Sputtering target

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a sputtering target used for forming a high specific resistance thin film forming a resistance element in a circuit by sputtering in the production of a high-density wiring board suitable for information processing equipment such as a computer and an electronic exchanger.

【0002】

[Conventional technology]

Conventionally, a thin film composed of Cr, Si, and O having a large resistivity has a small temperature coefficient of resistance, is thermally and chemically stable, and is known as a very useful thin film for forming a thin film resistance element. As a means for forming the thin film, described in Journal of Vacuum Science and Technology Vol. 4, No. 4 (1967), pp. 163 to 170 (J.Vac.Sci.Technol., 4 (1967) pp163-170). As described above, a method of heating a mixture of Cr powder and silicon monoxide (SiO) powder with an electron beam and depositing the mixture is described.

【0003】

Further, as described in JP-A-54-1898 and JP-A-58-82770, the above thin film can be obtained by performing reactive sputtering in an oxygen-containing atmosphere using a composite target or alloy target composed of Cr and Si. It is stated that it can be done.

【0004】

In addition, Cr powder and SiO as described in Thin Solid Films, Vol. 57 (1979), pp. 363-366 (Thin Solid Films, 57 (1979), pp363-366).₂There is also an example in which the above thin film is formed by using a mixture of powders as a powder as a sputtering target.

【0005】

Further, although the material system is different, metal tantalum (Ta) and SiO are used as sputtering targets for obtaining a thin film composed of tantalum (Ta), silicon (Si) and oxygen (O), which are known as thin films composed of metal, silicon and oxygen.₂Japanese Patent Application Laid-Open No. 58-119605 describes an example in which the powder of No.

【0006】

[Problems to be Solved by the Invention]

In all of the above-mentioned conventional examples for forming a thin film composed of Cr, Si, and O, the desired thin film can be obtained in the short term, but the thin film can be obtained over time with good reproducibility over a long period of time. There was a problem in industrial use because the stability was not taken into consideration and the composition was liable to shift. Also, metals Ta and SiO₂In the example of the sputtering target formed from tantalum and silicon, the chemical reaction between tantalum and silicon occurs at a high temperature, and as a result, the target becomes very brittle, so it is necessary to perform molding at a low temperature as much as possible. Therefore, the relative density does not increase, and even if various measures are taken, it remains at about 90%. Therefore, the in-plane distribution and the distribution in the thickness direction of the minute voids contained in the sputtering target are likely to occur, and there is also a problem in terms of long-term reproducibility (stability over time). Further, the minute voids not only serve as the starting point of cracks, but also facilitate the propagation of the fine voids, so that the target material having a low relative density has low mechanical strength and is easily cracked during use. In addition, large voids that can be seen with the naked eye cause local concentration of glow discharge during sputtering, which makes the discharge unstable. In order to prevent this, when pressure is applied at a high pressure to improve the relative density to 90% or more, heat is generated due to friction between particles during pressurization, and the progress of the reaction cannot be suppressed. Therefore, the obtained target material is very brittle and often cracks due to heat generation due to electric discharge during sputtering film formation, and cannot be used.

【0007】

An object of the present invention is to provide a sputtering target suitable for mass production for stably and mass-forming a thin film having a high resistivity composed of Cr, Si and O.

【0008】

[Means for solving problems]

The above objective is achieved by obtaining a homogeneous, mechanically strong, i.e., relative-dense, sputtering target composed of Cr, Si, and O. For this reason, Cr as a raw material and SiO, which is a stable oxide,₂The powder of 32 mesh under (particle size 500 μm or less) is selected by Tyler number, and after sufficiently removing water, it is mixed at a ratio of 20 to 80% by weight Cr to be mixed with the raw material powder. To do. Here, in order to prevent the reaction between Cr and Si from occurring due to heating for molding, a powder having a thin oxide film formed on the surface of Cr grains by heat treatment is used as SiO.₂May be mixed with and used as a raw material powder. After that, it is filled in a consolidation sealing can lined with a foil of a refractory metal such as niobium (Nb), and the gas in the can is exhausted while heating to 200 to 800 ° C, and then sealed and hot. A sputtering target is manufactured by pressure molding by a hydrostatic press.

【0009】

Alternatively, the mixed raw material powder is molded by a normal press, then mounted on a die and pressure-molded by a hot press to produce a sputtering target.

