JPH02189937A - Manufacture of charge-coupled device - Google Patents

Abstract

PURPOSE:To increase the quantity of storable transferable charges while improving insulating properties between transfer electrodes by separately forming first layer and second layer gate oxide films and an insulating oxide film, and thinning the gate oxide films while sufficiently thickening the insulating oxide film. CONSTITUTION:A first layer gate oxide film 3, an insulating oxide film 6 and a second layer gate oxide film 7 are shaped respectively. Each gate oxide film 3, 7 is thinned while the insulating oxide film 6 is formed in thick size. Consequently, insulating properties between transfer electrodes 5A, 8 are improved while the two contradictive conditions of the increase of the quantity of storable transferable charges can be satisfied. Since the first layer transfer electrode 5A is coated with the insulating oxide film 6 when the second layer gate oxide film 7 is manufactured in the manufacture, a polycrystalline silicon film containing an impurity is not exposed, thus preventing the generation of partial defective transfer due to the outer diffusion of the impurity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a charge coupled device (CCD), and more particularly to a method for manufacturing transfer electrodes arranged in two layers.

[Conventional technology]

Conventionally, as a method for manufacturing this type of charge-coupled device, there is a method shown in FIGS. 3(a) to 3(e).

These figures are longitudinal cross-sectional views of the charge-coupled device in the direction of charge transfer.

First, as shown in FIG. 3(a), several hundred first layer gate oxide films 3 are grown by thermal oxidation on a silicon substrate 1 on which wells 2 of a shift register are formed. Then, as shown in FIG. 3(b), several thousand first layer polycrystalline silicon films 5 are deposited on this gate oxide film 3 by chemical vapor deposition.

Next, as shown in FIG. 3(C), the first layer polycrystalline silicon film 5 is selectively etched by photolithography using a photoresist or the like (not shown) to form the first layer transfer electrode 5A.
form. At the same time, these first layer transfer electrodes 5
The surface of the substrate between A, that is, the silicon substrate in the region where the second layer polycrystalline silicon transfer electrode is to be formed is exposed.

Subsequently, as shown in FIG. 3(d), a second layer gate oxide film 9 with several hundred holes is grown by thermal oxidation.

After that, a second layer of polycrystalline silicon film is deposited on the entire surface by chemical vapor deposition, and selectively etched by photolithography, as shown in FIG. 3(e).
A second layer of transfer electrodes 8 is formed.

Note that the second layer gate oxide film 9 is the first layer transfer electrode 5A.
It functions as an insulating film between the transfer electrode 8 and the second layer transfer electrode 8.

[Problems to be Solved by the Invention] In the conventional method for manufacturing a charge transfer device described above, gate oxidation B in the second layer is '! , 9 becomes thicker.
The amount of charge that can be stored and transferred decreases. On the other hand, if the thickness of the "second layer" D1-oxide film 9 is made thinner in order to increase the amount of charge that can be stored and transferred, the insulation between the bi-inverting and reverse electrodes 5A18 will deteriorate. Therefore, there is a problem in that it is not possible to simultaneously satisfy the two requirements of increasing the insulation between the transfer electrodes and increasing the amount of charge that can be stored and transferred.

In addition, in order to increase the electrical conductivity, the transfer electrode 5 of [layer I] is
The impurity introduced into A diffuses outward during the step of growing the second layer I/oxide film 9 by thermal oxidation, and this impurity easily enters the exposed silicon substrate 1. This results in uneven concentration in well 2 of the shiftless disk.
There is also the problem that local transfer failures are more likely to occur.

An object of the present invention is to provide a method of manufacturing a charge transfer device that solves the above-mentioned contradictory problems and prevents transfer failures.

[Means for Solving the Problems] A method for manufacturing a charge transfer device of the present invention includes forming a first layer of oxide film on a semiconductor substrate, and forming a first layer of gate oxide film on the first layer of gate oxide film. a step of selectively forming a nitride film in a second layer transfer electrode formation region; a step of selectively forming a first layer transfer electrode of polycrystalline silicon on the first layer gate oxide film; A step of growing a thick insulating oxide film on the surface of the first layer transfer electrode, and removing the nitride film and the first layer D1-oxide film to form a second layer transfer electrode on the surface of the semiconductor substrate. a step of exposing the semiconductor substrate, a step of growing a second layer of gate oxide film on at least the exposed surface of the semiconductor substrate, and a step of forming a second layer of transfer electrode on the top of this second layer of gate oxide. Include the process.

[Effect]

In the two-speed manufacturing method, the first and second gate oxide films and the insulating oxide film can be manufactured separately, and each gate oxide film can be formed thinly, while the insulating oxide film can be formed sufficiently thick ( Also, when growing the second layer gate oxide film,
By covering each transfer electrode with an insulating oxide film, diffusion of impurities from the transfer electrode can be prevented.

[Example] Next, the present invention will be explained with reference to the drawings.

11m(a) to 1(h) are views showing one embodiment of the present invention in the order of manufacturing steps, and are longitudinal sectional views parallel to the transfer direction.

First, as shown in FIG. 1(a), a first layer gate oxide film 3 with several hundred holes is grown by thermal oxidation on a silicon substrate 11 on which wells 2 of a shift resist are formed, and then several hundred holes are grown. A nitride film 4 is deposited by chemical vapor deposition. Thereafter, as shown in FIG. 1(b), the nitride film 4 in the first layer transfer electrode formation region is selectively removed by photolithography using a photoresist or the like (not shown), and later the second layer 1 is removed. ”
Leave only the area where the transfer electrode will be formed.

