Molybdenum sputtering target having high transverse rupture strength

Abstract

The molybdenum sputtering target assembly includes a molybdenum sputtering target that is directly diffused to a molybdenum backing plate. The molybdenum sputtering target is composed of molybdenum, and the molybdenum backing plate is composed of molybdenum or a molybdenum alloy.

Description

[0001] Cross-reference of related applications

[0002] This application claims priority to U.S. Application No. 19 / 040,855, filed January 29, 2025, and U.S. Provisional Application No. 63 / 554,541, filed February 16, 2024, the full text of which is incorporated herein by reference. Technical Field

[0003] This disclosure relates to a molybdenum sputtering target, a method for preparing the sputtering target, and a method for selecting a molybdenum material for the sputtering target. The molybdenum sputtering target can be used in semiconductor manufacturing. Background Technology

[0004] Physical vapor deposition (PVD) is widely used to form thin films of materials on a variety of substrates. One important application of this deposition technology is semiconductor manufacturing. Figure 1 The diagram illustrates a portion of an exemplary physical vapor deposition (“PVD”) apparatus 8. In one configuration, the sputtering target assembly 10 includes a backplate 12 to which a target 14 is coupled. A substrate 18 (such as a semiconductive material wafer) is located within the PVD apparatus 8 and is positioned spaced apart from the target 14. The surface 16 of the target 14 is the sputtering surface. As shown, the target 14 is disposed above the substrate 18 and positioned such that the sputtering surface 16 faces the substrate 18. In operation, sputtering material 22 is displaced from the sputtering surface 16 of the target 14 and used to form a coating (or thin film) 20 on the substrate 18.

[0005] Copper and aluminum are currently used as interconnect materials in semiconductor manufacturing. Molybdenum is a next-generation candidate material for interconnects in advanced technology nodes. High power is typically required for sputtering molybdenum sputtering targets. Therefore, diffusion-bonded targets may be necessary. The most commonly used backplane material is a copper alloy. However, molybdenum and copper alloys have very different coefficients of thermal expansion (CTE). Molybdenum has a CTE of 4.8 µm / (m·K), while copper alloys can have a CTE of approximately 20 µm / (m·K), depending on the alloy. During cooling down from the diffusion-bonded temperature or sputtering cycle, according to the equation ΔL = Lo... a ΔT (ΔL is the length change, Lo is the original length, a is the CTE, and ΔT is the temperature change) indicates that the length change of the molybdenum target billet is much smaller than that of the copper alloy backing plate. Therefore, large thermal stresses are generated at the interface between the molybdenum target and the copper alloy backing plate, leading to delamination or cracking of the molybdenum target.

[0006] An improved molybdenum sputtering target assembly is needed. Summary of the Invention

[0007] In embodiment 1, a method for selecting molybdenum powder for a powder metallurgy sputtering target includes: vacuum hot pressing a sample of high-purity molybdenum powder from a source to form a sample; determining the transverse fracture strength of the sample; and selecting a source of molybdenum powder for manufacturing a powder metallurgy molybdenum sputtering target if the transverse fracture strength of the sample is greater than or equal to a predetermined value.

[0008] In implementation scheme 2, the method described in implementation scheme 1 is used, wherein the predetermined value is approximately 120 ksi (827 MPa).

[0009] In Implementation Scheme 3, according to the method described in Implementation Scheme 1, the high-purity molybdenum powder sample consists of molybdenum and unavoidable impurities.

[0010] In implementation scheme 4, the method described in implementation scheme 1 is used, wherein the predetermined value is approximately 150 ksi (1034 MPa).

[0011] In Implementation 5, the method described in Implementation 1 is used, wherein the transverse breaking strength is determined by ASTM B528-16.

[0012] In embodiment 6, the sputtering target assembly includes a powder metallurgy high-purity molybdenum sputtering target having a transverse fracture strength of at least 120 ksi (827 MPa); and a copper alloy backing plate diffusely bonded to the sputtering target.

[0013] In embodiment 7, the sputtering target assembly according to embodiment 6 is provided, wherein the sputtering target has a transverse fracture strength of at least 150 ksi (1034 MPa).

[0014] In embodiment 8, the sputtering target assembly according to embodiment 6 is wherein the copper alloy backplate is a copper-zinc backplate.

[0015] In embodiment 9, the sputtering target assembly according to embodiment 6 is provided, wherein the high-purity molybdenum sputtering target is composed of molybdenum and unavoidable impurities.

