PHOTODIODES AND METHODS FOR FABRICATING PHOTODIODES

Abstract

A photodiode includes an opening over an active photodiode region so that a top passivation layer and interlayer dielectric layers (ILDs) do not affect the spectral response of the photodiode. A dielectric reflective optical coating filter, which includes a plurality of dielectric layers, fills at least a portion of the opening and thereby covers the active photodiode region, to shape a spectral response of the photodiode. Alternatively, the dielectric reflective optical coating filter is formed prior to the opening, and the opening is formed by removing a top passivation coating and ILDs to expose the dielectric reflective optical coating filter.

Description

PRIORITY CLAIM

This application claims priority under 35 U.S.C. 119(e) to the following provisional patent applications, each of which is incorporated herein by reference: U.S. Provisional Patent Application No. 61/244,817, entitled WAFER-LEVEL COATING FOR AMBIENT SENSOR AND PROXIMITY SENSOR, filed Sep. 22, 2009; U.S. Provisional Patent Application No. 61/259,475, entitled OPTICAL SENSOR INCLUDING WAFER-LEVEL OPTICAL COATINGS AND TINTED PACKAGING EPDXY TO SHAPE SPECTRAL RESPONSE, filed Nov. 9, 2009; and U.S. Provisional Patent Application No. 61/257,595, entitled INFRARED SUPPRESSING PHOTO-PATTERNABLE COATING FOR PHOTODETECTING SEMICONDUCTOR DIE GLASS APPLICATIONS, filed Nov. 3, 2009.

BACKGROUND

Photodiodes can be used as ambient light sensors (ALSs), e.g., for use as energy saving light sensors for displays, for controlling backlighting in portable devices such as mobile phones and laptop computers, and for various other types of light level measurement and management. For more specific examples, ambient light sensors can be used to reduce overall display-system power consumption and to increase Liquid Crystal Display (LCD) lifespan by detecting bright and dim ambient light conditions as a means of controlling display and/or keypad backlighting. Without ambient light sensors, LCD display backlighting control is typically done manually whereby users will increase the intensity of the LCD as the ambient environment becomes brighter. With the use of ambient light sensors, users can adjust the LCD brightness to their preference, and as the ambient environment changes, the display brightness adjusts to make the display appear uniform at the same perceived level; this results in battery life being extended, user eye strain being reduced, and LCD lifespan being extended. Similarly, without ambient light sensors, control of the keypad backlight is very much dependent on the user and software. For example, keypad backlight can be turned on for 10 second by a trigger which can be triggered by pressing the keypad, or a timer. With the use of ambient light sensors, keypad backlighting can be turned on only when the ambient environment is dim, which will result in longer battery life. In order to achieve better ambient light sensing, ambient light sensors preferably have a spectral response close to the human eye response and have excellent infrared (IR) noise suppression.

SUMMARY

In accordance with certain embodiments, a photodiode includes a first semiconductor type surface region (e.g., 302), and a second semiconductor type surface layer (e.g., 303) formed in a portion of the first semiconductor type surface region (e.g., 302), such that an active photodiode region is formed by a PN junction of the first semiconductor type surface region (e.g., 302) and the second semiconductor type surface layer (e.g., 303). A passivation coating (e.g., 314) is on the second semiconductor surface layer (e.g., 303). An etch stop coating (e.g., 315) is on a portion of the passivation coating (e.g., 314). The photodiode also includes an opening (e.g., 340) over at least a portion of the active photodiode region, where the opening (e.g., 340) extends through the etch stop coating (e.g., 315) down to the passivation coating (e.g., 314). A dielectric reflective optical coating filter (e.g., 350), which includes a plurality of dielectric layers, fills at least a portion of the opening (e.g., 340) and thereby covers the active photodiode region. The opening (e.g., 340) allows a portion of light incident on the photodiode to be received by the active photodiode region. The dielectric reflective optical coating filter (e.g., 350) reflects a portion of light incident on the photodiode and thereby shapes a spectral response of the photodiode. The dielectric reflective optical coating filter (e.g., 350) includes a top surface that is generally parallel to a top surface of the passivation coating (e.g., 314) and sidewalls (e.g., 355) that extend from the top surface towards the passivation coating (e.g., 314). In accordance with an embodiment, a dark mirror (e.g., 360) covers the top surface and the sidewalls (355) of the dielectric reflective optical coating filter (e.g., 350).

In accordance with alternative embodiments, there is no passivation coating (e.g., 314) on the second semiconductor surface layer (e.g., 303). In such embodiments, the opening (e.g., 340) over at least a portion of the active photodiode region extends down to the second semiconductor type surface layer (e.g., 303) or a thin oxide layer on the second semiconductor type surface layer (e.g., 303).

In other embodiments, the dielectric reflective optical coating filter (e.g., 350) is formed above the second semiconductor type surface layer (e.g., 303), and an etch stop coating (e.g., 315) is on a portion of the dielectric reflective optical coating filter (e.g., 350). In such embodiments, an opening (e.g., 340) is over at least a portion of the active photodiode region, with the opening (e.g., 340) extending through the etch stop coating (315) down to the dielectric reflective optical coating filter (e.g., 350). In such embodiments, a passivation coating (e.g., 314) may or may not be between the second semiconductor surface layer (e.g., 303) and the dielectric reflective optical coating filter (e.g., 350).

