Image pickup apparatus, image pickup system, and method for manufacturing image pickup apparatus

An image pickup apparatus includes a semiconductor layer that constitutes a pixel circuit region and a peripheral circuit region. An element isolation portion is disposed in the pixel circuit region and the peripheral circuit region, defines an element portion of the semiconductor layer, and contains an insulator. The element isolation portion in the pixel circuit region has a hydrogen concentration 10 times or more higher than the hydrogen concentration of the element isolation portion in the peripheral circuit region.

BACKGROUND OF THE INVENTION

Field of the Invention

The present technique relates to an image pickup apparatus including a pixel circuit region and a peripheral circuit region.

Description of the Related Art

Image pickup apparatuses include a monolithic semiconductor device that includes a pixel circuit region and a peripheral circuit region on a single semiconductor layer. Different conditions are required to improve the characteristics of the pixel circuit region and the peripheral circuit region. More specifically, the pixel circuit region requires noise reduction in the pixel circuit, and the peripheral circuit region requires improved reliability of the peripheral circuit. It is known that hydrogen termination of a dangling bond on a surface of a semiconductor layer is effective in reducing noise in the pixel circuit region. However, the presence of hydrogen in the peripheral circuit region may be responsible for low reliability of the peripheral circuit. Thus, the characteristics of the pixel circuit region and the peripheral circuit region should be simultaneously improved.

Japanese Patent Laid-Open No. 2009-188068 discloses a solid-state image pickup element that includes a pixel unit, a peripheral circuit unit, and a passivation film on the pixel unit and the peripheral circuit unit, wherein the passivation film serving as a hydrogen supply source is configured to have different residual hydrogen contents on the pixel unit and the peripheral circuit unit. It is stated that such a structure can ensure the reliability of a miniaturized transistor in the peripheral circuit unit with respect to temporal changes in threshold and satisfactorily decrease dark voltage on a surface of the pixel unit. The pixel unit and peripheral circuit unit in Japanese Patent Laid-Open No. 2009-188068 correspond to the pixel circuit region and peripheral circuit region in the image pickup apparatus.

In the technique described in Japanese Patent Laid-Open No. 2009-188068, hydrogen supply to a semiconductor layer in an image pickup apparatus is not fully studied. In the image pickup apparatus, a conductive line or an insulating film on a hydrogen supply path extending from the passivation film to the semiconductor layer can restrict hydrogen supply from the passivation film to the semiconductor layer. Thus, different residual hydrogen contents of the passivation film in the pixel circuit region and the peripheral circuit region are not sufficient to cause a great difference in the amount of hydrogen supplied to the semiconductor layer between the pixel circuit region and the peripheral circuit region. Consequently, the characteristics of the pixel circuit region and the peripheral circuit region cannot be simultaneously improved.

SUMMARY OF THE INVENTION

The present disclosure provides an advantageous technique for improving the characteristics of both the pixel circuit region and the peripheral circuit region.

The present disclosure provides an image pickup apparatus including a semiconductor layer that constitutes a pixel circuit region and a peripheral circuit region. An element isolation portion is disposed in the pixel circuit region and the peripheral circuit region, defines an element portion of the semiconductor layer, and contains an insulator. The element isolation portion in the pixel circuit region has a hydrogen concentration 10 times or more higher than the hydrogen concentration of the element isolation portion in the peripheral circuit region.

The present disclosure also provides an image pickup apparatus including a semiconductor layer that constitutes a pixel circuit region and a peripheral circuit region. An element isolation portion is disposed in the pixel circuit region and the peripheral circuit region, defines an element portion of the semiconductor layer, and contains an insulator. A gate-insulating film of a MIS transistor in the peripheral circuit region has a thickness of 35 angstroms or less on a silicon oxide basis. The element isolation portion in the pixel circuit region has a higher hydrogen concentration than the element isolation portion in the peripheral circuit region.

The present disclosure also provides an image pickup apparatus including a semiconductor layer that constitutes a pixel circuit region and a peripheral circuit region. An element isolation portion is disposed in the pixel circuit region and the peripheral circuit region, defines an element portion of the semiconductor layer, and contains an insulator. A passivation film containing hydrogen, a first conductive line between the passivation film and the semiconductor layer, and a second conductive line between the first conductive line and the passivation film are disposed on the semiconductor layer in the pixel circuit region. The first conductive line and the second conductive line include an aluminum layer and a barrier metal portion containing at least one of titanium nitride and titanium. The element isolation portion in the pixel circuit region has a higher hydrogen concentration than the element isolation portion in the peripheral circuit region.

The present disclosure also provides a method for manufacturing an image pickup apparatus including a semiconductor layer that constitutes a pixel circuit region and a peripheral circuit region. The method includes preparing a semiconductor layer in the pixel circuit region and the peripheral circuit region, the semiconductor layer including an element portion defined by an element isolation portion containing an insulator, forming a member on the semiconductor layer, the member overlapping the element isolation portion in the peripheral circuit region and not overlapping at least part of the element isolation portion in the pixel circuit region, and implanting accelerated hydrogen ions into the element isolation portion in the pixel circuit region using the member as a mask.

DESCRIPTION OF THE EMBODIMENTS

The present inventor came up with the idea that an insulator of an element isolation portion near a surface of a semiconductor layer can be used as a hydrogen supply source. The present inventor found that the characteristics of a pixel circuit region and a peripheral circuit region can be simultaneously improved by making the concentration of hydrogen in the insulator of the element isolation portion higher in the peripheral circuit region than in the pixel circuit region.

Embodiments of the present technique will be described below with reference to the accompanying drawings. Like components are denoted by like reference numerals throughout the drawings and will not be described again.