[0016] In embodiment 10, the sputtering target assembly according to embodiment 6 is wherein the aluminum intermediate layer is located between the powder metallurgy high-purity molybdenum sputtering target and the copper alloy backplate.

[0017] In embodiment 11, the method of preparing a sputtering target assembly includes selecting powdered molybdenum, wherein the powdered molybdenum produces a specimen having a transverse fracture strength of at least a predetermined value; forming a powder metallurgy sputtering target from the selected powdered molybdenum; and attaching the powder metallurgy sputtering target to a backplate, wherein the predetermined value is 120 ksi (827 MPa).

[0018] In embodiment 12, according to the method of embodiment 11, the powdered molybdenum consists of molybdenum and unavoidable impurities.

[0019] In implementation scheme 13, the method described in implementation scheme 11 is used, wherein the predetermined value is 150 ksi (1034 MPa).

[0020] In embodiment 14, the method described in embodiment 11 is used, wherein the transverse breaking strength is determined by ASTM B528-16.

[0021] In embodiment 15, according to the method of embodiment 11, attaching the powder metallurgy sputtering target to the backplate includes attaching the powder metallurgy sputtering target to the copper alloy backplate.

[0022] In embodiment 16, according to the method of embodiment 15, attaching the powder metallurgy sputtering target to the copper alloy backing plate includes: diffusion bonding the powder metallurgy sputtering target to the copper alloy backing plate.

[0023] In Implementation Scheme 17, the method described in Implementation Scheme 15 is wherein the copper alloy backplate is a copper-zinc backplate.

[0024] In embodiment 18, the method of embodiment 17 is used, and further includes an aluminum interlayer between the copper-zinc backing plate and the powder metallurgy sputtering target.

[0025] In embodiment 19, the method according to embodiment 11 is used, wherein a sample is formed using powdered molybdenum before selecting powdered molybdenum, and the transverse fracture strength of the sample is determined.

[0026] In embodiment 20, according to the method of embodiment 11, forming the powder metallurgy sputtering target includes hot pressing the selected molybdenum powder.

[0027] While several embodiments have been disclosed, other embodiments of the invention will become apparent to those skilled in the art from the following detailed description illustrating and describing exemplary embodiments of the invention. Therefore, the drawings and detailed description should be considered illustrative rather than restrictive in nature. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a sputtering device.

[0029] Figure 2 This is a schematic cross-sectional view of an exemplary molybdenum sputtering target assembly.

[0030] Figure 3 This is a block diagram for preparing molybdenum sputtering targets.

[0031] Figure 4This is a block diagram for selecting molybdenum powder for sputtering targets.

[0032] Figure 5 This is a schematic diagram of Example 2. Detailed Implementation

[0033] This paper discloses an improved molybdenum sputtering target and its preparation method. A method for selecting molybdenum powder for the sputtering target is also disclosed.

[0034] Figure 2 This is a schematic cross-sectional view of a sputtering target assembly 100 including a backplate 102 and a molybdenum sputtering target 104. In some embodiments, the backplate 102 and the molybdenum sputtering target 104 are joined by a diffusion joint.

[0035] In some embodiments, the molybdenum sputtering target 104 is formed of 100% molybdenum and unavoidable impurities. For example, the molybdenum sputtering target 104 may be composed of molybdenum or substantially composed of molybdenum. The sputtering target 104 has a sufficient average grain size for interconnect materials. For example, the molybdenum sputtering target 104 has an average grain size of less than about 100 micrometers (μm). In some examples, the molybdenum sputtering target 104 has an average grain size of less than about 50 μm.

[0036] As described herein, the molybdenum sputtering target 104 can be formed by powder metallurgy. For example, the molybdenum sputtering target 104 can be formed by vacuum hot pressing.

[0037] In some embodiments, the backplate 102 may be formed of a copper alloy (such as a copper-zinc alloy). In some embodiments, an intermediate layer 106 may be positioned between the backplate 102 and the sputtering target 104. For example, an aluminum intermediate layer 106 may be positioned between the backplate 102 and the sputtering target 104.

[0038] The molybdenum sputtering target 104 and the backplate 102 are diffusely bonded to each other. In some embodiments, the molybdenum sputtering target 104 and the backplate 102 are bonded by hot isostatic pressing (HIP) or vacuum thermopressing.

[0039] Thermal stress occurs at the bonding interface between the molybdenum sputtering target 104 and the backing plate 102 as the sputtering target assembly cools after diffusion bonding. Thermal stress may also occur at the bonding interface during the sputtering cycle. Thermal stress can lead to delamination or cracking of the molybdenum sputtering target 104.

