WO2022128701A1

WO2022128701A1 - Intergrated wire-grid polarizer

Info

Publication number: WO2022128701A1
Application number: PCT/EP2021/084873
Authority: WO
Inventors: Franz Lechner
Original assignee: Ams-Osram Ag
Priority date: 2020-12-14
Filing date: 2021-12-09
Publication date: 2022-06-23
Also published as: GB202019679D0

Abstract

A device (100, 200, 300, 400, 500) fabricated in a MOS process is disclosed, wherein the device comprises a plurality of conductive elements (110, 210, 310, 410, 510) separated by sidewall spacer structures (115, 215, 315, 415, 515) and configured as an integrated wire-grid polarizer. Also disclosed is an integrated ambient light sensor (600), and an associated method of fabricating a device in a MOS process.

Description

INTERGRATED WIRE-GRID POLARIZER

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure is in the field of ambient light sensing, and particularly relates to implementations of wire-grid polarizers for use in ambient light sensors.

BACKGROUND

A polarizer is a radiation filter that allows radiation of a specific polarization pass through while blocking radiation of other polarizations. As such, a polarizer can filter a beam comprising radiation of a mixed or undefined polarization into a beam of a defined polarization.

Various types of polarizers may be implemented, for example thin-film polarizers or birefringent polarizers. Another type of polarizer is known as a wire-grid polarizer. A wire-grid polarizer typically comprises a plurality of conductive elements or wires arranged in parallel and in a plane.

When radiation is incident upon a wire-grid polarizer, electromagnetic waves having a component of their electric fields aligned parallel to the wires induce a flow of electrons along the length of the wires. The wires behave in a similar manner to a reflective metal surface, thereby reflecting the radiation. In contrast, for electromagnetic waves having a component of their electric fields aligned orthogonal to the wires, a flow of electrons is inhibited by the relatively narrow width of each wire. As such, the radiation is not reflected and the incident wave passes through the wire-grid, resulting in linearly polarized electromagnetic radiation

It is necessary for a pitch of the wires in the polarizer to be less than a wavelength of the incident radiation. Similarly, the width of wires in the polarizer should be a relatively small proportion of the pitch. In order to achieve the necessary dimensions, such wiregrid polarizers may be manufactured using known lithographic techniques.

In the field of ambient light sensing, it can be desirable to detect polarized light over both an infrared and visible light range. However, polarizers having the necessary dimensions and being suitable for polarizing such visible and/or infrared light having wavelengths in the range of approximately 380 to 1100 nanometers, may present manufacturing challenges when using existing processes such as lithography. Furthermore, existing wire-grid polarizers may be relatively costly and require specialized materials and manufacturing processes to implement, thus increasing an overall cost of an ambient light sensing system implementing such polarizers.

It is therefore desirable to provide means for implementing wire-grid polarizers having the appropriate pitch and dimensions for polarizing visible and/or infrared light, wherein the means is also suitable for implementation for mass-production of such polarizers. Furthermore, it is desirable that such wire-grid polarizers be suitable for use in ambient light sensing applications and are cost-effective to manufacture.

It is therefore an aim of at least one embodiment of at least one aspect of the present disclosure to obviate or at least mitigate at least one of the above identified shortcomings of the prior art.

SUMMARY

The present disclosure is in the field of ambient light sensing, and particularly relates to implementations of wire-grid polarizers for use in ambient light sensors, wherein the wire-grid polarizers are integrated with radiation-sensitive devices.

According to a first aspect of the disclosure, there is provided a radiation-sensitive device fabricated in a MOS (metal-oxide-semiconductor) process, the device comprising a plurality of conductive elements separated by sidewall spacer structures and configured as an integrated wire-grid polarizer.

Advantageously, integration of a wire-grid polarizer into a device manufactured in a MOS process may enable low-cost manufacture suitable for mass-production processes. That is, Metal-Oxide-Semiconductor (MOS) manufacturing processes, such as CMOS processes, are well-established manufacturing processes, thus enabling mass-production efficiencies and cost-savings to be realized.

Furthermore, substantial costs saving may be realized by mitigating a requirement to implement a discrete polarizer. Furthermore, substantial miniaturization of devices may be advantageously more readily achievable by using such highly integrated components.

Advantageously, using conductive elements together with sidewall spacer structures to define a wire-grid polarizer enables manufacture of the device based on a use of existing Front End-of-line (FOEL) MOS structures. For example, gates of Field- Effect Transistors manufactured in the MOS process (MOSFETs) are known to be implemented with sidewall spacer structures, wherein such sidewall spacers are normally disposed on opposite sidewalls of a gate structure to isolate the gate structure from heavily-doped source and drain regions of the transistor and/or to prevent the source and drain regions immediately next to the gate structure from being heavily doped. In some embodiments, the sidewall spacers may be formed from a silicon nitride layer.

Advantageously, the sidewall spacer structures and the conductive elements may be, at least in part, formed using lithographic processes and/or etching. As such, using standard lithographic FEOL processes, the sidewall spacer structures and the conductive elements may be formed in dimensions small enough to provide an optical pitch for use in polarizing visible and infrared ambient light. This is, for example, in contrast to using back-end-of-line (BEOL) processes to implement a wire-grid polarizer using only deposition of metal layers, wherein due to manufacturing limitations of the BEOL process a minimum pitch of the wire may be insufficient to achieve polarization of visible and infrared ambient light.