Embodiments of the present invention are also directed to methods for fabricating photodiodes. In accordance with an embodiment, a method include implanting and thereby forming a second semiconductor type shallow surface layer (e.g., 303) into a portion of a first semiconductor type surface region (e.g., 302), wherein an active photodiode region is formed by a PN junction of the first semiconductor type surface region and the second semiconductor type shallow surface layer. A passivation coating (e.g., 314) is formed on the shallow surface layer (e.g., 303), wherein the passivation coating (e.g., 314) comprises a thin oxide layer (e.g., 311) on the shallow surface layer (e.g., 303) and a second dielectric layer (e.g., 312) different from the thin oxide layer on the thin oxide layer. An etch stop coating (e.g., 315) is formed on the second dielectric, wherein the etch stop coating (e.g., 315) comprises at least one layer (e.g., 316) resistant to oxide etch. At least some of interlayer dielectric (ILD) processing, metal processing, contact processing, via processing and passivation processing are then performed, which results in multiple layers being formed above the etch stop coating (e.g., 315). The method further includes removing at least a portion of the multiple layers formed above the etch stop coating (e.g., 315) and at least a portion of the etch stop coating (e.g., 315) to produce an opening (e.g., 340) that extends down to the passivation coating (e.g., 314) over at least a portion of the active photodiode region. At least a portion of the opening (340) is filled with a dielectric reflective optical coating filter (350) so that the dielectric reflective optical coating filter (350) covers the at least a portion of the active photodiode region. Additionally, a top surface (e.g., 357) and sidewalls (e.g., 355) of the dielectric reflective optical coating filter (350) can be covered with a dark mirror (360).

In alternative embodiments, there is no passivation coating (e.g., 314) formed on the second semiconductor surface layer (e.g., 303). In such an embodiment, an opening (e.g., 340) is formed by removing at least a portion of the multiple layers formed above the remaining etch stop coating (e.g., 315) and at least a portion of the remaining etch stop to produce an opening that extends down to the second semiconductor type surface layer (e.g., 303) or a thin oxide layer on the second semiconductor type surface layer (e.g., 303).

In other embodiments, the dielectric reflective optical coating filter (350) is formed over at least a portion of the active photodiode region, before an opening (e.g., 340) is formed.

Further and alternative embodiments, and the features, aspects, and advantages of the embodiments of invention will become more apparent from the detailed description set forth below, the drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary spectral response of a photodiode without any spectral response shaping.

FIG. 2 illustrates the typical spectral response of a human eye.

FIG. 3A illustrates a cross section of a photodiode 300a after a window has been opened over an active photodiode region down to a passivation coating, in accordance with an embodiment.

FIG. 3B illustrates a cross section of a photodiode 300b, according to an embodiment, which includes a dielectric reflective optical coating filter filling a portion of a window opened over an active photodiode region down to a passivation coating.

FIG. 3C illustrates a cross section of a photodiode 300c that is similar to the photodiode 300b of FIG. 3B, but with a dark mirror added to cover sidewall and a top surface of the dielectric reflective optical coating filter, in according with an embodiment.

FIG. 3D illustrates a cross section of a photodiode 300d that is similar to the photodiode 300b of FIG. 3B, but with the area of the diffusion region (and thus, the active photodiode region) made substantially smaller than the opening formed by the sidewalls 355 of the dielectric reflective optical coating filter, in accordance with an embodiment.

FIG. 3E illustrates a cross section of a photodiode 300e that is similar to the photodiode 300c of FIG. 3C, but where the dielectric reflective optical coating filter fills the entire window and extends above the window, in accordance with an embodiment.

FIG. 4 illustrates a cross section of a photodiode 400, according to an embodiment, where the dielectric reflective optical coating filter is formed before the window is opened.

FIG. 5A illustrates a cross section of a photodiode 500a after a window has been opened over an active photodiode region down to a diffusion region of the photodiode or down to a thin oxide covering the diffusion region.

FIG. 5B illustrates a cross section of a photodiode 500b, according to an embodiment, which includes a dielectric reflective optical coating filter filling a portion of a window opened over an active photodiode region down to a diffusion region of the photodiode or down to a thin oxide covering the diffusion region.

FIG. 5C illustrates a cross section of a photodiode 500c that is similar to the photodiode 500b of FIG. 5B, but with a dark mirror added to cover sidewalls and a top surface of the dielectric reflective optical coating filter, in according with an embodiment.

FIG. 5D illustrates a cross section of a photodiode 500d that is similar to the photodiode 500b of FIG. 5B, but with the area of the diffusion region (and thus, the active photodiode region) made substantially smaller than the opening formed by the sidewalls 355 of the dielectric reflective optical coating filter, in accordance with an embodiment.

FIG. 5E illustrates a cross section of a photodiode 500e that is similar to the photodiode 500c of FIG. 5C, but where the dielectric reflective optical coating filter fills the entire window and extends above the window, in accordance with an embodiment.

FIG. 6 illustrates a cross section of a photodiode 600, according to an embodiment, where the dielectric reflective optical coating filter is formed above the diffusion region before the window is formed.

