JPS5950097B2 - Method for manufacturing thin film circuits - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a thin film circuit based on a metal having a valve action formed into a thin film on an insulating substrate.

Metals with valve action (valve metals) such as tantalum, titanium, and niobium can be easily converted into oxides of these metals by anodization, and these oxides are excellent dielectrics, so thin film CR It is widely used as a circuit material.

An example of a commonly used method for manufacturing a thin film capacitor in a thin film CR circuit using tantalum is as follows. That is, first, a tantalum thin film is formed on the entire surface of an insulating substrate by sputtering.

At this time, it is desirable that the thickness of the tantalum thin film be as thick as possible in order to reduce the series resistance of the completed thin film capacitor, but approximately 5000Λ is usually considered appropriate.
Next, a thin film capacitor pattern is formed by etching unnecessary parts of the tantalum using a photoetching method, and the surface of the part of the thin film capacitor pattern that is to become a dielectric is usually etched by 280 mm.
It is anodized at a voltage of about V and changed to tantalum pentoxide of about 4,500 Λ. Furthermore, nichrome and gold are usually formed on the entire surface of the substrate with a thickness of about 300 Λ and 3000 Λ, respectively, by vacuum evaporation, and finally, the unnecessary parts of the gold and nichrome are etched, and as a result, as shown in the cross-sectional view in Figure 1, tantalum is formed. (Lower electrode) 21 - Tantalum pentoxide (dielectric) 31 - Nichrome, gold (upper electrode) A laminated structure of 41, and a lower electrode extraction electrode 43 and upper electrode extraction electrodes 42 and 44 made of nichrome and gold. A thin film capacitor consisting of the following is obtained. The thin film capacitor shown in Figure 1 obtained by the method described above has the most common and basic structure at present, but this is by no means satisfactory in terms of manufacturing and reliability. .

That is, as can be seen from the above description of the manufacturing method and FIG. 1, the thickness of the tantalum film 21 formed on the insulating substrate 11 is approximately 5000.
λ, and furthermore, since tantalum pentoxide with a thickness of about 4,500 Λ is formed on its surface, the film thickness of the tantalum pentoxide end 34 on the upper electrode extraction electrode side of the thin film capacitor shown in FIG. 1 is about 7,500 Λ. Therefore, there is a sharp step of 7,500 at the tantalum pentoxide-substrate boundary. The lead-out electrodes 42 and 44 of the upper electrode are wired on top of this sharp step, and the above-mentioned lead-out electrodes are made of nichrome and gold, and the combined film thickness of both is about 3300mm. Therefore, naturally, the film thickness of the extraction electrode portion 44 of the upper electrode on the tantalum pentoxide end portion 34 is extremely thin, and in extreme cases, a disconnection state may occur. This is what is called a "stage break" and is a cause of lowering the manufacturing yield and reliability of thin film capacitors and even thin film CR circuits. The present invention provides a manufacturing method that eliminates the above-mentioned so-called "step discontinuity", thereby improving the manufacturing yield and increasing the reliability of the resulting thin film CR circuit.The present invention is based on the following facts. There is.

In other words, when trying to convert a thin film of valve-acting metals on an insulating substrate into oxides of these metals by thermal oxidation, the oxidation rate (oxide formation rate) is lower than the oxides formed on the surface by anodization. It is a fact that if it is formed, it will be significantly suppressed. For example, in the case of tantalum, approximately 5,000 tantalum thin films are formed on an insulating substrate by the sputtering method. Two types of samples were prepared, one with tantalum pentoxide, and the other with tantalum pentoxide, and both were thermally oxidized in air at 520°C.
While all tantalum in humans is converted to tantalum pentoxide,
In the latter sample, which was oxidized under the same conditions, oxidation hardly progressed, and the film thickness of tantalum pentoxide in this sample after thermal oxidation was almost the same as the film thickness of tantalum pentoxide previously formed by anodization. The fact is that it does not change. In addition to tantalum, this phenomenon can also be observed in niobium, zirconium, etc., which can be used in the present application in exactly the same way as tantalum. That is, the method for manufacturing a thin film circuit according to the present invention involves forming a metal layer having a valve action on an insulating substrate, and then forming a metal layer having a valve function on an insulating substrate. The metal layer is selectively anodized partially in the thickness direction to form a chemical oxide film, and the metal layer is selectively thermally oxidized throughout the thickness direction using at least this chemical oxide film as a mask. That is.

