JP2006332124A - Solid-state image pickup element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a solid-state image pickup element having a small dark current by effectively terminating dangling bond on the surface of a silicon substrate for reducing an interface level. <P>SOLUTION: An insulating film 18 made of silicon oxide is formed on the surface of a substrate 1, and a photoelectric conversion section 15 that is a photodiode in which a hole accumulation layer 15A is provided is formed directly below the insulating film 18. A vertical transfer 24A is formed at one side of the photoelectric conversion section 15 via a read-out section 16. A light-shielding film 26 having an opening at the upper portion of the center of the photoelectric conversion section 15 is formed on the insulating film 18. A transparent insulating film 31 that is a silicon oxide film is formed on the light-shielding film 26 so that an opening is buried. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device and a manufacturing method thereof, and more particularly, to a solid-state imaging device with a reduced interface state near the surface of a semiconductor substrate and a manufacturing method thereof.

  In a CCD (Charge Coupled Device) type solid-state imaging device, an output component is observed even if all light input to a photoelectric conversion unit such as a photodiode is blocked. This is called a dark current, which is a kind of a thermally generated leak current, which increases as the temperature rises. When such dark current increases, the amount of signal charge that can be transferred by the vertical transfer unit decreases, and noise due to fluctuations in the dark current itself occurs, resulting in a problem of deteriorating imaging characteristics.

One of the causes of such dark current is the interface state existing on the surface of the silicon substrate on which the photoelectric conversion portion is formed. The charge thermally excited through the interface state is the dark current. Occupies the majority. For this reason, silicon dangling bonds at the interface between silicon (Si) and silicon oxide (SiO ₂ ), which cause interface states, are terminated with hydrogen, or a silicon nitride film containing releasable hydrogen is formed and hydrogen annealing is performed. It has been studied to reduce the interface state by combining with treatment.

For example, a silicon nitride film containing hydrogen is formed as a transparent protective layer on the light shielding film that prevents unnecessary light from entering the photoelectric conversion unit. Subsequently, a technique is disclosed in which heat treatment is performed in an atmosphere containing hydrogen, hydrogen is released from the silicon nitride film, and the released hydrogen is diffused to the surface of the silicon substrate to reduce the interface state on the surface of the silicon substrate. (For example, see Patent Document 1). In addition, a technique of forming a silicon nitride film immediately below the light shielding film to promote reduction of the interface state is also disclosed (see, for example, Patent Document 2).
JP-A 63-44761 Japanese Patent Laid-Open No. 9-92913

  However, when the silicon nitride film containing hydrogen is formed on the upper side of the light shielding film, the distance between the silicon nitride film and the silicon substrate is increased, so that hydrogen released from the silicon nitride film is effectively dangling silicon. There is a problem that the bond cannot be terminated.

  On the other hand, when the silicon nitride film is formed under the light shielding film, the size of the silicon nitride film that is a hydrogen supply source is limited, so that the absolute amount of released hydrogen is reduced and dangling bonds are not formed. There is a problem that it cannot be reliably terminated.

  Furthermore, in recent solid-state imaging devices, there is a strong demand for downsizing and high pixels. When the size of the photoelectric conversion unit is reduced to advance this, the signal charge per unit pixel rapidly decreases, and the relative In addition, since the dark current component becomes large, further interface state reduction technology is required.

  The present invention solves the above-described conventional problems, and can effectively realize a solid-state imaging device and a method for manufacturing the same that reduce interface states by effectively terminating dangling bonds on the surface of a silicon substrate and reduce dark current. The purpose is to.

  In order to achieve the above object, according to the present invention, a solid-state imaging device is provided with a transparent insulating film made of silicon oxynitride.

  Specifically, the solid-state imaging device of the present invention is formed on a semiconductor substrate and performs photoelectric conversion, an insulating film formed on the upper surface of the semiconductor substrate, and formed on the insulating film. A light-shielding film having an opening exposing the upper portion; and a transparent insulating film formed on the light-shielding film so as to fill the opening and transmitting light. The transparent insulating film is a silicon oxynitride film It is characterized by.

  According to the solid-state imaging device of the present invention, since the transparent insulating film is a silicon oxynitride film, a sufficient amount of hydrogen released from the transparent insulating film can be secured. Therefore, dangling bonds on the substrate surface can be reliably terminated, and as a result, it is possible to realize a solid-state imaging device with reduced interface states and less dark current.

