JPH02213490A - Production of high-purity titanium and equipment thereof and high-purity titanium target material - Google Patents

Abstract

PURPOSE:To obtain high-purity metallic titanium extremely little in the contents of alkali metal, radioactive elements, heavy metal and oxygen by utilizing a titanium raw material wherein titanium sponge is compressed to a briquette state and utilizing high-purity Ni for the members and parts brought into contact with molten salt and electrolyzing this molten salt. CONSTITUTION:In the production of high-purity titanium by an electrolytic method of molten salt, the parts or the members such as a crucible, a basket made of titanium sponge, an anode and a cathode which are brought into contact with molten salt are constituted of high-purity nickel. In this electrolyzer of molten salt, NaCl is generally utilized as molten salt and a basket housing titanium sponge is connected to the anode side and titanium is electrodeposited on the cathode of the cathode side. In this case, when the average atomic value of titanium in the electrolytic bath is regulated to 2.1-2.3, excellent electrolysis is enabled and electrodeposited dendritic titanium which has high purity and is large in crystal grain contg. a hexagonal plate is obtained. As a result, high purity-titanium is obtained which has sufficiently high purity capable of being utilized even for applications of sputtering in a semiconductor domain and is industrially profitable.

Description

Detailed Description of the Invention The present invention relates to a method and apparatus for producing high-purity titanium, and a high-purity titanium target material, and particularly to a high-purity titanium material suitable for producing a high-purity titanium target for manufacturing semiconductor devices. It is related to the production of. The titanium target produced based on the present invention is VLS
The use of I as a barrier layer and as a wiring material in place of aluminum is seen as promising.

Traditionally, silicon oxide films have been mainly used as barrier materials between the eyebrows in semiconductor devices, but with the increasing integration of LSIs, high melting point metals such as molybdenum and tungsten have been used, especially There is growing interest in the use of titanium. Further, attempts are being made to use titanium as a wiring material in place of the conventionally used aluminum. Such titanium interlayer barriers and interconnects are typically formed by sputtering a titanium target in argon. A titanium target is manufactured by molding, sintering, and melting a commercially available titanium raw material, and then performing machining.

In order to improve the reliability of the performance of semiconductor device elements, (1) alkali metals such as Na, Li, etc., (2) U
, radioactive elements such as Th, (3) heavy metals such as Fe and Cr, and (4) impurities such as oxygen. Alkali metals such as Na and Ni easily move in the gate insulating film,
-Causes deterioration of LSI interface characteristics. Radioactive elements such as U cause soft errors in devices due to alpha rays emitted from the elements. Heavy metals such as Fe also cause trouble at interfacial joints. Oxygen causes property deterioration (.

By the way, the purity of the titanium target required for recent IMDRAM and 4MDRAM is 5N (99,999%).
(excluding gas components). That is, Nas
The content of alkali metals such as K is 0.1 pp- or less, and the content of radioactive elements such as U and Th is 1 pp each.
The content of heavy metals such as Fe and Cr must be 0.5 ppm or less, and the oxygen content must be 150 ppm or less.
The content is required to be less than ppm, preferably less than 100 ppm.

The pure titanium currently produced industrially contains a large amount of alkali metal elements in addition to the heavy metal elements and gas components mentioned above, and cannot be used in the semiconductor field at its current purity.

As a method for further purifying pure titanium, JP-A-62-
There are titanium iodide pyrolysis processes, such as those described in US Pat. However, this method has a limit in purification purity, and according to its examples, for example, Fe 5
0pp-, which is much higher than the required level, making it unsuitable for semiconductor applications.Furthermore, the titanium iodide thermal decomposition method is originally a method for experimental scale, and is not suitable for industrial scale production.The reason is that the titanium precipitation rate is is too small,
For example, if the diameter of the titanium plate is 10 cm, 176 g in 10 hours,
The amount of precipitation per hour is only 17.6, and the high temperature (
Induction heating is used to maintain thermal decomposition at a temperature of 1,100 to 1,500°C, but the amount of titanium deposited per electric power is 0.59.
g/kwh, which is very small.

