occurrence of a white scratch by reducing effectively a dark current without giving a bad influence on a performance clearing a stored charge by an overflow drain, in a solid state imaging element of a vertical overflow drain structure corresponding to colorization. <P>SOLUTION: In response to a wavelength of light, the depth of a first conductive layer (160, 162, and 164) is optimized for constituting a photodiode, a first conductive layer (162, 164) of a photodiode is shallowly formed for receiving each light of green (G) and blue (B) of short wavelength, and it eliminates a useless structure. Moreover, directly under the photodiode for the green (G) and the blue (B), additional overflow barrier layer (121, 123) is formed, and the difference is reduced in height of potentials of overflow barriers. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device and a manufacturing method thereof, and in particular, a solid-state imaging having a vertical overflow drain structure including a photodiode that photoelectrically converts each light of red (R), green (G), and blue (B). The present invention relates to an element and a manufacturing method thereof.

  In a solid-state imaging device using a CCD, incident light is converted into electric charge by a photodiode, and the accumulated electric charge is converted into a voltage and taken out. In order to increase the sensitivity of such a solid-state imaging device, various techniques for deeply forming photodiodes in the vertical direction have been proposed (see, for example, Patent Document 1). In the technique of Patent Document 1, an N-type layer serving as a charge storage layer is formed deeply for each photodiode that photoelectrically converts red (R), green (G), and blue (B) light. The N-type layer is formed in multiple stages to optimize the concentration profile.

  Further, it is desirable to empty the charge of the photodiode when imaging with the solid-state imaging device is started. As a configuration of such a solid-state imaging device, a vertical overflow drain structure capable of emptying the accumulated charge at all pixels simultaneously is known (see, for example, Patent Document 2). In this vertical overflow drain structure, an NPN structure is formed in the depth direction of the semiconductor substrate (they have a function as a bulk type vertical transistor), and an intermediate P is changed by changing the substrate bias. When the potential barrier (generally called an overflow barrier) formed by the mold layer is eliminated, the accumulated charge can be cleared simultaneously for all the pixels.

FIG. 12 is a diagram illustrating a potential characteristic for explaining an operation for clearing accumulated charges in a solid-state imaging device having an overflow drain structure.
In the figure, T1 indicates the potential characteristic in the state where the overflow barrier (OFB) is formed, and T2 indicates the potential characteristic in the state where the overflow barrier (OFB) disappears. By changing the bias voltage of the substrate, the potential curve changes from T1 to T2, whereby the accumulated charge Q is released to the drain all at once, and the accumulated charges of all the pixels can be cleared simultaneously.
JP 2003-86783 A JP 2004-228140 A

  In the technique described in Patent Document 1, the depths of the photodiodes for R, G, and B colors are uniformly increased, and then an N-type layer as a charge storage layer is formed by multiple ion implantations. Thus, the impurity concentration profile is controlled. However, according to the inventor's diligent study, when the photodiodes are uniformly formed deeply, the sensitivity is improved for the photodiodes that receive red (R) light having a long wavelength, but the green (G) that has a short wavelength. For photodiodes receiving blue (B) light, the effect of improving sensitivity due to the deep formation of the photodiodes is not necessarily obtained. On the contrary, there is a conspicuous adverse effect such as an increase in so-called white scratches due to an increase in dark current. The knowledge of becoming was obtained.

  That is, green (G) and blue (B), which have shorter wavelengths than red (including infrared light), do not reach the deepest part (of the N-type layer) of the deepened photodiode. In many cases, the deepest part does not contribute much to photoelectric conversion. On the other hand, as the N-type layer constituting the photodiode becomes deeper, its surface area increases, dark current increases, and white defects increase.

  The present invention has been made on the basis of such considerations, and an object of the present invention is to provide a solid-state imaging device including a photodiode that receives light of each color of red (R), green (G), and blue (B). The object is to effectively reduce the dark current and suppress the occurrence of white scratches.

The above object of the present invention is realized by the following configuration.
(1) A first conductivity type semiconductor substrate (100, 110), a second conductivity type overflow barrier layer (120) provided on the semiconductor substrate, and a low impurity concentration provided on the overflow barrier layer A layer (158), and first, second, and third photodiodes that photoelectrically convert red (R), green (G), and blue (B) light provided in the low impurity concentration layer; A solid-state imaging device having a vertical overflow drain structure, comprising: first, second, and third photodiodes that photoelectrically convert each of the red (R), green (G), and blue (B) light. Each is constituted by an upper second conductive type layer (170, 172) and a lower first conductive type layer (160, 162, 164) functioning as a charge storage region, and the first, second and In each of the third photodiodes When the depths of the lower first conductivity type layers (160, 162, 164) are d1, d2, and d3, respectively, a relationship of d1> d2 ≧ d3 is satisfied, and the second and third photodiodes Suppresses fluctuations in the height of the overflow barrier caused by reducing the depth (d2, d3) of the first conductivity type layer (162, 164) below the lower first conductivity type layer (162, 164). An additional overflow barrier layer (121, 123) for forming a solid-state imaging device.

