JP5139409B2 - Pure Al or Al alloy sputtering target - Google Patents

Description

  The present invention relates to an Al-based alloy sputtering target, and in particular, when a thin film is formed using a sputtering target, problems that occur in the initial stage of sputtering (for example, an increase in the number of splashes, The present invention relates to an Al-based alloy sputtering target that can eliminate an increase in electrical resistance and the like and can shorten the pre-sputtering time.

  Al has a low electrical resistivity and is easy to process, so it has a liquid crystal display (LCD), a plasma display panel (PDP), and an electroluminescence display (ELD). Widely used in fields such as flat panel displays (FPD) such as field emission display (FED) and micro electro mechanical systems (MEMS) displays, touch panels, and electronic paper. It is used for materials such as electrode films and reflective electrode films.

  For example, an active matrix liquid crystal display includes a TFT substrate having a thin film transistor (TFT) that is a switching element, a pixel electrode composed of a conductive oxide film, and wiring including scanning lines and signal lines. Yes. In general, pure Al or Al-Nd alloy Al-based alloy film is used as the wiring material constituting the scanning lines and signal lines.

  By the way, generally the sputtering method using a sputtering target is employ | adopted for formation of Al group alloy film. The sputtering method is a method in which a plasma discharge is formed between a substrate and a sputtering target (target material) made of the same material as the thin film material, and a gas ionized by the plasma discharge is collided with the target material. This is a method for producing a thin film by knocking out atoms of a material and depositing them on a substrate. Unlike the vacuum deposition method, the sputtering method has an advantage that a thin film having the same composition as the target material can be formed. In particular, an Al alloy film formed by sputtering can dissolve an alloy element such as Nd that does not form a solid solution in an equilibrium state, and exhibits excellent performance as a thin film. Development of a sputtering target material that is a production method and is a raw material thereof is underway.

  The Al-based alloy sputtering target used in the sputtering method is manufactured by, for example, a spray forming method or a melt casting method. In the initial stage of sputtering, an operation called pre-sputtering is generally performed. This pre-sputtering is performed for the purpose of removing dirt or the like because sputtering is not stable due to dirt on the surface of the sputtering target in the initial stage of use of the sputtering target and the characteristics of the resulting thin film are not stable. It is. For example, when a thin film is formed using an Al-based alloy sputtering target, many splashes (fine molten particles) are generated in the initial stage of sputtering, and the electrical resistance of the formed wiring thin film is increased. There are defects, and on-site pre-sputtering is performed until these become stable. However, an increase in pre-sputtering time results in a decrease in productivity.

  As a method for reducing splash, for example, Patent Document 1 discloses an Al-based alloy sputtering target in which the hardness is controlled to 25 or less in terms of Vickers hardness (Hv).

  Further, although not intended for an Al-based alloy sputtering target, as a method for reducing the generation of massive foreign matter based on the splash phenomenon, Patent Document 2 discloses a Mo— with a maximum height Ry of the sputtering surface of 10 μm or less. A W alloy sputtering target is disclosed. Further, since abnormal discharge that causes the splash phenomenon is likely to occur between adjacent convex portions, the width of the concave portion having a depth of 5 μm or more existing on the sputtering surface is preferably set to 70 μm as the interval between the local peaks of the roughness curve. The above control is also disclosed.

  Further, although not intended for an Al-based alloy sputtering target, Patent Document 3 discloses that a surface to be sputtered has a predetermined curvature in order to reduce particles (fine dust) generated during sputtering. A Ti sputtering target is disclosed which has a concave surface and is mirror-finished on the sputtering surface so that its arithmetic average roughness Ra is controlled to 0.01 μm or less.

Japanese Patent No. 3410278 JP 2001-316808 A JP-A-10-158828

  The object of the present invention is to solve the problems that occur at the initial stage of sputtering (increase in the number of splashes and increase in the electrical resistance of the formed wiring thin film) and reduce the pre-sputtering time. It is to provide a base alloy sputtering target.

  The Al-based alloy sputtering target of the present invention that has been able to solve the above problems has an arithmetic average roughness Ra of 1.50 μm or less when the surface roughness of the sputtering surface is measured by the method defined in JIS B0601 (2001). And the maximum height Rz is 10 μm or less and the height of the peak from the center line to the summit or valley bottom in the roughness curve exceeds (0.25 × Rz) is P or Q, respectively, and the reference length When counting P and Q sequentially over a length of 100 mm, the gist is that the average value of the distance L between P, Q appearing immediately after it, and P appearing immediately thereafter is 0.4 mm or more. It is what you have.

  Since the Al-based alloy sputtering target of the present invention is controlled so that not only the surface roughness of the sputtering surface but also the average value (period) of the peak interval represented by the L value is increased, the initial stage of use of the sputtering target The electric resistance of the thin film formed with the sputtering target and the sputtering target can be quickly reduced to a predetermined level. Therefore, when the sputtering target of the present invention is used, the pre-sputtering time that is performed until the splash and the thin film electrical resistance are stabilized can be shortened.

FIG. 1 is a schematic diagram for explaining an L value (peak interval) defined in the present invention. 2A shows the sample No. 1 in Example 1. FIG. 7 (comparative example), the surface roughness curve of the sputtering surface is shown in FIG. The surface roughness curves of 2 (invention example) sputtered surfaces are shown respectively.

  The present inventors can solve problems such as splash (initial splash) generated in the initial stage of use of the sputtering target and an increase in electrical resistance of a thin film formed on the sputtering target, and shorten the pre-sputtering time. In order to provide a possible Al-based alloy sputtering target, investigations have been repeated. As a result, the Al-based alloy sputtering target controlled not only to appropriately control the surface roughness of the sputtering surface (Ra and Rz in the present invention) but also to increase the average value of the peak interval represented by the L value. As a result, it was found that the intended purpose was achieved, and the present invention was completed.

  That is, the Al-based alloy sputtering target of the present invention has an arithmetic average roughness Ra of 1.50 μm or less and a maximum height Rz when the surface roughness of the sputtering surface is measured by the method specified in JIS B0601 (2001). A peak height that is 10 μm or less and the height from the center line to the peak or valley bottom in the roughness curve exceeds (0.5 × Rz) is P or Q, respectively, over a reference length of 100 mm, When P and Q are counted sequentially, there is a feature that the average value of the interval L between P, Q appearing immediately after it, and P appearing immediately thereafter is 0.4 mm or more.

  First, in the Al-based alloy sputtering target of the present invention, the arithmetic average roughness Ra is controlled to 1.50 μm or less and the maximum height Rz is controlled to 10 μm or less. By controlling Ra to 1.50 μm or less and Rz to 10 μm or less, the number of initial splashes and the electrical resistance of the deposited thin film are both reduced to a certain level (stabilized) until the pre-sputtering time is reduced. (See the examples below). Preferred upper limits for Ra and Rz are Ra: 1.0 μm and Rz: 8.0 μm, and more preferred upper limits for Ra and Rz are Ra: 0.8 μm and Rz: 6.0 μm. In addition, the lower limit of Ra and Rz is not particularly limited from the above viewpoint, and it is better as it is smaller. However, in consideration of accuracy in machining and polishing, Ra: 0.1 μm, Rz: 1.0 μm. Preferably there is.

  Further, the Al-based alloy sputtering target of the present invention is characterized in that the average value of the peak interval represented by the L value is controlled to 0.4 mm or more. As shown in the examples described later, the desired characteristics cannot be obtained by simply controlling Ra and Rz. Only when all these three requirements are combined, both the initial splash and the reduction of the thin film electrical resistance can be quickly achieved. And the pre-sputtering time can be shortened.

  The L value that characterizes the present invention will be described with reference to FIG. FIG. 1 is a diagram showing an outline of a roughness curve when the sputtering surface of a sputtering target is measured by a method defined in JIS B0601 (2001). The L value is a value obtained by arbitrarily taking a roughness curve with a reference length of 100 mm and calculating as follows. The apex in the mountain direction across the center line of the roughness curve is called the peak (mountain peak), and the bottom point in the valley direction is called the valley bottom (valley peak). In the present invention, the center line + (0.25 × Rz) The summit exceeding the position of P is P, and the trough bottom exceeding the center line − (0.25 × Rz) is Q.

  First, refer to FIG. In the roughness curve of the above figure, the reference length is 100 mm, and H indicates the position of the center line ± (0.25 × Rz). When the peak (mountain peak) above (center line + H) is P, and the valley bottom (valley peak) below (center line -H) is Q, in FIG. Q1, P2, Q2, P3, and so on. In the present invention, the peak interval L value is a distance between P1 → Q1 → P2, and more specifically, an intersection point (p1, when a perpendicular is drawn from each point of P1, Q1, and P2 toward the center line. When q1, p2) is taken, it is the distance between p1-q1-p2. The peak interval L value is obtained as described above over a reference length of 100 mm, and the average value is calculated. The same operation is performed for any three locations on the roughness curve, the average value is calculated, and the average value of the L values is obtained.

  FIG. 1A is an example in which P and Q exceeding the position of (center line ± H) are alternately and sequentially formed. The roughness curve is, for example, FIG. As shown in FIG. 4, there may be a peak or valley between P and Q that does not exceed the position of H. The calculation method of the L value in this case is as follows. Hereinafter, the peak that does not exceed the position of H is denoted by P ′, and the valley that does not exceed the position of H is denoted by Q ′.

  Referring to FIG. 1B, in order from the leftmost side, the peak P1 that exceeds the position of H, the peak P2 that exceeds the position of H, the peak P′1 that does not exceed the position of H, and the position of H are not exceeded. A valley bottom Q′1, a peak P3 exceeding the H position, a valley bottom Q1 exceeding the H position, and a peak P4 exceeding the H position are continuously formed. In this case, the peak interval L value is a distance between P1 → Q1 → P4.

  In FIG. 1B, P2 appears after P1, but P2 is ignored when the summit exceeding H appears twice in succession. In the present invention, the order of the summit → the bottom of the valley → the summit is emphasized. In the present invention, even if a peak (P ′) not exceeding H or a valley (Q ′) not exceeding H appears, it is ignored. According to the basic experiments of the present inventors, it was found that the peak interval defined as described above has a close correlation with the rapid reduction of the initial splash and the rapid reduction of the thin film electrical resistance. Because.

  The average value of the L values calculated in this way is preferably as large as possible, preferably 0.5 mm or more, and more preferably 0.6 mm or more. However, in order to increase the average value of the L value, the processing time spent for machining and surface polishing becomes too long, so the preferable upper limit is 2.0 mm, and more preferably 1.0 mm.

  In the present invention, the reason why the reduction of the splash and the reduction of the electric resistance of the formed thin film can be realized quickly by controlling the average value of the L values as described above is not clear in detail, but the peak interval is wide. As the cycle becomes longer, the surface area of the sputtering target is reduced, so that the Al oxide layer present on the surface is reduced, and as a result, the amount of oxygen in the formed thin film is also reduced. Inferred. The amount of oxygen in the thin film is thought to have a large effect on the number and time of pre-sputtering, but according to the present invention, the reduction in the amount of oxygen quickly reduced the electrical resistance of the thin film after splash and film formation. It seems to be.

  The average value of the surface roughness and the peak interval that characterize the present invention has been described above.

  Further, the Al-based alloy sputtering target of the present invention preferably has a Vickers hardness (Hv) of 26 or more. For example, in Patent Document 3 described above, the occurrence of splash is reduced by setting Hv to 25 or less, whereas in the present invention, Hv is controlled to 26 or more (generally, approximately 26 to 50 Hv). Thus, the above-described surface roughness and L value average value can be easily controlled, and the occurrence of splash and the like can be reduced. The reason for this is unknown in detail, but Patent Document 2 targets Mo alloys with poor workability, whereas in the present invention, the amount of pure Al or alloy element added is described in detail below. Al alloy with a very low workability of about 2.0 atomic% is practically targeted, and it is speculated that such a difference in the composition of the matrix alloy appears as a difference in hardness. Is done.

  The Al-based alloy used in the present invention is an Al-Nd alloy containing an element such as Nd, which is widely used as an Al-based alloy sputtering target for wiring thin films, in addition to pure Al; constitutes a pixel electrode without using a barrier metal layer An Al—Ni alloy for providing a direct contact technology capable of being in direct contact with the conductive oxide film, and an Al—Ni—rare earth element alloy further containing a rare earth element such as Nd and Y are included. The amount (total amount) of alloy elements such as Nd, Ni, and Y is preferably about 2.0 atomic% or less. Pure Al and Al alloy contain, as an inevitable impurity, for example, elements inevitably mixed in the manufacturing process, for example, Fe, Si, Cu, C, O, N, and the like.

  Next, a method for producing the sputtering target of the present invention will be described.

  The average value of the surface roughness and L value specified in the present invention is obtained by machining into a predetermined shape by a conventional method and then machining conditions for finishing the sputtered surface, and if necessary, along with the machining. This can be realized by appropriately controlling the conditions of the surface polishing performed. The machining is typically performed using a milling machine, and the rotational speed is about 2500 to 4500 rpm (more preferably 3000 to 4000 rpm), and the cutting amount is about 0.02 to 0.2 mm (more preferably). 0.05 to 0.15 mm), and the feed rate is preferably controlled to about 400 to 1800 mm / min (more preferably about 600 to 1000 mm / min).

  The surface polishing is performed as necessary after the above-described machining, but it is preferable to perform polishing using a grindstone having an appropriate particle size so that desired surface properties can be easily obtained. Specifically, it is preferable to grind until a desired property is obtained using a nonwoven fabric coated with abrasive grains having a grain size number (abrasive grains) of approximately 200 to 1200. A more preferable lower limit of the abrasive grains is approximately 400. In the present invention, it is most preferable to polish using approximately 800 abrasive grains. The grain size (abrasive grain) of the grindstone becomes finer as the abrasive grain number increases.

  The present invention is characterized in that the surface properties are controlled by appropriately controlling machining or surface polishing as described above, and other manufacturing processes are not particularly limited. The process normally used for manufacture is employable. Specifically, a known spray forming method or melt casting method can be employed. The spray forming method used in the present invention is not particularly limited. For example, JP 2009-35766 A, JP 2008-240141 A, JP 2008-127623 A, JP 2007-247006 A, JP 2005-2005 A. Reference can be made to the description of -82855. In order to reduce manufacturing costs, it is preferable to employ a melt casting method.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and may be implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all possible and are within the scope of the present invention.

Example 1
An Al-based alloy (remainder: Al and inevitable impurities) having the composition shown in Table 1 was prepared, and a sputtering target was prepared by the following method.

  Among these, Al—Nd alloy is sprayed with a high-pressure inert gas sprayed on a molten Al alloy flow in a chamber in an inert gas atmosphere, and rapidly cooled into a semi-molten state, a semi-solid state, and a solid state. An ingot was produced using a spray forming method to obtain a shaped material (preform) having a predetermined shape, and heat treatment and hot working (rolling) were performed. In addition, pure Al was cast by ingot casting of 100mm thickness by DC casting method, then soaked at 400 ° C for 4 hours, then cold worked at room temperature with 75% reduction, and then heat treated at 200 ° C. Then, it was cold-rolled at a reduction amount of 40% at room temperature.

  Next, the Al—Nd alloy and pure Al rolled plate obtained in this way were cut, and the surface of the rolled plate was machined or machined and polished under the processing conditions shown in Table 1. Each sample of the sputtering target was obtained.

  Using the samples thus obtained, arithmetic average roughness (Ra) and maximum height (Rz) were measured based on surface roughness. The arithmetic average roughness (Ra) and the maximum height (Rz) were measured using a Mitutoyo surface roughness measuring instrument SJ-301. The evaluation length was 100 mm. Furthermore, the average value of the L values was calculated based on the method described above.

  Moreover, a thin film was formed using each sample of the sputtering target, and the pre-sputtering time until the thin film satisfied a predetermined condition was evaluated.

  Specifically, film formation by pre-sputtering and sputtering was performed by a DC magnetron sputtering method. During pre-sputtering, a shutter was inserted between the target and the substrate so that no film was formed on the substrate, and during sputtering, the shutter was opened to form a film on the substrate. The details of the pre-sputtering conditions and the sputtering conditions are as follows, and are the same except that the sputtering power is different.

Sputtering equipment (common)
: "Sputtering system HSR-542S" manufactured by Shimadzu Corporation
Pre-sputtering conditions Back pressure: 0.43 × 10 ⁻³ Pa or less Ar gas pressure: 0.67 Pa
Sputtering power: 800W
Sputtering conditions Back pressure: 0.43 × 10 ⁻³ Pa or less Ar gas pressure: 0.67 Pa
Sputtering power: 300W
Distance between electrodes: 100mm
Substrate temperature: Room temperature Substrate: Glass substrate (size: 6 inches in diameter)

  Specifically, using each sample of the sputtering target, pre-sputtering is performed for 5 minutes under the above conditions, and then sputtering is performed under the above conditions to form a thin film (film thickness: 300 nm) as one set. (1) Pre-sputtering time until the number of splashes becomes below the reference value, and (2) Pre-sputtering time until the electric resistance (wiring resistance) of the formed thin film becomes + 15% or less with respect to the steady value. Was measured as follows.

