CN102263130A - Charge-coupled device (CCD) unit structure capable of reducing CCD dark current - Google Patents

Abstract

The invention discloses a charge-coupled device (CCD) unit structure capable of reducing CCD dark current. The CCD unit structure comprises a CCD unit consisting of a plurality of polysilicon electrodes which are arranged sequentially, and a buried channel corresponding to the CCD unit, wherein the buried channel consists of a first buried channel and a second buried channel; the doping concentration of the second buried channel is smaller than that of the first buried channel; the position of the second buried channel is rightly opposite to one of the polysilicon electrodes; the position of the first buried channel is opposite to other polysilicon electrodes; and the width of the second buried channel is the same as that of the opposite polysilicon electrode. The CCD unit structure has the advantage that: heat generation dark current in an interfacial state in a surface area can be reduced effectively, so the total dark current of a CCD can be reduced; therefore, the CCD can image a target under weaker light.

Description

Reduce the CCD cellular construction of CCD dark current

Technical field

The present invention relates to a kind of CCD structure, relate in particular to a kind of CCD cellular construction of the CCD of reduction dark current.

Background technology

CCD(Charge-coupled Device, the Chinese full name: dark current charge coupled device) is meant that CCD is under the situation of no light signal or signal of telecommunication input, signal by the material production of CCD: because CCD is working under dark spent condition, heat generation because of charge carrier, potential well can be filled up gradually, even under the situation that does not have the input of the light signal or the signal of telecommunication, this thermogenetic charge carrier still exists, form the dark current of CCD.

Its main source is that the heat that heat produces, depletion region is interior of backing material produces and the heat of surface region interfacial state produces, and is example with N raceway groove CCD, total dark current of CCD

Mainly from following several parts:

Be the total dark current of CCD device,

Be the heat generation dark current of backing material,

Be the heat generation dark current of depletion region,

Heat generation dark current for the surface region interfacial state.

At concrete CCD device, can calculate respectively by following formula

, , With

Numerical value:

Be electron charge,

Be the intrinsic carrier concentration in the silicon body,

Be electron diffusion length,

Be substrate concentration,

It is the electronic carrier life-span.

Be the substrate depletion region width,

It is the buried channel width.

Be to capture the interfacial state caputure area,

Be the electronics heat movement speed,

Be Boltzmann constant,

Be absolute temperature, It is interface state density.

With one group of practical devices parameter is example, and we calculate , With

Concrete numerical value, each parameter value is as follows:

Value is 1.6E-19C,

Value is 1.45E10/cm ³,

Value is 0.187cm,

Value is 5E14/cm ³,

Value is 0.001s,

Value is 0.0005cm,

Value is 0.00005cm,

Value is 1.0E-15cm ²,

Value is 1.0E7cm/s,

Value is 8.61E-5eV/K,

Value is 295K,

Value is 1.0E10/eV/cm ²

Based on aforesaid parameter value, by

Formula can be regarded as

Be 1.43E-11 ampere/square centimeter; By

Formula can be regarded as

Be 6.38E-10 ampere/square centimeter; By

Formula can be regarded as

Be 9.47E-9 ampere/square centimeter; From result of calculation as can be known, the heat of surface region interfacial state produces dark current and has accounted for 93.6% of dark current sum, if there is not the heat of surface region interfacial state to produce dark current in other words, it is original 6.4% that dark current will be reduced to, and promptly the main contributor of CCD dark current is

If can reduce

Numerical value, then can make total CCD dark current

Numerical value decline to a great extent.

Summary of the invention

At the problem in the background technology, the present invention proposes the CCD cellular construction that a kind of heat that reduces the surface region interfacial state produces dark current, its structure is: comprise the CCD unit of being made up of a plurality of polysilicon electrodes, the buried channel channel corresponding with the CCD unit, the buried channel channel is made up of the first buried channel channel and the second buried channel channel, the doping content of the second buried channel channel is lower than the doping content of the first buried channel channel, the position of the second buried channel channel is provided with over against one of them polysilicon electrode, the position of the first buried channel channel is relative with remaining polysilicon electrode, and the width of the second buried channel channel is identical with the width of a polysilicon electrode.

Described CCD unit has a plurality of, and a plurality of CCD unit becomes row setting; Corresponding one the second buried channel channel in each CCD unit, the spacing distance of adjacent two second buried channel channels is identical.

The doping content of the first buried channel channel is 3.0 * 10 ¹⁶/ cm ³The doping content of the second buried channel channel is 1.0 * 10 ¹⁶/ cm ³

Useful technique effect of the present invention is: the heat that can effectively reduce the surface region interfacial state produces dark current, thereby reduces the total dark current of CCD device, makes the CCD can be to the realization of goal imaging under more weak illumination.