According to this solid-state imaging device, the depth of the first conductivity type layer constituting the photodiode is optimized according to the wavelength of light to be subjected to photoelectric conversion, and short wavelengths of green (G) and blue (B ), A useless portion is removed from the photodiode that receives each light, thereby reducing a dark current and suppressing the occurrence of white scratches. That is, long-wavelength red (R) light reaches the deep portion of the first conductive type layer (hereinafter referred to as N-type) that constitutes the photodiode, so that the charge generated in the deep portion is effectively used. In order to achieve this, it is desirable that the photodiode be formed sufficiently deep, but the short wavelengths of green (G) and blue (B) do not reach as deep as red (R), so they are adjusted to their arrival positions. Thus, the depth of the N-type layer constituting the photodiode is reduced. That is, when the depths of the N-type layers of the first, second, and third photodiodes that photoelectrically convert red (R), green (G), and blue (B) light are d1, d2, and d3. In addition, the depth of each N-type layer is adjusted so that the relationship of d1>d2> d3 or d1> d2 = d3 is established.
Further, when the depth of the N-type layer constituting each photodiode is changed in accordance with the wavelength of received light, the solid-state imaging device has a bottom of the N-type layer and a P-type overflow barrier layer for each photodiode. In some cases, the substrate potential (hereinafter referred to as the overflow potential) required for completely clearing the accumulated charge varies for each photodiode. That is, a low-concentration layer having a low impurity concentration (in principle, P-type is desirable between the bottom of the N-type layer constituting the photodiode and the P-type overflow barrier layer, but this is not a limitation. This low-concentration layer extends the depletion layer according to the bias of the photodiode and smoothly raises the potential curve of the overflow drain structure, though it may be N-type or non-doped). Since the thickness of the low concentration layer is larger, the potential of the overflow barrier (OFB) is lower. Therefore, in the photodiodes for green (G) and blue (B) in which the depth of the N-type layer is reduced, the accumulated charge may not be completely cleared unless the overflow drain potential is set higher. This may cause a rise in drive voltage, variation in reset voltage, and the like. Therefore, an additional overflow barrier layer is formed immediately below the green (G) and blue (B) photodiodes, thereby forming the bottom of the N-type layer and the P-type overflow barrier layer (additional) constituting each photodiode. Variation in the distance between the first and second overflow barrier layers). Therefore, the difference in height of the overflow barrier potential between the photodiodes for the respective colors is reduced, and variations in the overflow drain potential can be suppressed.

  (2) The solid-state imaging device according to (1), wherein a thickness of the overflow barrier layer is set corresponding to a thickness of the first conductivity type layer.

  According to this solid-state imaging device, the difference in the potential height of the overflow barrier is reduced by setting the thickness of the overflow barrier layer corresponding to the thickness of the first conductivity type layer.

  (3) The solid-state imaging device according to (2), wherein the low-concentration layer immediately below the first conductive type layer (160, 162, 164) of the lower layer in the first, second, and third photodiodes (158) The thickness of all is substantially the same (H1), The solid-state image sensor characterized by the above-mentioned.

  According to this solid-state imaging device, the thickness of the low concentration layer interposed between the bottom of the N-type layer constituting each photodiode and the P-type overflow barrier layer (including the additional overflow barrier layer) is substantially the same. By doing so, variations in overflow drain potential can be sufficiently suppressed.

  (4) The solid-state imaging device according to (1), wherein an impurity concentration of the overflow barrier layer is set corresponding to a thickness of the first conductivity type layer.

  According to this solid-state imaging device, the difference in potential height of the overflow barrier is reduced by setting the impurity concentration of the overflow barrier layer corresponding to the thickness of the first conductivity type layer.

