CN102637715A - Image sensor - Google Patents

Abstract

The invention relates to the technical field of semiconductors and discloses an image sensor. According to the image sensor, a reflection structure is arranged below a sensitization structure, and under the condition that a depletion layer is not thick enough, incident light is reflected on the bottom of the depletion layer, and the transmission optical distance of the incident light in the depletion layer is increased, thereby ensuring the response speed of a component and improving quantum efficiency. As the superficial area of the reflection structure is larger than the superficial area of the sensitization structure, the incident light can be better reflected, and the quantum efficiency is improved; and by virtue of the selection on proper dielectric materials, dielectric thickness, periods and other parameters, the incident light in a specific wavelength range can be reflected with relatively high efficiency and even are totally reflected.

Description

Imageing sensor

Technical field

The present invention relates to technical field of semiconductors, particularly a kind of imageing sensor that has catoptric arrangement.

Background technology

As everyone knows, imageing sensor is a kind of semiconductor device that can optical imagery be converted to the signal of telecommunication.Imageing sensor can be divided into charge coupled cell (Charge-Coupled Device substantially; Be called for short " CCD ") and complementary metal oxide semiconductors (CMOS) (Complementary Metal Oxide Semiconductor is called for short " CMOS ") imageing sensor.

According to its playback mode; The existing C mos image sensor roughly can be divided into passive type element sensor (Passive Pixel Sensor; Abbreviation " PPS "), active formula element sensor (Active Pixel Sensor; Be called for short " APS ") with three types of digital pixel transducers (Digital Pixel Sensor, abbreviation " DPS ").

In photoelectric conversion process, after semiconductor was by rayed, if the energy of photon equals energy gap, promptly hv equaled Eg (wherein, h is a planck constant, and v is a light frequency), and then semiconductor can absorb photon and produce electron-hole pair; If hv is greater than Eg, then except meeting produces electron-hole pair, unnecessary energy (hv-Eg) will loose with the form of heat and consume; If when hv less than Eg, then only existed by the energy state that chemical impurity or physical imperfection caused in the forbidden band, photon just can be absorbed.

Suppose that semiconductor is Ф by a photon energy hv greater than Eg and photon flux ₀The light source irradiation of (is unit with the number of photons that every cubic centimetre of per second was had); When this photon flux gets into semiconductor; The absorbed ratio of photon is to be directly proportional with the intensity of flux, and therefore in a distance of increment Δ x, absorbed photon number is α Ф (x) Δ x; Wherein α is a proportionality constant, is absorption coefficient.

Sensor devices commonly used in the cmos image sensor is a photodiode; With the PN junction photodiode is example; It is the PN junction or the metal-semiconductor contact that work in reverse biased basically; When light signal was beaten on photodiode, depletion region can be separated by the electron-hole pair that light produces, and therefore just had electric current to flow to external circuit.In the prior art, in cmos image sensor, photosensitive structure is generally the PN junction light sensitive diode, and its opto-electronic conversion is accomplished at depletion layer, in order under high frequency, to work, depletion region as much as possible attenuation to reduce the transit time; On the other hand, in order to increase quantum efficiency, depletion layer must be enough thick, so that most of incident light all is absorbed.Therefore, generating technique contradiction between response speed and quantum efficiency must get to some extent and accept or reject.Fig. 1 is the structural representation of imageing sensor in the prior art; Be the PN junction depletion layer of realizing opto-electronic conversion shown in 1 wherein; Shown in 2 is PN junction photodiode (Photo Diode; Be called for short " PD "), shown in 3 is the floating diffusion region (Floating Diffusion is called for short " FD ") that is used for the photogenerated charge storage in the 4T type pixel readout circuit.

Summary of the invention

The object of the present invention is to provide a kind of imageing sensor, thereby can when guaranteeing response device speed, improve quantum efficiency.

For solving the problems of the technologies described above; Execution mode of the present invention discloses a kind of imageing sensor; Comprising the photosensitive structure that incident light is changed into the signal of telecommunication; There is a catoptric arrangement at the back side of photosensitive structure, is used for from the positive incident of this photosensitive structure and penetrate this photosensitive structure of light reflected back of this photosensitive structure.

