Spectroscopic sensor having a wire connected to a substrate through a hole of a filter region

A spectroscopic sensor 1A comprises an interference filter unit 20A having a cavity layer 21 and first and second mirror layers 22, 23 and a light detection substrate 30 having a light-receiving surface 32a for receiving light transmitted through the interference filter unit 20A. The interference filter unit 20A has a first filter region 24 corresponding to the light-receiving surface 32a and a ring-shaped second filter region 25 surrounding the first filter region 24. The light detection substrate 30 has a plurality of pad units 33a contained in the second filter region 25, while the second filter region 25 is formed with through holes 6 for exposing the pad units 33a to the outside.

TECHNICAL FIELD

The present invention relates to a spectroscopic sensor.

BACKGROUND ART

Known as a conventional spectroscopic sensor is one comprising an optical filter unit for selectively transmitting therethrough a predetermined wavelength range of light according to an incident position thereof and a light detection substrate for detecting the light transmitted through the optical filter unit. In spectroscopic sensors disclosed in Patent Literatures 1 and 2, for example, the optical filter unit is provided so as to correspond to a light-receiving surface of the light detection substrate and functions as a whole as a filter region for transmitting therethrough light to be incident on the light-receiving surface of the light detection substrate.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Since the optical filter unit as a whole functions as a filter region for transmitting therethrough light to be incident on the light-receiving surface of the light detection substrate, however, filter characteristics may immediately deteriorate if a side face of the optical filter unit is adversely affected in any way in the spectroscopic sensors disclosed in Patent Literatures 1 and 2. Also, noise light may easily enter the optical filter unit from a side face thereof.

It is therefore an object of the present invention to provide a spectroscopic sensor which can prevent filter characteristics of a filter region transmitting therethrough light to be incident on the light-receiving surface of the light detection substrate from deteriorating and restrain noise light from entering the filter region.

Solution to Problem

The spectroscopic sensor of the present invention comprises an interference filter unit, having a cavity layer and first and second mirror layers opposing each other through the cavity layer, for selectively transmitting therethrough a predetermined wavelength range of light according to an incident position thereof from the first mirror layer side to the second mirror layer side; and a light detection substrate, having a light-receiving surface for receiving the light transmitted through the interference filter unit, for detecting the light incident on the light-receiving surface; the interference filter unit having a first filter region corresponding to the light-receiving surface as seen in a predetermined direction intersecting the light-receiving surface and a ring-shaped second filter region surrounding the first filter region as seen in the predetermined direction; the light detection substrate having a plurality of pad units for wiring contained in the second filter region as seen in the predetermined direction; the second filter region being formed with a through hole for exposing the pad units to the outside; a wire being connected to each of the pad units through the through hole.

In this spectroscopic sensor, the first filter region for transmitting therethrough light to be incident on the light-receiving surface of the light detection substrate is surrounded by the ring-shaped second filter region as seen in a predetermined direction intersecting the light-receiving surface. This makes the second filter region protect the first filter region and thus can prevent filter characteristics of the first filter region from deteriorating. The second filter region is also formed with a through hole for connecting the pad unit and a wire to each other. As a consequence, when seen in the predetermined direction, a part of the second filter region continuously exists in a ring-shaped area about the first filter region passing the inside of the through hole, whereby this part favorably functions as a filter even when the through hole for connecting the pad unit and the wire is formed, whereby noise light can be restrained from entering the first filter region.

Here, a plurality of through holes may be formed for the respective pad units. This structure allows a part of the second filter region to exist in an area between the through holes adjacent to each other, which can more strongly restrain noise light from entering the first filter region.

The distance in the predetermined direction between the first and second mirror layers may be variable in the first filter region and fixed in the second filter region. This structure can further narrow the wavelength range of light transmittable through the second filter region, thereby more strongly restraining noise light from entering the first filter region. By “fixed” is meant not only completely fixed but also substantially fixed within ranges of errors in manufacture and the like.

The spectroscopic sensor may further comprise an optical filter unit for transmitting therethrough at least the light incident on the second filter region, a wavelength range of the light transmitted through the optical filter unit and a wavelength range of the light transmitted through the second filter region being different from each other. This structure lets the optical filter unit and the second filter region cooperate with each other, so that the wavelength range of light transmittable through both of the optical filter unit and second filter region becomes narrower, thereby making it possible to more strongly restrain noise light from entering the first filter region.

The cavity layer may be formed continuously in the first and second filter regions. This structure can stabilize the cavity layer in terms of strength and characteristic.

The first mirror layer may be formed continuously in the first and second filter regions, while the second mirror layer may be formed continuously in the first and second filter regions. This structure can stabilize the first and second mirror layers in terms of strength and characteristic.

