JPH088400A - Tantalum oxide thin film capacitor - Google Patents

Abstract

PURPOSE:To prevent deterioration of breakdown voltage by employing a material having high free energy for producing oxide in the electrode. CONSTITUTION:Pt is deposited by 200nm, as a lower electrode 3, on an Si substrate 4 and tantalum oxide is deposited, by 20-300nm, thereon followed by deposition of gold by 300nm as an upper electrode 1. A static opposing magnetron high frequency sputtering system is employed in the formation of the lower electrode 3 using Pt of 99.9% purity having diameter of 100 mm as a target, and in the deposition of tantalum oxide 2 using tantalum of 9.99% purity having diameter of 100m as a target. A resistor heating vacuum deposition system is employed in the deposition of gold for the upper electrode 1 with the deposition rate being controlled to a constant rate of 1nm/sec. This structure eliminates the abrupt deterioration of breakdown voltage in the vicinity of 450 deg.C of a conventional tantalum oxide thin film capacitor with regard to the relationship between the heat treatment temperature and the breakdown voltage of a tantalum oxide thin film capacitor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tantalum oxide thin film capacitor used for a semiconductor integrated circuit, a hybrid integrated circuit module substrate, or a multi-chip module substrate.

[0002]

2. Description of the Related Art Currently, semiconductor manufacturers are energetically promoting high integration of integrated circuits. Passive elements such as capacitors, resistors and coils are incorporated in the integrated circuit together with active elements. By reducing the area occupied by these passive elements, the chip size can be reduced and the manufacturing cost per chip can be reduced.

Among passive elements, each manufacturer is trying to use tantalum oxide having a relative dielectric constant of 25 as a dielectric material in order to reduce the occupied area of a capacitor, and especially DRAMs.
The application study is being actively promoted. In the Si substrate IC, Si is used as the lower electrode material of the thin film capacitor in order to simplify the process. In this case, in the heat treatment after forming the tantalum oxide thin film capacitor, extremely thin SiO ₂ having excellent pressure resistance is formed on the surface of the Si electrode, so that the withstand voltage of the tantalum oxide thin film capacitor does not deteriorate. However, since SiO ₂ having a small relative permittivity of 4 is present between the tantalum oxide and the electrode, the total capacitance is reduced. For example, when the film thickness of SiO ₂ is 1/4 of the film thickness of tantalum oxide, the capacitance is reduced to about 1/2. Therefore, a thin film capacitor having an MIM structure in which a metal is used instead of Si as an electrode material is currently receiving attention.

As an example of a tantalum oxide thin film capacitor having an MIM structure for application to DRAM, iEeTransaction on Electron Devices, Edee 37 (1990) No. 1
939 to 1947 (IEEE Transact
ion on Electron Devices, V
ol. ED-37 (1990), PP1939-194
There is a conventional example in which W is used for the upper electrode and the lower electrode as described in 7).

[0005]

As shown in FIG. 2, the tantalum oxide thin film capacitor having the MIM structure shown in the above-mentioned prior art has its breakdown voltage rapidly deteriorated to about 10 V by heat treatment at 450 ° C. or higher during the semiconductor manufacturing process. There was a problem. In case of DRAM, the memory capacity is 4Mb, 16Mb,
The operating voltage is 5 V, 3.
Since it tends to decrease to 3 V and 1.6 V, a withstand voltage of 5 V is sufficiently applicable after 64 Mb. On the other hand, for example, the operating voltage of the MMIC used in the front end portion of the portable radio telephone is 5V, and there is a problem that the required specifications of withstand voltage of 15V or higher are not satisfied. It is an object of the present invention to supply a tantalum oxide thin film capacitor whose breakdown voltage does not deteriorate due to the temperature profile during the process of manufacturing a semiconductor such as MMIC. However,
The breakdown voltage here is the voltage when the current density flowing through the thin film capacitor exceeds 1 μA / cm ² .

[0006]

In order to achieve the above object, a material having a higher free energy of oxide formation than tantalum as an upper and lower electrode material in contact with a tantalum oxide dielectric material, specifically, gold, Noble metals such as platinum, palladium and silver were used.

