Method of manufacturing a highly purified titanium metal and a sputtering target

Abstract: This is a highly purified metal comprising one metal selected from the group consisted of titanium, zirconium and hafnium. The highly purified metal has an Al content of not more than 10 ppm. It also has an oxygen content of more than 250 ppm, each of Fe, Ni and Cr contents not more than 10 ppm and each of Na and K contents not more than 0.1 ppm. The highly purified metal is obtained by either purifying crude metal by the iodide process or surface treating crude metal to remove a contaminated layer existing on the surface thereof and then melting The surface treated material with electron bean in a high vacuum.

Description: The present invention relates to a highly purified titanium suitable as a target material for the formation of electrode, contact part and barrier layer of a semi-conductor device, a method for the manufacture of the same and a sputtering target using the same. As the material to form wiring layer and electrode of a semi-conductor device like LSI, a silicide of a metal having a high melting point such as Mo, W, Ta, Ti, Zr and Hf have been used. Further, because there is a tendency of furthering high integration of semi-conductor devices and calling for more minute wiring structures, the possibility of various problems has been watched with misgivings. In the case of, for example an Al wiring, minute wiring and higher current density required therefore give rise to electromigration that Al atoms are carried away in the direction of the electron movement or an increase of working heat. These lead to a problem that Al wirings are susceptible to burn-out. Further, an increase in wiring resistance due to minute wiring materials causes delay of signals. Thus, particularly Ti silicides have attracted attention as the wiring and electrode material because they not only have a high melting point but also a low resistance. For example, when a Ti silicide is intended for use as the material for electrode, a Ti film is formed over a polysilicon film by the sputtering process. Then the Ti film is heat-treated to make a slicide out of Ti. What is called a polycide structure prepared in this way has been put to use. On the other hand, an attempt has been made to make contact parts of a Ti silicide as the built-in protection in order to reduce contact resistance. Further, a contact part is inlaid with, for example a Ti film serving as a diffusion barrier layer in order to prevent Si from precipitating into Al wirings. In this sense, a laminated structure of Al/TiN/TiSi 2 has been used. A TiN film is formed of a reactive sputtering material and the like. As stated above, a TiN film or a TiSi 2 film is made by the sputtering process. Therefore, the sputtering target required for the process must be made of a Ti material. It is important that the Ti target for that purpose has a high purity. When a Ti target contains an impurity of oxygen, the film formed therefrom has high electric resistance, causing a trouble of delay of signals or burn-out of wirings. Further, a heavy metal such as Fe, Ni and Cr collects on the interface of a laminated film and form a deep level, causing leakage at the joint thereof. An alkali metal such as Na and K readily sets Si free, deteriorating the properties of the device. Meanwhile, a Ti material for the above mentioned Ti target generally is manufactured according to the so-called Kroll method or Hunter method to thermally reduce a Ti compound such as TiCl 4 with an active metal such as Na and Mg or the fused salt electrolysis process using a fused salt consisting of alkaline metal compound. In recent years when metal purification technology has advanced and manufacturing processes have been well managed, incorporation of impurities such as heavy metal has been brought down to a very low level. However, even in the case where a TiSi 2 film for use in contact parts is formed of a Ti target having a very low content of such impurities as heavy metal, there is a problem that leakage at the junction cannot be sufficiently prevented because of very minute wiring. This makes an important cause of the loss of fidelity of semi-conductor devices. Further, in a barrier layer, an increase of current density which is caused by reduction of wiring width, leading to malfunction of the layer and leakage at the junction. It is expected that these problems will be exacerbated in the future as integration of semi-conductor devices advances. Purified Zr or Hf having highly reduced contents of oxygen and other non-metallic and metallic impurities is described in Winkler et al, ,,Vacuum Metallurgy", Elsevier, London 1971, pp 270-271. Zirconium having an Al content of 7 ppm and 2 ppm, respectively, and an oxygen content of 70 and 117 ppm, respectively, is obtained by vacuum melting of high purity zirconium at 2700° C and 10 -5 Torr. Furthermore, hafnium having an Al content of 22 ppm, a Cr content of 2 ppm, an Fe content of 9 ppm and an O content of 210 ppm was prepared by electron beam melting (10 kg/h). Additionally, hafnium having an oxygen content of 100 ppm is obtained by electron