Machining method of titanium-aluminum alloy target material

Abstract

The invention relates to the technical field of machining of brittle alloy Ti-Al intermetallic compounds, in particular to a machining method of a titanium-aluminum alloy target material, which is suitable for preparing a high-purity sputtering target material with the purity of more than 4N5 for a chip with the specification of below 28nm thread. According to the method, the titanium-aluminum alloy target blank is subjected to surface machining by adopting a constant linear speed numerical control turning and axial vacuum chuck fixing mode for the cast target blank. By optimizing the target blank clamping mode and numerical control machining process parameters, the problems of deformation, corner chipping and non-uniform surface roughness in the machining process of the fragile titanium-aluminum alloy target blank are solved, so that the titanium-aluminum alloy target material obtains good size control and surface integrity; and stable control over the size precision and the conductivity of the titanium-aluminum alloy target material which is high in brittleness and prone to deformation is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical processing of brittle alloy Ti-Al series intermetallic compounds, in particular to a mechanical processing method of a titanium-aluminum alloy target material, which is suitable for preparing high-purity sputtering targets with a purity of 4N5 or above for chips with a thread size below 28nm. Background Art

[0002] High-purity Ti50Al alloy is one of the core materials for sputtering coating of large-scale integrated circuits of chips below 28nm. The technical requirements for sputtering targets are as follows: 1. Ti:Al = 50%: 50% (±1at%), Ti:Al = 64%: 36% (±0.8wt%), purity > 4N5; 2. Target size: 3. The machined surface shall be free from deformation, stain and scratch, and the roughness Ra shall be less than 0.5 μm.

[0003] High-purity 4N5 large-size titanium-aluminum targets are particularly difficult to prepare due to their brittle material, large size, and high purity. The power management chips, display driver chips, automotive electronic chips and other products that are currently in short supply on the market are 28nm processes. In terms of cost, the process of 28nm chips is relatively mature, the IP library is relatively complete, and the cost performance is high. At present, domestic leading semiconductor companies have actively carried out the development of high-purity titanium-aluminum targets for integrated circuits, and use cold-wall copper crucibles for high-clean smelting and casting to prepare TiAl alloy targets. The test results show that compared with the existing powder metallurgy target material with an Al content of 0.53 to 0.47, the sputtering process content decreases, and the Al content of the casting target is maintained at the optimal 0.5 value unchanged, showing a very good service life. However, the processing of large-size target blanks of brittle titanium-aluminum alloys has always affected the delivery qualification rate of products, which is specifically reflected in the warping deformation of the target material, the edge collapse and the inconsistent surface roughness, resulting in large differences in conductivity. Summary of the invention

[0004] In view of the difficulties existing in the prior art, the purpose of the present invention is to provide a method for machining a titanium-aluminum alloy target. The method described can obtain a large-size, high-precision Ti50Al alloy target and solve the quality problems that occur during the machining of the titanium-aluminum alloy target and lead to scrapping.

[0005] The technical solution of the present invention is:

[0006] A mechanical processing method for a titanium aluminum alloy target material, firstly adopting a radial mechanical clamping method, fixing a target blank by radial mechanical pressure jaws of a mechanical preload chuck, and then performing lathe processing and thinning, after the straightness of both surfaces is ≤1mm and the roughness is ≤Ra6.4μm to meet the basic profile requirements, the target blank is fixed by an axial vacuum suction cup, and after the thickness is thinned to a single-side margin of 2.5-3.5mm, the edge of the target blank is rounded; then the thickness of the target blank is thinned by a constant linear speed processing method, and the target blank is processed to a specified thickness dimension in the thickness direction by converting the front and rear surfaces, and the edge rounding is removed accordingly; finally, the arc of the circumferential edge of the target blank is removed to obtain a target material with a qualified size.

[0007] In the mechanical processing method of the titanium aluminum alloy target material, during the target blank processing, the traditional mechanical preload chuck is eliminated and the multi-angle radial mechanical pressure claws are replaced with multiple axial vacuum suction cups for fixing.

[0008] The mechanical processing method of the titanium aluminum alloy target material comprises 4 to 8 radial mechanical pressure claws with a preload force of 100N to 1000N; 6 to 20 axial vacuum suction cups with a diameter of 20 to 50mm and a suction force of 100N to 500N.

