JPH05114698A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To suppress the growth of SiO2 on the interface of an oxide film while the oxide film is made compacter. CONSTITUTION:A process for forming a capacitance element section used for DRAMs is constituted of a process for forming a lower polysilicon electrodes 3, process for forming a tantalum oxide film 4 on the electrode 3, process for performing a plasma process of a gas containing oxygen, process for heat- treating the film 4 in an inert gas atmosphere of N2, etc., and a process for forming an upper electrodes 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a capacitive element portion used in VLSI such as dynamic random access memory (DRAM).

[0002]

2. Description of the Related Art It has been proposed to use a tantalum oxide film capable of increasing a capacitance value per unit area in a capacitive element portion of a VLSI memory device such as a 64 Mbit DRAM (eg, 1989 VLSI Technology Symposium Page 25 ( Prc.of
1989 VLSI technology Symp
osium p. 25)).

FIG. 4 shows the general structure of the proposed capacitive element section. A process of forming the capacitive element portion shown in FIG. 4 will be described next. Polysilicon is deposited on the N-type substrate 1 by a chemical vapor deposition method, element isolation regions 2 are formed, phosphorus (P) is ion-implanted and activated, and then a polysilicon lower electrode 3 is formed by a normal lithography technique. To form (Fig. 4
(A), (b)).

A tantalum oxide film 4 is formed on the polysilicon lower electrode 3 by a low pressure chemical vapor deposition method using ethoxy tantalum as a main material (FIG. 4C), and a film densification process is performed in an oxygen atmosphere. (FIG. 4D) Subsequently, the upper tungsten electrode 15 is formed to complete the capacitive element portion shown in FIG.

[0005]

The conventional capacitive element using the tantalum oxide film has a big problem to be solved. The problem is that the capacitance value does not increase as designed because a silicon oxide film of 10 to 20 Å is formed at the interface between the polysilicon lower electrode and the tantalum oxide film. The present inventor conducted a detailed process study to clarify the cause. As a result, it was found that this silicon oxide film is mainly formed when a tantalum oxide film is deposited by the chemical vapor deposition method and then heat-treated in an oxygen (O ₂ ) atmosphere. The natural oxide film on the polysilicon is not a problem because it can be removed by a complete pretreatment. However, when the chemical vapor deposition method using organic tantalum as a raw material (which is excellent in mass productivity) is adopted, densification treatment after film deposition is essential.

Therefore, an object of the present invention is to provide a method of manufacturing a semiconductor device in which a densification treatment is found instead of a heat treatment in an oxygen atmosphere which has been conventionally used.

[0007]

In order to achieve the above object, in a method of manufacturing a semiconductor device according to the present invention, a super LSI such as a dynamic random access memory is provided.
In the process of forming the capacitive element portion used for, a polysilicon lower electrode is formed, and a tantalum oxide film (Ta ₂ O ₅ )
After the formation, a process of performing a plasma treatment of a gas system containing oxygen, further performing a heat treatment in an atmosphere of an inert gas such as N ₂ and subsequently forming an upper electrode is included.

The polysilicon lower electrode is doped with phosphorus (P).

The tantalum oxide film is formed by a chemical vapor deposition method using organic tantalum as a raw material.

The heat treatment temperature is 600 to 100.
It is set in the range of 0 ° C.

The upper electrode is made of titanium nitride, tungsten or molybdenum, and the electrode is formed by a sputtering method or a chemical vapor deposition method.

[0012]

In the capacitor element forming process of the present invention, a polysilicon lower electrode is formed, and a tantalum oxide film (Ta ₂ O ₅ ) is formed thereon.
After the formation, a plasma treatment of a gas system containing oxygen is performed, a heat treatment is further performed in an atmosphere of an inert gas such as N ₂ , and then a metal upper electrode is formed.

By treating the tantalum oxide film deposited by the chemical vapor deposition method with oxygen plasma and then heat-treating it in an inert gas atmosphere, the same densification as in the conventional heat treatment in an oxygen atmosphere is achieved. Moreover, the problem that the polysilicon lower electrode is oxidized does not occur.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a flowchart showing Embodiment 1 of the present invention in the order of steps.

In FIG. 1A, an LOCOS (Local Oxidation) is formed on an N-type silicon single crystal substrate 1.
This shows the formation of an element isolation region 2 called Separation).

Next, a polysilicon film is deposited on the substrate 1 by a chemical vapor deposition method, patterned by a usual lithography / etching technique, and phosphorus (P) is doped by a thermal diffusion method to form a polysilicon lower electrode. 3 (Fig. 1
(B)).

Then, after removing the natural oxide film on the polysilicon lower electrode 3, the tantalum oxide film 4 is immediately grown by chemical vapor deposition (FIG. 1 (c)). In the chemical vapor deposition process for the tantalum oxide film 4, a normal vertical LPCVD (low pressure chemical vapor deposition) device was used. As tantalum raw material,
Ethoxy tantalum [Ta (OC ₂ H ₅ ) ₅ ] was used. A general N ₂ bubbling method was used as a means for vaporizing ethoxy tantalum, which is a liquid material (room temperature). As the growth conditions for the tantalum oxide film, an ethoxy tantalum gas flow rate of 10 sccm, an oxygen gas flow rate of 100 sccm, a reaction gas pressure of 0.5 Torr, and a growth temperature of 450 ° C. were used.
The film deposition rate under this growth condition was 5Å / min, and in this example, a tantalum oxide film of 50 to 100Å was deposited.

After depositing the tantalum oxide film, O ₂ plasma treatment was performed as shown in FIG. 1 (d). Since this O ₂ plasma treatment is a step characterizing the present invention, the apparatus used here will be described with reference to the drawings. A plasma processing apparatus used in connection with the present invention is shown in FIG.