[0040] It has been found that using a molybdenum sputtering target 104 with high transverse fracture strength (TRS) provides a powder metallurgy sputtering target with a lower likelihood of cracking. In one example, the molybdenum sputtering target 104 has a TSR of at least 120 kpsi (827 MPa). In another example, the molybdenum sputtering target 104 has a TSR of at least 150 kpsi (1034 MPa).

[0041] In some implementations, the molybdenum sputtering target 104 is manufactured using high-purity molybdenum powder and vacuum hot pressing. Figure 3 This is a diagram of a method 200 for preparing a molybdenum sputtering target 104. In step 202, powder is loaded into a mold (such as a graphite mold) of a vacuum hot press. The powder can be high-purity molybdenum powder. For example, the molybdenum powder can have 100% purity, but may contain unavoidable impurities. That is, the molybdenum powder can consist of molybdenum and unavoidable impurities.

[0042] In step 204, the powder in the mold is vacuum hot-pressed using a vacuum hot press to form a molybdenum sputtering target. In some examples, the vacuum hot press is operated at a temperature exceeding about 1600 degrees Celsius (about 2912 degrees Fahrenheit), a hydraulic pressure exceeding about 3 ksi (20.7 MPa), and a holding time of at least 2 hours. In some embodiments, the vacuum hot press is operated at a temperature from about 1600 degrees Celsius (about 2912 degrees Fahrenheit) to about 1780 degrees Celsius (about 3236 degrees Fahrenheit), a hydraulic pressure from about 3 ksi to about 4 ksi (about 20.7 MPa to about 27.6 MPa), and a holding time from about 2 hours to about 4 hours. After vacuum hot pressing, the sputtering target has a TSR of at least 120 ksi (827 MPa) or at least 150 ksi (1034 MPa).

[0043] Optionally, in step 206, after hot pressing, the molybdenum sputtering target may be machined and / or measured. For example, the density of the sputtering target may be determined. In some embodiments, the sputtering target is machined, the density is tested, and then the sputtering target is machined a second time.

[0044] In step 208, a molybdenum sputtering target is bonded to a backing plate to form a sputtering target assembly. In some embodiments, the sputtering target may be diffuse-bonded to a copper alloy, such as a copper-zinc alloy backing plate.

[0045] After assembly, the sputtering target assembly is machined in step 210.

[0046] In step 212, the sputtering target is cleaned to remove debris from the surface of the sputtering target assembly during the manufacturing process. In step 214, the sputtering target assembly is encapsulated. For example, the sputtering target assembly may be placed in plastic packaging material.

[0047] Transverse fracture strength (TRS) defines the stress required to break a specimen, calculated by the flexural formula, for a simple beam supported near the ends with the force applied in the middle between the centers of the support's fixed lines. The TRS of powder metallurgy specimens (such as sputtering target 104) can be determined using ASTM B528-16. This is a destructive test. In some embodiments, TRS is used to select the molybdenum powder for forming the sputtering target of method 200. TRS is not a standard design value and was not previously considered when selecting the source material. Because TRS analysis is a destructive test, it is not possible to determine the TRS of the sputtering target to be used. Instead, the TRS of the powder must be evaluated for use with the sputtering target.

[0048] Figure 4 This is a diagram of method 400 for evaluating and selecting molybdenum for a sputtering target. In step 402, the molybdenum powder sample to be evaluated is formed into a powder metallurgy specimen. The powder should be consolidated, and the specimen is collected from the material using the same process as the powder will be used to form the desired sputtering target. For example, when selecting molybdenum powder for the sputtering target in method 200, the molybdenum powder sample is processed according to method 200.

[0049] In step 404, the TRS of the specimen is determined. For example, the TRS of the specimen can be determined by testing the specimen according to ASTM B528-16.

[0050] In step 406, powder for preparing a high-purity molybdenum sputtering target is selected based on the TSR obtained in step 404. In some embodiments, powder can be selected if the TSR of the sample is equal to or greater than a predetermined value. In some embodiments, molybdenum powder can be used to prepare a high-purity diffusion-bonded molybdenum sputtering target if the sample has a TSR of at least 120 ksi (827 MPa) or at least 150 ksi (1034 MPa). In some embodiments, using ASTM B528-16, the sample may not break. In this case, it is assumed that the sample has a TSR of at least 150 ksi (1034 MPa), and the powder can be used to form a high-purity molybdenum sputtering target.

