Patent ID: 12218163

DETAILED DESCRIPTION

Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties.

For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, the embodiment of the sensors has not been described in detail, the disclosed embodiments being compatible with the usual embodiments of the sensors.

Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements.

In the following disclosure, unless indicated otherwise, when reference is made to absolute positional qualifiers, such as the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc., or to relative positional qualifiers, such as the terms “above”, “below”, “higher”, “lower”, etc., or to qualifiers of orientation, such as “horizontal”, “vertical”, etc., reference is made to the orientation shown in the figures.

Unless specified otherwise, the expressions “around”, “approximately”, “substantially”, “practically” and “in the order of” signify within 10%, and preferably within 5%. Furthermore, it is considered here that the terms “insulating” and “conductive” respectively mean “electrically insulating” and “electrically conductive”.

Unless otherwise specified, the expressions “the set of elements”, “all of the elements” and “each element” mean between 95% and 100% of the elements. Unless otherwise specified, the expression “it comprises only the elements” means that it comprises at least 90% of the elements, preferably that it comprises at least 95% of the elements.

In the remainder of the disclosure, unless otherwise specified, a layer or a film is said to be opaque to a ray when the transmittance of the ray through the layer or the film is less than 10%. In the remainder of the disclosure, a layer or a film is said to be transparent to a ray when the transmittance of the ray through the layer or the film is greater than 10%.

Embodiments of optical systems will now be described for optical systems comprising an array of optical elements of micrometric size in the case where each optical element of micrometric size corresponds to a lens of micrometric size, or microlens, made up of two diopters. However, it is clear that these embodiments can also be implemented with other types of optical elements of micrometric size, each optical element of micrometric size being able to correspond, for example, to a micrometric Fresnel lens, a micrometric gradient index lens or a micrometric diffraction grating.

In the remainder of the disclosure, visible light refers to an electromagnetic ray having a wavelength inclusively between 400 nm and 700 nm. In this range, red light refers to an electromagnetic ray whose wavelength is inclusively between 600 nm and 700 nm, blue light refers to an electromagnetic ray whose wavelength is inclusively between 450 nm and 500 nm and green light refers to an electromagnetic ray whose wavelength is inclusively between 500 nm and 600 nm.

FIG.1shows, in partial and schematic sectional view, one embodiment of an image acquisition device11.

According to the embodiment illustrated inFIG.1, the image acquisition device11comprises three laterally separate parts, in the orientation of the figure: a connecting part13, shown on the left inFIG.1; a logic part15, shown in the center ofFIG.1; and a sensor part17, shown on the right inFIG.1.

According to the embodiment illustrated inFIG.1, the three parts13,15and17include a stack19of insulating layers, conductive tracks with different levels of metallization21between the insulating layers and conductive vias (not shown) connecting the tracks with different levels of metallization. The stack19preferably has a thickness in the order of 2 μm.

The device11preferably comprises a layer23, or substrate, covering the stack19and extending over practically all of the upper face of the stack19in the logic part15and the sensor part17. The substrate23is preferably made from a semiconductor material, for example from silicon. The substrate23, for example, comprises insulating trenches (not shown) making it possible to insulate portions of the substrate23from one another, in particular in the sensor part17. The substrate23, for example, has a thickness in the order of 3 μm.

The device11further comprises electronic components, formed in the substrate23and/or on the face of the substrate23located on the side of the stack19, these electronic components being symbolized by rectangles25and27inFIG.1. As an example, in the logic part15, the components25comprise insulated gate field effect transistors, or MOS (Metal Oxide Semiconductor) transistors, in particular made using CMOS (Complementary Metal Oxide Semiconductor) technology and, in the sensor part17, the components27comprise photodetectors.

According to one embodiment, the device11comprises a conductive layer29extending so as to cover the surface of the substrate23in the logic part15. The layer29is, for example, opaque at the wavelengths of the application in question. The layer29is, for example, made from tungsten and has a thickness in the order of 200 μm.

