Curved image sensor and electronic device having the same

A curved image sensor includes a supporting substrate, a bonding pattern provided over the supporting substrate a sensing substrate provided over the supporting substrate and in contact with the bonding pattern, and having a curved surface receiving incident light, and a fixing pattern provided over the supporting substrate and surrounding a periphery of the sensing substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present document claims priority of Korean Patent Application No. 10-2014-0180216, entitled “CURVED IMAGE SENSOR, METHOD FOR FABRICATING THE SAME AND ELECTRONIC DEVICE HAVING THE SAME” and filed on Dec. 15, 2014, which is incorporated herein by reference in its entirety.

BACKGROUND

Exemplary embodiments of the present invention relate to a semiconductor device and, more specifically, to a curved image sensor.

An image capturing device, e.g., a camera, includes an image sensor and a lens. The lens is provided over a light receiving surface. When an image of an object is formed, there is lack of focus between the center and periphery of the image due to chromatic aberrations of the lens, a phenomena referred to as field curvature. Thus, field curvature correction (or lens aberration correction) is necessary.

To address this issue, a curved image sensor has been suggested. In the curved image sensor, a light receiving surface is curved to correspond to the curvature of the lens. Photoelectric conversion elements are arranged on the curved surface, i.e., the light receiving surface, with the goal of improving image quality.

SUMMARY

Various embodiments are directed to an image sensor with high productivity, a method for fabricating the same, and an electronic device including the same.

A curved image sensor according to an embodiment of the present invention includes a supporting substrate, a bonding pattern provided over the supporting substrate, a sensing substrate provided over the supporting substrate and in contact with the bonding pattern, and having a curved surface receiving incident light, and a fixing pattern provided over the supporting substrate and surrounding the periphery of the sensing substrate. The curved image sensor may further include a closed air cavity enclosed by the sensing substrate, the supporting substrate, and the fixing pattern. The closed air cavity may have a lower pressure than the outside of the curved image sensor.

The sensing substrate may include a device wafer. The supporting substrate may include a carrier wafer. The bonding pattern may be in contact with a center of the sensing substrate. The area of the bonding pattern may be 10-20% of the area of the sensing substrate. A width-length ratio of the bonding pattern may be approximately the same as a width-length ratio of the sensing substrate. The fixing pattern may be in contact with a sidewall of the sensing substrate. The sensing substrate may have an inclined sidewall. The fixing pattern may have a donut shape. The fixing pattern may include thermosetting material.

The curved image sensor may further include a logic circuit layer provided over the supporting substrate and in contact with the bonding pattern and the fixing pattern, and a plurality of connectors passing through the fixing pattern and suitable for electrically connecting the sensing substrate to the logic circuit layer.

A method for fabricating a curved image sensor according to an embodiment includes providing a device wafer including a plurality of die regions and a scribe lane, forming a bonding pattern over each of the die regions, bonding a carrier wafer to the device wafer to be in contact with the bonding pattern, selectively etching the device wafer corresponding to the scribe lane to form a trench, wherein the trench divides the die regions from each other, filling the trench to form a fixing layer, wherein the fixing layer extends under the trench to form a closed air cavity enclosed by the fixing layer, the carrier wafer and each of the die regions, sawing the scribe lane to separate the die regions into a plurality of dies, and curving an upper surface of each of the dies and forming a fixing pattern supporting the curved surface.

The bonding pattern may be located in a center of each of the die regions. The area of the bonding pattern may be 10-20% of the area of each of the die regions. A width-length ratio of the bonding pattern may be approximately the same as a width-length ratio of each of die regions. The method may further include forming a sacrificial layer over the device wafer before the bonding of the carrier wafer to the device wafer and removing the sacrificial layer before the forming of the fixing layer. The sacrificial layer may have a surface flush with a surface of the bonding pattern. The trench may have an inclined sidewall. The curving of the upper surface of each of the dies and the forming of the fixing pattern supporting the curved surface may include expanding air in the closed air cavity and transforming the shape of the fixing layer through a set annealing temperature. The expanding and the transforming may be performed simultaneously. The fixing layer may include an elastic polymer. The elastic polymer may be a thermosetting polymer.