Description of drawings

Fig. 1, existing C CD device architecture schematic diagram;

Fig. 2, CCD device architecture schematic diagram one of the present invention;

Fig. 3, CCD device architecture schematic diagram two of the present invention.

Embodiment

The structure of existing C CD structure is: substrate 1 is arranged at the branch that buried channel channel 6(buried channel channel 6 on the substrate 1 has N type and P type again), be arranged at the SiO on the buried channel channel 6 ₂ Layer 3 is arranged at SiO ₂ Polysilicon electrode 5 numbers that each CCD unit of a plurality of polysilicon electrode 5(on the layer 3 is comprised can be 3 to 6), insulation between adjacent two polysilicon electrodes 5.Existing buried channel channel 6 is the single overall structure of doping content.

Based on aforesaid existing structure, CCD when the light integration or ccd signal when being in temporary state, the SiO under that phase electrode of storage signal electronics ₂Interfacial potential between layer 3 and the buried channel channel 6 must be higher than substrate 1 electromotive force, otherwise signal will be gone to adjacent electrode, and CCD can not storage signal, the SiO under the electrode ₂Interfacial potential and substrate 1 electromotive force between layer 3 and the buried channel channel 6 are unequal, help surface region interfacial state emitting electrons, produce a large amount of dark current, and Here it is

The reason that numerical value is bigger.

In order to reduce

Numerical value, on aforementioned existing CCD architecture basics, what the present invention did is improved to: buried channel channel 6 is made as the first buried channel channel 6-1 and second buried channel channel 6-2 two parts, and the doping content of the second buried channel channel 6-2 is lower than the doping content of the first buried channel channel 6-1, the position of the second buried channel channel 6-2 is provided with over against neat one of them polysilicon electrode 5, the position of the first buried channel channel 6-1 and remaining polysilicon electrode 5 relative (also promptly covering remaining polysilicon electrode 5 The corresponding area), the width of the second buried channel channel 6-2 is identical with the width of a polysilicon electrode 5.

After adopting the solution of the present invention, SiO ₂Interfacial potential, SiO between the layer 3 and first buried channel channel 6-1 ₂The layer 3 with the second buried channel channel 6-2 between interfacial potential all identical with substrate 1 electromotive force; Because the doping content of the second buried channel channel 6-2 is lower than the doping content of the first buried channel channel 6-1, signal electron is stored in the first buried channel channel 6-1 and can go in the second buried channel channel 6-2, because SiO ₂Interfacial potential, SiO between the layer 3 and first buried channel channel 6-1 ₂ Layer 3 is all identical with substrate 1 electromotive force with interfacial potential between the second buried channel channel 6-2, and at this moment interfacial state is in stable state, is difficult to emitting electrons, at this moment

Numerical value can be reduced to negligible level, only remaining

With Dark current, can make total dark current of the identical CCD of all the other parameters be reduced to below 10% of total dark current of the CCD of existing structure, after dark current reduced, CCD can be to the realization of goal imaging under more weak illumination.

Formed structure was after improvement of the present invention was applied to ccd array: described CCD unit has a plurality of, and a plurality of CCD unit becomes row setting; Corresponding one the second buried channel channel 6-2 in each CCD unit, the spacing distance of adjacent two second buried channel channel 6-2 is identical.

The preferred version of the doping content of the first buried channel channel 6-1 and the second buried channel channel 6-2 is: the doping content of the first buried channel channel 6-1 is 3.0 * 10 ¹⁶/ cm ³The doping content of the second buried channel channel 6-2 is 1.0 * 10 ¹⁶/ cm ³

Claims (3)

1. CCD cellular construction that reduces the CCD dark current, comprise the CCD unit of forming by a plurality of polysilicon electrodes (5) of arranging in turn, the buried channel channel (6) corresponding with the CCD unit, it is characterized in that: buried channel channel (6) is made up of the first buried channel channel (6-1) and the second buried channel channel (6-2), the doping content of the second buried channel channel (6-2) is lower than the doping content of the first buried channel channel (6-1), the position of the second buried channel channel (6-2) is provided with over against one of them polysilicon electrode (5), the position of the first buried channel channel (6-1) is relative with remaining polysilicon electrode (5), and the width of the second buried channel channel (6-2) is identical with the width of a polysilicon electrode (5).

2. the CCD structure of reduction CCD dark current according to claim 1, it is characterized in that: described CCD unit has a plurality of, and a plurality of CCD unit becomes row setting; Corresponding one the second buried channel channel (6-2) in each CCD unit, the spacing distance of adjacent two second buried channel channels (6-2) is identical.

3. the CCD structure of reduction CCD dark current according to claim 1 and 2, it is characterized in that: the doping content of the first buried channel channel (6-1) is 3.0 * 10 ¹⁶/ cm ³The doping content of the second buried channel channel (6-2) is 1.0 * 10 ¹⁶/ cm ³

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