The second filter region may contain the first filter region as seen in a direction parallel to the light-receiving surface. This structure lets the second filter region receive external forces, if any, acting along a direction perpendicular to the light-receiving surface and thus can prevent the first filter region from being damaged.

The predetermined direction may be a direction perpendicular to the light-receiving surface. This configuration can simplify the structure of the spectroscopic sensor.

Advantageous Effects of Invention

The present invention can provide a spectroscopic sensor which can prevent filter characteristics of a filter region for transmitting therethrough light to be incident on the light-receiving surface of the light detection substrate from deteriorating and restrain noise light from entering the filter region.

DESCRIPTION OF EMBODIMENTS

In the following, preferred embodiments of the present invention will be explained in detail with reference to the drawings. In the drawings, the same or equivalent parts will be referred to with the same signs while omitting their overlapping descriptions.

First Embodiment

As illustrated inFIG. 1, a spectroscopic sensor1A of the first embodiment comprises an interference filter unit20A, a light detection substrate30, and a package2containing the interference filter unit20A and light detection substrate30. The package2is formed from a resin or the like into a rectangular parallelepiped box and opens on one side (the light entrance side of the interference filter unit20A and light detection substrate30) in the height direction. In the following explanation, X, Y, and Z axes are set in the length, width, and height directions of the package2, respectively.

The light detection substrate30is secured onto a bottom wall2awithin the package2. The interference filter unit20A is joined onto the light detection substrate30with a coupling layer3interposed therebetween. An optical filter layer (optical filter unit)4is formed on the interference filter unit20A, while a protective film5is formed on the optical filter layer4. For example, the coupling layer3is a silicon oxide film formed by film-forming processing using TEOS (Tetraethyl Orthosilicate, Tetraethoxysilane) as a material gas and has a thickness on the order of several tens of nm to several tens of μm. The optical filter layer4is a dielectric multilayer film or organic color filter (color resist) and has a thickness on the order of several tens of nm to several tens of μm. The protective film5is made of SiO2or the like and has a thickness on the order of several tens of nm to several tens of μm.

The light detection substrate30is a semiconductor light-receiving element having a semiconductor substrate31shaped into a rectangular plate whose longitudinal and thickness directions lie along the X and Z axes, respectively. A light-receiving unit32is formed in a part including a surface31aon one side of the semiconductor substrate31. The light-receiving unit32is a photodiode array in which linear photodiodes each extending along the Y axis are arranged one-dimensionally along the X axis. The light-receiving unit32has a light-receiving surface32aon which light transmitted through the interference filter unit20A is incident, while the light detection substrate30is constructed such as to detect the light incident on the light-receiving surface32a. For example, the semiconductor substrate31has a thickness on the order of several tens of μm to several hundreds of μm. The light-receiving unit32has a length along the X axis on the order of several hundreds of μm to several tens of mm and a width along the Y axis of several μm to several tens of mm. The light detection substrate30may also be any of other semiconductor light-receiving elements (C-MOS image sensors, CCD image sensors, infrared image sensors, and the like).

Pad units33afor leads33for inputting and outputting electric signals with respect to the light-receiving unit32are formed on the surface31aof the semiconductor substrate31. A protective film34is formed on the surface31aof the semiconductor substrate31so as to cover the light-receiving unit32and leads33, while a planarization layer35whose surface on the interference filter unit20A side is planarized by CMP (Chemical Mechanical Polishing) is formed on the protective film34. For example, the protective film34is made of SiO2or the like and has a thickness on the order of several tens of nm to several tens of μm. The planarization layer35is made of SiO2or the like and has a thickness on the order of several tens of nm to several tens of μm.

The interference filter unit20A has a cavity layer21and first and second mirror layers22,23opposing each other through the cavity layer21. The interference filter unit20A is an LVF (Linear Variable Filter) which selectively transmits therethrough a predetermined wavelength range of light according to an incident position thereof from the first mirror layer22side to the second mirror layer23side. For example, the cavity layer21is a silicon oxide film (SiO2film) formed by thermally oxidizing silicon and has a thickness on the order of several tens of nm to several tens of μm. Each of the mirror layers22,23is a DBR (Distributed Bragg Reflector) layer constituted by a dielectric multilayer film made of SiO2, SiN, TiO2, Ta2O5, Nb2O5, Al2O3, MgF2, Si, Ge, and the like and has a thickness on the order of several tens of nm to several tens of μm.

As illustrated inFIGS. 1 and 2, the interference filter unit20A has a first filter region24, a second filter region25, and a connection region26. The first filter region24corresponds to the light-receiving surface32aof the light detection substrate30as seen in the Z axis (a direction perpendicular to the light-receiving surface32a). That is, the first filter region24and light-receiving surface32aare formed such that one of them contains the other as seen in the Z axis (encompassing a case where they are equal to each other in terms of at least one of the length along the X axis and width along the Y axis). The second filter region25surrounds the first filter region24like a ring (a rectangular ring here) with the connection region26interposed therebetween as seen in the Z axis. The second filter region25contains the first filter region24as seen in a direction perpendicular to the Z axis (i.e., a direction parallel to the light-receiving surface32a). For example, the connection region26has a width on the order of several μm to 1 mm.

