[introduction]CMOS image sensor (CMOS Image Sensor, CIS) is one kind can mix the color of the light that captures through camera lens brightness changeover is electronic signal, transmit its the sensor to processor. Accordingly, what image sensor acts as is the mobile equipment such as smartphone or flat computer ” eye ” part. In recent years, as virtual reality (VR) , enhance reality (what drive AR) , automatically is arisen, CIS technology makes industry a crucial technology of 4. People predicts, CIS technology what can serve as equipment not only ” eye ” , still will have on the function further development.

CMOS image sensor (CMOS Image Sensor, CIS) is one kind can mix the color of the light that captures through camera lens brightness changeover is electronic signal, transmit its the sensor to processor. Accordingly, what image sensor acts as is the mobile equipment such as smartphone or flat computer ” eye ” part. In recent years, as virtual reality (VR) , enhance reality (what drive AR) , automatically is arisen, CIS technology makes industry a crucial technology of 4. People predicts, CIS technology what can serve as equipment not only ” eye ” , still will have on the function further development.

SK Hailishi established CIS to develop a group before 15 years. Besides shine with DRAM and NAND outside putting the business of core semiconductor memory that is a delegate, hailishi returns SK to devote oneself to CIS of semiconductor of development and manufacturing blame memory all the time, in order to enhance oneself competition ability. Hailishi had developed SK numerous equipment and engineering technology, the technical gap with the person of the same trade is narrow with each passing day, still developed dimension resembling element to be micron of 0.64 μ M(only at present) , the CIS product that has resolution of freeboard of 50 million above resembling element. The article will be based on the sea of the 10th SK that held in November 2022 conference of force person learning (content of SK Hynix Academic Conference) is crucial to CIS one of technologies the back takes form (Backside Illumination, BSI) technology undertakes introductory.

Form is taken before (FSI) technology and its limitation

Form is taken before inchoate CIS product is used like element (FSI) structure, this kind of structure is based on optical structure park the circuit of CMOS1) craft to go up. This technology applies to the most CIS solution that is 1.12 μ M and above like element dimension, be used extensively at mobile equipment, closed-circuit television (sheet of recorder of CCTV) , drive a vehicle, number turns over camera, car to wait for a product with sensor.

Semiconductor of oxide of 1) complementary metal (Complementary Metal Oxide Silicon, CMOS) : By didymous N raceway groove and MOSFET(Metal-Oxide-Semiconductor Field-Effect Transistor of P raceway groove, field effect is in charge of semiconductor of low-pressure metal oxide) complementary and logistic circuit of composition. The power comsumption of CMOS parts of an apparatus is extremely low, be applied in DRAM product and CPU, because although this kind of processor that parts of an apparatus carries is relatively complex, but can undertake large scale integration however.

Graph 1.  Form is taken before (FSI) structure and unit resemble element sketch map

Although a high-powered image sensor is in below weak smooth condition, also should present the picture that gives bright clarity quite, and should achieve this one result, need improves the quanta efficiency that resembles element (QE)2) . Accordingly, the metallic wiring design of circuit of lower level resembling element should be a foundation with FSI structure, with averting smooth interference as far as possible.

2) quanta efficiency (QE) : With Yu Heng the quantity becomes the target that changes incident photon the effectiveness that is an electron like equipment. If the quanta efficiency of a sensor is 100% and expose fall in 100 photon, can change for 100 electrons signal.

Graph 2.  Quanta efficiency (form is taken before QE) equation is mixed (FSI) structure plan

However, normally the circumstance falls, cross aperture when successive light or all round the object when, can produce diffractive phenomenon 3) . With respect to aperture character, as aperture aperture dimension decrease, more smooth meetings diffuse as the addition of diffractive quantity.

3) diffractive phenomenon: The sound wave and light-wave phenomenon that travels point-blank in the deviate when crossing fraise or aperture. From the point of smooth angle, when be equal to when the dimension of fraise or aperture or be less than the wavelengh that passes light-wave, can produce diffractive phenomenon.

Same, external light is achieved individual when resembling element, diffractive phenomenon also cannot avoid. With respect to FSI structure character, because get the influence of layer of wiring of the metal in lower level circuit, this kind of structure is affected diffractively more easily. Although FSI resembles element dimension decreasing, the area that is covered by the metal also keeps changeless. Accordingly, the district that carries solely becomes smaller, diffractive phenomenon increases, the color in bringing about image mixes together.

Graph 3.  Guang Yan is shot and resemble the relation of element size

However, control also is not like the diffraction of element impossible. To improve the diffraction of individual area, can shorten according to diffractive computation formula small lens arrives silicon (the distance of Si) . For this, people put forward a kind of back to take form (BSI) craft, through retroflexioning brilliant circle uses its the reverse side, remove metallic interference with this. SK Hailishi begins to use BSI technology under the product of 1.12 μ M from dimension resembling element.