【0010】

[Action]

Cr and SiO₂The powders are sorted so that the particle size of each of the powders is 32 mesh or less (particle size 500 μm or less), and these are set to a ratio in the range of 20 to 80% by weight Cr and sufficiently stirred to obtain a uniform mixed raw material powder. Obtainable. By using this mixed raw material powder, local Cr and SiO₂It is possible to produce a sintered body in which the variation in the ratio of the above is very small. In addition, due to the original properties of Cr, a natural oxide film is formed on the surface of Cr grains simply by leaving the Cr powder in the atmosphere, and Cr and SiO are formed even during the molding process by high temperature and high pressure.₂In order to prevent a chemical reaction with the Si inside, the sintered body is not destroyed due to the formation of a brittle compound or the volume change at the time of compound formation, and stable production can be performed. Further, a more reliable effect can be obtained by forming an oxide film on the surface of Cr grains by heat treatment. Since both are stable even when pressurized at high temperatures, the temperature is about 1200 ° C and 1000 kg / cm.²SiO between Cr particles during molding under high pressure conditions₂Softens and flows to fill the voids, so the space between Cr particles is almost completely SiO₂It will have a mixed two-phase structure filled with, and the relative density of the sintered body will be 95% or more. Further, the Nb foil, which is the reaction prevention layer lined on the sealing can, reacts with the material of the sealing can and the raw material powder, and the constituent elements of the sealing can are mixed in the pressure molded body or the surface of the pressure molded body. Prevents the sealing can from becoming unremovable. Such anti-reaction treatment is also necessary for dies when pressure molding is performed by hot pressing. Local Cr and SiO in the sintered body due to the overall effect of these manufacturing methods₂Since the variation in the ratio of the above is small, it is possible to obtain a sintered body which is very homogeneous and has a relative density of 95% or more and high mechanical strength. The thin film obtained by using the present sputtering target having such characteristics has a small in-plane distribution of film characteristics, and it is possible to obtain a thin film with good reproducibility over a long period of time.

【0011】

[Example]

Hereinafter, examples of the present invention will be described with reference to the drawings.

【0012】

[Example 1] As shown in FIG. 1, a Cr powder having a purity of 99.5% or more as a raw material has a particle size of 120 mesh or less and a SiO having a purity of 99.5% or more.₂Each powder is sorted so that the particle size is 200 mesh or less. Since Cr powder has relatively little water adsorption, it may be used as a raw material powder as it is after sorting if care is taken in storage. In addition, if there is concern about moisture adsorption during storage, it is possible to reliably remove moisture by stirring while heating to about 200 ° C in the atmosphere, and at the same time, an oxide film is formed on the entire surface of the Cr grains, which is at high temperature. SiO in₂It works to prevent the reaction with. If the heating during drying is set to a high temperature exceeding 300 ° C, the surface oxidation of Cr grains becomes remarkable and the oxygen content of the target as a whole is also affected. Therefore, the above temperature range is appropriate. SiO₂Moisture must be removed from the powder by heating it to 800 ° C or higher and stirring it in the air or in a dry atmosphere such as nitrogen. SiO₂Depending on the manufacturing method, the powder may contain about 10% by weight of water in the form of water of crystallization, and it also adsorbs a considerable amount of water in the atmosphere during storage. Drying treatment at such a high temperature is indispensable. SiO₂When water remains in the powder, it becomes water vapor at a high temperature of about 1000 ° C during sintering, which causes the Cr powder to be extremely oxidized and becomes a brittle oxide, so that it cannot be substantially sintered.

【0013】

After that, Cr and SiO adjusted to the specified weights, respectively.₂Was thoroughly mixed to obtain a raw material powder. Here, if the mixing ratios of the raw material powders are significantly different, such as 20% by weight Cr or less and 80% by weight Cr or more, it becomes difficult to uniformly mix the raw material powders, and Cr or SiO even in the sputtering target.₂Is likely to be unevenly distributed. Therefore, the composition of the sputtering target needs to be in the range of 20% by weight Cr to 80% by weight Cr. In order to suppress reactions such as alloying with mixed powder under high temperature and high pressure, it is packed in a steel compaction sealing can lined with niobium (Nb) or tantalum (Ta) foil with a thickness of several tens of μm, and 200 ~ Exhaust the air in the container over several hours while heating in the range of 800 ° C. The higher the temperature, the faster and more reliable the exhaust can be, but if it exceeds 800 ° C, Cr will sublimate, so it is necessary to keep it within the above range. Exhaust should be performed until the pressure inside the vessel is 0.01 Pa or less, and 0.001 Pa or less is effective enough to prevent excessive oxidation during sintering due to residual air and moisture, and as a sputtering target. The reproducibility of various characteristics is also good. After the exhaust is completed, the container is sealed and welded, and this is subjected to a hot hydrostatic press at a temperature of 1000 ° C to 1400 ° C and 1000 to 1200 kg / cm.²Sinter under the pressure of. After sintering, it is gradually cooled to room temperature over a period of 10 hours or more, and after the cooling is completed, the consolidation sealing can is mechanically cut and removed to take out the sintered compact. By this sintering process, the volume of the sealed can is reduced by about 10 to 20%. When the relative density of the obtained molded product was measured, it became clear that a density of 98% was obtained. Then, after machining the molded product into a predetermined shape, it is washed and dried with an organic solvent, pure water, or the like, and the target is adhered to a backing plate to facilitate attachment to a sputtering apparatus to complete the process.