  (5) A method of manufacturing a solid-state imaging device having a vertical overflow drain structure including first, second, and third photodiodes that photoelectrically convert red (R), green (G), and blue (B) light. An impurity layer (130, 140) serving as a charge transfer path in a portion above the second conductivity type overflow barrier layer (120) formed in the first conductivity type semiconductor substrate (110); A low impurity concentration layer (158) to be a photodiode is formed, a transfer electrode for controlling charge transfer is formed on the impurity layer (130, 140) to be the transfer path, and then a photo diode is completed. A diode forming step, wherein the photodiode forming step is arranged in the low impurity concentration layer (158) in the photodiode forming region (Z2) of the semiconductor substrate. The first conductive type layers (160, 162, 164) constituting the second and third photodiodes are formed, and the first conductive type layer (160, 162, 164) and the upper first layer forming the PN junction are formed. A step of forming two conductivity type layers (170, 172), and the depth of the first conductivity type layer (160, 162, 164) in each of the first, second, and third photodiodes is defined as d1 , D2, and d3, the relation of d1> d2 ≧ d3 is satisfied, and ion implantation is performed after the formation of the first conductivity type layer, thereby forming the second and third photodiodes. Additional overflow that suppresses fluctuations in the height of the overflow barrier caused by reducing the depth (d2, d3) of the first conductivity type layer (162, 164) below the one conductivity type layer (162, 164). A method of manufacturing a solid-state imaging device, comprising forming a barrier layer (121, 123).

According to this method for manufacturing a solid-state imaging device, after forming an overflow barrier layer, forming an impurity layer constituting a charge transfer path, a low-concentration layer in which a photodiode is formed later, and forming a transfer electrode, In the photodiode forming step, the depth of the first conductivity type layer constituting the photodiode is formed while being optimized according to the wavelength of light. N-type layers having different depths can also be formed, for example, by appropriately controlling acceleration energy at the time of ion implantation. The depth can also be controlled by implanting counter ions into the deep portion of the N-type layer. As a result, useless portions are removed from the photodiodes that receive short-wavelength green (G) and blue (B) light, dark current is reduced, and occurrence of white scratches is suppressed. In the fifth step, a light shielding film and a flattening layer are formed, and further, a color filter layer and an on-chip lens are formed, so that a solid-state imaging device corresponding to a color image can be formed without difficulty.
In this photodiode forming step, an additional overflow barrier layer can be formed without difficulty by ion implantation, and the fluctuation of the height of the overflow barrier due to the difference in the depth of the first conductivity type layer is suppressed. Can do.

  (6) The method for manufacturing a solid-state imaging device according to (5), wherein the additional overflow barrier layer (121, 123) is formed by using the first conductivity type layer (the first, second, and third photodiodes). 160, 162, 164), and forming the low-concentration layer (158) directly below the same thickness (H1).

  According to this solid-state imaging device manufacturing method, the thickness of the low-concentration layer interposed between the bottom of the N-type layer constituting each photodiode and the P-type overflow barrier layer (including the additional overflow barrier layer) is reduced. By making them substantially the same, variations in the overflow drain potential can be sufficiently suppressed.

  (7) A method of manufacturing a solid-state imaging device having a vertical overflow drain structure including first, second, and third photodiodes that photoelectrically convert red (R), green (G), and blue (B) light. An impurity layer (130, 140) serving as a charge transfer path in a portion above the second conductivity type overflow barrier layer (120) formed in the first conductivity type semiconductor substrate (110); A low impurity concentration layer (158) to be a photodiode is formed, a transfer electrode for controlling charge transfer is formed on the impurity layer (130, 140) to be the transfer path, and then a photo diode is completed. A diode forming step, wherein the photodiode forming step is arranged in the low impurity concentration layer (158) in the photodiode forming region (Z2) of the semiconductor substrate. The first conductivity type layers (160, 162, 164) constituting the second and third photodiodes are formed at substantially the same depth, and the first conductivity type layers (160, 162, 164) and the PN junction are formed. An upper second conductive type layer (170, 172) to be formed is formed, and then the first conductive type layer (160, 160) constituting the second and third photodiodes is used as a counter impurity. A second conductivity type impurity is introduced, thereby canceling the conductivity type at the bottom of the first conductivity type layer (160, 160), and the depth of the potential well region constituting the first, second and third photodiodes. Forming a first conductivity type layer (160, 162, 164) having different lengths from each other.

  According to this method for manufacturing a solid-state imaging device, after the N-type layer is formed at a uniform depth, the photodiodes for green (G) and blue (B) are of the opposite conductivity type (that is, the second conductivity type). Counter impurities (boron) are introduced into the deep part to neutralize the charge, and the N-type layer in that part is extinguished, resulting in a shallow N-type layer. For the formation of the first N-type layer, it is not necessary to change the implantation energy for each photodiode, and after that, it is only necessary to add a step of introducing a counter impurity (that is, it can be handled by changing the mask). The burden can be reduced.

