JPS6314452Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a thin film capacitor with reinforced mechanical strength.

Tantalum thin film integrated circuits are produced by sputtering a thin film of tantalum (Ta) or tantalum nitride (Ta ₂ N) to a predetermined thickness on a ceramic substrate made of alumina or the like, and then applying vacuum evaporation onto this thin film. Thus, a thin metal film layer that becomes an electrode or conductive metal is created,
Pattern formation and selective etching are performed using photolithography to form microcircuits consisting of thin film capacitors, resistors, etc.

Here, Ta thin film capacitors are made with a composition of Ta thin film/Ta ₂ O ₅ oxide film/metal electrode.

That is, after sputtering Ta to a thickness of about 5000 Å on a ceramic substrate such as alumina, a well-known photolithography technique is applied.
The pattern of the capacitor circuit was formed using the photoresist film, and tantalum oxide (Ta ₂ O ₅ ) was applied to the exposed capacitor pattern using electrolytic oxidation.
Forms an oxide film consisting of

In electrolytic oxidation, a phosphoric acid (H ₃ PO ₄ ) aqueous solution is used as a chemical liquid, and the metal (Ta in this case) on which the oxide film is to be formed is used as the anode, and platinum (Pt) or the like is used as the cathode to reach the required withstand voltage. In this method, an oxide film (Ta ₂ O ₅ in this case) of a corresponding thickness is grown by applying an equal DC voltage.

Next, an electrode metal consisting of nichrome (NiCr) and gold (Au) is vacuum-deposited as a counter electrode on the oxide film, and then an electrode pattern is formed again by photolithography to complete a Ta thin film capacitor.

The Ta thin film integrated circuit is composed of thin film resistors and thin film capacitors as passive elements, but capacitors are significantly inferior to resistors in terms of mechanical strength.

The reason for this is that the failure mode for both components is a short circuit for capacitors and an open circuit for resistors, but the thickness of the Ni/Cr and Au deposited films used for electrodes in thin film integrated circuits is only a few thousand Å. First, because the electrode metal is thin, it is easily damaged due to misalignment with other substrates or scratches during the handling of the integrated circuit, or the generated strain causes a difference in the electric field strength within the oxide film, resulting in short circuits. It becomes easy.

On the other hand, in the case of a resistor, even if the electrode section is partially damaged, this rarely leads to disconnection.

The purpose of this invention is to increase the mechanical strength of thin film capacitors against contact damage, etc. Therefore, the resist film used for pattern formation is left as is without peeling and used as a protective film for the capacitor. Of course, a protective film may be formed again after peeling.

The present invention will be described below with reference to Examples.

The inventors prepared an alumina substrate with a length of 20 mm and a width of 9 mm, with four capacitors each having a chemical formation voltage of 120 V and a capacitance of 5,000 PF, and determined whether or not there was a resist protective film, and the optimal resist film. The effects of thickness, resist curing temperature, etc. were investigated. The resist used here is a positive resist.
OFPR.

As a method for comparing the protective effects, five samples each were placed in a ball mill together with a 2 mm diameter porcelain ball and rotated at a speed of 40 revolutions for one minute to give a mechanical shock.

Figures 1 and 2 show the results, with the horizontal axis representing the rotation time of the ball mill, and the vertical axis representing the leakage current value in amperes/farads in the case of Figure 1.
Figure 2 also shows the non-defective rate in the form (A/F).

In both figures, conventional sample 1 without a protective film is 1
When I took it out after a few minutes, all the capacitors were shorted. On the other hand, Sample 2, which was coated with resist and sufficiently heated, showed no increase in leakage current even though mechanical shock was applied to each other for 16 minutes.

The curing conditions for the resist OFPR used here were heating at 115°C or higher and 225°C for 25 minutes.

On the other hand, in sample 3, which was heated for 30 minutes at 115°C, which is the preheating condition for this resist, the adhesion of the protective film was insufficient, and the number of short circuits gradually increased, and the leakage current value of the remaining capacitor also increased. After 8 minutes, the total number had been shortened. This indicates that the protective film has little protective effect if the curing treatment is insufficient.

Next, the minimum thickness of the resist protective film is 1μ.
A film thickness of at least m is required, and there is no significant difference even if it is thicker than this, but the conditions for this film thickness are the same as the resist film thickness used in photolithography, that is, the resist film used for pattern formation is This means that it can be used as a protective film without being removed.

The present invention uses the resist film used to form the capacitor pattern as a protective film to prevent short circuits from occurring in the capacitor part during handling of Ta thin film integrated circuits.This treatment improves the reliability of the capacitor. You can increase the degree.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between the rotation time and the leakage current of the sample when a mechanical shock is applied by a ball mill, and FIG. 2 shows the relationship between the rotation time of the ball mill and the yield rate. In the figure, 1 is a conventional sample without a protective film, 2 is a sample according to the present invention with a resist film, and 3 is a sample in which the resist film is insufficiently cured.

Claims (1)

[Scope of utility model registration request] A thin film capacitor characterized in that a resist film for forming a thin film capacitor pattern is used as a protective film without being removed.