RU2352684C1 - Tungsten-titanic target formagnetron sputtering and method of its receiving - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: it is implemented deep vacuum refinement by multiple remelting of tungsten and titanium with receiving of polycrystalline ingots of titanium and tungsten monocrystal. Then from the polycrystalline ingot of titanium it is manufactured disk, in which in diffusing area per two concentric circles alternate there are bored holes and by press fit there are fixed in it cast cylindrical inserts from tungsten monocrystal, preliminarily subject to grinding and cutting per exact lengths. Target, recived by mentioned method, consists of cast disk made of high-clean titanium and cast cylindrical inserts made of high-clean monocrystalline tungsten, located in diffusing area of disk by two concentric circles alternate. Additionally area ratio on surface of target, taken up by tungsten and titanium, provides receiving of films at magnetron sputtering composition 35-40 wt % of titanium, tungsten is the rest.

EFFECT: improving and reliability growth of applied films of barrier plate tungsten - titanic alloy.

3 cl, 4 dwg, 1 ex

Description

The invention relates to the field of production of sprayable metal targets for microelectronics. In the technology for the production of silicon ultra-large integrated circuits (VLSI), tungsten alloys with titanium are used as diffusion barrier layers between the silicon substrate and metallization from aluminum alloys. Tungsten-titanium thin-film barriers are made by sputtering tungsten-titanium targets. Such targets are produced by mixing the starting tungsten and titanium powders, followed by heating and pressing.

Closest to the claimed object is US patent No. 5896553 dated 04/20/1999 (prototype), which describes single-phase tungsten-titanium sputtering targets and a method for their production, which consists in mixing tungsten and titanium powders and pressing at a temperature, pressure and exposure sufficient to achieving a mutual solid solution of tungsten and titanium with the formation of a beta phase. The disadvantages of the prototype include the following:

- The product is obtained as a result of a set of operations, including pressing and annealing a mixture of powder materials, which is fraught with the conservation or introduction of uncontrolled impurities, including carbon, oxygen and nitrogen, i.e. The impurity composition of the target is predetermined by the manufacturing method itself.

- It is difficult to achieve the minimum porosity of the target material. The target produced according to the description has a specific density of 90-95% of theoretical, as a result of exploitation there is instability of sputtering, swelling of the target due to gas evolution from the volume, and the formation of a columnar microstructure in sprayed tungsten-titanium films.

- Obtaining single-phase beta-phase targets is difficult to achieve. In the production of sputtered tungsten-titanium targets, due to the passing mutual diffusion processes, equilibrium is never achieved in real time, therefore tungsten and titanium are unevenly distributed, the microstructure is multiphase and all this negatively affects the quality of the deposited barrier layers.

- The use of high pressure (up to 40 kpsi) in combination with high temperatures (up to 1650 ° C) in an inert gas atmosphere or in vacuum for 3-6 hours leads to extraordinary hardware and technological complication and cost of the entire process of manufacturing targets.

The technical task is to improve the quality and reliability of the barrier layers of a tungsten-titanium alloy by using targets for magnetron sputtering, obtained by vacuum metallurgy methods. In this case, cast targets with a specific gravity of 100%, without the drawbacks inherent to cermet targets, are sprayed. Variants of the process can be the use of targets composed of cast blocks of high-purity tungsten and titanium, or the simultaneous sputtering (co-sputtering) of two cast targets of high purity tungsten and titanium. The latter case is interesting because of the possibility of producing tungsten-titanium films of any composition by choosing the deposition rate and time for each metal. This method was used by the authors to work out the modes for producing films with optimal electrophysical parameters. The desire to ensure maximum purity of the starting materials of the targets led to the development of the design of a composite target. In this case, the results obtained by the authors during co-sputtering of two cast targets were used. The composite tungsten-titanium target is a flat base of high-purity titanium with cylindrical inserts of high-purity single-crystal tungsten. In this case, for the manufacture of titanium ingots, double electron beam remelting in high vacuum was used, tungsten single crystals were obtained by electron beam melting in high vacuum with refining in several liquid-phase passes by the molten zone. On a titanium disk made of a polycrystalline ingot, in the sprayed zone (erosion zone), holes were drilled in two concentric circles in a checkerboard pattern into which tungsten cylindrical inserts were pressed from polished in diameter and cut into measured lengths of a single crystal.

Figure 1 presents a General view of a composite target for implementing the inventive method: 1 - titanium disk, 2 - insertion of a single crystal of tungsten in the amount of 56 pieces. Tungsten inserts of a certain diameter and quantity were placed so that the ratio of the areas of the tungsten and titanium sections on the sprayed surface of the target in the erosion zone corresponded to the required ratio in tungsten-titanium films.