FIG. 7 illustrates how that a filter response (F) can be shifted relative to a target response (T), so that when the filter is used with a photodiode having a photodiode response (P), the target response (T) is achieved.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary spectral response of a photodiode without any spectral response shaping, e.g., using a filter to covering an active photodiode region. FIG. 2 illustrates the typical spectral response of a human eye. As can be appreciated from FIGS. 1 and 2, a problem with using a photodiode as an ambient light sensor is that it detects both visible light and non-visible light, such as infrared (IR) light, which starts at about 700 nm. By contrast, notice from FIG. 2 that the human eye does not detect IR light. Thus, the response of a photodiode can significantly differ from the response of a human eye, especially when the light is produced by an incandescent light, which produces large amounts of IR light. This would provide for significantly less than optimal adjustments if the photodiode were used as an ambient light detector, e.g., for adjusting backlighting, or the like.

Referring to FIG. 3A, in accordance with an embodiment, a photodiode 300a can be fabricated by starting with a substrate, e.g., P+ substrate 301, having a first semiconductor type surface region, e.g., P− surface region 302 on at least a portion of the substrate 301. Alternatively, the surface region 302 can simply be a surface of the substrate 301. A second semiconductor type shallow surface layer, e.g., N+ diffusion layer 303 (also referred to as a diffusion region), can be formed into a portion of the surface region 302 to thereby form an active PN junction photodiode region. The P+ substrate 301, the P− surface region 302, and the N+ diffusion layer 303 can be formed from Silicon (Si), but are not limited thereto. The N+ diffusion layer 303 can be formed, e.g., by doping Si with As or Sb, but is not limited thereto.

In FIG. 3A, a passivation coating 314 is formed on the shallow surface layer 303. In accordance with an embodiment, the passivation coating 314 includes two dielectric layers. The top layer 312 of the passivation coating 314 can be a nitride, e.g., silicon nitride (Si3N4). In accordance with an embodiment of the present invention, when used for an optical application, the nitride layer preferably has a thickness in the range of about 20-40 nm (e.g., 30 nm) so that the nitride layer does not adversely affect the spectral response of the photodiode. However, the relatively shallow thickness of the nitride layer may cause stopping on the nitride as an etch stop to be difficult. To overcome this, the thickness of the nitride can be increased so that during the etching some of the nitride is etched, leaving a nitride layer within the desired thickness range. Alternatively, a sacrificial etch stop layer (e.g., a metal) can be added to protect an area that is not already covered by a top metal. This sacrificial etch stop layer can then be removed by another masking step. The bottom layer 311 of the passivation coating 314 can be a thin silicon dioxide (SiO₂) layer. The thin silicon dioxide (SiO₂) layer 311 (e.g. 1.5 to 8 nm) reduces tension/stress between the underlying Si and the silicon nitride (Si₃N₄) layer 312 or other second dielectric layer of the passivation coating 314. The second dielectric layer (e.g., Si₃N₄) 312 seals the N+ diffusion layer 303 from moisture. Although the second dielectric layer 312 of the passivation coating 314 is generally described herein as being silicon nitride, the invention is not limited to silicon nitride as the second dielectric layer 312. For example, the second dielectric layer 312 can be silicon rich SiO₂, silicon rich SiO_N or silicon rich Si₃N₄. An exemplary known technique for depositing such silicon rich layers is using plasma enhanced deposition systems.

In FIG. 3A, an etch stop coating 315 is formed on the passivation coating 314. In accordance with an embodiment, the etch stop coating 315 includes at least one layer resistant to oxide etch 316, e.g., silicon nitride (Si₃N₄) or polysilicon, above an oxide (e.g., SiO₂) layer 317.

After the passivation coating 314 and the etch stop coating 315 are formed, a portion of the etch stop coating 315 and the passivation coating 314 is removed outside the active photodiode region down to the first semiconductor type surface region, e.g., the P− surface region 302, to make room for metalization. Such removal can be performed, e.g., using resist patterning followed by an etch and resist removal. The etch stop coating should also be cleared from a CMOS gate topography (not shown). In the case of a Si etch stop layer a variety of plasma etches stopping on the underlying oxide can be used. In the case of a Si₃N₄ etch stop layer, plasma or wet etches can be employed, the latter generally including an oxide hard mask material (about 30 nm or thicker) deposited over the Si₃N₄ etch stop layer. The oxide layer 317 between the passivation coating 314 and the etch stop layer resistant to oxide etch 316 can be removed using wet chemistry prior to the photo resist mask removal, but is not limited thereto.

Thereafter, interlayer dielectric (ILD), metal, contact, via and passivation processing can be performed to add interlayer dielectric (ILD) layers 321, 322, 323, 324 and 325, metalization 330, and a top passivation layer 326 (e.g., an oxide layer capped with a nitride layer). The ILD layers 321, 322, 323, 324 and 325 are typically oxides, portions of which can be removed using an oxide etch. In FIG. 3A, metallization 330 is coupled to a P+ contact 305 for low resistance contact to the P-surface region 302. An N+ diffusion contact is not shown in FIG. 3A. The N+ diffusion contact can be referred to as the cathode of the photodiode, and the P+ contact 305 can be referred to as the anode of the photodiode.