An electronic device according to an embodiment may include an optical system, a curved image sensor suitable for receiving light from the optical system, and a signal processing element suitable for processing a signal outputted from the curved image sensor. The curved image sensor may include a supporting substrate, a bonding pattern provided over the supporting substrate, a sensing substrate provided over the supporting substrate and in contact with the bonding pattern, and having a curved surface receiving incident light, and a fixing pattern provided over the supporting substrate and surrounding a periphery of the sensing substrate. The electronic device may further include a logic circuit layer provided over the supporting substrate and in contact with the bonding pattern and the fixing pattern; and a plurality of connectors passing through the fixing pattern and suitable for electrically connecting the sensing substrate and the logic circuit layer.

A curved image sensor includes a bonding pattern and a fixing pattern to form a curved sensing substrate which incident light hits. This structure may improve productivity of the curved image sensor significantly. Also, it is possible to miniaturize a package including the curved image sensor.

In addition, the curved image sensor employs a logic circuit layer and a connector to improve the integration degree thereof. Thus, a device including the curved image sensor may be small in size and its operation speed may be improved.

In addition, the curved image sensor is formed at a wafer level before packaging. Therefore, productivity of the curved image sensor improves and the size (especially, height/thickness) of the package including the curved image sensor may be reduced.

DETAILED DESCRIPTION

Embodiments according to the present invention provide a curved image sensor with high productivity, a method for fabricating the same, and an electric device including the same. A conventional curved image sensor is made by three-dimensionally bending its surface so that the surface has substantially the same curvature as a curved surface of a lens. A plurality of photoelectric conversion elements are provided over the curved surface of the image sensor (i.e. the surface receiving light). The curved surface according to conventional art is formed during the packaging process, when the individual chips are packaged. Thus, productivity of the image sensor is significantly reduced and it is difficult to reduce the size of the image sensor.

An image sensor is a semiconductor device that converts an optical image into an electrical signal. Image sensors are typically classified into CCD (Charge Coupled Device) image sensors and CMOS (Complementary Metal Oxide Semiconductor) image sensors.

Compared with a CCD image sensor, a CMOS image sensor is advantageous in that its driving mechanism is relatively simple and various scanning methods may be employed. In addition, circuits, e.g., circuits for processing signals transferred from pixels, may be integrated into a single chip using a CMOS process. Thus, the device size may be reduced, and production cost may be saved, and power consumption may be lowered. Due to these advantages, CMOS Image sensors have been extensively studied and various CMOS image sensors have been developed. The CMOS image sensor may be further classified into front-side illumination type devices and back-side illumination type devices.

The back-side illumination type device is known for having superior operation characteristics (e.g., sensitivity) relative to the front-side illumination type device. Thus, in the following description, a back-side illumination type CMOS image sensor will be exemplified as an embodiment.

FIG. 1shows a curved image sensor according to an embodiment of the present invention. Specifically,FIG. 1is a plan view briefly showing a structure of a curved image sensor which is an embodiment of the present invention.

As shown inFIG. 1, the image sensor according to an embodiment of the present invention may include a pixel array2. In the pixel array2, pixels are two-dimensionally arranged and photoelectric conversion elements are included. Each pixel1of the pixel array2is coupled to the photoelectric conversion elements and a pixel circuit (not shown). The pixel circuit includes a plurality of transistors and capacitors. The plurality of photoelectric conversion elements may share a part of the pixel circuit. The pixel circuit may be provided on the same side as the photoelectric conversion elements (e.g., the side receiving incident light) or may be provided on the opposite side of the photoelectric conversion elements (e.g., opposite to the side receiving incident light).

As will be described below, in a curved image sensor according to an embodiment of the present invention, a fixing pattern may have a donut shape surrounding the periphery of the pixel array2. A bonding pattern may be disposed in the center of the pixel array2. In a peripheral area of the pixel array2, a peripheral circuit, e.g., a vertical driving circuit3, a column signal processing circuit4, a horizontal driving circuit5, a system control circuit6, etc., may be provided.

The peripheral circuit and the pixel array2may be provided on the same substrate (SeeFIGS. 2A and 2B). In another embodiment, the peripheral circuit and the pixel array2may be provided on different substrates. In the latter case, a member, e.g., a connector, for electrically connecting the pixel array2to the peripheral circuit may be provided on the bonding pattern and/or the fixing pattern (SeeFIGS. 3A and 3B).

