JPS5942966B2 - Method of manufacturing thin film capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to thin film capacitors, and relates to a method of manufacturing a tantalum thin film capacitor which has excellent heat resistance.

Hybrid integrated circuits made of tantalum thin films (hereinafter referred to as HyIC) are compatible with the fact that tantalum can be used to form resistors and capacitors from the same material, and the resulting elements are extremely stable and highly reliable. It is mainly used in communication equipment.

However, despite these advantages, it is currently not widely used in fields other than communication equipment, except for special equipment.

This is because the price requirements in these fields are even stricter than in the case of communication equipment, making them unprofitable.

One of the reasons why this HyIC is expensive is that low-level solder cannot be used to attach components and external leads, and other expensive methods such as thermocompression bonding must be used.

This is because when the HyIC includes a tantalum thin film capacitor, this capacitor cannot withstand the temperature for soldering.

Therefore, the development of tantalum thin film capacitors that can withstand temperatures of 250° C. or more for soldering is urgently needed to reduce the cost of HyICs.

Now, the conventional method of manufacturing tantalum thin film capacitors is as follows.

That is, first, a tantalum thin film is formed on an insulating substrate such as glass or ceramic by sputtering.

This sputtered tantalum thin film is suitable for use in capacitors because it has excellent dielectric properties such as capacitance, insulation resistance, and loss coefficient (tan δ), as well as excellent reproducibility and stability during manufacturing. The type called `` is mainly used.

Next, the tantalum thin film formed by the sputtering method is defined into an arbitrary pattern using a well-known photolithography technique, and the surface portion on the pattern that is to be used as the dielectric of the capacitor is anodized, and tantalum pentoxide as the dielectric is formed. Then, a thin metal film of good conductivity made of gold or the like is formed on the entire surface of the substrate obtained in the previous steps, and unnecessary parts of this thin metal film of good conductivity are etched again using photolithography to define the electrode pattern of the capacitor. Finally, tantalum - tantalum pentoxide (dielectric) -
The thin film capacitor has a structure in which metals with good conductivity are laminated in this order.

However, the capacitor obtained through the conventional process shown above is
Initially, for example, the insulation resistance value when DC25V is applied is 10.
The janδ value is 0 when over 10,000 MQ or IKHzO bias
．． Although it is an excellent value of 21%, it is
, each characteristic becomes 10M when left in heat for 10 minutes.
It deteriorated significantly to less than Ω and 1.4%, making it unusable as a capacitor.

An object of the present invention is to provide a method for manufacturing a thin film capacitor which is made of the same material as conventional thin film capacitors, such as beta-tantalum, but which does not suffer from characteristic deterioration due to heat as described above and therefore has excellent heat resistance.

The present invention has been made based on the following knowledge.

In other words, as mentioned above, the dielectric of a capacitor manufactured using the conventional method uses anodized oxidation to change the tantalum surface to tantalum pentoxide, but immediately after oxidation, the oxygen near the tantalum pentoxide-tantalum boundary The concentration distribution has a step-like shape that rapidly decreases as shown by curve 1 in FIG. 1, and it is considered that the capacitor exhibits good characteristics in this state.

If this state is left in a high temperature, the oxygen in the tantalum pentoxide will thermally diffuse into the tantalum, and as a result, the oxygen concentration distribution near the boundary will have a gentle slope, as shown by curve 2 shown by the broken line in Figure 1. It is thought that the greater the amount of oxygen diffusion, the greater the deterioration of the capacitor's characteristics.

Therefore, based on this knowledge, it can be seen that in order to obtain a heat-resistant capacitor, it is sufficient that there is no diffusion of oxygen in tantalum pentoxide into tantalum when it is left exposed to heat, or even if there is, only a small amount of oxygen diffuses into tantalum. .

That is, the method for manufacturing a thin film capacitor according to the present invention includes the steps of forming a metal layer having a valve action on an insulating substrate, and exposing the surface of a predetermined portion of this metal layer to a high temperature oxidizing atmosphere to reduce the thickness of a portion of the metal layer. It is characterized by comprising the steps of forming an oxide or diffusing oxygen throughout the body, and anodizing a predetermined portion of the hind limb to form a dielectric layer.