According to the present invention, the depth of the first conductivity type layer constituting the photodiode is optimized according to the wavelength of light to be subjected to photoelectric conversion, so that the short wavelengths of green (G) and blue (B) It is possible to remove useless portions from the photodiodes that receive each light, thereby reducing dark current and suppressing the occurrence of white scratches.
In addition, when optimizing the depth of the first conductivity type layer constituting each photodiode, an additional overflow barrier layer is also formed immediately below the green (G) and blue (B) photodiodes. Thus, variation in the distance between the bottom of the N-type layer constituting each photodiode and the P-type overflow barrier layer (including the additional overflow barrier layer) can be suppressed. Therefore, the difference in the height of the potential of the overflow barrier between the photodiodes for each color is suppressed, and variations in the overflow drain potential can be suppressed.

  Furthermore, the control of the depth of the first conductivity type layer constituting each photodiode and the formation of an additional overflow barrier layer cannot be achieved by adjusting the acceleration energy of ion implantation or adding a few processes during ion implantation. It is possible to realize without.

  According to the present invention, in a solid-state imaging device including a photodiode that receives light of each color of red (R), green (G), and blue (B), the dark charge is not adversely affected on the operation of clearing accumulated charges by the overflow drain. It is possible to effectively reduce the current and suppress the occurrence of white scratches.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a solid-state imaging device according to the present invention (example corresponding to a color, having a vertical overflow drain structure, the depth of each photodiode being optimized, and an additional overflow barrier layer being formed). It is sectional drawing of the device which shows the structure of these.

  As shown in the figure, this solid-state imaging device includes an N-type semiconductor substrate (NSub) 100, an N-type epitaxial layer 110, a P-type overflow barrier layer 120, and a P-type low-concentration layer 158. . The low concentration layer 158 functions to extend the depletion layer in accordance with the bias of the photodiode and smoothly change the potential curve of the vertical overflow drain structure. Note that the conductivity type of the low-concentration layer 158 may be N-type in some cases, or may be a non-doped layer.

  The photodiode that photoelectrically converts red (R) light includes a lower N-type layer 160 (depth d1) and an upper P + type layer 170 formed in the low-concentration layer 158.

  The P-type layer 172 is a diffusion layer for preventing inversion. The P + type layer 150 is a diffusion layer for element isolation. The N-type diffusion layer 140 and the P-type diffusion layer 130 are diffusion layers that constitute a transfer path. Similarly, a photodiode that photoelectrically converts green (G) light includes a lower N-type layer 162 (depth d2) and an upper P + type layer 170 formed in the low-concentration layer 158. Similarly, a photodiode for photoelectrically converting blue (B) light includes a lower N-type layer 164 (depth d3) and an upper P + type layer 170 formed in the low-concentration layer 158.

A gate insulating film (for example, ONO film) 180 is formed on the surface of the semiconductor substrate.
PY1 and PY2 are transfer electrodes formed of polysilicon of the first layer and the second layer, respectively. Reference numeral 182 is an inter-transfer electrode insulating film, and reference numeral 184 is an overcoat insulating film. The transfer electrodes PY1 and PY2 are covered with a titanium nitride (TiN) layer 190 as a barrier metal and a light shielding film 192 made of tungsten (W).

  A BPSG film 200 is formed on the semiconductor substrate, and a silicon nitride (SiN) film 210 as a planarizing layer is formed thereon. On the planarizing layer 210, color filter layers 220, 222, and 224 of red (R), green (G), and blue (B) are formed of colored transparent resists.

  An on-chip lens 230 is formed on the color filter layers 220, 222, and 224 via a planarizing layer 229 made of an organic film.

  The solid-state imaging device of FIG. 1 is characterized by optimizing the depths (d1, d2, d3) of the N-type layers (160, 162, 164) constituting the photodiode according to the wavelength of light, and reducing the short wavelength green. (G), blue (B) is a point which eliminates a useless part from the photodiode which receives each light, thereby reducing a dark current and suppressing generation | occurrence | production of a white crack.

  That is, since the long wavelength red (R) light reaches the deep part of the N-type layer 160 constituting the photodiode, the N-type layer 160 is used in order to validate the charge generated in the deep part. It is desirable to form it sufficiently deep.

  On the other hand, short-wavelength green (G) and blue (B) light does not reach as deep as red (R) light (or because the arrival rate is small), so Even if the N-type layer is deepened as in the photodiode that receives light, it does not directly improve the sensitivity, but rather increases the surface area unnecessarily and increases the dark current.