beam melting (5 kg/h). EP-A-0 316 580 discloses a process for making Zr alloys comprising electron beam melting sponge zirconium to form a zirconium material containing less than 300 ppm (preferably 50 ppm) iron, less than 400 ppm (preferably 175 ppm) oxygen and less than 5 ppm (less than 2 ppm in experimental runs) aluminum. In a preferred embodiment, the metallic Zr is obtained by reducing zirconium tetrachloride utilizing low oxygen magnesium, distilling and prebaking the metallic zirconium, subjecting it to ultra-slow electron beam melting and double or triple vacuum arc melting. EP-A-0 408 383 discloses a highly purified Ti material suitable for a sputtering target or a wiring network on a semi-conductor device surface comprising not more than 250 ppm oxygen, not more than 10 ppm of each of Fe, Ni and Cr and Na and K contents of not more than 0.1 ppm each. Furthermore, a method comprising preparing crude Ti particles by molten salt electrolysis or iodide method, acid-treating the crude Ti particles to remove a contaminated surface layer or 300 Å thickness and melting the acid-treated crude Ti particles by using an electron beam is described. EP-A-0 248 338 concerns highly pure titanium useful as material for forming a wiring network on the surface of a semi-conductor device comprising not more than 200 ppm oxygen, not more than 30 ppm of each of Fe, Ni, and Cr, not more than 0.1 ppm of each of Na and K and not more than 0.001 ppm each of U and Th. The titanium material is prepared by electron beam melting crude Ti obtained by molten salt electrolysis in a high vacuum. FR-A-2 359 221 discloses a method of electrolytically reducing titanium halogenide to obtain titanium having a purity of 99.994 %. The main impurities comprise Al at a level of 5 ppm and Fe at a level of 0.3 ppm. The Ti material may be used for electronic applications. The abstract of JP-A-62292618 describes a method to produce titanium iodide extremely reduced in impurities. Titanium iodide is distilled and purified by stepwise changing and controlling distillation temperature and collection temperature and exhausting volatile matters in the initial period to the outside of the system. Titanium iodide having a content of several impurities including Al, Fe, Cr and Ni of less than 1 ppm is disclosed. Therefore, an object of the present invention is to provide a method of manufacturing a highly purified titanium for the production of an electrode and a contact part capable of preventing malfunctions thereof in a highly integrated semi-conductor device and for the formation of a barrier layer capable of sufficiently preventing an increase of leakage at the junction. Another object of the present invention is to provide a method for the manufacture of highly purified titanium sputtering target making it possible to manufacture well reproducible highly purified titanium having the above-mentioned properties. This sputtering target is capable of forming well reproducibly an electrode, a contact part, a barrier layer and the like respectively having high fidelity. The present inventors have gone ahead with the researches of impurities contained in Ti target materials resulting in the findings that the above mentioned problems are accounted for by Al which has not been given much thought among other impurities of conventional targets. In other words, it has been brought to light that the Al content need be lowered as much as possible on top of that of heavy and alkali metals, when an electrode, a contact part, a barrier layer and the like of a semi-conductor device are made of a target of Ti according to the sputtering method. However, the Al content cannot be sufficiently reduced according to conventional manufacturing methods, remaining at a level such as 2000 ppm if it is a high side and finding no place as a forming material for highly integrated semi-conductor devices. The highly purified titanium of the present invention has been achieved on the basis of the above mentioned finding and is characterized by having a Al content of not more than 10 ppm. The sputtering target of the present invention is characterized in that it is made by molding the above mentioned highly purified titanium into a desired form. The highly purified titanium is useful as a wiring material for use in LSI, VLSI, and ULSI. Namely, the present invention enables a wiring network to be formed on a substrate in a semi-conductor device and containing 10 ppm or less of Al and, specifically speaking, comprising a silicide or a nitride of the titanium mentioned above. The wiring network like this can be obtained, for example according to the undermentioned production method. This is a production method comprising a step of forming a thin film from the sputtering target on a substrate in a semi-conductor device and a step of subjecting the thin film to etching treatment to eliminate portions other than the desired wiring network. The wiring network comprises an electrode, a contact part and a barrier layer of a semi-conductor device. The titanium having a least possible Al content of the present invention has been brought to completion by the finding