Embodiment of the present invention compared with prior art, the main distinction and effect thereof are:

Below photosensitive structure; Be provided with a catoptric arrangement; Under the thick inadequately situation of depletion layer (light absorbing zone of photosensitive region), realize reflection of incident light is increased the light path that incident light transmits in depletion layer in the depletion layer bottom; Thereby can when guaranteeing response device speed, improve quantum efficiency.

Further, the surface area of catoptric arrangement can be realized reflection of incident light more than or equal to the surface area of photosensitive structure better, improves quantum efficiency.

Further, through selecting parameters such as suitable dielectric material, dielectric thickness and cycle, can realize the incident light in the particular range of wavelengths is played the reflection even the total reflection effect of greater efficiency.

Description of drawings

Fig. 1 is the structural representation of a kind of imageing sensor in the prior art;

Fig. 2 is the structural representation of a kind of imageing sensor in the first embodiment of the invention;

Fig. 3 is the structural representation of a kind of catoptric arrangement of imageing sensor in the first embodiment of the invention;

Fig. 4 is a kind of structural representation of pixel readout circuit of 3T type structure;

Fig. 5 is a kind of structural representation of pixel readout circuit of 4T type structure;

Fig. 6 is the transmission spectrum sketch map of the catoptric arrangement of a kind of imageing sensor in the first embodiment of the invention;

Fig. 7 is the structural representation of a kind of catoptric arrangement of imageing sensor in the second embodiment of the invention;

Fig. 8 is the structural representation of a kind of catoptric arrangement of imageing sensor in the third embodiment of the invention.

Embodiment

In following narration, many ins and outs have been proposed in order to make the reader understand the application better.But, persons of ordinary skill in the art may appreciate that even without these ins and outs with based on the many variations and the modification of following each execution mode, also can realize each claim of the application technical scheme required for protection.

For making the object of the invention, technical scheme and advantage clearer, will combine accompanying drawing that execution mode of the present invention is done to describe in detail further below.

First embodiment of the invention relates to a kind of imageing sensor.Fig. 2 is the structural representation of this imageing sensor.

Specifically; As shown in Figure 2; Comprise the photosensitive structure 2 that incident light is changed into the signal of telecommunication in this imageing sensor, have a catoptric arrangement 4 at the back side of photosensitive structure 2, be used for from these photosensitive structure 2 positive incidents and penetrate this photosensitive structure 2 of light reflected back of this photosensitive structure 2.

As can be seen from the figure, photosensitive structure 2 places the surface of this catoptric arrangement 4.And the surface area of catoptric arrangement 4 is more than or equal to the surface area of photosensitive structure 2.

The surface area of catoptric arrangement 4 can be realized reflection of incident light more than or equal to the surface area of photosensitive structure 2 better, improves quantum efficiency.

In Fig. 2, shown in 1 is depletion layer, and shown in 3 is floating diffusion region FD.

In this execution mode, photosensitive structure 2 is photodiode (Photo Diode is called for short " PD "), for example can be PN junction light sensitive diode, PIN intrinsic semiconductor diode or metal-semiconductor contact photodiode etc.Preferably, photosensitive structure 2 is the PN junction light sensitive diode, at this moment, among Fig. 21 be depicted as PN junction depletion layer (that is: the light absorbing zone of photosensitive structure 2), in this zone, can realize absorption of incident light, produce photogenerated charge.

In some other execution mode of the present invention, photosensitive structure 2 also can be photogate.Photogate is claimed optical gate (photogate) again.

Catoptric arrangement 4 comprises the periodic stack structure that first dielectric material and second dielectric material alternately form, and wherein, first dielectric material is different with the dielectric constant of second dielectric material.

The cycle of periodic stack structure, preferred, the cycle is more than or equal to 4, and was more excellent more than or equal to 2, and the cycle equals 10.

First dielectric material has different refractive indexes with second dielectric material, is respectively n1, n2, and each first thickness of dielectric layers is d1, and each second thickness of dielectric layers is d2, and d1 and d2 can equate, also can not wait.

Fig. 3 is the structural representation of the catoptric arrangement of A and B two media periodic arrangement.Wherein, A representes first dielectric material, and thickness is d1; B representes second dielectric material, and thickness is d2.

Adopt the ABAB... alternative stacked as catoptric arrangement 4; Can realize the different wavelength range reflection of incident light through selecting suitable dielectric material and thickness of dielectric layers; Make 4 pairs of incident lights of catoptric arrangement have high reflection efficiency, even can realize total reflection the incident light in single wavelength or the particular range of wavelengths.