The vertical driving circuit3may be a shift register. The vertical driving circuit3may select a pixel driving line7wired up to the pixel array2, provide a pulse signal to the selected pixel driving line7, and drive the pixels connected to the selected pixel driving line7and arranged in the pixel array2on a row basis. The vertical driving circuit3may sequentially select and drive each row of the pixels in the pixel array2as a basic unit. Pixel signals, which are generated in respective pixels in response to intensity of incident light, are provided to the column signal processing circuit4.

The column signal processing circuit4is provided in every single column of the pixel array2. The column signal processing circuit4processes, on a column basis, signals outputted from the pixels coupled to the same column to eliminate noise from the signals. That is, the column signal processing circuit4may perform, e.g., Correlated Double Sampling (CDS), signal amplification, Analog Digital Conversion (ADC), etc.

The horizontal driving circuit5may be a shift register. Horizontal pulses are sequentially provided to sequentially select respective column signal processing circuits4. As a result, pixel signals are outputted from the respective column signal processing circuits4. An output circuit processes the signals provided from the respective column signal processing circuits4and outputs the processed signals. The processing by the output circuit may include, for example, buffering, either alone or in combination with, dark level adjustment, row deviation adjustment, various types of digital signal processing, etc.

The system control circuit6may receive data signifying input clocks, operation modes, etc., and outputs internal information of the image sensor. For example, the system control circuit6may generate a clock signal or a control signal in response to a vertical synchronization signal, a horizontal synchronization signal, and a master clock. The clock signal and the control signal are reference signals for operation of the vertical driving circuit3, the column signal processing circuit4, and the horizontal driving circuit5. The generated clock signal and control signal are provided to the vertical driving circuit3, the column signal processing circuit4, and the horizontal driving circuit5.

FIGS. 2A and 2Bshow a curved image sensor according to a first embodiment of the present invention. Specifically,FIG. 2Ais a plan view andFIG. 2Bis a cross-sectional view taken along the line A-A′ inFIG. 2A.

As shown inFIGS. 2A and 2B, a curved image sensor according to the first embodiment may include a supporting substrate120, a bonding pattern130provided over the supporting substrate120, a sensing substrate110provided over the supporting substrate120and in contact with the bonding pattern130, which includes a plurality of photoelectric conversion elements (not shown) and has a curved surface S1receiving incident light, and a fixing pattern140provided over the supporting substrate and surrounding a periphery of the sensing substrate110.

An air cavity is enclosed by the supporting substrate120, the sensing substrate110, and the fixing pattern140. The air cavity may be a closed air cavity150and blocked from external air. The closed air cavity150may have a pressure lower than outside (or room pressure).

The sensing substrate110may be a device wafer. The supporting substrate120may be a carrier wafer or a handle wafer. For example, the sensing substrate110may be a part of a device wafer on which a plurality of image sensors is formed. The supporting substrate120may be a part of a carrier wafer. The sensing substrate110and the supporting substrate120may be formed thin by a thinning process. The supporting substrate120, in addition to the bonding pattern130and the fixing pattern140, may support the sensing substrate110with a curved light receiving surface S1. The sensing substrate (110), the supporting substrate120, or both may include a semiconductor substrate. The semiconductor substrate may be a single crystal material and may include silicon-containing material. That is, the sensing substrate110, the supporting substrate120, or both may include a monocrystalline silicon-containing material. For example, either the sensing substrate110or the supporting substrate120may be a bulk silicon substrate.

When the image sensor according to the first embodiment is a back-side illumination type CMOS image sensor, the curved light receiving surface S1of the sensing substrate110may constitute a backside of the sensing substrate110. The opposite side S2to the curved light receiving surface S1may be a front side of the sensing substrate110. Even though not shown in drawings, the curved image sensor according to an embodiment may further include an interlayer insulating layer. The interlayer insulating layer (not shown) may be formed on the front side of the sensing substrate110, i.e., the opposite side S2, and includes a signal generating circuit. The interlayer insulating layer (not shown) may include an oxide layer, a nitride layer, an oxynitride layer, or a stack layer thereof.

The signal generating circuit formed inside the Interlayer insulating layer (not shown) may include a plurality of transistors, a multi-layered metal line, a plurality of capacitors, and a plurality of contact plugs. The plurality of contact plugs connects the plurality of transistors, the multi-layered metal line, and the plurality of capacitors to each other. The signal generating circuit may include the pixel circuit and the peripheral circuits described with respect toFIG. 1.

