Method for producing a scandium aluminum nitride target for pld

Abstract

This invention relates to a method for manufacturing an aluminum scandium nitride (ScAlN) target for pulsed laser deposition (PLD), the method comprising the following steps: ˗ providing an aluminum scandium alloy body; ˗ pulverizing the aluminum scandium alloy body into aluminum scandium particles; ˗ nitriding the aluminum scandium particles into aluminum scandium nitride particles; ˗ hot-pressing the aluminum scandium nitride particles into an aluminum scandium nitride target.

Description

Technical Field

[0001] This invention relates to a method for manufacturing an aluminum scandium nitride (ScAlN) target for pulsed laser deposition (PLD). Prior Technology

[0002] Using a PLD, a film can be deposited on a substrate by irradiating a target material with a laser beam. Due to the high energy of the laser beam, a plasma is generated from the target material. This plasma is then deposited onto a substrate, resulting in the formation of a film of the target material.

[0003] Aluminum nitride (AlN) is a well-known piezoelectric thin film material. Its piezoelectric performance can be significantly improved by doping with up to 50 at% scandium. Specifically, aluminum nitride scandium films are suitable as piezoelectric layers in acoustic filters for radio frequency (RF) applications and in microelectromechanical systems (MEMS) such as miniature microphones and ultrasonic transducers.

[0004] We know that a target is formed by hot-pressing a mixture of one powder of scandium nitride and one powder of aluminum nitride. Although the manufactured target is not composed of ScAlN, the film formed on a substrate by PLD will be ScAlN because scandium nitride and aluminum nitride will mix in the plasma and deposit as a ScAlN film during the plasma generation of the target material.

[0005] However, the target formed from a mixture of scandium nitride powder and aluminum nitride powder results in differences in laser light absorption during the PLD process. Furthermore, the mixture of the two powders has a relatively low density. This is due to the difference in particle size between the two powders, making it difficult to obtain a homogeneous mixture and hindering high-pressure compression. When the mixture is compressed under high pressure, the differences in particle size and thermal expansion between the two powders will lead to localized stress and thus cracks in the target.

[0006] If this target is used for an extended period in a PLD process, the composition of the ScAlN deposited film may undergo a shift because scandium nitride particles can behave slightly differently from aluminum nitride particles in the target when irradiated by a laser beam to generate a plasma. The band gap for light absorption in scandium nitride in the target is 2.0 eV, while that of aluminum nitride is 6.15 eV. The energy of an ultraviolet laser used in a PLD process is typically between 4 eV and 6 eV. Therefore, it is clear that the PLD process is inefficient with a target composed of two different materials because the laser absorption of the two materials is significantly different. Consequently, numerous droplets will be ejected from the target, which is undesirable. Summary of the Invention

[0007] One object of the present invention is to reduce or even eliminate the above-mentioned disadvantages.

[0008] This objective is achieved according to the present invention by a method as stated in the foreword of the claim, the method comprising the following steps: Provides scandium-aluminum alloy body; The scandium-aluminum alloy body is crushed into scandium-aluminum particles; Scandium aluminum particles are nitrided into aluminum scandium nitride particles; Aluminum scandium nitride particles are hot-pressed into aluminum scandium nitride targets.

[0009] Using the method according to the invention, scandium aluminum particles are converted into aluminum scandium nitride particles via a nitriding process. Then, since a target is hot-pressed using a single type of particle, a higher density target can be obtained using higher pressure than in prior art methods where a target is hot-pressed using a mixture of two types of particles.

[0010] The resulting target is composed of genuine aluminum scandium nitride. This single-phase material will have a single band gap. The exact band gap depends on the scandium content, but will certainly be lower than the energy of UV lasers with scandium doping up to 50 at%. Therefore, UV laser absorption is highly efficient and enables one of the extended uses of the target in a PLD process that achieves droplet-free formation.

[0011] According to a preferred method of the present invention, the nitridation of scandium aluminum particles includes the following steps: supplying scandium aluminum particles in a gas stream of nitrogen or ammonia (NH3) while maintaining the temperature of the mixture of gas and scandium aluminum particles above 500°C.

[0012] By supplying scandium aluminum particles to the ammonia gas stream, good contact between the scandium aluminum particles and ammonia is achieved, which ensures that the particles are reliably converted into scandium aluminum nitride particles.

[0013] In another preferred embodiment of the method according to the invention, aluminum scandium nitride particles are hot-pressed in a uniform hot-pressing process. A uniform hot-pressing process allows pressure to be applied to the particles in all directions. This allows for a more uniform density within the manufactured target.

[0014] Using a uniform hot pressing method, aluminum scandium nitride particle powder is, for example, placed in a flexible mold, which is then positioned within a pressure vessel supplied with a pressurized fluid. The flexible mold is deformable, allowing the pressurized fluid to act directly on the powder and compress the aluminum scandium nitride particles into a target.

[0015] Preferably, the aluminum nitride scandium particles are hot-pressed at a pressure exceeding 90 MPa, more preferably at a pressure between 150 MPa and 250 MPa.

[0016] Furthermore, preferably, the aluminum nitride scandium particles are hot-pressed at a temperature exceeding 1600°C, more preferably at a temperature between 1750°C and 2200°C.

[0017] This will result in a target composed of ScAlN with a high density and homogeneous particle distribution.

[0018] In another embodiment of the method according to the invention, the scandium-aluminum alloy body is crushed by grinding the body.

[0019] In yet another embodiment of the method according to the invention, after the pulverization step, the scandium aluminum particles have a particle size of less than 10 micrometers, more preferably less than 1 micrometer.

[0020] This particle size ensures that the nitriding step of scandium aluminum particles results in scandium aluminum nitride particles.

[0021] In yet another embodiment of the method according to the invention, the aluminum scandium nitride target comprises at least 20 at% scandium.

[0022] In another embodiment of the method according to the present invention, aluminum scandium nitride particles are hot-pressed into an aluminum scandium nitride target having a relative density of more than 80%, more preferably more than 98%.

[0023] Using this high density, good absorption of the laser beam in a PLD process is achieved to allow for extended use of the target in the PLD process to deposit an aluminum nitride scandium film on a substrate. Simple Explanation of the Diagram

[0024] These and other features of the present invention are schematically illustrated in the accompanying drawings.

[0025] Figure 1 schematically illustrates the steps of one embodiment of the method according to the present invention.

[0026] Figures 2A and 2B illustrate the differences between a target manufactured according to the prior art and a target manufactured according to the method of the present invention in a PLD process. Implementation

[0027] In Figure 1, a scandium aluminum (ScAl) alloy body 1 is first provided. Then, for example, this ScAl body 1 is pulverized into one type of scandium aluminum particle powder 2 by grinding.

[0028] Next, ScAl powder 2 is fed into a fluidized bed reactor 3, where ammonia (NH3) is drawn in by a pump 4 while the temperature is maintained at, for example, 500ºC. This allows the particles of ScAl powder 2 to be nitrided into aluminum scandium nitride particles.

[0029] After a certain period of time, the scandium nitride particles are removed from the fluidized bed reactor 3 and placed in a flexible mold 5. The flexible mold 5 is placed in a pressure vessel 6, which is supplied with a suitable pressure P, so that the mold 5 is subjected to a balanced pressure. Therefore, the scandium aluminum nitride particles in the mold 5 will be compressed into a target 7.

[0030] Figure 2A schematically shows a target 10 according to one of the prior art, having individual scandium nitride particles 11 and aluminum nitride particles 12. Due to the different types of particles 11 and 12, voids 13 exist in the target 10.

