FIELD

This disclosure is in the field of manufacture of optical elements such as metal- dielectric filters and mirrors, and relates in particular to manufacture of corrosion- resistant optical elements.

BACKGROUND

Optical elements, such as interference filters, may be implemented from alternating layers of optical coatings having different refractive indices formed upon a substrate. By controlling the thickness, quantity and/or refractive indices of the layers, characteristics of the manufactured optical element may be selected to suit particular requirements.

Optical elements, such as interference filters, may be implemented in a variety of applications, including radiation-sensing applications wherein the optical elements may have functions ranging from relatively simple anti-reflective coatings or wavelength selective mirrors to sophisticated narrow band-pass filters.

For example, optical devices such as sensors for ambient light sensing or multi- spectral sensors for color-matching applications may implement one or more interference filters formed over a radiation-sensitive element, thereby enabling detection of radiation of particular selected wavelengths.

The dielectric materials used to implement optical elements such as interference filters or mirrors, e.g. dichroic mirrors, may exhibit excellent optical properties and may also be generally environmentally robust. That is, dielectric material based optical elements may be relatively unaffected by high temperatures and/or humidity in target applications, and therefore may provide high reliability.

However, some applications require very precise and reliable implementations of optical elements. It is known to introduce metallic layers, for example Ag and/or Al, into optical elements such as interference filters and/or mirrors to improve their performance. For example, metallic layers may improve stop-band suppression, reduce overall filter thickness and reduce an angle-shift incurred by the filter or mirror.

While such metallic layers may provide beneficial optical properties, they may be susceptible to corrosion, such as corrosion through oxidation. For example, while implementation of a metallic layer comprising silver may be improve optical properties of an optical element, silver is known to be particularly susceptible to corrosion through oxidation or reaction with sulfur in the environment.

Corrosion may lead not only to a degradation in the desired optical properties, but may also jeopardize the structural integrity and the longevity of the optical element. Corrosion may lead to structural weaknesses, delamination, and/or undesired crystal growth due to reactions with elements from the environment.

It is therefore desirable to provide an optical element such as an interference filter or mirror, that exhibits the enhanced optical properties that may be provided by inclusion of a metallic layer, yet also exhibits the environment stability and resistance to corrosion of an optical element that does not comprise any metallic layers.

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 manufacture of optical elements such as metal-dielectric filters and mirrors, and relates in particular to manufacture of corrosion- resistant optical elements.

According to a first aspect of the disclosure, there is provided a method of manufacturing an optical element on a substrate, comprising steps of: deposition of a layer of metallic material; and deposition of an encapsulating layer of dielectric material, such that the layer of metallic material is encapsulated between the encapsulating layer of dielectric material and the substrate or a preceding layer of dielectric material, wherein deposition of the encapsulating layer of dielectric material is more isotropic than deposition of the layer of metallic material.

Advantageously, by completely encapsulating the layer of metallic material, corrosion of the layer of metallic material, such as due to reaction with oxygen, sulfur or any other element within the environment, may be prevented.

The deposition of the layer of metallic material may be a sputter deposition.

The deposition of the encapsulating layer of dielectric material may be a sputter deposition. Such sputter depositions may comprise, for example, ion-beam sputtering, reactive sputtering, ion-assisted sputtering, gas-flow sputtering, or the like. Furthermore, in some embodiments, deposition of different layers of the optical element may be implemented using different sputtering configurations. That is, different sputtering techniques may be used for deposition of different layers of an optical element manufactured according to the disclosed method.

The method may comprise deposition of at least one further layer before and/or after deposition of the layer of metallic material. The at least one further layer may be configured as a barrier layer. The at least one further layer may be configured as an adhesion promoter. The at least one further layer may be configured as a barrier layer and as an adhesion promoter. The at least one further layer may be provided as an intermediate layer between the layer of metallic material and the preceding or encapsulating layer of dielectric material.

Advantageously, the provision of the adhesion promoter may enhance a connection between the layer of metallic material and the preceding layer of dielectric material and/or the encapsulating layer of dielectric material.

Advantageously, the provision of the barrier layer may protect the layer of metallic material from corrosion during and after processing.