The curved image sensor according to an embodiment may further include color filters (not shown) formed on the backside of the sensing substrate110, i.e., the curved light receiving surface S1, and micro lenses (not shown) formed on the color filters. The color filters (not shown) are arranged to correspond to the respective photoelectric conversion elements.

The photoelectric conversion elements formed on the sensing substrate110may include photodiodes. For example, the photoelectric conversion elements may include one or more photoelectric conversion parts which are vertically stacked on the sensing substrate110. Each of the photoelectric conversion parts may include a P-type impurity region and an N-type impurity region. In addition, the photoelectric conversion elements may include organic photoelectric conversion elements formed on the sensing substrate110.

The bonding pattern130on the supporting substrate120may serve as an adhesive member for bonding the sensing substrate110(including a device wafer) and the supporting substrate120(including a carrier wafer). The bonding pattern130may be in contact with the opposite side S2of the sensing substrate110. The bonding pattern130may include an insulating material. Specifically, the bonding pattern130may include one or more of oxide material, nitride material, and oxynitride material. For example, when the sensing substrate110and the supporting substrate120include silicon-containing material, the bonding pattern130may include silicon oxide or silicon nitride. In addition, the bonding pattern130may contribute to forming of the curved light receiving surface S1of the sensing substrate110.

As will be described below, the bonding pattern130may hold the sensing substrate110while air within the closed air cavity150expands to make the light receiving surface S1curved. Thus, the bonding pattern130may be in contact with the center of the sensing substrate110so that a curved light receiving surface S1may have a given curvature. Specifically, the bonding pattern130may be in contact with the center of the pixel array formed on the sensing substrate110. The bonding pattern may be in a quadrangle shape, in a polygon shape, or in a circle shape when viewed from the top.

The width-length ratio (or, aspect ratio) of the bonding pattern130may be the same as the width-length ratio of the sensing substrate110. To provide sufficient bonding between the supporting substrate120and the sensing substrate110, the size (or area) of the bonding pattern130or the contact area between the bonding pattern130and the sensing substrate110may be 10-20% of the size (or area) of the sensing substrate110. When the size of the bonding pattern is less than 10%, it is difficult to provide sufficient adhesion. When the size of the bonding pattern is more than 20%, the curved light receiving surface S1may be uneven or non-uniform and may not have constant curvature, deteriorating the performance of the image sensor.

The fixing pattern140may contribute, in addition to the bonding pattern130, to bonding of the supporting substrate120and the sensing substrate110. The fixing pattern140may contribute, in addition to the supporting substrate120and the sensing substrate110, to forming of the closed air cavity150. For this purpose, the fixing pattern140may have a donut shape. The fixing pattern140may include thermosetting material.

The fixing pattern140may keep the light receiving surface S1of the sensing substrate110curved. The fixing pattern140may surround the periphery of the sensing substrate140and may be thicker (or higher) than the bonding pattern130. Specifically, the fixing pattern140may be in contact with a sidewall of the sensing substrate110. More specifically, the fixing pattern140may be in contact with a front side of the periphery of the sensing substrate110, a back side of the periphery of the sensing substrate110, and a sidewall of the periphery of the sensing substrate110. That is, the periphery of the sensing substrate110may extend into and may be buried in the fixing pattern140. In order to increase the contact area between the fixing pattern140and the sensing substrate110and to ensure bonding between the fixing pattern140and the sensing substrate110, the sensing substrate110may have an inclined sidewall.

The curved image sensor according to the first embodiment uses the bonding pattern130and the fixing pattern140to provide the curved light receiving surface S1of the sensing substrate110, thereby improving its productivity significantly. In addition, the curved image sensor may be included in a reduced sized package. These advantages may be more apparent after viewing the illustrations of a method for fabricating the curved image sensor (SeeFIGS. 4A through 4F).

FIGS. 3A and 3Bshow a curved image sensor according to a second embodiment. Specifically,FIG. 3Ais a plan view andFIG. 3Bis a cross-sectional view taken along the line A-A′ shown inFIG. 3A. The same reference numerals are used in both of the first embodiment and the second embodiment to denote the same or like members. For simplicity and conciseness, explanations on elements already described with respect to the first embodiment will be omitted.