As described above, the titanium iodide thermal decomposition method has a limited purification purity, poor productivity, and is extremely expensive.

Another known method is molten salt electrolysis.

The molten salt electrolytic method has been studied for the purpose of electrowinning titanium, but purification of titanium sponge is also being considered.For example, see Bureau of Mines J
(1957) pp. 1-43 Report of
For investment, a mixed salt of rLiCl-KCI was melted in an iron crucible, and TiCl4 was first blown into 11 grooves in the crucible to melt T.
Next, the iron basket containing the Ti sponge and the TI cathode are replaced, and electrolysis is performed using the Ti sponge as an anode and TiC1□ as a carrier to deposit pure titanium on the T1 cathode. ” method is described. The Fe content of precipitated titanium is 20
It is at an extremely high level of 0 ppm.

Furthermore, when similar electrolytic refining was carried out using another apparatus using a mild steel cell, the Fe content of the precipitated titanium was 110 pp.

In both cases, the iron content was extremely high, and the purification of Fe < ippm, which is the objective of the present invention, was completely impossible with such methods and equipment.

TiCl4 and TiC instead of iron crucibles or containers
Stainless steel, graphite, etc. have been considered as structural materials that can withstand 1g of molten salt;
A small amount of molten salt (00 to 850°C) eroded and eluted, contaminating the precipitated titanium.

Furthermore, since titanium sponge has a low bulk density, the amount charged is small, which hinders productivity. The oxygen content of the purified product was also high.

Menzutachi 11 In view of the above-mentioned current situation, the present invention is to establish a titanium purification technology that is sufficiently pure to be used even for sputtering applications in the semiconductor field and is industrially profitable.

In particular, the present invention aims to obtain a titanium material suitable for producing a high-purity metallic titanium target, which has an extremely low content of oxygen gas as well as alkali metals, radioactive elements, and heavy metals.

The inventor of the present invention basically believes that molten salt electrolysis is most suitable for this purpose, and as a result of examining various materials that can be used in molten salt electrolysis, the inventor found that nickel is suitable for molten salt electrolysis. It has been discovered that this material is suitable as a structural material for various parts and members of equipment.

Due to its low strength, nickel was never considered for use as a structural material, and at first it was thought that the amount of migration would be small because it was a sensitive metal, but a small amount of migration was still unavoidable. In addition, this is the first time that it has been found that it does not contaminate titanium.

Thus, the present invention provides: 1) A method for producing high-purity titanium by molten salt electrolysis, in which a titanium raw material obtained by compressing a titanium sponge into a priquet shape is used, and at least the members or parts that come into contact with the molten salt are highly purified. 2) A method for producing high-purity titanium characterized by carrying out electrolytic operation using a molten salt electrolyzer made of pure nickel; A high-purity titanium production apparatus characterized by being constructed from high-purity nickel. 3) A sleeve made of polytetrafluoroethylene is inserted for electrical insulation at the sliding seal portion of the vibrator or rod associated with the cathode or anode. 2. The device according to item 2, in which the sleeve is divided into upper and lower parts and packing is interposed therebetween; and 4) the alkali metal content is 0.1 pp.
The present invention provides a high-purity titanium target material having a radioactive element content of 1 ppb or less, a heavy metal content of 0.5 ppm+ or less, and an oxygen content of 1100 pp or less.

In this specification, the alkali metal refers to a metal belonging to Group 1A of the periodic table, and is represented by Na, K, and LL. The radioactive element refers to an element having radioactivity such as U and Th. Heavy metals are Fe, Cr, which have relatively heavy atomic weights.
, Ni, Mn, etc.