Advantageously, by having sputter deposition of the dielectric material that is more isotropic than the deposition of the metallic material, it can be assured that the dielectric material completely encapsulates the metallic material. That is, in a more isotropic deposition, the sputtered particles may be scattered across a relatively large area of a surface of the layer of metallic material or any preceding barrier layer and/or adhesion promoter that may have been implemented. However, a less isotropic deposition, e.g. a more anisotropic deposition, may result in a narrower distribution of sputtered particles spread across a relatively smaller area.

The method may comprise a preceding step of providing a mask over the substrate defining an area for deposition of the encapsulating layer of dielectric material and the layer of metallic material. An edge of the mask defining the area may comprise a sidewall having an undercut region.

Advantageously, provision of such a mask may inhibit substantial propagation of sputtered particles beyond a defined area. Furthermore, the mask may function synergistically with the aforementioned variations in isotropy of the deposition of each layer to limit a lateral extent of the deposition of sputtered particles of each layer. For example, because the sputter deposition of the encapsulating layer of dielectric material is more isotropic than sputter deposition of the layer of metallic material, the sputtered particles of dielectric material may extend further into the undercut region than the more anisotropically deposited sputtered particles of metallic material.

That is, in an isotropic deposition, some sputtered particles may be allowed to scatter into the undercut region, thereby being deposited on the preceding layer of dielectric material, or any preceding barrier layer and/or adhesion promoter that may have been implemented, in the undercut region. However, in a less isotropic deposition, e.g. an anisotropic deposition, more directional and/or ballistic sputtered particles may substantially limit a scattering of sputtered particles into the undercut region. For example, in an example embodiment the layer of deposited dielectric material may extend in the region of 3 to 5 micrometers beyond a perimeter of the deposited layer of metallic material.

Advantageously, due to the use of depositions of different isotropies, the same mask may be used for deposition of the encapsulating layer of dielectric material and the layer of metallic material. Furthermore, the same mask may be used for deposition of any preceding or subsequent layers of dielectric material and/or metallic material. Furthermore, the same mask also may be used for deposition of any intermediate layers, such as the above-described barrier layer and/or adhesion promoter.

A depth of the undercut region may be at least as deep as an eventual thickness of the optical element.

Advantageously, by ensuring the undercut region is sufficiently deep, formation of fence regions or other artefacts in the deposited material may be avoided, as described in further detail below.

Furthermore, by ensuring the undercut region is sufficiently deep, a buildup of deposited sputtered particles against the sidewall may be prevented, thus minimizing a risk that a deposited layer of dielectric material may be damaged during a process of lift-off of the mask.

For example, in an example embodiment an eventual thickness, e.g. a thickness after all layers of dielectric and metallic material required to manufacture the metal-dielectric filter have been deposited, may be in the region of 4 pm. In such an embodiment an example depth of the undercut region may be 5 pm, or greater. The mask may be formed from a photoresist material. The method may further comprise a subsequent lift-off process to remove the mask after deposition of the encapsulating layer of dielectric material.

Advantageously, the photoresist material may be deposited using known photolithographic techniques. Similarly, by forming the mask from a photoresist material, subsequent lift-off may remove both the mask and any sputtered particles that may be deposited on the mask.

The mask may be provided as a removable substrate.

Advantageously, a mask provided as a separate substrate may mitigate a requirement for process-steps associated with deposition and subsequent lift-off of the photoresist-based mask.

A gas pressure in a vacuum chamber of an apparatus in which the sputter deposition takes place may be controlled to define an isotropy of each sputter deposition.

Advantageously, by varying the gas pressure a precise control over the isotropy of the deposition may be achieved. For example, at relatively low pressures the sputtered particles may be ejected from a target material towards the substrate or preceding layer of dielectric material with a relatively high energy. Such high-energy particles may travel in predominantly straight lines toward the substrate, thus resulting in a highly anisotropic deposition of material on the substrate, or on a preceding layer of material formed on the substrate.

Alternatively, at higher gas pressures, the sputtered particles may be more scattered, resulting in a relatively isotropic deposition. In particular, in some embodiments the particles at the higher gas pressure may scatter further into the above-described undercut region of the mask, thus resulting in deposition of particles over a relatively large area compared to that of an area of deposition when the gas pressure is lower.

The gas pressure measured in Pascals during deposition of the encapsulating layer of dielectric material may be at least 10 times greater than the gas pressure measured in Pascals during deposition of the layer of metallic material.