As shown inFIGS. 3A and 3B, a curved image sensor according to a second embodiment may include a supporting substrate120, a logic circuit layer210provided over the supporting substrate120, a bonding pattern130provided over the logic circuit layer210, a sensing substrate110provided over the supporting substrate120in contact with the bonding pattern130, and having a curved surface S1which receives incident light, a fixing pattern140provided over the logic circuit layer210and surrounding a periphery of the sensing substrate110, and a plurality of connectors220passing through the fixing pattern140and electrically connecting the sensing substrate110and the logic circuit layer210.

A cavity formed by the supporting substrate120, the sensing substrate110, and the fixing pattern140may be a closed air cavity150. External air is blocked from flowing into the closed air cavity150. When the image sensor according to this embodiment is a back-side illumination type image sensor, the curved light receiving surface S1of the sensing substrate110may constitute the backside of the sensing substrate110and the opposite side S2of the light receiving surface S1may constitute the front side of the sensing substrate110.

Even though not shown in drawings, the curved image sensor according to this embodiment may further include an interlayer insulating layer formed on the front side of the sensing substrate110, i.e., the opposite side S2. The interlayer insulating layer may include a signal generating circuit. The interlayer insulating layer may be an oxide layer, a nitride layer, an oxynitride layer, or a stack layer thereof. The signal generating circuit formed in the interlayer insulating layer may include a plurality of transistors, a multi-layered metal line, a plurality of capacitors, and a plurality of contact plugs. The plurality of contact plugs connects the plurality of transistors, the multi-layered metal line, and the plurality of capacitors to each other.

The signal generating circuit may include the pixel circuit and the peripheral circuits described above with respect toFIG. 1. The curved image sensor may further include color filters (not shown) and micro lenses (not shown) formed on the color filters. The color filters are formed on the back side of the sensing substrate110, i.e., the curved light receiving surface S1, and are arranged to correspond to the respective photoelectric conversion elements.

The logic circuit layer210, formed on the supporting substrate120, may further include the peripheral circuit described above with respect toFIG. 1or an image processing circuit including Image Signal Processing (ISP). Similar to the interlayer insulating layer, the logic circuit layer210may include a plurality of transistors, a multi-layered metal line, a plurality of capacitors, a plurality of contact plugs and a pad connected to the connector220. The plurality of contact plugs connects the plurality of transistors, the multi-layered metal line, and the plurality of capacitors to each other.

In the second embodiment, the plurality of connectors220is formed in the fixing pattern140. However, in another embodiment, the plurality of connectors220may be formed in the bonding pattern130as well, in addition to the fixing pattern140.

The curved image sensor according to the second embodiment uses the bonding pattern130and the fixing pattern140to provide the curved light receiving surface S1of the sensing substrate110, thus improving its productivity significantly. In addition, the curved image sensor may be formed in a smaller size. These advantages will be more apparent from the following description of a method for fabricating the curved image sensor according to an embodiment (SeeFIGS. 4A through 4F). The curved image sensor also includes the logic circuit layer210and the connector220to increase integration, reduce size, and improve operation speed.

FIGS. 4A to 4Fare perspective views illustrating a method for fabricating a curved image sensor according to an embodiment of the present invention. Hereinafter, a method for fabricating the curved image sensor according to the first embodiment will be described. The perspective views ofFIGS. 4A to 4Fshow the cross-sections taken along the line A-A′ inFIG. 2A.

As shown inFIG. 4A, a device wafer10with a plurality of die regions and a scribe lane is prepared. The device wafer10may be a single crystal material and may include silicon-containing material. For example, the device wafer10may be a bulk silicon wafer.

Next, an image sensor (not shown) including a plurality of photoelectric conversion elements (not shown) is formed on each of the die regions. For example, even though not shown in drawings, a plurality of photoelectric conversion elements is formed on the device wafer10. An interlayer insulating layer including signal generating circuits may be formed on the device wafer10.

Next, a bonding pattern12is formed on each of the die regions. The bonding pattern12may improve the bonding strength between the two wafers. The bonding pattern12forms a cavity between the two wafers. The bonding pattern12contributes to forming of the curved light receiving surface. The bonding pattern12may include insulating material. Specifically, the bonding pattern12may include oxide, nitride, oxynitride, or a combination thereof. For example, the bonding pattern12may be formed of silicon nitride.