  The solid-state imaging device of the present invention preferably further includes a hydrogen permeation suppression film made of silicon nitride and formed on the transparent insulating film. With such a configuration, hydrogen desorbed from the transparent insulating film can be reliably diffused to the surface of the substrate.

  In the solid-state imaging device of the present invention, the silicon oxynitride film preferably has a higher oxygen content in the lower part than in the upper part and a higher nitrogen content in the upper part than in the lower part. With such a configuration, the amount of hydrogen generation can be increased in the lower part, and the effect of suppressing hydrogen permeation can be enhanced in the upper part.

  In this case, the nitrogen content of the silicon oxynitride film is preferably continuously changing. With such a configuration, the interface between the silicon oxynitride film and the silicon nitride film can be eliminated, reflection and interference of incident light at the interface can be prevented, and a decrease in sensitivity can be suppressed.

  In the solid-state imaging device of the present invention, a plurality of photoelectric conversion units are formed in a matrix on a semiconductor substrate, and a vertical transfer unit that transfers signal charges read from each photoelectric conversion unit in the column direction and a transfer from the vertical transfer unit And a horizontal transfer unit that transfers the signal charges in the row direction, and preferably functions as a CCD type solid-state imaging device.

  The solid-state imaging device manufacturing method according to the present invention includes a step (a) of forming a photoelectric conversion unit that performs photoelectric conversion on a semiconductor substrate, and a step of forming an insulating film that covers the photoelectric conversion unit on the semiconductor substrate (b). And (c) forming a light shielding film having an opening exposing the upper portion of the photoelectric conversion portion on the insulating film, and plasma enhanced chemical vapor deposition so as to fill the opening on the light shielding film. A step (d) of forming a transparent insulating film using a method, wherein the step (d) includes a first step of depositing a silicon oxynitride film by supplying monosilane gas and oxygen dinitride gas as source gases; A second step of depositing the silicon oxynitride film while further supplying ammonia gas as the source gas and gradually decreasing the amount of oxygen dinitride gas contained in the source gas and simultaneously increasing the amount of ammonia gas. Characterized in that it comprises and.

  According to the method for manufacturing a solid-state imaging device of the present invention, the step of forming the transparent insulating film includes the first step of depositing the silicon oxynitride film by supplying monosilane gas and oxygen dinitride gas as the source gas, A second step of further supplying ammonia gas as a gas and depositing a silicon oxynitride film while gradually decreasing the amount of oxygen dinitride gas contained in the source gas and simultaneously increasing the amount of ammonia gas. Therefore, a silicon oxynitride film having a high hydrogen supply capability and a high oxygen content can be formed below the transparent insulating film, and a silicon oxynitride film having a high hydrogen content and a high nitrogen content can be formed on the top. Accordingly, hydrogen desorbed from the transparent insulating film can be efficiently diffused to the surface of the substrate, and dangling bonds on the surface of the substrate can be terminated.

In the method for manufacturing a solid-state imaging device of the present invention, the step (d) preferably includes a step of forming a silicon nitride film by supplying monosilane gas and ammonia gas as source gases after the second step.
With such a configuration, a silicon nitride film having a high hydrogen permeation inhibiting ability can be formed on the surface of the transparent insulating film on the surface, and the interface between the silicon oxynitride film and the silicon nitride film serving as a charge trap can be formed. Since it can be eliminated, reflection and interference of incident light can be suppressed, and a decrease in sensitivity can be prevented.

  The method for manufacturing a solid-state imaging device of the present invention preferably further includes a step of performing an annealing process in a hydrogen atmosphere after the step (d). With such a configuration, hydrogen can be efficiently desorbed from the transparent insulating film, and dangling bonds can be reliably terminated.

  In this case, the annealing treatment is preferably performed at a treatment temperature of 500 ° C. or lower. With such a configuration, the annealing process can be performed without disturbing the impurity diffusion profile.

  According to the solid-state imaging device and the manufacturing method thereof of the present invention, a solid-state imaging device and a manufacturing method thereof that reduce the interface state by effectively terminating dangling bonds on the surface of the silicon substrate and reduce the dark current. realizable.

(One embodiment)
A solid-state imaging device and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a cross-sectional structure of a unit pixel region of a solid-state imaging device according to an embodiment of the present invention.