[0009] In the mechanical processing method of the titanium aluminum alloy target material, preferably, the number of the multiple axial vacuum suction cups is 10 to 15, the diameter is 25 to 40 mm, and the suction force is 200 to 350N.

[0010] In the mechanical processing method of the titanium aluminum alloy target material, during the process of processing the large-size surface of the target blank, the machining parameters are changed from constant angular velocity input to constant linear velocity input control.

[0011] In the mechanical processing method of the titanium aluminum alloy target material, during lathe processing, the constant angular velocity range parameter 1 to 10 r / s is changed to a constant linear velocity range of 1400 to 14000 mm / s.

[0012] In the machining method of the titanium aluminum alloy target material, preferably, the constant angular velocity range parameter of 3 to 8 r / s is changed to a constant linear velocity range of 4200 to 11200 mm / s.

[0013] The mechanical processing method of the titanium aluminum alloy target material is to pre-process the fillet and then perform constant linear speed thickness thinning processing when processing the circumferential edge of the target blank.

[0014] In the mechanical processing method of the titanium-aluminum alloy target material, the fillet radius R of the pre-machined circumferential edge of the target blank is in the range of 6 to 10 mm.

[0015] In the mechanical processing method of the titanium aluminum alloy target material, preferably, the pre-processed fillet radius R of the circumferential edge of the target blank is in the range of 7.5 to 9.0 mm.

[0016] The design idea of ​​the present invention is:

[0017] The present invention designs a rotatable axial vacuum suction cup to replace the traditional disk mechanical clamp, thereby avoiding the target material warping deformation caused by the radial clamping force of the target blank with large diameter and thin thickness, resulting in excessive target material flatness.

[0018] The target material processing of the present invention adopts the constant linear velocity parameter input of the CNC lathe to replace the angular velocity parameter, so as to obtain good and consistent roughness of the target material surface (the roughness is closely related to the travel speed of the tool) and ensure the stable conductivity of the inner and outer surfaces of the target material.

[0019] In order to solve the problem of chipping of the outer edge of the target material, the present invention adopts a prefabricated rounded corner design so that the movement of the tool during processing the edge has no impact on the target material substrate. After processing to the designed thickness, the rounded corners are also removed layer by layer to ensure that the contour of the target material meets the requirements of the drawing.

[0020] The advantages and beneficial effects of the present invention are:

[0021] 1. If Figure 1-Figure 3 As shown, the present invention optimizes the processing method of pancake-shaped brittle materials, so that the radial clamping of the titanium-aluminum alloy target blank is changed to the suction fixation of the axis, avoiding the warping deformation of the titanium-aluminum alloy target blank with large diameter and thin thickness due to the application and release of the clamping force, and ensuring that high-precision target materials can be processed. This processing method optimizes the vacuum suction position and suction force of the target blank, and the three-face change processing can not only achieve the technical requirement of flatness less than 0.02mm, but also has no interference from radial claws, and can ensure the accessibility of the tool at the circumferential edge of the target blank, avoid the destructiveness of traditional mechanical clamping to the brittle edge, and ensure that the target material has a good and stable dimensional profile ( Figure 3 ).

[0022] 2. The present invention optimizes the processing sequence of brittle pancake-shaped brittle targets. The traditional method is to first process the circumferential dimension to 454±0.2mm and then process the thickness to 11.8±0.02mm. This will form a right angle at the edge of the pancake. Each thickness reduction process will cause a tool breakage impact at this position, which often leads to corner chipping for brittle titanium aluminum materials, and the target material is scrapped. Figure 4(a), (c). The present invention pre-processes the R-radius in the circumferential processing (the R radius is calculated), and then the tool gradually fits the target material substrate during the thickness thinning process, and no obvious impact is formed; in addition, the rounded corner structure also ensures that no corner chipping occurs. After the thickness direction is processed to the ideal thickness size, the fillet radius is synchronously reduced (≤0.1mm), which meets the target material profile requirements. This optimized processing method for brittle materials significantly improves the probability of successful target material processing. Figure 4 (b), (d).