At this point, there are numerous ILD layers (e.g., layers 321, 322, 323, 324 and 325) and a top passivation layer 326 over the active photodiode region, which layers affect the spectral response of the underlying active photodiode region. Even if there was an attempt to optimize the thicknesses of these ILD layers to achieve a desired spectral response (e.g., a spectral response similar to that of a human eye), because normal semiconductor fabrication thickness control is in the range of +/−10 to 20%, there is too much thickness variation to provide for a well controlled and predictable spectral response. Accordingly, in accordance with specific embodiments of the present invention, the ILD layers and the top passivation layer over the active photodiode region are removed. In other words, a window 340 is formed over the active photodiode region. Thereafter, as will be described below, an optical filter is formed within the window 340, to provide for the desired spectral response (e.g., a spectral response similar to that of a human eye).

A photoresist can be patterned to open the window 340 (also referred to as an opening or a trench) over the active photodiode region. More specifically, a portion of top passivation coating 326, ILD layers and the etch stop coating 315 is removed so that the opening 340 extends all the way down to the passivation coating 314 over at least a portion of the active photodiode region. This can include removing at least a portion of the oxide layer 317 using an oxide etch, and removing at least a portion the etch step coating 315 that is over the active photodiode region to expose at least a portion of the passivation coating 314 that is over the active photodiode region. In accordance with an embodiment, the area of the opening 340 is less than the area of the active photodiode region, as shown in FIG. 3A.

After the above described trench 340 is formed, an optical filter 350 can be formed above the passivation coating 314. In contrast to thickness control for semiconductor fabrication, thickness control for optical filters is typically in the range of +/−1%. In accordance with an embodiment, a wafer including a plurality of the photodiodes 300a having the window 340 over the active photodiode region is manufactured at a semiconductor fabrication plant (commonly called a fab). Thereafter, the wafer is transferred to an optoelectronic and/or optical device fabrication facility, where the optical filters 350 are added. The wafer with filters can then be returned to a semiconductor fab where the wafer can be diced into photodiode dies, and packaging can be added to produce photodiode integrated circuit (IC) chips. It is also possible that all of the above steps occur within the same facility, if such facility is appropriately equipped to perform both semiconductor and optical fabrication.

In accordance with an embodiment, the optical filter 350 is a dielectric reflective optical coating filter. Depending on the depth for the trench 340, and the thickness of the dielectric reflective optical coating filter 350, the dielectric reflective optical coating filter 350 can fill only a portion of the trench, or can fill the entire trench and even extend above the trench. In FIG. 3B the dielectric reflective optical coating filter 350 is shown as filling only a portion of the trench 340 of the photodiode 300b.

The dielectric reflective optical coating filter 350 can be constructed from thin layers of materials such as, but not limited to, zinc sulfide, magnesium fluoride, calcium fluoride, and various metal oxides (e.g., titanium dioxide), which are deposited onto the underlying optical substrate. By careful choice of the exact composition, thickness, and number of these layers, it is possible to tailor the reflectivity and transmissivity of the filter 350 to produce almost any desired spectral characteristics. For example, the reflectivity can be increased to greater than 99.99%, to produce a high-reflector (HR) coating. The level of reflectivity can also be tuned to any particular value, for instance to produce a mirror that reflects 90% and transmits 10% of the light that falls on it, over some range of wavelengths. Such mirrors have often been used as beam splitters, and as output couplers in lasers. Alternatively, the filter 350 can be designed such that the mirror reflects light only in a narrow band of wavelengths, producing a reflective optical filter.

High-reflection coatings work the opposite way to antireflection coatings. Generally, layers of high and low refractive index materials are alternated one above the other. Exemplary high refractive index materials include zinc sulfide (n=2.32) and titanium dioxide (n=2.4), and exemplary low refractive index materials include magnesium fluoride (n=1.38) and silicon dioxide (n=1.49). This periodic or alternating structure significantly enhances the reflectivity of the surface in the certain wavelength range called band-stop, which width is determined by the ratio of the two used indices only (for quarter-wave system), while the maximum reflectivity is increasing nearly up to 100% with a number of layers in the stack. The thicknesses of the layers are generally quarter-wave (then they yield to the broadest high reflection band in comparison to the non-quarter-wave systems composed from the same materials), designed such that reflected beams constructively interfere with one another to maximize reflection and minimize transmission. Using the above described structures, high reflective coatings can achieve very high (e.g., 99.9%) reflectivity over a broad wavelength range (tens of nanometers in the visible spectrum range), with a lower reflectivity over other wavelength ranges, to thereby achieve a desired spectral response. By manipulating the exact thickness and composition of the layers in the reflective stack, the reflection characteristics can be tuned to a desired spectral response, and may incorporate both high-reflective and anti-reflective wavelength regions. The coating can be designed as a long-pass or short-pass filter, a bandpass or notch filter, or a mirror with a specific reflectivity.

In accordance with specific embodiments of the present invention, dielectric reflective optical coating filter 350 is used to shape the spectral response of a photodiode to obtain a spectral response that is similar to that of a typical human eye response (shown in FIG. 2). Alternative spectral responses are possible, and within the scope of the present invention.

Referring now to the photodiode 300c of FIG. 3C, in accordance with an embodiment of the present invention, in order to reduce and preferably minimize light piping effects, a dark mirror coating 360 (also referred to simply as a dark mirror) can be added to cover the sidewalls 355 of the dielectric reflective optical coating filter 350. The dark mirror 360 can also cover the top surface 357 of the dielectric reflective optical coating filter 350, from which the sidewalls 355 extend downward from. The dark mirror coating 360 is patterned so that there is an opening in the dark mirror coating over the active photodiode region. A dark mirror is a low reflective, low transmissive filter. In an embodiment, the dark mirror coating 360 provides a low reflectivity surface that absorbs visible light.