Alternatively, in the method for manufacturing a thin film capacitor according to the present invention, a dielectric is formed by anodizing, and a portion to be anodized is formed prior to the anodizing in a method for manufacturing a thin film capacitor having a structure in which a tantalum dielectric and a good conductor metal are laminated in this order. It is characterized by performing high-temperature heat treatment in an oxidizing atmosphere.

Such heat treatment may be carried out under conditions such that oxygen is diffused from the surface of the metal layer such as tantalum over a part of its thickness; for example, in the case of tantalum, a temperature range of 300° C. to 570° C. is preferable.

An embodiment of the present invention will be described below with reference to FIG.

First, as shown in FIG. 3a, beta-tantalum is formed as a tantalum-based thin film on the entire surface of an insulating substrate 10 made of glass, ceramic, etc. by sputtering using about 5,000 sputtering methods.

Next, unnecessary portions of the beta-tantalum are etched away using a commonly used photolithography technique to form a capacitor pattern 1.
Define 1.

The capacitor pattern 11 consists of a portion on which tantalum pentoxide (dielectric) will be formed in a later anodizing process and a lead-out portion of the anode electrode of the capacitor.

After defining the capacitor pattern 11, an anti-oxidation film 12 is formed on the extended portion of the anode electrode of the capacitor on the pattern to prevent the same portion from being oxidized in a subsequent heat treatment process.

This anti-oxidation film 12 can be, for example, a metal thin film such as aluminum, titanium, nichrome, or gold, or an insulating thin film such as silicon dioxide or borosilicate glass.
Since it is necessary to remove it later, it is desirable to have a material that is easy to remove and allows the use of chemicals that do not attack beta-tantalum, especially if it is removed by chemicals, and in this respect, aldinium is convenient.

After the formation of the anti-oxidation film 12 is completed, the capacitor pattern 11 is subjected to high temperature heat treatment as shown in FIG.

Temperature, time, and atmosphere are important in this heat treatment, and in order to obtain a sufficiently heat-resistant capacitor, if the atmosphere is air or oxygen, the treatment temperature must be 250°C or less.
The purpose cannot be achieved with a processing time of about 0 hours,
It is known that when the temperature exceeds 570° C., the characteristics of the capacitor obtained even after a short treatment of 5 minutes, especially the loss coefficient (tan δ), become unsatisfactory.

Furthermore, when the atmosphere is water vapor, it has been found that even if the treatment temperature is about 300° C., it is effective if the treatment time is 10 hours or more.

In the end, in order to obtain a sufficiently heat-resistant capacitor, it is necessary to form a sufficiently thick film of tantalum oxide on the surface of beta-tantalum through this heat treatment, and for this reason, the higher the treatment temperature, the better. The longer the time, the better; however, if the time is too high or too long, the beta-tantalum will be oxidized too much and the resistance value of this part will increase when used as a capacitor, which will increase the loss coefficient of the capacitor. be.

In this embodiment, in consideration of the above, heat treatment is performed in air at 450° C. for 2 hours to convert beta-tantalum into a tantalum oxide layer 13 having a thickness of approximately 1000λ.

This tantalum oxide layer 13 has a large amount of oxygen on the surface side,
The inner side shows an oxygen profile with less oxygen.

After the heat treatment, the anti-oxidation film 12 on the anode electrode extension portion on the capacitor pattern is removed, and as shown in FIG. is anodized to turn it into tantalum pentoxide 15.

This anodization can be carried out in the usual way, and the voltage can be determined based on the final capacitance value of the capacitor, but from the viewpoint of heat resistance, the lower the anodization voltage, the better. It has been found that the higher the temperature, the higher the temperature or length of the previous heat treatment is required.

In this embodiment, anodic oxidation is carried out using a 0.01% citric acid solution as an electrolyte and a voltage of 200 .mu.m.

