JPH071721B2 - Thin film resistor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride thin film resistor, and more particularly to a thin film resistor comprising a highly reliable nitride thin film resistor having a small resistance change even when used at high temperatures.

(Prior Art) III-V group nitride thin film, that is, tantalum nitride, titanium nitride, zirconium nitride, hafnium nitride, aluminum nitride, niobium nitride, boron nitride,
Alternatively, the chromium nitride thin film is stable at high temperatures and has excellent electrical characteristics. These nitrides alone or in combination of two or more types have high reliability with a small temperature coefficient of resistance and high reliability. It is used as a high-grade thin film resistor.

The above-mentioned nitride thin film resistor is formed on an insulating substrate such as glass or ceramic by an electron beam vapor deposition method, an ion beam vapor deposition method, a flash vapor deposition method, a cathode sputtering vapor deposition method or the like. Besides, it can be formed by a hot press method, a sublimation recrystallization method, a discharge reaction method, a gas phase reaction method, or the like. Most commonly, it is formed by a reactive sputtering method performed in an atmosphere of high purity nitrogen gas and high purity argon.

Electrodes for external connection are formed on these nitride thin film resistors. As the external connection electrode, for example, Cr-Cu, Cr-A
u, Ni-Cu, Ni-Au, Ni-Ag, NiCr-Au, Ti-Pd, -Au, Ti-W
-Multilayer electrodes such as Au are used. Of the external connection electrodes with a multilayer structure, the first layer of Cr, Ni, NiCr, Ti acts as an adhesion layer with the nitride thin film resistor, and Cu, Au, Ag acts as a soldering layer. .

(Problems to be Solved by the Invention) Although the characteristics are not changed only by carrying out a life test, for example, a humidity and load test at room temperature, on the resistor composed of the above-mentioned nitride thin film resistor, at high temperature, for example, 175 ° C. When left to stand, or when a rated voltage load life test was performed at 70 ° C, a change in resistance was observed. This phenomenon was observed whether the resistor was coated with an insulating resin or not, and when it was hermetically sealed, and the rate of change in resistance value was the same in all cases.

This indicates that the resistance film changed at high temperature. As a result of investigating the cause, a change in the resistance value of the nitride thin film resistor is such that at the contact portion between the resistance film and the external connection electrode, a part of nitrogen in the resistance film is dissociated to form an electrode at high temperature. It was found to be due to the shift to metal. For example, a nitride thin film resistor is
N), the first layer made of NiCr and the second layer made of Au for the external connection electrode, the zirconium nitride thin film in the vicinity of the external connection electrode with the passage of time when left at 150 ° C Changes in color tone, gradually changing from brown to colorless and transparent film. When this phenomenon is analyzed by means such as ESCA or EMX, nitrogen in the zirconium nitride thin film is gradually desorbed, and Ni of the external connection electrode is removed.
It was found that the nitrogen was transferred to Cr, and this transfer of nitrogen to the electrode was the cause of discoloration of the resistance film and further change to the resistance value.

That is, at the contact portion between the nitride thin film resistor and the metal of the electrode for external connection, the reaction shown in the following equation occurs.

Me'N + Me '→ Me'N _1-X + Me'N _X (Nitride thin film resistor) (External connection electrode) This is an external connection electrode when the high temperature load is applied because the external connection electrode is made of metal. The metal deprives the nitrogen of the nitride thin film resistance that the reaction of nitriding this electrode proceeds.

As a result of studies conducted by the inventors to prevent such a phenomenon, a stable metal nitride layer or a nitrogen-doped metal layer, that is, an intermediate layer is formed between the nitride thin film resistor and the external connection electrode. It has been found that the interposition prevents the above reaction.

(Object of the Invention) Accordingly, an object of the present invention is to provide a resistor having a resistance thin film made of a nitride thin film resistor, in which a change in resistance value is small at a high temperature.

(Structure of the Invention) That is, the gist of the present invention is that between the nitride thin film resistor and the external connection electrode, a metal nitride layer having a resistivity lower than that of the nitride thin film resistor, or a nitride A thin film resistor characterized in that a nitrogen-doped metal layer, that is, an intermediate layer is interposed so as not to deprive the thin film resistor of nitrogen.

Among those constituting the above-mentioned intermediate layer, the metal nitride layer having conductivity is nickel nitride, tungsten nitride, titanium nitride, vanadium nitride, manganese nitride, iron nitride, cobalt nitride, tantalum nitride, hafnium nitride, yttrium nitride. At least one of molybdenum nitride, chromium nitride, and niobium nitride is used. Moreover, as the metal layer doped with nitrogen, any metal having conductivity can be applied.

As the nitride thin film resistor which is the resistance element, all the ones already explained in the prior art are targeted, but regarding what kind of conductive metal nitride layer is adopted as the intermediate layer, it is a selection criterion. It is necessary to choose a more stable metal nitride layer with a lower resistivity than the nitride thin film resistor.
On the other hand, the metal layer doped with nitrogen as the intermediate layer is not particularly limited, but the metal layer must be sufficiently doped with nitrogen so as not to deprive the nitride thin film resistor of nitrogen.

Specifically, in the former example, for example, when the nitride thin film resistor is zirconium nitride, tantalum nitride is selected for the intermediate layer, and when the nitride thin film resistor is tantalum nitride, nickel nitride is selected for the intermediate layer. In the latter example, if the nitride thin film resistor is zirconium nitride, for example, nitrogen-doped nickel is selected as the intermediate layer.

In many cases, the intermediate layer is generally formed by a sputtering method, and whether it is a conductive metal nitride or a nitrogen-doped metal is performed by the following treatment. That is, if the nitrogen partial pressure at the time of sputtering is increased, it becomes a nitride, and if the nitrogen partial pressure is decreased, it becomes a metal doped with nitrogen. Moreover, if the nitrogen partial pressure is constant, the two can be formed separately by the film forming speed, that is, the difference in the sputtering power. For example, when the film forming rate is slow, nitriding proceeds completely to form a nitride, and conversely, when the film forming rate is high, nitriding is insufficient and nitrogen remains in the metal.

Although the above-mentioned example describes the case where the intermediate layer is formed by the sputtering method, other vacuum deposition methods,
The same applies to the dry thin film forming means such as the ion plating method.

(Example) Example 1. Reactive sputtering was carried out on a alumina substrate using metal zirconium as a target in a mixed gas of nitrogen and argon under the following conditions to form a thin film resistor of zirconium nitride.

Substrate temperature: 300 ℃ Mixed gas ratio: Nitrogen / Argon = 20/80 (volume ratio) Introduced gas pressure: 1kg / cm ² Introduced gas flow rate: 20cc / min DC output: 400W (3.0W / cm ² ) Gas pressure: 7.5 × 10 ^-4 ~2.0 × 10 ^-2 Torr Thereafter, the alumina substrate Place the mask to expose the point of the intermediate layer formed on the thin film resistor of zirconium nitride. Then, using the metal tantalum as a target, the reactive sputtering was performed under the following conditions to form an intermediate layer made of tantalum nitride.

Substrate temperature: 250 ℃ Mixed gas ratio: Nitrogen / Argon = 40/60 (volume ratio) Introduced gas pressure: 1kg / cm ² Introduced gas flow rate: 100cc / min DC output: 500W (4.0W / cm ² ) Gas pressure: 5 × 10 ^-3 Torr Furthermore, a metal layer for soldering, that is, Cu as an electrode for external connection was formed on this tantalum nitride by a vacuum deposition method.

A lead wire was soldered to Cu of the thin film resistor thus obtained, and the whole was covered with an epoxy resin. When the change in resistance after 1000 hours at 175 ° C was compared to the initial resistance, the rate of change was small.
It was less than 0.1%. No change was observed in the color tone of the thin film resistor.

Example 2 By the same method as described in Example 1, a zirconium nitride thin film resistor was formed on an alumina substrate.

Next, a mask was placed on the alumina substrate to expose the portion of the intermediate layer formed on the zirconium nitride thin film resistor.
Then, using the metal nickel as a target, a reactive sputtering was performed under the following conditions to form an intermediate layer made of nitrogen-doped nickel.