[0023] 3. If Figure 5 As shown, the present invention combines the effect of the surface roughness of titanium-aluminum alloy target material on contact conductivity, breaks through the concept of constant angular velocity processing parameter input in the traditional processing industry, and creatively writes a constant linear velocity program for a CNC lathe (the rotation speed increases from the outside to the inside, and the tool linear velocity remains unchanged) to form a uniform and consistent roughness on the target material processing surface, thereby achieving stable control of the conductive properties of the titanium-aluminum target material surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the machining method of the target blank radial mechanical clamping device, where (a) is the side view and (b) is the front view.

[0025] Figure 2 Schematic diagram of machining method of axial vacuum suction cup fixing device, where (a) is the front view and (b) is the side view.

[0026] Figure 3 This is a diagram showing the effect of no warping of the Ti50Al alloy target after processing under the fixing condition of the suction cup bracket of the present invention.

[0027] Figure 4 Schematic diagram of the target blank circumferential edge before and after the rounding treatment to prevent chipping and the processing effect. Among them, (a) before the rounding treatment, (b) after the rounding treatment, (c) before the rounding treatment, (d) after the rounding treatment.

[0028] Figure 5 The effect of optimizing the input constant angular velocity to the uniform roughness and stable conductivity of the target surface under the condition of constant linear velocity during lathe processing. Among them, (a) is the roughness of the target surface at 10 points under the condition of constant angular velocity (c) = 0.733μm, (b) is the roughness of the target surface at 10 points under the condition of constant linear velocity (c) = 0.497μm, (c) is the distribution of measurement points of roughness and conductivity.

[0029] Reference numerals in the figure: 1 target blank, 2 radial mechanical pressure claws, 3 axial vacuum suction cup, 4 suction cup bracket, 5 vacuum suction tube. DETAILED DESCRIPTION

[0030] In the specific implementation process, the purity of the titanium aluminum alloy target of the present invention is greater than 99.995wt%, in terms of atomic percentage, Ti:Al=50%:50% (±1at%), the gas content of oxygen is less than 500ppm, nitrogen is less than 50ppm, and hydrogen is less than 20ppm. The size of the titanium aluminum target is The target blank used for titanium aluminum target machining is made of sponge titanium with a purity of 99.9wt% and Al beans with a purity of 99.9999%. After being uniformly mixed and pressed according to the required percentage of components, the ingot is obtained by vacuum arc consumable melting VAR + vacuum induction melting casting.

[0031] like Figure 1 As shown in (a)-(b), during the processing of the target blank 1, when a traditional target blank radial mechanical clamping device is used, the radial mechanical pressure claws 2 of the mechanical preload chuck are evenly distributed around the target blank 1 in the radial direction.

[0032] like Figure 2 As shown in (a)-(b), during the processing of the target blank 1, the axial vacuum suction cup 3 of the axial vacuum suction cup fixing device is installed on one side of the suction cup bracket 4, the axial vacuum suction cup 3 is evenly distributed and corresponds to the back side of the target blank 1, and the other side of the suction cup bracket 4 is connected to the vacuum pump through the vacuum suction pipe 5, and the vacuum pump is connected to the suction cup bracket 4 and the channel of the axial vacuum suction cup 3 in sequence through the vacuum suction pipe 5.

[0033] like Figure 3 As shown, after the Ti50Al alloy target is processed under the fixing condition of the suction cup bracket of the present invention, there is no warping deformation.

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1

[0036] In this embodiment, Ti50Al (Ti:Al = 50%: 50% (±1at%)) high-purity raw materials are uniformly mixed according to the required composition and then pressed. After the TiAl alloy is obtained by a combined smelting method of primary vacuum arc consumable melting VAR + secondary vacuum arc consumable melting VAR, the secondary smelted ingot is sawn into four parts, each of which is 50 kg and placed in a vacuum induction water-cooled copper crucible ISM (Induction Skull Melting, i.e., induction shell melting technology) to melt and cast TiAl alloy target blank material. The casting target blank has a diameter of Thickness H30mm, with fine and uniform structure.