  The solid-state imaging device of this embodiment includes a plurality of photoelectric conversion units made of photodiodes arranged in a matrix on a substrate 1 made of silicon, and a vertical direction that transfers signal charges read from each photoelectric conversion unit in the column direction. This is a CCD (Charge Coupled Device) type solid-state imaging device including a transfer unit and a horizontal transfer unit that transfers signal charges transferred from the vertical transfer unit in the row direction.

  As shown in FIG. 1, an overflow barrier 11 is formed near the surface of a substrate 1 made of silicon, and an insulating film 18 made of silicon oxide is formed on the surface of the substrate 1. In the well 12 formed between the overflow barrier 11 and the insulating film 18, a photoelectric conversion unit 15 that is a photodiode provided with a hole accumulation layer 15 </ b> A immediately below the insulating film 18 is formed.

  A vertical transfer unit 24A is formed on one side of the photoelectric conversion unit 15 with a reading unit 16 interposed therebetween. The vertical transfer portion 24A is a vertical transfer composed of a vertical transfer channel 20 which is an impurity diffusion layer formed in the well 12, and an insulating film 21 and a polysilicon film 22 sequentially formed above the vertical transfer channel 20 in the insulating film 18. And the electrode 23. A silicon oxide film 25 is formed on the upper surface and side surfaces of the vertical transfer electrode 23.

  On the other side of the photoelectric conversion unit 15, a vertical transfer unit 24 </ b> B that transfers a signal charge read from another adjacent photoelectric conversion unit (not shown) is formed. The photoelectric conversion unit 15 and the vertical transfer unit Between 24B, a channel stop portion 17 is formed.

  On the insulating film 18, a light shielding film 26 having an opening in a region above the central portion of the photoelectric conversion unit 15 is formed. The light shielding film 26 covers the upper and side surfaces of the vertical transfer electrode 23 covered with the silicon oxide film 25 and the upper side of the outer edge portion of the photoelectric conversion unit 15, and light is incident on a region other than the light receiving region of the photoelectric conversion unit 15. To prevent.

  A transparent insulating film 31 made of silicon oxynitride (SiON) is formed on the light shielding film 26 so as to fill the opening. A transparent protective film 32 for protecting the pixel region and the peripheral circuit portion (not shown) is formed on the transparent insulating film 31. On the transparent protective film 32, an in-layer lens 33, a color filter ( (Not shown), a micro on-chip lens (not shown), etc. are formed as needed.

  In the present embodiment, the transparent insulating film 31 is formed of SiON. Since SiON has a larger amount of hydrogen desorption during annealing than silicon nitride (SiN), the transparent insulating film 31 made of SiON functions as an efficient hydrogen supply source. FIG. 2 shows the relationship between the amount of hydrogen desorbed from the SiON film and the SiN film and the temperature. In FIG. 2, the horizontal axis represents temperature, and the vertical axis represents signal intensity serving as an index of hydrogen desorption. The amount of hydrogen desorption was measured by thermal desorption mass spectrometry (TDS).

  As shown in FIG. 2, the SiON film begins to desorb hydrogen at a lower temperature than the SiN film, and has a larger cumulative hydrogen desorption amount up to about 500 ° C. than the SiN film. Therefore, it is clear that the SiON film is a better hydrogen supply source than the SiN film.

  In the present embodiment, since the transparent insulating film 31 made of SiON that is an excellent hydrogen supply source is formed so as to be in contact with the insulating film 18 on the upper side of the photoelectric conversion unit 15, in the solid-state imaging device of the present embodiment. The hydrogen can be effectively supplied to the interface between the insulating film 18 and the silicon substrate 1 by the low temperature annealing treatment at 500 ° C. or lower. Therefore, dangling bonds generated on the surface of the substrate 1 can be terminated with hydrogen, and as a result, the interface state and thus the dark current can be greatly reduced. Further, since the annealing process is performed at a temperature of 500 ° C. or lower, it is possible to prevent the impurity profile formed so far from fluctuating greatly.

  Below, the manufacturing method of the solid-state image sensor of this embodiment is demonstrated. As in the conventional case, p-type impurities are implanted into a predetermined position in the surface layer portion of the silicon substrate 1 to form the overflow barrier 11. Subsequently, the readout unit 16 and the channel stop unit 17 are formed at predetermined intervals. Next, n-type impurities are implanted, the photoelectric conversion unit 15 is formed between the readout unit 16 and the channel stop unit 17, and the vertical transfer channel 20 is formed outside the readout unit 16 and the channel stop unit 17, respectively. .

