JP2014043643A - SPUTTERING TARGET FOR FORMING Cu ALLOY THIN FILM AND MANUFACTURING METHOD OF THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sputtering target for forming Cu alloy thin films which is used in forming Cu-Mn alloy thin films useful for electrode films of display devices such as liquid crystal displays, wherein, in sputtering, the sputtering target reduces abnormally grown cluster particles and generates little particles or splashes, and to provide a manufacturing method of the target.SOLUTION: A sputtering target for forming Cu alloy thin films according to the invention includes at least Mn of which content is 2 atom% or more and 20 atom% or less. The target is controlled such that Vickers hardness of the cross sectional plane at t/2 in the target thickness direction is 50HV or more and 100HV or less.

Description

  The present invention relates to a sputtering target for forming a Cu alloy thin film and a method for producing the same. Specifically, the present invention relates to a sputtering target for forming a Cu alloy thin film capable of reducing abnormally coarsened cluster particles called particles or splash generated during sputtering and a method for manufacturing the same. The Cu alloy sputtering target of the present invention is a thin film for an electrode of a thin film transistor (TFT) used for an electronic device such as a display device such as a liquid crystal display or an organic EL display or a touch sensor, a thin film for a reflective electrode, and an electric connection wiring to a sensor. Thin film and the like; suitably used for forming a thin film such as a reflective film and a semi-transmissive film used for optical recording media such as CD, DVD, HD-DVD and BD.

  For example, Cu thin films have low electrical resistance and are relatively easy to process compared to Al. For example, wiring thin films constituting scanning electrodes and signal electrodes of display devices such as liquid crystal displays, and electronic devices such as touch sensors Used for electrical connection wiring thin film. However, pure Cu is inferior in adhesion to a substrate such as glass. Further, pure Cu has problems such as being easily oxidized and discoloring its surface, and having a large diffusion coefficient in a semiconductor. Therefore, in order to improve such problems of pure Cu, various Cu alloy thin films containing an appropriate selection element according to the application have been proposed.

  For example, Patent Document 1 discloses Mn, Ga as a Cu alloy for an electrode wiring of a liquid crystal display device capable of forming an oxide coating layer capable of suppressing the progress of Cu oxidation on a Cu surface in an oxidizing atmosphere containing oxygen. Cu alloys containing elements such as Li and Li are disclosed. In particular, it is described that Mn forms an oxide that is easier to form an oxide than Cu and that hardly allows oxygen to pass through, even though the melting point is higher than that of Cu.

  Patent Document 2 discloses an optical recording medium that prevents or suppresses sulfidation of a Cu recording layer due to diffusion of S from the protective layer and that does not cause a recording bit error, particularly in an optical disk using a protective layer containing ZnS. Metal elements such as Mn and Zn are described as elements capable of obtaining the above.

Japanese Patent No. 4065959 Japanese Patent No. 4603004

  In general, a Cu thin film is formed by a sputtering method using a sputtering target. In the sputtering method, first, an inert gas such as argon is introduced into the vacuum vessel at a low gas pressure, and a high voltage is applied between the substrate and a sputtering target composed of the same material as the thin film material, A plasma discharge is generated. After that, the gas ionized by the plasma discharge (here argon) is accelerated and collided with the sputtering target, the constituent atoms of the sputtering target are knocked out by inelastic collision, and the constituent elements are attached and deposited on the substrate to form a thin film. It is a method of forming. In addition to the above-described sputtering method, a vacuum vapor deposition method can be mainly cited as a method for forming a metal thin film. The sputtering method has an advantage that a thin film having the same composition as the sputtering target can be continuously formed. In particular, when the metal thin film to be formed is an alloy material, according to the sputtering method, an alloy element such as a rare earth element that does not dissolve in Cu can be forcibly dissolved in the thin film. Further, the sputtering method is an industrially very advantageous film forming method in which continuous and stable film formation on a large area substrate is possible.

