JP2010050260A - Semiconductor image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein the reduction of height in a semiconductor image sensor is limited by two factors, namely a decrease in red sensitivity in a pixel portion (1) and size (thickness) in an electrical connection means (2). <P>SOLUTION: The semiconductor image sensor includes: a photosensitive region 40 composed on a semiconductor substrate; and a connection region 41 including an electrical connection means to the outside of the semiconductor substrate. In the semiconductor image sensor, a partial thickness of the semiconductor substrate at the connection region is made smaller than that of the semiconductor substrate at the photosensitive region. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a thin and thin semiconductor image sensor.

  Image sensors that utilize semiconductor technology have become increasingly widespread in many image input devices due to advances in the number of pixels and miniaturization that have led to advances in semiconductor technology. In particular, digital cameras and mobile phones are increasingly used as image recording and scanners, and there is a strong demand for downsizing and further lowering the price of image sensors, including further increasing the number of pixels and reducing the height. The semiconductor image sensors currently in practical use are mainly CMOS type and CCD type, and are assembled by well-known semiconductor technologies such as chip separation, wire bonding, and package encapsulation. In the image sensor, a photosensitive region, a signal readout region, a signal processing / driving region, and the like are integrated on the first main surface of the Si semiconductor substrate, and wire bonding is provided for electrical connection from the first main surface side to an external circuit. It has been.

  In a stationary image input apparatus, if a semiconductor image sensor having the structure having the number of pixels satisfying the resolution characteristics required by the apparatus is mounted, a practical apparatus can be realized. However, in portable devices represented by mobile phones, there is a strong demand for miniaturization of semiconductor image sensors, and the conventional structure cannot cope with them. In particular, it has been a challenge to reduce the thickness of the sensor, that is, to reduce the height and to make the package size as close as possible to the chip size.

  In order to solve such a problem, the following cited Patent Document 1 proposes to employ a through electrode and take out the wiring from the back side of the image sensor. According to this configuration, it is possible to reduce the height and size of the image sensor, which has been difficult in the past.

FIG. 18 shows a structure of a semiconductor image sensor using a through electrode and configured as a color image sensor. In the figure, reference numeral 1 denotes a sensor portion manufactured by a known semiconductor process, a semiconductor substrate 2 made of Si or the like, and a plurality of photodiodes which are photosensitive elements provided in the vicinity of the first main surface (front surface) of the semiconductor substrate. 3. A filter 4 for color separation, a microlens 5 for enhancing a light collecting effect, and the like. Reference numeral 6 denotes a cover glass having a surface protecting function, which is bonded to 1 by an adhesive layer 7. The wiring layer for reading signals from the photodiode includes a pad region 8 for connection to an external circuit. The electrical connection to the pad region 8 is a through-hole formed from a second main surface (back surface) side of the semiconductor substrate 2 and filled with a conductive material, and a ball grid array connection. This is realized on the second main surface side by the terminal group 10. By adopting such a structure, which is also called a BGA (Ball Grid Array) structure, the image sensor is compared with the connection means from the first main surface side of the semiconductor substrate 2 by a bonding wire that has been widely used conventionally. There is an advantage that it can be mounted in an area substantially equal to the area and the height can be lowered. Such advantages can greatly contribute to miniaturization and thinning of mobile phones and cameras that are application devices of image sensors.
JP 2007-67017 A

  However, when pursuing a further reduction in height, the structure illustrated in FIG. 18 has a limit. This limiting factor is described in detail below.

  19 is an enlarged view of the pixel portion of the semiconductor image sensor shown in FIG. 18, and the same reference numerals as those in FIG. 18 denote the same components. 20 in the figure is an example of incident light. After passing through the cover glass 6, 20 is effectively condensed by the microlens 5, separated by a color filter, and then incident on the photodiode 3. Although the photoelectric conversion is performed in the photodiode, not all incident light energy contributes to the photoelectric conversion, but a part of the energy passes through the photodiode 3 and is photoelectrically converted in the deep part of the substrate 2. However, energy that has not been subjected to photoelectric conversion even in the deep part flows out of the semiconductor substrate 2. It is known that the light absorption rate in a semiconductor substrate, that is, the rate of incident light energy that is photoelectrically converted has wavelength dependency of incident light. It is known that this dependency is such that the longer the wavelength (red), the lower the absorptance, and the smaller the amount of energy that is photoelectrically converted in the photodiode and the semiconductor substrate. For this reason, if the thickness of the semiconductor substrate 2 is reduced, the efficiency of photoelectric conversion with respect to red light is reduced, and the red sensitivity is lowered. That is, there is a lower limit in the thickness 21 of the sensor portion shown in FIG. 19, which becomes a limiting factor in reducing the height.

  20 is a view showing only the end portion of the semiconductor image sensor shown in FIG. 18, and the same reference numerals as those in FIG. 18 denote the same components. In the figure, reference numeral 30 denotes one of the ball grid arrays constituting the electrical connection means. The ball grid is a component frequently used in the semiconductor field, and its size is determined by the arrangement density, the number of connections, the manufacturing method, and the like. In general, since the size is several hundred μm to several tens μm, the thickness (height) indicated by 31 in FIG. The trend of higher density in the semiconductor field is remarkable, and there is an effort to reduce the size of this ball grid, but realizing a very small size of several μm is an aspect of allowable current, reliability, etc. There is a limit. That is, even if an attempt is made to reduce the height of the semiconductor image sensor, a lower limit of 31 occurs at the electrical connection means, which becomes a limiting factor for reducing the height.

  As outlined in FIG. 19 and FIG. 20, the reduction in height is limited by two factors: (1) a decrease in red sensitivity at the pixel portion, and (2) a size (thickness) at the electrical connection means. It will end up.

