JPH05304251A - Semiconductor device - Google Patents

Abstract

PURPOSE:To provide a semiconductor device in which a capacitor dielectric film is protected against degradation of withstanding voltage and capacity is increased by entirely making thin the capacitor insulation film. CONSTITUTION:The semiconductor device includes a capacitor formed by depositing a capacitor dielectric film 18 on a capacitor lower electrode 17 and then providing a capacitor upper electrode 22 of aluminum or aluminum alloy thereon. The capacitor dielectric film 18 has multilayer structure composed of three or more layers 19, 20, 21 in which the intermediate layer 20 is composed of a film less reactive to aluminum than the uppermost layer 21 which is composed of a film having selectivity in the etching of the intermediate layer 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly, it can be applied to an LSI having a capacitor having a metal electrode such as Al formed on the upper part thereof, and particularly prevents deterioration of withstand voltage of a capacitor insulating film. The present invention relates to a semiconductor device capable of increasing the capacitance by reducing the thickness of the entire capacitor insulating film.

In recent years, LSIs such as PLLs (Phase Locked Loops) and prescalers have been widely used in many communication devices such as telephones and exchanges. However, these LSIs are conventionally attached externally as the devices become smaller. The number of cases in which the previously used capacitor element (used for a resonance circuit or the like) is mounted on an LSI is increasing. In this case, in view of compatibility with existing processes, an Al gate is used as an upper electrode without using a poly Si gate widely used in MOS memories and the like. In addition, a nitride film is also used as the capacitor insulating film in terms of compatibility with existing processes and capacity.

[0003]

2. Description of the Related Art FIG. 5 is a cross-sectional view showing the structure of a conventional semiconductor device, and here shows the structure of a capacitor portion. In FIG. 5, 31 is a substrate such as Si and 32 is a substrate
A field oxide film such as SiO ₂ formed on 31 is a capacitor lower electrode such as poly Si formed on the field oxide film 32. Next, 34 is a capacitor insulating film made of a silicon nitride film formed on the capacitor lower electrode 33, and 35 has an opening 36a on the capacitor lower electrode 33 and an opening 36b on the capacitor insulating film 34. It is an insulating film made of SiO ₂ or the like. 37a is a capacitor upper electrode such as Al formed on the capacitor insulating film 34 in the opening 36b, and 37b is an electrode such as Al formed so as to contact the capacitor lower electrode 33 in the opening 36a. Is.

In the conventional semiconductor device, Al-based metal is used for the capacitor upper electrode 37a as described above. However, when the electrode is formed of Al-based metal, heat treatment at high temperature may be performed in order to stabilize the electrode characteristics. This heat treatment causes a reaction between Al of the capacitor upper electrode 37a and the nitride film of the capacitor insulating film 34 to form a pinhole in the capacitor insulating film 34 of the nitride film, resulting in a problem that the breakdown voltage deteriorates.

Further, A is formed on the capacitor insulating film 34 made of a nitride film.
A method of forming a two-layer structure using an oxide film that does not react with l can be considered. However, since the Al capacitor upper electrode 37a is formed on this oxide film, when the insulating film covering this two-layer structure is opened, the oxide film is etched by an etching treatment such as hydrofluoric acid, so that the withstand voltage is reduced. It is not preferable because it deteriorates significantly. For this reason, conventionally, a method has been adopted in which the effect of pinholes is reduced and the breakdown voltage is secured by simply thickening the capacitor insulating film 34 of a nitride film.

[0006]

However, as described above, when the thickness of the capacitor insulating film 34 of the nitride film is increased in order to secure the breakdown voltage, there is a problem that the capacitance is reduced. Therefore, miniaturization of the LSI, and eventually the LSI
It was a big obstacle in reducing the size of the device equipped with.

On the other hand, if the capacitor insulating film 34 of the nitride film is thinned in order to increase the capacitance, as described above, the capacitor insulating film 34 of the nitride film is formed by the reaction with Al during the heat treatment.
There was a problem that pinholes were likely to be formed inside and the breakdown voltage deteriorated. Therefore, it is an object of the present invention to provide a semiconductor device capable of preventing the breakdown voltage of the capacitor insulating film from being deteriorated and further increasing the capacitance by reducing the thickness of the entire capacitor insulating film.