  However, in the sputtering method, abnormally coarse cluster particles called particles or splash are generated during sputtering and may be taken into the thin film. When coarsened cluster particles are taken into the thin film, protrusions remain on the surface of the thin film, which may cause electrical shorts, or malfunctions may occur during wiring pattern formation, resulting in pattern abnormalities. This will cause harmful effects such as a broken line. There are various causes for the generation of such abnormal cluster particles. In terms of materials, it is often the case that it originates from the non-uniformity of the structure and crystal grains of the sputtering target, the shape of the sputtering target, contamination of foreign matter into the sputtering target, segregation of alloy elements in the sputtering target, etc. It has been.

  The Cu alloy thin films described in Patent Documents 1 and 2 described above are also described as being formed using a sputtering method, but the above-described problems at the time of sputtering are not mentioned at all. Moreover, in the Example of patent document 2, the Cu alloy thin film was not formed using the sputtering target, but the protective film of ZnS was only coat | covered with respect to the Cu-Mn ingot produced pseudo. Therefore, the said subject at the time of use of a sputtering target is not grasped | ascertained at all.

  Among the various alloy elements described in the above-mentioned patent documents, Mn preferentially reacts with oxygen over Cu to suppress the oxidation of Cu, or in the Cu recording layer due to the diffusion of S from the ZnS-containing protective layer. Very useful for preventing or inhibiting sulfidation. Therefore, a Cu—Mn alloy containing Mn is highly expected to be used as a thin film forming material such as an electrode thin film for a display device. However, since Mn is easily concentrated on the surface, the Cu—Mn alloy sputtering target containing Mn is likely to segregate Mn during sputtering, and there is a concern that abnormal discharge such as splash may occur more significantly.

  The present invention has been made in view of the above circumstances. The purpose is a sputtering target used to form a Cu-Mn alloy thin film useful as an electrode film for display devices such as liquid crystal displays, etc. Another object of the present invention is to provide a sputtering target for forming a Cu alloy thin film with less generation of splash and splash, and a method for producing the same.

  The sputtering target for forming a Cu alloy thin film of the present invention that has solved the above problems is a Cu alloy sputtering target containing at least Mn and having a Mn content of 2 atomic% or more and 20 atomic% or less. The gist is that the Vickers hardness of the t / 2 cross section in the thickness direction of the target is 50HV or more and 100HV or less.

  In a preferred embodiment of the present invention, the sputtering target has a Mn content of 2 atomic% or more and 10 atomic% or less.

  In a preferred embodiment of the present invention, the Vickers hardness of the t / 2 cross section in the thickness direction of the sputtering target is 60 HV or more and 90 HV or less.

  Moreover, the manufacturing method of the sputtering target for Cu alloy thin film formation which concerns on this invention which was able to solve the said subject is 50% or more of the total rolling reduction rate at the time of hot rolling with respect to Cu alloy which satisfies the said composition. The main point is that annealing after hot rolling is performed at a temperature of 450 ° C. or more and 600 ° C. or less for 2 hours or more.

  In a preferred embodiment of the present invention, the total rolling reduction during the hot rolling is 50% or more and 75% or less.

  In a preferred embodiment of the present invention, the annealing temperature after the hot rolling is 450 ° C. or higher and 550 ° C. or lower.

  In a preferred embodiment of the present invention, the annealing time after the hot rolling is 2 hours or more and 5 hours or less.

  If the Cu—Mn alloy sputtering target of the present invention is used, abnormal discharge such as particles and splash generated during sputtering is reduced, so that the sputtering method has excellent discharge stability stably from the initial stage of sputtering to the life end. Can be formed.

  Furthermore, according to the present invention, a Cu—Mn alloy thin film with excellent in-plane uniformity is obtained with little variation in composition, film thickness, and electrical resistance within the substrate plane (in the same plane) even for large-area substrates. It is done. As a result, the yield of final products such as display devices including the Cu—Mn thin film is significantly improved.

FIG. 1 is a graph of No. 1 in Table 1 in Example 1. FIG. It is a figure which shows the EPMA test result of 16 Cu-Mn alloy sputtering targets.

