JPH073852B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor device including a three-layer laminate in which an insulating film is sandwiched between semiconductor layers or conductor layers, and more particularly to the three-layer laminate. The present invention relates to improving the characteristics of a semiconductor device in which the capacitance of a capacitor formed of a body is very large per unit area.

2. Description of the Related Art In the recent semiconductor field, trends such as high integration, miniaturization, and high speed operation have been observed, and IC and LSI have been developed accordingly. That is, by using these, various benefits such as system miniaturization, high performance, and improvement in economic efficiency can be expected, and there are wide application fields such as memory, logic circuit, and microcomputer. is doing.

As ICs for memory, bipolar ICs, MOSICs, etc. are well known. Especially, the latter is inferior to the former in terms of high-speed operability, but it does not require isolation between elements and enhances the MOSFET's enhancement characteristics. Is suitable for switching, has low power consumption, and has a function of a temporary memory due to accumulated charges of gate capacitance, and is therefore widely used for obtaining a dynamic memory circuit.

In this way, the progress of electronic devices centering on semiconductor devices is remarkable, and the requirements are becoming more and more stringent with it, but in order to meet these requirements, not only improvements related to the active element part, Improvement of passive elements such as resistors and capacitors is also an important issue that must be done in parallel with the above improvement.

Conventionally, a three-layer laminated body in which an insulating film is sandwiched between semiconductor layers or conductor layers has been used in various semiconductor devices. Recently, attention has been paid particularly to the above-mentioned MOS.
It is used as a charge storage capacitor of a dynamic memory. That is, although the high integration of this type of memory has been remarkable in recent years, the area of the capacitor must be reduced accordingly.

However, even if the area is reduced, the capacitance of the capacitor cannot be reduced so much in terms of circuit operation.
Therefore, as one method for solving this problem,
It has been considered to use, for example, tantalum oxide, niobium oxide, titanium oxide, hafnium oxide, zirconium oxide, or aluminum oxide having a high dielectric constant as the insulating film of the layer stack.

Conventionally, the insulating film used for such a purpose has a drawback that the leak current is large. To overcome this drawback, a method using an anodic oxide film with a relatively small leak current [eg, IEEE Transactions on Electron. Devices (Trans.Electron.Devices), ED
-29, pp.368-376, 1982.] or a method of using a two-layer film of the above oxide film and a silicon thermal oxide film with an extremely small leak current [eg, Proceedings of Symposium on VLSI Technology]. (Proc.Symp.VLSI T
ech.), pp.86-87, 1983.] and the like.

However, since the former uses an electrolytic solution, there is a risk of contamination from the electrolytic solution, and the latter has a low dielectric constant of the silicon thermal oxide film, so that the effective dielectric constant decreases. There were drawbacks and none were satisfactory.

Problems to be Solved by the Invention As described above, in MOS dynamic memories for electronic computers and the like, it is necessary to reduce the area of capacitors because of the demand for miniaturization and high integration. However, its capacitance cannot be so small for reasons of circuit operation.

Therefore, it becomes necessary to develop a capacitor having a large capacitance per unit area, and various methods as described above have been proposed for that purpose, but no satisfactory method has been obtained so far.

On the other hand, an insulating film formed by a usual sputtering method, a vapor deposition method or the like without utilizing the solutions disclosed in the above two documents was too large in leak current and could not be put into practical use. .

Therefore, a first object of the present invention is to sandwich the insulating film between a semiconductor layer or a conductor layer in which the capacitance per unit area is significantly improved by reducing the leak current of the insulating film. Another object of the present invention is to provide a semiconductor device including the three-layer laminated body as a capacitor.

A second object of the present invention is to provide a method of manufacturing a semiconductor device including the above capacitor.

Means for Solving the Problems In view of the above-mentioned present situation of the semiconductor device having the capacitor having the three-layer laminated structure as described above, the present inventors have made an insulating film formed by a usual sputtering method, an evaporation method or the like. As a result of various investigations to reduce the leakage current of, the inventors have found that it is extremely advantageous to increase the purity of the insulating film material, and have completed the present invention.

That is, the semiconductor device of the present invention has a three-layer structure including a first semiconductor layer or a conductor layer, an insulating film formed thereon, and a second semiconductor layer or a conductor layer provided on the insulating film. In a semiconductor device including a laminated body, the insulating film is a high-purity film that is substantially free of alkali metals, alkaline earth metals, heavy metals, semiconductor substances and radioactive elements.

As the insulating film material useful in the semiconductor device of the present invention, an insulating material having a high dielectric constant, such as tantalum oxide, niobium oxide, titanium oxide, hafnium oxide, zirconium oxide,
Aluminum oxide etc. can be illustrated. Impurities that have a detrimental effect on capacitance, that is, that may lower the capacitance, include alkali metals such as sodium and potassium, alkaline earth metals such as calcium, heavy metals such as chromium, iron and nickel, and molybdenum, Metals such as niobium, tungsten, zirconium,
It is a semiconductor such as silicon or a radioactive element such as uranium.