that Al contained in crude Ti particles by the fused salt electrolysis process is converged and stays on the particle surface region and can be efficiently removed by the application of surface treatment technology. Namely, the method for the manufacture of highly purified titanium metal of the present invention having an Al content of not more than 10 ppm and each of Na and K contents of 0.1 ppm or less, each of U and Th contents of 0.001 ppm or less, each of Fe, Ni and Cr contents of 10 ppm or less and an oxygen content of 250 ppm or less comprises the step of purifying a crude titanium material prepared by molten salt electrolysis wherein a contaminated surface layer of more than 5 µm depth is removed and the step of melting the purified titanium material with an electron beam (EB) in a high vacuum. The present invention provides an easy method for obtaining good reproducible Ti metal material, highly purified with the least possible Al content. A metal film and a metal compound film respectively having a low Al content can be well reproducibly formed by using said Ti metal as a target material of the sputtering method, serving for an electrode, a contact part or a barrier layer of a highly integrated semi-conductor device and contributing much to the promotion of semi-conductor device fidelity. Fig. 1 show an example of the purifying apparatus for use in the present invention. Fig. 2 is to describe the structure of a diode prepared in one embodiment of the present invention. Fig. 3 shows the relationship of the Al content of a Ti target prepared in one embodiment of the present invention with the leakage current of a diode having a TiSi 2 film formed of said Ti target. Fig. 4 shows the relationship of Ti film prepared in one embodiment of the present invention with specific resistance of a TiSi 2 film formed of said Ti film. Fig. 5 relates to the fused salt electrolysis process used in one embodiment of the present invention, showing the relationship of the distance between the surface of the electrolyte and the location of a Ti material made therefrom with the Al content of said Ti material. Fig. 6 is a cross-section outlining the structure of a semi-conductor package obtained in connection with one embodiment of the present invention. Fig. 7 is a cross-section outlining the structure of a semi-conductor chip used in the semi-conductor package shown in Fig. 6. The methods of manufacturing the highly purified metal and the sputtering target of the present invention will now be described in detail with reference to embodiments. Basically, the highly purified Ti material should have an Al content of not more than 10 ppm but the content of other impurities is at a low level as well. The oxygen content is not more than 250 ppm, each of the Fe, Ni and Cr contents is not more than 10 ppm and each of the Na and K contents is not more than 0.1 ppm. Further, the U and Th contents are not more than 0.001 ppm. Here follows the reason why the Al content is limited to the above mentioned range: there is a sudden, high incidence of unacceptable quality of semi-conductor devices on account of leakage current when their electrodes, contact parts and barrier layers are made from Ti compounds using targets with the Al content exceeding 10 ppm. The highly purified titanium obtainable with the present invention is obtained by the application of the manufacturing method as above mentioned. Next, the manufacturing process for highly purified titanium of the present invention will be described. Under this manufacturing process, crude metal particles are prepared at first according to the fused salt electrolysis process. For example, sponge Ti is used as a starting material therefore. Further, an electrolyte comprising KCl-NaCl and the like is preferable. The electrolytic temperature is preferably 730°C - 755°C and the voltage 6.0V-8.0V. Meanwhile, since crude Ti particles contain impurities of metal elements including Al and oxygen which are converged in the neighbourhood of the particle surface, the contaminated layer on the surface of more than 5 µm should be selectively removed. This contaminated surface layer is preferably removed, for example by (1) a method for surface treating said layer with an acid or an alkali or (2) a method for volatilizing and removing said layer with a halogen gas, such as iodine, fluorine, chlorine and bromine. The above mentioned method (1) is preferably implemented in an atmosphere of such inactive gas such as argon gas to prevent the surface layer from recontamination particularly due to oxygen, conducting washing with purified water and drying afterwards. The treatment solution to be used therefore is an acidic solution such as hydrofluoric acid, nitric acid, sulfuric acid and their mixture or an alkaline solution such as a sodium hydroxide solution. Further, heavy metals can easily be eliminated by the fused salt electrolysis process and it is possible to attempt to remove selectively Al alone as it is existing in the neighborhood of the surface. The use of sulfuric acid or sodium hydroxide solution is efficient in this case. The above mentioned method (2) is carried out