After forming the dielectric, the wax 14 is removed, the substrate is thoroughly cleaned, and a good conductive metal, for example, 300 and 3000 nichrome, respectively, is formed on the entire surface by vapor deposition, and then the gold and nichrome are deposited by ordinary photolithography. Unnecessary portions of the capacitor are etched away to define upper electrodes 16 and lower electrode terminals 17 as conductor patterns as shown in FIG. 3d, thereby completing a thin film capacitor.

The thin film capacitor obtained in this example has a structure in which beta tantalum, tantalum pentoxide (dielectric) and a good conductor metal are laminated in this order, and this is the same structure as that obtained by the conventional manufacturing method. As shown below, it has much better heat resistance than conventional products.

That is, the capacitor obtained in this example has an IKHzO
Capacitance value per fight 2 at bias 640PF loss coefficient 0.
The insulation resistance value when applying 18V and 25V is more than 100,000MΩ, but after being heated at 300℃ for 10 minutes, the characteristics are 640PF, 0.20%, and 100,000MΩ, respectively.
As described above, the properties hardly change before and after being left to heat, and the material has excellent heat resistance.

The reason why the thin film capacitor obtained by the manufacturing method of the present invention has excellent heat resistance is considered to be as follows.

That is, the manufacturing method of the present invention is characterized by performing heat treatment in a high-temperature oxidizing atmosphere before forming the dielectric by anodic oxidation, and this high-temperature heat treatment changes the tantalum surface to tantalum oxide, and at this time, the tantalum oxide surface changes to tantalum oxide. Since oxidation of the oxygen concentration distribution at the tantalum boundary is thought to occur due to thermal diffusion of oxygen, the curve A-B-C-D shown in Figure 2
It is thought that the oxygen concentration distribution has a gentle slope as shown in Figure 2, and when anodizing is performed on this, the oxygen concentration distribution becomes the curve A-B- in Figure 2.
It is considered that the capacitor has the characteristics shown in the example.

If this state is heated for 10 minutes at 300°C, the oxygen in the tantalum pentaoxide will diffuse into the tantalum oxide, but the tantalum oxide in the vicinity of the tantalum pentoxide already contains oxygen corresponding to CD in Figure 2. Therefore, the amount of diffusion is extremely small, and the oxygen concentration distribution after being left to heat will be at most the curve A-B-F-G-D in FIG.

This is considered to be the reason why the capacitor obtained by the manufacturing method of the present invention has heat resistance.

As is clear from the above, by applying the manufacturing method of the present invention, it is possible to obtain a thin film capacitor with excellent heat resistance. It is expected that the use of tantalum-based solder will enable the use of tantalum-based thin films to reduce the cost of Hy IC, and that the fields of its application will further expand.

In the present invention, although beta-tantalum is used, the present invention can be similarly applied to cases where other valve-acting metals are used.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the oxygen concentration distribution in the dielectric of a thin film capacitor obtained by the conventional manufacturing method, and FIG. 2 is a diagram showing the oxygen concentration distribution in the dielectric of the thin film capacitor obtained by the manufacturing method of the present invention. FIGS. 3a to 3d are cross-sectional views showing main steps in a method for manufacturing a thin film capacitor according to an embodiment of the present invention. Symbols in the figure: 1...Curve showing the oxygen concentration distribution immediately after formation of a conventional thin film capacitor, 2...Curve showing the oxygen concentration distribution after heat treatment of a conventional thin film capacitor, 10 ...Insulating substrate, 11..Beta tantalum film, 12..Aluminum film, 13.
... Tantalum oxide layer, 14 ... Wax, 15 ... Tantalum pentoxide layer, 16 ...
- Upper electrode, 17...lower electrode terminal.

Claims (1)

[Claims] 1. A step of forming a metal layer having a valve action on an insulating substrate, a step of exposing a predetermined portion of the metal layer to a high temperature oxidizing atmosphere, and a step of converting the predetermined portion into a dielectric material by anodizing. A method for manufacturing a thin film capacitor, comprising: