Preparation method of high-purity aluminum target material

Abstract

The invention discloses a preparation method of a high-purity aluminum target material. The preparation method comprises the following steps: carrying out forging, equal channel angular extrusion, cold rolling and annealing treatment on a high-purity aluminum cast ingot; the processing temperature of the equal channel angular pressing is 150-200 DEG C. According to the preparation method, the preparation technology is optimized, the finally prepared high-purity aluminum target material has the small and uniform average grain size, in the equal channel angular pressing process, the surface of the high-purity aluminum target material keeps the relatively intact appearance, and the phenomena of surface cracking, tail end breakage and falling off and the like do not occur.

Description

Technical Field

[0001] The invention relates to the field of plastic deformation processing of metal materials, and in particular to a method for preparing a high-purity aluminum target material. Background Art

[0002] Using high-purity metal sputtering targets for physical vapor deposition (PVD) is an important process for producing semiconductor chips and thin-film transistor liquid crystal displays (TFT-LCD). High-purity aluminum and ultra-high-purity aluminum are among the most widely used materials in metal sputtering targets for semiconductors. The purity of ultra-high-purity aluminum used in the sputtering targets for preparing semiconductor integrated circuit silicon wafers reaches 99.999% (5N) or more, and the metal target blanks are required to have fine grains and uniform structure. According to the principle of sputtering process, the finer the target grains, the lower the surface roughness of the target, and the better the quality of the film deposited on the surface of the silicon wafer by physical vapor deposition than the target with large grains. The more uniform the target structure, the better the film deposition rate and uniformity, which can reduce film breakdown. If there are impurities and heterogeneous structure particles inside the high-purity aluminum target, or casting defects (such as pores, shrinkage, etc.), it will cause film contamination or breakdown. In order to ensure the quality of semiconductor chips, it is hoped that the high-purity aluminum sputtering targets used have high purity (above 5N), fine and uniform grains, and low oxygen content.

[0003] Since the Young's modulus of aluminum is relatively low, it is easy for the grains to be greatly deformed but not broken, or for the fine grains to grow quickly. The higher the purity of aluminum, the higher the grain boundary mobility of its nucleation, which leads to stronger dynamic recovery and recrystallization behavior, making it very difficult to refine its grains. Therefore, after the high-purity aluminum is refined to a certain extent through traditional forging and rolling processes, it is very difficult to further refine the grains. According to patent CN101638760A, the aluminum plate is first subjected to multi-pass equal-angle extrusion, and then deep-cold-treated with liquid nitrogen before rolling to prevent the temperature from rising due to rolling deformation, which causes the grains to grow during heat recrystallization. This method can produce an aluminum target blank with an average grain size of 100-300 microns and equiaxed grains. However, it is difficult to use liquid nitrogen to soak the aluminum plate to minus 80°C and then roll it, and the temperature is not easy to control, so the production feasibility is not high. Honeywell's patent CN1432070A in China introduces the method of doping 10-100ppm of trace elements such as Si, Sc, Mg, In, Sb into 4N aluminum, and then performing equal-diameter angular extrusion, combined with forging and rolling, to obtain an aluminum target blank with an average grain size of less than 50 microns. However, the impurity content of 4N aluminum is one order of magnitude higher than that of 5N aluminum used for semiconductors. The higher-purity 5N aluminum material is more difficult to recrystallize and nucleate, not to mention that high-purity aluminum used for semiconductors is not suitable for doping with other materials above 10ppm, and the target material obtained in this way is prone to cracking, so this method is not suitable. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defect that the surface of the high-purity aluminum target is easy to crack during equal-channel angular extrusion in the process of preparing the high-purity aluminum target in the prior art and the subsequent target production cannot be carried out, and a preparation method of the high-purity aluminum target is provided. The preparation method of the present invention optimizes the preparation process, and the high-purity aluminum target finally prepared has a small and uniform average grain size, and during the equal-channel angular extrusion process, the surface of the high-purity aluminum target maintains a relatively intact morphology, and there is no surface cracking, end breakage and shedding, etc.

[0005] The present invention adopts the following technical solutions to solve the above technical problems.

[0006] The present invention provides a method for preparing a high-purity aluminum target, which comprises the following steps:

[0007] The high-purity aluminum ingot is forged, equal-angle extruded, cold-rolled and annealed;

[0008] The processing temperature of the equal channel angular extrusion is 150-200°C.

[0009] In the present invention, the high-purity aluminum ingot refers to an aluminum ingot with a purity of 5N or above, such as a 5N aluminum ingot, a 5N5 aluminum ingot or a 5N7 aluminum ingot. Those skilled in the art will understand that 5N means that the purity of the high-purity aluminum ingot is 99.999%. 5N5 means that the purity of the high-purity aluminum ingot is 99.9995%. 5N7 means that the purity of the high-purity aluminum ingot is 99.9997%.

[0010] In the present invention, the purpose of the forging is to eliminate casting defects and preliminarily refine the grains of the high-purity aluminum ingot.

[0011] In the present invention, the initial forging temperature may be 250-300°C, preferably 280-300°C, such as 290°C.

[0012] In the present invention, the total deformation of the forging can be 70%-85%, preferably 80%-85%, for example 83%. The total deformation of the forging refers to the ratio of the size of the high-purity aluminum ingot after forging to the original size.

[0013] In the present invention, a cutting step is preferably included after the forging and before the equal-channel angular extrusion. The purpose of the cutting is to match the high-purity aluminum ingot with the mold cavity of the equal-channel angular extrusion. The shape of the high-purity aluminum ingot after the cutting can be changed according to the shape of the mold of the equal-channel angular extrusion, and can generally be cylindrical or rectangular. The height-to-diameter ratio of the high-purity aluminum ingot after the cutting can be (2.5-5): 1, for example 3: 1. The fitting clearance between the high-purity aluminum ingot after the cutting and the mold cavity of the equal-channel angular extrusion can be 0.05-0.1mm on one side, preferably 0.1mm.

[0014] In the present invention, the equal-channel angular extrusion operation is preferably carried out in an equal-channel angular extrusion die. The equal-channel angular extrusion die is preferably a conventional heatable equal-channel angular extrusion die in the art.

[0015] The die inner angle Φ of the equal-channel angular extrusion die may be 100-120°, preferably 120°. The die outer angle ѱ of the equal-channel angular extrusion die may be 15-30°, preferably 30°.

[0016] Wherein, the equal-diameter angular extrusion die preferably includes a concave die and a convex die. The concave die and the convex die are preferably combined with each other in a concave-convex manner to limit the relative movement of the concave die and the convex die along the extrusion direction of the billet. The concave die is preferably provided with a channel for accommodating the billet. The channel for accommodating the billet is preferably L-shaped and is provided with a feed port and a discharge port. The diameter of the discharge port is preferably designed to be 0.1-0.2 mm smaller than the diameter of the feed port. The inner angle Φ of the channel for accommodating the billet may be 100-120°, preferably 120°. The outer angle ѱ of the channel for accommodating the billet may be 15-30°, preferably 30°.

[0017] The outer die of the equal channel angular extrusion die is preferably provided with a heating rod and a temperature measuring thermocouple. The heating rod may be an aluminum rod with a resistance furnace. The heating rod and the temperature measuring thermocouple are preferably respectively arranged on both sides of the concave die.

[0018] In a preferred embodiment, the equal-diameter angular extrusion die is provided with a die, a punch, a channel for accommodating the blank, a heating rod and a temperature measuring thermocouple. The die and the punch are combined with each other in a concave-convex manner to limit the relative movement of the die and the punch along the extrusion direction of the blank; the die is provided with a channel for accommodating the blank, the channel for accommodating the blank is L-shaped, and is provided with a feed port and a discharge port. The diameter of the discharge port is 0.1 mm smaller than the diameter of the feed port, and its internal angle Φ is 120°, and the external angle ѱ is 30°. The heating rod and the temperature measuring thermocouple are respectively arranged on both sides of the die.

[0019] In the present invention, the processing temperature of the equal channel angular extrusion is preferably 180-200° C., for example, 190° C. If the conventional cold equal channel angular extrusion (for example, at room temperature) is used, as the number of extrusion passes increases, the internal stress of the blank increases, the material hardens, and surface cracks, end damage and shedding occur.

[0020] In the present invention, the number of passes of the equal channel angular extrusion can be a multiple of 4, preferably 4-32 passes, such as 8, 12 or 16 passes.

[0021] In the present invention, the equal channel angular extrusion operation is preferably performed by: after each extrusion pass, High purity aluminum casting after forging ingotAfter rotating 90° around the central axis in the same direction, the next extrusion is carried out.

[0022] In the present invention, after the equal-channel angular extrusion and before the rolling, a step of cooling the billet is generally included. The cooling method can be conventional in the art, such as water cooling. The temperature after cooling can be room temperature, generally 10-35°C.

[0023] In the present invention, the cold rolling means rolling under the condition of normal ambient temperature. Although the temperature of the ingot will rise due to rolling during the processing, it is still called cold rolling. Normal temperature is generally 10-40°C.

[0024] In the present invention, the total deformation of the cold rolling may be 5%-20%, such as 10% or 15%. The total deformation of the cold rolling refers to the ratio of the size of the blank after the cold rolling to the original size.

[0025] In the present invention, the number of cold rolling passes may be 10-15, preferably 15.

[0026] In the present invention, a correction step is preferably performed after the cold rolling and before the annealing treatment. The purpose of the correction is to perform flattening correction and fine adjustment on the cold-rolled billet.

[0027] In the present invention, the temperature of the annealing treatment may be 100-200°C, for example, 150°C.

[0028] In the present invention, the annealing treatment time may be 1-3 hours, such as 1 hour or 2 hours.

[0029] In the present invention, in the method for preparing the high-purity aluminum target, preferably no element that can inhibit grain growth is added. The element that can inhibit grain growth is preferably one or more of Si, Sc, Mg, In and Sb.

[0030] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0031] The reagents and raw materials used in the present invention are commercially available.

[0032] The positive and progressive effects of the present invention are:

[0033] The present invention introduces an equal-channel angular extrusion process carried out at a specific temperature and cooperates with other forging and rolling processes to perform multiple plastic deformation processes on the high-purity aluminum ingot. The high-purity aluminum target material finally obtained has a small and uniform average grain size (for example, below 100 μm), and during the equal-channel angular extrusion process, the surface of the high-purity aluminum target material maintains a relatively intact morphology, and no surface cracking, end breakage, or the like occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic flow chart of the method for preparing a high-purity aluminum target in the embodiment.

[0035] Figure 2 This is a simplified design diagram of the die for equal-diameter angular extrusion used in the present invention: Φ-die inner angle, ѱ-die outer angle, punch-1, die-2, blank-3, heating rod-4, temperature measuring thermocouple-5; channel-6 for accommodating the blank; feed port-601, discharge port 602.

[0036] Figure 3 This is a metallographic photograph of the high-purity aluminum target prepared in Example 1.

[0037] Figure 4 This is a metallographic photograph of the high-purity aluminum target prepared in Example 2.

[0038] Figure 5 This is a metallographic photograph of the high-purity aluminum target prepared in Example 3.

[0039] Figure 6 This is a metallographic photograph of the high-purity aluminum target prepared in Example 4.

[0040] Figure 7 This is a metallographic photograph of the high-purity aluminum target prepared in Example 1.

[0041] Figure 8 This is a metallographic photograph of the high-purity aluminum target prepared in Example 2. DETAILED DESCRIPTION

[0042] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0043] Figure 1 Schematic diagram of the process for preparing a high purity aluminum target in the following embodiment.

[0044] Figure 2 It is a schematic diagram of the die design for equal channel angular extrusion used in the present invention.

[0045] Example 1

[0046] The high-purity aluminum ingot (purity of 5N) is first deformed by forging (the initial temperature of forging is 300℃; the total deformation of forging is 85%) to refine the grains. The forged billet is then cut into a cylindrical shape (the height-to-diameter ratio of the billet is 3:1), so that the clearance between the cut billet and the die cavity of the equal-diameter angular extrusion is 0.1mm. The cut billet is then heated to 200℃, and then put into the equal-diameter angular extrusion die at a temperature of 200℃ (the inner angle Φ of the equal-diameter angular extrusion die is 120°, and the outer angle ѱ is 30°) for 4 extrusions. After any extrusion in the equal-diameter angular extrusion process, the billet is rotated 90° in the same direction before the next extrusion. After the extruded billet is water-cooled to room temperature, it is cold-rolled for 15 times at room temperature (20-30℃) (the total deformation of cold rolling is 15%) and corrected into the required target billet size. Finally, the target blank was annealed at 150°C for 1 hour. The average grain size of the high-purity aluminum target after treatment was 102 μm. Figure 3 shown.