In FIG. 2, 6 is a single-wafer plasma chamber. 7 is a susceptor made of a titanium alloy, which is installed in terms of electric potential. 8 is a shower mechanism for introducing O ₂ gas (made of titanium alloy)
Thus, it also serves as a 13.56 MHz high frequency applying electrode for generating plasma. On the susceptor 7, a substrate 11 in an O ₂ plasma processing step is placed. 9 is a high frequency generator, and 10 is a pump. O ₂ plasma conditions are O ₂ gas flow rate of 100 sccm and gas pressure of 0.5 To.
rr, 13.5 MHz high frequency power 0.5 W / cm ² was used. Although a sufficient effect can be obtained if the treatment time is 10 seconds or more, in the present embodiment, the O ₂ plasma treatment was performed for 20 seconds.

After the O ₂ plasma treatment, the N ₂ heat treatment shown in FIG. 1 (e) was performed. For this N ₂ heat treatment apparatus, a heat treatment apparatus having a load lock mechanism and having a back pressure of a vacuum degree of 10 ⁻⁹ Torr was used. N
_{As the 2} gases, those having a high purity of 99.99999% were used. Although the heat treatment temperature achieves the object of the present invention within the range of 600 to 1000 ° C., in this embodiment, the N ₂ heat treatment was performed at 800 ° C. for 30 minutes, which is easy to control.

Successively, titanium nitride was deposited as an upper electrode by a sputtering method, and two layers of TiN / Ta ₂ O ₅ were simultaneously patterned by a usual lithography / etching technique, and Example 1 shown in FIG. The capacitive element of was formed.

In order to confirm the effect of the present invention, the current-electric field characteristic of the tantalum oxide film was measured by using the formed capacitance element, and it was found to be the same as the characteristic of the film formed by the conventional method. It was confirmed that the densification treatment in the invention has a sufficient effect on the densification. Further, the silicon oxide film formed at the interface between the tantalum oxide film and the polysilicon lower electrode is formed by the conventional method with 5 Å or less (evaluated from the capacitance-voltage characteristics of a 50-100 Å tantalum oxide film level capacitive element). It was much thinner than the case.

(Second Embodiment) Next, a second embodiment of the present invention will be described. The second embodiment is characterized in that the inert gas heat treatment after the O ₂ plasma treatment is a rapid heating short-time treatment method using a lamp heating device.

In this embodiment, the process flow is the same as in the first embodiment. However, in Example 2, O
_{2 As the} inert heat treatment after the plasma treatment (Fig. 1 (d)), a rapid heating short time treatment method was used. FIG. 3 shows a lamp heating device used for rapid heating and short-time treatment. This device basically comprises a single-wafer quartz chamber 12 and a heating lamp 1.
3 and 3. The substrate 11 is the quartz chamber 1
Heated by light through 2.

When the rapid heating short-time treatment method is used, the treatment temperature must be 850 ° C. or higher. In this example, the heat treatment with an inert gas after the O ₂ plasma treatment was performed at 900 ° C. for 30 seconds using a high-purity N ₂ (99.99999%) gas as an inert gas. Subsequently, a TiN upper electrode was formed in the same manner as in Example 1 to fabricate the capacitive element of Example 2 of the present invention.

With respect to the capacitive element formed in Example 2, the capacitance characteristics and the like were measured. As a result, as in Example 1, the effect of the present invention was confirmed.

[0028]

As described above, according to the present invention, in the step of forming the capacitive element portion, the polysilicon lower electrode is formed, the tantalum oxide film is deposited on the polysilicon lower electrode, and the plasma treatment is performed in a gas system containing oxygen. Since it is composed of a step of performing a heat treatment in an atmosphere of an inert gas such as N ₂ and then forming an upper electrode, a capacitance element having a large capacitance value is formed.
This is useful for manufacturing M to 1G DRAM.

[Brief description of drawings]

FIG. 1 is a flowchart showing Example 1 of the present invention in process order.

FIG. 2 is a conceptual diagram showing an apparatus for performing O ₂ plasma processing.

FIG. 3 is a conceptual diagram showing a single-wafer type N ₂ heat treatment apparatus used in Example 2.

FIG. 4 is a flowchart showing a conventional capacitive element formation step by step.

[Explanation of symbols]

 1 N-type silicon substrate 2 Element isolation region 3 Polysilicon lower electrode 4 Tantalum oxide film 5 Titanium nitride upper electrode 6 Single wafer plasma chamber 7 Susceptor 8 Shower mechanism 9 High frequency generator 10 Pump 11 Substrate 12 Single wafer quartz chamber 13 Heating Lamp 14 Substrate support mechanism 15 Tungsten electrode

Claims (5)

[Claims] 1. A step of forming a capacitive element portion used in a VLSI such as a dynamic random access memory, a polysilicon lower electrode is formed, a tantalum oxide film (Ta ₂ O ₅ ) is formed thereon, and then oxygen is added. A method of manufacturing a semiconductor device, comprising the steps of: performing a plasma treatment of a gas system containing the same, further performing a heat treatment in an atmosphere of an inert gas such as N ₂ , and then forming an upper electrode. 2. The polysilicon lower electrode is made of phosphorus (P).
The method for manufacturing a semiconductor device according to claim 1, wherein is doped with. 3. The method for manufacturing a semiconductor device according to claim 1, wherein the tantalum oxide film is formed by a chemical vapor deposition method using organic tantalum as a raw material. 4. The heat treatment temperature is 600 to 1000 ° C.
It is set to the range of 1.
A method of manufacturing a semiconductor device according to item 1. 5. The upper electrode is made of titanium nitride, tungsten or molybdenum, and the electrode is formed by a sputtering method or a chemical vapor deposition method. A method for manufacturing a semiconductor device as described above.