Substrate temperature: 250 ℃ Mixed gas ratio: Nitrogen / Argon = 10/90 (volume ratio) Introduced gas pressure: 1kg / cm ² Introduced gas flow rate: 100cc / min DC output: 500W (4.0W / cm ² ) Gas pressure: 5 × 10 ^-3 Torr Further, a metal layer for soldering, that is, Cu was formed as an electrode for external connection on the nickel-doped nickel by a vacuum deposition method.

The obtained thin film resistor was treated in the same manner as in Example 1 and heated at 175 ° C.
When the change in resistance value after 1000 hours of installation was compared with the initial resistance value, the change rate was 0.1 as in Example 1.
% Or less. No change was observed in the color tone of the thin film resistor.

Example 3 A tantalum nitride thin film resistor having an area resistance of 50 Ω / □ was formed on an alumina substrate by using metal tantalum as a target and performing reactive sputtering in a mixed gas of nitrogen and argon under the following conditions. .

Substrate temperature: 300 ℃ Mixed gas ratio: Nitrogen / Argon = 5/95 (volume ratio) Introduced gas pressure: 1kg / cm ² Introduced gas flow rate: 20cc / min DC output: 200W (2.5W / cm ² ) Gas pressure: 0.3 ˜2 × 10 ⁻² Torr Then, similarly to Example 1 and Example 2, a nickel nitride film and a nitrogen-doped nickel film were respectively formed as the intermediate layers.

Further, a metal layer for soldering, that is, Au as an electrode for external connection was formed on each intermediate layer by a vacuum vapor deposition method to form thin film resistors.

A lead wire was soldered to Au of the thin film resistor thus obtained. In this state, when the change in resistance value after being set at a temperature of 150 ° C for 1000 hours was compared with the initial resistance value, the rate of change was 0.01% or less.

Examples 4 to 17 Various nitride thin film resistors shown in the table were formed on an alumina substrate. Then, a mask was placed on the alumina substrate to expose the portion of the intermediate layer formed on the nitride thin film resistor. Then, the intermediate layer shown in the table was formed at this position. Further, the intermediate layer shown in the table was formed. Further, a solderable metal layer shown in the table, that is, an electrode for external connection was formed, and a lead wire was soldered to this metal layer to prepare a thin film resistor.

Comparative Example 1 A thin film resistor made of zirconium nitride was formed by the method described in Example 1.

Then, a NiCr layer was formed on the thin film resistor of zirconium nitride through a mask by a vacuum vapor deposition method, and solderable Cu was further formed thereon by a vacuum vapor deposition method to form an electrode for external connection.

A lead wire was soldered to Cu of the thin film resistor thus obtained, and the whole was covered with an epoxy resin. When placed in this state at a temperature of 175 ° C for 250 hours, the brown color of the zirconium nitride thin film resistance disappeared and changed to colorless and transparent, and the resistance value also changed by 10% or more compared to the initial resistance value.

Comparative Example 2 A thin film resistor made of tantalum nitride was formed by the method described in Example 3.

Then, through a mask over the tantalum nitride thin film resistor
A NiCr layer was formed by a vacuum vapor deposition method, and solderable Au was further formed thereon by a vacuum vapor deposition method to form an electrode for external connection.

The thin film resistor thus obtained was heated to a temperature of 150 ° C for 100
When installed for 0 hours, the resistance value is
It changed by 0.5%.

(Effect) As described above, according to the present invention, nitrogen is not taken from the metal nitride layer or the nitride thin film resistor having the conductivity lower than the nitride thin film resistor and having conductivity between the nitride thin film resistor and the external connection electrode. Since the metal layer doped with nitrogen is interposed as described above, the characteristic deterioration at high temperature, that is, the deterioration of the resistance value is small, and a thin film resistor having stable characteristics can be obtained.

Claims (1)

[Claims] 1. A nitride thin film resistor and an electrode for external connection,
What is claimed is: 1. A thin film resistor comprising a metal nitride layer having a conductivity lower than that of a nitride thin film resistor or a metal layer doped with nitrogen so as not to deprive nitrogen of the nitride thin film resistor.