Advantageously, by providing a difference between the pressure during deposition of the encapsulating layer of dielectric material and deposition of the layer of metallic material that is in the region of an order of magnitude, a strong isotropy for dielectric layer deposition at increased gas pressure can be provided relative to a pronounced anisotropic metallic layer deposition. Furthermore, such variations in pressure may function synergistically with the mask having a sidewall with an undercut region to vary a size of an area over which particles are deposited, as described in more detail below with reference to specific embodiments of the disclosure.

An incident angle of particles of the metallic material may be defined, at least in part, by a collimator provided between the substrate and a sputtering target during deposition of the layer of metallic material.

Advantageously, the use of the collimator may result in more pronounced anisotropy of the deposition, as the collimator may limit an angle of incidence of deposition particles as they propagate toward the substrate.

As such, the collimator may function synergistically with the above-mentioned variations in pressure and/or the undercut region of the sidewall to manufacture a filter comprising an anisotropically deposited metallic layer encapsulated by an isotropically deposited dielectric layer.

The at least one preceding layer of dielectric material may be deposited with a greater isotropy than the encapsulating layer of dielectric material.

Advantageously, by ensuring the preceding layer is deposited with greater isotropy, the preceding layer will extend laterally across a larger area of the substrate than the subsequent layer, ensuring any intermediate metallic layer is completely encapsulated between the preceding and subsequently deposited dielectric layers.

The substrate may comprise a CMOS sensor. The optical element, e.g. a metal-dielectric filter, may be formed over the CMOS sensor.

For example, the substrate may comprise a plurality of CMOS sensors, each sensor or group of sensors having an associated metal-dielectric filter.

The preceding layer of dielectric material and the encapsulating layer of dielectric material may have different refractive indices.

The layer of metallic material may comprise at least one of the following elements and/or an alloy comprising at least one of the following elements: silver; aluminum; niobium; titanium; tantalum; hafnium; zinc.

According to a second aspect of the disclosure, there is provided an optical element formed according to the method of the first aspect.

Advantageously, by completely encapsulating the layer of metallic material, corrosion of the layer of metallic material, such as due to reaction with oxygen, sulfur or any other element within the environment, may be prevented. As such, the optical element may be exhibit the enhanced optical properties that may be provided by inclusion of a metallic layer, yet also exhibit the environment stability and resistance to corrosion of an optical element that does not comprise any metallic layers.

The optical element may comprise a plurality of encapsulated metallic layers.

The optical element may be configured as at least one of: an interference filter; a polarization selective filter a wavelength selective mirror; an anti-reflective coating; a selective absorber; a high-pass, low-pass, band-pass, Gaussian or notch filter; a neutral density filter; a beam splitter; a Fabry-Perot filter..

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 1a depicts a representation of an isotropic sputter deposition of a layer of dielectric material according to an embodiment of the disclosure;

Figure 1b depicts a representation of an anisotropic sputter deposition of a layer of metallic material according to an embodiment of the disclosure;

Figure 1c depicts a representation of an isotropic sputter deposition of a further layer of dielectric material according to an embodiment of the disclosure;

Figure 2a depicts a representation of a mask having an undercut sidewall and a plurality of deposited layers of material according to an embodiment of the disclosure;

Figure 2b depicts a representation of a mask having an undercut sidewall and a plurality of deposited layers of material according to a further embodiment of the disclosure;

Figure 3a depicts a deposited layer of material prior to lift-off of the mask; Figure 3b depicts a deposited layer of material after lift-off of the mask; Figure 3c depicts a deposited layer of material after lift-off of the mask; Figure 4a depicts an example of a stack of layers forming an optical element according to an embodiment of the disclosure;

Figure 4b depicts an example of a portion of the stack of layers of Figure 4a, showing a layer of metallic material completely encapsulated by dielectric layers;

Figure 5 depicts use of a collimator to define an incident angle of sputtered particles; Figure 6 depicts a method of manufacturing an optical element according to an embodiment of the disclosure; and Figure 7 depicts an optical element formed over a CMOS sensor in accordance with an embodiment of the disclosure.

Detailed Description

Figure 1a depicts a representation of a method of isotropic deposition of a layer of dielectric material 105 according to an embodiment of the disclosure. Figure 1a corresponds to a step in a method of manufacturing a metal-dielectric filter. Figure 1a is shown in cross-section. In the ensuing description, the deposition is described as a sputter deposition. It will be appreciated that in other embodiments, other methods of deposition may be implemented for one or more layers of the optical element.

