Optical sensor and method for forming the same

An optical sensor includes a plurality of pixels disposed in a substrate and a light collimating layer. The light collimating layer is disposed on the substrate. The light collimating layer includes a light-shielding layer, a plurality of transparent pillars, and a plurality of first dummy transparent pillars. The light-shielding layer is disposed on the substrate. The plurality of transparent pillars pass through the light-shielding layer and are disposed correspondingly on the plurality of pixels. The plurality of first dummy transparent pillars that pass through the light-shielding layer are disposed on a first peripheral region of the light collimating layer, wherein the plurality of first dummy transparent pillars surround the plurality of transparent pillars from a top view.

BACKGROUND

Technical Field

The disclosure relates to an optical element, and more particularly to an optical sensor and a method for forming the same.

Description of the Related Art

Optical elements in an optical sensor may include a light collimator, a beam splitter, a focusing lens, and a linear sensor, wherein the light collimator is utilized to ensure that light which is incident to the sensor is parallel, to reduce energy loss from divergent light. For example, the light collimator may be applied to an optical sensor to enhance the performance of a fingerprint sensor device.

The light collimator includes transparent pillars and a light-shielding layer surrounding the transparent pillars to collimate lights. However, during the process of manufacturing the light collimator, transparent pillars at the edge of the transparent pillar array may collapse easily and become deformed due to their cohesion force or the stress of the light-shielding layer, which can negatively affect the performance of the light collimator and thereby reduce the production yield of optical sensors.

While existing optical sensors have been generally adequate for their intended purposes, they have not been satisfactory in all respects. There is a particular need for further improvements in the structural strength of the light collimators used in optical sensors.

SUMMARY

In one embodiment of the present disclosure, an optical sensor is provided, wherein the optical sensor includes a plurality of pixels disposed in a substrate and a light collimating layer. The light collimating layer is disposed on the substrate. The light collimating layer includes a light-shielding layer, a plurality of transparent pillars, and a plurality of first dummy transparent pillars. The light-shielding layer is disposed on the substrate. The plurality of transparent pillars through the light-shielding layer are disposed correspondingly on the plurality of pixels. The plurality of first dummy transparent pillars through the light-shielding layer are disposed on a first peripheral region of the light collimating layer, wherein the plurality of first dummy transparent pillars surround the plurality of transparent pillars from a top view.

In another embodiment of the present disclosure, a method for forming an optical sensor is provided, wherein the method includes: forming a plurality of pixels in a substrate and forming a light collimating layer on the substrate. The steps for forming the light collimating layer comprise: forming a plurality of transparent pillars and a plurality of first dummy transparent pillars on the substrate, wherein the plurality of transparent pillars are disposed correspondingly on the plurality of pixels and the plurality of first dummy transparent pillars are disposed on a first peripheral region of the light collimating layer; and forming a light-shielding layer between the plurality of transparent pillars and the plurality of first dummy transparent pillars, wherein the plurality of first dummy transparent pillars surround the plurality of transparent pillars from a top view.

In order to make the purposes, features and advantages of the present disclosure easy to understand, a detailed description is given in the following embodiments with reference to the accompanying drawings.

DETAILED DESCRIPTION

The terms “about”, “approximately”, and “substantially” used herein generally refer to the value of an error or a range within 20 percent, preferably within 10 percent, and more preferably within 5 percent, within 3 percent, within 2 percent, within 1 percent, or within 0.5 percent. If there is no specific description, the values mentioned are to be regarded as an approximation that is an error or range expressed as “about”, “approximate”, or “substantially”.

Although some embodiments are discussed with operations performed in a particular order, these operations may be performed in another logical order. Some of the steps that are described can be replaced or eliminated for different embodiments. Additional operations can be provided before, during, and/or after the steps described in the embodiments of present disclosure. Additional features can be provided to the optical sensors in embodiments of the present disclosure. Some of the features described below can be replaced or eliminated for different embodiments.

The embodiments of the present disclosure provide an optical sensor. In the light collimating layer of the optical sensor, in addition to disposing the transparent pillar array on the corresponding pixel array, dummy transparent pillars are disposed at the perimeter of the transparent pillars. The dummy transparent pillars can strengthen the structure of the transparent pillar array to prevent the transparent pillars at the edge of the array from deformation and collapse. The uniformity of the transparent pillars can be enhanced and the production yield can be improved as a result.