In particular, some radiation-sensitive devices implement a relatively high proportion of analogue circuitry, such as photodiodes and associated analogue-to-digital circuitry. Such circuitry may be suited to a particular MOS manufacturing process technology node. In an example embodiment, the radiation-sensitive device may be fabricated in a 180 nanometer CMOS or NMOS technology node. Technology trends for semiconductor devices comprising predominantly digital circuitry may be to migrate to lower, more cost-effective and higher-performance technology nodes over time, e.g. 150 nanometer, 130 nanometer, 110 nanometer or smaller. However, in instances wherein the radiation-sensitive device comprises substantial analogue circuity it may be neither cost-effective nor adequately performance enhancing to justify migration to a lower technology node. For example, an overall area of analogue circuitry may not scale well across technology nodes.

Continuing with the above example of a device formed in a 180 nanometer technology node, an associated BEOL process for a 180 nanometer CMOS device may not be suitable for implementing a wire-grid polarizer with sufficiently small pitch for polarizing visible and infrared ambient light. It will be understood that an optical pitch of the wire-grid polarizer may correspond to a sum of a width of one conductive element and a distance between adjacent conductive elements.

However, by advantageously implementing the sidewall spacer structures and/or the conductive elements using lithographic processes typically associated with FEOL processes, a sufficiently a small pitch may be achieved without necessitating migration to a lower technology node. As such, the present disclosure advantageously enables designs of existing radiation-sensitive devices to be enhanced with integrated wire-grid polarizer, without requiring substantial deviation from known MOS manufacturing processes.

The plurality of conductive elements may be arranged in parallel, e.g. arranged parallel relative to one another. The plurality of conductive elements may be arranged at substantially equal distances from one another, e.g. evenly spaced apart.

The sidewall spacer structures may be transparent to wavelengths of radiation that are polarized by the plurality of conductive elements.

It will be understood that the term “polarized by” refers to filtering of radiation to enable radiation of a specific polarization to pass through while blocking radiation of other polarizations, thereby filtering a beam of radiation of potentially undefined or mixed polarization into a beam exhibiting a well-defined polarization.

The sidewall spacer structures may be transparent to wavelengths of radiation that are filtered by a polarizer formed by the plurality of conductive elements.

Advantageously, such transparency of the sidewall spacer structure may allow polarized radiation to propagate through the integrated polarizer to a radiation-sensitive structure of the device, such as one or more photodiodes, or an array of photodiodes.

The radiation-sensitive device may comprise a photodiode, wherein the plurality of conductive elements are formed over an active region of the photodiode.

The radiation-sensitive device may comprise an array of photodiodes. The radiation-sensitive device may comprise one or more pinned photodiodes.

The radiation-sensitive device may be a pixel. The radiation-sensitive device may be a pinned photodiode based active pixel.

The active region may comprise a well, such as an N-well. In some embodiments, the photodiode is a n-type pinned photodiode.

The radiation-sensitive device may comprise an active-pixel sensor.

Advantageously, a signal-to-noise ratio of the photodiode may be enhanced if only radiation having a specifically defined polarization is incident upon the active region of the photodiode. This may be beneficial when ambient radiation, such as bright sunlight, interferes with detection of a particular radiation signal to be detected, and the signal to be detected has a significantly lower intensity than that of the ambient light.

Furthermore, in some embodiments the radiation-sensitive device may be a time- of-flight sensor or proximity sensor. In some embodiments, the radiation-sensitive device may be a component of a time-of-flight sensor or proximity sensor. Such a time-of-flight sensor or proximity sensor may comprise one or more lasers that are configured to emit a polarized beam of radiation, which may be reflected from a target and subsequently detected by the photodiode. Therefore, it can be advantageous to provide an integrated wire-grid polarizer to detect only radiation having the same polarity as that of the polarized beam of radiation emitted by the one or more lasers.

The plurality of conductive elements may be configured as an integrated wiregrid polarizer having an optical pitch of between 250 nanometers and 460 nanometers.

Advantageously, dimensions of the plurality of conductive elements and the sidewall spacer structures may be selected to polarize radiation of a particular wavelength.

For example, a sidewall spacer structure manufactured using a 180 nanometer CMOS technology node may comprise a lateral dimension, e.g. in a plane parallel to a substrate the device is implemented on, of approximately 100 nanometers. Corresponding conductive elements may have a width in the region of 120 to 180 nanometers. Such dimensions may provide a device having an effective integrated wiregrid polarizer having an optical pitch of approximately 250 nanometers, thereby suitable for polarizing radiation having a wavelength of approximately 400 nanometers, e.g. blue visible light.

Other embodiments suitable for polarizing radiation of other wavelengths are described in more detail below.

A subset of the conductive elements may comprise elongated poly-silicon structures.

Advantageously, the elongated poly-silicon structure may be structures normally associated with use as gates of transistors. That is, the elongated poly-silicon structure may be fabricated using the same MOS processes as would otherwise be used to fabricate a gate structure of a MOSFET. In some embodiments, the conductive elements may be elongated beyond a length that would typically be used to implement poly-silicon structures of a gate of a transistor in a MOS process. For example, in some embodiments the conductive elements may be elongated such that they extend completely across an active area, or radiation-sensitive area of one or more photodiodes.

The sidewall spacer structures may be arranged on opposite sidewalls of each elongated poly-silicon structure.