  Therefore, for the photodiodes that receive short-wavelength green (G) and blue (B) light, the depths of the N-type layers 162 and 164 that constitute the photodiodes are reduced in accordance with the arrival position of each light. That is, when the depths of the N-type layers of the first, second, and third photodiodes that photoelectrically convert red (R), green (G), and blue (B) light are d1, d2, and d3. In addition, the depth of each N-type layer (160, 162, 164) is adjusted so that the relationship of d1> d2> d3 or d1> d2 = d3 is established.

  The N-type layers (160, 162, 164) having different depths can be formed, for example, by appropriately controlling acceleration energy at the time of ion implantation. The depth of the diffusion layer can also be controlled by implanting counter ions into the deep portion of the N-type layer.

  In the structure of the solid-state imaging device shown in FIG. 1, an additional overflow barrier layer (121, 164) is provided immediately below the N-type layers (162, 164) constituting the photodiodes for green (G) and blue (B). 123) between the bottom of the N-type layer (160, 162, 164) constituting each photodiode and the P-type overflow barrier layer 120 and the additional overflow barrier layer (121, 123). Variations in distance are suppressed, and variations in overflow drain voltage are suppressed.

  The additional overflow barrier layers 121 and 123 are P-type layers like the overflow barrier layer 120, and are directly below the N-type layers (162 and 164) constituting the photodiodes for green (G) and blue (B). Only selectively formed. The additional overflow barrier layers 121 and 123 can be formed by adjusting the acceleration energy of ion implantation.

  The additional overflow barrier layers 121 and 123 are integrated with the underlying overflow barrier layer 120. The reason for providing the additional overflow barrier layers 121 and 123 is as follows.

  That is, if the depth of the N-type layer (160, 162, 164) constituting each photodiode is changed in accordance with the wavelength of received light, the bottom of the N-type layer and the P-type overflow are provided for each photodiode. The distance from the barrier layer is different, and the substrate potential (hereinafter referred to as the overflow potential) necessary for completely clearing the accumulated charge may vary for each photodiode. That is, the low concentration layer 158 having a low impurity concentration is interposed between the bottom of the N type layers (160, 162, 164) constituting the photodiode and the P type overflow barrier layer 120. 158 has a function of extending the depletion layer according to the bias of the photodiode and smoothly raising (changing) the potential curve of the overflow drain structure. Therefore, the thicker the low concentration layer, the lower the potential of the overflow barrier (OFB). Therefore, in the green (G) and blue (B) photodiodes in which the depths of the N-type layers (162, 164) are reduced, the accumulated charge may not be completely cleared unless the overflow drain potential is increased. This can cause problems such as an increase in drive voltage and variations in reset voltage.

  Therefore, an additional overflow barrier layer (121, 123) is formed immediately below the green (G) and blue (B) photodiodes. Thus, the distance between the bottom of the N-type layer (160, 162, 164) constituting each photodiode and the P-type overflow barrier layer 120 (and the additional overflow barrier layers 121, 123) is substantially the same (FIG. Among them, the distance H1) can be aligned. Therefore, the difference in height of the overflow barrier potential between the photodiodes for the respective colors is reduced, and variations in the overflow drain potential can be suppressed.

  FIG. 2 is a characteristic diagram for explaining how the height of the potential of the overflow barrier in each photodiode is controlled substantially uniformly by the solid-state imaging device of FIG.

  FIG. 2 shows changes in the potential of the semiconductor substrate in the depth direction. In the drawing, the range described as the PD region (B) is an N-type layer 162 that constitutes a blue (B) photodiode. Similarly, the range described as the PD region (R) indicates the range where the N-type layer 160 constituting the photodiode for red (R) exists.

  R (S) represents a vertical potential curve in the red photodiode.

  B (S1) is a case where the depth of the N-type layers (160, 162) constituting the photodiode is optimized and the additional overflow barrier layer 121 is formed as in the solid-state imaging device of FIG. 2 shows a vertical potential curve in a blue photodiode.

  B (S2) is the vertical direction of the blue photodiode when the depth of the N-type layers (160, 162) constituting the photodiode is optimized but the additional overflow barrier layer 121 is not formed. The potential curve is shown.

  Comparing the potential curves R (S) and B (S1), the height of the potential of the overflow barrier is almost the same, and the accumulated charge can be cleared at the same potential. On the other hand, in the potential curve B (S2), it can be seen that the region having a high potential of the overflow barrier becomes wide, and therefore, it is necessary to apply a larger overflow drain voltage in order to clear the accumulated charge.