as follows: a crude titanium material obtained by the fused salt electrolysis process is placed in the purification apparatus as shown in Fig. 1, gaseous halogen is introduced thereto, a temperature elevated to a prescribed level is maintained inside the reaction container for a prescribed span of time, the surface of the crude titanium is allowed to react with said halogen and then the product formed thereby is removed with suction. When the reaction container has a sufficiently high temperature, almost all halides of metallic impurities are easily carried away out of the container because of their high vapor pressure. The contaminated surface layer of the crude titanium is gradually removed by implementing this procedure repeatedly. The contaminated surface layer more than 5 µm deep, preferably more than 10 µm deep from the surface is removed by these methods. Further, the content of impurities including Al can be relatively reduced by selecting and using Ti particles of a comparatively small particle diameter which have smaller specific area. This helps in efficient removal of the contaminated surface layer. The substantially same effect can be achieved by sieving particles after the removal of their contaminated surface layer and selectively using those of comparatively larger particle diameter. After the contaminated surface layer is so removed, the EB melting is employed in a high vacuum in order to finally remove Al, Na, K and the like and obtain a highly purified titanium. The EB melting is a method for the separation of impurities using a difference of vapor pressure and highly efficient in removing particularly Al, Na and K each having a high vapor pressure. Various metals are subjected to the EB melting, keeping a vacuum preferably not more than 5 x 10 -5 mbar, more preferably not more than 2 x 10 -5 mbar in the EB melting furnace, while preventing the entrance of a diffusion pump oil into said furnace with the use of a freon baffle. The operating conditions of EB melting are not particularly limited, but it is required that a melting speed should be determined taking into consideration the efficiency of purifying Na and K and the contamination due to the oxygen absorption. For example, a melting speed of 1.75 kg/hr - 2.3 kg/hr is preferable. Further, a filament with a precipitated metal can be used as an electrode for the EB melting as it is. Since said melting is implemented in a vacuum assuring less contamination due to oxygen and nitrogen, titanium of high purity can be obtained. Ordinarily, when the EB melting is intended, it is thought that the Ti particles previously obtained should be compressed into a solid by a molding press and that the so obtained solid should be used as an electrode for the EB melting. In this case, however, recontamination on account of deformation incidental to molding is likely. Thus, for the purpose of preventing recontamination, it is preferable under the present invention that Ti particles are placed as they are into a vibrating granulator and subjected to the EB melting. Titanium metals obtained according to the above method have an Al content of satisfying not more than 10 ppm, a reduced content of other impurities and a high purity to a satisfaction. With regards to other impurities, the oxygen content is not more than 250 ppm (preferably not more than 200 ppm), each of the Fe, Ni and Cr contents is not more than 10 ppm (preferably not more than 5 ppm each) and each of the Na and K contents is not more than 0.1 ppm (preferably not more than 0.05 ppm each). Further, sputtering targets of the present invention are obtained by cold-forging the highly purified Ti material, into a desired shape, while preventing their recontamination. Said cold-forging is carried out in a cold condition (at about room temperature), taking into consideration the properties of, for example the Ti material with high gas absorption and the feasibility of preventing recontamination due to gas absorption. The processibility improved by satisfying a high purity makes cold-working possible. This is followed by machine-working of target materials to provide sputtering targets in a prescribed shape. Next, the specific embodiments of manufacturing the highly purified titanium of the present invention and the results of evaluating them will be described. Each embodiment of applying the method for the manufacture of highly purified titanium of the present invention will be shown below. Embodiment 1 First, needle shaped-Ti of the fused salt electrolysis process was immersed in a mixture of hydrofluoric acid, nitric acid and water in a ratio of 2:1:1 for 10 minutes in order to remove the contaminated surface layer. The so treated needle shaped-Ti was washed with running water to make a starting Ti material. Meanwhile, the contaminated surface layer 15 µm deep from the surface was removed. The iodide process and the EB melting were implemented according to the following procedure: The acid-treated Ti was set in the reaction container 1 of the purification apparatus, as shown in Fig. 1 and the amount of an iodine representing a ratio of 0.2 g/l was also placed therein. Said