1 Inhalation 1 Theft 11 The nickel used in the present invention has a purity of 3N (99.9%) or higher. As mentioned above, nickel is a heavy metal, and there are concerns about titanium contamination from nickel itself. Also, the use of especially high-purity materials as structural materials is questionable, and it is believed that small amounts can be leached into molten salts. was.

Contrary to such expectations, nickel has been found to be highly suitable as a material of construction for molten salt electrolyzers. This nickel is used in the crucible, titanium sponge basket, anode, cathode, tank inner wall surface, thermometer protection tube, etc. used in the molten salt electrolyzer (all components or members that come into direct contact with the molten salt). It is preferable that the inner surface of the device, which is exposed to the molten salt vapor, is also made of nickel, since it can become a source of impurity contamination when it adheres as droplets to the molten salt vapor and falls into the bath.
"Constructing" includes not only making a part or member from nickel itself, but also lining the surface or covering it with plating or other means.

The titanium molten salt electrorefining operation uses a stable, low melting point and high conductivity chloride, generally NaCl, as the molten salt, connects a basket containing sponge titanium to the anode side, and connects the titanium to the cathode on the cand side. This is done by electrodepositing. When performing electrolytic refining, if the average Ti valence of the electrolytic bath is 2.1 to 2.3, good electrolysis can be performed, and dendritic electrodeposited titanium with large crystal grains containing high purity hexagonal plates can be obtained. can get. For this purpose, TiCl4 is introduced into the bottom of the titanium sponge, and the following reaction TiCl4 + Ti → 2TLC1z
■TiC1i ÷TiCl4 → 2TLC1*
③ proceed, TiC1* and Tl in NaCl bath.
C1m is generated. ■ is the main reaction. As a result, TiC1m in the bath is usually 5 to 6% by weight and TiC1m
is 1.3-1.8% by weight, average TlC1g, +-x
, s. This average valence of 2.1 to 2.3 is an important condition for electrolytic refining.

FIG. 1 shows an example of a molten salt electrolyzer. An electrolytic cell container 1 is set in an electric furnace 2, and a container lid 3 is attached to its upper end via a seal such as a rubber O-ring. An upper chamber 5 is connected to the container lid 3 via a gate valve 4.
is installed.

For nickel preparation, nickel lined crucible 6 is container 1
charged inside. Two nickel anode vibes 7
A nickel basket 8 for storing titanium sponge is suspended in the container 1. A nickel cathode rod 9 is suspended and supported in the center of the container. Vibrator for exhausting the atmosphere inside the container or introducing inert gas
is formed directly under the container lid. An anode 11 is formed at the upper end of the anode vibe 7, and a cathode rod, 9
A cathode 12 is formed at the upper end of. 13a represents a cathode rod insulation seal, 13b represents an anode vibe insulation seal, and the container temperature is detected by a thermometer 14 inserted into a suitable protective tube. The container lid is provided with a boat 15 for charging and adding titanium sponge. 0 The above is an overview of the molten salt electrolyzer 0 In the present invention, a crucible, a titanium sponge basket, an anode vibrator, a cathode rod, Parts or members that come into direct contact with the molten salt, such as the thermometer protection tube, are made of nickel. The container 1 and the lid 3m are made of stainless steel, but the upper inner surface of the container and the inner surface of the container lid, where molten salt vapor tends to adhere as droplets to the wall surface, are also preferably lined with nickel.

An example of molten salt electrolysis operation will be explained based on the apparatus shown in FIG.

First, a predetermined amount of powdered anhydrous purified sodium chloride (NaCl) is charged into a nickel crucible 6, and the crucible is inserted into the electrolytic cell container 1, the container lid 3 is attached in a sealed state, and this is set in the electric furnace 2.