The bonding pattern12may be formed by forming an insulating layer on the device wafer10and selectively etching the insulating layer. The bonding pattern12may be formed on the front side of the device wafer10and be located on the center of the die region. Specifically, the bonding pattern12may be formed on the center of the pixel array where a plurality of pixels is arranged two-dimensionally in the die region. The size of the bonding pattern12or the contact area between the bonding pattern12and the die region may be 10-20% of the area of the die region.

The bonding pattern12may be a quadrangle, a polygon, or a circle in shape when viewed from the top. The width-length ratio (aspect ratio) of the bonding pattern12may be the same as the width-length ratio (aspect ratio) of the die region. This is to form the curved light receiving surface with a uniform curvature in a subsequent process.

As shown inFIG. 4B, a sacrificial layer14filling between bonding patterns12is formed on the device wafer10. The sacrificial layer14may have an upper surface which is flush with an upper surface of the bonding pattern12. Thus, the sacrificial layer14may be formed by applying a material layer on the device wafer10to such a thickness sufficient to fill between the bonding patterns12.

Then, a planarization process, e.g., a chemical mechanical process (CMP), is performed against the material layer until an upper surface of the bonding pattern12is exposed. The sacrificial layer14may be formed of material whose residue is easy to remove. It is preferable that the material have an etch selectivity to the bonding pattern12. For example, when the bonding pattern12is formed of silicon nitride, the sacrificial layer14may be formed of carbon-containing material or silicon oxide.

Next, a carrier wafer30is prepared. The carrier wafer30may be single crystal material or include silicon-containing material. For example, the carrier wafer30may be a bulk silicon wafer.

Next, the carrier wafer30is bonded to the device wafer10where the bonding pattern12and the sacrificial layer14are formed. A wafer bonding process is performed so that the bonding pattern12is in contact with both of the device wafer10and the carrier wafer30. The wafer bonding process may be performed by various conventional methods.

As shown inFIG. 4C, a thinning process is performed against the back side of the device wafer10to reduce the thickness of the device wafer10. Even though not shown in drawings, color filters (not shown) and micro lenses (not shown) are formed on the back side of the device wafer10and arranged to correspond to the respective photoelectric conversion elements. Hereinafter, the device wafer10which is obtained upon completion of the thinning process is referred to as the numerical reference10A.

Next, the scribe lane of the device wafer10A is etched to form a trench16, dividing the device wafer10A into a plurality of die regions. The trench16may have an inclined sidewall. Accordingly, each die region has an inclined sidewall as well. Specifically, the width of the trench16may increase from the bottom to the top. The trench16may be formed by a dry etching process. The etching process to form the trench16may be performed until the sacrificial layer14is exposed or the carrier wafer30is exposed.

Next, the sacrificial layer14is removed. Upon removal of the sacrificial layer14, a cavity18may be formed between the die region of the device wafer10A and the carrier wafer30. The sacrificial layer14may be removed by various methods depending on the material forming the sacrificial layer14. For example, when the sacrificial layer14is formed of carbon-containing material, it may be removed by an ashing process. When it is formed of silicon oxide material, it may be removed, e.g., using a HF etchant.

In another embodiment for fabricating the curved image sensor, the wafer boding process may be performed without forming the sacrificial layer14. In this case, an additional process for removing the sacrificial layer14is not necessary. Upon completion of the wafer bonding process, a cavity18is formed between the device wafer10A and the carrier wafer30.

As shown inFIG. 4D, a fixing layer20filling the trench16is formed. By the fixing layer20, the cavity18becomes a closed air cavity22which is isolated from outside. The fixing layer20filling the trench16may be in contact with a sidewall of each of the die regions.

To prevent the fixing layer20from completely filling the closed air cavity22, the fixing layer20may be formed of a polymer with high viscosity. The polymer may be thermosetting material. When the fixing layer20is formed of a polymer with high viscosity, the polymer may extend under the trench16to be in contact with the carrier wafer30and the front side of the periphery of the die region.

