JPH01290766A - Ti-containing high-purity ta target and its production - Google Patents

Abstract

PURPOSE:To develop the title Ti-contg. high-purity Ta sintered target for sputtering capable of forming a high-quality Ta2O5 film by crushing the high- purity hydrides of Ta and Ti, mixing both materials in a specified ratio, dehydrogenating the mixture, sintering, and then homogenizing the product by heating. CONSTITUTION:The Ta target is used when a high permittivity Ta2O5 film is formed by sputtering as an insulating film between the electrode wiring layers in a semiconductor device. At the time of producing the target, the 5-6N high-purity Ta and Ti produced by the electron-beam melting method are heated in a hydrogen atmosphere, and hydrogenated to TaH2 and TiH2. The hydrides are crushed, and mixed so that the Ti concn. is controlled to 0.1-2atom%. The mixture is heated in a vacuum to dehydrogenate the TaH2 and TiH2, pressed, formed, hot-worked at high temp. and pressure, sintered, further heated at 1600-2000 deg.C, and homogenized by mutual diffusion. By this method, a Ti-contg. high-purity Ta sitered target for sputtering capable of forming a Ta2O5 film with an extremely less leakage current is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Ti-containing high-purity Ta sintered target and a method for manufacturing the same. The present invention also relates to the above-mentioned homogeneous target and a very useful manufacturing method for manufacturing the same. The present invention can be applied to SiO□ film or 5
The Ta2e film, which has a larger dielectric constant than the iJ4 film and has a sufficient capacity even in Brainer cells, can be used in DRAMs of 4M or more.

Menzutate 11 Traditionally, silicon oxide films (SiOx films) have been used as insulating films between electrode wiring layers in semiconductor devices. The performance is no longer sufficient, and attempts are being made to use a tantalum oxide film (TazOs), which has a higher dielectric constant. Furthermore, 4M DRAM (Dyna
mic Random Access Memory
) development of large-capacity DRAM is progressing. Many LSI manufacturers have adopted trench capacitors because brainer cells using SiO□ or 5isN4 films as dielectrics do not have sufficient capacity, but recently, trench capacitors are being used to avoid the technical difficulties associated with trench technology. Therefore, much attention is being paid to Brehner cells that use a tantalum oxide film with a high dielectric constant as a dielectric for capacitors. The tantalum oxide film has a high dielectric constant of 25 to 30, and has a sufficient capacity even in a Brainer cell, making it practical.

Thus, it is inevitable that tantalum oxide films will play an important role in the future semiconductor device field.

Useful methods for forming a tantalum oxide film are a CVD method using an organic reactive gas and a sputtering method in which a tantalum target (referred to as a Ta target) is sputtered in an argon-oxygen mixed gas. From a comprehensive standpoint, the sputtering method is considered advantageous.

The TaJs film contains many trap centers in the film, so leakage current easily flows. It is thought that the main cause of leakage current is impurities, and therefore, the applicant et al.
We are proceeding with the development of high-purity Ta targets and
, 999% to 99.9999% purity), and achieved many results.

This high-purity Ta target is produced by dissolving raw material Ta in hydrofluoric acid or a mixed acid containing it to produce a tantalum-containing aqueous solution, and adding an aqueous solution containing potassium ions to the tantalum-containing aqueous solution to precipitate potassium tantalum fluoride crystals. The recovered potassium tantalum fluoride crystals are reduced to produce metal tantalum powder, the metal tantalum powder recovered by washing is pressure-molded and sintered, and then a metal tantalum ingot is formed by electron beam melting. It is obtained through a series of processes that combine chemical and physical refining to process a target from a tantalum metal ingot, including Nb, Mo, W, and Zr.
High melting point metals such as Fe, Ni, Cr, etc., Na,
Alkali metals such as Ni and radioactive metals such as U are reduced to trace amounts.

Ta2 formed using the above-mentioned high-purity Ta target
Although the 05 film has achieved many results, there is a desire in the industry to further reduce leakage current in order to manufacture higher quality semiconductor devices.

By the way, tankurpentaethoxide (
In connection with the CVD method using Ta(OCJ@)s), T
It has been reported that oxygen vacancies in the axes film cause leakage current, and that by injecting tetravalent titanium into the oxygen-deficient portions, the leakage current can be reduced by making it substantially equivalent to Ta2's. As the titanium-containing gas, titanium tetrapropoxide (Ti (OC3H-) 4)
was used (Sem1connduC+orWor
ld 1987.3 pp45-50), however, 5. The properties and behavior of the Ta205 film in the sputtering method using a target in relation to - and h are still completely unknown.