acid-treated Ti was purified by the iodide process under the conditions that the temperature of the filament 5 was maintained at 1400° C and that of the reaction container 1 at 600° C. The filament 5 had a diameter of 2 mm when the purification was started and Ti was allowed to precipitate thereon until the diameter was increased to about 30 mm. The filament with precipitated Ti was used as a starting material for EB melting to conduct the EB melting under the conditions of a high vacuum of 1 x 10 -5 mbar in the furnace, preventing the entrance of diffusion pump oil into the furnace with the use of freon baffle, a voltage of 20 kV, a filament current of 1.5 A- 2.0 A, an EB output fo 30 KW - 40 KW and a melting speed of 4 kg/hr. Thus, ingots having a diameter of 135 mm are respectively obtained. Further said Ti ingots were forged in a cold condition (at about room temperature), followed by machine grinding thereof and the sputtering targets in a prescribed shape were obtained. The so obtained Ti targets were analysed, resulting in the determinations shown in Table 1. Embodiment 2 In the reaction container 1 of the purification apparatus as shown in Fig. 1, the needle shaped Ti which had been used as the crude Ti material in Embodiment 1 was placed, a gaseous iodine was introduced therein after vacuum exhaust, the temperature was maintained at 600 °C and the surface of the needle shaped Ti was allowed to react with the iodine. Then, the reaction product was eliminated by vacuum exhaust. This procedure was repeated 3 times to remove the contaminated surface layer. The contaminated surface layer 15 µm deep from the surface was removed. Meanwhile, the used purification apparatus had an exhaust system connected with the reaction container via an iodide trapping mechanism which is missing in the illustration. Subsequent to the removal of the contaminated surface layer, the filament 5 was electrically charged, the iodide process and the EB melting were carried out and Ti ingots were obtained. Then, Ti targets were made thereof. The so obtained targets were analyzed, resulting in the determinations shown in Table 1 as well. The crude Ti material used in Embodiments 1 and 2 was also analyzed, the results shown in Table 1 respectively as the Comparative Embodiment 1. As evident from Table 1, the Ti materials of all the above-mentioned embodiments have a low content of Al that should not adversely affect the properties of electrode, contact part or barrier layer in a semi-conductor device, keeping the content of other impurities at a reduced level and satisfying the purity as it should be. The properties were evaluated on each of the semi-conductor device which was produced by forming the wiring network of titanium silicide film on the substrate with use of each of the Ti targets obtained in connection with the embodiment and the comparative embodiment. The production method, the evaluating method and the results thereof will now be described in detail. The influences by Al contained in various titanium targets were evaluated and the results thereof will be described at first. As shown in Fig. 2, over the polycrystalline Si layer 12 above the n-Si substrate 11, a Ti film 60 nm thick, was respectively formed by the sputtering method using a Ti target which was produced according to substantially the same procedure as in the corresponding embodiment and each type of which has different Al content. After each film was treated by etching to remove portions other than the desired wiring network, the remaining film was subjected to 2 step annealing treatment to comprise a silicide and form a titanium silicide film (TiSi 2 film)over the polycrystal Si layer 12 and at the same time both the source region 14 and the drain region 15 were made to comprise a silicide and the diode of the titanium silicide film was produced. Each type of Ti target contained Al in an amount of not more than 54 ppm, 3 ppm and 1 ppm. Other impurities contained in these targets were in an equal amount. The leakage current was measured by applying an inverse bias voltage to the so obtained diodes to obtain the results in Fig. 3. As evident from Fig. 3, the leakage current increased as the Al content increased. Meanwhile, 10 diodes were made of titanium targets and when they were subjected to a measurement according to the substantially same procedure, there was a finding that each of these diodes shows a same inclination. In other words, an electrode or a contact part having a high fidelity for a highly integrated semi-conductor device can be accomplished by making a sputtering target of a titanium material having a low Al content as obtained in the abovementioned embodiments, producing a metal target of said sputtering target and forming a desired form therefrom. Next, the relationship between the oxygen content of a Ti target and specific resistance of a TiSi 2 made thereof will be described below. 