According to one aspect of the present invention, a step of forming a metal thin film having a valve action on an insulating substrate, and a process of selectively anodizing the surface of this metal thin film to prevent oxidation of the underlying metal thin film are performed. a step of forming a metal oxide layer; a step of forming an oxidation prevention layer on the surface of the metal thin film to selectively prevent oxidation of the metal thin film; A step of thermally oxidizing all of the metal thin film other than that part, a step of removing the anti-oxidation layer if necessary, a step of anodizing the oxide layer again if necessary, a step on the oxide layer,
A method for manufacturing a thin film circuit characterized by comprising a step of forming a good conductive metal thin film on the oxidation-preventing layer or on the metal thin film exposed after removing the oxidation-preventing layer. Alternatively, according to another aspect of the present invention, the steps include forming a first metal layer having a valve action on an insulating substrate, and selectively anodizing a portion of the first metal layer from the surface in the thickness direction. forming a second metal layer different from the first metal layer on a predetermined portion of the surface of the first metal layer, and forming the chemical oxide film of the first metal layer and A step of forming a thermally oxidized layer by thermal oxidation over the entire thickness of the part where the second metal layer is not formed, a tantalum nitride layer on the entire surface of the structure obtained up to the above step, and a tantalum nitride layer a step of forming a good conductor metal layer thereon; a step of selectively removing the good conductor metal layer and the tantalum nitride layer and then subjecting tantalum nitride as a resistor to a stabilization treatment if necessary; It is characterized by comprising a step of re-forming the beta-tantalum oxidation prevention layer, and a step of forming a good conductive metal layer on the entire surface or part of the structure obtained up to the above steps, and etching away unnecessary parts thereof. This is a method for manufacturing thin film circuits.

Next, a first embodiment of the present invention will be explained in detail using FIG. 2.

As shown in FIG.
A tantalum layer 21 is formed by sputtering.

Next, as shown in Figure 2b, the surface of the tantalum layer was selectively anodized in 0.1% citric acid at 250V, and
A human tantalum pentoxide layer 32 is produced. This tantalum pentoxide layer later plays the role of an oxidation prevention layer that prevents the tantalum below this layer (which becomes the lower electrode of the thin film capacitor) from turning into tantalum pentoxide during the thermal oxidation process. The thickness is preferably 600 Å or more (formation voltage 40 V or more). Next, as shown in FIG. 2C, the surface of the portion of the tantalum layer 21 that will form the lead electrode of the lower electrode of the thin film capacitor in a later step is subjected to a subsequent thermal oxidation step to prevent this portion from being oxidized. An aluminum layer 51 having a thickness of approximately 1 μm is formed as an oxidation prevention layer for the purpose of the present invention. The anti-oxidation layer of the tantalum layer is not necessarily limited to aluminum, but may be a metal layer simply made of gold, nichrome, or gold, or an insulating layer such as silicon oxide. Note that the process of forming the metal layer as an oxidation-preventing layer and the previous anodizing process do not necessarily have to be as in this embodiment, and the order may be reversed. After forming the aluminum layer,
The substrate was left in the air at 520°C for 8 hours, and as shown in Figure 2d, all of the tantalum layer whose surface had been exposed until the previous process was thermally oxidized to form a tantalum pentoxide layer 33 due to thermal oxidation. change. At this time, the tantalum pentoxide layer 32 formed by anodization
The tantalum in the lower layer of the aluminum layer 51 is prevented from being oxidized by these elements, so that it is hardly or not oxidized at all. The thermal oxidation conditions (temperature and time) in this step are determined by the thickness of the tantalum film formed by sputtering, but the point is that conditions should be selected so that the entire tantalum layer turns into tantalum pentoxide. Furthermore, although air is used as the oxidizing atmosphere in this embodiment, it has been found that the oxidation time can be significantly shortened by using water vapor at the same oxidation temperature. When the thermal oxidation is completed, the aluminum layer 51 is etched away as a tantalum oxidation prevention layer as shown in FIG. 2d. In this example, since aluminum is used as the anti-oxidation layer for tantalum, the surface of the aluminum layer 51 in the previous thermal oxidation process changes to aluminum oxide, but if this aluminum layer is not removed, the thin film capacitor will be capacitated in the later process. Due to the aluminum oxide on the surface of the aluminum layer, the electrical connection between this lead electrode and the lower electrode made of tantalum is insufficient, resulting in an increase in the series resistance of the thin film capacitor. Therefore, the aluminum layer 51 is removed, but a metal (for example, gold) whose surface is not oxidized in the thermal oxidation process is used as an oxidation-preventing layer for the tantalum layer, and the bottom electrode made of tantalum is used to form an extraction electrode of the bottom electrode to be formed later. If the electrical connection with the electrode is made without any problems, it is not necessary to remove the metal layer as an oxidation prevention layer of the tantalum layer.
Following the removal of the aluminum layer 51, the tantalum pentoxide layer 32 previously formed by anodization is again anodized to form the tantalum pentoxide layer 31 as a dielectric of the thin film capacitor.
(Figure 2e). The voltage for this re-anodization is the first
If the anodization voltage is too low compared to the first anodization voltage, the regeneration of tantalum pentoxide will be insufficient and a good quality dielectric will not be obtained.
It has been confirmed that a voltage of 1% or more is appropriate, and the upper limit of the re-anodization voltage can be as high as it is, but considering the characteristics of the thin film capacitor obtained, it is
It has been found that voltages up to about 0% higher are appropriate. In this example, re-anodization was performed at 25% in 0.1% citric acid solution.
This is carried out at a voltage of 5 V, and as shown in FIG. 2e, a structure is obtained in which the step at the boundary between the tantalum pentoxide layer (dielectric) 31 and the tantalum pentoxide layer 33 formed by thermal oxidation is extremely small.
Finally, nichrome and gold were deposited on the entire surface of the substrate obtained through the above steps using a vacuum evaporation method.
After adhering 0Λ, unnecessary parts of gold and nichrome are removed by photolithography, and as shown in FIG.
3 to complete a thin film capacitor according to the manufacturing method of the present invention. Although the above-mentioned embodiment shows only the case of manufacturing a thin film capacitor, in the first embodiment of the present invention, tantalum in the lower layer of the tantalum pentoxide layer 32 obtained by anodization is used as a resistor. Thin film CR circuits can also be manufactured.