[0007]

[Function] The breakdown voltage is caused by the fact that oxygen in tantalum oxide is bound to the metal of the electrode material to lose oxygen in tantalum oxide and the tantalum oxide, which is an insulator, becomes conductive. Therefore, by using a material having a higher free energy of oxide formation as compared with tantalum, that is, a noble metal material that is difficult to oxidize for the electrode, it is possible to prevent the oxygen in tantalum oxide from binding with the electrode material and prevent the breakdown voltage from deteriorating. It will be possible.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.

A platinum film having a thickness of 200 nm is formed as a lower electrode 3 on a Si substrate 4 having a diameter of 3 inches, a tantalum oxide film 2 having a film thickness of 20 nm to 300 nm is formed thereon, and an upper electrode 1 is formed. Gold having a film thickness of 300 nm was formed by a resistance heating vapor deposition method. In order to examine the heat treatment temperature dependence of the withstand voltage of the tantalum oxide thin film capacitor thus manufactured, heat treatment was performed in a nitrogen gas atmosphere at 300 ° C. to 600 ° C. for 1 hour.

A static opposed magnetron high-frequency sputtering apparatus was used to deposit platinum on the lower electrode 3, and platinum having a diameter of 100 mm and a purity of 99.9% was used as a target. Argon was used as the discharge gas, and the pressure during film formation was 0.2P.
a, the discharge power is 4 W / cm ² , the distance between the target and the substrate is 55 mm, and the substrate temperature is room temperature or 300 ° C.
The film formation was performed under the conditions of heating to the following temperatures. The tantalum oxide film 2 was formed by using a stationary opposed magnetron high-frequency sputtering device, with a target having a diameter of 100 mm and a purity of 9
Tantalum of 9.99% was used. The discharge gas is a mixed gas of argon and oxygen, and the oxygen flow rate is 60% of the total flow rate.
Fixed to. The pressure during film formation was 0.2 Pa, and the discharge power was 4
The film formation was performed under the conditions of W / cm ² , the distance between the target and the substrate was 55 mm, and the substrate temperature was room temperature or a temperature of 300 ° C. or lower. For the gold film formation of the upper electrode 1, a resistance heating type vacuum vapor deposition apparatus was used and the film formation was performed at a constant film formation rate of 1 nm / sec. At this time, an upper electrode was formed by providing a mask on which holes having a diameter of 0.3 mm were opened at intervals of 2 mm on the vapor deposition surface.

FIG. 3 shows the relationship between the withstand voltage and the heat treatment temperature of a tantalum oxide thin film capacitor having a tantalum oxide film thickness of 100 nm.
Shown in It can be seen that the breakdown voltage gradually decreases from room temperature to 600 ° C., but the conventional tantalum oxide thin film capacitor as shown in FIG. FIG. 3 shows the relationship between the capacitance of the tantalum oxide thin film capacitor formed by the above method and the film thickness of the tantalum oxide layer. It can be seen that the relative permittivity shown in the figure is in good agreement with the calculated value of 25.

A second embodiment of the present invention will be described with reference to FIG.

A semiconductor substrate 4 made of GaAs or the like has a thickness of 400
The interlayer insulating film 5 using PSG of nm is formed by the thermal CVD method. A molybdenum film having a thickness of 250 nm and a gold film or a platinum film having a thickness of 500 nm are formed thereon by vapor deposition. Here, molybdenum is PS which is an interlayer insulating film.
It was inserted to obtain sufficient adhesion strength between G and gold or platinum. Unnecessary regions of this metal film are removed by argon ion milling using the photoresist as a mask to form the lower electrode 3. A 700 nm-thick PSG interlayer insulating film 5 is formed thereon by a thermal CVD method, and the PSG interlayer insulating film in the capacitor forming region is used as a mask for CF4.
It is removed by dry etching using gas. Further, a thickness of 200 n was obtained by the method and conditions described in the first embodiment.
m of tantalum oxide 2 is formed into a film, and unnecessary tantalum oxide other than the capacitor region is CF ₄ by using a photoresist as a mask.
By dry etching using a mixed gas of oxygen and oxygen, and in order to establish electrical continuity with the lower electrode 3, P
A contact hole is formed in the SG interlayer insulating film 5 by dry etching using CF ₄ . Finally, a 500 nm-thick gold film was formed by an evaporation method, and an unnecessary region was removed by argon ion milling using a photoresist as a mask to form the upper electrode 1.