6 types of Ti target each having a different oxygen content (oxygen content: 80 ppm, 120 ppm, 200 ppm, 300 ppm, 550 ppm and 700 ppm) were made according to the substantially same procedure as in the abovementioned embodiments. The film forming apparatus was evacuated to 1 x 10 -5 Torr, then an Ar gas was introduced thereto up to 5 x 10 -3 and over a polycrystalline Si a Ti film, 0.2 µm thick, was formed of each type of said Ti target by DC magnetron sputtering at film forming speed of 2.0 µm/h. After specific resistance of these films were measured, they were subjected to annealing at 700 °C, Ti and Si were allowed to react each other and a TiSi 2 was complete. These TiSi 2 films were measured for their specific resistance. The resistance of the film times the thickness of the film makes specific resistance. The resistance of the film was measured according to the direct-current 4 points probe method (the production of NAPUSON Kabushiki Kaisha, RESISTEST-8A). The relationship between the oxygen content of Ti targets and specific resistance of TiSi 2 films is shown in Table 2. The relationship between specific resistance of Ti films and that of TiSi 2 films is shown in Fig. 4. Oxygen content(ppm) 700 550 300 120 80 Specific resistance Ti film( µ Ω. cm) 123 115 105 70 65 It is evident from Table 2 and Fig. 4 that specific resistance of Ti films can be reduced by decreasing the oxygen content of Ti targets. Further, specific resistance of TiSi 2 films can also be lowered by lowering specific resistance of Ti films. Particularly, TiSi 2 having as low specific resistance as 15 µΩ.cm are not obtained by using Ti targets having an oxygen content of more than 250 ppm. A TiSi 2 film having low resistance means the prevention of delay of signals in a semi-conductor device to make possible a semi-conductor device having high fidelity. Next, a further embodiment will be described. Embodiment 3 An electrode made of sponge Ti was placed in an electrolyte comprising KCl-NaCl (KCl: 16% by weight, NaCl: 84% by weight) and subjected to fused salt electrolysis process at an electrolytic temperature of 755 °C, a current of 200A and a voltage of 80V in order to produce a crude needle-shaped Ti particle. The contaminated surface layer of these crude needle-shaped Ti materials was removed by means of an aqueous solution of hydrochloric acid. Said acid treatment was conducted by immersing the crude Ti materials in said aqueous solution of hydrochloric acid in an argon gas atmosphere for each different from span of time and then they were washed with purified water and dried. In this way, several types of Ti materials in which the amount of the surface layer removed by acid treatment is different from each other were prepared. Prior to the acid treatment, said crude needle shaped Ti materials were analyzed to determine the relationship of the Al content with the thickness of the removed layer or the distance ban the surface of particles and the bottom of the removed layer. The results are shown in Fig. 5. As evident from Fig. 5, the content of impurities can be significantly decreased by removing the surface layer about 10 µm deep from the particle surface. Next, the crude Ti particles immersed in the acid for different spans of time were used as a starting material for EB melting and placed in a vibrating granulator. Said granulator was introduced into an EB melting furnace in a vacuum, while preventing the contamination. EB melting was conducted under the conditions of a high vacuum of 1 x 10 -5 mbar in the furnace, preventing the entrance of diffusion pump oil into the furnace with a freon baffle, voltage of 20KV, a filament current of 1.3A-1.5A, an EB output of 26KW-30KW and a meltin g speed of 4 kg/h in order to make ingots having a diameter of 135 mm. Each of the so obtained Ti materials was analyzed for impurities. The relationship between the Al content and the amount of the removal by acid treatment is shown in Table 3. With regards to other impurities, each of the Fe, Ni and Cr contents was not more than 1 ppm, each of the Na and K contents was not more than 0.01 ppm and the oxygen content was not more than 200 ppm. As evident from Table 3, the embodiment showed that the Ti material having a satisfactorily high purity, a low content of Al adversely affecting the properties of electrode, contact part and barrier layer of semi-conductor devices and a reduced content of other purities was obtained by removing the surface layer from the crude Ti material and then EB melting it. Next, the present invention will be described by the following embodiment in connection with a semi-conductor package using the wiring network obtainable with the present invention. Fig. 6 is a drawing outlining the structure of one instance of the semi-conductor package. Here, 21 is a semi-conductor chip set on an insulation substrate 22 by a solder layer 23. The semi-conductor chip 21 is electrically connected with a lead frame 25 by a Au lead wire 25. The semi-conductor chip 21, Au lead wire 24 and lead frame 25 are sealed together in a molding by a sealing resin 26. The semi-conductor chip 21 comprises the highly purified metal of the present invention and is used as the material for a part of the wiring network. The semi-conductor chip 21 and the method for producing the same will be described referring to Fig. 7. First, a p-Si substrate 31 is treated by