JP4415303B2 - Sputtering target for thin film formation - Google Patents

Description

  The present invention relates to a sputtering target used for forming a metal thin film wiring used for electrical wiring, electrodes, etc. of thin film electronic components such as liquid crystal displays, thin film sensors, and magnetic heads.

  In recent years, low resistance Al, Cu, and Ag have been used for electric wiring films used for thin film transistor type liquid crystal displays (TFT-LCDs) for forming thin film devices on glass substrates and thin film sensors for forming elements on ceramic substrates. Further, pure metal films such as Au or alloy films mainly composed of them have been used. In general, these films are inferior in any of heat resistance, corrosion resistance, and adhesion required as an electric wiring film, and thus have a problem that they cannot sufficiently withstand the process for forming the electric wiring.

Therefore, in order to solve the above problems, it is considered to form a thin film such as Cr, Mo, Ti, which is a refractory metal, as a base film or a cover film for the substrate, among which heat resistance, corrosion resistance, Mo and Mo alloys have been widely used from the viewpoints of adhesion, cost, and environmental conservation. For example, in a liquid crystal display device, an alloy film in which Cr, Ti, Ta, and Nb are added to Mo has been proposed as a Mo alloy film laminated with an Al wiring (see, for example, Patent Document 1).
JP 2000-284326 A

  Although the above-mentioned Mo alloy film is described as being excellent in heat resistance and etching properties as a laminated film with an Al wiring, it has a lower resistance than Al and adhesion with Ag and Ag alloy, and further Ag and Ag alloy films There is no disclosure of a Mo alloy having excellent properties as a base film or a cover film that suppresses an increase in resistance value.

Furthermore, in order to produce a thin film device using the metal wiring as described above with high efficiency, a method of manufacturing a large number of devices at once using a large substrate is used. For example, in order to manufacture a large 12 inch diagonal LCD, the substrate size is increased from the conventional 370 x 470 mm to 550 x 650 mm, and further to 650 x 830 mm. LCD can be manufactured. At present, sputtering is generally used as a method for forming metal wiring. Therefore, a sputtering target used for forming these metal films is also used for forming a high-quality film stably on the substrate. A large-sized integrated product without a large size is required, and its flat area exceeds 0.4 m ² , and the size is further increased. In order to manufacture these large integrated target materials, it is necessary to use a high-density and high-strength material. However, there is no clarification about a Mo alloy target for stably obtaining a Mo alloy film which is a high melting point metal.

  An object of this invention is to provide the sputtering target which can form Mo alloy film in a large area with sufficient reproducibility in view of the said problem.

  In order to search for a desired Mo alloy film as a base film or a cover film for Ag, an Ag alloy film, the present inventor created a Mo alloy target obtained by adding various additive elements to Mo, and systematically sputtering the Mo alloy. A film was formed and the Mo-Ti alloy was found desirable. Furthermore, Mo-Ti alloy target materials for stably forming a Mo-Ti alloy film were studied, and desirable structures and mechanical properties were found, leading to the present invention.

That is, the sputtering target for forming a thin film of the present invention is a sputtering target for forming a Mo alloy film on a substrate, and its composition contains 30 to 50 atomic% of Ti, and the balance is Mo and inevitable impurities. A thin film forming sputtering target having a relative density of 98 % or more and a bending strength of 300 MPa or more.

  Further, the metal structure of the above-described sputtering target for forming a thin film preferably has a crystal grain size of 300 μm or less. Moreover, it is desirable that the sputtering target for forming a thin film has a metal structure composed of a single phase and a diffuse phase of Mo and Ti, or a metal structure composed of a diffuse phase composed of Mo and Ti.

  Furthermore, the sputtering target for forming a thin film of the present invention has a purity in which the total of Mo and Ti is 99.9% by mass or more, excluding gas components, and preferably the O content as a gas component is 1000 ppm or less. The C content is 500 ppm or less.

  As described above, according to the present invention, the large Mo-Ti sputtering necessary for forming a Mo-Ti film having excellent corrosion resistance and excellent adhesion to Ag or an Ag alloy film over a large area with high reproducibility. It is possible to stably manufacture the target material. For this reason, it is effective for the formation of metal thin film wiring used for electric wiring, electrodes, etc. of thin film electronic components, and its industrial utility value is high.