【0014】

[Example 2] The particle size of the raw material powder is Cr under 32 mesh, SiO₂Although the sputtering target can be manufactured by the same process as in Example 1 even if the amount is 200 mesh under, the local uneven distribution of Cr powder in the target is conspicuous and the relative density is slightly lower than that in the above example 96. It was about%. When using the sputtering target, sufficient attention must be paid to the film quality reproducibility, and it was possible to use the sputtering target as a sputtering target by adjusting the film forming conditions according to the fluctuation.

【0015】

[Example 3] In the same manner as in Example 1, the raw material powder is prepared, mixed uniformly at the desired ratio, and then filled in a mold having a desired shape to about 400 kg / cm.²Powder molding is performed at the pressure of. This is attached to a carbon container and exhausted to a vacuum degree of 0.01 Pa inside the container. After this, at a temperature of 1300 ° C, about 260 kg / cm is passed through a carbon spacer coated with boron nitride.²Pressure was applied to the molded product, and this pressurized state was maintained for about 2 hours. By this method as well, a sputtering target equivalent to that of Example 1 could be obtained.

【0016】

In this manufacturing method, since it is possible to obtain a sputtering target with a small relative density by reducing the pressure and sintering, a product with a relative density of about 80% was manufactured and 3.0 W / cm.²Although it was discharged at the power density of, the target was broken by the discharge for several minutes and it could not be put into practical use. On the other hand, for the targets having a relative density of 95% or more, no signs of damage due to electric discharge were observed in any of the targets produced by any method including those described in Examples 1 and 2.

【0017】

[Example 4] 66% by weight Cr-34% by weight SiO obtained in Examples 1, 2 and 3.₂When the surface of the target having the composition of is polished and observed with an optical microscope, SiO is shown as shown in FIG.₂The structure is such that Cr grains 1 are scattered inside. This is SiO under high temperature and high pressure₂Is fluid and flows between Cr grains 1 to almost completely fill the voids, resulting in such a structure. When fluorescent X-ray analysis is performed on a sample having such a structure, Cr grains 1 and SiO are shown in Fig. 3.₂Between Cr characteristic X-ray intensity 4 and SiO₂Since the X-ray intensity 3 of the characteristic X-ray intensity 3 shows a sharp rise and fall and is reversed, it can be seen that mutual diffusion does not occur and a clear boundary exists. It is considered that this is because the natural oxide film or thermal oxide film on the surface of Cr grains acted as a barrier to prevent mutual diffusion under high temperature and high pressure in the sintering process. Relative density of sintered body having such a structure (theoretical density in this case is 4.06 g / cm)³) Was measured, and it was a value of about 98%, which was a sufficiently high value.

【0018】

[Example 5] Cr and SiO₂Comparing the mechanical strengths of the targets sintered under the same conditions by changing the particle size of the powder, as shown in Table 1, the mechanical strength depends on the particle size of the Cr powder, and the larger the Cr particles, the more brittle. Under the condition 1 in the table, cracks occurred at the machining stage after sintering, and it could not be evaluated as a sputtering target. However, a rectangular sputtering target was manufactured using the conditions 2 in the table, and 3.1 W / cm was used for this.²RF power was applied at the power density of the above, and the load of generating glow discharge was applied for a total of 200 hours, but it could be used without any abnormality. Therefore, it is clear that the upper limit of the particle size of Cr powder is between conditions 1 and 2 in the table, and those finer than 2 are sufficiently usable.

