Specific embodiment
The manufacture and use of embodiments herein are discussed further below.However, it should be understood that this application providesMany feasible inventive concepts that can implement under various specific backgrounds.The specific embodiment discussed is only to illustrate to manufactureConcrete mode with the application is used, does not limit the scope of the application.
Fig. 1 (a) show the knot of transmission transistor in the cmos image sensor according to shown in the application one embodimentStructure schematic diagram.It can be P type substrate according to one embodiment of the application, 102,104 can be n-type doping region, with substrate102 form photodiode, and photodiode receives the light injected from transmission transistor bottom, and generates photo-generated carrier.The n-type doping region 104 of photodiode can be used as the source electrode of transmission transistor.Transmission transistor further includes that a N-type is mixedDrain electrode of the miscellaneous floating diffusion region 108 as the transmission transistor.P type substrate can be semiconductor base, also may include halfConductor substrate and it is laid with epitaxial layer thereon, the material of semiconductor base can be general semiconductor-based such as silicon, germanium, GaAsBottom materials.
Transmission transistor further includes gate oxide 120, and the polysilicon gate 110 on gate oxide 120.According to thisOne embodiment of application, polysilicon gate are divided into two parts, and the doping type close to the part 111 of source electrode can be P+, i.e. PType heavy doping, the doping close to the part 112 of drain electrode can be N+, i.e. N-type heavy doping.111 and 112 be all polysilicon gate 110A part, each other without interval or separation.Doping concentration is the needs according to design and determination, for example, both mixMiscellaneous concentration can be greater than 1019, even up to 1020To 1021The order of magnitude.According to another embodiment, close to the part 111 of source electrodeDoping type can be N-, the doping type of part 112 close to drain electrode can be N+.The part of these polysilicon gates is oneBody, no interval or separation each other.
When closing transmission transistor, the control signal Tx of such as -1V can be applied to polysilicon gate 110.Such as Fig. 1 (b)Shown, the potential of the channel region under polysilicon gate 110 is lower than the potential level of source electrode 104 and drain electrode 108.According to this ShenOne embodiment please, the potential of the channel region below partial polysilicon grid 111 can be such as -0.45V, and part polycrystallineThe potential of channel region below Si-gate 112 can be slightly above the potential of the channel region below partial polysilicon grid 111.
When opening transmission transistor, the control signal Tx of such as 2.8V can be applied to polysilicon gate 110.Such as Fig. 1 (c)Shown, Potential Distributing gradually rises from source electrode 104 to drain electrode 108.Particularly, the channel region below partial polysilicon grid 111Potential can differ such as 1V with the potential of the channel region below partial polysilicon grid 112.Due to this potential gradientIn the presence of the photo-generated carrier such as electronics generated by photodiode, so that it may by the source of slave transmission transistor rapidly and efficientlyPole is transferred to drain electrode.
When being again switched off transmission transistor, grid voltage can be reduced to -1V again, due under partial polysilicon grid 112The potential of the channel region in face can be higher than the potential of the channel region below partial polysilicon grid 111, therefore remain in channelThe electrons in region flow to floating diffusion region 108 and then are reset under the action of potential gradient, without flowing back to photoelectricity twoInterference in pole pipe, so as to avoid the generation of feedthrough phenomenon and its to image.In the present embodiment, not by polysilicon gate 110The top of the partial region of the photodiode 104 of covering further includes pinning layer 106.According to another embodiment, in two pole of photoelectricity104 top of n-type doping region of pipe all has pinning layer 106 (situation is not shown).In addition, including 111 and 112 being formedIn the manufacturing process of partial polysilicon gate 110 may be selected first using ion doping injection etch again to be formed polysilicon gate orFirst etching forms gate shapes, and doping injection forms polysilicon gate 110 respectively again.
Fig. 2 (a) show transmission transistor in the cmos image sensor according to documented by another embodiment of the applicationStructural schematic diagram.Polysilicon gate 210 may include three parts, close to the P+ doped portion 113 of source electrode, close to the N+ of drain electrodeDoped portion 115, and the undoped part 114 among the two, the part of these polysilicon gates be it is integrated, each other itBetween be not spaced or separate.
It can be loaded on polysilicon gate 210 and close the transmission transistor under the control signal of such as -1V, and loaded for exampleThe voltage of 2.8V opens the transmission transistor.It is not only more in part since the doping situation of 210 different piece of polysilicon gate is differentThe gradient that potential can be generated between the channel region below of crystal silicon grid 113 and 115, undoped partial polysilicon grid 114 withAlso the variation that potential can be generated in lower channel region, as shown in Fig. 2 (b)-(c).In the present embodiment, not by polysilicon gate 210The top of the partial region of the photodiode 104 of covering further includes pinning layer 106.According to another embodiment, in two pole of photoelectricity104 top of n-type doping region of pipe all has pinning layer 106 (situation is not shown).In addition, including 113,114 being formedIt etches to form polysilicon gate again with may be selected first to inject using ion doping in the manufacturing process of the polysilicon gate 210 of 115 partsPole or first etching form gate shapes, and doping injection forms polysilicon gate 210 respectively again.