  The sputtering target for forming a thin film of the present invention is a Mo alloy target containing Ti mainly composed of Mo, does not contain harmful Cr, and has high heat resistance, corrosion resistance and adhesion as a base film of Ag or an Ag alloy film. The metal thin film which has can be obtained. Although there are various forms of the sputtering target for forming a thin film of the present invention depending on the production method, a technique suitable for obtaining the high density, high strength, uniform structure and high purity required as a sputtering target can be used. For example, a target method using an ingot manufactured by a melting method suitable for obtaining a low-oxygen material, and a target method consisting of a powder sintering method that easily obtains a uniform structure can be exemplified.

  The reason for selecting Ti as an element to be added to Mo is that it has an effect of improving the corrosion resistance of Mo. Further, since Ti is an element having a solid solution region for both Ag and Mo, adhesion is improved by adding Ti to Mo as a base film or a cover film for a low-resistance Ag or Ag alloy film. Furthermore, it is because the effect of suppressing an increase in the resistance value of Ag or an Ag alloy film is high by reducing misfit of the crystal lattice.

Here, the addition amount of Ti is desirably 2 to 50 atomic%. If it is less than 2 atomic%, the effect of improving the corrosion resistance of the formed film is low, and if it exceeds 50 atomic%, the etching property is lowered. Further, it is desirable that the amount of Ti added be 10% or more in order to sufficiently match the lattice of the Ag and Ag alloy films. This is because the crystal lattice misfit with Ag becomes as large as 5% or more at 10% or less.
Ti, like Ag, has a solid solution region with Cu and Au. For this reason, the Mo—Ti alloy film in which Ti is added to Mo also improves the adhesion with an alloy film mainly composed of Cu, Au, Cu, and Au. Therefore, these films are used as a base film and a cover film for these films. It is possible.

  As described above, the composition of the film formed by sputtering has a strong correlation with the target composition, and by using the target having the above composition, it is possible to form a film having the same composition and excellent in various characteristics. A metal film is obtained.

  The relative density of the sputtering target is preferably high because it affects the sputtering rate involved in productivity when forming a thin film and more important film characteristics. As a result of various studies, when the relative density is less than 95%, the sputtering rate decreases, and further, the formed film stress increases and the specific resistance increases. Moreover, when the relative density is less than 95%, there is a concern that a large defect remains in the target or there is a pore connected from the surface to the inside. These defects lead to partial peeling and cracking during the machining of the target manufacturing process, resulting in a decrease in target manufacturing yield and a decrease in film characteristics during sputtering due to penetration of processing oil or cleaning liquid into the interior. Therefore, the relative density of the sputtering target of the present invention needs to be at least 95%, desirably 98% or more.

  Furthermore, as the sputtering target, the higher the strength, the better. In the case of a Mo alloy target to which a predetermined amount of Ti of the present invention is added, it is necessary to have a bending strength of 300 MPa or more. As a result of the examination, if the bending strength is less than 300 MPa, cracking and surface peeling are likely to occur due to stress generated during machining in the target manufacturing process or when a backing plate that is a cooling plate is attached. In addition, cracks occur due to thermal stress due to surface heating during sputtering, and stable sputtering cannot be performed.

  The sputtering target of this invention is suitable as a target used for metal film formation of a large sized liquid crystal display. Since it is generally necessary to form a film in a short time in order to obtain high productivity, a high input power is applied to the target during sputtering. In order to withstand thermal shock and the like at this time, strength is required, and a bending strength of 300 MPa is required at the minimum. Desirably, it is 500 MPa or more.

  Furthermore, the sputtering target for forming a thin film of the present invention preferably has a crystal grain size of 300 μm or less in addition to high density and high strength. When a sputtering target is used, the target surface becomes a scraped surface called an “erosion area”. The surface shape becomes uneven due to the difference in crystal orientation of the crystal grains, and the unevenness increases as the crystal grain size increases.

  Concavities and convexities generated in the erosion area may cause abnormal discharge due to the sputtering apparatus used and film formation conditions. Further, the sputtered particles adhering to the uneven side surface may be peeled off to generate particles, which causes a decrease in yield depending on the film thickness and wiring width used for the thin film device to be manufactured. This unevenness can be suppressed by making the crystal grains finer. Therefore, the sputtering target of the present invention preferably has a crystal grain size of 300 μm or less, more preferably 100 μm or less.