  The present inventors processed a Cu-Mn alloy containing at least Mn into a sputtering target such as a sheet and formed a film on a large-area substrate with excellent in-plane uniformity such as composition and film thickness. In order to provide a Cu—Mn alloy sputtering target capable of stably forming a Cu—Mn alloy thin film for a long period of time without causing abnormal discharge, investigations have been repeated. As a result, (a) by controlling the Vickers hardness of the t / 2 cross section (t is the thickness of the sputtering target) in the thickness direction (direction perpendicular to the rolling direction) of the sputtering target within a predetermined range, (A) When such a Cu-Mn alloy sputtering target is produced by a melt casting method using a Cu-Mn alloy, the total rolling reduction particularly during hot rolling, and hot rolling It has been found that it can be obtained by appropriately controlling the subsequent annealing conditions, and the present invention has been completed.

  That is, the sputtering target for forming a Cu alloy thin film of the present invention is a Cu alloy sputtering target containing at least Mn and having a Mn content of 2 atomic% or more and 20 atomic% or less, in the thickness direction of the sputtering target. It is characterized in that the Vickers hardness of the t / 2 cross section is 50HV or more and 100HV or less.

  First, the composition of the Cu alloy will be described. Hereinafter, a Cu alloy containing Mn may be referred to as a Cu—Mn alloy.

  The Cu-Mn alloy contains at least Mn and contains Mn in a range of 2 atomic% to 20 atomic%. Mn is an element that dissolves in the Cu metal but does not dissolve in the Cu oxide film. Further, as described in Patent Document 1 and Patent Document 2 described above, Mn forms an oxide film that reacts with oxygen preferentially over Cu to suppress oxidation of Cu, or a ZnS-containing protective layer. It is very useful as an element that can prevent or suppress sulfidation of the Cu recording layer due to diffusion of S. When the Cu alloy in which Mn is dissolved is oxidized by heat treatment in the process of forming a thin film by sputtering, Mn diffuses and concentrates at the grain boundaries and interfaces, and the concentrated layer adheres to the transparent substrate. It is thought that the property improves.

  In order to effectively exhibit such an action of Mn, the Mn content in the Cu alloy is set to 2 atomic% or more. Preferably it is 4 atomic% or more, More preferably, it is 8 atomic% or more. However, if the upper limit of the Mn content exceeds 20 atomic%, there is a problem such as brittleness, so the upper limit is made 20 atomic% or less. Preferably it is 15 atomic% or less, More preferably, it is 10 atomic% or less.

  The Cu alloy may contain at least Mn in the above range, and the balance is Cu and inevitable impurities.

  Furthermore, the following elements can be further added to the Cu alloy for the purpose of imparting other characteristics.

  For example, even when at least one element selected from the group consisting of Ag, Au, C, W, Ca, Mg, Ni, Al, Sn, and B is added in the range of 0.2 to 10 atomic%. good. Thereby, adhesiveness with a board | substrate improves. These elements may be added alone or in combination of two or more. In addition, said content is a single quantity, when the said element is included independently, and when it contains 2 or more types, it is a total amount.

  Similarly, Zn may be added in the range of 0.2 to 10 atomic%. Thereby, adhesiveness with a board | substrate improves.

  The Cu alloy sputtering target of the present invention has the above-mentioned composition and has the greatest feature in that the Vickers hardness of the t / 2 cross section in the thickness direction of the sputtering target is 50 HV or more and 100 HV or less. As described above, by using the Cu alloy sputtering target in which the Vickers hardness is appropriately controlled, the occurrence of splash during sputtering film formation is reduced. When using a Cu—Mn alloy sputtering target containing at least Mn in the range of 2 to 20 atomic% as in the present invention, as demonstrated in the examples described later, even if the hardness of the sputtering target becomes too high. It has been found that splash is likely to occur. Preferred Vickers hardness is 50HV or more and 100HV or less, more preferably 60HV or more and 90HV or less.