As illustrated inFIG. 1, the front face21aof the cavity layer21in the first filter region24is parallel to the XY plane. On the other hand, the rear face21bof the cavity layer21in the first filter region24tilts from the XY plane such that one end21cin the X-axis direction of the rear face21bis separated from a plane including the light-receiving surface32a(e.g., the surface31aof the semiconductor substrate31) more than is the other end21din the X-axis direction of the rear face21b. For example, the thickness of the cavity layer21in the first filter region24gradually decreases toward one side in the X-axis direction within the range on the order of several tens of nm to several μm.

The front face21aand rear face21bof the cavity layer21in the second filter region25are parallel to the XY plane. The distance along the Z axis (which will hereinafter be simply referred to as “distance”) from the plane including the light-receiving surface32ato the front face21aof the cavity layer21in the second filter region25equals the distance from the plane including the light-receiving surface32ato the front face21aof the cavity layer21in the first filter region24. On the other hand, the distance from the plane including the light-receiving surface32ato the rear face21bof the cavity layer21in the second filter region25equals the distance from the plane including the light-receiving surface32ato the other end21dof the rear face21bof the cavity layer21in the first filter region24. For example, the thickness of the cavity layer21in the second filter region25is about 700 nm.

The front face21aand rear face21bof the cavity layer21in the connection region26are parallel to the XY plane. The distance from the plane including the light-receiving surface32ato the front face21aof the cavity layer21in the connection region26equals the distance from the plane including the light-receiving surface32ato the front face21aof the cavity layer21in the first filter region24. On the other hand, the distance from the plane including the light-receiving surface32ato the rear face21bof the cavity layer21in the connection region26equals the distance from the plane including the light-receiving surface32ato one end21cof the rear face21bof the cavity layer21in the first filter region24. For example, the thickness of the cavity layer21in the connection region26is about 500 nm.

As in the foregoing, the cavity layer21is formed continuously over the first filter region24, second filter region25, and connection region26. The front face21aof the cavity layer21is flush in the first filter region24, second filter region25, and connection region26. On the other hand, the rear face21bof the cavity layer21has a difference in level between the first filter region24and the connection region26which becomes the smallest (0 here) at one end21cand the largest at the other end21d. The rear face21bof the cavity layer21has a fixed difference in level between the second filter region25and the connection region26.

The first mirror layer22is formed continuously on the front face21aof the cavity layer21over the first filter region24, second filter region25, and connection region26. On the other hand, the second mirror layer23is formed continuously on the rear face21bof the cavity layer21and the vertical surfaces of the difference in level (risers) over the first filter region24, second filter region25, and connection region26. Hence, the distance between the first and second mirror layers22,23varies in the first filter region24. The distance between the first and second mirror layers22,23is fixed in the second filter region25.

As illustrated inFIGS. 1 and 2, a plurality of pad units33afor the leads33in the light detection substrate30are formed on the surface31aof the semiconductor substrate31so as to be contained in the second filter region25as seen in the Z axis. More specifically, a plurality of pad units33aare provided in a row along the Y axis in each of both end regions in the X-axis direction of the surface31a. As illustrated inFIGS. 1 and 3, a plurality of through holes6for exposing the pad units33ato the outside are formed in the second filter region25for the respective pad units33a. Each through hole6penetrates through the protective film34, planarization layer35, coupling layer3, second filter region25(i.e., the cavity layer21and first and second mirror layers22,23), optical filter layer4, and protective film5along the Z axis, so as to expose a part (or whole) of the pad unit33ato the outside. SinceFIG. 1emphasizes the thickness of each layer,FIGS. 1 and 3differ from each other in their aspect ratios, so thatFIG. 3is closer to the actual aspect ratio thanFIG. 1. The opening edge of the protective film34, which is on the outer side of that of the other layers (the planarization layer35, coupling layer3, second filter region25, optical filter layer4, and protective film5) in the structure ofFIGS. 1 to 3, may be located at the same position as with the latter as seen in the Z axis.

A wire7is connected to each pad unit33athrough the through hole6. For example, the wire7is made of Au and has one end with a ball part7awhich is bonded to the surface of the pad unit33aunder thermocompression while being provided with ultrasonic vibrations. A gap is formed between the inner surface of the through hole6and the ball part7ain order to prevent the second filter region25and the like from being damaged in contact with the ball part7a. The other end of the wire7is connected through the bottom wall2aof the package2to a mounting pad unit8disposed on the outer surface of the bottom wall2a.