FIG. 1Aillustrates an image pickup device IC, which constitutes the whole or part of an image pickup apparatus. The image pickup device IC is a semiconductor device including an integrated circuit, and the image pickup apparatus is a semiconductor apparatus. The semiconductor device may be a semiconductor chip manufactured by dicing a semiconductor wafer.

The image pickup device IC includes a pixel circuit region2and a peripheral circuit region3on a substrate1. The pixel circuit region2includes pixel circuits PXC arranged in a matrix. The peripheral circuit region3includes a peripheral circuit. InFIG. 1A, the pixel circuit region2is a region within the dash-dot line. The pixel circuit region2includes at least a pixel circuit that forms an effective pixel and optionally includes a pixel circuit for reference signals and/or a pixel circuit for focus detection signals. The pixel circuit that forms an effective pixel may also serve as a pixel circuit for focus detection signals.

InFIG. 1A, the peripheral circuit region3is a region between the dash-dot line and the dash-dot-dot line and surrounds the pixel circuit region2. A peripheral circuit in the peripheral circuit region3includes a signal processing unit40, an output unit50, and a drive unit60, for example. The signal processing unit40processes signals from a column of the pixel circuits PXC. The signal processing unit40includes an amplifying circuit41including a plurality of column amplifiers, a conversion circuit42including a plurality of column AD converters, and a horizontal scanning circuit43for selecting an output from the conversion circuit42and outputting the output to the output unit50. The drive unit60includes a vertical scanning circuit61for driving a row of the pixel circuits PXC and a timing generating circuit62for controlling the operation timing of the horizontal scanning circuit43and the vertical scanning circuit61.

FIG. 1Billustrates an example of the circuit arrangement of the pixel circuit PXC. The pixel circuit PXC includes a photoelectric conversion unit PD, a transfer gate TX, an electric carrier detecting unit FD, an amplifying transistor SF, a reset transistor RS, and a selection transistor SL. A transistor that includes the photoelectric conversion unit PD as a source, the transfer gate TX as a gate, and the electric carrier detecting unit FD as a drain is referred to as a transfer transistor. The amplifying transistor SF, the selection transistor SL, and the reset transistor RS are collectively referred to as a pixel transistor PX. All of the transfer transistor and the pixel transistor PX in the present embodiment are N-type metal insulator semiconductor (MIS) transistors. However, the pixel circuit PXC may be composed of an N-type MIS transistor and a P-type MIS transistor or may be composed of a P-type MIS transistor alone. At least one transistor in the pixel circuit PXC may be a transistor other than MIS transistors, for example, a junction field effect transistor (JFET) or a bipolar transistor. The term “MIS transistors”, as used herein, are synonymous with insulated-gate field-effect transistors, and the material of gate-insulating films is not limited to pure silicon oxide. The material of gate-insulating films may be silicon nitride, silicon oxide containing nitrogen, or a low-k material, such as hafnium oxide.

The transfer gate TX transfers signal carriers from the photoelectric conversion unit PD to the electric carrier detecting unit FD. The electric carrier detecting unit FD is coupled to a gate of the amplifying transistor SF. The amplifying transistor SF is coupled to a power supply line VDD. The amplifying transistor SF is coupled to an output line OUT via the selection transistor SL. The amplifying transistor SF constitutes a source follower circuit and outputs signals to the output line OUT according to the electric potential of the electric carrier detecting unit FD. The selection transistor SL enables or disables output from the pixel circuit PXC. The reset transistor RS resets the electric potential of the electric carrier detecting unit FD to the reset voltage. In the present embodiment, the electric potential from the power supply line VDD is used as a reset voltage. The pixel circuit PXC may further include a switching unit for changing the capacity of the electric carrier detecting unit FD, in addition to the transfer gate TX, the amplifying transistor SF, and the reset transistor RS. Part of the functions of a signal-processing circuit coupled to a column of the pixel circuits PXC may be incorporated into the pixel circuits PXC.

FIG. 1Cillustrates an image pickup system SYS including an image pickup apparatus IS. The image pickup system SYS is an information terminal having a camera or a photographing function. The image pickup apparatus IS may further include a package PKG for housing the image pickup device IC. The package PKG may include a base to which the image pickup device IC is fixed, a lid facing the image pickup device IC, and a connection member for coupling a terminal of the base to a terminal of the image pickup device IC. The image pickup apparatus IS may include a plurality of the image pickup devices IC in the package PKG. The image pickup apparatus IS may include another semiconductor device IC disposed on the image pickup device IC in the package PKG.

The image pickup system SYS may include an optical system OU for focusing on the image pickup apparatus IS. The image pickup system SYS may include at least one of a control unit CU, a processing unit PU, a display unit DU, and a memory unit MU. The control unit CU controls the image pickup apparatus IS. The processing unit PU processes signals sent from the image pickup apparatus IS. The display unit DU displays images sent from the image pickup apparatus IS. The memory unit MU stores images sent from the image pickup apparatus IS.

With respect to an image pickup apparatus IS according to a first embodiment,FIG. 2illustrates a partial section structure of one pixel circuit PXC in the pixel circuit region2and a partial section structure of a peripheral circuit in the peripheral circuit region3illustrated inFIG. 1A.

The image pickup apparatus IS includes a semiconductor layer100, which constitutes the pixel circuit region2and the peripheral circuit region3. Typically, the semiconductor layer100is a single-crystal silicon layer. The semiconductor layer100may be an epitaxial layer on the substrate1, may be an impurity layer in bulk silicon, or may be a semiconductor layer on the substrate1with an interlayer insulating film interposed therebetween.