【0019】

Also, Cr and SiO₂If the particle size of the powder is large, local Cr and SiO in the part₂The variation in the ratio of the above becomes large, and the reproducibility of the film characteristics of the thin film deteriorates. Therefore, the raw materials Cr and SiO₂From this point as well, the particle size of the powder must be finer than 32 mesh, and SiO₂The powder must be as fine as or finer than the Cr powder in terms of uniform mixing. However, even if the Cr powder is too thin, the mechanical strength will be saturated, and the amount of oxygen will increase more than the expected amount due to the quantitative increase of the oxide layer accompanying the increase in the surface area of the Cr grains, and the inclusion of impurities. There is no advantage even if it is finer than 1000 mesh under because the influence such as a relatively large amount becomes remarkable. SiO₂As for the powder, the finer the powder, the more water is adsorbed, and the agglutination of the grains becomes remarkable. Therefore, the result is effectively the same as that of the coarse powder, so there is no advantage even if the powder is finer than 1000 mesh under. Therefore, when actually manufacturing a sputtering target, Cr and SiO are considered in consideration of the impurity content of the raw material powder, ease of handling, and the characteristics of the target.₂The optimum particle size for both powders is in the range of 32 to 1000 mesh under.

【0020】

[table 1]

【0021】

[Example 6] 127 × 381 mm square Cr-SiO₂When a sintering target was manufactured, attached to a substrate moving film formation type sputtering device, and discharged with an RF power of 1.5 kW to form a thin film, the sheet resistance distribution of the obtained thin film was ± on a 127 mm square substrate. It was less than 3%. In addition, the film formation reproducibility under certain film formation conditions was investigated with this device, and the relationship between the cumulative number of batches and the average sheet resistance value is shown in Fig. 4. From this figure, Cr plate and SiO₂This relationship 5 by the composite target with the same outer shape by combining the plates increases every time the batches overlap, and the number of batches that can obtain the above-mentioned sheet resistance and the thin film having its distribution characteristics was about 20 batches. However, in Example 6 using the sputtering target according to the present invention, the number of batches reached 300 or more, and a significant improvement in mass productivity was confirmed. In addition, through these studies, there was no sign that the sintering target was destroyed by electric discharge, and it was confirmed that the above manufacturing conditions were set appropriately.

【0022】

[Example 7] Cr and SiO₂Sputtering targets in which the mixing ratio of the powder was changed in the range of 55 to 80% by weight Cr were prepared, and a Cr-Si-O thin film was formed by RF sputtering using these. Figure 5 shows the specific resistance of the film as it is formed. As is clear from this figure, a thin film having a specific resistance of 1 μΩ · m, which is the same specific resistance as a generally known NiCr (nichrome) thin film, has a composition of 80% by weight Cr in the sputtering target of the present invention. Further, the thin film in the high resistivity region, which was difficult to obtain stably in the past, is SiO.₂It can be easily obtained over a wide range by increasing the amount of.

【0023】

From the viewpoint of the specific resistance of the obtained thin film, the range of 50 to 80% by weight Cr is particularly useful as the target composition. Further, when the amount of Cr is less than 20% by weight Cr, the obtained thin film becomes substantially an insulator, which deviates from the object of the present invention. As described above, the composition of the sputtering target according to the present invention needs to be in the range of 20% by weight Cr to 80% by weight Cr from the viewpoint of the characteristics of the obtained thin film, and 50 to 80% by weight Cr is particularly preferable. Is.

【0024】

[Effect of the invention]

According to the present invention, Cr and SiO₂It is possible to obtain a homogeneous sputtering target with no bias in the mixing ratio of. In addition, since this target has high mechanical strength and can withstand discharge over a long period of time, the usable time of the target can be 10 times or more that of the conventional target. Further, by using this target, a thin film having a desired specific resistance can be obtained with good reproducibility in a state where the distribution of the film quality in the substrate is small. Therefore, when this thin film is formed as a resistance element, the error of the element resistance value can be reduced. , The circuit characteristics of the thin film circuit can be greatly improved.

[Simple explanation of drawings]

[Figure 1]

Cr-SiO according to the present invention₂Diagram showing the manufacturing process of the sintered target, [Figure 2]

Cr-SiO according to the present invention₂Diagram showing the sintered target microscope structure, [Fig. 3]

The figure which shows the result of the ray analysis by fluorescent X-ray from A to A'in FIG. [Fig. 4]

The figure which compared the specific resistance variation with the use of the sintered target by this invention with that of the composite type target of the same shape, [Fig. 5]

SiO₂It is a figure which shows the mixing ratio dependence of the specific resistance of the thin film obtained by the sintering target which changed the mixing ratio of a powder.

[Explanation of symbols]

1 ... Cr particles, 2 ... SiO₂, 3 ... Si fluorescent X-ray detection intensity, 4 ... Cr fluorescent X-ray detection intensity, 5 ... Fluctuation of thin film sheet resistance due to wear in composite target, 6 ... INDUSTRIAL APPLICABILITY Fluctuations in thin film sheet resistance due to wear on the target. Is shown.