Below photosensitive structure 2; Be provided with a catoptric arrangement 4; Under the thick inadequately situation of depletion layer 1 (that is: the light absorbing zone of photosensitive structure 2), realize reflection of incident light is increased the light path that incident light transmits in depletion layer 1 in depletion layer 1 bottom; Thereby can when guaranteeing response device speed, improve quantum efficiency.

In addition, also comprise Semiconductor substrate and the pixel readout circuit that is formed at semiconductor substrate surface in this imageing sensor.

Semiconductor substrate can or have in the silicon, germanium, germanium silicon, strained silicon of insulating buried layer any one for silicon, germanium, germanium silicon, strained silicon.Photosensitive structure 2 all is formed at this semiconductor substrate surface with catoptric arrangement 4, and catoptric arrangement 4 is positioned at the below of photosensitive structure 2.

Pixel readout circuit can be 3T, 4T or 5T structure etc.

According to a transistorized number that pixel readout circuit comprised, the existing C mos image sensor is divided into 3T type structure and 4T type structure, and 5T type structure can also be arranged.

Fig. 4 is a kind of equivalent circuit structure figure of pixel readout circuit of cmos image sensor of existing 3T type structure; Comprise: a photodiode 10; Be used for when exposure, carrying out opto-electronic conversion; Convert the light signal that receives to the signal of telecommunication, said photodiode 10 comprises p type island region and N type district, said p type island region ground connection.

A reset transistor M1 is used for before exposure, said photodiode 10 being resetted, and resets and is controlled by reset signal Reset signal.In Fig. 4, said reset transistor M1 selects a N type Metal-oxide-semicondutor (N Metal-Oxide-Semiconductor is called for short " NMOS ") pipe for use, and the N type district of the source electrode of said reset transistor M1 and said photodiode 10 links to each other; The drain electrode of said reset transistor M1 meets power supply Vdd, and said power supply Vdd is a positive supply.When said reset signal Reset is high level; Said reset transistor M1 conducting also is connected to power supply Vdd with the N type district of said photodiode 10; Under the effect of said power supply Vdd; Make the said photodiode 10 anti-whole charges accumulated that partially also can remove said photodiode 10, realize resetting.Said reset transistor M1 also can be formed by the series connection of a plurality of NMOS pipe, or is formed by the parallel connection of a plurality of NMOS pipe, also can replace said NMOS pipe with the PMOS pipe.

An amplifier transistor M2 is the one source pole follower also, is used for the signal of telecommunication that said photodiode 10 produces is amplified.In Fig. 4; Said amplifier transistor M2 selects NMOS pipe for use; The grid of said amplifier transistor M2 meets the N type district of said photodiode 10, and the drain electrode of said amplifier transistor M2 meets said power supply Vdd, and the source electrode of said amplifier transistor M2 is the output of amplifying signal.Said amplifier transistor M2 also can be formed or formed by the parallel connection of a plurality of NMOS pipe by the series connection of a plurality of NMOS pipe.

A row selecting transistor M3 is used for the amplifying signal output with the source electrode output of said amplifier transistor M2.In Fig. 4; Said row selecting transistor M3 selects NMOS pipe for use; The grid of said row selecting transistor M3 meets row selection signal Rs, and the source electrode of said row selecting transistor M3 connects the source electrode of said amplifier transistor M2, and the drain electrode of said row selecting transistor M3 is an output.

Fig. 5 is a kind of equivalent circuit structure figure of pixel readout circuit of cmos image sensor of existing 4T type structure.Than 3T type structure, the pixel readout circuit structure chart of the cmos image sensor of existing 4T type structure has increased a transfering transistor M4, and said transfering transistor M4 is used for the signal of telecommunication that said photodiode 10 produces is input to said sense node N1.In Fig. 5; Said transfering transistor M4 selects NMOS pipe for use; The grid of said transfering transistor M4 switches through shifting signal TX; The source electrode of said transfering transistor M4 meets the N type district of said photodiode 10, and the source electrode that the drain electrode of said transfering transistor M4 meets said reset transistor M1 is said sense node N1.