Therefore, in light of these circumstances, the object of the present invention is to
Apart from the VD method, the purpose of this project is to develop a Ta target that makes it possible to produce a TazOs film with even lower leakage current than before, especially as an insulating material for large-capacity LSI capacitors, in a sputtering method.

In order to make it possible to stably deposit a high-quality film by sputtering, the following requirements are absolutely important for the target: (1) high purity, (2) homogeneity, and (2) high density.

Another object of the present invention is to establish an optimal manufacturing method for manufacturing the target while satisfying these requirements.

Juho ff1 As a result of repeated research aimed at the above-mentioned purpose, the present inventors discovered that even in Ta205 films produced by sputtering, oxygen vacancies cause leakage current, and by injecting titanium therein, the leakage current can be reduced. I have come to find out what is possible. However, while satisfying the above requirements, Ti
Obtaining a Ta-containing target is not as easy as one might think. Powder metallurgy and melting methods are known for producing targets, but with powder metallurgy it is difficult to satisfy the requirements for uniformity of composition and density, and on the other hand, with melting, it is difficult to satisfy the requirements for uniformity of composition and density. The vapor pressures of Ta and Ti are each 10-
2 torr and 102 torr or more, and there is a difference of more than four orders of magnitude, so Ti is selectively evaporated and removed, making it difficult to obtain a product with the target composition.

Due to these circumstances, it is extremely difficult to manufacture a Ti-containing Ta target that can be used as an LSI capacitor and has vine characteristics.

Under these circumstances, the present inventors hydrogenated high-purity Ta and Ti obtained by the electron beam melting method by a method combining electron beam melting method and powder metallurgy method, and then produced the pulverized products. High density, high purity and uniform Ti-containing Ta is obtained by mixing, then dehydrogenating, then sintering and heat treating for uniformity.
We learned that it is possible to obtain targets. Furthermore, it has been found that in order to compensate for oxygen vacancies in the Ta205 film, it is good to include Ti in a concentration of 0.1 to 2 at% in the target.

Based on these findings, the present invention provides: 1) a Ti-containing high-purity Ta sintered product target in which 5N to 6N high-purity Ta contains Ti at a concentration of 0.1 to 2 at%; and 2) electron beam melting. High purity Ta and Ti obtained by the method were hydrogenated and pulverized to obtain TaHz powder and TiHzi powder, and then both powders were reduced to 01-2 at%.
Production of a Ti-containing high-purity sintered product target characterized by blending and mixing to obtain a Ti concentration, followed by dehydrogenation treatment, then sintering to densify, and heat treatment for homogenization. method provided. Preferably, sintering is carried out by hot pressing or cold pressing followed by HIP.

The target of the present invention is a high-density and homogeneous fired crystal of 5N to 6N extremely high-purity Ta containing Ti at a concentration of 0.1 to 2 at%. characterized by something. Ta
The Ti concentration in the target is 0.1 to 2 at%, preferably 0.5 to 1. Oat%.

When sputtering such a target, Taz
The Ti content in the Os film is 0.01 to 0.2 at%, which corresponds to the oxygen vacancy concentration in the Ta205 film. If it is lower than this, there will be no effect of compensating for oxygen vacancies, while if it is higher than this, the T1 atoms themselves will act as impurities and instead cause leakage current.

The target needs to be of very high purity, between 5N and 6N. This is necessary to reduce leakage current and also to improve the reliability of semiconductor device performance.6 For example, alkali metals such as Na, K, Li, etc.
It easily moves in the gate insulating film and deteriorates the interface properties. Radioactive metals such as U and Th have a fatal effect on the operational reliability of semiconductor devices due to radiation from them. This is called a soft error and is considered serious in the computer industry. Heavy metals such as Fe, Ni, Cr, etc. generate interface states and cause junction leakage, resulting in adverse effects. Furthermore, it has recently been recognized that high melting point metals such as Nb, Mo, W, Zr, and Hf have high electrical conductivity in their oxides and cause leakage current. To avoid the harmful effects of these impurities, a purity of 5N or higher, currently between 5N and 6N, is required.

For reference, an example of the impurity content of a 6N purity Ta target manufactured by the applicant is shown in the following table.