(1) Evaluation method of pre-sputtering time until the number of splashes becomes a reference value or less The number of generated splashes (initial splash) was measured under the following conditions for the thin film formed under the above sputtering conditions.

Using a particle counter (manufactured by Topcon Co., Ltd .: wafer surface inspection device WM-3), the position coordinates, size (average particle diameter), and number of particles observed on the surface of the thin film were measured. Here, particles having a size of 3 μm or more were regarded as particles. Thereafter, the surface of the thin film was observed with an optical microscope (magnification: 1000 times), a hemispherical shape was regarded as a splash, and the number of splashes per unit area was measured. In this example, pre-sputtering and sputtering were repeated until the number of initial splashes thus obtained was 8 / cm ² or less. In this example, a sample having a pre-sputter time of 60 minutes or less until the number of initial splashes was 8 / cm ² or less was accepted.

(2) Measuring method of pre-sputtering time until electric resistance of thin film becomes + 15% or less with respect to steady value 320 Assuming thermal history received in actual process for thin film formed under the above sputtering conditions After performing a heat treatment for 30 minutes at a temperature, it was processed into a stripe pattern shape with a line width of 100 μm, and processed into a wiring resistance measurement pattern shape with a line width of 100 μm and a line length of 10 mm by wet etching. For the wet etching, a mixed solution of H ₃ PO ₄ : HNO ₃ : H ₂ O = 75: 5: 20 was used. The specific resistance value of the thin film processed into this pattern was measured at room temperature by a four-probe method.

  Pre-sputtering is performed until the specific resistance value thus obtained is + 15% or less with respect to the steady-state value (4.6 μΩ · cm for Al-2.0 atomic% Nd alloy, 3.2 μΩ · cm for pure Al). And sputtering were repeated. In this example, a sample having a pre-sputter time of 60 minutes or less until the specific resistance value reaches a steady value + 15% or less was accepted.

  These measurement results are shown in Table 1.

  For reference, the sample No. 1 is shown in FIG. 7 (comparative example), the surface roughness curve of the sputtering surface is shown in FIG. The surface roughness curves of the sputtering surface of No. 2 (Example of the present invention) are shown respectively.

  First, Sample No. processed under the recommended conditions of the present invention. 1 to 6, since the surface properties (Ra, Rz, average value of the peak interval L) are appropriately controlled, the number of splashes can be increased regardless of whether a pure Al sputtering target or an Al—Nd alloy sputtering target is used. Both the pre-sputtering time until reduction and the pre-sputtering time until the electric resistance was stabilized could be shortened.

  In contrast, No. 1 in Table 1. No. 7 is an example in which only the milling was performed using the Al—Nd alloy sputtering target, and the average values of Ra, Rz, and peak interval L are all within the scope of the present invention because the rotational speed during milling is too high. The pre-sputtering time until the number of splashes is reduced and the pre-sputtering time until the electric resistance is stabilized are increased.

  No. in Table 1 8 and no. No. 9 is an example in which milling (No. 8), both milling and surface polishing (No. 9) were performed using a pure Al sputtering target. Of these, No. In No. 8, since the rotational speed at the time of milling is too high, Ra and Rz are good, but the average value of the peak interval L is shortened, and the pre-sputtering time until the electric resistance of the thin film is stabilized is increased. . No. No. 9 is suitable for milling conditions, but because the abrasive grains during surface polishing are too coarse, the average value of the peak interval L is good, but Ra and Rz become large and the pre-processing until the number of splashes is reduced. Sputtering time became longer.

Claims (1)

When the surface roughness of the sputter surface is measured by the method specified in JIS B0601 (2001), the arithmetic average roughness Ra is 1.50 μm or less, and the maximum height Rz is 10 μm or less, and
The height of the peak from the center line to the peak or valley bottom in the roughness curve exceeding (0.25 × Rz) is P or Q, respectively, and P and Q are sequentially counted over a reference length of 100 mm. A pure Al or Al alloy sputtering target, characterized in that an average value of an interval L between P, Q appearing immediately after it, and P appearing immediately thereafter is 0.4 mm or more.

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