  On the other hand, a semiconductor image sensor has an undesirable characteristic that an increase in operating temperature degrades the quality of a reproduced image. This is because a pseudo signal called dark current increases due to an increase in operating temperature and is superimposed on the photoelectric conversion signal. This dark current is a pseudo signal component that is generated regardless of the brightness of the subject, and it is known that when the illuminance of the subject is low, the reproduced image looks rough. For this reason, it is also important to suppress an increase in operating temperature in the semiconductor image sensor. Furthermore, since an extremely dark subject needs to be imaged in a semiconductor image sensor for astronomical observation or the like, an operation frequency is set low, and further, the semiconductor image sensor is cooled to a low temperature. When the semiconductor image sensor is cooled in this way, it is difficult to directly cool the semiconductor substrate with the structure shown in FIG. Specifically, the semiconductor substrate 2 is cooled through the ball grid 10 and an electrical insulating layer (omitted in FIG. 18) located between the semiconductor substrate 2 and the ball grid 10. For this reason, there existed a fault that cooling efficiency became low. In order to avoid this drawback, the development of a structure that directly cools the semiconductor substrate 2 has been an issue.

  The application fields of semiconductor image sensors are diverse, but application to mobile phones is a typical example. Mobile phones are required to incorporate many functions in a limited space, and the reduction in height of semiconductor image sensors is a great need from the viewpoint of securing space. However, there is a problem with the imaging lens from the viewpoint of the imaging function. For example, in order to mount a low-priced camera function in a narrow space, the optical zoom function and lenses of a multi-group, multi-element configuration adopted in general digital cameras cannot be applied. For this reason, a single afocal single-focus plastic lens is used. However, with such a simple lens configuration, it is impossible to focus on the entire photosensitive region of the semiconductor image sensor, and it is difficult to avoid blurring in the peripheral image. If high-quality playback images can be obtained even at a low price, a large market can be secured in accordance with user needs. As one of the solutions, it is expected to realize a camera configuration in which the photosensitive area is not a flat surface but a curved surface so that a focus can be formed over the entire photosensitive area. Realization was an issue. However, with the current semiconductor image sensor technology, the sensor itself is hard and cannot be bent along a curved surface.

  It comprises a photosensitive region, a circuit region, and a connection region configured on the first main surface of the semiconductor substrate, and the connection region includes an electrical connection means for guiding a signal of the circuit region to the outside of the semiconductor substrate, The electrical connection means includes a through electrode provided on the semiconductor substrate and an electrical connection with the through electrode from the second main surface side opposite to the first main surface of the semiconductor substrate where the photosensitive region exists. In a semiconductor image sensor including a terminal that can be connected, a first thickness of a part of the semiconductor substrate in the connection region is set to a part of the semiconductor substrate in the photosensitive region and the circuit region. Less than the second thickness.

  The region having the first thickness is made equal to the region occupied by the connection region, and the region having the second thickness is made equal to the region occupied by the photosensitive region and the circuit region.

  The region having the first thickness includes all of the region occupied by the connection region and a part of the region occupied by the photosensitive region and the circuit region.

  The area having the second thickness includes all of the area occupied by the photosensitive area and the circuit area and a part of the area occupied by the connection area.

  The photosensitive region and the circuit region configured on the first main surface of the semiconductor substrate, and the connection region adjacent to at least one of the photosensitive region or the circuit region. The electrical connection means for guiding a signal in a region to the outside of the semiconductor substrate is included, and the electrical connection means includes the through electrode provided in the connection region and the semiconductor substrate in which the photosensitive region exists. In a semiconductor image sensor including the terminal that can be electrically connected to the through electrode from the second main surface side opposite to the first main surface, the semiconductor image sensor includes a region where the through electrode exists. The semiconductor substrate is removed from a part of the connection region.

In the solution described in the preceding paragraph, as a result of removing the semiconductor substrate from a part of the connection region including the region where the through electrode exists, the structure example in the region is insulated from the first main surface side. Layer → electrode pad and through electrode → land and connection terminal. Further, the structure examples in the photosensitive region and the circuit region are as follows: from the first main surface side, the microlens → insulating layer → color filter → insulating layer including a wiring layer
→ Photodiode → Semiconductor substrate.

  In the solution described in the preceding paragraph, since the reduction in height is one of the objects of the present invention, it is not necessary to remove the semiconductor substrate from all of the connection regions. For example, a form in which the semiconductor substrate is removed only in a region where the through electrode and a terminal that can be electrically connected to the through electrode are present is one of the preferable forms. In the photosensitive region and the circuit region, the semiconductor substrate may be removed from a region where no electrical element such as a photodiode or a transistor is disposed.

  A reflective layer is provided on the second main surface of the semiconductor substrate to reflect incident light that has passed through the photodiode and re-enter the photodiode.

  The second main surface of the semiconductor substrate in the photosensitive region and the circuit region is brought into contact with the substrate surface on which the semiconductor image sensor is mounted.

  The semiconductor image sensor is curved and mounted in accordance with the curved structure of the substrate surface on which the semiconductor image sensor is mounted as described above.

  According to the present invention, two limiting factors that have hindered a reduction in height in the conventional configuration are (1) a reduction in red sensitivity at the pixel portion, and (2) a size (thickness) at the electrical connection means. These two factors can be easily eliminated, and a low-profile semiconductor image sensor can be configured.

  By providing a layer capable of reflecting light on the second main surface, it is possible to prevent a decrease in photosensitivity due to a reduction in height.

  Since the second main surface of the semiconductor substrate in the photosensitive region and the circuit region can be brought into contact with the surface of the substrate on which the semiconductor image sensor is mounted, an increase in operating temperature causing deterioration of the characteristics of the semiconductor image sensor Can be prevented.

  By completely removing the semiconductor substrate that constitutes a part of the semiconductor substrate in the connection region, the through electrode is in direct contact with the insulating layer, so that a further reduction in height is achieved.

  Since the low-profile semiconductor image sensor can be mounted along a distorted surface, the imaging characteristics of a camera equipped with the semiconductor image sensor can be improved without complicating the imaging lens.

  The main feature of the present invention is that the object of realizing a low profile and small size of the semiconductor image sensor is achieved by partially changing the thickness of the semiconductor substrate constituting the image sensor. is there. Hereinafter, the present invention will be clarified by describing specific embodiments of the image sensor.