Referring now to the photodiode 300d of FIG. 3D, another way to reduce and preferably minimize light piping effects, is to make the area of the N+ diffusion region 303 (and thus, the active photodiode region) substantially smaller than the opening formed by the sidewalls 355 of the dielectric reflective optical coating filter 350. The embodiments of FIGS. 3C and 3D can also be combined so that the area of the N+ diffusion region 303 (and thus, the active photodiode region) is substantially smaller than the opening formed by the sidewalls 355 of the dielectric reflective optical coating filter 350, and a dark mirror coating 360 is added to cover the sidewalls 355 and top surface 357 of the dielectric reflective optical coating filter 350.

In FIGS. 3B-3D, the dielectric reflective optical coating filter 350 was shown as filling only a portion of the trench 340. FIG. 3E shows an embodiment where the dielectric reflective optical coating filter 350 fills the entire opening 340 of the photodiode 300e, and even extends above the trench 340. To reduce and preferably minimize light piping effects, the dark mirror coating 360 covers sidewalls 355 and a top surface 357 of the dielectric reflective optical coating filter 350. Alternatively, or additionally, the area of the N+ diffusion region 303 (and thus, the active photodiode region) can be made substantially smaller than the opening formed by the sidewalls 355 of the dielectric reflective optical coating filter 350, as was explained above with reference to the photodiode 300d of FIG. 3D.

In the embodiments of FIGS. 3B-3E, the dielectric reflective optical coating filter 350 was shown as being formed after the trench 340 was formed. In accordance with an alternative embodiment, described with reference to FIG. 4, the dielectric reflective optical coating filter 350 of the photodiode 400 is formed before the trench is formed. In FIG. 4, the dielectric reflective optical coating filter 350 is formed on the passivation coating 314. Thereafter, the etch stop coating 315 is formed on the dielectric reflective optical coating filter 350. In accordance with an embodiment, the etch stop coating 315 includes at least one layer resistant to oxide etch 316, e.g., silicon nitride (Si₃N₄) or polysilicon, above an oxide (e.g., SiO₂) layer 317. After the passivation coating 314, the dielectric reflective optical coating filter 350, and the etch stop coating 315 are formed, a portion of the etch stop coating 315 and the passivation coating 314 is removed outside the active photodiode region down to the first semiconductor type surface region, e.g., the P− surface region 302, to make room for metalization. Thereafter, ILD, metal, contact, via and passivation processing can be performed to add interlayer dielectric (ILD) layers 321, 322, 323, 324 and 325, metalization 330, and a top passivation layer 326 (e.g., an oxide layer capped with a nitride layer).

At this point, there are numerous ILD layers (e.g., layers 321, 322, 323, 324 and 325) and a top passivation layer 326 over the active photodiode region, which layers affect the spectral response of the underlying active photodiode region. The ILD layers and the top passivation layer over the active photodiode region are removed. In other words, a window 340 is formed over the active photodiode region, with the window extending down to the dielectric reflective optical coating filter 350. In a similar manner as was discussed above with regards to FIG. 3A, a photoresist can be patterned to open the window 340 (also referred to as an opening or a trench).

In accordance with an embodiment, a wafer including a plurality of active photodiode regions (i.e., PN junctions between regions 302 and 303) is manufactured at a semiconductor a fab. Thereafter, the wafer is transferred to an optoelectronic and/or optical device fabrication facility, where the dielectric reflective optical coating filter 350 is formed over substantially the entire wafer. The wafer with dielectric reflective optical coating filter can then be returned to a semiconductor fab where patterning can be performed, and ILD, metal, contact, via and passivation processing can be performed to add interlayer dielectric (ILD) layers 321, 322, 323, 324 and 325, metalization 330, and a top passivation layer 326 (e.g., an oxide layer capped with a nitride layer) for each active photodiode region. The window 340 can then be opened for each photodiode region. The wafer can then be diced into photodiode dies, and packaging can be added to produce photodiode integrated circuit (IC) chips. It is also possible that all of the above steps occur within the same facility, if such facility is appropriately equipped to perform both semiconductor and optical fabrication.

In the embodiments described with reference to FIGS. 3B-3E and 4, the dielectric reflective optical coating filter 350 was described as being formed on top of a passivation coating 315. In accordance with alternative embodiments, the dielectric reflective optical coating filter 350 is formed directly on top of the diffusion layer 303, or a thin oxide layer on the diffusion layer 303, as will now be described with reference to FIGS. 5A-5E and 6. In such embodiments, the bottom layers of the dielectric reflective optical coating filter 350 can be designed to perform the function of the passivation coating 315. For example, the lowest layer of the dielectric reflective optical coating filter 350 can be an oxide (e.g., SiO₂) to provide stress relief, and the second from the lowest layer can be a nitride (e.g., Si₃N₄), to protect the active photodiode region from moisture.