  Here, the t / 2 cross section in the thickness direction of the sputtering target is a plane parallel to the rolling direction among the cross sections perpendicular to the rolling surface, and t (thickness) with respect to the thickness t of the sputtering target. ) Means a cross section in the range of x1 / 2.

Specifically, the Vickers hardness of the sputtering target is calculated as follows. First, the sputtering target is cut so that the above-mentioned cross section (measurement surface) appears. At this time, cut pieces are collected from three places (the front end, the center, and the rear end with respect to the rolling direction). Next, polishing with emery paper or diamond paste is performed to smooth the measurement surface. Thereafter, electrolytic etching with Barker's solution (an aqueous solution in which HBF ₄ (tetrafluoroboric acid) and water are mixed at a volume ratio of 1:30) is performed, and the hardness at the center of the thickness of the measurement surface is measured by It is measured using a Vickers hardness meter (manufactured by Akashi Seisakusho, AVK-G2). Let the average value of the hardness of the measured three cut pieces be Vickers hardness.

  In the present invention, in measuring the Vickers hardness of the sputtering target, the t / 2 cross section in the thickness direction was measured in consideration of the uniformity of the structure.

  In the present invention, the reason why the occurrence of splash or the like can be reduced by appropriately controlling the Vickers hardness of the Cu—Mn alloy sputtering target is unknown in detail, but is presumed as follows. To stabilize the discharge by reducing the occurrence of splash and the like, it is effective to increase the annealing temperature and recrystallize. However, if the Vickers hardness becomes too high, the structure (crystal grains, etc.) is unsatisfactory. It becomes uniform and the discharge is considered unstable. On the other hand, if the Vickers hardness is too low, precipitation of Mn proceeds and segregates, and it is assumed that there is a possibility that the discharge becomes non-uniform.

  The Cu alloy sputtering target of the present invention has been described above.

  Next, a method for producing the Cu alloy sputtering target will be described.

  In the present invention, the Cu alloy sputtering target is manufactured by adopting a melting casting method for the purpose of reducing the manufacturing cost, the manufacturing process, and improving the yield. The melt casting method is a method for producing an ingot from a Cu alloy molten metal, and is widely used for producing a sputtering target.

  According to the above melting casting method, the sputtering target is usually manufactured by melting casting → (hot forging if necessary) → hot rolling → annealing (→ cold rolling → annealing if necessary). In the present invention, in order to produce a Cu—Mn alloy sputtering target in which the Vickers hardness is appropriately controlled, hot rolling conditions (particularly the total rolling reduction during hot rolling) and annealing conditions (annealing temperature, annealing time, etc.) ) Is important to control properly.

  Hereafter, the manufacturing method of this invention is demonstrated in detail for every process.

(Melting casting)
The melt casting process is not particularly limited, and a process usually used for manufacturing a sputtering target can be appropriately employed so that a Cu—Mn alloy ingot having a desired composition can be obtained. For example, typical casting methods include DC (semi-continuous) casting, thin plate continuous casting (double roll type, belt caster type, propel type, block caster type, etc.).

(Hot forging if necessary)
After the Cu—Mn alloy ingot is ingoted as described above, hot rolling is performed (details will be described later), but hot forging may be performed to adjust the shape as necessary. The hot forging in this case also serves as a soaking process. In order to control the Vickers hardness, it is preferable to control the hot forging temperature to about 800 to 900 ° C. and the hot forging heating time to about 3 to 18 hours.

(Hot rolling)
Hot rolling is performed after performing the above hot forging as necessary. For Vickers hardness control, the total rolling reduction during hot rolling is controlled to 50% or more. Preferably it is 55% or more. From the viewpoint of Vickers hardness control, the higher the total rolling reduction, the better. However, if it becomes too high, there is a problem such as cracking, so the upper limit is preferably made 75% or less. More preferably, it is 70% or less.

  In the present invention, it is sufficient that the total rolling reduction during hot rolling is controlled within the above range. For example, the maximum rolling reduction per pass is not particularly limited, but is preferably about 5 to 10%.