<First image sensor configuration>
FIG. 1 is a diagram in which the present invention is applied to a color image sensor. The same reference numerals as those in FIG. 18 denote the same components. In the figure, reference numeral 40 denotes a photosensitive area and a circuit area, and 41 denotes a connection area. In this specification,
Photosensitive area: An area in which a plurality of pixels including a photodiode 3, which is a photosensitive element, a switch transistor (not explicitly shown), a color filter 4, and a microlens 5 are arranged.
Circuit area: A circuit area in which circuit systems related to the operation of the semiconductor image sensor such as a drive pulse generation circuit, a bias supply circuit, and a signal processing circuit are integrated. In addition, this area may include a circuit system that transmits and receives signals to and from a circuit system in an application device on which the semiconductor image sensor is mounted to control the semiconductor image sensor.
Connection area: An area in which electrical connection means for supplying signals from the semiconductor image sensor to the outside and receiving signals from the outside are arranged.
It is said that. In FIG. 1, the semiconductor substrate 42 in the photosensitive region and the circuit region 40 is set to be thicker than the semiconductor substrate 43 in the connection region 41. Although there is no particular limitation on the difference in thickness, the thickness of the semiconductor substrate 42 is such that the photosensitivity of the semiconductor image sensor is not significantly reduced, and the thickness of the semiconductor substrate 43 is the lowest part of the ball grid 10. Although it is good to set so that it may become a position substantially equal to the lower surface (2nd main surface) of 42, it is not this limitation. For example, when the image sensor is mounted on a printed circuit board or the like, the ball grid 10 is melted and the height is reduced, so that electrical connection with the printed circuit board is realized. The difference in thickness between the semiconductor substrate 42 and the semiconductor substrate 43 is preferably set so as to come into contact with the substrate. Such a setting solves both of the lower-limit factors of the low profile, which has been a conventional problem.

  The configuration of FIG. 1 is similar to a conventional semiconductor image sensor using a through electrode, in which the sensor unit 1 is formed by a well-known semiconductor technology, and then a cover glass is laminated, and the semiconductor substrate is thinned in two stages. It is realized by. In general, in an image sensor using a through electrode, a semiconductor substrate is thinned in a process called back grinding for easy processing of a through hole. In this image sensor form, the thickness is reduced to the thickness of the semiconductor substrate 42 in the first thinning step, and then only the region 41 is partially thinned to the thickness of the semiconductor substrate 43 in the second thinning step.

  In the configuration of FIG. 1, the topmost part of the microlens 5 and the lower surface of the cover glass 6 are in contact with each other. This contact is an important design requirement for the realization of the present invention, as will be described in detail in the manufacturing method column in the next section. The details of this design guideline are described in a patent filed by the same applicant as the present invention [Japanese Patent Application No. 2008-146979].

<Details of the first thinning process>
FIG. 2 and FIG. 3 are diagrams for comparing and explaining the manufacturing method in the semiconductor image sensor, and show the first thinning process described above. FIG. 2 shows a case where the topmost part of the microlens 5 is located away from the cover glass 6, and FIG. 3 shows a case where the topmost part of the microlens 5 is in contact with the lower surface of the coverglass. These drawings show a state in which four structures shown in FIG. 1 are arranged in a line, and an alternate long and short dash line 50 is a boundary between the structures. The same reference numerals as those in FIG. 1 denote the same components. In FIG. 2A, the initial thickness of the semiconductor substrate 51 depends on the diameter of the wafer used in the semiconductor process, but is approximately several hundred μm. In FIG. 5B, the substrate 51 is thinned and processed into a thin substrate 52. In this thinning step, the back surface is mechanically and chemically removed simultaneously with the application of force from the second main surface (back surface) 51. In this technique, the surface of the cover glass 6 is protected with a flat plate made of resin or the like, and at the same time the strength of the entire wafer is maintained, but this is omitted in the figure. In this thinning process, the substrate 51 is processed to a thickness of about 100 μm or less. However, as the thickness of the substrate is reduced, a phenomenon occurs in which the main area of the image sensor in which microlenses, color filters, and the like are arranged is pushed into the cover glass side, and the thickness of the substrate becomes about several tens of μm. Become prominent. This phenomenon is caused by the existence of a space between the cover glass 6 and the sensor portion 1. When the thinning process is completed, the force applied to 51 is removed, so that the distance between the main area of the image sensor and the cover glass returns to the distance before the back surface polishing process. As a result, as shown in FIG. 5B, the second main surface side of 52 is not flat, and its main region is in a convex state. That is, unevenness occurs on the second main surface side of 52, and the state that should be originally flat is not maintained, and many inconveniences occur in the subsequent assembly process. As an example of such inconvenience, since the surface of the through hole and the conductive material is not flat, the surface of the ball grid array-like connection terminal group that is a connection means with an external circuit is not flat, For example, the connection reliability is lowered. Further, even when these disadvantages are not present, there is an increased risk that the semiconductor image sensor is destroyed by a force suddenly applied from the second main surface side 52 in the assembly process. In order to reduce these risks, it is conceivable to attach a reinforcing flat plate made of glass or the like to the second main surface side of 52, but this hinders a reduction in height and complicates the processing of forming a through hole. It is also disadvantageous in terms of cost.

  Furthermore, in the phenomenon where the main part is pushed into the cover glass side, the amount of movement pushed in depends on the thickness of the semiconductor substrate, the material of the adhesive layer 7 and the geometric dimensions, and the like. There is no mechanical structure that uniquely determines the amount of movement. For this reason, the state of the unevenness on the second main surface side is poor in reproducibility and varies between wafers or lots.

  On the other hand, in FIG. 3, even if the thickness of the substrate is reduced in the first thinning process, a phenomenon occurs in which the main area of the image sensor in which microlenses and color filters are arranged is pushed into the cover glass side. do not do. This is because the topmost part of the microlens 63 is in contact with the lower surface of the cover glass 6 to prevent the main region of the sensor from being deformed upward. As a result, even if the original thick substrate 61 is thinned and processed into a thin substrate 62, the flatness of the second main surface side of the substrate 62 is maintained.

  As shown in FIG. 3, in this first image sensor configuration, the contact between the microlens and the cover glass is an important design requirement, and even if the thickness of the semiconductor substrate 62 becomes several tens of μm or less, 1 thinning process can be carried out.

