JPS5933246B2 - tantalum thin film capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in tantalum thin film capacitors, particularly tantalum thin film capacitors using α-Ta.

For example, tantalum thin film capacitors for hybrid ICs generally use a crested alumina substrate with a highly smooth surface, which has a thin glass coating on the alumina substrate surface, and a tantalum thermal oxide film (Ta2O5) is formed on the substrate. A lower electrode made of a β-Ta thin film layer is disposed on top of the β-Ta thin film layer, and a β-Ta chemically formed film, which becomes a dielectric layer made by anodizing the upper part of the β-Ta thin film, is disposed, for example, using nichrome (NiC).
The electrode is made of a gold (Au) layer with r) as a base layer.

Since a tantalum thin film capacitor having such a structure uses a β-Ta chemically formed film as a dielectric layer, it has disadvantages of relatively large leakage current and low withstand voltage. That is, the leakage current value is about 2 A to several + A/F (value after 1 minute of application of 50 V), and the withstand voltage is at most 50 V or less. Therefore, in order to further reduce the leakage current and increase the withstand voltage, it has been proposed to use α-Ta instead of β-Ta. Current: O, 05A/
F (value after 1 minute of application of 50V), and the withstand voltage can be increased to about 120V. However, such performance improvement is only possible when using an expensive glazed alumina substrate. For example, a thin film capacitor constructed using α-Ta directly on an alumina substrate with a crane size of several micrometers is not possible as described above. No significant performance improvement was obtained, and the leakage current value gradually increased to 2 A/F or more after 1 minute of application of 50 V. As a result of various investigations, the inventors found that the cause of this problem was that nucleation at the initial stage of α-Ta film formation was not uniform, and as a result, the film condensed only on the crane of alumina, and when the film was chemically formed, the formation of nuclei was not uniform. It was confirmed that this was due to the formation of many gaps and pore-like defects in the film. In order to construct such a high-performance tantalum thin film capacitor, it is necessary to use an expensive clasped alumina substrate, which has been a major obstacle to lowering the price.

The present invention was made in view of the above points, and its purpose is to provide a tantalum thin film capacitor having a structure that has high performance and can be manufactured at low cost. In a tantalum thin film capacitor comprising an α-Ta thin film layer and an upper electrode disposed on the lower electrode via an α-Ta chemical layer, there is a , a thin film buffer layer is interposed to uniformize the formation of nuclei during the formation of the α-Ta thin film layer.

Embodiments of the present invention will be described below with reference to the drawings.

The figure is a sectional view of a main part for explaining the structure of an example of a tantalum thin film capacitor according to the present invention, in which 1 is an alumina substrate, and a buffer layer 2 (layer thickness: 001000A to 2000A) are formed by a sputtering method, and a lower electrode 3 made of an α-Ta thin film layer (film thickness approximately 1000A) formed by a sputtering method is disposed on the buffer layer 2. α-Ta chemical conversion layer 4 (layer thickness approximately 5 cm
000A to 6000A), the upper electrode 5 is disposed therebetween.

The upper electrode 5 is made of a NiCr layer 5a (layer thickness 100λ~20
Au layer 5b (for example, layer thickness 400
0 to 5,000 people), and a NiCr layer 6a (layer thickness 100λ to 20
Au layer 6b (layer thickness 4000A~5
000λ) is formed. In this way, the tantalum nitride thin film layer 2 formed on the alumina substrate 1 can uniformly form nuclei not only on the grains but also on the entire surface of the alumina substrate surface, and a homogeneous tantalum nitride thin film layer 2 can be easily formed.

Therefore, α-
When forming the Ta thin film layer 3, nucleation is uniform in the initial stage of film formation, and a homogeneous α-Ta thin film layer 3 can be formed. As a result, the α-Ta chemical layer 4 formed by anodic oxidation of the upper layer of the homogeneous α-Ta thin film layer 3 eliminates the gap-like formations that conventionally occur due to the heterogeneity of the α-Ta thin film. A homogeneous α-Ta conversion layer without pore-like defects can be obtained. Thus, the buffer layer 2 consisting of a homogeneous tantalum nitride thin film layer
By providing this on the alumina substrate 1, a high-performance tantalum thin film capacitor can be constructed using α-Ta on an inexpensive alumina substrate without using an expensive clasped alumina substrate.

In the tantalum thin film capacitor constructed in this way, the leakage current is about 0.05A/F (value after 1 minute of application of 50%), and there is no increase over time. Even when compared with the one constructed by

The tantalum nitride thin film layer 2 and the α-T4 film layer 3 can be formed in the same tank by simply switching the introduced gas, and as is clear from the above description, the process does not become complicated. The invention allows a high-performance tantalum thin film capacitor to be easily constructed using α-Ta on an inexpensive alumina substrate, and is extremely effective in reducing the cost.

[Brief explanation of the drawing]

The figure is a sectional view of a main part for explaining the structure of an example of a tantalum thin film capacitor according to the present invention. DESCRIPTION OF SYMBOLS 1... Alumina substrate, 2... Thin film buffer layer (tantalum nitride thin film layer), 3... Lower electrode (α-Ta), 4...
・α-Ta chemical layer, 5... Upper electrode, 6... Lower electrode terminal, 5a, 6a... NiCr layer, 5b, 6b...
Au layer.

Claims (1)

[Claims] 1. A tantalum thin film capacitor comprising an α-Ta thin film layer serving as a lower electrode on an alumina substrate, and an upper electrode disposed on the lower electrode via an α-Ta chemically formed film. -The α-
A tantalum thin film capacitor characterized by interposing a thin film buffer layer to uniformize nucleation during formation of a Ta thin film layer.