EXAMPLE OF IMPLEMENTATION OF THE METHOD

The implementation of the option of producing tungsten-titanium films with a given ratio of components by co-sputtering of two targets was carried out in order to determine the optimal sputtering conditions and the optimal ratio of elements in diffusion barrier layers, when the smallest mutual solubility at the interface with aluminum metallization is observed, high temperature resistance of the layer is achieved in combination with low electrical resistivity, high adhesion and optimal mechanical properties of the barrier layer. Targets, which are flat disks with a diameter of 78 mm, were made of polycrystalline ingots of high-purity titanium and tungsten. The films were deposited on a magnetron sputtering unit with separate magnetrons. The experiments showed that the deposition rates of both metals linearly depend on the discharge power. In the experiments, the sputtering power of each of the two targets necessary to obtain tungsten-titanium films with a given tungsten / titanium ratio was determined. To assess the quality of the deposited films by the value of surface resistance and thickness of the films, we measured the electrical resistivity. Figure 2 shows the dependence of the electrical resistivity of the films on the ratio of titanium and tungsten (figure 2, points A, 1, 2, 3, 4, 5, 6, B). When the tungsten-titanium layers were deposited on the same setup and under similar conditions, by spraying a cermet target obtained by powder metallurgy using high-purity initial powders and excluding the introduction of contaminants at the stages of the target manufacturing, the electrical resistivity was 130 μOhm. cm (figure 2, point C). In films of the same composition obtained by co-sputtering two cast targets from high-purity tungsten and titanium, the electrical resistivity was 62 μOhm. cm (figure 2, point E), i.e. two times lower.

It should be noted the structural features of the films obtained by sputtering powder and cast targets. Powder targets can be sprayed only at low power (<1 kW) due to gas evolution and swelling when the target is heated to 300 ° C during magnetron sputtering. Figure 3 presents a diagram of a cross section of a system with a barrier tungsten-titanium layer. At low speeds, a columnar structure forms. Pores decorate the boundaries of columns (crystallites) consisting of a dense core (matrix W (110) with microinclusions of titanium) surrounded by a less dense, porous material. Such a structure sharply reduces the barrier properties of the film: during annealing, tungsten diffuses into aluminum with the formation of WAl ₁₂ , and aluminum into a tungsten-titanium film with the formation of TiAl ₃ . Cast targets were sprayed at high speeds (power> 3 kW), while gas evolution and swelling did not occur, and the microstructure of the films was characterized by high dispersion with a grain size of 10–20 nm.

Based on the results obtained by co-sputtering two targets, a composite target is proposed (Fig. 4), which has been tested to study the reproducibility of the composition and properties of tungsten-titanium films. Figure 4 presents a composite target: a - a new target, b - a target generated by 20%. Spraying was carried out at the Oratorio-5 industrial plant in an argon atmosphere. The film deposition rate is 1.8 ± 0.1 nm. ^-1. Films were deposited on silicon wafers preheated to 250 ° C. The film thickness is 0.18 ± 0.02 μm, the electrical resistivity is less than 5 Ohm / □. The composition, structural features, reproducibility of the composition along the depth of the layer, and electrophysical parameters were controlled. Spectral analysis showed that the composition of the films deposited by sputtering a composite target at various stages of its operation (in particular, in the initial period and after 145 sputtering cycles when sputtering zone erosion) corresponds to a titanium content of 35-40 at.%, The rest is tungsten. The deviation from this ratio during the operation of the target did not exceed 2-3%. The electrical resistivity of the films was at the level of 60-70 μOhm. cm (figure 2, point E). So, the proposed target is designed in such a way that its sprayed surface has a ratio of the areas occupied by titanium and tungsten, providing tungsten-titanium films of the desired ratio, namely 35-40 at.% Titanium, the rest is tungsten.

Claims (3)

1. A method of manufacturing a tungsten-titanium target for magnetron sputtering, including deep vacuum refining by multiple remelting of tungsten and titanium to produce polycrystalline titanium ingots and tungsten single crystals, manufacturing a disk from a polycrystalline ingot of titanium, in which in a sprayed area along two concentric circles in a checkerboard pattern holes and press fit fasten in them cast cylindrical inserts of tungsten single crystals, previously subjected to grinding and cutting to measured lengths. 2. Tungsten-titanium target for magnetron sputtering, characterized in that it is obtained by the method according to claim 1 and consists of a cast disk of high-purity titanium and cast cylindrical inserts of high-purity single-crystal tungsten located in the sprayed area of the disk along two concentric circles in a checkerboard pattern . 3. The target according to claim 2, characterized in that the ratio of the areas on the surface of the target occupied by tungsten and titanium provides films by magnetron sputtering with a composition of 35-40 at.% Titanium, the rest is tungsten.

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