RU2454484C2 - Manufacturing method of cast target from molybdenum-based alloy for magnetron sputtering - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: manufacturing method of cast target for magnetron sputtering from molybdenum-based alloy and target obtained using the above method is proposed. Method involves obtaining of an ingot of alloy on the basis of molybdenum. First, high-purity polycrystalline molybdenum ingot is obtained by means of deep vacuum refining by electron-beam drip re-melting of a workpiece made from high-purity molybdenum; after that, arc vacuum remelting of high-purity polycrystalline molybdenum ingot is performed with strips from high-purity monocrystalline silicon; at that, the number of strips is chosen from the condition for obtaining polycrystalline alloy ingot with composition of molybdenum - 0.005-1.0 wt % of silicon, which is subject to machining.

EFFECT: improving the quality of semiconductor devices and integral circuits due to improvement of chemical resistance of films, as wells as stability of value of transient resistance of contacts at heat treatment.

2 cl, 2 tbl, 1 ex

Description

The invention relates to the field of metallurgical production of sprayed metal targets for microelectronics, as well as to materials science of conductive systems of semiconductor systems and integrated circuits. Molybdenum is of considerable interest in connection with its unique capabilities as a material of low-resistance contacts with silicon and conductive systems. Molybdenum has a low electrical resistivity and the coefficient of thermal expansion closest to silicon. However, the use of even high purity molybdenum is complicated by the difficulties in obtaining films with the physical properties of bulk samples. Currently, the main industrial technology for applying thin films in industry is magnetron sputtering of targets.

Known electrode material, including molybdenum with a content of more than 50 wt.% Silicon, which is a complex chemical compound of molybdenum and silicon non-stoichiometric composition [Japanese Patent No. 4926463]. This alloy is characterized by high resistivity and instability of properties, which is due to an extremely nonequilibrium state and is a significant drawback, especially in the case of high-temperature processing (up to 900 ° C) in the production of MOS structures using a technology with a self-locking shutter. Known material containing molybdenum, silicon and a platinum group metal [A.S. USSR No. 611520]. In this material, during the heat treatment of thin-film structures, chemical compounds and solid solutions are formed, which leads to a change in the electrophysical properties of the films and especially molybdenum-silicon contacts. In this case, the electrical resistance of the film, the electron work function, the potential barrier of contacts, etc., change uncontrollably.

Known methods adopted for the prototype, obtaining cast targets of high purity molybdenum [RU No. 2349657, RU No. 2356964], the spraying of which allows to apply thin-film metallization on silicon structures. For all the indisputable physical and technological advantages of high purity molybdenum cast targets, metallization causes problems of adhesion of molybdenum to silicon and uncontrolled formation of non-stoichiometric compounds at the molybdenum-silicon interface. Another disadvantage is the increased oxidation of molybdenum films during heat treatment in an inert atmosphere and during chemical treatment in a solution of monoethanolamine + dimethylformamide (1: 3), which negatively affects the stability, for example, of the threshold voltage in MOS structures (MOS - metal-oxide-semiconductor) . The best way to eliminate this disadvantage was doping of molybdenum with silicon while fully maintaining high purity of molybdenum for all other impurities. The presence of silicon in molybdenum in the case of using this material as a contact to the semiconductor increases the stability of hidden contacts during high-temperature treatments (up to 900 ° C) due to the restriction of the diffusion of silicon atoms from the substrate during the formation of the molybdenum-silicon phase at the molybdenum-silicon interface.

The objective of the invention is to improve the quality of semiconductor microdevices by increasing the chemical resistance of molybdenum used as a material of conductive systems, as well as the stability of the contact resistance of the contacts during heat treatment.

SUMMARY OF THE INVENTION

This is achieved by using a method for producing a cast target for magnetron sputtering from a molybdenum-based alloy, including producing an ingot of an molybdenum-based alloy, characterized in that a polycrystalline high-purity molybdenum ingot is preliminarily obtained by deep vacuum refining of a workpiece made by electron beam drop remelting of high purity molybdenum, then an arc vacuum remelting of a polycrystalline high purity molybdenum ingot with strips of m nanocrystalline silicon of high purity, the number of lanes is selected from the condition for producing polycrystalline alloy ingot with the composition of molybdenum - 0.005-1.0 wt% of silicon, which is subjected to machining.. A cast target for magnetron sputtering from a molybdenum-based alloy is obtained by the indicated method.

The lower limit of the selected ratio is limited by the low resistance of the proposed material to oxidation during heat treatment and chemical treatment, when the silicon content in high-purity molybdenum is less than 0.005 wt.%.

The upper limit of the silicon content in molybdenum is limited by the need to have a low electrical resistivity of the proposed material, as well as the possibility of reproducible production of thin-film elements during photolithographic processing. If the silicon content exceeds 1.0 wt.% In molybdenum, the specific resistance of the material increases significantly, which can lead to a decrease in the speed of integrated circuits, as well as to complicate the etching process of thin films of the proposed alloy.