According to the optical delivery matrix method, for the TE ripple, the eigenmatrix of single-layer medium is:

$M_i=\left[\begin{array}{cc}\cos \left(k_0\mathrm{nd}\cos \mathrm{\θ}\right)& -\frac{i}{\mathrm{\η}}\sin \left(k_0\mathrm{nd}\cos \mathrm{\θ}\right)\\ -\mathrm{i\η}\sin \left(k_0\mathrm{nd}\cos \mathrm{\θ}\right)& \cos \left(k_0\mathrm{nd}\cos \mathrm{\θ}\right)\end{array}\right]$

Wherein, k ₀Be the wave number in the vacuum, d is the thickness of medium,

ε is a dielectric constant, and μ is a magnetic permeability, and n is the refractive index of medium, and θ is the angle that incident direction and dielectric surface form.

The eigenmatrix of multilayer dielectricity is:

$M=\underset{i=1}{\overset{N}{\mathrm{\Π}}}{M}_i=\left[\begin{array}{cc}{T}_{11}& T_{12}\\ T_{21}& T_{22}\end{array}\right],$ Transmissivity $T={\left|t\right|}^2={\left|\frac{{2\mathrm{\η}}_0}{T_{11}{\mathrm{\η}}_0+T_{12}{\mathrm{\η}}_0{\mathrm{\η}}_{N+1}+T_{21}+T_{22}{\mathrm{\η}}_{N+1}}\right|}^2,$ η ₀, η _N+1Be laminated construction effective optical admittance of media of both sides up and down.Can obtain thus, the transmission spectrum of isoparametric catoptric arrangement 4 of selected media material, dielectric thickness and cycle, thus the incident light of particular range of wavelengths played the reflection even the total reflection effect of greater efficiency.

As a preferred embodiment, the first dielectric material A is Ag, and the second dielectric material B is MgF ₂, n1=0.18, d1=10nm, n2=1.378, d2=110nm, (that is: laminated construction comprises 4 layers of Ag layer and 4 layers of MgF alternately in cycle T=4 ₂Layer), at this moment, blue light, ruddiness transmitance lower (being lower than 20%) to the incident light of blue light and red range, can realize the reflectivity more than 80%.Because red light wavelength is longer, the absorption coefficient of light is less relatively, and the light path that the completion opto-electronic conversion needs is longer; Therefore, when depletion layer 1 thinner thickness of PN junction light sensitive diode, for the long ruddiness of wavelength; The introducing of catoptric arrangement 4; Can make incident light about the light path of depletion region 1 doubles, the absorption of incident light efficient that improves greatly has higher quantum efficiency.

As another preferred embodiment, the first dielectric material A is TiO ₂, n1=2.33, the second dielectric material B is SiO ₂, n2=1.45, d1=50nm, d2=120nm, T=8, at this moment, the green glow transmitance is almost 0.Its transmission spectrum is as shown in Figure 6, and at this moment, catoptric arrangement 4 can be realized the total reflection to green glow, has improved the quantum efficiency of imageing sensor greatly.

Can know based on prior art, in semiconductor, introduce the electronic state generation localization that unordered meeting makes band edge, cause effective band gap broadening, same principle also is applicable to optics.In the periodicity sandwich construction, introduce unorderedly, the light of any frequency range is because relevant back reflection can be by local, no matter and its incident angle with and whether be in the band gap.When introducing is unordered in the periodicity sandwich construction,, possibly make discrete narrow forbidden band be extended to continuous forbidden band owing to Bragg reflection effect and the unordered light local that causes of introducing.Through the reasonably geometric parameter and the degree of disorder of adjustment structure, high reflection can take place in very wide wave-length coverage, thereby realize the high reflection of the wide wavestrip of optics.In addition, the two media material refractive index of forming this catoptric arrangement 4 differs big more, and the energy gap that is produced is big more, and according to different-waveband reflection of incident light demand, adjustment dielectric material selection and respective thickness, cycle parameter get final product.

Second embodiment of the invention relates to a kind of imageing sensor.Fig. 7 is the structural representation of the catoptric arrangement of this imageing sensor.

Second execution mode improves on the basis of first execution mode, and main improvements are:

In catoptric arrangement 4, comprise the periodic stack structure that the first dielectric material A and the second dielectric material B alternately form more than 2 or 2; Wherein, In different periodic stack structures, the thickness of the first dielectric material A does not wait, and the thickness of the second dielectric material B does not wait yet.