When light enters the package2through the opening thereof in thus constructed spectroscopic sensor1A, only a predetermined wavelength range of light to be incident on the first filter region24of the interference filter unit20A in the light passing through the protective film5is transmitted through the optical filter layer4. Here, the wavelength range of light transmitted through the optical filter layer4and the wavelength range of light transmitted through the second filter region25of the interference filter unit20A differ from each other. For example, the wavelength range of light transmitted through the optical filter layer4is 800 nm to 1000 nm, while the wavelength range of light transmitted through the second filter region25is 800 nm or shorter and 1000 nm or longer.

When the light passing through the optical filter layer4is incident on the first filter region24, a predetermined wavelength range of the light is selectively transmitted therethrough according to its incident position. The light transmitted through the first filter region24passes through the coupling layer3, planarization layer35, and protective film34, so as to be made incident on the light-receiving surface32aof the light detection substrate30. Here, the wavelength of light incident on each channel of the light-receiving unit32of the light detection substrate30is determined uniquely by the thickness of the cavity layer21at the incident position and the materials and thicknesses of the first and second mirror layers22,23. As a consequence, different wavelengths of light are detected for the respective channels of the light-receiving unit32in the light detection substrate30.

In the spectroscopic sensor1A, as explained in the foregoing, the first filter region24for transmitting therethrough light to be incident on the light-receiving surface32aof the light detection substrate30is surrounded by the ring-shaped second filter region25as seen in the Z axis. This allows the second filter region25to protect the first filter region24, thereby preventing filter characteristics of the first filter region24from deteriorating. This can also protect a region surrounding the light-receiving unit32in the light detection substrate30. A plurality of through holes6for connecting the pad units33ato their corresponding wires7are also formed in the second filter region25for the respective pad units33a. Therefore, a part of the second filter region25exists continuously in a ring-shaped area about the first filter region24passing the inside of the through holes6as seen in the Z axis (seeFIG. 2). A part of the second filter region25also exists in an area between the through holes6,6adjacent to each other (seeFIG. 2). Hence, even when the through holes6for connecting the pad units33ato the wires7are formed, a part of the second filter region25can function favorably as a filter, thereby restraining noise light from entering the first filter region24.

In the second filter region25, the first and second mirror layers22,23have a fixed distance therebetween. This can further narrow the wavelength range of light transmittable through the second filter region25, thereby more strongly restraining various wavelengths of noise light from entering the first filter region24.

While the optical filter layer4transmitting therethrough not only the light incident on the first filter region24but also the light incident on the second filter region25is provided, the wavelength range of light transmitted through the optical filter layer4and the wavelength range of light transmitted through the second filter region25differ from each other. This lets the optical filter layer4and the second filter region25cooperate with each other, so that the wavelength range of light transmittable through both of the optical filter layer4and second filter region25becomes narrower, thereby making it possible to more strongly restrain noise light from entering the first filter region24.

The cavity layer21is formed continuously in the first and second filter regions24,25. This can stabilize the cavity layer21in terms of strength and characteristic.

The first mirror layer22is formed continuously in the first and second filter regions24,25, while the second mirror layer23is formed continuously in the first and second filter regions24,25. This can stabilize the first and second mirror layers22,23in terms of strength and characteristic.

The second filter region25contains the first filter region24as seen in a direction perpendicular to the Z axis. This lets the second filter region25receive external forces, if any, acting along the Z axis and thus can prevent the first filter region24from being damaged.

A method for manufacturing the above-mentioned spectroscopic sensor1A will now be explained. The following steps may be performed by using a wafer formed with a plurality of members corresponding to respective spectroscopic sensors1A, such that the wafer is finally diced into the spectroscopic sensors1A, each constructed by the light detection substrate30having the interference filter unit20A bonded thereto.

First, as illustrated inFIG. 4(a), principal surfaces50a,50bof a silicon substrate50are thermally oxidized, so as to form silicon oxide films52on principal surfaces51a,51bof a handle substrate51made of silicon, and the silicon oxide film52formed on one of the principal surfaces51a,51bof the handle substrate51is employed as a surface layer53. Here, the silicon oxide film52formed on one principal surface51aof the handle substrate51is assumed to be the surface layer53.

Subsequently, a resist layer54is applied onto the surface layer53as illustrated inFIG. 4(b)and then is patterned as illustrated inFIG. 5(a)in order to form the cavity layer21by etching. Thereafter, as illustrated inFIG. 5(b), the surface layer53disposed on the handle substrate51is etched (etched back) through the resist layer54serving as a mask, so as to form the cavity layer21.