DETAILED DESCRIPTION OF THE INVENTION

The method is as follows. The initial molybdenum preforms are placed in the melting chamber of an electron beam furnace, the chamber is evacuated to create a vacuum, and the preforms are gradually melted, bringing them under the electron beam created by the axial gun. Then the polycrystalline ingot of molybdenum with the addition of silicon is remelted in an electric arc vacuum installation with intense electromagnetic mixing of the melt. To create a longitudinal electromagnetic field, a direct current solenoid is used, wound on a cooling jacket of a vertical crystallizer. The rotation of the melt contributes to the averaging of the chemical composition over silicon, elimination of temperature gradients, and the formation of a fine-grained cast structure due to the destruction of crystallites and the appearance of additional crystallization centers.

An example implementation of the method

The implementation of the method was carried out in the manufacture of cast targets from an alloy based on molybdenum. As the starting material for obtaining molybdenum ingots, billets made by pressing high purity molybdenum powders were used. Refining was carried out by electron beam melting in high vacuum using a vertical crystallizer, resulting in high-purity polycrystalline molybdenum ingots with a diameter of 80 mm. The electron beam remelting rate was 0.5-0.6 kg / min. Along the polycrystalline ingot of high-purity molybdenum, strips of high-purity single-crystal silicon were fastened every 90-100 mm, for which a thin molybdenum wire was used. The number of fixed silicon bands depended on a given concentration of silicon in the alloy in the range of 0.005-1.0 wt.%. The second vacuum remelting of a high-purity polycrystalline ingot of molybdenum with fixed silicon strips was carried out in an electric arc vacuum unit equipped with a device for electromagnetic mixing of the melt. As a result, a polycrystalline ingot of a molybdenum-based alloy with a given silicon content was obtained. The diameter of the ingot is up to 200 mm with a length of 1000 mm. The ingot was cut on an electric spark tape machine into flat blanks for the manufacture of targets. The machining of the workpieces was carried out to obtain sprayed targets of a given geometry. The silicon content in the samples was controlled using mass spectrometry. Three ingots of a molybdenum-based alloy with a silicon content of 0.008, 0.1 and 0.8 wt.%, As well as one ingot of high purity molybdenum (without doping with silicon) were smelted. The diameter of the ingots is 200 mm. Two sprayed targets were made from each ingot - a total of 8 round sprayed targets with a diameter of up to 190 mm for the Oratorio-5 installation. A detailed study of both the processes of magnetron sputtering of targets of high purity molybdenum and thin films obtained by sputtering targets of all four alloys was carried out. Thin film layers of a molybdenum-silicon alloy (0.008 wt.%) With a thickness of 0.15 μm on test structures were obtained by sputtering targets of the corresponding composition. Then, photolithographic engraving of the obtained films was carried out with etching in a 50% HNO ₃ solution, after which an interlayer dielectric was deposited at a temperature of 140 ° C, in which contact windows were opened to the molybdenum surface by plasma-chemical etching through a photoresist mask and which was then removed in a solution of monoethanolamine + dimethylformamide (1: 3). The second level of the conductive layer was formed by applying an aluminum film 1.2 microns thick followed by photolithographic engraving. The obtained test structures were annealed in a nitrogen atmosphere at a temperature of 430 ° С for 15 min. The degradation of the test structures was determined on a microscope by the presence of dark areas on the outer part of the contacts, which indicates the oxidation of the material of the lower level of the conductive system. The test results of the test structures are shown in Table 1.

Table 1 Degradation of test structures Heat treatment conditions Degradation of test structures,% Conductive System Low Level Material Mo treble Mo + Si (0.008%) Mo + Si (0.8%) Mo + Si (0.8%) T = 430 ° C, t = 15 min, Nitrogen eleven 5.5 four 3

To assess the thermal stability of the molybdenum-silicon contacts, test structures were made that made it possible to measure the transition resistance of the contacts using the four-point method. Annealing of test structures with 0.2 μm films was carried out in an argon atmosphere at temperatures of 800 ° C and 900 ° C for 15 minutes. The test results of the test structures to increase the transient resistance are shown in Table 2.

table 2 Increase in transition resistance Heat treatment conditions The increase in transition resistance,% Contact material Mo treble Mo + Si (0.008%) Mo + Si (0.1%) Mo + Si (0.8%) T = 800 ° C, t = 15 min, argon 40 twenty fourteen 10 T = 900 ° C, t = 15 min, argon 53 26 17 13

Thus, the use of the proposed method for producing cast targets from silicon doped molybdenum can significantly improve the quality of integrated circuits by increasing the chemical resistance of the material of the conductive systems and the stability of the contact resistance of the contacts during heat treatment. Given the above set of advantages, this allows you to get a higher technical and economic effect, which is manifested in improving the quality of integrated circuits and increasing the yield of suitable products.

Claims (2)

1. A method of manufacturing a cast target for magnetron sputtering from a molybdenum-based alloy, comprising producing an ingot of a molybdenum-based alloy, characterized in that a polycrystalline ingot of high purity molybdenum is preliminarily obtained by deep vacuum refining by electron beam drop remelting a billet made of high molybdenum then an arc vacuum remelting of a high-purity polycrystalline ingot of molybdenum with high-purity single-crystal silicon strips is carried out purity, and the number of bands is selected from the conditions for obtaining a polycrystalline ingot of an alloy with a molybdenum composition of 0.005-1.0 wt.% silicon, which is subjected to mechanical processing. 2. Cast target for magnetron sputtering from an alloy based on molybdenum, characterized in that it is obtained by the method according to claim 1.