Further, the insulating film in the present invention may have a single layer (including a composite layer) of at least one kind of various raw materials as described above or a laminated structure composed of a plurality of layers.

Thus, the high-purity insulating film according to the present invention can be manufactured as follows. That is, the reactive sputtering method,
Various methods such as a thermal oxidation method, a chemical vapor deposition method, and a vapor deposition method can be used, but it is necessary to devise such that the purity of the insulating film can be maintained high.

For example, when the reactive sputtering method is used, a high-purity metal is used as a target on the conductor layer on the semiconductor substrate,
A corresponding oxide insulating film is obtained by reactive sputtering in a mixed gas atmosphere of argon and oxygen.The metal target is an ingot obtained by melting a metal with an electron beam under a high vacuum condition of 10 ⁻⁴ Torr or more. Form. At this time, impurities having a melting point lower than that of the metal are removed by evaporation. By performing this operation at least once, a high-purity metal ingot can be obtained, and this is rolled and processed to be a target. Of course, a method of using this as a vapor deposition source and then performing thermal oxidation is possible.

Further, in the chemical vapor deposition method, halides such as chlorides and other organometallic compounds containing a lower alkyl group such as methyl and ethyl are used as raw materials, and thermal decomposition and photodecomposition cause oxidation after the formation of a metal film. Alternatively, the metal oxide can be directly obtained by decomposing and oxidizing in an oxygen atmosphere. Also in this method, by using a high-purity raw material, it is possible to obtain the high-purity insulating film which is the object of the present invention.

It is necessary to keep the inside of the device clean in the above-mentioned insulating film forming operation and take sufficient care not to contaminate it.

Action To obtain a capacitor having a large capacitance per unit area, which is the object of the present invention, it is necessary to reduce the leak current of the insulating film.

That is, according to the knowledge of the present inventors, an insulating film formed by a normal sputtering method or the like without using the above-described method of using an anodized film or using a silicon thermal oxide film together It was found that the leak current was large and the reason was that the purity of the insulating film was low.

Therefore, even by the ordinary film forming method, as long as its purity is secured, a sufficient large capacitance per unit area can be obtained without using a special film forming method or using another film together. it can. From this point of view, an example of trying to improve the capacitor has not been known so far.

For example, a leakage current characteristic of a capacitor composed of a three-layer laminated body in which a commercially available tantalum target is sputtered in an atmosphere containing argon and oxygen to form tantalum oxide on a silicon substrate, and an aluminum layer is formed thereon is The curve a in FIG. 2 was obtained, and the concentration of main impurities in the tantalum target used at this time was as shown in the column of "conventional target" in the table below.

Although the results in the above table are the analysis results for tantalum, the upper limit of the allowable abundance of impurity elements is the numerical value shown in the column of "Target of the present invention" in the table, and niobium other than tantalum, titanium, Hafnium, zirconium,
The same applies to aluminum. Of course, when the target element and the impurity match (for example, niobium or zirconium), it is not necessary to satisfy the requirement as the impurity.

In the present invention, the upper limit of the above impurities is critical, and is an essential requirement for obtaining an insulating film having a desired performance, and thus a semiconductor device having predetermined physical properties.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and the effects thereof will be demonstrated, but the scope of the present invention is not limited to these Examples.

FIG. 1 shows a sectional view of a three-layer laminate manufactured according to the present invention. Tantalum oxide film 2 is formed on silicon substrate 1 by targeting high-purity tantalum and reactive sputtering in a mixed gas atmosphere of argon and oxygen. Next, aluminum is formed on the tantalum oxide film 2 by vapor deposition and patterned by photolithography to form the upper electrode 3. The semiconductor device thus formed has a silicon substrate 1 as a semiconductor layer and an aluminum upper electrode 3 as a conductor layer.
In addition, a semiconductor device including a three-layer laminated body in which a tantalum oxide film 2 which is a high-purity insulating film is sandwiched is formed.

The tantalum target used at this time was manufactured by the following procedure. First, after tantalum powder is sintered, this sintered body is
An ingot was formed by electron beam melting in a high vacuum of 10 ^-4 Torr. At this time, impurities having a melting point lower than that of tantalum were evaporated and removed. Although the electron beam melting is effective even once, the purity is improved with each repetition, so that the melting was performed three times in this example. Then, the ingot was rolled and processed to form a target. The concentrations of main impurities in the target were as shown in the column of "Target of the present invention" in the above table. That is, the amount of alkali metals or alkaline earth metals such as calcium, sodium and potassium is 0.1 ppm or less, which is decreased by one digit or more as compared with the conventional target. Also, heavy metals such as chromium, iron, and nickel are less than 0.5ppm, which is more than that of conventional targets.
It has decreased by an order of magnitude. The amount of semiconductors such as silicon is 0.05 ppm or less, which is more than two orders of magnitude lower than conventional targets. The amount of radioactive elements such as uranium is 0.0005ppm or less, which is about 3 orders of magnitude less than conventional targets. The impurity concentration of the tantalum oxide film 2 was almost the same. This could be achieved by keeping the inside of the sputter device clean and handling the silicon substrate 1 very carefully to avoid contamination.