The manufacturing method is almost the same as that for thin film capacitors, so the details are omitted, but Figure 3a shows a cross-sectional view of a thin film CR circuit obtained by the manufacturing method of the present invention, and Figure 3b shows its equivalent circuit. show. The structure of the capacitor part in FIG. 3a is exactly the same as that of the previous embodiment, and the tantalum pentoxide layer 35 in the resistor part is formed in the first anodization process, so that the area of the resistor layer 22 made of tantalum as the lower layer is The resistance value is determined by the anodization voltage. Although the tantalum pentoxide layer 35 in the resistor section can be re-anodized, it has been found that it is better not to perform anodization when considering the stability of the thin film resistor when completed. . However, it is a matter of course that re-anodization can be performed to adjust the resistance value. In addition, the terminal electrodes 45 and 46 of the resistor part are shaped simultaneously when forming the upper and lower electrodes of the thin film capacitor.
It is what was done. Next, a second embodiment of the present invention will be described using FIGS. 4a to 4f.

First, as shown in the cross-sectional view in FIG. 4a, a beta-tantalum layer 121 of about 5,000 layers is formed on the entire surface of an insulating substrate (ceramic) 111 by sputtering, and then a dielectric of a thin film capacitor is formed on the surface of the beta-tantalum 121. The portion to be treated is selectively anodized in a 0.1% citric acid solution by applying an anointing voltage of 250 V to produce a tantalum oxide layer 132 by about 4000 people's anodizing method.