  Next, an insulating film 18 is formed on the surface of the silicon substrate 1 by thermal oxidation or CVD. Subsequently, an insulating film 21 and a polysilicon film 22 made of silicon nitride and silicon oxide are sequentially formed on the insulating film 18. The formed insulating film 21 and polysilicon film 22 are patterned by a known lithography technique and etching technique to form a vertical transfer electrode 23 on the upper side of the vertical transfer channel 20, and then the surface of the vertical transfer electrode 23 is subjected to a thermal oxidation method or the like. Thus, a silicon oxide film 25 is formed. After the insulating film 21 formed above the photoelectric conversion unit 15 is removed by a known wet etching technique, a p-type impurity is implanted into a relatively shallow position of the surface layer portion of the silicon substrate 1, and the upper portion of the light receiving unit 15. Then, the hole accumulating portion 15A is formed.

  Next, after depositing a metal film such as aluminum and tungsten by sputtering or CVD, patterning is performed by a known lithography technique or etching technique to cover the vertical transfer electrode 23 and the center of the photoelectric conversion portion 15 in the insulating film 18. A light shielding film 26 having an opening is formed above the portion.

  Next, a transparent insulating film 31 made of SiON is deposited on the light shielding film 26 by a plasma CVD (chemical vapor deposition) method so as to fill the opening, and only on the transparent insulating layer 31 as a peripheral circuit portion protective layer. Instead, a transparent protective film 32 made of SiN that functions as a hydrogen permeation suppression layer is formed.

  Thereafter, annealing is performed for 30 minutes at a temperature of 450 ° C. in an atmosphere containing hydrogen. As a result, hydrogen is released from the transparent insulating film 31 to terminate dangling bonds on the surface of the substrate 1. Note that the annealing temperature is preferably 350 ° C. or higher in view of the accumulated hydrogen desorption amount, and is preferably 500 ° C. or lower which does not affect the impurity diffusion profile.

  Finally, the outermost surface is flattened by a known CMP technique, and an inner lens 33, a color filter (not shown), a micro-on-chip lens (not shown), and the like are formed as necessary.

  In the present embodiment, the transparent protective film 32 is formed separately after the transparent insulating film 31 is deposited. However, after depositing the transparent insulating film 31 made of SiON as shown in FIG. The transparent protective film may be formed integrally with the transparent insulating film 31 by continuously forming the SiN film 31 </ b> B serving as a hydrogen permeation inhibiting film. In this case, the transparent protective film for protecting the peripheral circuit portion can be substituted with a deposited film used for forming the inner lens.

Further, the composition of the transparent insulating film 31 may be changed continuously or stepwise in the film. For example, as shown in FIG. 4, when the transparent insulating film 31 is deposited by plasma CVD, monosilane (SiH ₄ ) gas and oxygen dinitride (N ₂ O) gas are supplied to the chamber at the start of deposition, and the oxygen content is high. SiON is deposited. Thereafter, the supply amount of N ₂ O gas is gradually decreased, and ammonia (NH ₃ ) gas is supplied while gradually increasing the amount instead. Thereby, SiON having a high nitrogen content is deposited on the transparent insulating film 31.

Thus, the lower portion of the transparent insulating film 31 becomes a high oxygen-containing region 31C having a high oxygen content and a large amount of hydrogen released, and the upper portion becomes a high nitrogen-containing region 31D having a high nitrogen content and excellent hydrogen permeation inhibiting properties. Further, the upper portion of the transparent insulating film 31 may be a film made of SiN by finally stopping the supply of N ₂ O gas.

  As described above, by changing the composition of the transparent insulating film 31 in the film, the interface between the SiN film and the SiON film which becomes a charge trap can be eliminated. For this reason, it becomes possible to reduce the dark current etc. based on the potential fluctuation | variation of the photoelectric conversion part 15 formed under the transparent insulating film 31. FIG. In addition, since reflection and interference of incident light are reduced, it is possible to suppress a decrease in sensitivity of the solid-state imaging device.