Advantageously, the sidewall spacer structures may be based on standard sidewall spacer structures of a MOS process. In some embodiments, the sidewall spacer structures may be elongated beyond a length that would typically be used to implement sidewall spacer structures of a gate of a transistor in a MOS process. For example, in some embodiments the sidewall spacer structures may be elongated such that they extend across an active area, or radiation-sensitive area of one or more photodiodes.

The conductive elements comprise a silicide layer.

For example, the silicide layer may be a silicide layer normally formed in a MOS process for forming electrical contacts between a gate structure and/or source drain regions of a transistor and a metal interconnect layer. The silicide layer may comprise a self-aligned silicide layer, known in the art as salicide. The silicide layer formed over a gate structure, in particular a poly-silicon gate structure, may be known in the art as a polycide layer, or more generally as a polycide gate.

The silicide layer may be formed by depositing a metal thin film over a MOS structure, and subsequently formed into a metal silicide by a process of annealing. The silicide layer may be formed into discrete conductive elements by a process of etching.

At least every second conductive element of the plurality of conductive elements may comprise a conductive contact formed on the silicide layer.

Advantageously, the conductive contact may be formed based on a BEOL process normally used to forming contacts between a MOS substrate and one or more metal interconnect layers.

In some embodiments, the conductive contact may comprise tungsten.

At least every second conductive element of the plurality of conductive elements may comprise a wire formed in one or more metal layers.

Advantageously, the wire may be formed based on a BEOL process normally used to form metal interconnect layers.

The MOS process may be a complementary metal-oxide-semiconductor (CMOS) process.

Advantageously, integration of a wire-grid polarizer over a radiation-sensitive device fabricated in a CMOS process enables use of processes based on low-cost and efficient industry-standard manufacturing processes. Furthermore, use of CMPS may enable integration of the wire-grid polarizer into low-power devices, suitable for portable battery-operated devices such as smartphones, tablets and the like.

According to a second embodiment of the disclosure, there is provided an integrated ambient light sensor comprising a plurality of photodiodes, wherein formed over each photodiode is: a plurality of conductive elements separated by sidewall spacer structures and configured as an integrated wire-grid polarizer. Advantageously, the integrated ambient light sensor may be formed with photodiodes configured to sense different wavelengths of radiation. For example, one or more photodiodes may be configured to sense a range of wavelengths of visible light and/or one or more photodiodes of the integrated ambient light sensor may be configured to sense a range of wavelengths of infrared light. Each photodiodes, or group of photodiodes, may have an associated an integrated wire-grid polarizer. As such, the integrated ambient light sensor may be capable of identifying different wavelengthranges of radiation and/or different polarities of the radiation. As such, the integrated ambient light sensor may be suitable for identifying or classifying ambient light sources, e.g. correlating known wavelength-ranges and/or polarities of radiation with known radiation sources.

In some embodiments, an interference filter may be formed over the/each integrated wire-grid polarizer.

A first plurality of conductive elements formed over a first photodiode may be arranged orthogonal to a second plurality of conductive elements formed over a second photodiode.

Advantageously, by orienting the polarizers orthogonal to one another, the integrated ambient light sensor may be capable of distinguishing between radiation sources emitting radiation of different polarities.

According to a third embodiment of the disclosure, there is provided an apparatus comprising an LED display, and an integrated ambient light sensor comprising the radiation-sensitive device according to the first aspect. The integrated ambient light sensor is disposed rearward of a radiation-emitting surface of the LED display and configured to receive radiation propagating through the LED display.

In some embodiments, radiation emitted by the LED display may have a particular polarity, or predominant polarity. Likewise, in some instances, ambient radiation may comprise radiation with particular polarity, or a predominant polarity.

As such, by advantageously implementing an integrated ambient light sensor comprising the radiation-sensitive device according to the first aspect behind an LED display, it may be possible to sense an ambient radiation propagating through the display and more easily distinguish the ambient radiation from radiation emitted by the LED display itself. Similarly, the use of such integrated polarizers may make it easier to filter or identify, from a total radiation sensed by the radiation-sensitive device, the ambient radiation or the radiation emitted by the LED display. The apparatus may be a mobile phone, a smartphone, a tablet computer, a laptop or desktop computer.

According to a fourth embodiment of the disclosure, there is provided a method of fabricating a device in a MOS process, the method comprising forming a plurality of conductive elements separated by sidewall spacer structures and configured as an integrated wire-grid polarizer.

The plurality of conductive elements may be formed over an active region of a photodiode.

The above summary is intended to be merely exemplary and non-limiting. The disclosure includes one or more corresponding aspects, embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. It should be understood that features defined above in accordance with any aspect of the present disclosure or below relating to any specific embodiment of the disclosure may be utilized, either alone or in combination with any other defined feature, in any other aspect or embodiment or to form a further aspect or embodiment of the disclosure.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

These and other aspects of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, wherein:

Figure 1 a depicts a cross-section of a radiation-sensitive device fabricated in a MOS process, according to a first embodiment of the disclosure;

Figure 1 b depicts a top view of the device of Figure 1a, showing the plurality of conductive elements;

Figure 2 depicts a cross-section of a radiation-sensitive device fabricated in a MOS process, according to a second embodiment of the disclosure;

Figure 3 depicts a cross-section of a radiation-sensitive device fabricated in a MOS process, according to a third embodiment of the disclosure;

Figure 4 depicts a cross-section of a radiation-sensitive device fabricated in a MOS process, according to a fourth embodiment of the disclosure;

Figure 5 depicts a cross-section of a radiation-sensitive device fabricated in a MOS process, according to a fifth embodiment of the disclosure; Figure 6 depicts an integrated ambient light sensor according to an embodiment of the disclosure; and

Figure 7 depicts an apparatus comprising an integrated ambient light sensor disposed rearward of a radiation-emitting surface of an LED display, according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1a depicts a cross-section of a radiation-sensitive device 100 fabricated in a MOS process, according to a first embodiment of the disclosure.

