Backside metal grid and metal pad simplification

An image sensor includes a semiconductor material including a plurality of photodiodes disposed in the semiconductor material. The image sensor also includes a first insulating material disposed proximate to a frontside of the semiconductor material, and an interconnect disposed in the first insulating material proximate to the frontside of the semiconductor material. A metal pad extends from a backside of the semiconductor material through the first insulating material and contacts the interconnect. A metal grid is disposed proximate to the backside of the semiconductor material, and the semiconductor material is disposed between the metal grid and the first insulating material disposed proximate to the frontside.

TECHNICAL FIELD

This disclosure relates generally to semiconductor fabrication, and in particular but not exclusively, relates to metal grid fabrication.

BACKGROUND INFORMATION

Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.

To differentiate between colors image sensors may use color filters. Color filters filter incident light on the image sensor by wavelength range, so that each photodiode in the image sensor only receives image light in a particular wavelength range. The raw data captured by the image sensor is converted into a full color image by a demosaicing algorithm which is tailored for the various color filters.

While there are a variety of ways to make color image sensors, reducing the number of steps in semiconductor processing applications is always important. Since every fabrication step adds cost and time on the assembly line, new techniques to enhance image sensor throughput are needed.

DETAILED DESCRIPTION

Semiconductor material101includes a plurality of photodiodes disposed in semiconductor material101(see e.g.,FIG. 3), and first insulating material103is disposed proximate to frontside151of semiconductor material101. In the depicted example, the photodiodes may be disposed proximate to the center of semiconductor material101, while logic circuits may be disposed on the edges of semiconductor material101(e.g., Si wafer). Interconnect105is disposed in first insulating material103proximate to frontside151of semiconductor material101. Metal pad115extends from backside153of semiconductor material101through first insulating material103and contacts interconnect105. As shown, one or more trenches extend through first insulating material103to connect metal pad115to interconnect105. Also a majority of metal pad115may be disposed proximate to a planar edge of semiconductor material101. In one example, metal pad115includes aluminum, and interconnect105includes copper, and in another or the same example, TiN liner167may be deposited at the metal interface to cover the whole trench. One of ordinary skill in the art will appreciate that frontside151is the side of image sensor100with circuitry (e.g., interconnect105), and frontside151is opposite the backside153. Metal grid117is disposed proximate to backside153of semiconductor material101, and semiconductor material101is disposed between metal grid117and first insulating material103.

In the illustrated example, second insulating material109and high-k oxide107are disposed between semiconductor material101and metal grid117on backside153of image sensor100. As depicted, high-k oxide107may be disposed between second insulating material109and semiconductor material101, and high-k oxide107and second insulating material109are different materials (e.g., hafnium oxide and silicon oxide, respectively). In the illustrated example high-k oxide107is disposed in contact with backside153of semiconductor material101. In one example, first insulating material103and second insulating material109have the same chemical composition (e.g., silicon oxide). Also shown are protective layers119/121disposed on either side of metal grid117, and metal grid117is disposed between protective layer119and second insulating material109. Disposed on protective layer119is antireflection coating123which may be a dielectric material to prevent light from reflecting off the surface of metal grid117. In one example, the logic circuitry may be disposed underneath, and optically aligned with, the large portion of metal grid117on the edge of semiconductor material101.

In the depicted example, a first metal segment in metal grid117extends through both high-k oxide107and second insulating material109. As shown, metal segments other than the first metal segment in metal grid117do not extend to semiconductor material101. In the depicted example, the gaps between metal grid117may be filled with a polymer or the like to create a color filter array such as a bayer pattern, EXR pattern, or the like. As shown, at least part of the image light incident on backside153of image sensor100that is oblique to surface normal of semiconductor material101, may be reflected by metal grid117into the plurality of photodiodes in semiconductor material101.

FIGS. 2A-2Dillustrate a method of image sensor fabrication. The order in which some or all process figures appear in the method should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the method may be executed in a variety of orders not illustrated, or even in parallel. Furthermore, the method may omit certain figures in order to avoid obscuring certain aspects. Alternatively, the method may include additional figures that may not be necessary in some embodiments/examples of the disclosure.

FIG. 2Ashows providing semiconductor material201including a plurality of photodiodes disposed in semiconductor material201. First insulating material203is disposed on the frontside of semiconductor material201, and second insulating material209is disposed on the backside of semiconductor material201. First insulating material203includes interconnect205disposed proximate to the frontside of semiconductor material201. As shown high-k oxide207and silicon nitride layer211may also be disposed proximate the backside of the image sensor. High-k oxide207and silicon nitride layer211and second insulating may be deposited via chemical vapor deposition, or the like. Any of these layers may be chemically mechanically polished post deposition to ensure a smooth surface and conformal growth of other material layers in subsequent processing steps.