For purposes of example, the layer of dielectric material 105 is being deposited on a substrate 110, for example a glass substrate or a CMOS substrate comprising a radiation sensor (not shown). While deposition of the layer of dielectric material 105 is described with reference to the substrate 110, it will be appreciated that the layer of dielectric material 105 may be deposited over a preceding layer of dielectric material, or over a preceding metallic layer, as described below in more detail.

In an isotropic deposition, sputtered particles are directed in various directions towards the substrate 110 as indicated by arrows 115 in Figure 1a.

The source of sputtered particles may be a target in an apparatus for sputter deposition, as is known in the art. That is, in such an apparatus, sputtered particles may be ejected from a target due to bombardment of the target by a plasma. Depending on various factors described below, the sputtered particles may exhibit a range of energy distributions and/or a range of angular trajectories. Also depicted in Figure 1a is a mask 120. The mask 120 is provided over the substrate 110, thereby defining an area 125 for deposition of the layer of dielectric material 105. An edge of the mask 120 comprises a sidewall having an undercut region 130.

In some embodiments, the mask 120 is formed from a photoresist material. That is, the mask 120 may be formed using photolithographic techniques. In other embodiments, the mask 120 may be provided as a removable substrate, e.g. a silicon mask, a glass substrate, a metal plate, or the like.

The undercut region 130 may be formed in the mask 120 using lithographic methods. For example, a method for forming a resist structure comprising an undercut region is described in US Patent No. 9,766,546 B2 “Method of producing a resist structure with an undercut sidewall” (Eilmsteiner et al.), which is hereby incorporated by reference in its entirety.

In use, the mask 120 inhibits substantial propagation of sputtered particles beyond the defined area 125. Furthermore, as described in more detail below, the mask 120 may function synergistically with the variations in isotropy of a sputter deposition, e.g. the deposition of the layer of dielectric material 105, to limit a lateral extent of the deposition of sputtered particles.

For example, because the sputter deposition of the layer of dielectric material 105 as described with reference to Figure 1a is an isotropic sputter deposition, the sputtered particles may exhibit a range of trajectories. Therefore, although a majority of particles may be deposited on the substrate 110 in an area 135 directly below an aperture 145 in the mask 120, a portion of the sputtered particles may extend into an area 140 below the undercut region 130 and thus may be deposited in the area 140 within the undercut region 130.

As shown in Figure 1a, a thickness of the deposited layer of dielectric material 105 may vary. A thickest portion 160 of the deposited layer of dielectric material 105 is formed in the area 135 directly below the aperture 145 in the mask 120. The thickest portion 160 may be deposited with a substantially uniform thickness over the area 135 directly below the aperture 145 of the mask 120. A tapering portion 165 is formed around a perimeter of the thickest portion 160. That is, a thickness of the layer of dielectric material 105 reduces, e.g. tapers, as the layer 105 extends from the thickest portion 160 into the undercut region 130.

A depth 155 of the undercut region 130, e.g. a depth 155 as measured from the aperture 145 to the undercut sidewall portion is at least as deep as an eventual thickness of a metal-dielectric filter formed according to the described method. Advantageously, by ensuring the undercut region 130 is sufficiently deep, formation of fence regions or other artefacts in the deposited material may be avoided, as described in further detail below. In an example embodiment an eventual thickness, e.g. a thickness after all layers of dielectric and metallic material required to manufacture the metal-dielectric filter have been deposited, may be in the region of 4 pm. In such an embodiment an example depth of the undercut region may be 5 pm, or greater.

A gas pressure in a vacuum chamber of an apparatus in which the sputter deposition takes place may be controlled to define an isotropy of each sputter deposition. For example, the sputter deposition illustrated in Figure 1a which is highly isotropic, e.g. sputter particles are travelling in multiple directions resulting in deposition of particles over a large area 125, is carried out under a high pressure relative to a pressure used for the anisotropic deposition described below with reference to Figure 1b.

Figure 1b depicts a representation of a further step in the method of anisotropic sputter deposition of a layer of metallic material 170 according to an embodiment of the disclosure. Figure 1b also corresponds to a step in a method of manufacturing a metal- dielectric filter. Figure 1b is shown in cross-section. The layer of metallic material 170 may comprise at least one of the following elements and/or an alloy comprising at least one of the following elements: silver; aluminum; niobium; titanium; tantalum; hafnium; zinc.