Fig. 7 is the structural representation that A and B two media difference periodic arrangement form the catoptric arrangement of two periodic stack structures.Wherein, A representes first dielectric material, and B representes second dielectric material; In first periodic stack structure, the thickness of A is d1, and the thickness of B is d2; In second period property laminated construction, the thickness of A is d3, and the thickness of B is d4.

Certainly, in some other execution mode of the present invention, can be that in different periodic stack structures, the thickness of first dielectric material equates that all the thickness of second dielectric material also all equates, and is so just the same with catoptric arrangement shown in Figure 34.Can be, in different periodic stack structures, the thickness of first dielectric material wait yet, and the thickness of second dielectric material is all equal, or the like.

Through selecting parameters such as suitable dielectric material, dielectric thickness and cycle, can realize that the incident light to particular range of wavelengths plays the reflection even the total reflection effect of greater efficiency.

Third embodiment of the invention relates to a kind of imageing sensor.Fig. 8 is the structural representation of the catoptric arrangement of this imageing sensor.

The 3rd execution mode improves on the basis of first execution mode, and main improvements are:

In catoptric arrangement 4, also comprise the periodic stack structure that the 3rd dielectric material C and the 4th dielectric material D alternately form, wherein, the 3rd dielectric material C is different with the dielectric constant of the 4th dielectric material D.

Fig. 8 is the structural representation of the catoptric arrangement of A, B and C, four kinds of medium period property arrangements of D.

As shown in Figure 8, A representes first dielectric material, and thickness is d1, and B representes second dielectric material, and thickness is d2, and C representes the 3rd dielectric material, and thickness is d3, and D representes the 4th dielectric material, and thickness is d4.

In addition, be appreciated that catoptric arrangement 4 can also comprise the 5th dielectric material and the 6th dielectric material in some other execution mode of the present invention, the 7th dielectric material and the 8th dielectric material ... the periodic stack structure that alternately forms.

Though through reference some preferred implementation of the present invention; The present invention is illustrated and describes; But those of ordinary skill in the art should be understood that and can do various changes to it in form with on the details, and without departing from the spirit and scope of the present invention.

Claims (10)

1. imageing sensor; Comprising the photosensitive structure that incident light is changed into the signal of telecommunication; It is characterized in that, have a catoptric arrangement at the back side of said photosensitive structure, be used for from the positive incident of this photosensitive structure and penetrate this photosensitive structure of light reflected back of this photosensitive structure.

2. imageing sensor according to claim 1 is characterized in that the surface area of said catoptric arrangement is more than or equal to the surface area of said photosensitive structure.

3. imageing sensor according to claim 2 is characterized in that, said catoptric arrangement comprises the periodic stack structure that first dielectric material and second dielectric material alternately form, and wherein, first dielectric material is different with the dielectric constant of second dielectric material.

4. imageing sensor according to claim 3 is characterized in that the cycle of periodic stack structure is more than or equal to 4 in the said catoptric arrangement.

5. imageing sensor according to claim 4 is characterized in that, in said catoptric arrangement, the thickness of first dielectric material and second dielectric material equates.

6. imageing sensor according to claim 4 is characterized in that, in said catoptric arrangement, the thickness of first dielectric material and second dielectric material does not wait.

7. imageing sensor according to claim 4; It is characterized in that; In said catoptric arrangement, comprise at least 2 periodic stack structures that alternately form by first dielectric material and second dielectric material; Wherein, in first dielectric material and second dielectric material, have at least the thickness of a dielectric material in different cycles property laminated construction not wait.

8. according to each described imageing sensor in the claim 1 to 7; It is characterized in that, in said catoptric arrangement, also comprise the periodic stack structure that the 3rd dielectric material and the 4th dielectric material alternately form; Wherein, the 3rd dielectric material is different with the dielectric constant of the 4th dielectric material.

9. imageing sensor according to claim 8 is characterized in that, said first dielectric material is Ag, and thickness is 10nm, and second dielectric material is MgF ₂, thickness is 110nm.

10. imageing sensor according to claim 8 is characterized in that, said first dielectric material is TiO ₂, thickness is 50nm, second dielectric material is SiO ₂, thickness is 120nm.

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