FIG. 2Bdepicts etching a first trench in first insulating material203to contact the interconnect205and etching a second trench in second insulating material209to contact semiconductor material201. As shown, etching the second trench includes etching through high-k oxide207, disposed between second insulating material209and semiconductor material201, and etching through silicon nitride layer211, where second insulating material209is disposed between silicon nitride layer211and high-k oxide207. In some examples, third insulating material223(e.g., a buffer oxide) may be disposed over silicon nitride layer211such that silicon nitride layer211is disposed between second insulating material209and third insulating material223. The first trench may be etched through third insulating material223as well. One of ordinary skill in the art will appreciate that the patterning of the trenches may be achieved with either a positive or negative photoresist, and etching may either be wet or dry depending on the specific trench geometry desired.

FIG. 2Cillustrates depositing a first metal in the first trench (to form metal pad215) and the second trench. As depicted, metal pad215may be disposed proximate to a lateral edge of semiconductor material201and may be deposited via thermal evaporation. Moreover after deposition of metal pad215, the surface of the device may be chemically mechanically polished. As shown, metal pad215may be in the periphery of the semiconductor device so that wire bonds or the like can be connected to the semiconductor device. As shown metal pad215may have a wider portion disposed proximate to the backside of semiconductor material201, and may have one or more narrower connection regions which extend from the larger portion through first insulating material203to contact interconnect205. In the depicted example there are two connecting portions but in other examples there may be any number depending on the specific device geometry desired.

FIG. 2Dshows depositing a second metal proximate to the backside of the device so that semiconductor material201is disposed between the second metal and first insulating material203.FIG. 2Dalso illustrates removing a portion of the second metal to form metal grid217proximate to the backside of the semiconductor material201. This may be achieved by etching the metal away using any of the processes detailed above. As shown, part of the first metal in the second trench extends to metal grid217with protective layer221disposed between. In some examples, metal grid217may be a divider for a color filter array and may be an optical reflector to prevent cross talk between neighboring pixels. In one example, the first metal and the second metal include the same chemical composition (e.g., aluminum or an alloy), and first insulating material203and second insulating material209include the same chemical composition (e.g., silicon oxide or the like).

FIG. 2Dalso shows depositing a protective layer219disposed on metal grid217, thus metal grid217is disposed between protective layer219and protective layer221. In one example, protective layers219/221may include titanium and/or nitrogen. Also shown is antireflection coating223deposited on protective layer219. Antireflection coating123may be deposited via CVD or the like.

FIG. 3is a block diagram illustrating one example of an imaging system300which may include the image sensor ofFIG. 1. Imaging system300includes pixel array305, control circuitry321, readout circuitry311, and function logic315. In one example, pixel array305is a two-dimensional (2D) array of photodiodes, or image sensor pixels (e.g., pixels P1, P2. . . , Pn). As illustrated, photodiodes are arranged into rows (e.g., rows R1to Ry) and columns (e.g., column C1to Cx) to acquire image data of a person, place, object, etc., which can then be used to render a 2D image of the person, place, object, etc. However, photodiodes do not have to be arranged into rows and columns and may take other configurations.

In one example, after each image sensor photodiode/pixel in pixel array305has acquired its image data or image charge, the image data is readout by readout circuitry311and then transferred to function logic315. In various examples, readout circuitry311may include amplification circuitry, analog-to-digital (ADC) conversion circuitry, or otherwise. Function logic315may simply store the image data or even manipulate the image data by applying post image effects (e.g., crop, rotate, remove red eye, adjust brightness, adjust contrast, or otherwise). In one example, readout circuitry311may readout a row of image data at a time along readout column lines (illustrated) or may readout the image data using a variety of other techniques (not illustrated), such as a serial readout or a full parallel readout of all pixels simultaneously. In one example, the metal pad and interconnects depicted inFIG. 1andFIGS. 2C-2Dare included in readout circuitry311.

In one example, control circuitry321is coupled to pixel array305to control operation of the plurality of photodiodes in pixel array305. For example, control circuitry321may generate a shutter signal for controlling image acquisition. In the depicted example, the shutter signal is a global shutter signal for simultaneously enabling all pixels within pixel array305to simultaneously capture their respective image data during a single acquisition window. In one example, the metal pad and interconnects depicted inFIG. 1andFIGS. 2C-2Dare included in control circuitry321. In another example, image acquisition is synchronized with lighting effects such as a flash.

In one example, imaging system300may be included in a digital camera, cell phone, laptop computer, automobile or the like. Additionally, imaging system300may be coupled to other pieces of hardware such as a processor (general purpose or otherwise), memory elements, output (USB port, wireless transmitter, HDMI port, etc.), lighting/flash, electrical input (keyboard, touch display, track pad, mouse, microphone, etc.), and/or display. Other pieces of hardware may deliver instructions to imaging system300, extract image data from imaging system300, or manipulate image data supplied by imaging system300.