  Thus, when optimizing the depth of the N-type layers (160, 162, 164) constituting each photodiode as in the solid-state imaging device of FIG. 1, green (G), blue (B ), An additional overflow barrier layer (121, 123) is formed immediately below the photodiode for the N-type layer (160, 162, 164) constituting the photodiode and a P-type overflow barrier layer 120. (And the additional overflow barrier layers 121 and 123) are substantially the same (H1), the difference in the height of the overflow barrier potential of the photodiodes for each color is suppressed, and the variation of the overflow drain potential is reduced. It becomes possible to suppress.

  That is, in the solid-state imaging device of FIG. 1, in the solid-state imaging device including photodiodes that receive light of each color of red (R), green (G), and blue (B), the accumulated charge clear operation by the overflow drain is adversely affected. The effect of reducing the dark current effectively and suppressing the occurrence of white scratches can be obtained.

  Here, with reference to FIGS. 3 to 11, a method of manufacturing the solid-state imaging device of FIG. 1 will be described below. 3 to 11 are cross-sectional views for each main manufacturing process of the solid-state imaging device of FIG.

  First, as shown in FIG. 3, an N type epitaxial layer (Nepi) 110 is formed on an N type semiconductor substrate (Nsub) 100, and ions are implanted into the N type epitaxial layer (Nepi) 110, and P A mold overflow barrier layer 120 is formed.

  Next, as shown in FIG. 4, in the transfer path formation region (Z1) in the upper part of the overflow barrier layer 120 of the N-type epitaxial layer (Nepi) 110, diffusion layers (130, 140 serving as transfer paths). Then, the element isolation diffusion layer 150 is formed, and the low impurity concentration layer (P− layer) 158 is further formed in the photodiode formation region (Z2).

  Next, as shown in FIG. 5, a gate insulating film 180 is formed on the surface of the semiconductor substrate, and subsequently, charge transfer is performed on the diffusion layer (130, 140) serving as a transfer path in the transfer path forming region (Z1). The transfer electrodes (PY1, PY2) made of polysilicon of the first layer / second layer for controlling the above are formed. Reference numeral 182 denotes a transfer electrode insulating film, and 184 denotes an overcoat insulating film.

  Next, as shown in FIG. 6, a photodiode formation step is performed. That is, first, the first, second, and third photodiodes (red, green, and blue photodiodes in the low impurity concentration layer ((P− layer) 158) in the photodiode formation region (Z2), respectively. An N-type layer (160, 160, 160) having the same depth as a lower layer constituting (certain) is formed by ion implantation.

  Further, an upper second conductive type layer (170, 172) that forms a PN junction with the N-type layer (160, 160, 160) is formed.

  Next, as shown in FIG. 7, boron (B) as a counter impurity is introduced into the N-type layers (160, 160) constituting the second and third photodiodes, whereby the N-type layer ( 160 and 160), the N-type layers (160, 162 and 164) having different depths constituting the first, second and third photodiodes are formed as a result. That is, as a result, first conductivity type layers (160, 162, 164) having different depths of potential well regions constituting the first, second and third photodiodes are formed. In FIG. 7, X1 and X2 indicate regions into which counter ions are implanted. Thus, a relationship of d1> d2 ≧ d3 is established with respect to the depths d1, d2, d3 of the N-type layers (160, 162, 164) in each of the first, second and third photodiodes.

  Next, as shown in FIG. 8, boron (B) is ion-implanted, and the N-type layer (162) is formed below the N-type layers (162, 164) constituting the second and third photodiodes. 164), an additional overflow barrier layer (121, 123) is formed to suppress fluctuations in the height of the overflow barrier due to the shallow depth (d2, d3). As a result, the thickness of the low concentration layer 158 immediately below the N-type layers (160, 162, 164) in the first, second, and third photodiodes becomes substantially the same (H1). The photodiode is completed through the above steps. In other words, by setting the thickness of the overflow barrier layer (121, 123) corresponding to the thickness of the first conductivity type layer (162, 164), the difference in potential height of the overflow barrier is reduced. In order to reduce the difference in potential height of the overflow barrier, the impurity concentration of the overflow barrier layer (121, 123) is set corresponding to the thickness of the first conductivity type layer (162, 164). Also good.

  Next, as shown in FIG. 9, a titanium nitride (TiN) film 190 as a barrier metal is formed on the transfer electrodes (PY1, PY2), and then a tungsten (W) film 192 as a light shielding film is formed. .

  Next, as shown in FIG. 10, after forming the BPSG film 200 and the silicon nitride (SiN) film 210 so as to cover the light shielding film 192, the silicon nitride film 210 is planarized by CMP or etch back.

  Next, as shown in FIG. 11, a color material is included at a position corresponding to each of the regions where the first, second, and third photodiodes are formed on the planarized silicon nitride film 210. Resist is sequentially applied to form red (R), green (G), and blue (B) color filter layers (220, 222, 224).