According to the embodiment illustrated inFIG.1, the device11comprises a layer31covering the layer29. More specifically, the layer31is located in the logic part15of the device11and extends over the entire upper face of the layer29. The layer31is preferably made from an organic material (for example, a resin) only allowing radiation to pass at the desired wavelengths. The layer31can be made in a single layer or a stack of several layers made from different materials, which makes it possible, for example, to reduce stray reflections. The layer31, for example, has a thickness in the order of 500 nm to 1000 nm.

The image acquisition device11further comprises a color filter array33. The color filter array33is located in the sensor part17of the device11on the upper face of the substrate23.

The color filter array33is made up of different resins, for example organic, so as to filter the incident rays while locally allowing only the red radiation, blue radiation or green radiation to pass.

The color filter array33thus comprises first color filters made up of a first resin, referred to as the red resin, allowing only the red radiation to pass, second color filters made up of a second resin, referred to as the blue resin, allowing only the blue radiation to pass and third color filters made up of a third resin, referred to as the green resin, allowing only the green radiation to pass. These color filters are organized in the form of blocks of resin substantially of the same size. The blocks of resin have, for example, a substantially square shape as seen in a direction perpendicular to the upper face of the substrate23. The characteristic dimension of the blocks is, for example, in the order of 600 nm to 900 nm. The blocks of resin are preferably organized in matrix form, as seen in a direction perpendicular to the upper face of the substrate23, in rows and columns, for example, according to a Bayer matrix. Thus, the blocks of resin are, for example, organized such that about 50% of the matrix is made up of blocks of green resin. The matrix is additionally made up of about 25% blocks of red resin and about 25% blocks of blue resin. The matrix, for example, has a thickness inclusively between 600 nm and 900 nm.

The device11also comprises an insulating layer35covering the entire upper face of the array of color filters33. The layer35further preferably covers the upper face of the layer31and covers the surfaces of the layer29in locations where the layer29is not covered by the layer31. The layer35can further cover the substrate23in locations where the substrate23is not covered by the layer29in the logic part15of the matrix33in the sensor part17.

The insulating layer35is made up of an inorganic material. According to one embodiment, the material making up the layer35is one or more of a silicon nitride (Si3N4) and/or a metal nitride. In a variant, the material making up the layer35is one or more of a silicon oxide (SiO2) and/or a silicon oxynitride (SiON) and/or a metal oxide. The material making up the layer35can, according to another variant, be a combination of several metal nitrides, a combination of several metal oxides or a combination of silicon nitride and/or silicon oxide and/or silicon oxynitride and/or one or several metal nitrides and/or one or several metal oxides. The layer35can have a single-layer structure or a multi-layer structure.

As an example, the metal nitrides are chosen from a group of materials including titanium nitride (TiN) and tantalum nitride (TaN). Still as an example, the metal oxides are chosen from a group of materials including manganese monoxide (MnO), titanium dioxide (TiO2), alumina (Al2O3), zinc oxide (ZnO), cobalt monoxide (CoO), indium tin oxide (ITO), Aluminum-doped Zinc Oxide (AZO) and molybdenum monoxide (MoO).

The layer35is, for example, made from a group of materials including silicon nitride, silicon dioxide coupled with alumina, silicon oxynitride, silicon oxynitride coupled with alumina or from alumina. The layer35is preferably made from silicon nitride.

The layer35, for example, has a thickness inclusively between 30 nm and 200 nm, preferably inclusively between 40 nm and 130 nm, more preferably equal to about 40 nm. The thickness of the layer35is configured so that the layer35is transparent in the visible domain (spectrum).

The device11comprises an array of lenses37, of micrometric size, for example, planar convex lenses covering the layer35in the sensor part17. The planar face of the microlenses37preferably rests on the upper face of the layer35and in contact with the layer35.

According to one embodiment, the microlenses37are located aligned with the color filter array33. The array of microlenses37is preferably arranged in the same matrix form as the color filter array33, the optical axis of each microlens37being combined with the center of a resin block. Each microlens37preferably covers a single resin block of the color filter array33and each resin block is covered by a single microlens37. The microlenses37can have a diameter substantially equal to the size of the sides of the resin blocks of the color filter array33.