Here, as a mask for this selective chemical formation, for example, a stack of an aluminum layer and a photoresist layer can be effectively used. The tantalum oxide layer 132 formed by this chemical conversion method serves as an oxidation prevention layer to prevent the underlying beta-tantalum layer from being oxidized in the subsequent thermal oxidation process, and therefore has a film thickness of 600 Å or more (forming voltage of 40 V or more). It is desirable that Next, as shown in FIG. 4b, a beta-tantalum layer 12, which is to be used as an extraction electrode for the lower electrode of the thin film capacitor, is formed.
Approximately 1 μm of anti-oxidation layer is applied to the surface of a predetermined portion of 1 to prevent this portion from being oxidized in the subsequent thermal oxidation process.
An aluminum layer 151 is formed. The anti-oxidation layer of the beta-tantalum layer 121 is not necessarily limited to aluminum, but may be simply gold, nichrome, gold or other metal layers, or even an insulating layer such as silicon dioxide.
Note that the process order of the formation process of the anti-oxidation layer for the part that forms the extraction electrode of the lower electrode of this beta-tantalum thin film capacitor and the previous chemical formation process is not necessarily the same as in this example, but there is a difference even if it is reversed. I can't support it. After forming the aluminum layer 151, the entire substrate was placed in air at 520°C for 8 hours.
After leaving it for a while, the exposed surface of the beta-tantalum layer 121 is thermally oxidized throughout its thickness as shown in FIG. At this time, the tantalum oxide layer 132 and the beta tantalum layer 121 under the aluminum layer 151 are prevented from being oxidized by chemical conversion, so that little or no thermal oxidation occurs. The thermal oxidation conditions (temperature and time) in this step are determined by the thickness of the beta-tantalum film formed by sputtering, but the important thing is to select conditions that will cause the entire thickness of the beta-tantalum layer to turn into tantalum oxide. Further, in this embodiment, air is used as the oxidizing atmosphere, but other than air, for example, water vapor can be used, and in this case, there is an advantage that the oxidation time can be shortened to a minimum at the same oxidation temperature. When the selective thermal oxidation of the beta-tantalum layer 121 is completed, the aluminum layer 151 serving as a beta-tantalum oxidation prevention layer in the lead-out electrode portion of the lower electrode is etched and removed. In this embodiment, since aluminum is used as an oxidation-preventing layer in the beta-tantalum electrode formation area, aluminum oxide (not shown) is formed on the surface of the aluminum layer 151 in the previous thermal oxidation process. If the layer 151 is not removed, the aluminum oxide formed on the surface of the aluminum layer 151 will cause an electrical connection between the lead electrode and the lower electrode made of beta-tantalum to be broken when the lead electrode of the thin film capacitor is formed in a later process. becomes sufficient and eventually increases the series resistance of the thin film capacitor. Therefore, the aluminum layer 151 is removed, but a metal that is not oxidized in the thermal oxidation process, such as gold, is used as the oxidation-preventing layer of the beta-tantalum layer 121. If the electrical connection is to be made without any problem, it is not necessary to remove the metal layer as an anti-oxidation layer. Following the removal of the aluminum layer 151, tantalum nitride in the so-called plateau region is sputtered on the entire surface of the substrate as a resistor to a thickness of about 1,000 layers, and then nichrome and gold are superimposed on this to a thickness of 300 layers and 3,000 layers, respectively. The lower part of the thin film capacitor is formed by vacuum deposition to a thickness of An anti-oxidation layer 17 for tantalum nitride made of tantalum nitride 141 and nichrome gold is applied to the lead-out electrode forming part and the part where a thin film resistance is to be formed on the tantalum oxide layer 133 by thermal oxidation.
1 pattern is defined. This anti-oxidation layer 171 for tantalum nitride protects the surface of the tantalum nitride layer 141 on the extraction electrode portion of the lower electrode and the electrode formation portion of the resistor during subsequent heat treatment (stabilization treatment) of the tantalum nitride portion used as a resistor. This layer is formed to ensure sufficient electrical connection between each oxide layer, and is not necessarily limited to nichrome-all-gold. If the subsequent heat treatment of tantalum nitride is not required, there is no need to form this layer. . Next, the substrate obtained through the above steps was heat treated at 250°C in air for 5 hours to stabilize the tantalum nitride, and then the part that will become the dielectric of the thin film capacitor (formed as an oxidation prevention layer of beta tantalum in the first chemical formation) The formed tantalum oxide layer 132 is re-formed in a 0.1% citric acid solution at a formation voltage of 255 to form the tantalum oxide layer 13 as a dielectric.
1 (restored as shown in Figure 3d).

At this time, as described in detail in the first embodiment, it is appropriate for the re-formation voltage to be about 90% or more of the initial formation voltage, and the upper limit may be as high as it is, but considering the characteristics of the thin film capacitor to be obtained, the initial It is appropriate to use a voltage up to about 10% higher than the voltage of . As a result of the steps up to this point, as shown in FIG. 3d, a tantalum oxide layer 131 and a tantalum oxide layer 1 formed by thermal oxidation are
A structure with an extremely small step at the boundary with 33 is obtained.
Finally, after depositing 300λ and 3000Λ of nichrome and gold as good conductor electrode metals on the entire surface of the structure obtained through the above steps, unnecessary portions of gold and nichrome were etched and removed by photolithography, as shown in Figure 4e. As shown in FIG.
A thin film CR circuit whose equivalent circuit is shown in FIG. f is obtained.

As is clear from the cross-sectional views of the thin film capacitor portion of the completed thin film CR circuit in FIGS. 2f and 4e, tantalum oxide (dielectric) 31 or The difference in level at the boundary between 131 and tantalum oxide 33 or 133 due to thermal oxidation is almost eliminated, completely eliminating the problem of so-called "step breaks" in wiring caused by conventional manufacturing methods. Note that the present invention is not limited to the above-described embodiments, and any modifications may be made, for example, wiring paths may be formed on a semiconductor substrate.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a thin film capacitor produced by a conventional manufacturing method, and FIGS. FIG. 3a is a sectional view of a thin film CR circuit manufactured by the manufacturing method of the first embodiment of the present invention, FIG. 3b is an equivalent circuit diagram thereof, and FIGS. FIG. 4F is a cross-sectional view of a sample showing each main process of manufacturing a thin film CR circuit according to the embodiment, and FIG. 4F is an equivalent circuit diagram thereof.

Claims (1)

[Claims] 1. A step of forming a metal layer that acts as a valve on a substrate, a step of selectively converting a part of the metal layer from the surface to the inside in the thickness direction into a chemical oxide film by anodization, and then the step of converting the metal layer into a chemical oxide film. A method for manufacturing a thin film circuit, comprising the step of selectively thermally oxidizing the metal layer over the entire thickness using a chemical oxide film as a mask.