In Figure 1b, the layer of metallic material 170 is being deposited over the layer of dielectric material 105 deposited in Figure 1a.

In an anisotropic deposition, sputtered particles are predominantly directed in a single direction, as indicated by arrows 150 in Figure 1b, from the source. Although in the anisotropic deposition of Figure 1b, the sputtered particles are depicted as having a trajectory that is near-normal to the substrate 110, it will be appreciated that the sputtered particles may have trajectories at an angle relative to near normal incidence with the substrate 110. For example, as described in more detail below with reference to the collimator 505 of Figure 5, in an example embodiment the collimator 505 may limit an angle of incidence of particles relative to the substrate to be in the region of 26 degrees. It will be appreciated that in other embodiments, the angle may be larger or smaller than 26 degrees.

Also depicted in Figure 1b is the mask 120 of Figure 1a, provided over the substrate 110. The layer of metallic layer 170 is deposited predominantly in the area 135 directly below the aperture 145 in the mask 120. The mask 120 inhibits substantial propagation of sputtered particles beyond the area 135. Due to the highly anisotropic nature of the deposition, there relatively little propagation of sputtered particles into the undercut region 130, relative to the isotropic deposition of Figure 1a.

That is, relative to the isotropic deposition of Figure 1a, relatively few sputtered particles are deposited in the area 140 below the undercut region 130.

A thickness of the deposited layer of metallic material 170 may vary. A thickest portion 175 of the deposited layer of metallic material 170 is formed in the area 135 directly below the aperture 145 of the mask 120. The thickest portion 175 may be deposited with a substantially uniform thickness over the area 135 directly below the aperture 145 in the mask 120. A tapering portion 180 is formed around a perimeter of the thickest portion 175. That is, a thickness of the layer of metallic material 170 reduces, e.g. tapers, as the layer extends from the thickest portion 175 into the undercut region 130.

However, due to the anisotropic state of the deposition of the layer of metallic material 170 relative to the isotropic state of the deposition of the layer of dielectric material 105, the tapering portion 180 of the layer of metallic material 170 does not extend as far into the undercut region 130 as a tapering portion 165 of the preceding layer of dielectric material 105. This is described in more below with reference to Figures 2a and 2b.

As previously described, the gas pressure in the vacuum chamber of the apparatus in which the sputter deposition a takes place may be controlled to define an isotropy of each sputter deposition. For example, the sputter deposition illustrated in Figure 1b which is highly anisotropic, e.g. sputter particles are travelling predominantly in a single direction toward the substrate 110, may be carried out under a low pressure relative to a high pressure used for the isotropic deposition described above with reference to Figure 1a.

Figure 1c depicts a representation of an isotropic sputter deposition of a further layer of dielectric material 190 according to an embodiment of the disclosure. As described above with regard to the isotropic sputter deposition of the first layer of dielectric material 105, the further layer of dielectric material 190 extends further into the undercut region 130 than the preceding metallic layer 170.

As depicted in Figure 1c, the further layer of dielectric material 190 is an encapsulating layer of dielectric material 190, which is deposited over the layer of metallic material 170 such that the layer of metallic material is completely encapsulated between the encapsulating layer of dielectric material 190 and the preceding layer of dielectric material 105. Sputter deposition of the encapsulating layer of dielectric material 190 is more isotropic than sputter deposition of the layer of metallic material 170. Advantageously, by completely encapsulating the layer of metallic material 170, corrosion of the layer of metallic material 170, such as due to reaction with oxygen, sulfur or any other element within the environment, may be prevented.

Figure 2a depicts a representation of a portion of the mask 120 having the undercut sidewall, and the plurality of deposited layers of material 105, 170, 190 according to an embodiment of the disclosure. It can be seen from Figure 2a that the layer of metallic material 170 is completely encapsulated between the encapsulating layer of dielectric material 190 and the preceding layer of dielectric material 105. In particular, the tapering portion 165 of the preceding layer of dielectric material 105 and a tapering portion 195 of the subsequently deposited layer of dielectric material 190 extend further into the undercut region 130 than the tapering portion 180 of the layer of metallic material 170, thereby encapsulating the layer of metallic material 170.