  Subsequently, a planarizing layer 229 is formed, a transparent resist is applied on each color filter layer (220, 222, 224), and the surface is processed into a spherical shape by a reflow process to form an on-chip lens 230.

  As described above, according to the present invention, the depth of the first conductivity type layer constituting the photodiode is optimized according to the wavelength of light to be subjected to photoelectric conversion, and the short wavelength green (G) , Blue (B) light, a useless portion is removed from the photodiode, thereby reducing the dark current and suppressing the occurrence of white scratches.

  In addition, when optimizing the depth of the first conductivity type layer constituting each photodiode, an additional overflow barrier layer is also formed immediately below the green (G) and blue (B) photodiodes. Thus, variation in the distance between the bottom of the N-type layer constituting each photodiode and the P-type overflow barrier layer (including the additional overflow barrier layer) can be suppressed. Therefore, the difference in height of the overflow barrier potential between the photodiodes for the respective colors is reduced, and variations in the overflow drain potential can be suppressed.

  In addition, the control of the depth of the first conductivity type layer constituting each photodiode and the formation of an additional overflow barrier layer cannot be achieved by adjusting the acceleration energy of ion implantation or adding a few steps during ion implantation. It is possible to realize without.

  In the above-described embodiment, the description has been given with the configuration of color detection of three colors of red (R), green (G), and blue (B). However, the configuration is not limited to three colors, but two colors or four colors or more. Even in this case, the present invention can be applied.

  The present invention provides a solid-state imaging device having a photodiode that receives light of each color of red (R), green (G), and blue (B). This has the effect of effectively reducing the current and suppressing the occurrence of white scratches, and is therefore useful as a solid-state imaging device having a color-compatible vertical overflow drain structure and a method for manufacturing the same.

Configuration of another example of solid-state imaging device of the present invention (example corresponding to color, having a vertical overflow drain structure, the depth of each photodiode being optimized, and an additional overflow barrier layer being formed) It is sectional drawing of the device which shows this. FIG. 2 is a characteristic diagram for explaining how the height of the potential of the overflow barrier in each photodiode is controlled substantially uniformly by the solid-state imaging device of FIG. 1. It is sectional drawing of the device in the 1st manufacturing process for demonstrating the manufacturing method of the solid-state image sensor of FIG. It is sectional drawing of the device in the 2nd manufacturing process for demonstrating the manufacturing method of the solid-state image sensor of FIG. It is sectional drawing of the device in the 3rd manufacturing process for demonstrating the manufacturing method of the solid-state image sensor of FIG. It is sectional drawing of the device in the 4th manufacturing process for demonstrating the manufacturing method of the solid-state image sensor of FIG. It is sectional drawing of the device in the 5th manufacturing process for demonstrating the manufacturing method of the solid-state image sensor of FIG. It is sectional drawing of the device in the 6th manufacturing process for demonstrating the manufacturing method of the solid-state image sensor of FIG. It is sectional drawing of the device in the 7th manufacturing process for demonstrating the manufacturing method of the solid-state image sensor of FIG. It is sectional drawing of the device in the 8th manufacturing process for demonstrating the manufacturing method of the solid-state image sensor of FIG. It is sectional drawing of the device in the 9th manufacturing process for demonstrating the manufacturing method of the solid-state image sensor of FIG. It is a figure which shows the potential characteristic for demonstrating the operation | movement for clearing the accumulation charge in the solid-state image sensor of an overflow drain structure.

Explanation of symbols

110 N-type epitaxial layer 120 Overflow barrier layer 121, 123 Additional overflow barrier layer 130, 140 Diffusion layer (impurity layer) constituting the charge transfer path
150 Diffusion layer for element isolation 158 Low concentration layer (P-layer)
160, 162, 164 Lower N-type layers constituting the photodiode (each thickness d1, d2, d3)
170 P-type diffusion layer of upper layer constituting photodiode 172 P-type diffusion layer for inversion prevention 180 Gate insulating film 182 Inter-transfer electrode insulating film 184 Overcoat insulating film 190 Titanium nitride (TiN) layer as a barrier metal 192 As light shielding film Tungsten (W) layer 200 BPSG film 210 Silicon nitride (SiN) film 220, 222, 224 as planarization layer Color filter layer 229 Planarization layer made of organic film 230 On-chip lens PY1 Transfer made of first layer polysilicon Electrode PY2 Transfer electrode made of second layer polysilicon

Claims (7)