In order to avoid oxidation of the titanium sponge due to moisture in the powdered NaCl, the NaCl is once melted and solidified as a pre-operation. The vibrator 1O is heated to about 750° C. in an electric furnace 2 while evacuating the inside using a vacuum pump. This heating completely removes the moisture in NaC1.Next, an inert gas such as Ar is sealed at a pressure above atmospheric pressure, and the NaC
The temperature is raised to above the melting point of 1 (801''C) to melt NaCl. Afterwards, the temperature is cooled while ensuring that the pressure does not drop below atmospheric pressure to solidify NaCl.

The container lid 3 is opened, the nickel vibrator 7 supporting the basket 8 containing the titanium sponge is attached to the lid 3, and the lid 3 is reset so that the basket is placed in the space above the solidified NaCl.

Next, without evacuation again, the NaCl is melted again, an inert gas is filled in, and the nickel basket containing the titanium sponge is lowered and submerged in the NaCl bath.

In the next operation, TlCl4 (liquid) is introduced at a predetermined flow rate into the bottom of the titanium sponge using a micropump through a nickel vibrator, thereby allowing the reaction equations (1) and (2) shown above to proceed. The main reaction (2) produces TiC1□ in the NaCl bath, and at the same time, the reaction (2) also partially occurs to produce TiC1s. It is necessary to maintain the temperature at a sufficiently high temperature and measure the diffusion of 1 g of TiC. The amount of TiCl4 injected is the TIC in the normal bath.
Im 5-6% by weight and TiCls 1.3-1.8
The weight percent is set to be TiC1t, l-1.8 on average. As mentioned above, this average valence of 2.1 to 2
．． 3 is an important condition for electrolytic refining.

Thereafter, the cathode rod 9 is lowered from the upper part of the upper chamber, and is set and fixed so that its lower end is slightly above the bottom surface of the crucible. Similarly, adjust the position of the basket to the same position by adjusting the vibrator.

In this way, electrolysis is performed using the anode 11 as the anode and the cathode 12 as the cathode. Cathode current density is 0.8
~1.2 A/c and the electrolytic sliding voltage is generally 1.0
~1.4V range. However, these values can vary considerably depending on conditions.

By electrolysis, the raw material Ti and impurities such as Na, K, U, and Th%Mn whose electrode voltage is less noble than Ti are eluted at the anode. On the other hand, Fe, Cr, Ni, Cu, etc., which are caused by electrode voltage rather than TI, remain in the sponge without being eluted or settle as slime. On the other hand, at the cathode, only Ti and more serious metals are deposited. In the present invention, since virtually no impurities are dissolved into the liquid, these impurities are not deposited together with titanium during electrodeposition.

If electrolysis is continued for a certain period of time, the sliding voltage will be 0.6 to 0.8v.
At that point, the first electrolysis operation is completed.

The titanium electrodeposited on the cathode rod is pulled up into the upper chamber while maintaining the electrolytic bath temperature, and the gate valve 4 is closed. After rapidly cooling the deposited titanium in a water cooling jacket in the upper chamber to prevent oxidation, remove the flange on the gate valve and take it out.

Set another cathode instead and perform a second electrolysis operation under the same conditions as before.

Repeat the electrolysis operation depending on the amount of raw material titanium sponge.
When the amount of raw material titanium sponge decreases, the basket is pulled up above the bath, and titanium sponge is charged from the boat 15 for supplementation. At this time, inert gas is flowed into the electrolytic cell to prevent air from entering.

In this way, electrolysis operation is carried out while repeating the replacement of the titanium sponge and the replacement of the cathode rod. For each complementary phase of titanium sponge, the concentration of TiC1g and TiC1s in the electrolytic bath was analyzed, and the average valence was 2.1 to 2.3, and Ti
Confirm that C1m is 5.5 to 6%, but if there is no air intrusion, there will be almost no change in the above operation.
The complementary phase of the titanium sponge can also continue electrolysis as it is.