  In the present invention, the hot rolling start temperature and the hot rolling end temperature are not particularly limited. However, considering the ease of control of Vickers hardness, it is preferable to control the hot rolling start temperature to about 600 to 800 ° C. and the hot rolling end temperature to about 400 to 500 ° C.

(Annealing)
After hot rolling as described above, annealing is performed. In order to control the Vickers hardness, it is necessary to anneal for 2 hours or more in a temperature range of 450 to 600 ° C.

  As demonstrated in the examples described later, when the annealing temperature is less than 450 ° C., the desired Vickers hardness cannot be obtained even if the annealing time is controlled to 2 hours or more. On the other hand, when the annealing temperature exceeds 600 ° C., there are problems such as coarsening of crystal grains. A preferable annealing temperature is 550 ° C. or less.

  Similarly, if the annealing time is less than 2 hours, the desired Vickers hardness cannot be obtained. In order to control the Vickers hardness, when annealing is performed in the above annealing temperature range, it is preferable that the annealing time is long. However, if the annealing time is too long, there is a problem such as coarsening of crystal grains. A more preferable annealing time is 4 hours or less.

(If necessary, cold rolling → annealing)
Although the Vickers hardness of the Cu—Mn alloy sputtering target can be controlled within a predetermined range by the above method, after that, further cold rolling → annealing (second rolling, annealing for strain relief) is performed. Also good. For Vickers hardness control, the cold rolling conditions are not particularly limited, but it is preferable to control the annealing conditions. For example, it is recommended to control the annealing temperature to about 150 to 250 ° C. and the annealing time to about 1 to 5 hours. In addition, what is necessary is just to let the cold rolling rate at the time of cold rolling be a normal range (for example, 20 to 40%).

  Thereafter, when machining into a predetermined shape, a sputtering target is obtained. You may join the obtained sputtering target to a desired backing plate as needed.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and can be implemented with modifications within a range that can meet the gist of the preceding and following descriptions. They are all included in the technical scope of the present invention.

Example 1
First, Cu—Mn alloy ingots (thickness: 100 mm) containing various amounts of Mn shown in Table 1 were formed by DC casting.

  Specifically, 4N purity Cu and 3N purity electrolytic Mn are dissolved at 1250 ° C., held at 1200 ° C. for 10 minutes, and then cooled to room temperature at an average cooling rate of 8 to 10 ° C./min. A supersaturated solid solution (ingot) was formed.

The ingot was hot forged and hot rolled under the conditions shown in Table 1 (hot-rolling finish temperature was 600 ° C.) and rolled into a thin plate having a thickness of 20 mm, and then annealed under the conditions shown in Table 1. In this example, subsequent cold rolling and annealing are not performed.
In this example, the hot rolling was performed at a total rolling reduction of 50% and an annealing time of 2 hours. However, the same applies if the total rolling reduction of 50% to 75% or less and the annealing time is within 2 hours to 5 hours. It has been confirmed that the results are obtained.

  Next, machining (rounding and turning) was performed to manufacture a disk-shaped Cu—Mn alloy sputtering target (size: diameter 101.6 mm × thickness 5.0 mm).

  The Vickers hardness (average value of three measurement points) of the t / 2 cross section in the thickness direction of each sputtering target thus manufactured was measured by the method described above. In the column of Vickers hardness in Table 1, in addition to the average value, the measured values at each of three locations are listed in the columns (1), (2), and (3).

  Next, what each said sputtering target processed into the shape of 4 inches (phi) x 5 mmt was prepared, and the presence or absence of the splash which generate | occur | produces when sputtering was performed on the following conditions was observed.

  First, DC magnetron sputtering was performed on a Si wafer substrate (size: diameter 101.6 mm × thickness 0.50 mm) using a magnetron sputtering apparatus of “Sputtering System HSR-542S” manufactured by Shimadzu Corporation. The sputtering conditions are as follows.