The radiation-sensitive device 100 is formed on a substrate 105, of which a portion is visible in Figure 1a. The substrate 105 may be a silicon wafer, e.g. a substrate for use in manufacture of MOS devices, such as CMOS devices.

The radiation-sensitive device 100 comprises a plurality of conductive elements 110a, 110b separated by sidewall spacer structures 115 and configured as an integrated wire-grid polarizer.

The conductive elements 110a, 110b are formed over an active region 120 of the radiation-sensitive device 100. The radiation-sensitive device 100 may be, for example, comprise a photodiode. In some embodiments, the radiation-sensitive device 100 may comprise, or may be a component of, an active-pixel sensor. The active region 120 of the radiation-sensitive device 100 may be a well, e.g. a doped region, of the substrate. In some embodiments, the active region 120 is an n-well of a photodiode.

Thus, the conductive elements 110a, 110b separated by sidewall spacer structures 115 are configured to filter radiation such that only radiation of a particular polarity is incident upon the active region 120.

Also depicted in Figure 1a is a contact etch stop layer 185 formed over the conductive elements 110a, 110b and the sidewall spacer structures 115. The contact etch stop layer 185 may, for example, comprise SiN.

In the example embodiment of Figure 1a, only nine conductive elements 110a, 110b are depicted. It will be appreciated that in other embodiments, substantially more than nine conductive elements 110a, 110b may be implemented. For example, in some embodiments a sufficient quantity of conductive elements 110a, 110b may be implemented to extend over a complete surface area of at least the active region 120 of the radiation-sensitive device 100.

The conductive elements 110a, 110b comprise first conductive elements 110a and second conductive elements 110b. The plurality of conductive elements 110a, 110b are formed as elongate elements, arranged in parallel with one another, as described below in more detail with reference to Figure 1 b.

Each first conductive element 110a comprises a poly-silicon structure 130. In some embodiments, the poly-silicon structure 130 is formed on an oxide layer 135. The poly-silicon structure 130 may be a structure normally associated with use as a gate of a transistor. That is, the poly-silicon structure 130 may be fabricated using a MOS process that would otherwise be used to fabricate a gate structure of a MOSFET.

In some embodiments, the first conductive elements 110a may be elongated beyond a length that would typically be used to implement poly-silicon structures of a gate of a transistor in a MOS process. For example, in some embodiments the first conductive elements 110a may be elongated such that they extend completely across the active area 120, e.g. the radiation-sensitive area, of one or more radiation-sensitive devices implemented in the substrate 105.

The sidewall spacer structures 115 are arranged on opposite sidewalls of each poly-silicon structure 130. In some embodiments, the sidewall spacer structures 115 are formed by depositing a material, such as silicon nitride, over the substrate 105, including over the poly-silicon structures 130, and subsequently patterning, e.g. etching, the material to define the sidewall spacers structures 115.

During manufacture, a silicide layer is formed on the substrate 105. For example, the silicide layer may be a silicide layer normally formed in a MOS process for forming electrical contacts between a gate structure and/or source drain region of a transistor and a metal interconnect layer. The silicide layer may be formed by depositing a metal layer, such as titanium, cobalt, nickel, platinum, tantalum or tungsten, over the silicon substrate 105, including over the poly-silicon structures 130, and subsequently annealing the substrate. The silicide layer may then be patterned, such as by etching, to define first portions 140 of the silicide layer formed over the poly-silicon structure 130 of each first conductive element, and second portions 145 of the silicide layer defining each second conductive element 110b.

As depicted in Figure 1a and also in Figure 1b, the first conductive elements 110a, sidewall spacer structures 115 and second conductive elements 110b may be arranged consecutively in sequence, such that each first conductive element 110a has associated sidewall spacer structures 115 arranged on opposite sidewalls of the polysilicon structure 130 of the first conductive element 110a, and between each first conductive element 110a is a second conductive element 110b. Also depicted is a portion of a resist protect oxide (RPO) layer 150 that, in some embodiments, may be formed over at least a portion of a surface of the substrate 105 to prevent silicide layer formation. In some embodiments, the resist protect oxide layer 150 may define a perimeter or boundary of the effective integrated wire-grid polarizer.

Figure 1b depicts a top view of a portion the radiation-sensitive device 100 of Figure 1a. The substrate 105 is depicted having the first conductive elements 110a and second conductive elements 110b separated by sidewall spacer structures 115 and configured as an integrated wire-grid polarizer.

The first conductive elements 110a and second conductive elements 110b are formed as elongate elements, arranged in parallel with one another. In some embodiments the conductive elements 110a, 110b may be implemented to extend over a complete surface area of at least the active region 120 of the radiation-sensitive device 100.

It can be seen that the sidewall spacer structures 115 are arranged on opposite sides of each first conductive element 110a.