In the pixel circuit region2, an element portion of the semiconductor layer100is defined by an element isolation portion102formed of an insulator. The element portion may also be referred to as an active region, and the element isolation portion may also be referred to as a field region. In the peripheral circuit region3, an element portion of the semiconductor layer100is defined by an element isolation portion103formed of an insulator. The element isolation portions102and103formed of an insulator may have a local oxidation of silicon (LOCOS) structure or a shallow trench isolation (STI) structure. The element isolation portions102and103may have an element isolation structure in which an insulator film on a surface of the semiconductor layer functions as an element isolation insulator, and part or all of the insulator film protrudes from the surface of the semiconductor layer. The element isolation portion102in the pixel circuit region2may have a different structure from the element isolation portion103in the peripheral circuit region3. For example, the element isolation portion102in the pixel circuit region2may have a LOCOS structure, and the element isolation portion103in the peripheral circuit region3may have a STI structure. The depth of the element isolation portion102in the pixel circuit region2from the surface of the semiconductor layer100may be larger than the depth of the element isolation portion103in the peripheral circuit region3from the surface of the semiconductor layer100. In the present embodiment, the insulators of the element isolation portions102and103contain a main component and hydrogen. Typically, the main component of the insulator of each of the element isolation portions102and103is silicon oxide. The hydrogen concentration CA of the insulator of the element isolation portion102in the pixel circuit region2is higher than the hydrogen concentration CB of the insulator of the element isolation portion103in the peripheral circuit region3(CB<CA). The hydrogen concentration CA of the insulator of the element isolation portion102in the pixel circuit region2is preferably 10 times or more the hydrogen concentration CB of the insulator of the element isolation portion103in the peripheral circuit region3(10×CB≦CA).

In a process of manufacturing an image pickup apparatus, the image pickup device IC have various defects. Such defects include point defects in the semiconductor layer100and interface states at the interface between the semiconductor layer100and the element isolation portion102. Such defects also include interface states at the interfaces between the semiconductor layer100and the gate-insulating films111and112and defects in the gate-insulating films111and112. These defects cause performance degradation of transistors and increased noise in a pixel circuit region. Noise in the pixel circuit region2directly affects image quality. Thus, it is desirable that the amount of hydrogen supplied in the pixel circuit region2be increased to promote hydrogen termination of defects. In contrast, it is desirable that the amount of hydrogen supplied in the peripheral circuit region3be reduced to ensure the reliability of a MIS transistor for the following reason. In the image pickup apparatus IS, a MIS transistor in the peripheral circuit region3is being miniaturized due to requirements for high-speed signal processing and lower power consumption. Such miniaturization can cause low reliability of the MIS transistor, such as low hot carrier resistance or negative bias temperature instability (NBTI). Excess hydrogen accelerates such characteristic degradation. The characteristics of the pixel circuit region2and the peripheral circuit region3can be simultaneously improved by satisfying CB<CA and 10×CB≦CA.

The concentration of hydrogen in the insulators of the element isolation portions102and103can be determined by secondary ion mass spectrometry (SIMS). The SIMS analysis of the element isolation portions102and103can be performed on a surface (back surface) of the semiconductor layer100opposite a surface (front surface) on which the element isolation portions102and103and the transistors are disposed. The SIMS analysis may be performed on the front surface of the semiconductor layer100after the layers other than the semiconductor layer100and other than the element isolation portions102and103are removed. A method for determining the hydrogen concentrations CA and CB will be described below.

FIG. 3Aillustrates an arrangement of element portions201and an element isolation portion102in the pixel circuit region2and also illustrates a SIMS analysis region202. The analysis region202is a rectangle having a side length of tens of micrometers or a circle having a diameter of tens of micrometers. The analysis region202has an area SC (cm2). The pixel circuit region2includes an array of pixel circuit patterns each having a size of several micrometers. Thus, the analysis region202includes several to tens of pixel circuit patterns. The hydrogen density DA (atoms/cm3) of the analysis region202is determined by SIMS. Because the pixel circuit region2includes an array of pixel circuit patterns, any area in the analysis region202has almost the same hydrogen density DA as measured by SIMS. The element portions201are made of silicon having a low hydrogen solubility limit, whereas the element isolation portion102is made of an insulator, such as silicon oxide, having a high hydrogen solubility limit. Thus, the element portions201have a negligible hydrogen concentration compared with the element isolation portion102. Since the analysis region202having the hydrogen density DA includes the element portions201and the element isolation portion102, the hydrogen density DA determined by SIMS is the average hydrogen density of the SIMS analysis region including the element portions201and the element isolation portion102. Since the element portions201have a negligible hydrogen concentration compared with the element isolation portion102, the hydrogen density DA determined by SIMS is not comparable to the hydrogen concentration CA of the element isolation portion102. This is because the element isolation portion102does not spread over the entire analysis region, but the element portions201and the element isolation portion102coexist in the analysis region. Thus, the actual hydrogen concentration CA of the element isolation portion102is determined as described below. First, the area occupancy OA of the element isolation portion102in the analysis region202is determined. The area occupancy can be calculated from the computer-aided design (CAD) data used for the layout design of the element isolation portion102. The area occupancy OA of the element isolation portion102is calculated by dividing the total area SA (cm2) of the element isolation portion102in a plan view of the analysis region202by the area SC of the analysis region202(OA=SA/SC). The hydrogen concentration CA of the insulator of the element isolation portion102is calculated by dividing the hydrogen density DA of the analysis region202by the area occupancy OA of the element isolation portion102(CA=DA/OA). The area occupancy OA is more than 0 and less than 1 and typically ranges from approximately 0.2 to 0.6. In the image pickup apparatus IS, in order to increase the light receiving area of the photoelectric conversion unit PD, the element portions201in the pixel circuit region2are larger than the element isolation portion102, and the area occupancy OA of the element isolation portion102may be 0.5 or less.