Next, as illustrated inFIG. 6(a), the second mirror layer23is formed on the cavity layer21. When forming the second mirror layer23, a film is formed by ion plating, vapor deposition, sputtering, or the like and, if necessary, photoetched and lifted off, or patterned by etching. Subsequently, as illustrated inFIG. 6(b), a silicon oxide film is formed so as to cover the second mirror layer23, and its surface is planarized by CMP, so as to form the coupling layer3.

Then, as illustrated inFIG. 7(a), the surface of the coupling layer3is directly bonded (by surface-activated bonding or the like) to the surface of the planarization layer35of the light detection substrate30. Subsequently, as illustrated inFIG. 7(b), grinding, polishing, etching, and the like are performed, so as to remove the silicon oxide film52and handle substrate51.

Thereafter, as illustrated inFIG. 8(a), the first mirror layer22is formed as with the second mirror layer23on the cavity layer21exposed by removing the handle substrate51. This makes the first and second mirror layers22,23oppose each other through the cavity layer21, thereby forming the interference filter unit20A.

Next, the optical filter layer4is formed on the first mirror layer22as illustrated inFIG. 8(b), and the protective film5is formed on the optical filter layer4as illustrated inFIG. 9(a). When forming the optical filter layer4from a dielectric multilayer film, film forming by ion plating, vapor deposition, sputtering, or the like and photoetching and liftoff, or patterning by etching are performed. When formed from an organic color filter, the optical filter layer4is patterned by exposure to light, development, and the like as with a photoresist.

Subsequently, as illustrated inFIG. 9(b), a part of the light detection substrate30which corresponds to each pad unit33ais etched, so as to form the through hole6. Then, as illustrated inFIG. 1, the light detection substrate30having the interference filter unit20A bonded thereto is secured to the bottom wall2aof the package2. Thereafter, one end of the wire7is connected to the pad unit33athrough the through hole6, while the other end of the wire7is connected to the pad unit8through the bottom wall2aof the package2, so as to yield the spectroscopic sensor1A.

As illustrated inFIG. 10, a light-transmitting substrate11may be attached to the opening of the package2in the spectroscopic sensor1A in accordance with the first embodiment. For example, the light-transmitting substrate11is made of glass or the like and has a thickness on the order of several hundreds of μm to several mm. The optical filter layer4may be formed on at least one of the front face11aand rear face11bof the light-transmitting substrate11. In this case, the optical filter layer4is not required to be formed on the first mirror layer22. Color glass or filter glass which can transmit therethrough a predetermined wavelength range of light may also be used as a material for the light-transmitting substrate11.

As illustrated inFIG. 11, the light-transmitting substrate11formed with the optical filter layer4may be joined onto the protective film5through an optical resin material or the like or by direct bonding. In this case, the optical filter layer4is not required to be formed on the first mirror layer22. Interstices between the light detection substrate30and interference filter unit20A and inner surfaces of side walls of the package2may be filled with a light-absorbing resin material12. This structure can more securely prevent noise light from entering the first filter region24. In all of the modes of the spectroscopic sensor1A, the protective film5may be omitted.

Second Embodiment

As illustrated inFIG. 12, a spectroscopic sensor1B of the second embodiment differs from the spectroscopic sensor1A of the first embodiment mainly in the structure of an interference filter unit20B. In the following, the spectroscopic sensor1B of the second embodiment will be explained with a focus on the structure of the interference filter unit20B.

In the spectroscopic sensor1B, the interference filter unit20B is formed on the planarization layer35of the light detection substrate30. The interference filter unit20B has the cavity layer21and the first and second mirror layers22,23opposing each other through the cavity layer21. The interference filter unit20B is an LVF which transmits therethrough a predetermined wavelength range of light according to its incident position from the first mirror layer22side to the second mirror layer23side.

The interference filter unit20B has the first filter region24, second filter region25, and connection region26. The first filter region24corresponds to the light-receiving surface32aof the light detection substrate30as seen in the Z axis. The second filter region25surrounds the first filter region24like a ring with the connection region26interposed therebetween as seen in the Z axis. The second filter region25contains the first filter region24as seen in a direction perpendicular to the Z axis.

The front face21aof the cavity layer21in the first filter region24tilts with respect to the XY plane such that one end21ein the X-axis direction of the front face21ais separated from the plane including the light-receiving surface32amore than is the other end21fin the X-axis direction of the front face21a. On the other hand, the rear face21bof the cavity layer21in the first filter region24is parallel to the XY plane.

The front face21aand rear face21bof the cavity layer21in the second filter region25are parallel to the XY plane. The distance from the plane including the light-receiving surface32ato the front face21aof the cavity layer21in the second filter region25equals the distance from the plane including the light-receiving surface32ato one end21eof the front face21aof the cavity layer21in the first filter region24. On the other hand, the distance from the plane including the light-receiving surface32ato the rear face21bof the cavity layer21in the second filter region25equals the distance from the plane including the light-receiving surface32ato the rear face21bof the cavity layer21in the first filter region24. For example, the thickness of the cavity layer21in the second filter region25is about 700 nm.