<Details of the second thinning process>
FIG. 4 is a diagram showing a second thinning process for creating the semiconductor image sensor configuration of FIG. In the figure, a state in which two structures of FIG. 1 are arranged is shown, and an alternate long and short dash line 70 is a boundary between the structures. The same reference numerals as those in FIG. 1 denote the same components. FIG. 4A shows a state in which the first thinning process shown in FIG. 3 has been completed, and is drawn with the front and back reversed for convenience of explanation. A mask layer 71 is formed on the entire upper surface (second main surface, corresponding to the back surface of the image sensor) in FIG. In FIG. 2B, a mask pattern 72 created by a photoresist technique is formed on 71. This pattern covers only the region 40 and the connection region 41 is an opening. In FIG. 6C, the mask layer 71 is selectively removed by etching using the photoresist pattern 72 as a mask, and an opening 73 is formed. In FIG. 4D, a part of the substrate 62 is etched by a technique called anisotropic etching to form a groove 74. Finally, all the mask layer 71 is removed. By such a second thinning process, a thick semiconductor substrate 42 remains in the region 40 and a thin semiconductor substrate 43 is formed in the connection region 41.

<Wet etching in the second thinning process>
Many etching solutions are used for the anisotropic etching described in the previous section. For example, EDP (ethylenediamine pyrocatechol), KOH (potassium hydroxide), hydrazine, TMA (trimethylaluminum), and the like. Both of the etching solutions utilize the fact that the etching rate at the <111> crystal plane of Si is extremely low. For this reason, in the groove 74 illustrated in FIG. 4D, the lateral etching is substantially finished when the <111> crystal plane is exposed on the side surface of the groove. If it is assumed that the main surface of the semiconductor substrate 62 is a <100> crystal plane, the angle formed by this side surface is 60.8 degrees. In the state shown in FIG. 4D, the thick semiconductor substrate 42 has a quadrilateral shape. In selecting the etching solution, it is necessary from the viewpoint of manufacturing technology to consider the etching rate, but the relationship with the mask material is also an important selection factor. A specific etching material requires a specific mask material. For example, silicon nitride (Si3N4) must be selected for EDP, and silicon oxide (SiO2) must be selected for hydrazine and TMA. In addition, if a micropyramid composed of four faces with <111> crystal planes is generated at the bottom of the groove 74, a defect is generated in a through electrode forming process described later. It is also necessary to set

  In the previous section, the wet etching used in the second thinning process has been outlined, but other known etching techniques can also be applied. For example, there are wet isotropic etching and dry reactive ion etching (RIE). In the wet isotropic etching, the side wall of the groove 74 does not become a flat surface having a constant angle, but has a rounded shape. However, it can be adopted when the depth of the groove 74 is shallow.

<Method of forming electrical connection means>
FIG. 5 is a diagram showing a method of forming electrical connection means performed after the second thinning step outlined in FIG. In the figure, the part centering on the boundary 70 in FIG. 4 is enlarged and displayed. In the figure, the same reference numerals as those in FIG. 1 denote the same components. In FIG. 3A, reference numeral 80 denotes a mask layer provided on the second main surface (upper surface in the drawing) of the sensor portion and patterned. Through the opening of the mask layer, the thin semiconductor substrate 43 and the insulating layer are etched, and a through hole 82 leading to the pad region 8 is opened. Since the shape of the through hole is deep in the vertical direction, anisotropic RIE, which is dry etching, is used to form the through hole, but this is not restrictive. Further, the through hole is preferably a cylindrical shape whose cross-sectional area does not change greatly in the vertical direction. In FIG. 4B, an insulating layer 84 is provided on the entire surface. At this time, an insulating layer must also be formed on the side wall of the through hole. Further, since this insulating layer adheres to the bottom of the through hole, it is necessary to remove the insulating layer at the bottom by RIE or the like. In FIG. 5C, the through hole is filled with a conductive material, and a land 85 having a certain area is formed on the surface of the through hole. This filling and land formation are not necessarily realized in one process, and a plurality of processes may be combined. For example, in the first stage, a thin conductive film may be formed by vapor deposition or the like, and then a thick conductive film may be formed by electroplating or electroforming to fill the through hole. In FIG. 4D, the ball grid 86 is formed on the land 85, and the formation of the electrical connection means is completed. Thereafter, the image sensors are separated into chips along the boundary 70, and the manufacturing process is completed.

  In addition, regarding the filling of the conductive material into the through hole, the hole need not be completely filled. Since this conductive material only needs to electrically connect the pad region 8 and the land 85, only a part of the through hole is filled with the conductive material and the remaining part is a gap or other material. It may be filled with. In the present specification, the term “filling” is merely used for convenience, and is not limited to the meaning of “complete filling”.

  Various methods are used to form the ball grid 86. For example, a metallic lump that has been processed into a spherical shape in advance may be temporarily bonded onto the land, and melted and re-solidified in a high-temperature atmosphere. In this method, the size of 86 has a lower limit, and it is difficult to form a fine grid having a size of several tens of μm. On the other hand, a metal layer used as a material for the ball grid may be partially adhered, dissolved, and re-solidified. This method has an advantage that a very small ball grid of 100 μm or less can be formed.

<Relationship between connection area, circuit area, photosensitive area and semiconductor substrate thickness>
FIG. 6 is a diagram showing the relationship between the aforementioned connection region, circuit region, and photosensitive region, and the thickness of the semiconductor substrate in each region. In the figure, the same reference numerals as those in FIG. 1 denote the same components. FIG. 4A shows a case where the thickness of the semiconductor substrate 43 in the connection region 41 is smaller than the thickness of the semiconductor substrate 42 in the circuit region and the photosensitive region 40. Note that FIG. 6A corresponds to FIG. On the other hand, in FIG. 4B, the connection region 41 is composed of a thin semiconductor substrate 43 portion and a thick semiconductor substrate 42 portion. That is, the thickness of the connection region 41 is not uniform, and only a part of the thickness is small. A ball grid constituting the connection means is arranged in the partial region where the thickness is small. Further, in FIG. 2C, the circuit region and the photosensitive region 40 are constituted by a thick semiconductor substrate 42 and a thin semiconductor substrate 43. That is, the thickness of the circuit area and the photosensitive area 40 is not uniform, and only a part of the thickness is large. In FIG. 3C, the semiconductor substrate having a small thickness in the region 40 is preferably present in the circuit region, not in the photosensitive region, but is not necessarily limited thereto. As shown in FIG. 6, the thickness of each semiconductor substrate in the connection region 41, the photosensitive region, and the circuit region 40 constituting the semiconductor image sensor does not have to correspond to one to one, and is a partially thick region. And a thin area may be mixed.