FIGS. 1A, 2A, and 3Aare cross-sectional views illustrating various steps in forming an optical sensor100, according to some embodiments of the present disclosure.FIGS. 1B, 2B, and 3Bare top views illustrating various steps in forming an optical sensor, according to some embodiments of the present disclosure.FIGS. 1A, 2A, and 3Aare cross-sectional views along the line segment A-A′ inFIGS. 1B, 2B, and 3B.

As shown inFIGS. 1A and 1B, a substrate102is provided. The substrate102may be a semiconductor substrate, such as a silicon substrate. Furthermore, in some embodiments, the semiconductor substrate may be an elemental semiconductor including germanium, a compound semiconductor including gallium nitride, silicon carbide, gallium arsenide, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide, an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP, or a combination thereof. In some embodiments, the substrate102may also be a semiconductor on insulator substrates, the semiconductor on insulator substrates may include a substrate, a buried oxide layer disposed on the substrate, and a semiconductor layer disposed on the buried oxide layer. In addition, the conductivity type of the substrate102may be N-type or P-type.

In some embodiments, the substrate102may include various isolation features (not shown) to define an active region and electronically isolate active elements in or on the substrate102. In some embodiments, examples of the isolation features include shallow trench isolation (STI) features, local oxidation of silicon (LOCOS) features, other suitable isolation features, or combinations thereof. In some embodiments, for example, forming the isolation features may include forming an insulating layer on the substrate102, selectively etching the insulating layer and the substrate102to form trenches in the substrate102, growing a nitrogen-rich (e.g., silicon oxynitride) liner layer in the trenches, filling insulating materials (e.g., silicon dioxide, silicon nitride, or silicon oxynitride) in the trenches using a deposition process, performing an annealing process on the insulating materials in the trenches, and performing a planarization process such as a chemical mechanical polishing (CMP) process on the substrate102to remove excess insulating materials such that the insulating materials in the trenches are level with the top surface of the substrate102.

In some embodiments, the substrate102may include various P-type doped regions and/or N-type doped regions which are formed by an ion implantation and/or a diffusion process. In some embodiments, the doped regions may be formed into transistors, photodiodes and so on. However, these elements are merely exemplary, and the present disclosure is not limited thereto.

In some embodiments, the substrate102may include various conductive features, such as a conductive line or a via (not shown). For example, the conductive features may be made of aluminum, copper, tungsten, other suitable conductive materials, an alloy thereof, or a combination thereof.

As shown inFIGS. 1A and 1B, in some embodiments, the optical sensor100is divided into a central region104C and a first peripheral region104P. As shown in the top view ofFIG. 1B, the first peripheral region104P surrounds the central region104C.

As shown inFIGS. 1A and 1B, in some embodiments, the substrate102may include pixels106. The pixels106may include a photodetector and readout circuitry. The photodetector may include a charged coupling device (CCD) sensor, a complimentary metal-oxide-semiconductor (CMOS) image sensor, an active sensor, a passive sensor, other suitable sensors, or a combination thereof. The readout circuitry may include a transfer transistor, a reset transistor, a source-follower transistor, a select transistor, one or more other suitable transistors, or a combination thereof. The pixels106may transform the received optical signals into electronic signals through a photodetector, and process the electronic signals through the readout circuitry. In such cases, a pixel106may correspond to at least one photodetector, such as at least one photodiode. As shown inFIG. 1B, the pixels106are arranged in an array from a top view and disposed in the central region104C of the substrate102. It should be noted that the number and arrangement of the pixel106array are merely an example, and the embodiments of the present disclosure are not limited thereto. The pixels106may be formed into an array with any number of rows and columns, or in any other arrangement.

Subsequently, as shown inFIGS. 2A and 2B, transparent pillars108and first dummy transparent pillars108D are formed on the substrate102. In some embodiments, a transparent layer may be blanketly formed on the substrate102first. In some embodiments, the transparent layer may include a transparent material, wherein the light transmittance of the transparent material to light with a wavelength in a range from 200 nm to 1200 nm is greater than 80%. The transparent material may include a light-curable material, a thermosetting material, or a combination thereof. In some embodiments, the transparent material may include polymethyl methacrylate (PMMA), perfluorocyclobutyl (PFCB), polymer, polyimide (PI), epoxy resins, other suitable materials, or a combination thereof. In some embodiments, the transparent material may be deposited on the substrate102through a process such as spin-coating, chemical vapor deposition (CVD), physical vapor deposition (PVD) (e.g. evaporation or sputtering), electro-plating, atomic layer deposition (ALD), other suitable processes, or a combination thereof.

Subsequently, the transparent material of the substrate102is selectively removed. In some embodiments, the transparent material is selectively removed by a patterning process and an etching process to form transparent pillars108correspondingly on the pixels106and to form first dummy transparent pillars108D around the transparent pillars108in the first peripheral region104P simultaneously. In some embodiments, the patterning process may include photoresist coating (e.g., spin-coating), soft baking, mask alignment, exposure, post-exposure baking, photoresist developing, rinsing and drying (e.g., hard baking), other suitable processes, or a combination thereof. The etching process may include such as a dry etching process (e.g., reactive ion etch (RIE), plasma etching, or ion milling), a wet etching process, other suitable processes, or a combination thereof.

Subsequently, as shown inFIGS. 3A and 3B, a light-shielding layer110is formed between the transparent pillars108and the first dummy transparent pillars108D on the substrate102. In some embodiments, the light-shielding layer110may include a light-shielding material, wherein the light absorptivity of the light-shielding material to light with a wavelength in a range from 200 nm to 1200 nm is greater than 80%. The light-shielding material may include a light-curable material, a thermosetting material, or a combination thereof. In some embodiments, the light-shielding material may include non-transparent photoresist, oil ink, molding compound, solder mask, other suitable materials, or a combination thereof. In some embodiments, the light-shielding material may be disposed between the transparent pillars108and the first dummy transparent pillars108D on the substrate102, and a curing process such as a light-curing process, a thermosetting process, or a combination thereof may be performed to cure the light-shielding material to form the light-shielding layer110.

As shown inFIGS. 3A and 3B, a light collimating layer112of the optical sensor100includes the transparent pillars108, the first dummy transparent pillars108D, and the light-shielding layer110. In some embodiments, other optical elements such as a color filter, a glass, a convexo-concave lens, and so on (not shown) may be included on the light collimating layer112. The incident lights through the optical elements on the light collimating layer112pass though the light collimating layer112to irradiate the pixels106. In such cases, the respective aspect ratio of the transparent pillars108and the first dummy transparent pillars108D is in a range from 5 to 20. If the transparent pillars108and the first dummy transparent pillars108D are too high, they are prone to deformation and collapse. If the transparent pillars108are too wide, the optical sensor101is prone to receiving unwanted incident lights and being difficult to achieve a good collimating performance. If the first dummy transparent pillars108D are too wide, the loading effect may occur and reduce the production yield.

In some embodiments, as shown inFIG. 3B, the arrangement of the transparent pillars108is also an array, since the transparent pillars108are correspondingly disposed on the pixels106. The transparent pillars108may cover the corresponding pixels106completely or partially. In this way, the transparent pillars108can protect the pixels106and prevent the pixels106from being covered with debris and/or contaminants during subsequent manufacturing. In some embodiments, as shown inFIG. 3B, the shape of each of the transparent pillars108is circular. In this way, the transparent pillars108cover a larger area than other patterns of equal diameter to increase the amount of light received by the pixels106, and further protect the corresponding pixels106.

In some embodiments, as shown inFIG. 3A, the first dummy transparent pillars108D do not correspond to any pixel106. Since the arrangement of the transparent pillars108is an array when viewed from a top view, the transparent pillars108at the edge of the array may be prone to deformation and collapse, due to the intermolecular cohesion force of the transparent material or the subsequent processes. By disposing the first dummy transparent pillars108D at the edge of the array of transparent pillars108to serve as a stress buffer to provide physical support, the structure of the array of transparent pillars108may be strengthened to prevent the deformation and collapse of the transparent pillars108at the edge of the array. The uniformity of the transparent pillars108can be maintained and the production yield can be improved as a result.

In some embodiments, as shown inFIG. 3B, the shape of each of the first dummy transparent pillars108D is oval. However, the present disclosure is not limited thereto. In other embodiments, the shape of the first dummy transparent pillars108D may be a circle, oval, or rectangle of any size according to design and processing requirements.

In some embodiments, as shown inFIG. 3B, the width W of each transparent pillar108is smaller than the width DW of each first dummy transparent pillar108D. In this way, the structure of the array of transparent pillars108can be strengthened further by the wider first dummy transparent pillars108D. However, the present disclosure is not limited thereto. In other embodiments, the width W of each transparent pillar108may be greater than or the same as the width DW of each first dummy transparent pillar108D. In such a case, the structure of the array of transparent pillars108can also be strengthened to prevent the transparent pillars108from deforming and collapsing. The uniformity of the transparent pillars108can be maintained and the production yield can be improved as a result.

In some embodiments, as shown inFIG. 3B, the pitch P of the transparent pillars108is the same as the pitch DP of the first dummy transparent pillars108D. In this way, the first dummy transparent pillars108D can be prevented from being too close to each other, which can cause them to collapse and become deformed. However, the present disclosure is not limited thereto. In other embodiments, if the process capability permits, the pitch DP of the first dummy transparent pillars108D can be smaller than the pitch P of the transparent pillars108. In this way, the structure of the array of transparent pillars108can be strengthened by the denser first dummy transparent pillars108D. Alternatively, in other embodiments, to prevent the first dummy transparent pillars108D from being too close to each other, which can cause them to collapse and become deformed, the pitch DP of the first dummy transparent pillars108D may be greater than the pitch P of the transparent pillars108.

In some embodiments, if the area of the transparent pillars108and the first dummy transparent pillars108D is too large, the peripheral elements of the light collimating layer112may be impacted. If the area of the transparent pillars108and the first dummy transparent pillars108D is too small, the area for sensing fingerprints is too small to sense fingerprints effectively.

In the embodiments above, the transparent pillars108and the first dummy transparent pillars108D may be formed by the same manufacturing process simultaneously and formed of the same material. In such cases, the cycle time and cost of the manufacturing process can be reduced. However, the present disclosure is not limited thereto. In other embodiments, the materials of the transparent pillars108and the first dummy transparent pillars108D may be different. For example, after forming the transparent pillars108on the pixels106and forming the light-shielding layer110between the transparent pillars108, a patterning process can be used to form openings in the light-shielding layer110in the first peripheral region104P around the transparent pillars108. The openings are filled with a transparent material which is different from that of the transparent pillars108to form the first dummy transparent pillars108D. Subsequently, a planarization process such as a chemical mechanical polishing (CMP) process may be performed on the transparent pillars108, the first dummy transparent pillars108D, and the light-shielding layer110to remove the excess transparent materials. By the different material of the first dummy transparent pillars108D, the structure of the array of transparent pillars108can be strengthened further to prevent the transparent pillars108at the edge of the array from deformation and collapse. The uniformity of the transparent pillars108can be maintained and the production yield can be improved as a result.

As described above, disposing dummy transparent pillars, which do not correspond to pixels, around the transparent pillar array of the light collimating layer of the optical sensor can strengthen the structure of the transparent pillar array to prevent the array from deforming and collapsing. The uniformity of the transparent pillars can be maintained and the production yield can be improved as a result.

FIG. 4is a top view illustrating an optical sensor, according to other embodiments of the present disclosure. The same or similar manufacturing processes or elements as those of the foregoing embodiments will be given the same reference numerals, and the details thereof will not be described again. The difference between the embodiments ofFIG. 4and the foregoing embodiments is that, as shown inFIG. 4, the optical sensor200includes multiple layers of first dummy transparent pillars208D in the first peripheral region104P.

In some embodiments, the different layers of the first dummy transparent pillars208D has the same material, and the different layers of the first dummy transparent pillars208D and the transparent pillars108are formed simultaneously. In other embodiments, the different layers of the first dummy transparent pillars208D are formed of different materials. The different layers of the first dummy transparent pillars208D with different materials are formed by several patterning processes after the forming of the light-shielding layer.

As shown in the embodiments inFIG. 4, the forming of the multiple layers of first dummy transparent pillars is used to strengthen the structure of the transparent pillar array to prevent the array from deforming and collapsing. The uniformity of the transparent pillars can be maintained and the production yield can be improved as a result.