  In addition, as shown in FIG. 5, you may form the antireflection film 35 which consists of SiN by the well-known low pressure CVD method or plasma CVD method in the upper part of the photoelectric conversion part 15 in the insulating film 18. As shown in FIG. In this case, the antireflection film 35 and the light shielding layer 22 are separated from each other, and the transparent insulating film 31 made of SiON is filled therebetween, so that the insulating film 18 and the transparent insulating film 31 are in contact with each other. With such a configuration, hydrogen is supplied from SiON at the portion where the insulating film 18 and the transparent insulating film 31 are in contact with each other, so that dark current can be reduced.

  The solid-state imaging device and the manufacturing method thereof according to the present invention realize a solid-state imaging device and a manufacturing method thereof with less dark current by effectively reducing dangling bonds on the surface of the silicon substrate to reduce the interface state. It is useful as a solid-state imaging device and a manufacturing method thereof.

It is sectional drawing which shows the unit pixel of the solid-state image sensor which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the amount of hydrogen desorption in the silicon oxynitride film used for the solid-state image sensing device concerning one embodiment of the present invention, and temperature compared with a silicon nitride film. It is sectional drawing which shows the unit pixel of the solid-state image sensor which concerns on one Embodiment of this invention. It is sectional drawing which shows the unit pixel of the solid-state image sensor which concerns on one Embodiment of this invention. It is sectional drawing which shows the unit pixel of the solid-state image sensor which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 11 Overflow barrier 12 Well 15 Photoelectric conversion part 15A Hole accumulation layer 16 Reading part 17 Channel stop part 18 Insulating film 20 Vertical transfer channel 21 Insulating film 22 Polysilicon film 23 Vertical transfer electrode 24A Vertical transfer part 24B Vertical transfer part 25 Silicon oxide film 26 Light-shielding film 31 Transparent insulating film 31A SiN film 31B SiN film 31C High oxygen-containing region 31D High nitrogen-containing region 32 Transparent protective film 33 In-layer lens 35 Antireflection film

Claims (9)

A photoelectric conversion unit that is formed on a semiconductor substrate and performs photoelectric conversion;
An insulating film formed on the upper surface of the semiconductor substrate so as to cover the photoelectric conversion unit;
A light shielding film having an opening formed on the insulating film and exposing an upper portion of the photoelectric conversion unit;
A transparent insulating film that is formed on the light shielding film so as to fill the opening and transmits light,
The solid-state imaging device, wherein the transparent insulating film is a silicon oxynitride film.   The solid-state imaging device according to claim 1, further comprising a hydrogen permeation suppression film made of silicon nitride and formed on the transparent insulating film.   3. The solid-state imaging device according to claim 1, wherein the silicon oxynitride film has a higher oxygen content in the lower part than in the upper part and a higher nitrogen content in the upper part than in the lower part.   The solid-state imaging device according to claim 3, wherein the nitrogen content of the silicon oxynitride film continuously changes. A plurality of the photoelectric conversion units are formed in a matrix on the semiconductor substrate,
A vertical transfer unit that transfers signal charges read from the photoelectric conversion units in a column direction;
A horizontal transfer unit for transferring the signal charges transferred from the vertical transfer unit in the row direction,
5. The solid-state imaging device according to claim 1, wherein the solid-state imaging device functions as a CCD type solid-state imaging device. 6. Forming a photoelectric conversion part for performing photoelectric conversion on a semiconductor substrate;
Forming an insulating film covering the photoelectric conversion part on the upper surface of the semiconductor substrate;
Forming a light shielding film having an opening exposing the upper portion of the photoelectric conversion part on the insulating film (c);
(D) forming a transparent insulating film on the light-shielding film using a plasma chemical vapor deposition method so as to fill the opening,
The step (d) includes a first step of depositing a silicon oxynitride film by supplying monosilane gas and oxygen dinitride gas as source gases, further supplying ammonia gas as the source gas, and supplying the source gas to the source gas And a second step of depositing a silicon oxynitride film while gradually increasing the amount of ammonia gas while gradually reducing the amount of oxygen dinitride gas contained therein.   7. The solid-state imaging device according to claim 6, wherein the step (d) includes a step of forming a silicon nitride film by supplying monosilane gas and ammonia gas as source gases after the second step.   The method for manufacturing a solid-state imaging device according to claim 6, further comprising a step of performing an annealing process in a hydrogen atmosphere after the step (d). The method for manufacturing a solid-state imaging device according to claim 7, wherein the annealing treatment is performed at a treatment temperature of 500 ° C. or less.

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