The microlenses37are, for example, made up of an organic resin. The microlenses37are preferably transparent in the considered wavelengths. The microlenses37are more preferably transparent in the visible domain.

According to the embodiment illustrated inFIG.1, the microlenses37are all the same, that is to say, they have the same chemical composition and the same dimensions.

In a variant, the microlenses37may not all have the same dimensions.

Preferably, the component material used to make the microlenses37extends in the logic part on the upper face of the layer35so as to form a layer38which covers the layer35.

The device11may further comprise a protective layer36covering the layer38and the lenses37and in contact with the microlenses37. The protective layer36can be made from an inorganic material, for example one of the materials previously described for the layer35.

According to one embodiment, the protective layer36is substantially tight with respect to moisture. The protective layer36, for example, has a thickness inclusively between 100 nm and 600 nm.

According to the embodiment illustrated inFIG.1, the device11comprises a connecting pad39, partially shown inFIG.1. The connecting pad39is, for example, located in the connecting part13of the device. The pad39is preferably, seen in a direction parallel to the upper face of the substrate23, U-shaped, the lower face being flush with the lower face of the substrate23. The side edges of the pad39extend vertically, from the lower face of the substrate23along the substrate23and the layer35, past the upper face of the layer35. The pad39is not covered by the layers35and36. The edges and the bottom of the pad39are, for example, made from a metal material, preferably from aluminum.

FIGS.2to6are partial and schematic sectional views of structures obtained in successive steps of one embodiment of a method for manufacturing the device shown inFIG.1.

FIG.2illustrates the structure41obtained after the formation of the components25and27, the formation of the stack19on the substrate23, the formation of the layer29and the formation of the connecting pad39.

FIG.3illustrates the structure43obtained after the formation of the color filter array33on the upper face of the structure41illustrated inFIG.2and the formation of the layer31.

The formation of the color filter array33is preferably done in three successive steps consisting, in a first step, of forming the blocks of green resin, in a second step, forming the blocks of blue resin and the layer31, then in a third step, forming the blocks of red resin.

It is understood that the order of these steps can be modified so as, for example, to form the blocks of red resin before the blocks of blue resin.

As an example, the step for forming the blocks of green resin consists of depositing a layer of the green resin on the entire structure41as illustrated inFIG.2followed by a partial removal of this same layer of resin in order to keep it only in the desired locations.

The deposition of the layer of green resin is, for example, done by deposition by centrifugation, also called spin-coating. The deposition is done on the full plate such that the entire upper face of the structure41is covered by the layer of green resin.

According to one embodiment, the localized removal of the layer of green resin is done by photolithography. In other words, the layer of green resin can, for example, be full-plate covered by a layer of photoresist that is partially removed by photolithography such that the photoresist only covers the future blocks of green resin. The structure thus obtained next undergoes etching so as to remove the parts of the layer of green resin, not topped by the photoresist, and to remove the photoresist.

In a variant, if the green resin is photosensitive, the partial removal of the green resin can be done directly through photolithography steps with no prior deposition of a photoresist.

The different steps to form blocks of red and blue resin can be identical to the steps for forming blocks of green resin previously described.

FIG.4illustrates the structure45obtained after a step for depositing the insulating layer35on the upper face of the structure43illustrated inFIG.3.

According to one preferred embodiment, the step for depositing the layer35is done by plasma-enhanced chemical vapor deposition (PECVD). The layer35is, for example, deposited from a plasma formed by silane, ammonia and nitrogen. As an example, the silicon oxide is deposited from a plasma formed by tetraethyl orthosilicate (TEOS), oxygen and helium. Still as an example, the silicon nitride is deposited from a plasma formed by silane, ammonia and nitrogen.

In a variant, the step for depositing the layer35is done using any other chemical vapor deposition (CVD) technique, such as low-pressure chemical vapor deposition (LPCVD). The step for depositing the layer35can also be done through a physical vapor deposition (PVD) technique or an atomic layer deposition (ALD) technique.

The deposition of the layer35is preferably done at a temperature below 250° C., more preferably less than or equal to 200° C. Still more preferably, the deposition is done at a temperature in the order of 200° C.