Figure 2b depicts a representation of a portion of the mask 120 having the undercut sidewall, and the plurality of deposited layers of material 105, 170, 190 according to a further embodiment of the disclosure. In the example of Figure 2b, the preceding layer of dielectric material 105 has been deposited with a greater isotropy than subsequently deposited encapsulating layer of dielectric material 190. As such, the tapering portion 165 of the preceding layer of dielectric material 105 extends further into the undercut region 130 than the tapering portion 195 of the subsequently deposited layer of dielectric material 190. Both tapering portions 165, 195 extend further into the undercut region 130 than the tapering portion 180 of the layer of metallic material 170, thereby encapsulating the layer of metallic material 170. Advantageously, by ensuring the preceding layer of dielectric material 105 is deposited with greater isotropy, the preceding layer 105 will extend laterally across a larger area of the substrate 110 than the subsequent layer of dielectric material 190, ensuring the intermediate layer of metallic material 170 is completely encapsulated.

As described above, a minimum depth of the undercut region 130 of the mask 120 is at least as deep as an eventual thickness of the optical element. Advantageously, by ensuring the undercut region 130 is sufficiently deep, formation of fence regions or other artefacts in the deposited material may be avoided, as described with reference to Figures 3a and 3b. For purposes of example, Figure 3a depicts a layer of material 305, e.g. a dielectric material, that has been isotopically deposited. However, unlike the examples of Figures 1a to 2b, an undercut region 330 of the mask 320 of Figure 3a is insufficiently deep. As such, the layer of material 305 extends to the sidewall of the mask 320. In some instances, this may lead to formation of a fence region 350, as depicted in the example of Figure 3b, which shows the layer of material 305 after lift-off of the mask 320. In other instances, this may lead to damage to an edge portion of the layer of material 305 adjacent the sidewall of the mask 320 when the mask is removed, as shown in Figure 3c.

Figure 4a depicts an example of a stack 400 of layers forming an optical element according to an embodiment of the disclosure. The stack 400 comprises a plurality of layers of dielectric material. The plurality of layers of dielectric material comprises a combination of high or low refractive index layers 405H/L, interspersed with low or high refractive index layers 405L/H. It will be appreciated that the stack 400 is provided for purposes of example only, and other combinations of layers of dielectric materials may be implemented in stacks falling within the scope of the disclosure. Furthermore, the thickness of the layers forming the stack in Figure 4a is indicative of an example embodiment only. It will be appreciated that a thickness of each layer of material forming the stack 400 may be selected to meet particular application requirements. Similarly, a quantity of layers and particular refractive indices of layers may be selected accordingly.

Figure 4a depicts a layer of metallic material 420. A further layer 410, e.g. an upper intermediate layer, is provided between the layer of metallic material 420 and an upper layer of low or high refractive index material 405L/H. Similarly, a further layer 415, e.g. a lower intermediate layer 415, is provided between the layer of metallic material 420 and a lower layer low or high refractive index material 405L/H.

In an example embodiment, the lower intermediate layer may be an adhesion promoter, for example NiCr, for enhancing a connection between the metallic layer, e.g. Ag, and the lower layer of low or high refractive index material 405L/H.

In an example embodiment, the upper intermediate layer may be a barrier layer, for example a layer comprising Si3N4 and/or ZnO, which protects the layer of metallic material, e.g. Ag, from corrosion during and after processing.

In other embodiments, only an upper or lower intermediate layer may be implemented. In other embodiments falling within the scope of the disclosure, either or both of the upper or lower intermediate layers may be an adhesion promoter, a barrier layer, or a combination of an adhesion promoter and a barrier layer.

Furthermore, although only a single layer of metallic material 420 is depicted in the stack 400 of Figure 4a, in other embodiments more than one layer of metallic material may be implemented. In embodiments comprising more than one layer of metallic material, the layers of metallic material may comprise the same or different metallic materials. Furthermore, one or more of the above-described intermediate layers may be provided adjacent each layer of metallic material, or each group, e.g. sub-stack, of layers of metallic materials.

Figure 4b depicts an example of a portion of the example stack 400 of layers of Figure 4a, showing a layer of metallic material 420 completely encapsulated by an upper layer of low or high refractive index dielectric material 405L/H and a lower layer of low or high refractive index dielectric material 405L/H. It can be seen that the layers of dielectric material 405L/H completely encapsulate the layer of metallic material 420 and, when present, also any intermediate layers 410, 415.

Figure 5 depicts use of a collimator 505 in a vacuum chamber of a sputter deposition apparatus 550. The collimator 505 is used to define, or limit, an incident angle of sputtered particles 510.

