JPS60107854A - Capacitor - Google Patents

Abstract

PURPOSE:To obtain the capacitor of large capacity occupying a small area by a method wherein insulating films for interelement isolation are provided on the circumferential part of an Si substrate, a lower electrode is formed on the region ranging from the substrate surface to the film edge part exposed between said interelement isolation insulating films, and when the capacitor is formed by providing an upper electrode on the whole area including the lower electrode through the intermediary of a Ta2O5 film, these electrodes are constituted by W, Mo, W-silicide, Mo-silicide and the like. CONSTITUTION:Insulating films 32 for interelement isolation are formed on the circumferential part of an Si substrate 31, a lower electrode 33 of approximately 1,000Angstrom in thickness, consisting of W, Mo, W-silicide, Mo-silicide and the like, is deposited on the region ranging from the surface of the substrate 31, exposed between the insulating film 32, and the film 32. Then, the entire surface including said lower electrode 33 is covered by a Ta2O5 film 34 of approximately 300Angstrom in thickness, and an upper electrode 35 of the same composition as the electrode 33 is coated on the film 34. As a result, an excellent capacitor having the capacitance density of 7.26fF/mum<2> and the characteristics wherein leak current will be maintained at 10<-6>A/cm<2> can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to large-scale integrated circuits, and more particularly to small-area, large-capacity capacitors necessary for realizing large-scale integrated circuits.

[Background of the invention]

In recent years, the integration of LSIs has been increasing. In particular, research into the practical use of dynamic memory (D-RAM) is progressing to the point where the degree of integration is 1 megabit (IMb) per chip. As the integration becomes higher, the individual elements' are becoming increasingly finer.

In dynamic memory memory cells, the reduction in the area of the charge product capacitor that performs the storage function is important for IMb.
This is the key to realizing dynamic memory, as shown in, for example, Nikkei Electronics Magazine 1983.7.18, Issue 196''.

As shown in the same magazine, even in the IMb dynamic memory, a memory cell can be made up of one transistor and one capacitor at a cost of $/4'. However, each capacitor needs to have a capacitance of at least 60 fF in order to prevent the memory from malfunctioning due to signal noise or incidence of alpha rays.

On the other hand, in order to fit the IMb memory cell into a chip with an area of about 1c4, the area of one capacitor is 10μm.
It is necessary to keep it below about 2.

Therefore, the capacitance per unit area of the capacitor is 6
It needs to be 1F/μm2 or more.

However, in order to have a sufficiently low defect density for application to LSI, thermally oxidized silicon, which is the dielectric material of capacitors used in conventional dynamic memories, needs to have a film thickness of 150 Å or more. However, the capacitance is less than 21F/μm2, making it difficult to realize an IMb dynamic memory using conventional capacitors.

Therefore, stack up to realize IMb dynamic memory! 51 (S T C: 5 tacked c
apactor ) and trench capacitor section /' (CCC
: corrugated capetor cell
) are being considered, but these cells have the following disadvantages.

In STC, 1. Polycrystalline Si for capacitor electrodes is laminated, so the steps are high and processing is relatively difficult.

2. A margin for adjusting the distance of the polycrystalline Si is required, and the degree of integration is not as high as expected.

In addition, since deep grooves are formed in CCC, the manufacturing process becomes complicated, making it difficult to reduce costs.

2. Stress is concentrated at the end of the deep groove, which tends to cause defects such as dislocations.

3. When the deep grooves are close together, a punch-through current flows at the bottom end of the monument and stored information tends to be lost.

In order to prevent the above cell defects, the base layer must be 10 μm thick.
It is also necessary to form a dielectric material having a capacitance density of 6 fF/μm 2 or more on a flat Si surface of m 2 . In addition, in order for the memory cell to retain stored information, the leakage current density of the capacitor is 10-'A at a memory operating voltage of 5V.
/cnl or less.