Due to high viscosity of the polymer and the inclined sidewall of the die region, the fixing layer20is prevented from extending to the bonding pattern12. That is, the fixing layer20is prevented from completely filling the closed air cavity22. In addition, the fixing layer may protrude from the trench16and may be in contact with the backside of the periphery of the die region. As a result, the fixing layer20may be formed over the carrier wafer30and surround the periphery of each of the die regions of the device wafer10A. As a result, the fixing layer20may be in contact with the front side, the sidewall, and the back side of the periphery of each of the die regions of the device wafer10A. In an embodiment, the periphery of the die region may be stuck in the fixing layer20.

Next, annealing is performed against the fixing layer20. By annealing, mechanical strength of the dies40increases enough to endure a subsequent sawing process. However, the annealing process is to stop before the fixing layer20is completely hardened.

As shown inFIG. 4E, the sawing process is performed along the scribe lane to separate the dies40from each other. The fixing layer20and the carrier wafer30are sawed. Hereinafter, the carrier wafer30and the device wafer10A which are singularized by the sawing process are referred to as a supporting substrate30A and a sensing substrate10B, respectively. The fixing layer20which is singularized by the sawing process is denoted with the reference numeral20A.

Each die40singularized by the sawing process may include the supporting substrate30A, the bonding pattern12formed over the supporting substrate30A, the sensing substrate10B provided over the supporting substrate30A and in contact with the bonding pattern12, and the fixing layer20A provided over the supporting substrate30A and surrounding the periphery of the sensing substrate10B. The sensing substrate10B of each die40, which is obtained upon completion of the sawing process, has a flat light receiving surface. The closed air cavity22is formed by the supporting substrate30A, the sensing substrate10B, and the fixing layer20A. The inside of the closed air cavity22has the same pressure as the outside. Before the sawing process, a thinning process may be performed against the carrier wafer30.

As shown inFIG. 4F, the die40is loaded in a chamber and annealing is performed, making the surface of the die40curved. At the same time, a fixing pattern24is formed to hold and maintain the curved surface. The curved surface may serve as a light receiving surface. Hereinafter, the sensing substrate10B with the curved light receiving surface is denoted with the reference number10C. The closed air cavity22formed in the die40and having the curved surface is denoted with the reference numeral22A.

As the annealing is performed, air in the closed air cavity22A expands. When air inside the closed air cavity22A expands with the center of the sensing substrate10C bonded to the supporting substrate30A by the bonding pattern12, the periphery of the sensing substrate10C expands/inflates and the light receiving surface becomes curved. The annealing may be performed until the fixing layer20A, which has thermosetting properties, transforms its shape. As the periphery of the sensing substrate10C expands, the shape (especially the height) of the fixing layer20A, which is in contact with the periphery of the sensing substrate10C, changes. That is, the fixing layer20A transforms into the fixing pattern24. The fixing pattern24may be formed higher than the fixing layer20A.

Upon completion of the annealing process, thermosetting properties of the fixing pattern24may maintain their transformed shape, regardless changes in outside temperature. Thus, the curved light receiving surface may be maintained. Since air in the closed air cavity22A expands, the air pressure inside the closed air cavity22A may lower than the external air pressure and the light receiving surface may remain curved. According to the processes described above, a curved image sensor according to an embodiment may be fabricated. Then, a conventional packaging process is performed to produce a device or a module including a curved image sensor.

As described above, according to a method for fabricating the curved image sensor, all processes are completed at a wafer level before the packaging process, thereby improving productivity. In addition, the size (especially, height/thickness) of a package including the curved image sensor may be effectively reduced.

The curved image sensor according to an embodiment may be employed in various electronic devices or systems. Hereinafter, a camera employing the curved image sensor will be described in reference toFIG. 5.

FIG. 5shows an electronic device including a curved image sensor according to an embodiment of the present invention. Referring toFIG. 5, an electronic device with a curved image sensor according to an embodiment may be a camera. The camera may take a still picture or a moving picture. The electronic device may include a curved image sensor300, an optical system (or an optical lens)310, a shutter unit311, a driving unit313for controlling and driving the curved image sensor300and the shutter unit311, and a signal processing unit312.

The optical system310guides an image of an object (incident light) to the pixel array2(seeFIG. 1) of the curved image sensor300. The optical system310may include a plurality of optical lenses. The shutter unit311controls emitting and blocking of incident light. The driving unit313controls transmission operations of the curved image sensor300and shutter operations of the shutter unit311. The signal processing unit312processes image signals outputted from the curved image sensor300. The processed image signal may either be stored in a memory or outputted to a monitor.