The first conductive elements 110a, sidewall spacer structures 115 and second conductive elements 110b may be arranged consecutively in sequence, such that each first conductive element 110a has associated sidewall spacer structures 115 arranged on opposite sidewalls of the poly-silicon structure 130 of the first conductive elements 110a, and between each pair of first conductive elements 110a is a second conductive element 110b.

As shown in Figure 1 b, the plurality of conductive elements 110a, 110b are arranged in parallel, e.g. arranged parallel relative to one another. It can also be seen that the plurality of first conductive elements 110a are arranged at equal distances from one another, e.g. evenly spaced apart. Similarly, the plurality of second conductive elements 110b, which intersperse the plurality of first conductive elements 110a, are also arranged at substantially equal distances from one another, e.g. evenly spaced apart.

Also depicted is a portion of a resist protect oxide layer 150 that, in some embodiments, may be formed over at least a portion of a surface of the substrate 105 to prevent silicide layer formation. In the example of Figure 1b, the resist protect oxide layer 150 defines a boundary of the effective integrated wire-grid polarizer formed from the conductive elements 110a, 110b separated by the sidewall spacer structures 115.

The sidewall spacer structures 115 are transparent to wavelengths of radiation that are filtered by the plurality of conductive elements. For example, in the embodiment of Figure 1 b, the radiation-sensitive device 100 is configured as an integrated wire-grid polarizer suitable for filtering visible radiation. A suitability of the integrated wire-grid polarizer for a particular range of wavelengths of light depends, at least, upon the particular selection of materials implementing the integrated wire-grid polarizer, and the particular dimensions of components of integrated wire-grid polarizer, as explained with reference to the embodiments described below.

In the example embodiment of Figure 1 b, a width 160, e.g. a lateral width in a plane parallel to a surface of the substrate 105, of the first conductive element 110a is approximately 180 nanometers. That is, the width 160 of the first portions 140 of the silicide layer defining each first conductive element 110a is approximately 180 nanometers.

A spacing 175 between each first conductive element 110a is approximately 320 nanometers. As such, a pitch 165 of the first conductive elements 110a is approximately 500 nanometers.

A width 180 of the second conductive elements 110b, e.g. the width 180 of the second portions 145 of the silicide layer defining each second conductive element 110b is approximately 120 nanometers.

A width 170 of each sidewall spacer 115 is approximately 100 nanometers.

As such, the radiation-sensitive device 100 of Figures 1a and 1b has an optical pitch of approximately 250 nanometers. Simulations of the radiation-sensitive device 100 have shown that the radiation-sensitive device 100 is suitable for filtering polarized radiation having wavelengths in the region of 400 nanometers.

It will be appreciated that the dimensions provided above, e.g. width 160, pitch 165, width 170, spacing 175 and width 180, are provided for purposes of example only, and variations in the dimensions such as to adapt a design of the integrated wire-grid polarizer for different wavelengths of radiation, would also fall within the scope of the disclosure.

Furthermore, in the embodiment of Figure 1a, the sidewall spacer structures 115 are transparent to at least wavelengths of radiation that are polarized by the plurality of conductive elements 110a, 110b, e.g., wavelengths of approximately 400 nanometers. Advantageously, such transparency of the sidewall spacer structures 115 enables polarized radiation to propagate past the plurality of conductive elements 110a, 110b to the radiation-sensitive device(s) 120 on the substrate 105. The first portions 140 and second portion 145 of the silicide layer are optically opaque to wavelengths of radiation that are filtered by the plurality of conductive elements 110a, 110b. In another example embodiment, the spacing 175 between each first conductive element 110a may be approximately 380 nanometers. As such, the pitch 165 of the first conductive elements 110a would be approximately 560 nanometers. In such an embodiment, the width 180 of the second conductive elements 110b, e.g. the width 180 of the second portions 145 of the silicide layer defining each second conductive element 110b may be approximately 180 nanometers. The width 170 of each sidewall spacer 115 may be approximately 100 nanometers. The width 160 of each first conductive element 110a may be approximately 180 nanometers.

Such a device would exhibit an optical pitch of approximately 280 nanometers. Simulations of such a device have shown that the radiation-sensitive device 100 is suitable for filtering polarized radiation having wavelengths longer than 400 nanometers.

Figure 2 depicts a cross-section of a radiation-sensitive device 200 fabricated in a MOS process, according to a second embodiment of the disclosure.

The radiation-sensitive device 200 is formed on a substrate 205, of which a portion is visible in Figure 2. The substrate 205 may be a silicon wafer, e.g. a substrate for use in manufacture of MOS devices, such as CMOS devices.

The radiation-sensitive device 200 comprises a plurality of conductive elements 210a, 210b separated by sidewall spacer structures 215 and configured as an integrated wire-grid polarizer. The conductive elements 210a, 210b are formed over an active region 220 of the radiation-sensitive device 200.

Each first conductive element 210a comprises a poly-silicon structure 230. In some embodiments, the poly-silicon structure 230 is formed on an oxide layer 235.

First portions 240 of a silicide layer formed are over the poly-silicon structures 230 of each first conductive element, and second portions 245 of the silicide layer define each second conductive element 210b.

The above features of the embodiment of Figure 2 are correspond to features of the embodiment of Figures 1a and 1 b, with corresponding reference numerals incremented by 100, and are therefore not described in further detail.