The curve b of FIG. 2 shows the leakage current characteristic of the capacitor composed of the three-layer laminate. It is clear from this figure that the leakage current is significantly reduced compared to the conventional capacitor.

According to the leakage current characteristics of FIG. 2, there is not much difference between the curve a indicating the leakage current of the capacitor of the conventional example and the curve b indicating the leakage current of the capacitor of the present embodiment, the slope itself. Both are considered to be pool-Frenkel type currents, which are currents due to hopping conduction of electrons through traps in the insulating film. Therefore, it is considered that the small leak current in this example is because the trap density in the insulating film is reduced because the impurity concentration of the alkali metal, the heavy metal, the semiconductor and the like is low.

In the above embodiments, the concept of the present invention has been described using the silicon substrate as the lower electrode and the aluminum as the upper electrode, but the lower electrode and the upper electrode may be different semiconductors, metals or other conductive materials. It was confirmed to give similar results. Further, although tantalum oxide is used as the intermediate insulating film in the description, it suffices that the insulating film has a high dielectric constant, and niobium oxide, titanium oxide, hafnium oxide, zirconium oxide, aluminum oxide or the like may be used. Of course, it was also confirmed that a similar effect can be obtained even with a multilayer film or a composite film made of some of these films. Further, although the reactive sputtering method has been used as the method for forming the insulating film, a thermal oxidation method, a chemical vapor deposition method, or a vapor deposition method may be used as long as the forming method can maintain the purity of the insulating film at a high level. Any method is included in the concept of the invention and gives equally good results.

Furthermore, although the concept of the present invention has been described in the above embodiments using a simple capacitor, any device may be used as long as it is a semiconductor device including a three-layer laminate in which an insulating film is sandwiched between semiconductor layers or conductor layers. It is obvious that the present invention can be applied without impairing the concept of the present invention, and can of course be applied to a groove type MOS capacitor. Needless to say, it may be the gate portion of the MOS type FET.

Further, according to the present invention, in addition to the reduction of the leak current, since the alkali metal in the insulating film, in other words, the mobile charge is small, there is little change in the electrical characteristics of the semiconductor device over time, and almost no radioactive element is contained. Therefore, there is an effect that the semiconductor device does not cause a so-called soft error, and the characteristics of the semiconductor device can be further improved.

EFFECTS OF THE INVENTION As described above, according to the present invention, the leakage current of the insulating film can be significantly reduced, so that the capacitance per unit area is very large, and the semiconductor layer or the conductor is excellent in insulation. A three-layer laminate of layer-insulating film-semiconductor layer or conductor layer is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a three-layer laminated body forming a capacitor, and FIG. 2 is a leakage current characteristic diagram of the capacitor as shown in FIG. 1 formed in the present invention and the conventional example. (Main reference numbers) 1 ... Silicon substrate, 2 ... Tantalum oxide film, 3 ... Aluminum upper electrode

Claims (4)

[Claims] 1. A three-layer laminate of a first semiconductor layer or a conductor layer, an insulating film formed thereon, and a second semiconductor layer or a conductor layer provided on the insulating film. In a semiconductor device, the insulating film contains at least one kind of material having a higher dielectric constant than a silicon thermal oxide film as a constituent substance, and the insulating film contains the following elements with the following amounts as upper limits. The semiconductor device described above. 2. The insulating film comprises tantalum oxide, niobium oxide,
The semiconductor device according to claim 1, which is a film containing at least one of titanium oxide, hafnium oxide, and aluminum oxide as a constituent material. 3. A method of manufacturing a semiconductor device including a three-layer laminated body obtained by forming an insulating film and a second semiconductor layer or conductor layer on a first semiconductor layer or conductor layer in this order. , The insulating film is a film containing at least one kind of material having a dielectric constant higher than that of the thermal silicon oxide film as a constituent substance, and reacts using a raw material containing the following elements with the following amounts as upper limits. The method for manufacturing a semiconductor device as described above, which is formed by a reactive sputtering method, a thermal oxidation method, a vapor deposition method or a chemical vapor deposition method. 4. The method according to claim 3, wherein the metal for the insulating film raw material is purified by at least one electron beam melting treatment under a high vacuum condition.