[0051] As used in this article, “about” can mean ±1%, ±2%, ±3%, ±4%, or ±5%.

[0052] Example 1

[0053] Hot-pressed molybdenum samples were prepared using various molybdenum powder sources. The molybdenum powders were 100% pure molybdenum, containing unavoidable impurities. Samples were prepared by vacuum hot-pressing the molybdenum powder in a graphite mold at 1740°C (3164°F) and 3.55 ksi (24.5 MPa) for 3 hours.

[0054] The samples were then tested using ASTM B528-16 to determine the transverse fracture strength of each powder metallurgy sample. The results are provided in Table 1.

[0055] Table 1 .

[0056]

[0057] Each of the tested molybdenum powders produced a sample with a TRS of at least 120 ksi (827 MPa). Therefore, each powder would be suitable for diffusion bonding to a high-purity molybdenum sputtering target with a backing plate.

[0058] Example 2

[0059] The sputtering target assembly was fabricated and the sputtering target / backplate interface was analyzed. First, as described in Example 1, a full-size molybdenum sputtering target was formed using 100% molybdenum powder and vacuum hot pressing. An additional molybdenum sputtering target blank was processed using the same parameters. The sputtering target blank had a TRS of 197.16 ksi (1359 MPa).

[0060] The sputtering target was diffuse-bonded to a copper-zinc alloy backing plate using an aluminum interlayer. The high-strength molybdenum sputtering target withstood the diffusion bonding process; the sputtering target did not crack. The bonding percentage was analyzed using C-scan analysis. The C-scan showed 100% bonding. The bonding strength between the sputtering target and the interlayer, and between the interlayer and the backing plate, was determined using a plunger tensile test method, as described in Zatorski, Z. (2007), Evaluation of Steel Clad Plate Weldability Using Ram Tensile Test Method. Engineering Transactions, 55(3), 229-238. Figure 5 As shown, the diameter of the sputtering target was sampled. The results are provided in Table 2.

[0061] Table 2

[0062]

[0063] The average bond strength between the sputtering target and the aluminum interlayer is 11.5 ksi (79.3 MPa). The average bond strength between the aluminum interlayer and the copper-zinc backing plate is 12.9 ksi (88.9 MPa).

[0064] Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the invention. For example, while the above embodiments relate to specific features, the scope of the invention also includes embodiments with different combinations of features and embodiments that do not include all of the above features.

Claims

1. A method for selecting molybdenum powder for a powder metallurgy sputtering target, the method comprising: Vacuum hot pressing of high-purity molybdenum powder from the source to form a sample; Determine the transverse fracture strength of the specimen; as well as If the transverse fracture strength of the specimen is greater than or equal to a predetermined value, then the source of powdered molybdenum for manufacturing the powder metallurgy molybdenum sputtering target is selected.

2. The method according to claim 1, wherein the predetermined value is about 120 ksi (827 MPa).

3. The method according to claim 1, wherein the high-purity molybdenum powder sample consists of molybdenum and unavoidable impurities.

4. A sputtering target assembly, comprising: A powder metallurgical high-purity molybdenum sputtering target, wherein the powder metallurgical high-purity molybdenum sputtering target has a transverse fracture strength of at least 120 ksi (827 MPa). and A copper alloy backplate, which is diffusely bonded to the sputtering target.

5. The sputtering target assembly of claim 4, wherein the high-purity molybdenum sputtering target is composed of molybdenum and unavoidable impurities.

6. A method for preparing a sputtering target assembly, the method comprising: Selecting powdered molybdenum, wherein the powdered molybdenum produces a specimen with a transverse fracture strength of at least a predetermined value; The powder metallurgy sputtering target is formed from the selected molybdenum powder; and The powder metallurgy sputtering target is attached to a backplate, wherein the predetermined value is 120 ksi (827 MPa).

7. The method of claim 6, wherein the powdered molybdenum consists of molybdenum and unavoidable impurities.

8. The method of claim 6, wherein attaching the powder metallurgy sputtering target to the copper alloy backing plate comprises: The powder metallurgy sputtering target is diffused and bonded to a copper alloy backing plate.

9. The method of claim 6, wherein a sample is formed using the powdered molybdenum before selecting the powdered molybdenum, and the transverse breaking strength of the sample is determined.

10. The method of claim 6, wherein forming the powder metallurgy sputtering target comprises: The selected molybdenum powder was hot-pressed.

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