FIG. 5A illustrates that the etch stop coating 315 can be formed directly on top of the diffusion layer 303 such that it extends beyond the boundary of the diffusion layer 303. A portion of the etch stop coating 315 is removed outside the active photodiode region down to the first semiconductor type surface region, e.g., the P− surface region 302, to make room for metalization. Thereafter, ILD, metal, contact, via and passivation processing can be performed to add interlayer dielectric (ILD) layers 321, 322, 323, 324 and 325, metalization 330, and a top passivation layer 326 (e.g., an oxide layer capped with a nitride layer). At this point, there are numerous ILD layers (e.g., layers 321, 322, 323, 324 and 325) and a top passivation layer 326 over the active photodiode region, which layers affect the spectral response of the underlying active photodiode region. A window 340 is then formed over the active photodiode region, with the window extending down to the diffusion region 303, or alternatively, a thin layer of the oxide 317 of the etch stop coating 315 can be kept. In a similar manner as was discussed above with regards to FIG. 3A, a photoresist can be patterned to open the window 340 (also referred to as an opening or a trench).

Referring now to FIG. 5B-5E, the dielectric reflective optical coating filter 350 can then be added. Depending on the depth for the trench 340 and the thickness of the dielectric reflective optical coating filter 350, the dielectric reflective optical coating filter 350 can fill only a portion of the trench (as in the photodiode 500b of FIG. 5B), or can fill the entire trench and even extend above the trench (as in the photodiode 500e of FIG. 5E). As shown in FIGS. 5C and 5E, the dark mirror coating 360 can be added to cover the sidewalls 355 and top surface 357 of the dielectric reflective optical coating filter 350. Alternatively, or additionally, as shown in FIG. 5D, the area of the N+ diffusion region 303 (and thus, the active photodiode region) can be made substantially smaller than the opening formed by the sidewalls 355 of the dielectric reflective optical coating filter 350, in a similar manner as was explained above with reference to FIG. 3D. The embodiments of FIGS. 5C and 5D can be combined so that the area of the N+ diffusion region 303 (and thus, the active photodiode region) is made substantially smaller than the opening formed by the sidewalls 355 of the dielectric reflective optical coating filter 350, and a dark mirror coating is added to cover the sidewalls 355 and the top surface 357 of the dielectric reflective optical coating filter 350.

In accordance with an alternative embodiment, described with reference to FIG. 6, the dielectric reflective optical coating filter 350 of the photodiode 600 is formed on the diffusion region 303 before the trench is formed. Thereafter, the etch stop coating 315 is formed on the dielectric reflective optical coating filter 350. A portion of the etch stop coating 315 and the dielectric reflective optical coating filter 350 is removed outside the active photodiode region down to the first semiconductor type surface region, e.g., the P− surface region 302, to make room for metalization. Thereafter, ILD, metal, contact, via and passivation processing can be performed to add interlayer dielectric (ILD) layers 321, 322, 323, 324 and 325, metalization 330, and a top passivation layer 326 (e.g., an oxide layer capped with a nitride layer).

At this point, there are numerous ILD layers (e.g., layers 321, 322, 323, 324 and 325) and a top passivation layer 326 over the active photodiode region, which layers affect the spectral response of the underlying active photodiode region. The ILD layers and the top passivation layer over the active photodiode region are removed. In other words, a window 340 is formed over the active photodiode region, with the window extending down to the dielectric reflective optical coating filter 350, in a similar manner as was discussed above with regards to FIG. 4. In a similar manner as was discussed above with regards to FIG. 3A, a photoresist can be patterned to open the window 340 (also referred to as an opening or a trench).

Referring back to FIG. 1, it can be appreciated that the spectral response of the photodiode (not covered by a dielectric reflective optical coating filter) is not flat. Thus, if the desire is to provide a photodiode with a spectral response similar to that of a typical human eye (shown in FIG. 2), then the spectral response of the reflective optical coating filter should be appropriately offset to compensate for the underlying photodiode response. In other words, if F is the response the filter made up of the dielectric reflective optical coating, T is the target response (i.e., a response similar to that of a typical human eye shown in FIG. 2), and P is the response of the photodiode (e.g., similar to the response shown in FIG. 1), then the response of the filter F should be designed such that F=T/P. This is illustrated in FIG. 7, which shows that the filter response (F) is shifted relative to the target response (T), so that when the filter is used with a photodiode having a photodiode response (P), the target response (T) is achieved. In accordance with an embodiment, the target response (so that the response resembles that of a human eye) has a low frequency 50% cut-off at about 500 nm (+/−10 nm), a peak at about 550 nm (+/−10 nm), and a high frequency 50% cut-off at about 600 nm (+/−10 nm).

There have been previous attempts to cover a silicon wafer with a dielectric reflective optical coating filter. However, such attempts have placed the dielectric reflective optical coating filter above a top passivation coating (e.g., similar coating 326), which has resulted in a spectral response that includes undesirable ripples due to interference effects at the top passivation layers. The embodiments of the invention described herein significantly reduce (or eliminate) the thickness of passivation coatings used in standard processes, therefore reducing such ripples in the spectral response. While described as being especially useful for producing an ambient light sensor (ALS), the photodiode structures described herein can be used with alternative dielectric reflective optical coating filter designs for other applications, such as, but not limited to, red (R), green (G) and blue (B) sensors.