FIG. 3Billustrates an arrangement of element portions301and an element isolation portion103in the peripheral circuit region3and also illustrates a SIMS analysis region203. The peripheral circuit region3is analyzed by SIMS in the same manner as described above. Unlike the pixel circuit region2, the peripheral circuit region3has a random circuit pattern. Thus, the area occupancy of the element isolation portion103in the analysis region203varies in different SIMS analysis areas. Thus, the area occupancy of each element isolation portion103in regions203aand203bin the peripheral circuit region3is determined. The outlines of the regions203aand203bare geometrically identical with the outline of the analysis region202in the pixel circuit region2. The average area occupancy OB of the element isolation portions103are calculated from the area occupancies thus determined. The area occupancies can be calculated from the CAD data used for the layout design of the element isolation portion103. The area occupancy OB is more than 0 and less than 1 and typically ranges from approximately 0.4 to 0.8. A region that has the average area occupancy OB and is geometrically identical with the analysis region202in the pixel circuit region2is selected as the analysis region203in the peripheral circuit region3. The hydrogen density DB (atoms/cm3) of the analysis region203is determined by SIMS. The hydrogen concentration CB of the insulator of the element isolation portion103is calculated by dividing the hydrogen density DB of the analysis region203by the area occupancy OB of the element isolation portion103(CB=DB/OB).

In the image pickup apparatus IS, in order to increase the light receiving area of the photoelectric conversion unit PD, the element portions201in the pixel circuit region2are larger than the element isolation portion102. Thus, the area occupancy OA of the element isolation portion102in the pixel circuit region2is lower than the area occupancy OB of the element isolation portion103in the peripheral circuit region3(OA<OB). The amount of hydrogen per unit volume supplied from the element isolation portion can be higher in the pixel circuit region2than in the peripheral circuit region3. The amount QA of hydrogen per unit volume available from the element isolation portion102in the pixel circuit region2is proportional to the product of the hydrogen concentration CA and the area occupancy OA (QA∝CA×OA). Likewise, the amount QB of hydrogen per unit volume available from the element isolation portion103in the peripheral circuit region3is proportional to the product of the hydrogen concentration CB and the area occupancy OB (QB∝CB×OB). Thus, satisfying QB<QA means satisfying CB×OB<CA×OA. In order to satisfy both OA<OB and CB×OB<CA×OA, 10×CB≦CA can be satisfied. On the basis of CA×OA=DA and CB×OB=DB, whether QB<QA is satisfied can be judged by comparing the amounts of hydrogen measured by SIMS in the analysis regions202and203having the same shape.

The photoelectric conversion unit PD inFIG. 1Bis a photodiode and is composed of an n-type impurity region105and a p-type impurity region106inFIG. 2. The impurity region105functions as an accumulation region in which signal carriers accumulate. The photodiode has an embedded structure in which a p-type impurity region107is disposed between the impurity region105and a surface of the semiconductor layer100.

A conductivity type in which electric carriers treated as signal carriers in the pixel circuit are majority carriers is hereinafter referred to as a first conductivity type, and a conductivity type in which electric carriers treated as signal carriers are minority carriers is hereinafter referred to as a second conductivity type. In the case that signal carriers are electrons, the n-type is the first conductivity type, and the p-type is the second conductivity type. In the case that signal carriers are positive holes, the p-type is the first conductivity type, and the n-type is the second conductivity type.

The p-type impurity region106functions as a well region. The impurity region106may be composed of a plurality of impurity regions having different p-type impurity concentrations. A first element portion including the impurity region105of the photoelectric conversion unit PD includes a gate electrode121and an impurity region104. The gate electrode121constitutes the transfer gate TX. The impurity region104functions as a floating diffusion region of the electric carrier detecting unit FD. A second element portion separated from the first element portion by the element isolation portion102includes a gate electrode122of the pixel transistor PX, an impurity region109constituting a source/drain, and an impurity region125coupled to a contact plug130.

A MIS transistor in the peripheral circuit is referred to as a peripheral transistor PR. In order to achieve high withstand voltage in the pixel circuit and high speed in the peripheral circuit, a gate-insulating film113of the peripheral transistor PR can have a smaller thickness than a gate-insulating film111of the transfer gate TX and a gate-insulating film112of the pixel transistor PX in the pixel circuit. For example, when the pixel circuit has a driving voltage of 3.3 V, the gate-insulating films111and112of the transfer gate TX and the pixel transistor PX have an equivalent oxide thickness (EOT) of approximately 80 angstroms on a silicon oxide basis. In contrast, when the peripheral circuit has a driving voltage of 1.3 V, the gate-insulating film of the peripheral transistor PR has an equivalent oxide thickness (EOT) of 35 angstroms or less on a silicon oxide basis. When the gate-insulating film113of the MIS transistor in the peripheral circuit has a small thickness, boron contained in a gate electrode123in the peripheral circuit region3diffuses into the semiconductor layer100through the gate-insulating film113. This causes a change in the threshold voltage of the P-type MIS (PMIS) transistor. In order to avoid this problem, a silicon oxide film doped with nitrogen can be used as a gate-insulating film. In general, use of a silicon oxide film doped with nitrogen can reduce changes in the threshold of the PMIS transistor but increase negative bias temperature instability (NBTI). This reduces the reliability of the peripheral transistor PR.

In order to improve the reliability of the peripheral transistor PR, the amount of hydrogen supplied to the peripheral transistor PR can be decreased. As described above, the characteristics of the pixel circuit region2and the peripheral circuit region3can be simultaneously improved by satisfying CB<CA and 10×CB≦CA.