  The sputtering target for forming a thin film of the present invention preferably has a metal structure consisting of a single phase of Mo and Ti and a diffusion phase composed of these elements. Since there is no great difference in the sputtering rates of these two elements, each may exist as a single metal, but having a diffusion phase at the grain boundary makes the grain boundary of each element unclear, Relieves irregularities in the erosion area and suppresses the generation of particles.

  The sputtering target for forming a thin film of the present invention can have a metal structure composed of a diffusion phase composed of Mo and Ti. In addition to the most desirable uniform structure in the target, these Tis are more likely to be oxidized than Mo. Therefore, the diffusion phase with Mo suppresses oxidation and suppresses the formation of an oxide layer on the target surface. It becomes possible. This makes it possible to shorten the pre-sputtering time initially performed to obtain stable film characteristics when using the target, thereby improving productivity.

  The sputtering target for forming a thin film of the present invention preferably contains as few impurities as possible in order to improve and stabilize the properties of the metal thin film obtained by sputtering in addition to its high density and high strength. Specifically, it is preferable that the sum of Mo and Ti has a purity of 99.9% by mass or more in a content ratio excluding gas components. In addition, it is desirable that Fe as a transition metal is 300 ppm or less, Ni is 200 ppm or less, Na, K, and Ca as alkali metals are 5 ppm or less, and U and Th as radioactive elements are each 1 ppm or less.

  In particular, when the Mo alloy target of the present invention is used for a thin film transistor-driven liquid crystal display using amorphous Si, which is the current mainstream, and high-definition low-temperature polycrystalline Si, it causes junction leakage of these semiconductor elements. Reduction of transition metals is effective, and Fe is preferably 300 ppm or less, Ni is 200 ppm or less, and further preferably 50 ppm or less. It is also effective to reduce radioactive elements that emit α-rays and cause malfunction of the semiconductor element, and it is desirable that U and Th be 1 ppm or less, and further 0.1 ppm or less. In addition, the above-described purity excluding gas components is also preferably 99.9% or more, and more preferably 99.99% or more.

  Furthermore, the sputtering target for forming a thin film of the present invention has an O (oxygen) content of 1000 ppm or less, which is a gas component involved in the film characteristics, in order to further improve and stabilize the characteristics of the metal thin film obtained by the sputtering. The C (carbon) content is preferably 500 ppm or less. When O in the target exceeds 1000 ppm, the O and C contents of the formed Mo alloy film increase due to the conditions such as the degree of vacuum of the sputtering apparatus and the cleaning state of the substrate used, and the resistance value and film As the stress increases, it affects the etchability. For this reason, it goes without saying that the O content in the target is preferably 1000 ppm or less, more preferably 300 ppm or less, and even more preferably 100 ppm or less. Similarly, the film characteristics can be further stabilized by setting the C content to 500 ppm or less, and further to 50 ppm or less.

  The sputtering target for forming a thin film of the present invention may be produced by any manufacturing method as long as the configuration can be achieved. For example, as the melting method, a vacuum induction heating melting method, an electron beam melting method, a plasma melting method, or the like can be used. These dissolution methods have various problems as described below, but have an advantage that a low-oxygen ingot can be produced.

  In the case of the Mo alloy used in the present invention, since the melting point is high, it is difficult to dissolve by the vacuum induction heating melting method, and the electron beam melting method has a problem that composition deviation is likely to occur due to a vapor pressure difference. It is possible to obtain a Mo-Ti alloy by controlling. Furthermore, the melting method requires a mold or the like for making the molten metal into an ingot, and the size of the target that can be manufactured is limited depending on the size. In addition, when solidified in a mold after melting at high temperature, there is a problem that the difference in structure between the surface of the ingot and the inside tends to occur due to the difference in cooling rate. Appropriate selection makes it possible to manufacture ingots with little structural difference.

  There is also a method using a plasma melting method. In this case, a process for producing a melted material is further required, but a temporary molded body formed by cold isostatic pressing (CIP) or powder sintering can be used as the melted material, and molten droplets are deposited. By doing so, an ingot can be manufactured. In this case, since the droplets are sequentially cooled, a fine structure can be obtained.