In the embodiment of Figure 2, every second conductive element 210b of the plurality of conductive elements 210a, 201b comprises a conductive contact 285 formed on the silicide layer. In some embodiments, the conductive contact 285 may comprise tungsten. For example, the conductive contact 285 may be formed based on a BEOL process normally used to forming contacts between a MOS substrate and one or more metal interconnect layers. At longer wavelengths of incident radiation, such as wavelengths greater than 400 nanometers of incident radiation, the silicide layer may become at least partially transparent to the incident radiation. However, the conductive contact 285, which in embodiments is formed of a metal such as tungsten, will not be transparent. Similarly, the poly-silicon structure 230 of the first conductive elements 210a may be opaque to incident radiation.

The sidewall spacer structures 215 are transparent to wavelengths of radiation that are filtered by the plurality of conductive elements 210a, 210b. For example, in the embodiment of Figure 2, the radiation-sensitive device 200 is configured as an integrated wire-grid polarizer suitable for filtering visible radiation.

In the example embodiment of Figure 2, a width 260, e.g. a lateral width in a plane parallel to a surface of the substrate 205, of the first conductive element 210a is approximately 180 nanometers. That is, the width 260 of the first portions 240 of the silicide layer defining each first conductive element 210a is approximately 180 nanometers.

A spacing 275 between each first conductive element 210a is approximately 460 nanometers. As such, a pitch 265 of the first conductive elements 210a is approximately 640 nanometers.

A width 280 of the conductive contact 285 forming the second conductive element 210b is approximately 220 nanometers.

A spacing 290 between each conductive contact 285 is approximately 420 nanometers. As such, a pitch 295 of the conductive contact 285 is approximately 640 nanometers.

A width 270 of each sidewall spacer 215 is approximately 100 nanometers.

As such, the radiation-sensitive device 200 of Figure 2 has an optical pitch of approximately 320 nanometers. Simulations of the radiation-sensitive device 200 have shown that the radiation-sensitive device 200 is suitable for filtering polarized radiation having wavelengths in the visible light range.

It will be appreciated that the dimensions provided above are provided for purposes of example only, and variations in the dimensions such as to adapt a design of the integrated wire-grid polarizer for different wavelengths or radiation, would also fall within the scope of the disclosure.

Furthermore, in the embodiment of Figure 2, the sidewall spacer structures 215 are transparent to at least wavelengths of radiation that are polarized by the plurality of conductive elements 210a, 210b, e.g., wavelengths in the visible light range. At some wavelengths within the visible light range, the first portions 240 and second portions 245 of the silicide layer may also be optically transparent to wavelengths of radiation that are filtered by the plurality of conductive elements 210a, 210b. However, the conductive contacts 285 and the poly-silicon structures 230 remain opaque to such visible light.

Further embodiments exhibiting a range of optical pitches are also described with reference to Figures 3, 4 and 5.

For example, Figure 3 depicts a cross-section of a radiation-sensitive device 300 fabricated in a MOS process, according to a third embodiment of the disclosure. The radiation-sensitive device 300 shares many of the features of the embodiment of Figure 2, and therefore such features are not described in detail.

The radiation-sensitive device 300 comprises a plurality of conductive elements 310a, 310b separated by sidewall spacer structures 315 and configured as an integrated wire-grid polarizer. The conductive elements 310a, 310b are formed over an active region 320 of the radiation-sensitive device 300 implemented on a substrate 305.

Each first conductive element 310a comprises a poly-silicon structure 330. In some embodiments, the poly-silicon structure 330 is formed on an oxide layer 335.

First portions 340 of a silicide layer formed are over the poly-silicon structures 330 of each first conductive element 310a, and second portions 345 of the silicide layer define each second conductive element 310b.

Each first conductive element 310a also comprises a wire 355 formed in a metal layer. The wire may be formed based on a BEOL process normally used to form metal interconnect layers.

In the embodiment of Figure 3, every second conductive element 310b of the plurality of conductive elements 310a, 310b comprises a conductive contact 385 formed on the silicide layer, and as generally described above with reference to the embodiment of Figure 2.

Dimensions of the features of the embodiment of Figure 3 may vary relative to that of the embodiment of Figure 2, to define a polarizer having a different optical pitch, and therefore targeted at operation over a different range of wavelengths of incident radiation.

For example, in the embodiment of Figure 3, the wires 355, the conductive contacts 385, and the second conductive elements 310b may each have a pitch of approximated 760 nanometers, corresponding to a wire-grid polarizer having an optical pitch of approximately 380 nanometers. Again, the sidewall spacer structures 315 are transparent to wavelengths of radiation that are filtered by the plurality of conductive elements 310a, 310b.

Figure 4 depicts a cross-section of a radiation-sensitive device 400 fabricated in a MOS process, according to a fourth embodiment of the disclosure. The radiationsensitive device 400 shares many of the features of the embodiment of Figure 3, and therefore such features are not described in detail.

In the embodiment of Figure 4, each first conductive element 410a comprises a poly-silicon structure 430. In some embodiments the poly-silicon structure 430 is formed on an oxide layer 435. Each first conductive element 410a also comprises a wire 455a formed in a metal layer.

Each second conductive element 410b of the plurality of conductive elements 410a, 410b comprises a conductive contact 485 formed on the silicide layer, and as generally described above with reference to the embodiment of Figure 2. Each second conductive element 410b also comprises a wire 455b formed in the metal layer.