DC: 260W
Pressure: 2mTorr
Ar gas pressure: 2.25 × 10 ⁻³ Torr
Ar gas flow rate: 30 sccm,
Distance between electrodes: 51.6mm
Substrate temperature: room temperature Sputtering time: 81 seconds

  In this example, the presence or absence of splash generated during discharge was evaluated by observing the surface of the thin film with an optical microscope (magnification: 1000 times). Here, those having protrusions of 1 μmφ or more are regarded as splash, and in the observation field of view, even one splash was evaluated as having a splash, and no splash was seen at all. evaluated.

  These test results are also shown in Table 1.

  From Table 1, it can be considered as follows.

  First, no. 1-4 are examples in which the amount of Mn in the Cu—Mn alloy is 2 atomic%. Of these, No. No. 4 is an example produced by a method that satisfies the requirements of the present invention, and since the Vickers hardness was appropriately controlled, no occurrence of splash was observed. In contrast, no. In Nos. 1 to 3, since the annealing temperature was low, the Vickers hardness exceeded the range defined in the present invention, and splash occurred.

  The results similar to the above were obtained when the No. 5-8 (Mn amount = 4 atomic%), No. 9-12 (Mn amount = 8 atomic%), No. It was also observed at 13 to 16 (Mn amount = 10 atomic%).

Furthermore, in order to confirm that according to the present invention, a sputtering target free of Mn segregation that becomes the starting point of splash is obtained, the No. in Table 1 above is obtained. About the sputtering target of 16 (invention example), Mn distribution was mapped using EPMA on the surface (t / 2) parallel to the rolling direction, which is the same surface as the surface on which the Vickers hardness was measured. The measurement conditions of EPMA are as follows.
Analyzer: “Electron Beam Microanalyzer JXA8900RL” manufactured by JEOL
Analysis conditions Acceleration voltage: 15.0 kV
Irradiation current: 5.012 × 10 ⁻⁸ A
Beam diameter: Minimum (0μm)
Measurement time: 100.00ms
Number of measurement points: 400 × 400
Measurement interval: 1 μm
Measurement area: 400 μm × 400 μm
Measurement position: Center in the thickness direction Number of fields of view: 1 field of view

  The result is shown in FIG. In FIG. 1, CP means a reflected electron image. As shown in FIG. 1, no Mn segregation is observed and it can be seen that the particles are uniformly dispersed. In other words, if there is Mn segregation, the electric field is locally concentrated due to the difference in conductivity and sputtering rate, the abnormal discharge occurs and splash occurs, and particles adhere to the film surface. The above results suggest that the generation of coarse particles can be reduced.

Claims (7)

A Cu alloy sputtering target containing at least Mn and having a Mn content of 2 atomic% or more and 20 atomic% or less,
A sputtering target for forming a Cu alloy thin film, wherein a Vickers hardness of a t / 2 cross section in the thickness direction of the sputtering target is 50 HV or more and 100 HV or less.   The sputtering target for forming a Cu alloy thin film according to claim 1, wherein the Mn content is 2 atomic% or more and 10 atomic% or less.   The sputtering target for Cu alloy thin film formation according to claim 1 or 2 whose Vickers hardness of t / 2 section of the thickness direction of said sputtering target is 60HV or more and 90HV or less. A method for producing a sputtering target for forming a Cu alloy thin film according to any one of claims 1 to 3,
With respect to the Cu alloy satisfying the composition according to any one of claims 1 to 3, the total rolling reduction during hot rolling is 50% or more, and the annealing after hot rolling is performed at a temperature of 450 ° C or higher and 600 ° C or lower. The manufacturing method of the sputtering target for Cu alloy thin film formation characterized by performing for 2 hours or more.   The manufacturing method of the sputtering target for Cu alloy thin film formation of Claim 4 performed by 50 to 75% of the total rolling reduction at the time of the said hot rolling.   The manufacturing method of the sputtering target for Cu alloy thin film formation of Claim 4 or 5 which performs the annealing after the said hot rolling at the temperature of 450 to 550 degreeC.   The manufacturing method of the sputtering target for Cu alloy thin film formation in any one of Claims 4-6 which performs annealing after the said hot rolling in 2 hours or more and 5 hours or less.