[0037] like Figure 1-Figure 2 As shown in the figure, the radial mechanical clamping method is first used to fix the target blank and then thin it by lathing. After the straightness (≤1mm) and roughness (≤Ra6.4μm) of both surfaces meet the basic profile requirements, it is fixed by an axial vacuum chuck. After the thickness is thinned to H17.8mm (single-side margin is 3mm), the edge of the target blank is rounded (R8.94mm). Figure 4 (b); The target blank is then thinned by constant linear speed machining at a linear speed of 5200 mm / s. The target blank is machined to the specified thickness (H11.8 -0.05 mm), and the edge fillet is removed by machining; finally, the arc of the circumferential edge of the target blank is removed to obtain the diameter The target material with qualified size is released, and the axial vacuum chuck fixing device is used to detect the Ti50Al target blank. The straightness is 0.02mm, and the roughness of the edge and central part is Ra0.2~0.4μm.

[0038] like Figure 3 , Figure 4 (d) Figure 5 As shown, the titanium aluminum alloy target blank prepared by the processing method in this embodiment has no warping deformation and no corner chipping defects, and its dimensional accuracy and surface roughness meet the technical index requirements. The conductivity of the target material measured at 10 points is in the range of 3 to 3.5MS / m, which meets the target material delivery standards.

[0039] Example 2

[0040] In this embodiment, the Ti50Al high-purity raw material is pressed after being uniformly mixed according to the required composition, and the TiAl alloy is obtained by a combination of primary vacuum arc consumable melting VAR + secondary vacuum arc consumable melting VAR. The secondary smelted ingot is sawn into four parts, and each part of 40 kg is placed in a vacuum induction water-cooled copper crucible ISM to melt and cast the TiAl alloy target blank material. The diameter of the cast target blank is Thickness H24mm, with fine and uniform structure.

[0041] like Figure 1-Figure 2 As shown in the figure, the radial mechanical clamping method is first used to fix the target blank and then thin it by lathing. After the flatness (≤0.8mm) and roughness (≤Ra3.2μm) of both surfaces meet the basic requirements, it is changed to axial vacuum chuck fixing. After the thickness is thinned to H15.8mm (single-side margin is 2mm), the edge of the target blank is rounded (R7.9mm), see Figure 4(b); The target blank is then thinned by constant linear speed machining at a linear speed of 8400 mm / s, and the target blank is machined to a specified thickness dimension (H11.8 +0.03 mm), and the edge fillet is removed by machining; finally, the arc of the circumferential edge of the target blank is removed to obtain the diameter The target material with qualified size is released, and the axial vacuum chuck fixing device is used to detect the Ti50Al target blank. The straightness is 0.015mm, and the roughness of the edge and central part is Ra0.2~0.3μm.

[0042] like Figure 3 , Figure 4 (d) Figure 5 As shown, the titanium aluminum alloy target blank prepared by this processing method has no rebound deformation and corner chipping defects, and its dimensional accuracy and surface roughness meet the technical index requirements. The conductivity of the target material measured at 10 points is in the range of 3 to 3.5MS / m, which meets the target material delivery standards.

[0043] Example 3

[0044] In this embodiment, the Ti50Al high-purity raw material is pressed after being uniformly mixed according to the required composition, and the TiAl alloy is obtained by three vacuum arc consumable melting VAR combined melting methods. The three-melted ingot is sawn into 6 parts, and each 60 kg portion is placed in a vacuum induction water-cooled copper crucible ISM to melt and cast the TiAl alloy target blank material. The casting target blank has a diameter of Thickness H35mm, with fine and uniform structure.

[0045] like Figure 1-Figure 2 As shown in the figure, the radial mechanical clamping method is first used to fix the target blank and then thin it by lathing. After the flatness (≤0.6mm) and roughness (≤Ra4.8μm) of both surfaces meet the basic requirements, it is fixed by an axial vacuum chuck. After the thickness is thinned to H16.8mm (single-side margin is 2.5mm), the edge of the target blank is rounded (R8.4mm). Figure 4 (b); The target blank is then thinned by constant linear speed machining at a linear speed of 12000 mm / s, and the target blank is machined to a specified thickness dimension (H11.8 -0.02 mm), and the edge fillet is removed by machining; finally, the arc of the circumferential edge of the target blank is removed to obtain the diameter The target material with qualified size is released, and the axial vacuum chuck fixing device is used to detect the Ti50Al target blank. The straightness is 0.012mm, and the roughness of the edge and central part is Ra0.15~0.3μm.