It should be noted that the number of layers of the dummy transparent pillars illustrated inFIG. 4is merely an example, and the present disclosure is not limited thereto. In the embodiments of the present disclosure, depending on the process and design requirements, more than three layers of dummy transparent pillars may also be included.

FIG. 5is a top view illustrating an optical sensor300, according to some embodiments of the present disclosure. The same or similar manufacturing processes or elements as those of the foregoing embodiments will be given the same reference numerals, and the details thereof will not be described again. The difference between the embodiments ofFIG. 5and the embodiments inFIG. 4is that, as shown inFIG. 5, the optical sensor300includes multiple layers of first dummy transparent pillars308D staggered with each other in the first peripheral region104P around the transparent pillars108. The phrase “staggered with each other” herein means that the first dummy transparent pillars308D in the neighboring two layers are not aligned in the X and the Y directions.

As shown in the embodiments inFIG. 5, the forming of the multiple layers of first dummy transparent pillars staggered with each other is used to strengthen the structure of the transparent pillar array to prevent the array from deforming and collapsing. The uniformity of the transparent pillars can be maintained and the production yield can be improved as a result.

FIG. 6is a top view illustrating an optical sensor, according to other embodiments of the present disclosure. The same or similar manufacturing processes or elements as those of the foregoing embodiments will be given the same reference numerals, and the details thereof will not be described again. The difference between the embodiments ofFIG. 6and the foregoing embodiment is that, as shown inFIG. 6, the optical sensor400not only includes multiple layers of first dummy transparent pillars408D1in the first peripheral region404P1around the transparent pillars108, but also includes multiple layers of second dummy transparent pillars408D2in the second peripheral region404P2around the first dummy transparent pillars408D1. In some embodiments, at least one of the shape, size, pitch, and arrangement of the dummy transparent pillars is different in the different peripheral regions. For example, the shape, size, pitch, and arrangement of the first dummy transparent pillars408D1in the first peripheral region404P1are different from those of the second dummy transparent pillars408D2in the second peripheral region404P2.

In some embodiments, as shown inFIG. 6, the shape of the first dummy transparent pillars408D1is circular from a top view, and the shape of the second dummy transparent pillars408D2is oval from a top view. However, the present disclosure is not limited thereto. In other embodiments, the shape of each of the first dummy transparent pillars408D1and second dummy transparent pillars408D2may be a circle, oval, or rectangle of any size from a top view. In some embodiments, the shape of each of the first dummy transparent pillars408D1and second dummy transparent pillars408D2may be the same from a top view. In other embodiments, the shape of each of the first dummy transparent pillars408D1and second dummy transparent pillars408D2may be different. The shape of each of the dummy transparent pillars408D1and408D2may vary depending on design and processing requirements.

In some embodiments, as shown inFIG. 6, the width DW1of each first dummy transparent pillar408D1is smaller than the width DW2of each second dummy transparent pillar408D2. In this way, the structure of the array of transparent pillars108can be strengthened by the wider second dummy transparent pillars408D2. However, the present disclosure is not limited thereto. In other embodiments, the width DW1of each first dummy transparent pillar408D1may be greater than or the same as the width DW2of each second dummy transparent pillar408D2. In such a case, the structure of the array of transparent pillars108can be strengthened to prevent the transparent pillars108at the edge of the array from deforming and collapsing. The uniformity of the transparent pillars108can be maintained and the production yield can be improved as a result.

In some embodiments, as shown inFIG. 6, the pitch DP1of the first dummy transparent pillars408D1is the same as the pitch DP2of the second dummy transparent pillars408D2. In this way, the second dummy transparent pillars408D2can be prevented from being too close to each other, which can cause them to collapse and become deformed. However, the present disclosure is not limited thereto. In other embodiments, if the process capability permits, the pitch DP2of the second dummy transparent pillars408D2can be smaller than the pitch DP1of the first dummy transparent pillars408D1. In this way, the structure of the array of transparent pillars108can be strengthened by the denser second dummy transparent pillars408D2. Alternatively, to prevent the second dummy transparent pillars408D2from being too close to each other, which can cause them to collapse and become deformed, the pitch DP2of the second dummy transparent pillars408D2may be greater than the pitch DP1of the first dummy transparent pillars408D1.

