JPH0499373A - Semiconductor memory cell - Google Patents

Abstract

PURPOSE:To increase a charge storage capacity, and to prevent difficulty of inversion of stored information even if charge leakage occurs by providing a plurality of cylinders for forming first electrodes of capacitors concentrically. CONSTITUTION:A first electrode 20 of a capacitor is formed of a disc 23 and two cylinders 24a, 24b provided concentrically on the disc 23, and a dielectric 21 and a second electrode 22 are provided on the outer surface of the electrode 20. The outer diameter of the disc 23 is set to substantially the same size and shape as those of prior art. An inner cylinder 24a is set to slightly larger inner diameter than that of a contact hole 16 of an insulating film 13, and smaller diameter than that of a conventional cylinder 24. On the other hand, the outer cylinder 24b is provided near the outer peripheral edge of the cylinder 23, and set to slightly larger inner diameter than that of the conventional cylinder 24. That is, in a capacitor, since the two cylinders 24a, 24b are provided, charge storage capacity is larger than that of prior art.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor memory element (memory cell) composed of a MOS transistor and a capacitor.

[Conventional technology]

A conventional semiconductor memory element of this type will be explained with reference to FIG. The figure shows a sectional view of the main part.

In the figure, 10 is a semiconductor substrate such as silicon, 11, 12 is an impurity diffusion layer that is diffused and formed adjacent to each other and spaced apart from each other inside the semiconductor substrate 1, and forms a source, an impurity diffusion layer that forms a drain, and 13 is a semiconductor. An insulating film made of an oxide film laminated on the substrate 10, 14 made of impurity-doped polysilicon etc. buried in the inside of the insulating film 13 between impurity diffusion 11i11 and 12 forming the source/drain. Gate electrode 1
4 and the gate oxide film 15 formed directly below M.
An OS transistor is configured.

20 is the 1'r! made of impurity-doped polysilicon or the like. j, pole; 21 is a dielectric made of an oxide film coated on the outer surface of the first electrode 20; 22 is a dielectric 21;
A second electrode made of impurity-doped polysilicon is coated on the outer surface of the capacitor, and these constitute a capacitor.

The first electrode 20 includes a disk portion 23 which is formed over the insulating film 13 above the MO3 transistor and whose central portion is in contact with the drain diffusion layer 12 through the contact hole 16, and an upper surface of the disk portion 23. It consists of a single cylindrical part 24 provided in the dielectric 21 and the second cylindrical part 24.
The electrode 22 has a shape that follows the outer shape of the first electrode 20.

In a semiconductor memory element having such a structure, the capacitance of a capacitor is determined by its surface area.

[Problem to be solved by the invention]

However, the conventional semiconductor memory element described above has the following disadvantages.

For example, a phenomenon occurs in which the charge accumulated in a capacitor leaks into the semiconductor substrate 10, but when the charge leakage is transformed, the amount of charge accumulated in the capacitor decreases.
This could even lead to information being reversed.

In order to avoid such inconveniences, it is desirable to increase the capacitance of the capacitor in semiconductor memory elements as much as possible, but with conventional devices, there is a limit to how much capacitance can be increased due to their structure, and the above-mentioned charge Leaks can cause inconveniences such as information being reversed.

The present invention was devised in view of the above circumstances, and an object of the present invention is to increase the capacity of a capacitor while suppressing the increase in the area occupied by the capacitor as much as possible.

[Means to solve the problem]

In order to achieve the above object, the present invention employs the following configuration in a semiconductor memory element composed of a MOS transistor and a capacitor.

In the semiconductor memory element of the present invention, the capacitor includes a disk portion provided on an insulating film covering a MOS transistor and partially in contact with an impurity diffusion layer forming a source or drain of the MOS transistor, and a disk portion of the disk portion. A first electrode consisting of a plurality of cylindrical portions formed concentrically above, and this first! It is characterized by being composed of a dielectric covering the outer surface of the pole and a second pole covering the further outer surface of the dielectric.

[Effect]

According to the above configuration, since a plurality of cylindrical portions constituting the first electrode of the capacitor are provided concentrically, the surface area thereof is increased and the charge storage capacity is increased compared to the conventional one. Note that by managing the inner diameter of each cylindrical portion to be as small as possible, it becomes possible to form a plurality of cylindrical portions within the area occupied by a conventional capacitor, and this does not hinder the increase in the capacity of the memory chip.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 shows an embodiment of the present invention. In this figure, the same parts as those shown in FIG. 3 of the conventional example are given the same reference numerals.

The semiconductor memory element of this example is basically the same as the conventional example shown in FIG. The structure of this embodiment, which has the same structure as that of the conventional example, differs from the conventional example in the structure of the capacitor.

This will be explained in detail below. That is, the first
The 1i pole 20 is composed of a disk portion 23 and two cylindrical portions 24a and 24b provided concentrically on the disk portion 23, and a dielectric 21 and a first electrode are provided on the outer surface of the first electrode 20. 2 is coated with a pole 22. And disk part 2
The outer diameter dimension of No. 3 is set to be approximately the same size and shape as that of the conventional example. Further, the inner cylindrical portion 24a is set to have an inner diameter slightly larger than the contact hole 16 of the insulating film 13, and has a smaller diameter than the conventional cylindrical portion 24. On the other hand, the outer cylindrical portion 24b is provided near the outer peripheral edge of the disk portion 23, and has an inner diameter slightly larger than that of the conventional cylindrical portion 24.