<Appearance (bottom) view of semiconductor image sensor>
FIG. 7 is an external view of the semiconductor image sensor after chip separation is viewed from the bottom side. In the figure, reference numeral 90 denotes a semiconductor image sensor chip, 92 denotes a photosensitive region and a circuit region corresponding to the semiconductor substrate 42 having a large thickness, and 93 denotes a connection region corresponding to the semiconductor substrate 43 having a small thickness. In the region 93, a plurality of ball grids represented by 10 are arranged. In the first image sensor form, since the ball grid must be arranged only in the connection region where the thickness of the semiconductor substrate is thin, it is illustrated as an arrangement of two rows in the figure. Unlike general logic ICs and central processing ICs (CPUs), the number of terminals of the electrical connection means of the semiconductor image sensor is relatively small. Therefore, even in such a configuration, the area necessary for the array is sufficiently large. It can be secured. As a matter of course, this arrangement need not be arranged evenly around the four sides of the chip, and can be determined as appropriate according to the number of terminals and the mounting form of the image sensor.

<Mounting form of semiconductor image sensor>
FIG. 8 is a view showing a structure in which the first image sensor form shown in FIG. 1 is mounted. In the figure, the same reference numerals as those in FIG. 1 denote the same components. In the figure, reference numeral 100 denotes a mounting board such as a printed circuit board, and 101 denotes a wiring pattern arranged on the board 100, which propagates signals of the semiconductor image sensor via the ball grid 10. Reference numeral 102 denotes a wiring pattern similar to 101, which is composed of a metal film having an area and shape substantially equal to the region 92. In the figure, a situation is shown in which the bottom of the region 42 with a large substrate thickness is in contact with this 102. This contact is not always necessary if limited to electrical mounting of the image sensor only. However, since the heat generation of the image sensor can be released to the substrate side through this contact surface in order to prevent the characteristic deterioration due to the temperature rise of the image sensor, it can be said that this figure is a preferable mounting example. As an example of characteristic deterioration, it is known that the reproduction image quality deteriorates particularly for a dark subject such as an increase in dark current and a decrease in dynamic range.

  In the configuration shown in FIG. 8, electrical connection with the wiring pattern 101 is realized by melting and re-solidifying the ball grid 10. It is desirable that the substrate 42 be strongly pressed against the pattern 102 by this re-solidification. For this purpose, it is desirable to appropriately select and set the size (thickness) of the ball grid 10 after resolidification and the difference in thickness (step) between the semiconductor substrate 42 and the semiconductor substrate 43. Considering only the heat dissipation effect, it is desirable that the substrate 42 and the pattern 102 are bonded together as a metal phase, but this is not restrictive. Further, when the substrate 42 and the pattern 102 are simply in contact with each other, it is preferable to sandwich a heat conductor such as silicone grease between them to eliminate the air layer in order to improve the heat dissipation effect. In this case, heat is dissipated through the path of the silicon substrate 42 → silicone grease → pattern 102 → printed circuit board 100.

  From the above overview, the first image sensor configuration shown in FIGS. 1 to 8 can simultaneously eliminate the two limiting factors that hindered the reduction in profile in the conventional configuration, and can achieve a further reduction in profile. It became clear.

<Second image sensor configuration>
FIG. 9 shows a second embodiment to which the present invention is applied. The same reference numerals as those in FIGS. 1 and 8 denote the same components. In the figure, reference numeral 110 denotes a reflective layer provided for each pixel in the photosensitive region on the second main surface side of the thick substrate 42. This reflective layer is formed by a known technique during or after the manufacturing process outlined in FIG. For example, it is composed of a metal vapor deposition film or the like. In the same figure, incident light 111 is effectively condensed by the microlens 5 and separated by the color filter 4 and then reaches the photodiode 3, but a part of incident energy passes through 3 and the reflection layer 110. Reach up to. However, the incident light 111 is reflected by 110, reaches the photodiode 3 again, and can contribute to photoelectric conversion. This second image sensor configuration is particularly effective when the thickness of the substrate 42 becomes extremely small. By adopting this form, there is an advantage that the reduction of the photosensitivity proposed in the problem can be largely prevented.

  Although the reflective layer 110 in FIG. 9 is arranged for each pixel, it is not necessarily limited to this configuration method. For example, the area of the reflective layer is approximately equal to the area of the region 40 described above, and one large pattern may be formed. Since the reflection of light is close to a specular reflection, even if the light is reflected by a large-area reflective layer directly under a specific pixel, it is unlikely to be mixed into the photodiode of the adjacent pixel. Further, when such a configuration in which one large reflective layer is formed over the entire photosensitive region is applied to the mounting form illustrated in FIG. 8, the semiconductor substrate 42 and the pattern 102 can be brought into contact with each other. it can. That is, heat is dissipated through the route of the silicon substrate 42 → the reflective layer 110 → silicone grease (applied as necessary) → the pattern 102 → the printed circuit board 100.

<Third image sensor configuration>
FIG. 10 shows a third embodiment to which the present invention is applied. The pixel portion is enlarged and displayed. In the figure, the same reference numerals as those in FIG. 1 denote the same components. In the figure, reference numeral 120 denotes a reflective layer provided for each pixel in the photosensitive region. The difference from FIG. 9 is that 120 is not a mirror surface and the reflected light is diffused. Incident light indicated by 121 passes through the microlens 5 and the color filter 4 and then enters the photodiode 3. Some energy cannot be absorbed by 3, reaches the substrate 42, and is reflected by 120. Since this reflection is not specular reflection, the reflected light is omnidirectionally diffused in all directions. A part of this diffused light again enters the photodiode 3 and can contribute to photoelectric conversion. In particular, when the thickness of the substrate 42 is small, for example, when it is about the pixel arrangement pitch or less, the possibility that the reflected light is mixed into the adjacent pixels is low. In this third image sensor form, the utilization efficiency of the reflected light due to the presence of the reflective layer is worse than in the case of FIG. 9, but this form is also effective because some of the advantages of the reflective layer are retained. Various methods can be applied to the 120 creation methods. For example, prior to forming the reflective layer 120, there is a method of forming irregularities on the second main surface of the substrate 42 and forming a metal vapor deposition film thereon. Note that, when the concave and convex portions are formed on the second main surface, the effective surface area is increased, so that the heat radiation effect from the substrate 42 to the lower space can be enhanced. In the case of increasing the heat radiation effect to the air layer due to the uneven surface shape, an opening is provided in the printed circuit board of the pattern 102 portion in the mounting form illustrated in FIG. 8, and the second main surface of the circuit board 42 is in the lower space. Exposing is an example of the configuration. Further, in FIG. 10, the reflective layer 120 is drawn as if it was buried in the substrate 42, but it may be attached to the surface of 42.