Conductive lines132,135, and138are electroconductive members (aluminum conductive lines) including a conductive portion CM and a barrier metal portion BM. The conductive portion CM is composed of aluminum. The barrier metal portion BM is composed of a titanium layer and/or a titanium nitride layer. The conductive portion CM composed of aluminum may contain a minute amount of copper. The aluminum conductive line may include Ti/TiN/Al/Ti/TiN layers in this order from the side of the semiconductor layer100. Plugs130,131,134, and137are electroconductive members each including a conductive portion and a barrier metal portion. The conductive portion is composed of a tungsten layer. The barrier metal portion is composed of a titanium layer and/or a titanium nitride layer. Like the conductive lines132,135, and138, an electroconductive member including a conductive portion composed of an aluminum layer and a barrier metal portion composed of a titanium layer and/or a titanium nitride layer may also be used as a light-shielding member. The conductive lines and plugs may also be electroconductive members (copper conductive lines) including a conductive portion composed of a copper layer and a barrier metal portion composed of a tantalum layer and/or a tantalum nitride layer.

In the barrier metal portion of the electroconductive members (conductive lines) above the semiconductor layer100, titanium occludes hydrogen, and titanium nitride restricts hydrogen diffusion. The conductive line132is disposed between a passivation film139and the semiconductor layer100. The conductive lines135and138are disposed between the conductive line132and the passivation film139. Such a barrier metal portion composed of a titanium layer and a titanium nitride layer above the semiconductor layer100prevents hydrogen supplied from above from reaching the semiconductor layer100.

In the present embodiment, the element isolation portion102near the semiconductor layer100contains more hydrogen than the element isolation portion103. Thus, hydrogen can be supplied to the semiconductor layer100with a minor influence of the titanium layer and/or the titanium nitride layer.

An interlayer insulating film129is disposed between the conductive line132and the semiconductor layer100in the pixel circuit region2and the peripheral circuit region3. An interlayer insulating film133is disposed between the conductive line132and the conductive line135. The plug134penetrates the interlayer insulating film133. An interlayer insulating film136is disposed between the conductive line135and the conductive line138. The plug137penetrates the interlayer insulating film136. The pixel circuit region2includes a silicon nitride layer110between the interlayer insulating film129and the element isolation portion102. The peripheral circuit region3includes a silicon nitride layer120between the interlayer insulating film129and the element isolation portion103. The plug130penetrates the silicon nitride layer110, and the plug131penetrates the silicon nitride layer120. The silicon nitride layers110and120may also restrict hydrogen diffusion. In the present embodiment, the element isolation portion102near the semiconductor layer100contains more hydrogen than the element isolation portion103. Thus, hydrogen can be supplied to the semiconductor layer100with a minor influence of the silicon nitride layers110and120.

The photoelectric conversion unit PD, the transfer gate TX, and the electric carrier detecting unit FD are covered with the silicon nitride layer110. The silicon nitride layer110also covers the pixel transistor PX, more specifically, the amplifying transistor SF. If the silicon nitride layer110restricts hydrogen supply from the outside, hydrogen supply to the photoelectric conversion unit PD and the amplifying transistor SF is also restricted. This can increase dark current in the photoelectric conversion unit PD, the transfer gate TX, and the electric carrier detecting unit FD, and increase random noise in the amplifying transistor SF. In the present embodiment, the element isolation portion102near the semiconductor layer100contains more hydrogen than the element isolation portion103. Thus, hydrogen can be supplied to the semiconductor layer100even in the presence of the silicon nitride layer110.

The interlayer insulating film129may be a borosilicate glass (BSG) layer, a phosphosilicate glass (PSG) layer, or a boron-phosphosilicate glass (BPSG) layer. The BSG layer, PSG layer, and BPSG layer may restrict hydrogen diffusion. When copper conductive lines are used, a silicon carbide layer or a silicon nitride layer is used as a diffusion-barrier layer. The silicon carbide layer or silicon nitride layer may also restrict hydrogen diffusion. Because the element isolation portion102near the semiconductor layer100contains more hydrogen than the element isolation portion103in the present embodiment, hydrogen can be supplied to the semiconductor layer100with a minor influence of the BSG layer, PSG layer, BPSG layer, silicon carbide layer, or silicon nitride layer. The interlayer insulating films133and136are silicon oxide layers.

At least the uppermost conductive line138in the peripheral circuit region3is covered with the passivation film139. The conductive line138functions as a grid-like light-shielding member in the pixel circuit region2. A light-shielding member (not shown) for shading a photoelectric conversion unit in a light shielded pixel is disposed at the same height as the conductive line138from the semiconductor layer100. The passivation film139extends over a plurality of the photoelectric conversion units PD in the pixel circuit region2. The passivation film139contains hydrogen and can supply hydrogen to the semiconductor layer100, in addition to hydrogen supply from the element isolation portions102and103to the semiconductor layer100. The passivation film139can include a silicon nitride layer mainly containing hydrogen and a silicon oxynitride layer for suppressing reflection from the top and/or bottom surface of the silicon nitride layer. A planarizing film140, a color filter141, and a microlens142are disposed on the passivation film139.

A method for manufacturing an image pickup apparatus IS according to a first embodiment will be described below with reference toFIGS. 4A to 4CandFIGS. 5A and 5B.

In a process a1illustrated inFIG. 4A, first, an element isolation portion101is formed on or above a semiconductor layer100in a pixel circuit region2and a peripheral circuit region3, for example, by a LOCOS method or a STI method. Impurity regions106and108are then formed as well regions. Gate-insulating films111and112of a pixel transistor PX and a gate-insulating film113of a peripheral transistor PR are then formed. The gate-insulating films111,112, and113can be converted into silicon oxide films containing nitrogen by thermal oxynitriding of the semiconductor layer100or by plasma nitriding of a silicon oxide film formed by thermal oxidation of the semiconductor layer100. Then, a gate electrode121is formed on the gate-insulating film111, a gate electrode122made of polysilicon is formed on the gate-insulating film112, and a gate electrode123is formed on the gate-insulating film113. The gate electrodes121and122may contain an n-type impurity, such as phosphorus. The gate electrodes121and123may contain a p-type impurity, such as boron. An electrical resistance124made of polysilicon is formed. Impurity regions104,105,109,107, and114are then formed.