[0046] like Figure 3 , Figure 4 (d) Figure 5 As shown, the titanium aluminum alloy target blank prepared by this processing method has no warping deformation and corner chipping defects, and its dimensional accuracy and surface roughness meet the technical index requirements. The conductivity of the target material measured at 10 points is in the range of 3 to 3.5MS / m, which meets the target material delivery standards.

[0047] Table 1 Comparison of the effects of two Ti50Al alloy target processing methods

[0048]

[0049] It can be seen from Table 1 that the present invention aims at the processing drawbacks of Ti50Al target blanks and proposes an optimization approach for machining Ti50Al target blanks of brittle materials. Through three targeted measures, the Ti50Al alloy target blanks can achieve good machining effects, which significantly improves the machinability of the target blanks and has good dimensional accuracy and stable conductivity.

[0050] The implementation results show that the mechanical processing method of the titanium aluminum alloy target material of the present invention comprises: surface processing of the Ti50Al alloy target blank by constant linear speed CNC lathe machining and axial vacuum chuck fixing of the cast target blank. The present invention optimizes the target blank clamping method and CNC machining process parameters to avoid the problems of deformation, corner collapse and uneven surface roughness during the machining of the brittle Ti50Al alloy target blank, so that the Ti50Al alloy target material has good size control and surface integrity, and realizes the stable control of the size accuracy and conductivity of the brittle and easily deformable Ti50Al alloy target material.

Claims

1. A method for machining a titanium aluminum alloy target, characterized in that: First, the radial mechanical clamping method is adopted. The target blank is fixed by the radial mechanical pressure jaws of the mechanical preload chuck, and then it is thinned by lathing. After the straightness of both sides is ≤1mm and the roughness is ≤Ra6.4μm to meet the basic contour requirements, the target blank is fixed by an axial vacuum suction cup. After the thickness is thinned to a single-side margin of 2.5-3.5mm, the edge of the target blank is rounded. The thickness of the target blank is then thinned by a constant linear speed processing method. The front and rear faces are converted and the target blank is processed to the specified thickness dimension in the thickness direction, and the edge fillet is removed accordingly. Finally, the arc of the circumferential edge of the target blank is removed to obtain a target material with qualified size.

2. The machining method of titanium aluminum alloy target according to claim 1, characterized in that: During the target blank processing, the traditional mechanical preload chuck is eliminated and the multi-angle radial mechanical pressure claws are replaced with multiple axial vacuum suction cups for fixation.

3. The machining method of titanium aluminum alloy target according to claim 2, characterized in that: The number of the multiple radial mechanical pressure claws is 4 to 8, and the preload force is 100N to 1000N; the number of the multiple axial vacuum suction cups is 6 to 20, and the diameter is 20 to 50mm, and the suction force is 100N to 500N.

4. The machining method of titanium aluminum alloy target according to claim 3, characterized in that: Preferably, the number of the multiple axial vacuum suction cups is 10 to 15, the diameter is 25 to 40 mm, and the suction force is 200 to 350N.

5. The machining method of titanium aluminum alloy target according to claim 1, characterized in that: In the process of machining large-size surface of target blank, the turning parameters are changed from constant angular velocity input to constant linear velocity input control.

6. The machining method of the titanium aluminum alloy target according to claim 5, characterized in that: During lathe processing, the constant angular velocity range parameter 1 to 10 r / s is changed to a constant linear velocity range of 1400 to 14000 mm / s.

7. The machining method of titanium aluminum alloy target according to claim 6, characterized in that: Preferably, the constant angular velocity range parameter 3 to 8 r / s is changed to a constant linear velocity range of 4200 to 11200 mm / s.

8. The machining method of titanium aluminum alloy target according to claim 1, characterized in that: When machining the circumferential edge of the target blank, the corners are pre-rounded and then the thickness is thinned at a constant linear speed.

9. The machining method of titanium aluminum alloy target according to claim 8, characterized in that: The radius R of the fillet pre-machined on the circumferential edge of the target blank is in the range of 6 to 10 mm.

10. The machining method of titanium aluminum alloy target according to claim 9, characterized in that: Preferably, the pre-processed fillet radius R of the circumferential edge of the target blank is in the range of 7.5 to 9.0 mm.

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