The tantalum oxide thin film capacitor thus formed was heat-treated in a nitrogen atmosphere at 450 ° C. for 1 hour to measure the change in withstand voltage. The result is shown in Figure 6.
Shown in Although there is only one point at 450 ° C., it can be seen that the breakdown voltage does not deteriorate due to the heat treatment.

Further, in this embodiment, the lower electrode was formed while changing the thickness of platinum to confirm the lower limit of the thickness of platinum for preventing the deterioration of breakdown voltage. FIG. 7 shows the result.
It can be seen from the figure that if the thickness of platinum is 50 nm or more, deterioration in withstand voltage can be prevented.

In the above embodiment, the upper electrode 1 or the lower electrode 3 has a laminated structure of gold or platinum, and molybdenum and gold or platinum, but palladium, silver or other noble metal is used instead of gold or platinum. However, the same effect can be obtained, and the same effect can be obtained by using a refractory metal such as tungsten instead of molybdenum.

In the above embodiment, the high frequency sputtering method was used to form the tantalum oxide thin film, but instead, another physical vapor phase thin film forming method such as an ion beam sputtering method or CV is used.
Similar effects can be obtained by using a chemical thin film forming method such as D method or sol-gel method.

According to the present embodiment, by using a noble metal such as gold, platinum, palladium, or silver in the portion of the electrode material that is in contact with tantalum oxide, it is possible to prevent the breakdown voltage at around 450 ° C. and to perform the heat treatment at 450 ° C. It was possible to suppress the decrease in breakdown voltage due to the above to 20% or less of the breakdown voltage before the heat treatment, and it was possible to obtain 25 as the dielectric constant of tantalum oxide. As a peculiar effect of the second embodiment, the breakdown voltage could be increased by 20% or more by the heat treatment at 450 ° C.

[0019]

According to the present invention, the oxygen deficiency of tantalum oxide can be prevented by using a noble metal such as gold, platinum, palladium, or silver in the portion of the electrode material that is in contact with tantalum oxide, so that the deterioration of withstand voltage due to heat treatment can be prevented. effective.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a diagram showing the heat treatment temperature dependency of the breakdown voltage of the prior art.

FIG. 3 is a diagram showing the heat treatment temperature dependency of the breakdown voltage of the example of the present invention.

FIG. 4 is a diagram showing the dependence of the capacitance of the embodiment of the present invention on the tantalum oxide film thickness.

FIG. 5 is a sectional view of an embodiment of the present invention.

FIG. 6 is a diagram showing the heat treatment temperature dependency of the breakdown voltage of the example of the present invention.

FIG. 7 is a diagram showing the platinum film thickness dependency of the breakdown voltage in the example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Upper electrode, 2 ... Dielectric material, 3 ... Lower electrode, 4 ... Substrate, 5 ... Interlayer insulating film.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01B 3/12 312 H01G 4/33 H01L 21/8242 27/108 H01L 27/10 325 J (72) Inventor Horikoshi Kazuhiko 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa, Ltd.

Claims (8)

[Claims] 1. A tantalum oxide thin film capacitor comprising a lower electrode, a tantalum oxide dielectric layer, and an upper electrode formed on a semiconductor substrate or a semiconductor layer crystal-grown on the semiconductor substrate, wherein tantalum oxide of the upper electrode and the lower electrode is formed. A tantalum oxide thin film capacitor characterized in that a noble metal material having a large free energy of oxide formation such as gold, platinum, palladium, silver is used in a portion in contact with. 2. The tantalum oxide thin film capacitor according to claim 1, wherein the upper electrode or the lower electrode has a laminated structure with a high dielectric metal in which the noble metal material is arranged in a portion in contact with tantalum oxide. Thin film capacitor. 3. The tantalum oxide thin film capacitor according to claim 2, wherein the noble metal material has a thickness of 50 nm or more in a portion of the upper electrode or the lower electrode in contact with tantalum oxide. 4. The tantalum oxide thin film capacitor according to claim 1, 2 or 3, wherein the upper electrode and the lower electrode are formed of the noble metal material different in contacting with tantalum oxide. . 5. A GaAs IC using the tantalum oxide thin film capacitor according to claim 1. 6. A GaAs IC using the tantalum oxide thin film capacitor according to claim 2. 7. A GaAs IC using the tantalum oxide thin film capacitor according to claim 3. 8. A GaAs IC using the tantalum oxide thin film capacitor according to claim 4.