In the embodiments described above, the target response was often described as being similar to that of a typical human eye viewing diffused light. However, that need not be the case. For example, other target responses can be for an optical sensor to only detect light of a specific color, such as red, green or blue. Such photodiodes can be used, e.g., in digital cameras, color scanners, color photocopiers, and the like. In these embodiments, the dielectric reflective optical coating filter 350 can be optimized for the specific color to be detected, and can be used alone or in combination with the various techniques for filtering out IR light that happens to make it through the dielectric reflective optical coating filter 350. For example, one or more photodiode(s) can be optimized to detect green light, one or more further photodiode(s) can be optimized to detect red light, and one or more further photodiode(s) can be optimized to detect blue light, with one or more of these photodiode(s) including a dielectric reflective optical coating filter.

In the above described embodiments, N regions are described as being implanted in a P region. For example, the N+ diffusion region 303 is implanted in P⁻ region 302. In alternative embodiments, the semiconductor conductivity materials are reversed. That is, a P region is implanted in an N region. For a specific example, a heavily doped P⁺ region is implanted in a lightly doped N⁻ region, to form the active photodiode region.

Certain embodiments of the present invention are also directed to methods of producing photocurrents that are primarily indicative of target wavelengths of light, e.g., wavelengths of visible light. In other words, embodiments of the present invention are also directed to methods for providing a photodiode having a target spectral response, such as, a response similar to that of the human eye. Additionally, embodiments of the present invention are also directed to methods of using the above described photodiodes.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention.

The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A photodiode, comprising:

a first semiconductor type surface region;

a second semiconductor type surface layer formed in a portion of said first semiconductor type surface region, wherein an active photodiode region is formed by a PN junction of said first semiconductor type surface region and said second semiconductor type surface layer;

a passivation coating on said second semiconductor surface layer;

an etch stop coating on a portion of said passivation coating;

an opening over at least a portion of said active photodiode region, said opening extending through said etch stop coating down to said passivation coating;

a dielectric reflective optical coating filter, comprising a plurality of dielectric layers, that fills at least a portion of said opening and thereby covers the at least a portion of said active photodiode region;

wherein said opening allows a portion of light incident on the photodiode to be received by said active photodiode region; and

wherein said dielectric reflective optical coating filter reflects a portion of light incident on the photodiode and thereby shapes a spectral response of the photodiode.

2. The photodiode of claim 1, wherein said dielectric reflective optical coating filter fills the entire said opening.

3. The photodiode of claim 1, wherein:

said dielectric reflective optical coating filter includes a top surface that is generally parallel to a top surface of said passivation coating and sidewalls that extend from said top surface of said dielectric reflective optical coating filter towards said passivation coating; and

further comprising a dark mirror covering said top surface and said sidewalls of said dielectric reflective optical coating filter.

4. The photodiode of claim 1, wherein:

said first semiconductor type is one of P type and N type; and

said second semiconductor type is the other one of P type and N type.

5. The photodiode of claim 1, wherein:

said passivation coating comprises an oxide layer on said second semiconductor type surface layer and a second dielectric layer different from said oxide layer on said oxide layer; and

said second dielectric layer, of said passivation coating, extends beyond said second semiconductor type surface layer.

6. The photodiode of claim 1, wherein said etch stop coating, on the portion of said passivation coating, comprises a layer resistant to oxide etch on an oxide layer.

7. The photodiode of claim 1, wherein the portion of said passivation coating, on which is said etch stop coating, comprises a peripheral portion of said passivation coating.

8. The photodiode of claim 1, wherein said etch stop coating comprises at least one of silicon nitride and polysilicon, and overlies and extends beyond a peripheral portion of said second semiconductor surface layer.

9. A photodiode, comprising:

a first semiconductor type surface region;

a second semiconductor type surface layer formed in a portion of said first semiconductor type surface region, wherein an active photodiode region is formed by a PN junction of said first semiconductor type surface region and said second semiconductor type surface layer;

an etch stop coating formed on a portion of said first semiconductor type surface region that surrounds said second semiconductor type surface layer;

an opening over at least a portion of said active photodiode region, said opening extending through said etch stop coating down to said second semiconductor type surface layer or down to a thin oxide layer on said second semiconductor type surface layer;

a dielectric reflective optical coating filter, comprising a plurality of dielectric layers, that covers said opening;

wherein said opening allows a portion of light incident on the photodiode to be received by said active photodiode region; and

wherein said dielectric reflective optical coating filter reflects a portion of light incident on the photodiode and thereby shapes a spectral response of the photodiode.

10. The photodiode of claim 9, wherein:

said dielectric reflective optical coating filter fills at least a portion of said opening;

said dielectric reflective optical coating filter includes a top surface that is generally parallel to a top surface of said passivation coating and sidewalls that extend from said top surface of said dielectric reflective optical coating filter towards said second semiconductor type surface layer; and

further comprising a dark mirror covering said top surface and said sidewalls of said dielectric reflective optical coating filter.

11. A photodiode, comprising:

a first semiconductor type surface region;

a second semiconductor type surface layer formed in a portion of said first semiconductor type surface region, wherein an active photodiode region is formed by a PN junction of said first semiconductor type surface region and said second semiconductor type surface layer;

a dielectric reflective optical coating filter, comprising a plurality of dielectric layers, above said second semiconductor type surface layer;

an etch stop coating on a portion of said dielectric reflective optical coating filter;

an opening over at least a portion of said active photodiode region, said opening extending through said etch stop coating down to said dielectric reflective optical coating filter;

wherein said opening allows a portion of light incident on the photodiode to be received by said active photodiode region; and

wherein said dielectric reflective optical coating filter reflects a portion of light incident on the photodiode and thereby shapes a spectral response of the photodiode.