Dimensions of the features of the embodiment of Figure 4 may vary relative to that of the embodiment of Figure 3, to define a polarizer having a different optical pitch, and therefore targeted at operation over a different range of wavelengths of incident radiation.

For example, in the embodiment of Figure 4, the wires 455a, 455b may have a pitch of approximated 460 nanometers. The conductive contacts 485 and a 445 portion of the silicide layer forming the second conductive element 410b may each have a pitch of approximated 920 nanometers, corresponding to a wire-grid polarizer having an optical pitch of approximately 460 nanometers. Again, the sidewall spacer structures 415 are transparent to wavelengths of radiation that are filtered by the plurality of conductive elements 410a, 410b. Again, it will be appreciated that such dimensions are provided for purposes of example only.

The radiation-sensitive device 400 of Figure 4 may be suitable for filtering radiation having wavelengths in a near infrared range, e.g. wavelengths of approximately 900 nanometers.

Figure 5 depicts a cross-section of a radiation-sensitive device 500 fabricated in a MOS process, according to a fifth embodiment of the disclosure. The radiationsensitive device 500 shares many of the features of the embodiment of Figure 4, and therefore such features are not described in detail.

In contrast to the embodiment of Figure 4, the first conductive elements 510a of the radiation-sensitive device 500 comprises conductive contacts 585a and the second conductive elements 510b of the radiation-sensitive device 500 also comprises conductive contacts 585b. In an example embodiment, a pitch of the conductive contacts 585a, 585b may be in the region of 460 nanometers, which may also correspond to the pitch of the wires 555a, 555b formed in a metal layer. The device 500 may also correspond to a wire-grid polarizer having an optical pitch of approximately 460 nanometers. Again, the sidewall spacer structures 515 are transparent to wavelengths of radiation that are filtered by the plurality of conductive elements 510a, 510b.

As such, Figures 1a to 5 describe a range of embodiments of the disclosure having optical pitches ranging from approximately 250 nanometers to 460 nanometers, and suitable for operating as a polarizing filter for radiation have wavelengths from approximately 400 nanometers to 900 nanometers respectively.

Figure 6 depicts an integrated ambient light sensor 600 according to an embodiment of the disclosure. The light sensor 600 comprises a plurality of radiationsensitive devices 610a-h. At least one of the radiation-sensitive devices 610a-h corresponds to a radiation-sensitive device 100, 200, 300, 400, 500 are described above with reference to Figures 1a to 5. That is, formed over at least one of the radiationsensitive device is a plurality of conductive elements separated by sidewall spacer structures and configured as an integrated wire-grid polarizer.

In the example embodiment of Figure 6, the light sensor 600 comprises six radiation-sensitive devices 610a-h. It will be appreciated that, in other embodiments, the light sensor 600 may comprise fewer than or greater than six radiation-sensitive devices 610a-h.

In the example of Figure 6, a sub-set of the radiation-sensitive devices 610a-f comprise optical filters 620a-f. The optical filters 620a-f may be, for example, interference filters. Such interference filters may function as band pass filers. As such, each radiationsensitive devices 610a-h of the integrated ambient light sensor 600 may correspond to a channel, wherein a channel corresponds to sensing of radiation within a particular range of wavelengths, which in some embodiments are defined by passband characteristics of the optical filters 620a-f. For example, in some embodiments the light sensor 600 may comprise a plurality of channels spanning at least a portion of the visible and/or near infrared wavelength range, e.g. from 400 nanometers to approximately 900 nanometers.

It will be understood that, for radiation-sensitive devices 610a-h configured for sensing a particular range of wavelengths, a plurality of conductive elements separated by sidewall spacer structures and configured as integrated wire-grid polarizers formed over any one of said radiation-sensitive devices 610a-h may be adapted for the wavelengths range of interest. By means of example, for a channel configured to sense radiation having wavelengths of approximately 400 nanometers, the radiation-sensitive device may have a plurality of conductive elements separated by sidewall spacer structures and configured as integrated wire-grid polarizers and having an optical pitch of approximately 250 nanometers, and generally corresponding to the embodiment of Figure 1.

In some embodiments, a first plurality of conductive elements formed over a first radiating sensitive device 610a of the integrated ambient light sensor 600 may be arranged to be orthogonal to a second plurality of conductive elements formed over a second radiation-sensitive device 610b of the integrated ambient light sensor 600.

Advantageously, by orienting the polarizers orthogonal to one another, the integrated ambient light sensor 600 may be capable of distinguishing between radiation sources emitting radiation of different polarities. For example, two radiation-sensitive devices may be configured for sensing radiation over the same wavelength range, wherein integrated wire-grid polarizers formed over each of the two radiation-sensitive devices, as described above with reference to Figures 1 to 5, are arranged to be orthogonal relative to one another.

Figure 7 depicts an apparatus 700 comprising an integrated ambient light sensor 710 disposed rearward of a radiation-emitting surface 715 of an LED display 720, according to an embodiment of the disclosure. In some embodiments, the integrated ambient light sensor 710 may be an integrated ambient light sensor 600 as described with reference to Figure 6. The integrated ambient light sensor 710 may comprise the radiation-sensitive device 100, 200, 300, 400, 500 of any of Figures 1a to 5.

The radiation-emitting surface 715 is configured to emit radiation 720. In embodiments of the disclosure, the apparatus 700 may be, for example, a smartphone, a cellular telephone, a tablet, a laptop, or a communications device.