The front face21aand rear face21bof the cavity layer21in the connection region26are parallel to the XY plane. The distance from the plane including the light-receiving surface32ato the front face21aof the cavity layer21in the connection region26equals the distance from the plane including the light-receiving surface32ato the other end21fof the front face21aof the cavity layer21in the first filter region24. On the other hand, the distance from the plane including the light-receiving surface32ato the rear face21bof the cavity layer21in the connection region26equals the distance from the plane including the light-receiving surface32ato the rear face21bof the cavity layer21in the first filter region24. For example, the thickness of the cavity layer21in the connection region26is about 500 nm.

As in the foregoing, the cavity layer21is formed continuously over the first filter region24, second filter region25, and connection region26. The front face21aof the cavity layer21has a difference in level between the first filter region24and the connection region26which becomes the largest at one end21eand the smallest (0 here) at the other end21f. The front face21aof the cavity layer21has a fixed difference in level between the second filter region25and the connection region26. On the other hand, the rear face21bof the cavity layer21is flush in the first filter region24, second filter region25, and connection region26.

The first mirror layer22is formed continuously on the front face21aof the cavity layer21and the vertical surfaces of the difference in level over the first filter region24, second filter region25, and connection region26. On the other hand, the second mirror layer23is formed continuously on the rear face21bof the cavity layer21over the first filter region24, second filter region25, and connection region26. Hence, the distance between the first and second mirror layers22,23varies in the first filter region24. The distance between the first and second mirror layers22,23is fixed in the second filter region25.

A plurality of through holes6for exposing the pad units33ato the outside are formed in the second filter region25for the respective pad units33a. Each through hole6penetrates through the protective film34, planarization layer35, coupling layer3, second filter region25(i.e., the cavity layer21and first and second mirror layers22,23), optical filter layer4, and protective film5along the Z axis, so as to expose a part (or whole) of the pad unit33ato the outside. The opening edge of the protective film34may be located at the same position as with that of the other layers (the planarization layer35, coupling layer3, second filter region25, optical filter layer4, and protective film5) as seen in the Z axis.

When light enters the package2through the opening thereof in thus constructed spectroscopic sensor1B, only a predetermined wavelength range of light to be incident on the first filter region24of the interference filter unit20B in the light passing through the protective film5is transmitted through the optical filter layer4. Here, the wavelength range of light transmitted through the optical filter layer4and the wavelength range of light transmitted through the second filter region25of the interference filter unit20B differ from each other.

When the light passing through the optical filter layer4is incident on the first filter region24, a predetermined wavelength range of the light is selectively transmitted therethrough according to its incident position. The light transmitted through the first filter region24passes through the planarization layer35and protective film34, so as to be made incident on the light-receiving surface32aof the light detection substrate30. Here, the wavelength of light incident on each channel of the light-receiving unit32of the light detection substrate30is determined uniquely by the thickness of the cavity layer21at the incident position and the materials and thicknesses of the first and second mirror layers22,23. As a consequence, different wavelengths of light are detected for the respective channels of the light-receiving unit32in the light detection substrate30.

In the spectroscopic sensor1B, as explained in the foregoing, the first filter region24for transmitting therethrough light to be incident on the light-receiving surface32aof the light detection substrate30is surrounded by the ring-shaped second filter region25as seen in the Z axis. This allows the second filter region25to protect the first filter region24, thereby preventing filter characteristics of the first filter region24from deteriorating. This can also protect a region surrounding the light-receiving unit32in the light detection substrate30. A plurality of through holes6for connecting the pad units33ato their corresponding wires7are also formed in the second filter region25for the respective pad units33a. Therefore, a part of the second filter region25exists continuously in a ring-shaped area about the first filter region24passing the inside of the through holes6as seen in the Z axis. A part of the second filter region25also exists in an area between the through holes6,6adjacent to each other. Hence, even when the through holes6for connecting the pad units33ato the wires7are formed, a part of the second filter region25can function favorably as a filter, thereby restraining noise light from entering the first filter region24.

In the second filter region25, the first and second mirror layers22,23have a fixed distance therebetween. This can further narrow the wavelength range of light transmittable through the second filter region25, thereby more strongly restraining noise light from entering the first filter region24.

While the optical filter layer4transmitting therethrough not only the light incident on the first filter region24but also the light incident on the second filter region25is provided, the wavelength range of light transmitted through the optical filter layer4and the wavelength range of light transmitted through the second filter region25differ from each other. This lets the optical filter layer4and the second filter region25cooperate with each other, so that the wavelength range of light transmittable through both of the optical filter layer4and second filter region25becomes narrower, thereby making it possible to more strongly restrain noise light from entering the first filter region24.