In a process b1illustrated inFIG. 4B, first, the semiconductor layer100in the pixel circuit region2and the peripheral circuit region3is covered with a dielectric film. The dielectric film formed in the process b1is a silicon nitride monolayer film or a multilayer film including a silicon nitride layer and a silicon oxide layer. While a portion of the dielectric film in the pixel circuit region2is covered with a mask, a portion of the dielectric film in the peripheral circuit region3is etched. Thus, a sidewall spacer115is formed on the side walls of the gate electrode123. An impurity region116is formed in the source/drain of the peripheral transistor PR using the sidewall spacer115as a mask. The high-concentration impurity region116and the low-concentration impurity region114can constitute a lightly doped drain (LDD) structure in the source/drain of the peripheral transistor PR. An impurity region is formed in the semiconductor layer100by ion implantation and is activated by heat treatment at a temperature in the range of approximately 800° C. to 1100° C.

The unetched portion of the dielectric film in the pixel circuit region2is a silicon nitride layer110. The silicon nitride layer110can function as a protective layer for protecting the pixel circuit region2from metal contamination or plasma damage and thereby reduce the number of white defects. The silicon nitride layer110more greatly restricts hydrogen diffusion than the silicon oxide layer. Thus, the silicon nitride layer110can restrict hydrogen supply when hydrogen is supplied to the semiconductor layer100from above during heat treatment in a downstream process.

In a process c1illustrated inFIG. 4C, first, the pixel circuit region2and the electrical resistance124are covered with an insulator layer117. The peripheral transistor PR is not covered with the insulator layer117. The semiconductor layer100in the pixel circuit region2and the peripheral circuit region3is then covered with a metal film. The material of the metal film can be cobalt, nickel, tungsten, molybdenum, tantalum, chromium, palladium, and/or platinum, typically, cobalt or nickel. A self-aligned silicide (salicide) process is then performed using the insulator layer117for silicide protection. More specifically, a contact portion between the semiconductor layer100and the metal film is selectively silicidized by heat treatment. The heat treatment is performed at a temperature in the range of 400° C. to 600° C. in a first stage for forming monosilicide and at a temperature in the range of 700° C. to 1000° C. in a second stage for forming disilicide. Thus, silicide regions118and119formed of a silicide of a metal contained in the metal film are formed in the peripheral transistor PR. Typically, the silicide regions118and119are cobalt silicide regions or nickel silicide regions. The silicide region118does not have to be disposed on the gate electrode123. The insulator layer117covering the electrical resistance124can prevent a decrease in electrical resistance resulting from silicidation of the electrical resistance124. Unreacted metals in the salicide process are removed from the insulator layer117.

In a process d1illustrated inFIG. 5A, a mask member310is formed over the semiconductor layer100thus formed. The mask member310is composed of a resin, such as a photoresist. The mask member310covers the element isolation portion103in the peripheral circuit region3. The mask member310has an opening311on at least part of the element isolation portion102in the pixel circuit region2. Thus, the mask member310does not overlap at least part of the element isolation portion102in the pixel circuit region2. Although the mask member310covers the element portion in the pixel circuit region2, the mask member310does not have to cover the element portion in the pixel circuit region2. The mask member310may be disposed only on the element isolation portion103in the peripheral circuit region3. Accelerated hydrogen ions are implanted into the element isolation portion102in the pixel circuit region2using the mask member310as a mask. The ion implantation is performed through the mask member310such that the concentration of hydrogen in the insulator of the element isolation portion102in the pixel circuit region2is higher than the concentration of hydrogen in the insulator of the element isolation portion103in the peripheral circuit region3. Although part of accelerated hydrogen ions may also be implanted into the element isolation portion103through the mask member310, the number of implanted hydrogen ions is much smaller in the element isolation portion103than in the element isolation portion102not covered with the mask member310. The ion implantation method allows hydrogen to be implanted into the element isolation portion102even when the element isolation portion102in the pixel circuit region2is covered with the silicon nitride layer110. Furthermore, even when the photoelectric conversion unit PD or the amplifying transistor SF is covered with the silicon nitride layer110, hydrogen can be implanted into the element isolation portion102, and therefore the element isolation portion102can supply sufficient hydrogen to the photoelectric conversion unit PD and the amplifying transistor SF. After hydrogen ions are implanted, the mask member310is removed.

In a process e1illustrated inFIG. 5B, the peripheral transistor PR in the peripheral circuit region3is covered with a silicon nitride layer120. The silicon nitride layer120does not cover the pixel transistor PX in the pixel circuit region2. The semiconductor layer100in the pixel circuit region2and the peripheral circuit region3is then covered with an interlayer insulating film129. The interlayer insulating film129is flattened by reflowing. The heat treatment temperature for the reflowing may range from 600° C. to 1000° C. In order to further improve flatness, the interlayer insulating film129is subjected to chemical mechanical polishing (CMP).