thermal oxidation to form a thermally oxidized film on the surface of p-Si substrate. Then, a field oxidized film 32 is optionally formed by thermal oxidation except for the source and drain regions. Portions of the thermally oxidized film on each of the source and drain regions were eliminated by formation of a resist film and etching treatment (hereinafter called PEP treatment for short) to give a thermally oxidized film 33 remaining on the gate region. Then, after the resist film is formed except for the source and drain regions, elements as the impurity are injected into the p-Si substrate 31 to produce the source region 34 and the drain region 35. Further, a Mo or W silicide film 36 is formed on the gate oxidized film 33. An insulation layer 37 comprising P-doped silica glass (PSG) is formed all over the p-Si substrate and then both the source region 34 and the drain region 35 were subjected to PEP treatment to remove portions of the P-doped silica glass layer 37 located thereon. Then, a barrier layer 38 is formed respectively on the source region 34 and the drain region 35 after portions of the P-doped silica glass layer 37 are removed therefrom. These barrier layers 38 are the film comprising the highly purified Ti metal obtained with the present invention. This material is treated by the reactive sputtering method in a nitrogen gas atmosphere to produce a TiN film which contains Al in a very small amount and is used to form the barrier layer 38. Thereafter, an Al film 39 is formed by vacuum evaporation to cover the whole surface and obtain the wiring network in a desired shape. Further, an insulating protection film 40 comprising Si3N4 and the like is formed all over, a portion thereof is subjected to PEP treatment to build an opening for bonding of the Au lead wire (24) and finally an semi-conductor chip (21) is complete. The barrier layer which is sound even when the wiring network is densely formed can be obtained by producing the TiN film, from the highly purified metal manufactured in accordance with the present invention. This is because content of impurities inside the barrier layer 38 can be controlled to be very small, including that of Al, oxygen, alkali and heavy metals, and as a result the semi-conductor package having the high operational reliability can be obtained. The description of the above mentioned embodiment relates only to the case where the highly purified titanium is used as the material for barrier layers but also is true in the case of using it as the material for electrodes and contact parts. Further, although an instance of DIP is described in the above mentioned embodiment, substantially the same effect can be obtained with respect to packages of QFP or PGA.

Claims: A method of manufacturing a highly purified titanium having an Al content of 10 ppm or less, each of Na and K contents of 0.1 ppm or less, each of U and Th contents of 0.001 ppm or less, each of Fe, Ni and Cr contents of 10 ppm or less and an oxygen content of 250 ppm or less for preparing a semiconductor element so as to reduce a junction leak current of the semiconductor element comprising the step of purifying a crude titanium material prepared by molten salt electrolysis wherein a contaminated surface layer of more than 5 µm depth is removed and the step of melting the purified titanium material with an electron beam in a high vacuum. A method of manufacturing a highly purified titanium as set forth in claim 1 wherein a contaminated surface layer of more than 10 µm depth is removed. A method of manufacturing a highly purified titanium as set forth in claim 1 or 2 wherein the step of removing the contaminated surface layer is performed by surface-treating the crude titanium material with an acid solution or an alkaline solution. A method of manufacturing a highly purified titanium as set forth in claim 1 or 2 wherein the step of removing the contaminated surface layer is performed by reacting the surface of the crude titanium material with a halogen gas selected from iodine, fluorine, chlorine and bromine and by removing the reaction product. A method of manufacturing a highly purified titanium sputtering target comprising the step of performing the method according to any of claims 1 to 4 to obtain a highly purified titanium, the step of cold-forging the obtained highly-purified titanium and the step of machine-working the cold-forged titanium.

Inventors: ANDO SHIGERU, ISHIGAMI TAKASHI, KAWAI MITUO, MAKI TOSHIHIRO, OBATA MINORU, SATOU MICHIO, YAGI NORIAKI, YAMANOBE TAKASHI, ANDO, SHIGERU, ISHIGAMI, TAKASHI, KAWAI, MITUO, MAKI, TOSHIHIRO, OBATA, MINORU, SATOU, MICHIO, YAGI, NORIAKI, YAMANOBE, TAKASHI, ANDO, SHIGERU, C/O INTELLECTUAL PROPERTY DIV., ISHIGAMI, TAKASHI, C/O INTELLECTUAL PROPERTY DIV., KAWAI, MITUO, C/O INTELLECTUAL PROPERTY DIV., MAKI, TOSHIHIRO, C/O INTELLECTUAL PROPERTY DIV., OBATA, MINORU, C/O INTELLECTUAL PROPERTY DIV., SATOU, MICHIO, C/O INTELLECTUAL PROPERTY DIV., YAGI, NORIAKI, C/O INTELLECTUAL PROPERTY DIV., YAMANOBE, TAKASHI, C/O INTELLECTUAL PROPERTY DIV.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: C22B34
IPC codes: C23C14, C22B34, H01L23, H01L21, C22B9