FIG. 1 shows a cross section of a capacitor portion of a conventional dynamic memory. Here, 1 is a Si substrate, 2 is an isolation insulating film, 3 is a Ta205 film with a film thickness of 100A to maintain a capacitance density of 61F/μm2 or more, and 4 is w
It is the t-pole. The current-voltage characteristics of this capacitor are shown in FIG. The capacitance density of this capacitor is 7.51F/μm
However, in order to be applied to IMb dynamic memory, it is necessary that the leakage current be less than 10 −6 A/cd1 at an operating voltage of 5 V. In Figure 1, the leakage current is 0.0 at the memory operating voltage of 5V. It is difficult to apply it to dynamic memory at IA/crl level. Therefore, the above W/Ta 205/S! type capacitor cannot satisfy the required characteristics of dynamic memory.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above drawbacks of the prior art, it is an object of the present invention to provide a small-area, large-capacity capacitor that is particularly necessary for realizing a highly integrated dynamic memory.

[Summary of the invention]

The structure of the present invention for achieving the above object is that the second electrode is made of at least one of the group consisting of W, Mo, W silicide, and MO silicide.

In the present invention, Ta2, which has a large dielectric constant, is placed on a flat Si surface.
When forming a capacitor using 05 film etc., S
By using a high-attractive metal such as W or Mo or a silicide of W or Mo at the interface between i and Ta205, a capacitor with a small area, large capacity, and good dielectric strength can be formed.

[Embodiments of the invention]

show. 3 is a Si substrate, 32 is an isolation insulating film between elements, 33
is a W film with a thickness of 1000 people, and 34 is a T film with a thickness of 300 people.
A205 film, 35 is a W electrode. The capacitance density of this capacitor is 7.26 fF/μm2.

FIG. 4 shows a positive characteristic for the current -1 of the same capacitor.

From this figure, when the leakage current is 10-'A/crA, the voltage is 10V or more, which has a sufficient margin for the operating voltage of 5V. Therefore, W/T a 20 according to the invention
It can be seen that the s/W capacitor provides the capacitor necessary to realize a dynamic memory.

Here, the former W/T 3205 (95 people)/Si
and W/Ta 20s (300 people)/W When comparing the characteristics of the capacitors, even though the capacitance density of both is almost the same, the former has a breakdown voltage of 2■ and the latter has IOV, so the latter capacitor is better than the former capacitor. It can be seen that five times as much charge can be stored. Here, the breakdown voltage and leakage current are 10
-' A/c4 was defined as the voltage. In this way, the reason for the remarkable difference in characteristics even though the same Ta205 film is used as the dielectric is that the former capacitor has T
Since SjO* is formed in an oxidizing atmosphere using a reactive sputtering method or the like, SjO* with a low dielectric material is formed at the interface between Ta21ls and Si, lowering the capacitance density.
It is thought that i diffuses into Ta205 and reduces the insulation properties of Ta205. On the other hand, in the capacitor of the present invention, no oxide is formed on the surface of W during the formation of Ta205, and it is thought that this prevents the diffusion of Si from the Si substrate. Furthermore, since the reactivity between W and Ta205 is relatively small, a capacitor with good heat resistance can be obtained by using W or the like for the upper electrode.

Although this embodiment has been described using W as the electrode of the capacitor, the presenters were able to obtain similar effects using at least MO, W silicide + Mo silicide, in addition to W.

In addition to tantalum oxide, niobium oxide, hafnium oxide, titanium oxide, aluminum oxide,
Silicon nitride or the like may also be used.

〔Effect of the invention〕

According to the present invention, a small-area, large-capacity capacitor required for realizing an IMb dynamic memory can be formed on a flat contact hole.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional capacitor, Fig. 2 is a current-voltage characteristic of a conventional capacitor, Fig. 3 is a cross-sectional view of a capacitor as an embodiment of the present invention, and Fig. 4 is a cross-sectional view of a capacitor of the present invention. This is a current-4EE characteristic. 1.31...Si substrate, 2,32...Inter-element isolation insulating film, 3...Ta205 film, 4...electrode, 33...
・Lower W power station 1st/3rd Figure 5 Summer 2 Figure Y4- Figure

Claims (1)

[Claims] 1. In a capacitor in which a first electrode/insulating film/second electrode/substrate are laminated, the second electrode is made of W.
, Mo, W silicide, and MO silicide. 2. The capacitor according to claim 1, wherein the first electrode is made of at least one member of the group consisting of W, Mo, W silicide, and MO silicide. 3. The capacitor according to claim 1, wherein the insulating film is made of tantalum oxide, niobium oxide, hafnium oxide, titanium oxide, aluminum oxide, or silicon nitride. 4. The capacitor according to claim 1, wherein the substrate is Sj.