The layer35is formed by solid (integral) plate, that is to say that the layer35is formed over the entire upper face of the structure43illustrated inFIG.3, including over the upper face of the connecting pad39.

The layer35preferably has a thickness inclusively between 30 nm and 200 nm, for example inclusively between 40 nm and 130 nm.

FIG.5illustrates the structure47obtained after a step for depositing the layer38of a resin making up the microlenses37on the upper face of the structure45illustrated inFIG.4.

The deposition of the layer38is preferably done by centrifugation such that the layer38covers the entire upper face of the structure45illustrated inFIG.4. In other words, the upper face of the layer35is covered by the layer38.

FIG.6illustrates the structure11obtained after a step for forming the lenses37, forming the layer36and partially removing the layer35.

According to one embodiment, the step for forming the microlenses37comprises a photolithography step followed by an annealing or heating. The microlenses37are thus shaped in the layer38shown in the structure47ofFIG.5.

According to one embodiment, the protective layer36is deposited, by a PECVD method, on the upper face of the structure obtained at the end of the formation of the lenses37. The protective layer36can, for example, cover the layer38and the microlenses37by surrounding them.

According to one embodiment, an etching step is carried out so as to remove the parts of the layers35,36and38covering the connecting pad39.

The layers36,35and38are, for example, removed outside the sensor17and logic15parts by photolithography.

FIGS.7A and7Billustrate two examples53and53′ of images captured by two different sets of image acquisition devices.

In order to show the improvement in performance resulting from the presence of the layer35within an image acquisition device, the inventors have conducted comparative tests of temperature and humidity resistance on a first set of image acquisition devices and a second set of image acquisition devices.

The image acquisition devices of the second set of devices have the same structure as the devices of the first set of devices, with the exception that they do not comprise a layer35between the color filter array33and the microlenses37.

In order to test the resistance to heat and humidity, the two aforementioned sets of devices have undergone highly accelerated stress tests (HAST) commonly used in order to test electronic circuits. The HAST test consists of exposing the devices to a temperature in the order of 130° C. and to a relative humidity percentage of 85% for 96 hours in a chamber in which the pressure is of two atmospheres. At the end of 96 hours, the two sets of devices are illuminated with a ray in particular comprising blue, green and red components, and the captured images are analyzed.

FIG.7Ashows the images53captured by the devices11of the first set which comprise the layer35.

FIG.7Bshows the images53′ captured by the devices of the second set which do not comprise the layer35.

InFIGS.7A and7B, each acquired image53and53′ is, for example, substantially rectangular and comprises about 500 pixels by 750 pixels.

While the structure of the devices of the first and second sets making it possible to acquire the images53and53′ illustrated inFIGS.7A and7Bonly differ by the presence of the layer35, the images53′ shown inFIG.7Bare dotted with black points55. These black points55represent local losses of sensitivity, for example inclusively between 2% and 10%. These black points55have a size, for example, in the order of several tens of micrometers.

The inventors have shown that, under the effect of the heat, significant mechanical stresses appear in the image acquisition device, in particular due to the differences in thermal expansion coefficients of the organic materials making up the microlenses and color filters and relative to most of the inorganic materials of the image acquisition device. Indeed, the expansion coefficients of the materials making up the microlenses and the color filters can be high, in particular between 120 ppm/° C. and 400 ppm/° C. while most of the other materials of the device can have a low expansion coefficient, for example in the order for example of 1 ppm/° C.

The mechanical stresses can cause the cracking of the protective layer36and a penetration of humidity in the lower layers, for example in the microlenses37and in the color filters33. The humidity having infiltrated the device11causes localized decreases in sensitivity of several percent, as observed inFIG.7B. In the presence of the layer35, no localized decrease in sensitivity is observed for the image acquisition devices.

One advantage of the described embodiments and modes of implementation is that they make it possible to improve the temperature and humidity resistance of the image acquisition devices.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art. In particular, the embodiments and modes of implementation can be combined. The described embodiments are not limited to the exemplary sizes and materials mentioned hereinabove.

Finally, the practical implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art based on the functional description provided hereinabove.