The cavity layer21is formed continuously in the first and second filter regions24,25. This can stabilize the cavity layer21in terms of strength and characteristic.

The first mirror layer22is formed continuously in the first and second filter regions24,25, while the second mirror layer23is formed continuously in the first and second filter regions24,25. This can stabilize the first and second mirror layers22,23in terms of strength and characteristic.

The second filter region25contains the first filter region24as seen in a direction perpendicular to the Z axis. This lets the second filter region25receive external forces, if any, acting along the Z axis and thus can prevent the first filter region24from being damaged.

A method for manufacturing the above-mentioned spectroscopic sensor1B will now be explained. The following steps may be performed by using a wafer formed with a plurality of members corresponding to respective spectroscopic sensors1B, such that the wafer is finally diced into the spectroscopic sensors1B, each constructed by the light detection substrate30having the interference filter unit20B bonded thereto.

First, as illustrated inFIG. 13(a), the second mirror layer23is formed on the surface of the planarization layer35of the light detection substrate30. When forming the second mirror layer23, a film is formed by ion plating, vapor deposition, sputtering, or the like and, if necessary, photoetched and lifted off, or patterned by etching. Subsequently, as illustrated inFIG. 13(b), a silicon oxide film52is formed on the second mirror layer23, and its surface is planarized by CMP if necessary.

Next, as illustrated inFIG. 14(a), the resist layer54is applied onto the silicon oxide film52and patterned in order to form the cavity layer21by etching. Then, as illustrated inFIG. 14(b), the silicon oxide film52is etched (etched back) through the resist layer54serving as a mask, so as to form the cavity layer21.

Subsequently, as illustrated inFIG. 15(a), the first mirror layer22is formed on the cavity layer21as with the second mirror layer23. This makes the first and second mirror layers22,23oppose each other through the cavity layer21, thereby forming the interference filter unit20B. Then, the optical filter layer4is formed on the first mirror layer22as illustrated inFIG. 15(b), and the protective film5is formed on the optical filter layer4as illustrated inFIG. 16(a).

Next, as illustrated inFIG. 16(b), a part of the light detection substrate30which corresponds to each pad unit33ais etched, so as to form the through hole6. Subsequently, as illustrated inFIG. 12, the light detection substrate30formed with the interference filter unit20B is secured to the bottom wall2aof the package2. Then, one end of the wire7is connected to the pad unit33athrough the through hole6, while the other end of the wire7is connected to the pad unit8through the bottom wall2aof the package2, so as to yield the spectroscopic sensor1B.

As illustrated inFIG. 17, the light-transmitting substrate11may be attached to the opening of the package2in the spectroscopic sensor1B of the second embodiment as in the spectroscopic sensor1A of the first embodiment. The optical filter layer4may be formed on at least one of the front face11aand rear face11bof the light-transmitting substrate11. In this case, the optical filter layer4is not required to be formed on the first mirror layer22. Color glass or filter glass which can transmit therethrough a predetermined wavelength range of light may also be used as a material for the light-transmitting substrate11.

As illustrated inFIG. 18, the light-transmitting substrate11formed with the optical filter layer4may be joined onto the protective film5through an optical resin material41. In this case, the optical filter layer4is not required to be formed on the first mirror layer22. Interstices between the light detection substrate30and interference filter unit20B and inner surfaces of side walls of the package2may be filled with the light-absorbing resin material12. This structure can more securely prevent noise light from entering the first filter region24. In all of the modes of the spectroscopic sensor1B, the protective film5may be omitted. Grooves formed in the connection region26may be filled with the protective film5as illustrated inFIG. 12or not as illustrated inFIG. 18.

While the first and second embodiments of the present invention are explained in the foregoing, the present invention is not limited thereto. For example, constituent members of the spectroscopic sensor may employ various materials and forms without being restricted to those mentioned above. By way of example, the cavity layer may be made of materials such as TiO2, Ta2O5, SiN, Si, Ge, Al2O3, and light-transmitting resins. A material for the first and second mirror layers may be a metal film constituted by Al, Au, Ag, or the like having a thickness on the order of several nm to several μm. The sizes of the constituent members of the spectroscopic sensor are illustrated by way of example only. By “fixed” in the present invention and embodiments is meant not only completely fixed but also substantially fixed within ranges of errors in manufacture and the like. The same holds for “same,” “parallel,” “perpendicular,” “equal,” “flush,” and the like.

In the first filter region of the interference filter unit, the thickness of the cavity layer may vary two-dimensionally (not only along the X axis but also along the Y axis) or stepwise. The light detection substrate is not limited to the one-dimensional sensor but may be a two-dimensional sensor. The light detection substrate may also be a back-illuminated semiconductor light-receiving element.