In some embodiments, the transparent pillars108, the first dummy transparent pillars408D1, and the second dummy transparent pillars408D2may be formed by the same manufacturing process simultaneously and formed of the same material. In such cases, the cycle time and cost of the manufacturing process can be reduced. However, the present disclosure is not limited thereto. In other embodiments, the materials of the transparent pillars108, the first dummy transparent pillars408D1, and the second dummy transparent pillars408D2may be different than each other. For example, after forming the transparent pillars108on the pixels106and forming the light-shielding layer110between the transparent pillars108, a patterning process can be used to form openings in the light-shielding layer110in the first peripheral region404P1around the transparent pillars108. The openings are filled with a transparent material which is different from that of the transparent pillars108to form the first dummy transparent pillars408D1. Subsequently, a planarization process such as a chemical mechanical polishing (CMP) process may be performed on the transparent pillars108, the first dummy transparent pillars408D1, and the light-shielding layer110to remove the excess transparent materials. Subsequently, a patterning process can be used again to form openings in the light-shielding layer110in the second peripheral region404P2around the first dummy transparent pillars408D1. The openings are filled with a transparent material which is different from that of the first dummy transparent pillars408D1to form the second dummy transparent pillars408D2. Subsequently, a planarization process such as a chemical mechanical polishing (CMP) process may be performed on the transparent pillars108, the first dummy transparent pillars408D1, the second dummy transparent pillars408D2, and the light-shielding layer110to remove the excess transparent materials.

By the different materials of the first dummy transparent pillars408D1and the second dummy transparent pillars408D2, the structure of the array of transparent pillars108can be strengthened further to prevent the transparent pillars108at the edge of the array from deformation and collapse. The uniformity of the transparent pillars108can be maintained and the production yield can be improved as a result.

In some embodiments, the first dummy transparent pillars408D1and the second dummy transparent pillars408D2may be arranged into a single layer or multiple layers. In some embodiments, the total number of layers of the first dummy transparent pillars408D1and the second dummy transparent pillars408D2is in a range from 3 to 5 layers. Depending on process and design requirements, the first dummy transparent pillars408D1and the second dummy transparent pillars408D2may be aligned or staggered with each other.

By using the same or different shapes, widths, pitches, materials, or arrangements for the first dummy transparent pillars and the second dummy transparent pillars around the transparent pillar array, the structure of the transparent pillar array can be strengthened further to prevent the transparent pillars at the edge of the array from deforming and collapsing. The uniformity of the transparent pillars can be maintained and the production yield can be improved as a result.

It should be noted that the number of peripheral regions illustrated inFIG. 6is merely an example, and the present disclosure is not limited thereto. For example, in other embodiment of the present disclosure shown inFIG. 7, the optical sensor500includes the first peripheral region404P1, the second peripheral region404P2, and the third peripheral region504P3. The first dummy transparent pillars408D1, the second dummy transparent pillars408D2, and the third dummy transparent pillars508D3are formed around the transparent pillar array, wherein the shape of each of the first dummy transparent pillars408D1, second dummy transparent pillars408D2, and third dummy transparent pillars508D3may be different (e.g. circular, oval, or rectangular) or the same, depending on process and design requirements.

By forming more than three layers of dummy transparent pillars with the same or different shapes, widths, pitches, materials, layers, or arrangements around the transparent pillars, the structure of transparent pillar array can be strengthened further to prevent the transparent pillars at the edge of the array from deforming and collapsing. The uniformity of the transparent pillars can be maintained and the production yield can be improved as a result.

In summary, the embodiments of the present disclosure provide an optical sensor. In the light-shielding layer of the light collimating layer in the optical sensor, in addition to forming the transparent pillars on the corresponding pixels, dummy transparent pillars are formed around the transparent pillar array. The geometric shapes, sizes, arrangements, and materials may be adjusted according to processing requirements. In such cases, the structure of the transparent pillar array can be strengthened according to process and design requirements to prevent the transparent pillars at the edge of the array from deformation and collapse. The uniformity of the transparent pillars can be maintained and the production yield can be improved as a result.

It should be noted that although the advantages and effects of some embodiments of the present disclosure have been described above, not all embodiments are required to achieve all of the advantages and benefits.