In order to perform electrolysis continuously and stably and to obtain high-quality, high-purity titanium with a low oxygen content, it is necessary to avoid the oxidizing effect of invading air as much as possible, as described above. The intruding air can be considered to be the one accompanying the raw material titanium sponge or the leaking oxygen from the atmosphere around the device.

Titanium sponge has a small bulk density of 0.7 to 1 kg/l.
Due to the small size, the amount charged to the electrolytic cell is small, which impedes the productivity of the device and increases the number of times the titanium sponge is complemented (which increases the risk of air leakage. Furthermore, the bulk of the titanium sponge The lower the density, the higher the void ratio, which inevitably entrains air when charging the electrolytic bath, and the constant intrusion of air into the inert atmosphere adversely affects the titanium valence of the electrolytic bath. Therefore, the higher the bulk density of the raw material and complementary titanium sponge, the better the result.In the present invention, the titanium sponge is placed in a mold, etc., and made into priquettes by pressing. Measures are taken to form the vacuum.In contrast to the vacuum degree of titanium, which is 4.5, it is preferable to make the sponge-like vacuum degree of 0.7 to 1.0 to 3.0 or higher in the priquet. Molding is not only effective as a measure to prevent oxygen leakage, but is also useful from the viewpoint of improving productivity and smooth continuous operation.

As mentioned in the operation description above, the anode vibrator is lifted out of the bath during bath preparation, titanium sponge complementation, etc.
The cathode rod is also lifted when pulling up the deposited titanium. Therefore, air leakage is likely to occur when the insulating seals 13a, b of the anode vibe or cathode rod slide.

To prevent this, the present invention provides a special seal for the anode vibe or cathode rod slide. An example thereof is shown in FIG. Here, it is shown as 16, which also serves as an anode vibrator or a cathode rod. This sliding part is electrically insulated by inserting a Teflon (trade name of polytetrafluoroethylene) sleeve 17 between the anode vibe or cathode rod 16 and the flange-connected vibe 21. In this case, the sleeve 17 is The parts are separated and a packing such as a rubber O-ring 18 is interposed therebetween. Furthermore, preferably a rubber gasket 19
is inserted between the upper end of the vibrator 21 and the flange of the lower part of the sleeve. This ensures a seal even when the vibrator or rod 16 is moved up and down. A water cooling jacket 20 is preferably provided to protect the sleeve and O-ring from thermal damage.

The electrodeposited titanium taken out is a dendrite crystal containing hexagonal plates, and after washing with water and pickling, it is vacuum-dried to obtain high-purity titanium.

High-purity titanium is made into an ingot using methods such as electron beam vacuum melting, and then processed into a sputtering high-purity titanium target through forging and other processing. It is preferable to employ an electron beam melting method, which has a large impurity removal effect. The molded body to be subjected to electron beam melting is preferably obtained by cold isostatic pressing.The obtained ingot is finally processed into a target of a desired shape. Plastic working, cutting, and surface finishing are performed by conventional methods, taking care to prevent contamination.

A film or wiring is formed by sputtering using this target in, for example, argon gas.

An example will be shown in which high purity titanium is purified by molten salt electrolysis using the apparatus shown in FIGS. 1 and 2.

Powdered anhydrous purified sodium chloride 40k in a nickel crucible
This was then inserted into the electrolytic cell container, the container lid was attached in a sealed state, and the container was set in an electric furnace.

In order to avoid oxidation of the titanium sponge due to moisture in powdered NaCl, as a pre-operation, NaCl was heated to about 750° C. while evacuating the inside using a vacuum pump.

Next, Ar was filled in to a gauge pressure of 0.1 kg/cm'', and the temperature was further raised to 850°C to melt NaCl.

Thereafter, it was cooled to about 500° C. while ensuring that the Ar pressure did not drop below atmospheric pressure.

After opening the lid, a nickel basket (3φ porous plate) containing 20 kg of titanium sponge was attached to a nickel vibrator lid supporting the lid, and the lid was reset so that the basket was placed in the space above the solidified NaCl.