[0047] The equal-diameter angular extrusion die is provided with a punch 1, a die 2, a channel 6 for accommodating the blank, a heating rod 4 and a temperature measuring thermocouple 5;

[0048] The punch 1 is in a "T" shape, and the punch 1 and the die 2 are combined with each other in a concave-convex manner to limit the relative movement of the punch 1 and the die 2 along the extrusion direction of the billet;

[0049] The die 2 is provided with a channel 6 for accommodating the blank. The channel 6 for accommodating the blank is L-shaped and is provided with a feed port 601 and a discharge port 602. The diameter of the discharge port 602 is 0.1 mm smaller than that of the feed port 601. Its inner angle Φ is 120° and its outer angle ѱ is 30°.

[0050] The heating rods 4 are respectively arranged on both sides of the concave mold 2, and the temperature measuring thermocouple 5 is arranged on the surface of the concave mold 2. The heating rods 4 are used to heat the blank; the temperature measuring thermocouple 5 is used to detect the temperature of the blank;

[0051] During specific use, the blank 3 is placed into the channel 6 for accommodating the blank from the top of the feed port 601 , and then the punch 1 is extended from the top of the channel 6 for accommodating the blank, thereby achieving extrusion of the blank 3 .

[0052] Example 2

[0053] The only difference from Example 1 is that the equal-channel angular extrusion die is extruded for 8 passes, and the average grain size of the high-purity aluminum target after treatment is 50 μm. Figure 3 shown.

[0054] Example 3

[0055] The only difference from Example 1 is that the equal-channel angular extrusion die is extruded 16 times, and the average grain size of the high-purity aluminum target after treatment is 43 μm. Figure 4 shown.

[0056] Example 4

[0057] The only difference from Example 1 is that the equal-channel angular extrusion die is extruded 32 times, and the average grain size of the high-purity aluminum target after treatment is 35 μm. Figure 5 shown.

[0058] Comparative Example 1

[0059] The only difference from Example 3 is that the die is not heated during the equal channel angular extrusion and the ambient temperature during the extrusion is 30°C.

[0060] In this comparative example, the billet had multiple surface cracks during the extrusion process, and after rolling, the surface cracks of the billet became more serious, and it could no longer be used for target production. The average grain size of the high-purity aluminum target after treatment was 51 μm. Compared with Example 3, this comparative example did not obtain finer grains. Figure 7 shown.

[0061] Comparative Example 2

[0062] The only difference from Example 3 is that during equal-channel angular extrusion, the billet is heated to 250° C., kept warm for 0.5 h, and then cold rolled, and the total deformation of the cold rolling is 15%.

[0063] The average grain size of the treated high-purity aluminum target is 176μm. Figure 8 shown.

[0064] Effect Example

[0065] In the process of preparing high-purity aluminum target materials in Examples 1-4, no cracking occurred on the surface of the target materials after being subjected to 4-32 equal-diameter angular extrusion passes through an equal-diameter angular extrusion die at a die temperature of 200°C.

[0066] The high-purity aluminum targets obtained in the above examples 1-4 and comparative examples 1-2 were subjected to metallographic examination. The metallographic examination method is as follows: the high-purity aluminum targets obtained in the above examples and comparative examples were ground with 400-mesh and 1200-mesh sandpapers, respectively, and then polished with a polishing cloth, and then electrolytically corroded in a 2.5% fluoroboric acid aqueous solution for 5-7 minutes, and then washed and dried and the crystal grains were observed with a metallographic microscope. The results are as follows: Figure 3-Figure 8 The average grain size is shown in Table 1.

[0067] Table 1

[0068] Experimental conditions Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Processing temperature of equal channel angular extrusion 200℃ 200℃ 200℃ 200℃ No heating 200℃ ECA passes 4 8 16 32 16 4 Rolling processing temperature normal temperature normal temperature normal temperature normal temperature normal temperature 250℃ Annealing process 150℃ for 1h 150℃ for 1h 150℃ for 1h 150℃ for 1h 150℃ for 1h 150℃ for 1h Grain size (μm) 102 50 43 35 51 176 Is the surface cracked? no no no no yes no

[0069] It can be seen from Table 1 that the average grain size of the high-purity aluminum targets prepared in Examples 1-4 is relatively small, ranging from 35 to 102 μm.