Transmission transistor in the cmos image sensor according to documented by the another embodiment of the application shown in Fig. 3 (a)Structural schematic diagram.Polysilicon gate 310 may include three parts, and close to the P+ doped portion 116 of source electrode, the N+ close to drain electrode mixesHetero moiety 119, close to the P- doped portion 117 of P+ doped portion 116, i.e. p-type is lightly doped, close to the N- of N+ doped portion 119Doped portion 118, i.e. N-type are lightly doped, these partial polysilicon grid are integrated, no interval or separation each other.
The switch state of transmission transistor shown in Fig. 3 can be controlled using control signal similar to the above.It is similar, rising into a ladder from source electrode 104 to drain electrode 108 is produced in the channel region below of polysilicon gate 310 respectivelyPotential Distributing, as shown in Fig. 3 (b)-(c).In the present embodiment, the portion for the photodiode 104 not covered by polysilicon gate 310Subregional top further includes pinning layer 106.According to another embodiment, above the n-type doping region 104 of photodiode allWith pinning layer 106 (situation is not shown).In addition, forming the polysilicon gate including 116,117,118 and 119 partsIt may be selected first to etch to form polysilicon gate or first etch again using ion doping injection in 310 manufacturing process to form gridDoping injection forms polysilicon gate 310 to shape respectively again.
The transmission transistor which above-mentioned seed type no matter used, in the state of its unlatching, due to more DOPOS doped polycrystalline siliconsThe presence of potential gradient in grid lower channel region, the photo-generated carrier such as electronics generated by photodiode, so that it may fastSpeed is efficiently transferred to drain electrode from the source electrode of transmission transistor.And the electricity in the polysilicon gate channel region below of single dopingGesture is distributed flat, and therefore, the transfer efficiency of photo-generated carrier will be significantly less than transmission transistor described in the applicationTransfer efficiency.
Due under the closed state that is reentered after transmission transistor is opened, non-uniform doping polysilicon gate ditch belowPotential Distributing in road region is still in a degree of ladder distribution, therefore remains in the electrons of channel region in potential ladderFloating diffusion region 108 is flowed under the action of degree, without flowing back in photodiode, thus avoid feedthrough phenomenon generation andIts interference to image.Pass through the reset to floating diffusion region, so that it may eliminate the influence of these residual carriers.
According to one embodiment of the application, the polysilicon gate 110,210 or 310 of the transmission transistor shown in Fig. 1-3On can also have one layer of metal silicide layer, control signal can be applied directly on metal silicide layer.
It can be controlled in the embodiment of the present application using the control signal for being traditionally used for control cmos image sensorCmos image sensor.Closing voltage-the 1V and cut-in voltage 2.8V for the transmission transistor spoken of above are only an example.According to different components size, technique setting can be adjusted the level of the control voltage.In addition, according to the one of the applicationA embodiment, for transmission transistor shown in Fig. 1-3, control signal can load more in the part of P+ and/or N+ dopingOn crystal silicon grid.
In addition, the transmission transistor in cmos image sensor disclosed in the present application can also include being located at substrate 102The P-doped zone (not shown) on surface, also known as pinning layer, it is dark caused by the defect for inhibiting silicon and silica surfaceElectric current.
In addition, at least part part in the polysilicon gate of the transmission transistor covers channel region, at least in additionPart covers at least part of photodiode.
The transmission transistor is also possible to buried channel transistor, that is to say, that its channel region is apart from semiconductor substrate surfaceWith a certain distance.
Manufacture the process flow and traditional technique of the transmission transistor in cmos image sensor disclosed in the present applicationProcess the difference is that, to generate the polysilicon gate with non-uniform doping.According to one embodiment, etching can be first passed throughTechnique forms the polysilicon gate of required size, then carries out doping heterogeneous to the grid again.Alternatively, according to another realityExample is applied, non-uniform doping first can be carried out to the polysilicon layer on transmission transistor gate oxide layers, then again to the polysiliconLayer performs etching the grid to form required size.
Those skilled in the art are easy for learning, can change material and method within the scope of application, such asDo not need in the case where making the creative labor, so that it may by n-type doping and p-type doping mutually exchange, corresponding carrier byIt is hole that electronics, which is exchanged, and constructs the transmission transistor complementary with the embodiment of the present application.It should also be understood that in addition toIn illustrating except the specific context of embodiment, the utility model provides many applicable inventive concepts.Correspondingly, appendedClaim is intended to include the range at them by such process, machine, manufacture, substance synthesis, device, method or stepIt is interior.