In other words, in the capacitor of this embodiment, the cylindrical portions 24a, 2
Since the number of 4b is two, the load storage capacity is larger than that of the conventional one. However, the diameter of each cylindrical portion 24a, 24b is controlled so that the overall size of the eleventh pole 20 of the capacitor is almost the same as that of the conventional one.

Next, an example of a method for manufacturing a semiconductor memory element having the above structure will be described with reference to FIG.

■ An insulating film 13 made of a silicon oxide film is placed on a semiconductor substrate 10 on which a MOS transistor is formed by a well-known method.
A contact hole 16 is formed in a region of the insulating film 13 corresponding to the impurity diffusion layer 12 forming the drain [see FIG. 2(a)].

■ By coating the entire upper surface with a polysilicon film doped with n-type impurities such as phosphorus using CVD technology and patterning this polysilicon film by anisotropic etching, the 11th disk portion 20 of the pole 20 is [Figure 2 (
bl].

(2) A silicon oxide film 1 is laminated on the entire upper surface in a thickness corresponding to the desired height of the inner cylindrical portion 24a (see FIG. 2, 10+).

(2) By patterning this silicon oxide film 1 using photolithography, a cylindrical silicon oxide film 1 corresponding to the size of the contact hole 16 is left [see FIG. 2 (di)].

■ The entire upper surface is coated with n such as phosphorus using CVD technology.
A polysilicon film 2 doped with type impurities is coated [see FIG. 2 (el)].

■ By patterning the polysilicon film 2 by anisotropic etching, only the polysilicon film 2 surrounding the outer peripheral surface of the above-mentioned cylindrical silicon oxide film 1 is left [see Fig. 2 (fl)].This remaining polysilicon film 2 is the inner cylindrical portion 24a.

■ A silicon oxide film 3 is formed on the entire upper surface, and a suitable solvent containing an oxide film component is applied to the entire upper surface by SOG (spin-on glass method) and annealed to form the desired outer cylindrical portion 24b. An oxide film 4 having a thickness corresponding to the height dimension is formed [see FIG. 2 (illustration)].

(2) Thereafter, by etching back the top surface of the oxide film 4, the top surface of the inner cylindrical portion 24a is exposed (see FIG. 2).

■ By patterning the silicon oxide film 3 and the oxide film 4 using photolithography technology, the inner cylindrical part 24 is formed.
Only the silicon oxide film 3 and oxide film 4 around a are left in a cylindrical shape, and the outer peripheral edge portion of the disk portion 23 and the surface of the insulating film 13 are exposed [see FIG. 2 (1)].

[Phase] This entire upper surface is made of polysilicon l! doped with n-type impurities such as phosphorus using CVD technology, similar to the above (■). 5 [see Figure 2 01].

0 By patterning the polysilicon film 5 by anisotropic etching, only the cylindrical silicon oxide film 3 and the polysilicon film 5 around the oxide film 4 left in step (3) are left in a cylindrical shape [Fig. (See kl) This remaining polysilicon film 5 becomes the outer cylindrical portion 24b.

■ Inner cylindrical part 24 with appropriate wet etching
cylindrical polysilicon film 1 and inner cylindrical portion 24 in a
The cylindrical silicon oxide film 3 and the oxide film 4 surrounded by the inner cylindrical part 24a and the outer cylindrical part 24b are removed to completely expose the inner cylindrical part 24a and the outer cylindrical part 24b [FIG. 2 (1)]
reference〕.

■ After this, the inner cylindrical part 24a that constitutes the first electrode 20
By forming a dielectric 21 made of a thermal oxide film and a second electrode 22 made of a polysilicon film doped with an n-type impurity such as phosphorus on the outer surfaces of the outer cylindrical part 24b and the disk part 23, the second electrode 22 is formed. The structure is shown in Figure 1.

In the above embodiments, the first electrode 20 constituting the capacitor is provided with two cylindrical portions 24a and 24b, but the present invention also includes structures having two or more cylindrical portions.

〔Effect of the invention〕

As described above, in the semiconductor memory element of the present invention, the shape of the capacitor is devised to make the surface area larger than that of the conventional one, thereby increasing the charge storage capacity compared to the conventional one, so that charge leakage does not occur. It is possible to prevent the occurrence of inconveniences such as the information being reversed when it is memorized.
It can contribute to improving credibility.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 show one embodiment of the present invention;
The figure is a vertical cross-sectional view of a semiconductor memory element, and FIG.
2 is a process diagram showing the manufacturing process of the semiconductor memory element shown in FIG. 1. FIG. FIG. 3 is a longitudinal sectional view showing a conventional semiconductor memory element. 11... Impurity diffusion layer 12... Impurity diffusion layer 13... Insulating film 16... Contact hole 20... First electrode 21... Dielectric 2
2... 2nd'W1 pole 23... Disc part 24a
...Inner cylindrical part 24b...Outer cylindrical part 4a/Figure

Claims (1)

[Claims] (1) A semiconductor memory element composed of a MOS transistor and a capacitor, the capacitor being provided on an insulating film covering the MOS transistor and partially in contact with an impurity diffusion layer forming the source or drain of the MOS transistor. a first electrode consisting of a disk portion and a plurality of cylindrical portions formed concentrically above the disk portion; a dielectric covering an outer surface of the first electrode; and a further outer surface of the dielectric. a second electrode covering the semiconductor memory element.