1.
-mN b < 0.2 High melting point M o < 0.2 Metal
W 0.3Zr<
0.2 Alkaline Na <0.02K
<0.02 Fe <0.05 Heavy metal Ni <0.02 Next, a method for manufacturing this target will be described.

(A) First, high-purity Ta and Ti ingots obtained by electron beam melting Ta and Ti raw materials are cut, and the cut pieces are hydrogenated and crushed to obtain TaHzM powder and TiHzi powder. , 0.1
They are blended and mixed so that the concentration of Ti is ~2 at%, and then dehydrogenation treatment is performed.

It is important to mix Ta and Ti in the form of hydrides and to convert them into hydrogen after mixing. By using Ta and Ti in the form of hydrides, pulverization becomes very easy, and a powder having a particle size with good sinterability can be obtained during subsequent sintering. Dehydrogenation results in a surface active powder that further promotes sintering. Furthermore, it is effective in preventing oxygen contamination. Together, these contribute to densification and homogenization of the final target. Eliminate the main process to zero: Of course, it is better to have high purity from the mechanical standpoint of Ta or hair processing, but since impurities can be removed in the electron beam melting process, it is not necessary to have particularly high purity. However, it is necessary to remove high melting point metals such as MOLW, which cannot be removed by the electron beam melting process, in advance. For this purpose, it is preferable to use a raw material that has been subjected to a chemical purification process in which crystals are collected from a solution and reduced, as explained in the section of the prior art. commercially available,
Metal or oxide powder with a purity of 3N to 4N can be chemically purified and used if necessary.

11 The electron beam melting method is a method of melting Ta and Ti sintered electrodes as objects to be melted in vacuum by applying an electron beam to them, and utilizes the difference in vapor pressure of the contained substances. High purity Ta and Ti materials can be obtained by selectively evaporating and removing impurities with high vapor pressure.

11 Cuttings of the ingot obtained by Kisui Koshin electron beam melting are heated to 400 to 800°C, preferably 500 to 600"C.
Heat in a hydrogen atmosphere for 10-15 hours. At a temperature lower than 400°C, the hydrogenation reaction does not proceed, while at a temperature higher than 800°C, the amount of solid solution of H in Ta is low and no hydride is formed. To obtain sufficient hydrogenation at these temperatures, 10~
A relatively long treatment time of 15 hours is required. The hydride is very brittle and can be easily ground using a mill or the like, thus obtaining TaHz powder.

The method for applying 1 part of Ti standing ice water is based on the above Ta. Cutting pieces at 300-500℃
, preferably at 350 to 450° C. for 1 to 5 hours in a hydrogen atmosphere. Ti) I2 powder is obtained.

■ The separately prepared TaHz powder and TiH2 powder now contain 0.1 to 2 at%, preferably 0.5 to 1.0 at%.
% T1 concentration and mixed using, for example, a type mixer.

1 Water 1 Vacuum heating at 600-700°C removes the hydrogen from the mixture and regenerates it into the form of Ta and Ti metals. These have properties suitable for sintering. (B) After this, the dehydrogenated mixture is sintered to densify by cold pressing followed by HIP or by hot pressing and subjected to a heat treatment for homogenization.

It is carried out by cold press mold pressing or CIP at a pressure of 1300 kg/cm2 or more. The upper limit of the pressure is determined by the capacity of the vine press used, for example 1500 k
g/cm" level is sufficient for practical use. When the pressure is 1300
If the density is less than "kg/am", the density will not increase sufficiently.After this, the density will be reduced to 0.
Degassing in vacuum for 5 to 3 hours is preferred.

"Scorched Earth 2 Ink" The above molded product is stored in an appropriate capsule and heated to a temperature of 1200.
~1500°C, preferably 1350~1400°C and pressure cuff 00 kg/cm2 or more, preferably 1500°C
Hot isostatic processing is performed at kg/cm2 or higher.

The upper limit of pressure is still the maximum capacity of the equipment. The upper temperature limit is the limit temperature at which the capsule material used does not melt. If the temperature is lower than 1200°C, the density will be insufficient. 7
If the pressure is less than 0.00 kg/cm2, the density will still be insufficient and appropriate target properties will not be obtained. 0 at specified pressure
．． It is maintained for a sufficient period of time, such as 5 to 3 hours.