[0008]

To achieve the above object, a semiconductor device according to the present invention has a capacitor insulating film formed on a capacitor lower electrode, and a capacitor upper electrode made of aluminum or an alloy thereof is formed on the capacitor insulating film. In the semiconductor device having the capacitor, the capacitor insulating film has a laminated structure of at least three or more insulating films, and in the laminated structure, the intermediate layer is a film that is less likely to react with aluminum than the uppermost layer. And the uppermost layer is a film having etching selectivity with respect to the intermediate layer.

In the present invention, the upper electrode is formed on the laminated structure via a barrier metal for preventing the reaction between aluminum and silicon, and in the laminated structure, the uppermost layer and the uppermost layer are formed. The lower layer is made of a silicon nitride film, and the intermediate layer is preferably made of a silicon oxide film, a tantalum oxide film, or alumina.

As the capacitor upper electrode according to the present invention, a metal film containing at least Al can be preferably applied, and examples thereof include a metal film of Al, Al alloy or the like. The oxide film may be at least an oxide film that suppresses the reaction with the main component forming the capacitor upper electrode, and examples thereof include a silicon oxide film, a tantalum oxide film, and alumina. Note that if this oxide film is formed too thick, the capacity decreases and it is difficult to control. Therefore, it is preferable to form the oxide film appropriately.

In the present invention, the preferable total film thickness of the capacitor insulating film is 550 Å or less, and when it exceeds 550 Å, the capacity is extremely reduced, which is not preferable.

[0012]

In the present invention, as shown in FIGS. 1 and 2 of Embodiment 1 described later, a capacitor is formed by using a capacitor insulating film 18 in which a silicon nitride film 19, a silicon oxide film 20 and a silicon nitride film 21 are sequentially formed. I am configuring. As described above, since the uppermost layer of the capacitor insulating film 18 is composed of the silicon nitride film 21, it is possible to prevent the capacitor insulating film 18 from being damaged by the hydrofluoric acid treatment before forming the Al capacitor upper electrode 22. Moreover, since the intermediate layer between the uppermost silicon nitride film 21 and the lowermost silicon nitride film 19 is made of the silicon oxide film 20, the Al of the Al capacitor upper electrode 22 is heat-treated.
Even if the uppermost silicon nitride film 21 reacts with each other to form a pinhole in the uppermost silicon nitride film 21, the intermediate silicon oxide film 20 is unlikely to react with Al of the capacitor upper electrode 22. The silicon oxide film 20 can prevent the effect of pinholes. Further, the capacitance of the capacitor itself can be ensured by the two layers of the intermediate silicon oxide film 20 and the lowermost silicon nitride film 19.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a sectional view showing the structure of a semiconductor device according to Embodiment 1 of the present invention, in which a bipolar transistor portion A and a capacitor portion B are shown. The illustrated example is ESPER (Emitter-Base Self-a).
llgned Structure with Pol
isilicon Electric loads and R
This is a case where the present invention is applied to a semiconductor device called esistors). In FIG. 1, 1 is a substrate such as Si, and 2
Is a field oxide film such as SiO ₂ formed by oxidizing the substrate 1, and 3 and 4 are, for example, p ^{+ type} external base diffusion layers, for example, p type internal base diffusion layers. Then
Reference numeral 5 is, for example, an n ⁺ type emitter diffusion layer formed in the internal base diffusion layer 4, and reference numerals 6 and 7 are each an external base lead-out electrode such as poly-Si contacting the external base diffusion layer 3 and a collector diffusion layer. It is a collector lead-out electrode made of poly-Si or the like. Next, 8 is an insulating film such as SiO ₂ , 9 is an emitter extraction electrode such as poly-Si formed so as to contact the emitter diffusion layer 5 in the emitter opening 10, and 11 is an emitter extraction electrode 9 It is a sidewall conductive film made of poly-Si or the like that contacts with.
Next, 12 is a collector electrode such as Al formed so as to contact the collector extraction electrode 7 in the collector opening 13, and 14 is an emitter electrode such as Al formed so as to contact the emitter extraction electrode 9. Yes,
Reference numeral 15 is a base electrode such as Al formed so as to contact the external base lead electrode 6 in the base opening 16. Next, 17 is a capacitor lower electrode such as poly-Si formed on the field oxide film 2, and 18 is a silicon nitride film 19, a silicon oxide film 20, and a silicon nitride film 21 formed on the capacitor lower electrode 17. It is a capacitor insulating film composed of layers. 22 is a capacitor upper electrode such as Al formed on the capacitor insulating film 18 in the opening 23, and 24 is a capacitor such as Al formed so as to contact the capacitor lower electrode 17 in the opening 25. Lower electrode
17 This is an electrode for extraction.