  Further, a powder sintering method can be used as a method for obtaining the sputtering target of the present invention. As a method of obtaining a sintered body, the raw material powder is most simply a method of mixing Mo and Ti pure metal powders as raw material compositions at a predetermined ratio (that is, mixing Mo powder and Ti powder into the target composition) Method). Further, there is a method using a powder alloyed in advance with a predetermined composition (that is, a method using a Mo—Ti alloy powder having a target composition).

  Also, a method of mixing alloy powders of various compositions so as to have a predetermined composition (for example, Mo-5 atomic% Ti alloy powder and Mo-50 atomic% Ti alloy powder are mixed to make Mo-15 atomic% Ti. Method), a method of mixing alloy powder and pure metal powder so as to have a predetermined composition (for example, a method of mixing Mo-TI powder and pure Mo powder into a target composition), and so on. It is possible to manufacture Mo alloy targets having various compositions and structures.

  In addition, the powder sintering method is a method of hot pressing a powder adjusted to a predetermined composition in a carbon mold, or a hot isostatic pressing (HIP) after degassing and sealing in a metal capsule. ) And a method of sintering a powder formed by cold isostatic pressing (CIP). The Mo alloy suitable for the sputtering target having the composition of the present invention has a heating temperature of 1000 to 1500 ° C. and a surface pressure of 20 MPa or more in the case of hot pressing, and a heating temperature of 900 to 1200 ° C. and a pressure of 100 MPa or more in the case of HIP. By performing sintering molding under conditions, a sintered body having a relative density of 95% or more can be obtained.

  The heating temperature range varies depending on the sintering method. In the case of hot pressing, the pressure is low, so the density does not improve at less than 1000 ° C, and the Ti component reacts with the carbon that is the mold when it exceeds 1500 ° C. It is. Moreover, in the case of HIP, when it exceeds 1200 ° C., a reaction occurs between a soft steel or Fe alloy capsule generally used as a container and a powder component, and the capsule may be dissolved. In addition, by heating and sintering the mixed powder in a reducing atmosphere such as a hydrogen atmosphere, it is possible to reduce oxygen, a low-melting-point metal that is not necessary for the configuration of the present invention, and the like.

  Furthermore, when manufacturing the Mo alloy sputtering target of this invention, it is also possible to perform hot plastic working to the ingot or sintered body manufactured by the above-mentioned melting method or powder sintering method. For example, with an increase in the size of a flat panel display such as a liquid crystal display using a thin film wiring using a metal thin film, the size of the substrate used is also increased, and the sputtering target is also required to be increased in size. Large size can be easily achieved by hot plastic working.

  There are various methods of hot plastic working such as pressing, forging and rolling. The heating temperature at that time is important for performing stable plastic working that does not cause cracks and the like. In particular, in the Mo alloy in which a predetermined amount of Ti is added to the Mo of the present invention, the elongation and squeezability of the material necessary for plastic working are significantly reduced at less than 800 ° C., and the tensile strength is lowered at over 1200 ° C. Therefore, 800 to 1200 ° C. is appropriate. The hot plastic working method may be selected according to the required size of the sputtering target and may be combined.

  It is also possible to obtain a more uniform and fine structure by controlling the heat treatment recrystallized structure by the plastic working rate during the hot plastic working and the subsequent heat treatment. Furthermore, in the composition range of the present invention, depending on the composition, there are some which can achieve higher density by crushing voids of the sintered body by performing hot plastic working rather than remaining in the sintered body. The plastic working rate at that time is preferably 10% or more. This is because when the voids remain in the sintered body, the processing rate of less than 10% is often insufficient to increase the density because the voids cannot be crushed in many cases. In addition, when the processing rate is less than 10%, the surface of the material and the amount of internal deformation tend to be uneven.

  Furthermore, in order to obtain a uniform recrystallized structure by heat treatment, the heat treatment temperature is desirably 800 to 1000 ° C. When the temperature is lower than 800 ° C., recrystallization does not occur sufficiently, and when the temperature exceeds 1000 ° C., crystal grains grow and become coarse particles. For this reason, 800-1000 degreeC is desirable as heat processing temperature in order to obtain a uniform structure | tissue. Using the above method, it becomes possible to obtain a high-strength, high-density target by eliminating voids and homogenizing the structure.