A contact hole is formed in the interlayer insulating film129in the pixel circuit region2. In the formation of the contact hole, the silicon nitride layer110can function as an etching stopper. A contact plug130coupled to the semiconductor layer100or the gate electrode121or122is then formed in the contact hole. A contact hole is formed in the interlayer insulating film129in the peripheral circuit region3. In the formation of the contact hole, the silicon nitride layer120can function as an etching stopper. A contact plug131coupled to the semiconductor layer100or the gate electrode123is then formed in the contact hole. The contact hole for the contact plug130and the contact hole for the contact plug131may be simultaneously or separately formed. The contact plug130and the contact plug131may be simultaneously or separately formed. Before the contact plug130is formed, the impurity region125may be formed by implanting an impurity into the well through a desired contact hole (ion implantation). This can stabilize contact resistance. In order to activate the impurity region125, heat treatment may be performed at a temperature in the range of 600° C. to 900° C. Before the contact plug130is formed, the contact hole for the contact plug130may be washed with an acidic or alkaline solution, such as hydrofluoric acid or an ammonia hydrogen peroxide mixture. The contact hole can be washed after an impurity is implanted into the contact hole. This can reduce contamination of the semiconductor layer100with metals. After the contact plug130is formed, a portion of the semiconductor layer100in contact with the contact plug130may be silicidized by heat treatment at 600° C. or less so as to decrease contact resistance. In this case, a silicide region of tungsten or titanium contained in the contact plug130may be formed in the portion of the semiconductor layer100in contact with the contact plug130.

After that, the structure illustrated inFIG. 2is formed. A conductive line132and an interlayer insulating film133are formed on the interlayer insulating film129. A via plug134coupled to the conductive line132is formed in the interlayer insulating film133. A conductive line135and an interlayer insulating film136are formed on the interlayer insulating film133. A via plug137coupled to the conductive line135is formed in the interlayer insulating film136. A conductive line138is formed on the interlayer insulating film136. The interlayer insulating films133and136may be silicon oxide films formed by high-density plasma (HDP)-chemical vapor deposition (CVD). This can increase the hydrogen contents of the interlayer insulating films133and136. The conductive line138is covered with a passivation film139. The passivation film139may be a monolayer film including a silicon nitride layer or a multilayer film including a silicon nitride layer and a silicon oxynitride layer for antireflection disposed on the top and/or bottom surface of the silicon nitride layer.

A portion of the passivation film139disposed on a pad electrode (PAD) for input to or output from the outside is opened. Hydrogen is then supplied from the passivation film139to the semiconductor layer100by heat treatment in an atmosphere of N2, H2, or a mixture thereof. The heat treatment temperature ranges from 350° C. to 450° C., for example.

The insulator of the element isolation portion102in the pixel circuit region2has a higher hydrogen concentration than the insulator of the element isolation portion103in the peripheral circuit region3. The element isolation portion102is closer than the conductive lines132,135, and138and the plugs131,134, and137to the semiconductor layer100. The conductive lines132,135, and138include a titanium nitride layer that occludes hydrogen or restricts hydrogen diffusion. Thus, the element isolation portion102is an effective hydrogen supply source. This can reduce the amount of hydrogen supplied in the peripheral circuit region3and increase the amount of hydrogen supplied in the pixel circuit region2.

After the heat treatment, the planarizing film140, the color filter141, and the microlens142are formed on the passivation film139.

In general, after the process d1of hydrogen ion implantation, it is desirable that the process temperature be lowered to prevent hydrogen in the element isolation portion102from diffusing into the outside. In the present embodiment, however, not only the photoelectric conversion unit PD but also the pixel transistor PX and the element isolation portion102are entirely covered with the silicon nitride layer110. The silicon nitride layer110can prevent hydrogen in the element isolation portion102from diffusing into the outside. The silicon nitride layer110preferably has a thickness of 50 nm or more in order to prevent hydrogen from diffusing into the outside.

A method for manufacturing an image pickup apparatus IS according to a second embodiment will be described below with reference toFIGS. 6A to 6CandFIGS. 7A and 7B.

The present embodiment is different from the first embodiment in that the silicon nitride layer110in the first embodiment is replaced with a silicon nitride layer210. The timing of hydrogen ion implantation is also different from the first embodiment.

A process a2illustrated inFIG. 6Acan be performed in the same manner as the process a1and will not be described here.

In a process b2illustrated inFIG. 6B, first, the semiconductor layer100in the pixel circuit region2and the peripheral circuit region3is covered with a dielectric film. While a portion of the dielectric film disposed on the photoelectric conversion unit PD in the pixel circuit region2is covered with a mask, portions of the dielectric film disposed on the pixel transistor PX and the peripheral transistor PR are etched. Thus, a sidewall spacer115is formed on the side walls of the gate electrodes122and123. An impurity region116is formed in the source/drain of the peripheral transistor PR using the sidewall spacer115. The high-concentration impurity region116and the low-concentration impurity region114can constitute a lightly doped drain (LDD) structure in the source/drain of the peripheral transistor PR.

The dielectric film formed in the process b2is a silicon nitride monolayer film or a multilayer film including a silicon nitride layer and a silicon oxide layer. The unetched portion of the dielectric film in the pixel circuit region2is the silicon nitride layer210. The silicon nitride layer210can function as a protective layer for protecting the pixel circuit region2from metal contamination or plasma damage and thereby reduce the number of white defects. The silicon nitride layer210more greatly restricts hydrogen diffusion than the silicon oxide layer. Thus, the silicon nitride layer210can restrict hydrogen supply when hydrogen is supplied to the semiconductor layer100from above during heat treatment in a downstream process.

In a process c2illustrated inFIG. 6C, silicide regions118and119are formed in the peripheral transistor PR by a salicide process in the same manner as the process c1.