Next, FIG. 2 is a diagram for explaining a method of manufacturing a semiconductor device according to the first embodiment of the present invention. Here, FIG.
3 shows a method of manufacturing the capacitor part B of FIG. In FIG. 2, the same reference numerals as those in FIG. 1 denote the same or corresponding portions, and 17a
Is a polysilicon film. Next, a method of manufacturing the semiconductor device will be described. Here, a method of manufacturing the capacitor unit will be specifically described.

First, as shown in FIG. 2A, the LOCO
The Si substrate 1 is thermally oxidized by the S method to form a field oxide film 2 with a film thickness of about 5000Å, and poly-Si is deposited on the field oxide film 2 by a CVD method to form a polysilicon film 17a with a film thickness of about 3000Å. After that, the polysilicon film 17a is doped with phosphorus. Then, Si ₃ N ₄ , SiO ₂ and Si ₃ N ₄ are sequentially deposited on the polysilicon film 17a by the CVD method to form a silicon nitride film 19 having a film thickness of about 300Å and a film thickness 1
A silicon oxide film 20 of about 00Å and a silicon nitride film 21 of about 100Å are sequentially formed.

Next, as shown in FIG. 2B, the silicon nitride film 21, the silicon oxide film 20, and the silicon nitride film 19 are etched by RIE or the like to form a capacitor insulating film 18, and then poly-etched by RIE or the like. The silicon film 17a is etched to form the capacitor lower electrode 17. Next, FIG.
As shown in (c), after depositing SiO ₂ on the entire surface by a CVD method to form an insulating film 8 having a film thickness of about 5000 Å, the insulating film 8 is wet-etched to form a silicon nitride film 21 of the capacitor insulating film 18. The opening 23 exposed is formed, and the opening 25 exposing the capacitor lower electrode 17 is formed.

Then, the capacitor insulating film 18 in the opening 23
By forming the Al capacitor upper electrode 22 thereon and the Al electrode 24 so as to contact the capacitor lower electrode 17 in the opening 25, a capacitor portion as shown in FIG. 2D can be obtained. it can. Before forming the Al electrode, a pretreatment with hydrofluoric acid or the like is performed to remove the exposed native oxide film formed on the surfaces of the capacitor insulating film 18 and the capacitor lower electrode 17.

That is, in this embodiment, the silicon nitride film
A capacitor is formed by using a capacitor insulating film 18 in which a silicon oxide film 20, a silicon oxide film 20, and a silicon nitride film 21 are sequentially formed. As described above, since the uppermost layer of the capacitor insulating film 18 is composed of the silicon nitride film 21, it is possible to prevent the capacitor insulating film 18 from being damaged by the hydrofluoric acid treatment before forming the Al capacitor upper electrode 22. Moreover, since the intermediate layer between the uppermost silicon nitride film 21 and the lowermost silicon nitride film 19 is composed of the silicon oxide film 20, it is possible to perform Al by heat treatment.
Al of capacitor upper electrode 22 and uppermost silicon nitride film
Even if 21 reacts and a pinhole is formed in the uppermost silicon nitride film 21, the intermediate silicon oxide film 20 does not easily react with Al of the capacitor upper electrode 22, so the intermediate silicon oxide film 20 has a pinhole. Can stop the effect of.