<Fourth image sensor configuration>
FIG. 11 shows a fourth embodiment to which the present invention is applied. The pixel portion is enlarged and displayed. In the figure, the same reference numerals as those in FIG. 1 denote the same components. In the figure, reference numeral 130 denotes a concave reflection layer provided for each pixel in the photosensitive region. This 130 is formed by processing the substrate 42 into a curved surface from below and providing a reflective layer made of a metal vapor deposition film or the like. Incident light indicated by 131 passes through the microlens 5 and the color filter 4 and then enters the photodiode 3. Some energy cannot be absorbed by 3 and reaches the substrate 42, is reflected and collected by 130, and then reaches the photodiode 3 again. Note that the shape of the concave reflecting layer is not necessarily spherical or arcuate, and may be a shape approximated by a polygon (consisting of a plurality of planes). The configuration of FIG. 11 is more complex than that of FIG. 9, but has an advantage that the efficiency of using reflected light can be increased.

<Fifth image sensor configuration>
FIG. 12 is a diagram showing a fifth image sensor form to which the present invention is applied. The same reference numerals as those in FIG. 1 denote the same components. In the figure, 132 is a convex lens-like reflective layer provided on the lower side of the substrate 42 and having a reflective film formed on the surface thereof. This reflective layer is formed by the same method as the condensing microlens of the semiconductor image sensor. For example, a patterned resin layer is formed on the lower side of the substrate 42 and then processed in a high temperature atmosphere to create a convex lens shape, and a metal thin film is formed on the surface by vapor deposition or the like. This metal thin film may be formed not only on the convex lens-shaped part but on the entire lower surface of the substrate 42. In the drawing, incident light indicated by 133 passes through the microlens 5 and the color filter 4 and then enters the photodiode 3. Some energy cannot be absorbed by 3 and reaches the substrate 42, is reflected and collected by 132, and then reaches the photodiode 3 again. Note that the shape of the reflective layer in this case is not necessarily spherical or arcuate, and may be a shape approximated by a polygon (consisting of a plurality of planes). In the configuration of FIG. 12, since the back surface of the semiconductor image sensor is not flat, a part of the mounting substrate may be cut out or a groove may be formed when mounting. Alternatively, a known surface flattening layer may be newly added to the lower surface of the substrate 42 in order to flatten the back surface.

  9 to 12 show a structure in which a reflective layer is provided on the second main surface of the substrate. However, the configuration method of the reflective layer is not limited to the illustrated one, and there is a corner cube configuration although processing is complicated. All of these reflection mechanisms are included in the present invention.

<Sixth image sensor configuration>
FIG. 13 is a diagram showing a sixth image sensor form to which the present invention is applied. The same reference numerals as those in FIG. 1 denote the same components. In the figure, reference numeral 140 denotes a semiconductor substrate in the region 40. In this embodiment, no semiconductor substrate exists in the connection region 41, and only electrical connection means exists. Such a configuration is realized by removing all of the semiconductor substrate in the connection region by extending the formation time of the groove 74 in the second thinning step illustrated in FIG. In other words, this is a form in which the reduction in height is further promoted. Even in such a configuration, it is possible to form the through holes illustrated in FIG. 5 and to fill the conductive material, and FIG. 13 can be said to be a feasible configuration. However, in the configuration of FIG. 13, the semiconductor substrate 140 is in an electrically floating state, and there is a risk of destabilizing the operation of the image sensor.

<Seventh image sensor configuration>
FIG. 14 shows a configuration example for achieving a stable image sensor operation by fixing the potential of 140. The same numbers as those in FIG. 1 indicate the same components. In the figure, reference numeral 150 denotes a transistor constituting the circuit area described above formed in a part of the substrate 140. Reference numeral 151 denotes an electrode for fixing the potential of the substrate 140 provided in the vicinity of the transistor 150. Reference numeral 153 denotes a second pad region provided in the same wiring layer as the pad region 8, and is connected to the electrode 151 by an interlayer wiring 152. 153 is electrically connected to the ball grid 154 via a through electrode. With this configuration, the substrate 140 can be fixed with electric potential from the outside via the ball grid 154, and the image sensor can be stably operated. Even if the potential fixing electrode 151 is not specially provided, it is often arranged in a normal semiconductor IC, so that it can be used.

<Eighth image sensor configuration>
FIG. 15 is a diagram showing another configuration method for fixing the potential of the substrate 140. The same reference numerals as those in FIG. 14 denote the same components. In the figure, reference numeral 160 denotes a wiring layer provided at an inclined portion of the end portion of the substrate 140 and electrically connected to the substrate 140. The wiring layer 160 is connected to the ball grid 161, and the potential of the substrate 140 can be fixed as in FIG.

  The image sensor configuration shown in FIGS. 13 to 15 can significantly reduce the height. Specifically, a configuration in which the thickness of the substrate 140 is set to several μm, the height of the ball grid is set to the same level, the thickness of the cover glass is set to 100 μm or less, and the thickness of the entire image sensor is set to about 100 μm. It becomes possible. Furthermore, by replacing the material of the cover glass with a resin material, it is possible to give the image sensor mechanical flexibility. Further, even when the cover glass is made of glass, a certain degree of flexibility can be achieved by making the thickness extremely thin.