12. The photodiode of claim 11, wherein said dielectric reflective optical coating filter is on said second semiconductor type surface layer.

13. The photodiode of claim 11, further comprising:

a passivation coating between said second semiconductor surface layer and said dielectric reflective optical coating filter.

14. The photodiode of claim 13, wherein:

said passivation coating comprises an oxide layer on said second semiconductor type surface layer and a second dielectric layer different from said oxide layer on said oxide layer; and

said second dielectric layer, of said passivation coating, extends beyond said second semiconductor type surface layer.

15. The photodiode of claim 11, wherein said etch stop coating, on the portion of said passivation coating, comprises a layer resistant to oxide etch on an oxide layer.

16. The photodiode of claim 11, wherein:

said first semiconductor type is one of P type and N type; and

said second semiconductor type is the other one of P type and N type.

17. A method of a fabricating a photodiode, comprising:

(a) implanting and thereby forming a second semiconductor type shallow surface layer into a portion of a first semiconductor type surface region, wherein an active photodiode region is formed by a PN junction of the first semiconductor type surface region and the second semiconductor type shall surface layer;

(b) forming a passivation coating on said shallow surface layer, wherein said passivation coating comprises a thin oxide layer on said shallow surface layer and a second dielectric layer different from said thin oxide layer on said thin oxide layer;

(c) forming an etch stop coating on said second dielectric layer, wherein said etch stop coating comprises at least one layer resistant to oxide etch;

(d) performing at least some of interlayer dielectric (ILD) processing, metal processing, contact processing, via processing and passivation processing, which results in multiple layers being formed above said etch stop coating;

(e) removing at least a portion of said multiple layers formed at step (d) and at least a portion of said etch stop coating to produce an opening that extends down to said passivation coating over at least a portion of said active photodiode region; and

(f) filling at least a portion of said opening with a dielectric reflective optical coating filter so that said dielectric reflective optical coating filter covers said at least a portion of said active photodiode region.

18. The method of claim 17, wherein step (f) comprising filling the entire said opening with said dielectric reflective optical coating filter.

19. The method of claim 17, wherein after step (f) said dielectric reflective optical coating filter includes a top surface that is generally parallel to a top surface of said passivation coating and sidewalls that extend from said top surface towards said passivation coating, and further comprising:

(g) covering said top surface and said sidewalls of said dielectric reflective optical coating filter with a dark mirror.

20. A method of a fabricating a photodiode, comprising:

(a) implanting and thereby forming a second semiconductor type shallow surface layer into a portion of a first semiconductor type surface region, wherein an active photodiode region is formed by a PN junction of the first semiconductor type surface region and the second semiconductor type shallow surface layer;

(b) forming an etch stop coating over said second semiconductor type shallow surface layer, wherein said etch stop coating comprises at least one layer (316) resistant to oxide etch;

(c) performing at least some of interlayer dielectric (ILD) processing, metal processing, contact processing, via processing and passivation processing, which results in multiple layers being formed above said etch stop coating;

(d) removing at least a portion of said multiple layers formed at step (c) and at least a portion of said etch stop coating to produce an opening, over at least a portion of said active photodiode region, that extends down to said second semiconductor type shallow surface layer or down to a thin oxide that covers said second semiconductor type shallow surface layer; and

(e) filling at least a portion of said opening with a dielectric reflective optical coating filter so that said dielectric reflective optical coating filter covers said at least a portion of said active photodiode region.

21. The method of claim 20, wherein step (e) comprising filling the entire said opening with said dielectric reflective optical coating filter.

22. The method of claim 20, wherein after step (e) said dielectric reflective optical coating filter includes a top surface that is generally parallel to a top surface of said passivation coating and sidewalls that extend from said top surface towards said passivation coating, and further comprising:

(f) covering said top surface and said sidewalls of said dielectric reflective optical coating filter with a dark mirror.

23. A method of a fabricating a photodiode, comprising:

(a) implanting and thereby forming a second semiconductor type shallow surface layer into a portion of a first semiconductor type surface region, wherein an active photodiode region is formed by a PN junction of the first semiconductor type surface region and the second semiconductor type shall surface layer;

(b) forming a dielectric reflective optical coating filter over at least a portion of said active photodiode region;

(c) forming an etch stop coating over said dielectric reflective optical coating filter, wherein said etch stop coating comprises at least one layer resistant to oxide etch;

(d) performing at least some of interlayer dielectric (ILD) processing, metal processing, contact processing, via processing and passivation processing, which results in multiple layers being formed above said etch stop coating; and

(e) removing at least a portion of said multiple layers formed at step (d) and at least a portion of said etch stop coating to produce an opening that extends down to said dielectric reflective optical coating filter over at least a portion of said active photodiode region.

24. The method of claim 23, further comprising:

between steps (a) and (b), forming a passivation coating on said shallow surface layer, wherein said passivation coating comprises a thin oxide layer on said shallow surface layer and a second dielectric layer different from said thin oxide layer on said thin oxide layer; and

wherein step (b) comprises forming said dielectric reflective optical coating filter on said passivation coating.