In the interference filter unit, the first filter region and the second filter region surrounding the same may be connected directly to each other without forming the connection region. A region where the distance between the first and second mirror layers is not fixed or a region free of the first and second mirror layers may be formed about the second filter region.

The interference filter unit may have a plurality of first filter regions. In this case, the second filter region may be formed for each first filter region or a plurality of first filter regions so as to surround the same.

The through hole6for connecting the pad unit33aand the wire7to each other may be formed for a plurality of pad units33ain the second filter region25. That is, one through hole6may expose a plurality of pad units33ato the outside. A part of the second filter region25exists continuously in the ring-shaped area about the first filter region24passing the inside of the through holes6also in this case. Therefore, this part favorably functions as a filter even when the through hole6for connecting the pad unit33aand the wire7is formed, whereby noise light can be restrained from entering the first filter region24.

For joining the light detection substrate and the interference filter unit to each other, bonding with an optical resin material or at an outer edge part of the spectroscopic sensor may be employed. Examples of optical resin materials usable for bonding include organic materials of epoxy, acrylic, and silicone types and hybrid materials composed of organic and inorganic substances. The bonding at the outer edge part of the spectroscopic sensor may be done with low-melting glass, solder, or the like while holding a gap with a spacer. In this case, the area surrounded by the bonding part may be left as an air gap or filled with an optical resin material.

The interference filter unit may have a first filter region corresponding to the light-receiving surface of the light detection substrate as seen in a predetermined direction intersecting the light-receiving surface and a ring-shaped second filter region surrounding the first filter region as seen in the predetermined direction. The light detection substrate may have a plurality of pad units for wiring contained in the second filter region as seen in the predetermined direction. Here, the structure of the spectroscopic sensor can be simplified when the predetermined direction is perpendicular to the light-receiving surface of the light detection substrate.

In the light detection substrate30, the protective film34may be formed in an area similar to that of the planarization layer35so as to function as a planarization layer. In this case, the planarization layer35is not required to be provided separately. As for the optical filter layer4and protective film5formed on the interference filter unit20A,20B, the protective film5may be formed on the interference filter unit20A,20B side, and the optical filter layer4may be formed on the protective film5. The second filter region25may be formed thinner than the first filter region24. An antireflection film for preventing light incident on the light-receiving surface32aof the light detection substrate30from being reflected may be provided between the light-receiving surface32aand the second mirror layer23. For example, the antireflection film is a single-layer film or multilayer film made of Al2O3, TiO2, Ta2O5, SiO2, SiN, MgF2, or the like and has a thickness on the order of several tens of nm to several tens of μm. The protective film34or planarization layer35may be a film functioning as an antireflection film. Instead of providing such an antireflection film, the surface on the interference filter unit20A,20B side of the light detection substrate30may be subjected to antireflection processing. Examples of the antireflection processing include surface roughening such as black silicon processing and nanopillar structures. The antireflection film and antireflection processing can restrain stray light from occurring due to multireflection and interference of light between the second mirror layer23and the light-receiving surface32aof the light detection substrate30, thereby further improving filter characteristics.

As illustrated inFIGS. 19 and 20, the cavity layer21may have an outer edge part21gformed along its outer edge. The outer edge part21gis formed thinner than the cavity layer21in the second filter region25and connection region26. For example, the thickness of the cavity layer21is about 700 nm in the second filter region25and about 500 nm in the connection region26, while the thickness of the outer edge part21gis on the order of 400 nm to 500 nm. The width of the outer edge part21gis 50 μm or less. Thus constructed outer edge part21gyields the following effects. The first and second mirror layers22,23also formed on both sides of the outer edge part21gcan further restrict light transmitted through the outer side of the second filter region and restrain it from becoming stray light. When dicing a wafer formed with a plurality of members each corresponding to the spectroscopic sensor1A,1B, dicing lines are formed by photoetching and etching. Reflected light and transmitted light change their colors between parts where the cavity layer21is thinner (the outer edge part21g) and thicker (the cavity layer21in the second filter region25). Light may also scatter strongly at an edge between the parts where the cavity layer21is thinner and thicker. These make it possible to discern (recognize) the dicing lines clearly.

The spectroscopic sensor can be constructed as SMD (Surface Mount Device), CSP (Chip Size Package), BGA (Ball Grid Array), COB (Chip On Board), COF (Chip On Film), COG (Chip On Glass), and the like.

INDUSTRIAL APPLICABILITY

The present invention can provide a spectroscopic sensor which can prevent filter characteristics of a filter region transmitting therethrough light to be incident on the light-receiving surface of the light detection substrate from deteriorating and restrain noise light from entering the filter region.

REFERENCE SIGNS LIST