In a process d2illustrated inFIG. 7A, an interlayer insulating film129and contact plugs130and131are formed over the semiconductor layer100in the same manner as the process e1. A mask member320is then formed on the interlayer insulating film129. The mask member320is composed of a resin, such as a photoresist. The mask member320covers the element isolation portion103in the peripheral circuit region3. The mask member320has an opening321on at least part of the element isolation portion102in the pixel circuit region2. Thus, the mask member320does not overlap at least part of the element isolation portion102in the pixel circuit region2. Although the mask member320covers the element portion in the pixel circuit region2, the mask member320does not have to cover the element portion in the pixel circuit region2. The mask member320may be disposed only on the element isolation portion103in the peripheral circuit region3. Accelerated hydrogen ions are implanted into the element isolation portion102in the pixel circuit region2using the mask member320as a mask. The ion implantation is performed through the mask member320such that the concentration of hydrogen in the insulator of the element isolation portion102in the pixel circuit region2is higher than the concentration of hydrogen in the insulator of the element isolation portion103in the peripheral circuit region3. Although part of accelerated hydrogen ions may also be implanted into the element isolation portion103through the mask member320, the number of implanted hydrogen ions is much smaller in the element isolation portion103than in the element isolation portion102not covered with the mask member320.

The energy for the hydrogen ion implantation is not particularly limited as long as the hydrogen concentration peak (Rp) is located within the insulator of the element isolation portion102in the pixel circuit region2. The hydrogen ion implantation dosage can be determined such that the hydrogen concentration of the element isolation portion102is 10 times or more the hydrogen concentration of the element isolation portion103even after the subsequent processes. The hydrogen dosage is 5×1015(atoms/cm2) or more, for example.

The ion implantation method allows hydrogen to be implanted into the element isolation portion102even when the element isolation portion102in the pixel circuit region2is covered with the silicon nitride layer110. Furthermore, even when the photoelectric conversion unit PD or the amplifying transistor SF is covered with the silicon nitride layer110, hydrogen can be implanted into the element isolation portion102, and therefore the element isolation portion102can supply sufficient hydrogen to the photoelectric conversion unit PD and the amplifying transistor SF. After hydrogen ions are implanted, the mask member320is removed.

In the present embodiment, the silicon nitride layer210has an opening on the pixel transistor PX and on the element isolation portion102in the pixel circuit region2. Thus, the silicon nitride layer210does not overlap at least part of the element isolation portion102in the pixel circuit region2. A high process temperature in the manufacturing process after the hydrogen ion implantation therefore causes significant diffusion of hydrogen from the insulator of the element isolation portion102into the outside. Thus, the heat treatment temperature can be lowered after the process d2of hydrogen ion implantation. In the present embodiment, the process d2is preceded by a process involving heat treatment at a temperature of more than 600° C. for the purpose of activation of an impurity region, a reaction between a metal and the semiconductor layer100, or reflowing of an insulator. The processes after the hydrogen ion implantation are performed such that the temperature of the semiconductor layer100is 600° C. or less. For example, heat treatment for supplying hydrogen from the passivation film to the device region can be performed at a temperature of 600° C. or less. The film-forming temperature of conductive lines and insulating films can also be 600° C. or less. The processes after the hydrogen ion implantation can be performed such that the temperature of the semiconductor layer100is 450° C. or less. In the present embodiment, the element isolation portion102can supply hydrogen to the semiconductor layer100. Thus, even when heat treatment in a process of supplying hydrogen from the passivation film after the hydrogen ion implantation is performed at a temperature of 450° C. or less, noise in the pixel circuit region2can be sufficiently reduced.

In a third embodiment, after the process e1in the first embodiment, if necessary, the semiconductor layer100can be made thinner after the passivation film139is formed. The semiconductor layer100is attached to a supporting substrate. A color filter or microlens may be disposed on a surface of the semiconductor layer100opposite the transistors and conductive lines. Thus, a backside illuminated image pickup apparatus can be provided.

A method for manufacturing an image pickup apparatus according to the present embodiment is a method for manufacturing an image pickup apparatus including a semiconductor layer that constitutes a pixel circuit region and a peripheral circuit region, comprising:

preparing a semiconductor layer in the pixel circuit region and the peripheral circuit region, the semiconductor layer including an element portion defined by an element isolation portion containing an insulator;

forming a member on the semiconductor layer, the member overlapping the element isolation portion in the peripheral circuit region and not overlapping at least part of the element isolation portion in the pixel circuit region; and

implanting accelerated hydrogen ions into the element isolation portion in the pixel circuit region using the member as a mask.

In the manufacturing method, the member may be removed after the implanting.

In the manufacturing method, a silicon nitride layer may be disposed on the element isolation portion in the pixel circuit region and on a photoelectric conversion unit in the pixel circuit region in the implanting.

In the manufacturing method, the silicon nitride layer may be disposed on an amplifying transistor in the pixel circuit region in the implanting.

The manufacturing method may include forming a silicide region in a transistor in a peripheral circuit region before the implanting and forming a passivation film covering the pixel circuit region after the implanting.

The manufacturing method may include forming a contact plug before the implanting, the contact plug being coupled to the semiconductor layer, and forming a conductive line after the implanting.

The manufacturing method may include before the implanting a process in which the temperature of the semiconductor layer is more than 600° C. and after the implanting no process in which the temperature of the semiconductor layer is more than 600° C.

In the manufacturing method, a silicon nitride layer may be disposed on a photoelectric conversion unit in the pixel circuit region in the implanting, and the silicon nitride layer does not overlap at least part of the element isolation portion in the pixel circuit region.

The manufacturing method may include after the implanting no process in which the temperature of the semiconductor layer is more than 450° C.

The present technique can simultaneously improve the characteristics of both the pixel circuit region and the peripheral circuit region.

This application claims the benefit of Japanese Patent Application No. 2015-101335 filed May 18, 2015, which is hereby incorporated by reference herein in its entirety.