<Ninth image sensor configuration>
FIG. 16 is a diagram illustrating a configuration example of a mechanically flexible semiconductor image sensor. In FIG. 2A, reference numeral 170 denotes a thin (low-profile) semiconductor image sensor, 171 denotes a wiring means including a flexible printed circuit board connected to the 170 ball grid, and 172 denotes a printed circuit board. Reference numeral 175 denotes an imaging lens, which is a single lens. In the configuration example of FIG. 16A, 170 is mounted along a curved jig 176 using the flexibility of the image sensor 170. The shape of the curved surface is generally an arc shape, and all the positions of the curved surface are set to be equidistant from the center of the imaging lens. That is, the distance to the center of the image sensor (indicated by 177) and the distance to the end (indicated by 178) are substantially equal. In a small consumer device such as a mobile phone, it is difficult in terms of size and price to make the imaging lens into a multi-group and multi-piece configuration, and an aspheric plastic single plate lens is often used. In such a simple and inexpensive lens, the aberration is large, and when the surface of the image sensor is flat, the focal position is different between the central portion and the peripheral portion. However, with a curved image sensor having a curved surface as shown in FIG. 16A, it is possible to focus on the entire photosensitive region. That is, the image sensor form according to the present invention has a great advantage that a good image can be obtained even by using a simple and inexpensive imaging lens.

  In FIG. 16A, the surface shape of the jig 176 is not necessarily a three-dimensional spherical shape. For example, the image sensor 170 may be mounted in a shape as indicated by 179 in FIG. 5B, that is, a shape bent along a cylinder. In this configuration, the direction indicated by the arrow in FIG. 5B should be the longitudinal direction of the image. In the configuration shown in FIG. 6B, the imaging lens cannot be focused over the entire photosensitive region, but a constant good image quality can be obtained because the imaging lens is focused in the longitudinal direction.

<Tenth image sensor configuration>
FIG. 17 is a diagram showing a tenth image sensor form to which the present invention is applied. The same reference numerals as those in FIG. 13 denote the same components. This figure only shows the cross-sectional structure conceptually, and the vertical and horizontal scales are ignored. In the figure, reference numeral 180 denotes a wiring board such as a printed circuit board, and 181 denotes a wiring pattern formed on the 180. The configuration shown in FIG. 1 includes (1) mounting the semiconductor image sensor shown in FIG. 13 on the wiring board 180, (2) melting and re-solidifying the ball grid 10, and electrically connecting to the wiring pattern 181. (3) Resin was filled between the lower side of the sensor part 1 and the printed circuit board 180 to form an underfill layer 182. (4) The resin was processed and solidified. (5) The surface of the sensor part 1 was protected. It is formed by the procedure of removing the cover glass. The semiconductor image sensor having the configuration shown in FIG. 17 includes a semiconductor substrate 140 in a region 40, an insulating layer 185 in which a wiring layer and a color filter are arranged, the microlens 5 and the ball grid 10. The electrical connection means is a major component. As a result, the sensor portion 1 can be formed with a thickness as small as several μm, which can be said to be the ultimate low profile case. Note that FIG. 17 shows a case where the underfill layer 182 exists also between the semiconductor substrate 140 and the printed circuit board 180, but this is not restrictive. That is, when the semiconductor substrate 140 is in close contact with or extremely close to the printed circuit board 180 in the region 40, an underfill layer is not formed in this portion, but such a configuration may be used. . In the configuration shown in FIG. 17, mechanical strength is ensured by the underfill layer 182 and the wiring board 180. Therefore, when selecting materials for the materials 182 and 180, sufficient examination of physical properties such as strength and thermal expansion coefficient is required. is important. Furthermore, in the configuration of FIG. 17, the surface of the semiconductor image sensor is not protected at all, so dust non-adherence in the mounting process must be prevented by other means. In addition, the configuration of FIG. 17 is preferably integrated with other members constituting the apparatus, such as a lens housing, and assembled in a form that is hermetically sealed as a whole.

  In the present specification, a configuration in which the image sensor is covered with a cover glass is described. If the term “cover glass” in the present specification is described more strictly, it will be “a flat plate having at least the property of being transparent in a specific light wavelength region”. That is, the cover glass may have not only a function of covering the image sensor to protect the image sensor but also various functions. For example, when an image sensor is applied to a digital camera, there is an infrared cutoff filter function that optically removes near-infrared light that affects the imaging effect. In the case of an image sensor for black-and-white imaging, the near-infrared light energy contained in the incident light may be actively used to increase the apparent light sensitivity. In such a case, the cover glass needs to be transparent to the wavelength range from visible light to near infrared light. In addition, in the case where the image sensor is applied to an infrared imaging device whose purpose is thermal image detection, an infrared filter that removes visible light affecting the imaging effect can be cited. In these applications, these filters are created on the front or back surface of the cover glass. As the structure of the filter, there are a method of directly forming an interference filter in which multiple layers of metal and dielectric thin films are laminated on the cover glass surface, and a method of stretching a plastic film laminated in multiple stages and stretching it on the cover glass surface. An example of a function added to the cover glass is mounting a microlens. An example of this is forming a microlens equal to the pixel pitch on the front or back surface of the cover glass. In such a configuration, the above-described microlens in the sensor portion may not be necessary, and moreover, the microlens in the semiconductor image sensor portion and the microlens in the cover glass are double-group and multiple-group (in the simple configuration, two groups In some cases, two lens systems may be formed. Another example of the function added to the cover glass is a color filter. An example of this is forming a color filter array equal to the pixel pitch on the front or back surface of the cover glass. In such a configuration, the color filter array may be directly formed on the cover glass surface by a well-known method, or the color filter array may be formed on a glass thin plate different from the cover glass and then attached to the cover glass. good. The term “cover glass” in this specification includes these function examples illustrated in this section, and in the above-described embodiment, these functions may be included.

  In this specification, an example in which the cover glass is fixed to the sensor portion with the adhesive layer 7 is shown. However, the present invention is not limited to this configuration, and a more complicated fixing method may be used. For example, a hermetic sealed fixing method that can obtain high reliability even in a severe operating environment may be used.