Therefore, even if the overall thickness of the capacitor insulating film 18 is reduced to secure the capacitance, the breakdown voltage can be prevented from deteriorating. (Embodiment 2) FIG. 3 is a sectional view showing the structure of a semiconductor device according to Embodiment 2 of the present invention, in which a capacitor portion is shown. In FIG. 3, the same reference numerals as those in FIGS. 1 and 2 denote the same or corresponding portions, and in the first embodiment, the case where the silicon oxide film 20 is formed on the silicon nitride film 19 by the CVD method has been described. As described above, first, the silicon nitride film 19 is grown to about 300Å, and the silicon nitride film 19 is thermally oxidized (wet oxidation, 900 ° C, 30 ° C) as an intermediate layer.
Alternatively, the silicon nitride film 21 having a film thickness of about 30Å may be formed, and then the silicon nitride film 21 having a film thickness of about 200Å may be grown on the silicon oxide film 20 as the uppermost layer. In the case of this thermal oxidation, the silicon oxide film 20 can be formed in a thinner film than in the case of the first embodiment in which the silicon oxide film 20 by the CVD method is used for the intermediate layer, so that the capacitance can be further increased. (Embodiment 3) FIG. 4 is a sectional view showing the structure of a semiconductor device according to Embodiment 3 of the present invention, in which the capacitor portion is shown. 4, the same reference numerals as those in FIGS. 1 to 3 denote the same or corresponding parts. When forming the bipolar transistor part together with the capacitor part as shown in FIG.
In the bipolar transistor part, Al forming the electrode is S
A barrier metal may be interposed between the electrodes so as not to react with i. In this case, a barrier metal is also formed on the electrode of the capacitor due to the process consistency. In FIG. 4A of this embodiment, Al having a film thickness of about 200Å is used.
A capacitor upper electrode 22 is formed from an Al.Si film 28 having a film thickness of about 5000Å through a contact metal film 26 and a TiN barrier metal film 27 having a film thickness of about 1000Å. When forming the capacitor upper electrode 22 through the TiN barrier metal film 27 as described above, after the TiN barrier metal film 27 is formed as shown in FIG. By performing the above, the barrier property can be further improved. At the time of this barrier annealing, there is a possibility that pinholes may be generated by reacting with Al in the conventional capacitor insulating film having only a single layer of silicon nitride film. The reaction can be stopped by the intermediate silicon oxide film 20.

In the first to third embodiments, the case where the silicon oxide film 20 is used as the intermediate layer between the uppermost silicon nitride film 21 and the lowermost silicon nitride film 19 has been described. The film is not limited to this, as long as it is a film that suppresses the reaction with Al of the capacitor upper electrode 22, and it may be configured using a tantalum oxide film, alumina, or the like.

[0021]

According to the present invention, it is possible to prevent the breakdown voltage of the capacitor insulating film from being deteriorated and to increase the capacitance by reducing the thickness of the entire capacitor insulating film.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a method of manufacturing a semiconductor device according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing a structure of a semiconductor device according to a second embodiment of the present invention.

FIG. 4 is a sectional view showing a structure of a semiconductor device according to a third embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a structure of a conventional semiconductor device.

[Explanation of symbols]

 17 Capacitor lower electrode 17a Polysilicon film 18 Capacitor insulating film 19 Silicon nitride film 20 Silicon oxide film 21 Silicon nitride film 22 Capacitor upper electrode 23 Opening 24 Electrode 25 Opening 26 Al contact metal film 27 TiN barrier metal film 28 Al ・ Si film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 21/318 M 7352-4M

Claims (3)

[Claims] 1. A semiconductor device having a capacitor in which a capacitor insulating film is formed on a capacitor lower electrode and a capacitor upper electrode made of aluminum or an alloy thereof is formed on the capacitor insulating film. It has a laminated structure of three or more insulating films, and in the laminated structure, the intermediate layer is made of a film that is less likely to react with aluminum than the uppermost layer, and the uppermost layer has an etching selection for the intermediate layer. A semiconductor device comprising a film having properties. 2. The upper electrode is formed on the laminated structure via a barrier metal for preventing a reaction between aluminum and silicon.
The semiconductor device described. 3. The laminated structure according to claim 1, wherein the uppermost layer and the lowermost layer are made of a silicon nitride film, and the intermediate layer is made of a silicon oxide film, a tantalum oxide film, or alumina. The semiconductor device described.