[0031] When this prior art target 10 is irradiated with a laser beam 14, only a portion of the energy is absorbed by the particles 11 and 12. However, due to the band gap difference between scandium nitride and aluminum nitride, scandium nitride particles 11 are more likely to transfer into a plasma than aluminum nitride particles 12, and aluminum nitride particles 12 tend to escape from the target 10 as unwanted droplets 15.

[0032] Figure 2B schematically illustrates a target 20 manufactured according to the method of the present invention. The target 20 consists of a single type of particle 21, specifically, aluminum scandium nitride particles. Because a single type of particle can be better compressed into a target, the density of the target 20 is significantly higher than that of the prior art target 10. This has improved the absorption of the laser beam 22 that generates the plasma plume 23.

[0033] Because scandium aluminum nitride has a band gap that is one level lower than that of aluminum nitride, the laser beam 22 can more easily, reliably, and without producing droplets transfer the target material into a plasma plume 23.

[0034] 1: Scandium-aluminum (ScAl) alloy body 2:ScAl powder 3: Fluidized bed reactor 4: Pump 5: Flexible mold 6: Pressure Vessel 7: Target 10: Target 11: Scandium nitride particles 12: Aluminum nitride particles 13: Gap 14: Laser Beam 15: Droplets 20: Target 21: Particle 22: Laser Beam 23: Plasma feather P: Suitable pressure

Claims

1. A target for forming an aluminum scandium nitride film in a pulsed laser deposition process, the target comprising a target body having a particle size of less than 10 micrometers, and the target body comprising scandium, aluminum, and nitrogen.

2. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as claimed in claim 1, wherein the target comprises a relative density of more than 80%.

3. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as claimed in claim 2, wherein the target comprises a relative density of more than 98%.

4. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as claimed in claim 1, wherein the target comprises at least 20 at% scandium.

5. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as claimed in claim 4, wherein the target comprises up to 50 at% scandium.

6. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as described in claim 1, wherein the particle size is less than 1 micrometer.

7. A target for forming an aluminum scandium nitride film in a pulsed laser deposition process, the target comprising a target body formed of particles having a size of less than 10 micrometers, and the target body comprising scandium, aluminum, and nitrogen.

8. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as claimed in claim 7, wherein the target body comprises a relative density of more than 80%.

9. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as claimed in claim 8, wherein the target comprises a relative density of more than 98%.

10. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as claimed in claim 7, wherein the target comprises at least 20 at% scandium.

11. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as claimed in claim 10, wherein the target comprises up to 50 at% scandium.

12. The target for forming an aluminum scandium nitride film in a pulsed laser deposition process, as claimed in claim 7, wherein the target system is formed of particles having a size of less than 1 micrometer.

13. A system for executing a pulsed laser deposition (PLD) procedure, the system comprising: laser; And a target configured to provide scandium, aluminum, and nitrogen to form an aluminum scandium nitride film on a substrate via a PLD when the target is irradiated by the laser, the target including a target body having a particle size of less than 10 micrometers and the target body including scandium, aluminum, and nitrogen.

14. The system for performing a pulsed laser deposition (PLD) procedure as claimed in claim 13, wherein the target comprises a relative density of more than 80%.

15. The system for performing a pulsed laser deposition (PLD) procedure as claimed in claim 14, wherein the target comprises a relative density of more than 98%.

16. The system for performing a pulsed laser deposition (PLD) procedure as claimed in claim 13, wherein the target comprises at least 20 at% scandium.

17. The system for performing a pulsed laser deposition (PLD) procedure as claimed in claim 16, wherein the target comprises up to 50 at% scandium.

18. The system for performing a pulsed laser deposition (PLD) procedure as described in claim 13, wherein the particle size is less than 1 micrometer.

19. The system for performing a pulsed laser deposition (PLD) procedure as claimed in claim 13, wherein the band gap of the target is lower than the energy of the laser.

20. The system for performing a pulsed laser deposition (PLD) procedure as claimed in claim 19, wherein the laser is an ultraviolet laser.

Images