In use, a target 515 in the sputter deposition apparatus may be bombarded with a plasma, causing particles 510 to be ejected from the target 515. The ejected particles 510, e.g. ‘sputtered particles’ may have different trajectories. As described above, in some embodiments a pressure in the vacuum chamber may be selected to influence trajectories of ejected particles 510. That is, the sputtered particles 510 may exhibit a range of energy distributions and/or a range of angular trajectories.

The collimator 505 may be formed from a plate comprising a plurality of channels. The channels may, for example, be provided in a lattice-like or honeycomb arrangement, this maximizing a ratio of aperture-to-surface-area of the collimator 505.

Particles 510 passing through the collimator 505 have a trajectories substantially aligned with the channels of the collimator 505. As such, the collimator 505 may limit the trajectories of particles 510 moving toward a substrate 520, thus ensuring a highly anisotropic deposition. That is, the collimator 505 limits an angle of incidence of deposition particles 510 as they propagate toward the substrate 520. For example, as described above, in a non-limiting example embodiment, the collimator 505 may limit the angle of incidence of particles 510 relative to the substrate 520 to be in the region of 26 degrees.

In an example embodiment, the target 515 may be disposed at a distance 525 in the region of 60 millimeters from the collimator 505. In an example embodiment, the collimator 505 may be disposed at a distance 530 in the region of 15 millimeters from the substrate 520.

The collimator 505 may function synergistically with the above-mentioned variations in pressure and/or the undercut region of the sidewall to manufacture a filter comprising an anisotropically deposited metallic layer encapsulated by an isotropically deposited dielectric layer.

Figure 6 depicts a method of manufacturing an optical element 705 on a substrate. The method comprises a step 610 of deposition of a layer of metallic material. The deposition of the layer of metallic material may be a sputter deposition.

The method comprises a subsequent step 620 of deposition of an encapsulating layer of dielectric material, such that the layer of metallic material is encapsulated between the encapsulating layer of dielectric material and the substrate or a preceding layer of dielectric material. The deposition of the encapsulating layer of dielectric material may be a sputter deposition.

In the above-described method, deposition of the encapsulating layer of dielectric material is more isotropic than deposition of the layer of metallic material.

Figure 7 depicts an optical element 705 formed over a CMOS sensor 710 formed in a substrate 725 in accordance with an embodiment of the disclosure. In the example of Figure 7, the optical element 705 is depicted as comprising two layers of metallic material 715a, 715b. Each layer of metallic material 715a, 715b is completely encapsulated by surrounding layers of dielectric material 720a, 720b, 720c, 720d.

In the example embodiment of Figure 6, the optical element 705 is configured as an interference filter. In other embodiments, the optical element may be configured as, for example, at least one of: a polarization selective filter a wavelength selective mirror; an anti-reflective coating; a selective absorber; a high-pass, low-pass, band pass, Gaussian or notch filter; a neutral density filter; a beam splitter; a Fabry-Perot filter..

It will be appreciate that the particular arrangement of layers forming the optical element 705 of Figure 7 is provided for example only, and other optical element 705 having fewer or greater than the number of metallic and/or dielectric layers depicted in Figure 7 would also fall within the scope of the disclosure. Also, in some embodiments the layers of dielectric material comprise different refractive indices. In some embodiments the layers of dielectric material are arranged to have alternating refractive indices.

Furthermore, although a single CMOS sensor 710 is depicted, in other embodiments a plurality of CMOS sensors 710 may be formed in the substrate 725, each sensor 710 having an associated optical element 705.

Although the disclosure has been described in terms of preferred 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.

Reference Numerals

105 layer of dielectric material 305 layer of material

110 substrate 320 mask

115 arrows 330 undercut region

120 mask 350 fence region

125 area 40 400 stack

130 undercut region 405H/L layer of high or low refractive

135 area index dielectric material

140 area 405L/H layer of low or high refractive

145 aperture index dielectric material

150 arrows 45 410 further layer

155 depth 415 further layer

160 thickest portion 420 layer of metallic material

165 tapering portion 505 collimator

170 layer of metallic material 510 particles

175 thickest portion 50 515 target

180 tapering portion 520 substrate

190 layer of dielectric material 525 distance

195 tapering portion 530 distance sputter deposition apparatus 5 710 sensor step 715a-b layers of metallic material step 720a-d layers of dielectric material optical element 725 substrate