Then, as shown in FIG. 1C, several thousand first layer polycrystalline silicon films 5 are deposited thereon by chemical vapor deposition. Then, the first layer of polycrystalline silicon film 5 is selectively etched by a photolithography method using a resist or the like on photo 1 (not shown) to form the first layer of transfer electrode 5A as shown in FIG. 1(d). do. At this time, if the mask used when removing the nitride film 4 is used as is, the nitride film 4
It is possible to easily form the first layer transfer electrode 5A only in the region where the transfer electrode 5A does not exist.

Furthermore, as shown in FIG. 1(e), a sufficiently thick insulating oxide film 6 of several thousand layers is grown on the surface of the first layer transfer electrode 5A by thermal oxidation. At this time, the insulating oxide film 6 hardly grows on the nitride film 4 due to the oxidation resistance of the nitride film 4.

Next, as shown in FIG. 1(f), the nitride film 4 is selectively etched away, and then the oxide films 3 and 6 are etched. At this time, since the insulating oxide film 6 is sufficiently thick,
Even after the first layer gate oxide film 3 is etched away to expose the silicon substrate 1 in the second layer transfer electrode formation region,
The insulating oxide film 6 has a thickness of several hundred to several thousand layers on the first layer transfer electrode 5A.

Subsequently, as shown in FIG. 1(g), several hundred second layer gate oxide films 7 are grown over the entire surface by thermal oxidation. Then, by growing a second layer of polycrystalline silicon film over the entire surface and selectively etching it, a second layer of transfer electrode 8 is formed as shown in FIG. 1(h).

In the structure of the transfer electrode formed in this way, the first layer of gate oxide film 3. Insulating oxide film 6. Since the gate oxide film 7 and the second layer gate oxide film 7 are formed separately, it is possible to make the insulating oxide film 6 thick while making each gate oxide film 3 and 7 thinner, so that the gate oxide film 7 between the transfer electrodes 5A and 8 can be made thicker. It becomes possible to satisfy the two contradictory conditions of increasing the amount of charge that can be stored and transferred while improving the insulation properties of the semiconductor device.

In addition, in this manufacturing method, when manufacturing the second layer gate oxide film 7, the first layer transfer electrode 5A is covered with the insulating oxide film 6, so that the polycrystalline silicon film containing impurities is coated with the insulating oxide film 6. It is also possible to prevent local transfer failures due to outward diffusion of impurities.

FIG. 2 shows another embodiment of the present invention, and is a longitudinal sectional view showing a part of the manufacturing process, that is, a step corresponding to FIG. 1(d).

In this embodiment, as shown in FIGS. 1(a) to 1(c), the first layer of gate oxide film 3. Nitride films 4 and 1
After forming the first layer of polycrystalline silicon film 5, the first layer of transfer electrode 5A is formed.
It is characterized in that a portion of A is formed so as to overlap with the nitride film 4.

Thereafter, the transfer electrode structure is completed by the same steps as in FIGS. 1(c) to 1(h).

In this example, since a part of the first layer transfer electrode 5A is overlapped with the nitride film 4, even if a horizontal positional shift occurs when forming the first layer transfer electrode 5A, the transfer of the second layer 1] Preventing the surface of the silicon substrate 1 in the electrode formation region from being exposed,
Intrusion of impurities into the silicon substrate 1 can be reliably prevented. Therefore, it is possible to increase the degree of freedom in forming the first layer transfer electrode 5A.

〔Effect of the invention〕

As explained above, in the present invention, since the first and second gate oxide films and the insulating oxide film are manufactured separately, these gate oxide films can be formed thinly, while the insulating oxide film can be formed sufficiently. It can form thickly and accumulate.

While increasing the amount of charge that can be transferred, it is possible to improve the insulation between the transfer electrodes. In addition, when growing the second layer gate oxide film, the first layer transfer electrode is covered with an insulating oxide film, which prevents impurities from diffusing from the transfer electrode into the silicon substrate. This has the effect of preventing density unevenness in the area and preventing local transfer failures from occurring.

[Brief explanation of the drawing]

FIG. 1(a) to FIG. 1(h) are vertical cross-sectional views showing one embodiment of the present invention in the order of manufacturing steps, and FIG. 2 is a vertical cross-sectional view showing a part of the manufacturing process of another embodiment of the present invention. 3(a) to 3(e) are vertical sectional views showing a conventional manufacturing method in the order of manufacturing steps. ■...Silicon substrate, 2...Well, 3...1st layer gate oxide film, 4...Nitride film, 5...1st layer polycrystalline silicon film, 5A...1 Layer transfer electrode, 6.
... Insulating oxide film, 7... Second layer gate oxide film, 8.
...Second layer transfer electrode, 9...Second layer gate oxide film. Figure ■ Figure 3

Claims (1)

[Claims] 1. Forming a first layer of gate oxide film on a semiconductor substrate, and selectively forming a nitride film in a region where a second layer of transfer electrode is to be formed on this first layer of gate oxide film; a step of selectively forming a first layer transfer electrode using polycrystalline silicon on the gate oxide film of the first layer; a step of growing a thick insulating oxide film on the surface of the first layer transfer electrode; and a step of growing the nitride film. and removing the first layer gate oxide film to expose the surface of the semiconductor substrate in the second layer transfer electrode formation region;
The method includes at least the steps of growing a second layer of gate oxide film on the exposed surface of the semiconductor substrate, and forming a second layer of transfer electrode on this second layer of gate oxide film. A method for manufacturing a charge-coupled device.