Next, specific examples of the present invention will be described.
First, pure metal and Mo alloy target were manufactured by the various manufacturing methods described below.
[Production method A]
A method in which an ingot having a diameter of 150 mm is manufactured using an electron beam melting apparatus having an ultimate pressure of 3 × 10 ⁻³ Pa in vacuum and cut to manufacture a target (AE). A method of manufacturing an ingot having a diameter of 100 mm by plasma melting and manufacturing in the same manner is referred to as (AP).
[Production method B]
In this method, powders are mixed and sintered so as to have a predetermined composition. Among them, a method of inserting into a carbon mold and cutting out from a sintered body manufactured by hot pressing is referred to as (BP). The surface pressure of the hot press was 30 MPa, and the temperature was 1300 ° C. for the Mo alloy. On the other hand, a method of encapsulating in a mild steel capsule and cutting out from a sintered body manufactured by HIP treatment is (BH). In the Mo alloy, the HIP treatment pressure was 120 MPa, and the heating temperature was 1000 ° C. Further, a method of sintering a powder that has been formed into a pressure-formed body by cold isostatic pressing (CIP) is referred to as (BS). In the sintering, a hydrogen sintering furnace was used and the heating temperature was 1700 ° C.

Further, in the above-described production methods A and B, (R) is used as a subscript for the method of performing forging and rolling plastic working on the ingot or sintered body produced by the melting method. During the plastic working, the material was heated to improve workability, and the temperatures were set to 1200 ° C., 1000 ° C., 600 ° C. for Cr, Mo, and Ti, and 800 to 1000 ° C. for the Mo alloy. The material was enclosed in a capsule and plastic processing was performed.
A plate-like target material was produced by the various production methods described above, and a target having a predetermined size was produced by machining.

  Targets having the compositions shown in Table 1 were produced by various production methods, attached to a sputtering apparatus, and formed to a thickness of 20 nm on a glass substrate. After the formation, the film was immersed in pure water at a temperature of 80 ° C. for 30 minutes, and then the presence or absence of discoloration on the film surface was confirmed to evaluate the corrosion resistance. Similarly, a 40 nm-thick film having a thickness of 40 nm was used as a base film, and an Ag—Zr—Cu alloy film was formed to 200 nm thereon. Thereafter, a scotch tape was attached on the Ag alloy film and peeled off at an angle of 45 ° C. to evaluate the adhesion with the Ag alloy film. The case where the film was completely peeled off was rated as x, the case where part of the film was peeled off was rated as Δ, the case where the film was not peeled but had defects was marked as ○, and the case where no film was peeled off was marked as ◎.

  When the corrosion resistance was evaluated, the pure Mo film and the pure Ti film were discolored, and the Mo-60Ti alloy film having a Ti content exceeding 50 atomic% was also discolored. However, the pure Cr film and Mo-Ti with 2-50 atomic% added Ti were added. The alloy film did not change color. For this reason, it can be seen that the pure Cr film and the Mo—Ti alloy film of the present invention have good corrosion resistance. The adhesion with the Ag alloy is that of sample No. 3 pure Ti film is preferable. It can also be seen that the Mo alloy is a Mo—Ti alloy film containing 2 atomic% or more of Ti and has good adhesion. From the above, it can be seen that the base film having good corrosion resistance and adhesion to the Ag alloy is a Mo—Ti alloy, and its addition amount is 2 to 50 atomic%.

  Next, according to the manufacturing method similar to Example 1, the large target of the dimension 800 * 900 * thickness 8 (mm) of the Mo-Ti alloy of various Ti addition amount was produced. The composition of the target, the relative density, the bending strength, and the presence or absence of target cracking during production were confirmed, and the results are shown in Table 2.

  As shown in Table 2, it can be seen that, regardless of the production method, the target having a density of less than 95% and a bending strength of less than 300 MPa is cracked during production. A high density of 95% or more and a bending strength of 300 MPa or more are required to stably produce a target that does not generate cracks necessary to form a uniform Mo alloy film on a large substrate of a flat panel display. It can be seen that it is.