Next, without evacuation again, the NaCl was melted again, an inert gas was filled in, and the nickel basket containing the titanium sponge was lowered and submerged in the NaCl bath.

Next, pass the nickel vibrator through the T to the bottom of the titanium sponge.
iC14 (liquid) at 15g per minute by micro pump
Each flow rate was introduced for 2.5 hours. This resulted in 5.5% by weight of 1g of TiC and 1.5% by weight of 1m of 7iC in the bath, so the average valence was 2.1-2.2.

Place the lower end of the cathode rod and the basket 3 CIs from the bottom of the crucible.
It was set to Il.

The cathode current density is 1. OA/cm" and the electrolytic sliding voltage was 1.2 V.

After being energized for about 70 hours, the sliding voltage was 0.6 to 0.8.
V, and the first electrolysis operation was stopped.

While maintaining the electrolytic bath temperature at 850°C, the titanium deposited on the canned rod is pulled up into the upper chamber, the gate valve 4 is closed, and after cooling the deposited titanium to 50°C, the flange on the gate valve is removed and taken out. Ta. The electrodeposited titanium taken out weighed about 5 kg and was a dendrite crystal containing hexagonal plates of about 1 cm. After washing with water and pickling with 5% HCI, it was vacuum dried to obtain high purity titanium.

Electrolysis was performed intermittently three times in this way, and the Ni basket was lifted onto the bath and 15 kg of 50 mm diameter titanium priquets were complemented from the boat. Even after titanium priquet complementation, electrolysis could be continued as is.

The analysis values of titanium sponge and deposited titanium were as shown in the following table: Table (Unit: ppm a g I e r I u n h 0.1 < 0.02 < 0.1 0.1 0.2 0 .2 0.1 <0.1 cl <0.5 <1ppb <1ppb <10 <10 6: Crucible 7: Anode vibe 8: Basket 9: Cathode rod 10: Vibe 11 Near node 12: Cathode 13a: Cathode rod insulation Seal 13b Near node vibe insulation seal 14: Thermometer 15: Titanium bonnet/complementary boat 16: Anode pipe or cathode rod 17: Sleeve 18: Packing 19: Gasket 20: Water cooling jacket 21: ° pipe and l mill and Mars present invention By using this method, titanium with a purity of 5N to 6N and an oxygen content of 100 ppm or less can be obtained.By using this, a highly reliable glabella film barrier material for LSI can be obtained in semiconductor devices, which are becoming increasingly highly integrated. It also makes it possible to manufacture targets on an industrial scale at low cost, which enable the manufacture of component parts such as wiring materials.

[Brief explanation of the drawing]

FIG. 1 is a front view of an example of the molten salt electrolyzer of the present invention. FIG. 2 is a sectional view of the vibrator and the insulating seal of its sliding portion. : Electrolytic tank container: Electric furnace: Container lid: Gate valve: Upper chamber Diagram 1

Claims (1)

[Claims] 1) In a method for producing high-purity titanium by molten salt electrolysis, a titanium raw material obtained by compressing a titanium sponge into a priquet shape is used, and at least the members or parts that come into contact with the molten salt are made of high-purity nickel. A method for producing high-purity titanium, characterized by carrying out electrolytic operation using the constructed molten salt electrolyzer. 2) An apparatus for producing high-purity titanium by a molten salt electrolysis method, characterized in that at least members or parts that come into contact with the molten salt are made of high-purity nickel. 3) A claim in which a polytetrafluoroethylene sleeve is inserted into a sliding seal portion of a pipe or rod associated with the cathode or anode for electrical insulation, and the sleeve is divided into upper and lower parts, with packing interposed between them. The device according to paragraph 2. 4) Alkali metal content is 0.1 ppm or less, radioactive element content is 1 ppb or less, and heavy metal content is 0.5 p.
pm or less, and further has an oxygen content of 100 ppm or less.