The integrated ambient light sensor 710 is configured to receive ambient radiation 725 propagating through the LED display 710. In some embodiments, the LED display 710 may be an organic LED (OLED) display 710.

Advantageously implementing an integrated ambient light sensor 710 behind an LED display 720, wherein the integrated ambient light sensor 710 comprises radiationsensitive devices 100, 200, 300, 400, 500 having integrated wire-grid polarizers arranged orthogonal to one another as described above with reference to Figure 6, it may be possible to more easily distinguish ambient radiation 725 propagating through the display from radiation 725 emitted by the LED display itself.

Although the disclosure has been described in terms of particular embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure, which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in any embodiments, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

LIST OF REFERENCE NUMERALS

100 radiation-sensitive device 295 pitch

105 substrate 300 radiation-sensitive device

110a first conductive elements 320 active region

110b second conductive elements 305 substrate

115 sidewall spacer structures 40 310a first conductive element

120 active region 310b second conductive element

130 poly-silicon structure 315 sidewall spacer structures

135 oxide layer 330 poly-silicon structure

140 first portions 335 oxide layer

145 second portions 45 340 first portions

150 resist protect oxide layer 345 second portions

160 width 355 wire

165 pitch 385 conductive contact

170 width 400 radiation-sensitive device

175 spacing 50 410a first conductive element

180 width 410b second conductive element

185 contact etch stop layer 415 sidewall spacer structures

200 radiation-sensitive device 430 poly-silicon structure

205 substrate 435 oxide layer

210a first conductive element 55 455a wire

210b second conductive element 455b wire

215 sidewall spacer structures 485 conductive contact

220 active region 500 radiation-sensitive device

230 poly-silicon structure 510a first conductive elements

235 oxide layer 60 515 sidewall spacer structures

240 first portions 585a conductive contacts

245 second portions 510b second conductive elements

260 width 585b conductive contacts

265 pitch 555a wires

275 spacing 65 555b wires

280 width 600 ambient light sensor

285 conductive contact 610a-h radiation-sensitive devices

290 spacing 620a-f optical filters apparatus 720 LED display ambient light sensor 5 720 radiation radiation-emitting surface 725 ambient radiation

Claims

22 CLAIMS:

1. A radiation-sensitive device (100, 200, 300, 400, 500) fabricated in a MOS process, the device comprising a plurality of conductive elements (110, 210, 310, 410, 510) separated by sidewall spacer structures (115, 215, 315, 415, 515) and configured as an integrated wire-grid polarizer.

2. The radiation-sensitive device (100, 200, 300, 400, 500) of claim 1 , wherein the sidewall spacer structures (115, 215, 315, 415, 515) are transparent to wavelengths of radiation that are polarized by the plurality of conductive elements (110, 210, 310, 410, 510).

3. The radiation-sensitive device (100, 200, 300, 400, 500) of any preceding claim comprising a photodiode, wherein the plurality of conductive elements are formed over an active region (120, 220, 320) of the photodiode.

4. The radiation-sensitive device (100, 200, 300, 400, 500) of any preceding claim, wherein the plurality of conductive elements (110, 210, 310, 410, 510) are configured as an integrated wire-grid polarizer having an optical pitch of between 250 nanometers and 460 nanometers.

5. The radiation-sensitive device (100, 200, 300, 400, 500) of any preceding claim, wherein a subset of the conductive elements (110, 210, 310, 410, 510) comprise elongated poly-silicon structures.

6. The radiation-sensitive device (100, 200, 300, 400, 500) of claim 5, wherein the sidewall spacer structures are arranged on opposite sidewalls of each elongated poly-silicon structure.

7. The radiation-sensitive device (100, 200, 300, 400, 500) of any preceding claim, wherein the conductive elements (110, 210, 310, 410, 510) comprise a silicide layer.

8. The radiation-sensitive device (100, 200, 300, 400, 500) of claim 7, wherein at least every second conductive element of the plurality of conductive elements (110, 210, 310, 410, 510) comprises a conductive contact (285, 385, 485, 585) formed on the silicide layer. The radiation-sensitive device (100, 200, 300, 400, 500) of any preceding claim, wherein at least every second conductive element of the plurality of conductive elements (110, 210, 310, 410, 510) comprises a wire formed in one or more metal layers. The radiation-sensitive device (100, 200, 300, 400, 500) of any preceding claim, wherein the MOS process is a CMOS process. An integrated ambient light sensor (600) comprising a plurality of photodiodes, wherein formed over each photodiode is a plurality of conductive elements separated by sidewall spacer structures and configured as an integrated wiregrid polarizer The integrated ambient light sensor (600) of claim 12, wherein a first plurality of conductive elements formed over a first photodiode is arranged orthogonal to a second plurality of conductive elements formed over a second photodiode. An apparatus (700) comprising: an LED display (720); and an integrated ambient light sensor (600) comprising the radiationsensitive device (100, 200, 300, 400, 500) according to claims 1 to 10; wherein the integrated ambient light sensor is disposed rearward of a radiationemitting surface of the LED display and configured to receive radiation propagating through the LED display. A method of fabricating a device in a MOS process, the method comprising forming at least one layer comprising a plurality of conductive elements separated by sidewall spacer structures and configured as an integrated wire-grid polarizer. The method of claim 14, wherein the plurality of conductive elements are formed over an active region of a photodiode.