CN104766873A - Inner Line Transfer CCD Structure and Manufacturing Method - Google Patents

Abstract

An internal line transferring CCD structure comprises a silicon substrate, wherein a transferring area and a photosensitive area are adjacently arranged on the silicon substrate. The internal line transferring CCD structure is characterized in that a polycrystalline silicon transferring grid is arranged on the surface of the silicon substrate within the range of the transferring area and covered with a light shading layer, a backflow layer deposits on the surface of the light shading layer and covers the photosensitive area, and the light shading layer is made of refractory metal or refractory metal alloy. The internal line transferring CCD structure has the advantages that high-melting metal is used for replacing aluminum, the light shading layer can be directly formed on the polycrystalline silicon transferring grid, and the light leaking rate of elements is reduced.

Description

Inner Line Transfer CCD Structure and Manufacturing Method

technical field

The present invention relates to a charge-coupled device manufacturing technology, in particular to an internal transfer CCD structure and a manufacturing method thereof.

Background technique

Internal line transfer CCD is a major category of CCD. Its pixel unit can be divided into photosensitive area and transfer area according to function. The photosensitive area generates electrons under the irradiation of visible light, and the electrons are transferred to the periphery of the device through the transfer area and output. The working mode of the internal line transfer CCD requires that the area outside the photosensitive area on the device must be covered with a light-shielding layer to avoid crosstalk between the stray signal generated by the photosensitive area outside the photosensitive area and the photosensitive area signal, and reduce the CCD imaging quality.

In the prior art, the typical structure of the internal line transfer CCD is shown in Figure 1. It can be seen from the figure that the light-shielding layer is located above the reflow layer. The reason why this structure is adopted in the prior art is: based on the conventional design, Generally, an aluminum film is used to form the light-shielding layer, and the reflow layer is generally made of BPSG borophosphosilicate glass. Based on existing theories, the melting point of metal aluminum is much lower than the process temperature of the reflow layer deposition process, so the reflow layer deposition can only be carried out first. area, and then make a light-shielding layer; the problem is: because the reflow layer exists between the light-shielding layer and the polysilicon transfer gate, the light-shielding layer made on the reflow layer cannot completely block the polysilicon transfer gate. , a part of the light will irradiate obliquely to the outer area of the photosensitive area and form light leakage through the polysilicon transfer gate, which will cause crosstalk, and as the thickness of the reflow layer increases, the light leakage rate will become more and more serious. In addition, in addition to In addition to the problem of light leakage, during processing, there are also problems such as high process difficulty caused by large step height differences on the surface of the device, and problems such as leakage and short circuit between metal layers are prone to occur between the light-shielding layer and the lead, resulting in low device yield.

Contents of the invention

Aiming at the problems in the background technology, the present invention proposes an internal line transfer CCD structure, comprising a silicon substrate, on which a transfer region and a photosensitive region are adjacently arranged, and its innovation lies in: the silicon within the range of the transfer region The surface of the substrate is provided with a polysilicon transfer gate, the surface of the polysilicon transfer gate is covered with a light-shielding layer, and a reflow layer is deposited on the surface of the light-shielding layer, and the reflow layer covers the photosensitive area; the light-shielding layer is made of refractory metal or refractory metal alloy make.

The principle of the present invention is: use metal aluminum to make the light-shielding layer, although the material cost and process cost are relatively low, but because its structure is affected by the process characteristics of metal aluminum, the light-shielding layer can only be made after the reflow layer, resulting in the device The light leakage rate remains high. In severe cases, the light leakage rate can be as high as 15%, which has a great impact on device performance; from the perspective of improving device performance, the inventor believes that if the light-shielding layer is directly fabricated on the surface of the polysilicon transfer gate, it will be from To a large extent, the problem of light leakage was solved, so the inventor conducted a lot of experiments and explorations, and finally proposed the solution of the present invention. In the solution of the present invention, a refractory metal or a refractory metal alloy is used to make the light-shielding layer. It is known from the field of science and basic common knowledge in this field that the melting point temperature of refractory metals or refractory metal alloys is very high, mostly higher than the process temperature of the reflow layer deposition process, which makes the light-shielding layer can be made before the reflow layer, so that The light-shielding layer is directly deposited on the surface of the polysilicon transfer gate to form a good coverage of the polysilicon transfer gate and improve the problem of high light leakage rate of the device; based on the basic knowledge in the field, the function of the reflow layer is to improve the surface flatness of the device. It has nothing to do with the function of the device, so the position of the reflow layer does not affect the performance of the device; in addition, after adopting the solution of the present invention, the reflow layer covers the light-shielding layer, which can well avoid leakage and short circuit between the light-shielding layer and the metal leads question.

Preferably, titanium is used as the refractory metal; tungsten disilicide is used as the refractory metal alloy.

Preferably, the thickness of the light-shielding layer is 200-1000 nm.

Preferably, the polysilicon transfer gate is fabricated by a secondary polysilicon process or a tertiary polysilicon process.