  In this specification, as shown in FIG. 1, a configuration of an image sensor considered as a standard configuration is described. However, there are various image sensor configurations, and the present invention can be applied to all of them. For example, a configuration in which a microlens is not mounted, a configuration in which a microlens in a pixel area is not transparent and has a color filter function, a configuration of a black and white image sensor without a color filter, a microlens and A configuration where the space between the cover glass is in a vacuum state, a configuration of a so-called back-illuminated image sensor for increasing sensitivity, an amplification function for each pixel for increasing sensitivity, or a photodiode itself amplifying function The structure of a so-called amplification type image sensor said to have a CCD type image sensor that executes signal readout from a pixel via a horizontal / vertical register, and further, the image sensor itself has a laminated structure and has an imaging function for each layer. Signal processing function, memory function, input / output control function etc. are assigned There is such dimension of the structure. The present invention can be easily applied to such a plurality of configuration examples.

  The present invention can be applied not only to a semiconductor image sensor but also to a three-dimensional IC in which a plurality of chips are stacked. By applying to this field, the overall height of the multilayer chip can be reduced, which can greatly contribute to downsizing of the device.

It is a figure which shows the structure of the semiconductor image sensor of this invention. (First image sensor configuration) It is a figure which shows a 1st thin film formation process. (When there is a space above the micro lens) It is a figure which shows a 1st thin film formation process. (When there is no space above the micro lens) It is a figure which shows a 2nd thin film formation process. It is a figure which shows the process of forming an electrical connection means. It is a figure which shows the relationship between the thickness of a connection area | region, a circuit area | region, a photosensitive area | region, and a semiconductor substrate. It is the external view which looked at the semiconductor image sensor of FIG. 1 from the bottom face side. It is a figure which shows the mounting form of the semiconductor image sensor of FIG. It is a figure which shows the structure of the semiconductor image sensor of this invention. (When there is a reflective layer on the back) (Second image sensor configuration) It is a figure which shows the pixel structure of this invention. (When there is a diffuse reflection layer on the back side) (Third image sensor configuration) It is a figure which shows the pixel structure of this invention. (When there is a concave reflective layer on the back) (Fourth image sensor configuration) It is a figure which shows the pixel structure of this invention. (When there is a convex lens-like reflective layer on the back side) (Fifth image sensor configuration) It is a figure which shows the structure of the semiconductor image sensor of this invention. (Sixth image sensor configuration) It is a figure which shows the structure of the semiconductor image sensor of this invention. (Fixed substrate potential-1) (Seventh image sensor configuration) It is a figure which shows the structure of the semiconductor image sensor of this invention. (Fixed substrate potential-2) (Eighth image sensor configuration) It is a figure which shows the structure of the semiconductor image sensor of this invention. (Mounting using flexibility) (9th image sensor configuration) It is a figure which shows the structure of the semiconductor image sensor of this invention. (Remove cover glass after mounting) (Tenth image sensor configuration) It is a figure which shows the structure of the conventional semiconductor image sensor which employ | adopted the penetration electrode. It is a figure which shows the pixel structure of FIG. 18 in detail. It is a figure which shows only the edge part of FIG. 18 in detail.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sensor part 2, 42, 43, 51, 52, 61, 62, 140 Semiconductor substrate 3 Photodiode 4 Color filter 5, 63 Micro lens 6 Cover glass 7 Adhesive layer 8, 153 Pad area 9 Through electrode 10, 30, 86 154, 161 Connection terminal (ball grid)
20, 111, 121, 131, 133 Incident light beam 21, 31 Thickness 40, 92 Photosensitive region and circuit region 41, 93 Connection region 50, 70 Boundary 71, 80 Mask layer 72 Mask pattern 73 Opening 74 Groove 82 Through hole 84, 185 Insulating layer 85 Land 90 Sensor chip 100, 172, 180 Printed circuit board 101, 102, 181 Wiring pattern 110, 120, 130, 132 Reflective layer 150 Transistor 151 Electrode 152 Interlayer wiring 160 Wiring layer 170 Semiconductor image sensor 171 Wiring means 175 Imaging Lens 176 Jig 177, 178 Distance 179 Shape 182 Underfill layer

Claims (8)

A photosensitive region, a circuit region, and a connection region configured on the first main surface of the semiconductor substrate,
The connection region includes electrical connection means for guiding the signal of the circuit region to the outside of the semiconductor substrate,
The electrical connection means includes a through electrode provided on the semiconductor substrate;
A terminal capable of being electrically connected to the through electrode from the second main surface side opposite to the first main surface of the semiconductor substrate in which the photosensitive region exists;
In semiconductor image sensors that contain
A semiconductor image sensor, wherein a first thickness of a part of the semiconductor substrate in the connection region is smaller than a second thickness of a part of the semiconductor substrate in the photosensitive region and the circuit region. The region having the first thickness is equal to the region occupied by the connection region;
2. The semiconductor image sensor according to claim 1, wherein the region having the second thickness is equal to a region occupied by the photosensitive region and the circuit region. In the region having the first thickness,
All of the area occupied by the connection area;
A portion of the area occupied by the photosensitive area and the circuit area;
The semiconductor image sensor according to claim 1, wherein In the region having the second thickness,
All of the area occupied by the photosensitive area and the circuit area;
A portion of the area occupied by the connection area;
The semiconductor image sensor according to claim 1, wherein The photosensitive region and the circuit region configured on the first main surface of the semiconductor substrate;
The connection area adjacent to at least one of the photosensitive area or the circuit area,
The connection region includes the electrical connection means for guiding the signal of the circuit region to the outside of the semiconductor substrate,
The electrical connection means includes the through electrode provided in the connection region;
The terminal capable of being electrically connected to the through electrode from the second main surface side opposite to the first main surface of the semiconductor substrate in which the photosensitive region exists;
In semiconductor image sensors that contain
A semiconductor image sensor characterized in that a region from which the semiconductor substrate is removed exists in a part of the connection region including a region where the through electrode exists.   6. The semiconductor image according to claim 1, wherein a reflection layer that reflects incident light that has passed through a photodiode and re-enters the photodiode is provided on the second main surface of the semiconductor substrate. Sensor   7. The structure according to claim 1, wherein the second main surface of the semiconductor substrate in the photosensitive region and the circuit region is in contact with a substrate surface on which the semiconductor image sensor is mounted. Semiconductor image sensor 8. The semiconductor image sensor according to claim 1, wherein the semiconductor image sensor is mounted in a curved manner in accordance with a curved structure of a substrate surface on which the semiconductor image sensor according to claim 1 is mounted.