Be based on the occurrence of the technology resembling element of BSI

2011, mobile phone of malic IPhone 4 comes out, its were deployed first use the CIS product of BSI technology at that time. Malic company claims at that time the amount receiving light with BSI technology and FSI technology larger than can capturing bearing, because this is OK emersion more the image of high quality.

Following plan institute show malic company and the BSI technological process that current and whole industry uses. With respect to BSI technology character, make all circuit part in a side of brilliant circle above all, retroflexion brilliant circle next convert, so that found can the optical structure that overleaf collects the light. Can remove the interference that circuitry of the metal in FSI causes so, the space that below the condition of element of same big figurine the light passes is larger, can improve quanta efficiency thereby.

Graph 4.  The back takes form (graph of BSI) technological process

Graph 5.  Different structure issues small lens and photoelectricity diode (the distance between PD) is compared

Technology of BSI of have the aid of, make 1.12 μ M and the application of the following dimension resembling element become a possibility, was the open up of 16 million high resolution product that resembles element and above to give the market. Unlike the FSI structure that can be disturbed by wiring, the optical technology that is based on BSI is having taller freedom to spend. Profit from this, back side deep groove is kept apart (case of BDTI) , W bar (W Grid) and air bar case (all sorts of optics that wait inside resemble Air Grid) element structure is come out by development, in order to improve the quanta efficiency of the product.

• Back side deep groove is kept apart (BDTI) craft

Although use the BSI structure that overcomes smooth diffractive problem to be able to improve quanta efficiency, but still need to use resemble element additionally breaking up a structure, the dimension resembling element that narrows in order to comply with a smartphone ceaselessly photographs F resembling a head to be worth 4) with what reduce ceaselessly. In this respect, back side deep groove is kept apart (BDTI) structure is to provide representative example most, this kind of structure can be outside chip of radial edge CIS skew promotes to entered area complete inside reflection (TIR) effect 5) , add signal thereby. Current, this technology is applied extensively at great majority to be based on the CIS product of BSI technology.

4) F value: Decide the value of aperture brightness. The F cost of camera is lower, aperture leaves more greatly, the capacity that receive light is more, make camera can take the picture of bright clarity in darker place, reduce point of image a confusion of voices at the same time.

5) is complete inside reflex (TIR) : It is to point to light by medium (include water or glass) all round the phenomenon that the surface is reflexed to answer former medium interior entirely. When an angle of incidence is more than critical role, can produce total reflection phenomenon.

Graph 6.  Traditional back takes form (BSI) structure and as add the back side deep groove that breaks up a structure like element is kept apart (BDTI) craft

• Chromatic filter keeps apart a structure

Structure of chromatic filter segregation is another kind of technology that keeps abreast of with BDTI structure, it is to pass in filter color implement between inlet manage protective screen raises those who be based on BSI to resemble element function. Because be after use BSI structure, small lens and photoelectricity diode the distance between 6) can no more shorten, what because this kind of structure prevented,cause by systole resembling element is diffractive. The representative structure that chromatic filter keeps apart includes W bar case and SK of great capacity case of bar of air of force person proprietary (Air Grid) structure. Cut off with simple light what case of structural W bar differs is, use complete inside case of catoptric air bar can improve quanta efficiency, consequently hopeful makes new generation technology.

6) photoelectricity diode (PD) : The smooth signal changeover that receives CIS sensor is telegraphic date.

Graph 7.  Texture of W bar case and texture of air bar case

SK sea Li Shiji did not come at the technology resembling element of BSI foreground is bright

After be based on the CIS product of BSI to appeared on the market first 2011, CIS industry by reshuffle, bring about a lot of CIS sensor manufacturers to exit shift to carry the market. And SK Hailishi mastered BSI skill quickly by right of oneself actual strength, apply at be 1.12 μ M or the following product like element dimension, acquired the core technology such as case of bar of BDTI, air again.

BSI technology of Hailishi is developing SK continuously in. Recently, hailishi develops SK successfully to mix bond (Hybrid Bonding) technology, will " copper, cupreous bond (Cu-to-Cu Bonding) " apply at be based on TSV (Through Silicon Via, silicon via technology) stack type sensor, expand to rise to be mixed in the competition ability of chip measure respect multilayer technology of brilliant round bond laid a foundation. Future, these technical achievement are used hopeful at development to apply to equipment of artificial intelligence, medical treatment, AR(to enhance reality) with VR(virtual reality) all sorts of sensor that wait for a domain, enlarge the market further thereby.

(Author: SK Hailishi, CIS craft is compositive Technical Leader Li Gengyin)

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