Temperature: 1300-1650℃, preferably 1500-1650℃
C. and a pressure of 200 kg/cm" or more, preferably 300 to 350 kg/cm". The upper limit of pressure depends on the strength of the die used. 200
A pressure lower than kg/cm2 results in insufficient density. 13
At temperatures lower than 00°C, density is likely to be insufficient.

If the temperature exceeds 1650℃, Ti may dissolve.
Uneven distribution of Ti may occur. Furthermore, since the process is performed in a vacuum, evaporation of Ti is likely to occur.

Temperature: 1600~2000℃, preferably 165o~1750℃
Carry out at a temperature of °C. The purpose of this treatment is to homogenize the alloy by promoting mutual diffusion of Ti and Ta, and requires conditions for obtaining a sufficient Ti diffusion distance.

As a rough guide, a Ti diffusion distance of about 100 μm is sufficient for homogenization. At temperatures lower than 1600°C, only enough T is required for alloying within practical time (within 24 hours).
No diffusion of i atoms occurs. The higher the temperature, the faster the diffusion, but
Because Ti evaporation and grain coarsening occur, the temperature is less than 2000°C, preferably 1750°C or less. In order to prevent Ti evaporation as much as possible, it is recommended that the process be carried out in an Ar pressurized atmosphere.

This heat treatment is very important in the present invention. 1st
- Figure 4 shows the results after heat treatment at 1650°C for 10 hours, after heat treatment at 1670°C for 10 hours, and after heat treatment at 1670°C for 10 hours while in the HIP state.
It is a micrograph showing the metal structure of a Ti-containing Ta alloy after 90'CX heat treatment for 3 hours (black parts are titanium). The effectiveness of heat treatment is clearly understood.

(C) Finally, the sintered body is finished as a Ti-containing high purity Ta sintered product target through required steps such as machining and surface polishing. The target is generally disc-shaped.

These are carried out by conventional methods, taking care to prevent contamination.

High purity Ta and Ti ingots obtained by electron beam melting Ta and T1 raw materials with >4N were cut, the cut pieces were hydrogenated and crushed, respectively.
Ta) I2 powder and TiLi powder were obtained. Both are blended and mixed so that the concentration of Ti is 0.8 at%, and then 6
Dehydrogenation treatment was performed at 50°C.

Then cold pressing at 1500 kg/cm2 - 700°C xi) Degassing at lr - 1400°C x 1
By HIP treatment at 500 kg/cm2x 2 Hr or at 1600°C x 300 kg/cm"x 2
Shaping and sintering was carried out by hot pressing at Hr.

These were heated at 1690°C under Ar pressure of 5 kg/cm2.
31 (r) heat treatment was carried out. The obtained structure was as shown in FIG. 4 above.

Films formed by sputtering in an argon and oxygen atmosphere using this target showed reduced leakage current. The quality of the produced film was also equivalent to that of the pure target.

With the development of a high-quality Ta target containing Ti, it has become possible to form a high-quality Ta21s film with a much lower current density using the highly useful sputtering method, and it has become possible to form a high-quality Ta21s film with a much lower current density, making it possible to form a high-quality Ta21s film with a much lower current density. The dielectric constant is large compared to
4M Ta205 film that has sufficient capacity even in brainer cells
This makes it possible to use the present invention in the above DRAMs. Furthermore, we developed a manufacturing method that combines electron beam melting and powder metallurgy, and succeeded in establishing a method for manufacturing high-density, homogeneous targets with stable quality.

[Brief explanation of the drawing]

Figures 1 to 4 show 1650'CXl0 while in HIP state.
FIG. 3 is a micrograph showing the metal structure of a Ti-containing Ta alloy after heat treatment for 1 hour, after heat treatment at 1670° C. for XIO hours, and after heat treatment at 1690° C. for 3 hours. ＃、.

Claims (1)

[Scope of Claims] 1) A Ti-containing high-purity Ta sintered target in which 5N to 6N high-purity Ta contains Ti at a concentration of 0.1 to 2 at%. 2) High purity Ta and Ti obtained by electron beam melting are hydrogenated and pulverized to form TaH_2
After making powder and TiH_2 powder, these powders were 0.1
A Ti-containing high-purity sintered product target characterized by blending and mixing Ti at a concentration of ~2 at%, followed by dehydrogenation treatment, then sintering to increase density, and homogenization by heat treatment. Production method. 3) The method for producing a Ti-containing high-purity sintered product target according to claim 2, wherein the sintering is performed by hot pressing or cold pressing followed by HIP.