[0070] Depend on Figure 3-Figure 6 It can be seen that the grain size distribution of the high-purity aluminum target materials prepared in Examples 1 to 4 is uniform. Furthermore, compared with Example 1, the average grain size of the high-purity aluminum target materials prepared in Examples 2 to 4 does not exceed 50 μm, and the grain size distribution is fine and uniform.

Claims

1. A method for preparing a high-purity aluminum target, characterized in that: It includes the following steps: The high-purity aluminum ingot is forged, equal-angle extruded, cold-rolled and annealed; The processing temperature of the equal channel angular extrusion is 150-200°C.

2. The method for preparing a high-purity aluminum target according to claim 1, characterized in that: The method for preparing the high-purity aluminum target satisfies one or more of the following conditions (1) to (4): (1) The processing temperature of the equal channel angular extrusion is 180-200°C; (2) The number of passes of the equal channel angular extrusion is a multiple of 4; (3) The operation of the equal-diameter angular extrusion is that after each extrusion, the forged high-purity aluminum ingot is rotated 90° around the central axis in the same direction before the next extrusion; and, (4) The equal-channel angular extrusion operation is carried out in a heatable equal-channel angular extrusion die.

3. The method for preparing a high purity aluminum target according to claim 2, characterized in that: The method for preparing the high-purity aluminum target material satisfies the following conditions (1) and / or (2): (1) The processing temperature of the equal channel angular extrusion is 190°C; (2) The equal-channel angular extrusion is performed in a number of passes ranging from 4 to 32.

4. The method for preparing a high-purity aluminum target according to claim 1, characterized in that: The method for preparing the high-purity aluminum target satisfies one or more of the following conditions (1) to (4): (1) The high-purity aluminum ingot is an aluminum ingot with a purity of 5N or above; (2) The initial forging temperature is 250-300°C; (3) the total deformation of the forging is 70%-85%; and, (4) After the forging and before the equal-diameter angular extrusion, a cutting step is also included, and the height-to-diameter ratio of the high-purity aluminum ingot after cutting is (2.5-5):

1.

5. The method for preparing a high purity aluminum target according to claim 4, characterized in that: The method for preparing the high-purity aluminum target satisfies one or more of the following conditions (1) to (4): (1) The high-purity aluminum ingot is a 5N aluminum ingot, a 5N5 aluminum ingot or a 5N7 aluminum ingot; (2) The initial forging temperature is 280-300°C; (3) the total deformation of the forging is 80%-85%; and, (4) After the forging and before the equal-diameter angular extrusion, a cutting step is also included, and the height-to-diameter ratio of the high-purity aluminum ingot after cutting is 3:

1.

6. The method for preparing a high purity aluminum target according to claim 1, characterized in that: The method for preparing the high-purity aluminum target satisfies one or more of the following conditions (1)-(3): (1) After the equal-diameter angular extrusion and before the cold rolling, the step of cooling the billet is also included, wherein the cooling method is water cooling, and the temperature after cooling is 10-35°C; (2) the total variation of the cold rolling is 5%-20%; and, (3) The cold rolling is performed 10 to 15 times.

7. The method for preparing a high purity aluminum target according to claim 1, characterized in that: The method for preparing the high-purity aluminum target material satisfies the following conditions (1) and / or (2): (1) The total variable of the cold rolling is 10% or 15%; (2) The number of cold rolling passes is 15.

8. The method for preparing a high purity aluminum target according to claim 1, characterized in that: After the cold rolling and before the annealing treatment, a correction step is also performed.

9. The method for preparing a high purity aluminum target according to claim 1, characterized in that: The method for preparing the high-purity aluminum target material satisfies the following conditions (1) and / or (2): (1) The annealing temperature is 100-200°C; (2) The annealing treatment time is 1-3 hours.

10. The method for preparing a high purity aluminum target according to claim 1, characterized in that: The method for preparing the high-purity aluminum target material satisfies the following conditions (1) and / or (2): (1) The temperature of the annealing treatment is 150°C; (2) The annealing treatment time is 1 hour or 2 hours.

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