  Next, a 15 mm square sample as a sample for observing the structure was prepared from the Mo alloy target prepared in Example 2, and a target having a diameter of 200 φ × thickness 6 (mm) was used for particle evaluation. First, the sample was polished, the microstructure was observed with an optical microscope, and the crystal grain size was measured. Then, the prepared target was attached to a sputtering apparatus, and a Mo alloy film having a thickness of 100 nm was formed on a 6-inch Si wafer with an input power of 2 kW and an Ar pressure of 0.5 Pa. After the specific resistance was stabilized, the number of particles of 0.3 μm or more confirmed on the Mo alloy film obtained by forming a film on 50 Si wafers was investigated and converted as an average value per substrate. . The results are shown in Table 3 together with the crystal grain size of the target.

  From Table 3, it can be seen that as the crystal grain size of the target increases, the number of particles in the formed film increases. In particular, when the crystal grain size exceeds 300 μm, particles having a size of 0.3 μm or more greatly increase. However, it can be seen that many particles are generated in the case of a target having a low density even though the crystal grains are fine. Therefore, it can be seen that the target of the present invention that implements both high density and fine crystal grains is effective in suppressing the generation of particles. In order to reduce the generation of particles, the crystal grain size is preferably finer, and can be further reduced by setting it to 100 μm or less.

  Sample No. of Example 3 19 microstructures are shown in FIG. It can be seen that there is an amorphous Ti grain in equiaxed crystal Mo with a small grain size, and the surrounding structure has a diffusion layer of Mo and Ti. Since the crystal grain size is fine, it has been confirmed that the generation of particles is small.

  A Mo—Ti target containing 30 atomic% of Ti was prepared by various production methods shown in Example 1, and the relative density and the bending strength were measured in the same manner as the method shown in Example 2. Furthermore, the structure was observed by the method shown in Example 3, the element distribution image was measured using an electron microscope, and the structure of the structure was observed. In addition, as in Example 3, the target was fabricated and the particle was evaluated, and the specific resistance of the formed film was measured by the four-terminal method, and the pre-sputtering time until the specific resistance was stabilized was investigated. did. The results are shown in Table 4.

  First, a target having a relative density of less than 95% has a long pre-sputtering time and many particles are generated. Even when the relative density is 95% or more, the target having an alloyed diffusion layer has a shorter pre-sputtering time and less generation of particles than the structure in which each single element exists. I understand that. As described above, the Mo—Ti target is preferably a structure having a diffusion layer that is partially alloyed than a structure in which only a single element is present, and further, an alloyed structure in which no single element is present. Is desirable.

  A sample was cut out from the sample No. 16 created in Example 2, and impurity analysis was performed using GD-Mass (glow discharge mass spectrometry) to determine purity. As a result, the total mass ratio (purity) of Mo and Ti as a content ratio excluding the gas component is 99.96%, transition metal Fe, which is a typical impurity, is 50 ppm, Ni is 30 ppm, and an alkali metal. Na was 2 ppm, and U as a radioactive element was 0.1 ppm or less. In addition, oxygen, which is a gas component, is 250 ppm and carbon is 30 ppm, which satisfies the purity for LCD of thin film transistor (TFT) operation that requires a high-purity metal film, and stable operation even in these applications. It is possible to form a metal film.

It is a micromicrograph of 100-times magnification which shows an example of the metal structure which the sputtering target for thin film formation of this invention has.

Claims (6)

In a sputtering target for forming a Mo alloy film on a substrate, the composition contains 30 to 50 atomic% of Ti, the balance is Mo and inevitable impurities, the relative density is 98 % or more, and the bending strength Is a sputtering target for forming a thin film, characterized by being 300 MPa or more.   The sputtering target for forming a thin film according to claim 1, wherein the crystal grain size is 300 μm or less.   The sputtering target for forming a thin film according to claim 1 or 2, wherein the sputtering target has a metal structure composed of one or more single phases of Mo and Ti and a diffusion phase composed of these elements.   The sputtering target for forming a thin film according to claim 1 or 2, wherein the sputtering target has a metal structure composed of a diffusion phase composed of Mo and Ti.   The sputtering target for forming a thin film according to any one of claims 1 to 4, wherein a total of Mo and Ti has a purity of 99.9% by mass or more excluding gas components.   The sputtering target for forming a thin film according to any one of claims 1 to 5, wherein the O content is 1000 ppm or less and the C content is 500 ppm or less.