Based on the aforementioned scheme, the present invention also proposes a method for manufacturing an internal line transfer CCD, the innovation of which is: making an internal line transfer CCD according to the following steps: 1) providing a silicon substrate; 2) fabricating a photosensitive area and a transfer area on the silicon substrate; 3 ) Fabricate a polysilicon transfer gate on the silicon substrate; 4) Deposit a light-shielding layer on the surface of the polysilicon transfer gate; 5) Deposit a reflow layer on the surface of the device, and the reflow layer will completely cover the light-shielding layer and the photosensitive area; 6) Fabricate a metal Leads; wherein, the light-shielding layer is made of refractory metal or refractory metal alloy. In this manufacturing method, the processes adopted are all common processes in the semiconductor industry in the prior art. The difference from the prior art lies in the process steps and the material of the light-shielding layer. Specifically, in the method of the present invention, the light-shielding layer is first made Make the reflow layer, and in the prior art, make the reflow layer first and then make the light-shielding layer, in addition, use refractory metal or refractory metal alloy to make the light-shielding layer in the method of the present invention, and use metal aluminum to make in the prior art Shading layer.

Preferably, the thickness of the light-shielding layer is 200-1000 nm.

Preferably, the polysilicon transfer gate is fabricated by a secondary polysilicon process or a tertiary polysilicon process.

Preferably, titanium is used as the refractory metal; tungsten disilicide is used as the refractory metal alloy.

The beneficial technical effects of the present invention are: a new internal transfer CCD structure and manufacturing method are proposed, and the light-shielding layer can be directly formed on the polysilicon transfer gate by replacing aluminum with a high-melting point metal material, reducing the light leakage rate of the device.

Description of drawings

Figure 1. The typical schematic structure of the existing internal transfer CCD;

Fig. 2, structural representation of the present invention;

The names corresponding to each mark in the figure are: silicon substrate 1, polysilicon transfer gate 2, light-shielding layer 3, reflow layer 4, transfer region A, photosensitive region B, and visible light incident direction C.

Detailed ways

An internal line transfer CCD structure, including a silicon substrate 1, on which a transfer region A and a photosensitive region B are adjacently arranged, and its innovation lies in: the surface of the silicon substrate 1 within the range of the transfer region A is arranged The polysilicon transfer gate 2, the surface of the polysilicon transfer gate 2 is covered with a light-shielding layer 3, and the surface of the light-shielding layer 3 is deposited with a reflow layer 4, and the reflow layer 4 covers the photosensitive area B; the light-shielding layer 3 is made of refractory metal or refractory Molten metal alloy production.

Further, titanium is used as the refractory metal; tungsten disilicide is used as the refractory metal alloy.

Further, the thickness of the light-shielding layer 3 is 200-1000 nm.

Further, the polysilicon transfer gate 2 is fabricated by a secondary polysilicon process or a tertiary polysilicon process.

A method for manufacturing an internal line transfer CCD, the innovation of which lies in: making an internal line transfer CCD according to the following steps: 1) Provide a silicon substrate; 2) Fabricate a photosensitive area B and a transfer area A on the silicon substrate; 3) Fabricate on the silicon substrate Polysilicon transfer gate 2; 4) Deposit light-shielding layer 3 on the surface of polysilicon transfer gate 2; 5) Deposit reflow layer 4 on the surface of the device, and the reflow layer 4 completely covers light-shielding layer 3 and photosensitive area B; 6) Make metal Leads; wherein, the light-shielding layer 3 is made of refractory metal or refractory metal alloy.

Further, the thickness of the light-shielding layer 3 is 200-1000 nm.

Further, the polysilicon transfer gate 2 is fabricated by a secondary polysilicon process or a tertiary polysilicon process.

Further, titanium is used as the refractory metal; tungsten disilicide is used as the refractory metal alloy.

It has been verified by experiments that after adopting the solution of the present invention, the light leakage rate of the product can be reduced to about 2%.

Claims (8)

1. an interior lines transfer CCD structure, comprise silicon substrate (1), the upper vicinity of described silicon substrate (1) is provided with transition range (A) and photosensitive area (B), it is characterized in that: the silicon substrate (1) in described transition range (A) scope is provided with polysilicon TG transfer gate (2) on the surface, polysilicon TG transfer gate (2) surface coverage has light shield layer (3), light shield layer (3) surface deposition has reflux layer (4), and photosensitive area (B) covers by described reflux layer (4); Described light shield layer (3) adopts refractory metal or refractory metal alloy to make.

2. interior lines transfer CCD structure according to claim 1, is characterized in that: described refractory metal adopts Titanium; Described refractory metal alloy adopts tungsten silicide.

3. interior lines transfer CCD structure according to claim 1, is characterized in that: described light shield layer (3) thickness is 200 ~ 1000nm.

4. interior lines transfer CCD structure according to claim 1, is characterized in that: described polysilicon TG transfer gate (2) adopts secondary polysilicon process or three polysilicon process to make.

5. an interior lines transfer CCD manufacture method, is characterized in that: following steps for manufacturing interior lines transfer CCD:1) silicon substrate is provided; 2) photosensitive area (B) and transition range (A) is made on a silicon substrate; 3) polysilicon TG transfer gate (2) is made on a silicon substrate; 4) at polysilicon TG transfer gate (2) surface deposition light shield layer (3); 5) at device surface deposit reflux layer (4), light shield layer (3) and photosensitive area (B) all cover by described reflux layer (4); 6) metal lead wire is made; Wherein, described light shield layer (3) adopts refractory metal or refractory metal alloy to make.

6. interior lines transfer CCD manufacture method according to claim 5, is characterized in that: described light shield layer (3) thickness is 200 ~ 1000nm.

7. interior lines transfer CCD manufacture method according to claim 5, is characterized in that: described polysilicon TG transfer gate (2) adopts secondary polysilicon process or three polysilicon process to make.

8. interior lines transfer CCD manufacture method according to claim 5, is characterized in that: described refractory metal adopts Titanium; Described refractory metal alloy adopts tungsten silicide.