A first conductivity type semiconductor substrate (100, 110), a second conductivity type overflow barrier layer (120) provided on the semiconductor substrate, and a low impurity concentration layer (158) provided on the overflow barrier layer. ) And first, second and third photodiodes that are provided in the low impurity concentration layer and photoelectrically convert red (R), green (G), and blue (B) light. A solid-state imaging device having a vertical overflow drain structure,
Each of the first, second, and third photodiodes that photoelectrically convert the red (R), green (G), and blue (B) light includes an upper second conductive type layer (170, 172). A lower first conductivity type layer (160, 162, 164) functioning as a charge storage region, and the lower first conductivity type layer in each of the first, second and third photodiodes When the depths of (160, 162, 164) are d1, d2, and d3, respectively, there is a relationship of d1> d2 ≧ d3,
The depth (d2, d3) of the first conductivity type layers (162, 164) is made shallower under the lower first conductivity type layers (162, 164) in the second and third photodiodes. A solid-state imaging device, wherein an additional overflow barrier layer (121, 123) is formed to suppress fluctuations in the height of the overflow barrier due to. The solid-state imaging device according to claim 1,
A solid-state imaging device, wherein a thickness of the overflow barrier layer is set corresponding to a thickness of the first conductivity type layer. The solid-state imaging device according to claim 2,
The thicknesses of the low-concentration layers (158) immediately below the first conductive type layers (160, 162, 164) of the lower layers in the first, second, and third photodiodes are substantially the same (H1). There is a solid-state imaging device. The solid-state imaging device according to claim 1,
The solid-state imaging device, wherein an impurity concentration of the overflow barrier layer is set corresponding to a thickness of the first conductivity type layer. A method of manufacturing a solid-state imaging device having a vertical overflow drain structure including first, second, and third photodiodes that photoelectrically convert red (R), green (G), and blue (B) light,
An impurity layer (130, 140) serving as a charge transfer path, a photodiode, and a portion above the second conductivity type overflow barrier layer (120) formed in the first conductivity type semiconductor substrate (110) Forming a low impurity concentration layer (158) to be formed, forming a transfer electrode for controlling charge transfer on the impurity layer (130, 140) to be the transfer path, and then completing a photodiode Have
In the photodiode forming step, the first conductivity type constituting the first, second and third photodiodes in the low impurity concentration layer (158) in the photodiode forming region (Z2) of the semiconductor substrate. Forming a layer (160, 162, 164) and forming an upper second conductivity type layer (170, 172) that forms a PN junction with the first conductivity type layer (160, 162, 164), When the depths of the first conductivity type layers (160, 162, 164) in the first, second, and third photodiodes are d1, d2, and d3, respectively, the relationship of d1> d2 ≧ d3 is established. To have and
Further, ion implantation is performed after the formation of the first conductivity type layer, and the first conductivity type layer (162, 164) is formed below the first conductivity type layers (162, 164) constituting the second and third photodiodes. The additional overflow barrier layer (121, 123) that suppresses the variation in the height of the overflow barrier due to the shallow depth (d2, d3) of 162, 164) is formed. . It is a manufacturing method of the solid-state image sensing device according to claim 5,
The additional overflow barrier layer (121, 123) is formed in the thickness of the low concentration layer (158) immediately below the first conductivity type layer (160, 162, 164) in the first, second, and third photodiodes. Are formed so as to be substantially the same (H1). A method of manufacturing a solid-state imaging device having a vertical overflow drain structure including first, second, and third photodiodes that photoelectrically convert red (R), green (G), and blue (B) light,
An impurity layer (130, 140) serving as a charge transfer path, a photodiode, and a portion above the second conductivity type overflow barrier layer (120) formed in the first conductivity type semiconductor substrate (110) Forming a low impurity concentration layer (158) to be formed, forming a transfer electrode for controlling charge transfer on the impurity layer (130, 140) to be the transfer path, and then completing a photodiode Have
In the photodiode forming step, the first conductivity type constituting the first, second and third photodiodes in the low impurity concentration layer (158) in the photodiode forming region (Z2) of the semiconductor substrate. The layers (160, 162, 164) are formed at substantially the same depth, and the first conductive type layers (160, 162, 164) and the second conductive type layers (170, 172) that form PN junctions are formed. And
Next, a second conductivity type impurity as a counter impurity is introduced into the first conductivity type layers (160, 160) constituting the second and third photodiodes, whereby the first conductivity type layer (160 , 160), the first conductivity type layers (160, 162, 164) having different depths of potential well regions constituting the first, second and third photodiodes. A method for manufacturing a solid-state imaging device, comprising: forming a solid-state imaging device.

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