Plasma etching method

Abstract

Disclosed herein is an apparatus and method for plasma etching an additive-containing aluminum nitride film containing an additive element selected from the group consisting of scandium (Sc), yttrium (Y) or erbium (Er). The method includes placing a workpiece on a substrate support within a plasma chamber, the workpiece including a substrate having a metal film disposed thereon, an additive-containing aluminum nitride film deposited on the metal film, and a mask disposed on the additive-containing aluminum nitride film, the mask defines at least one trench; introducing a BCl3 gas into the chamber at a BCl3 flow rate in sccm as a unit; introducing an H2 gas into the chamber at an H2 flow rate in sccm; introducing an inert diluent gas into the chamber at an inert diluent gas flow rate in sccm; and establishing a plasma in the chamber to plasma etch the additive-containing aluminum nitride film exposed in the trench, wherein the ratio of the inert diluent gas flow rate to the BCl3 flow rate is in the range of 1: 3 to 1: 11, and the ratio of the BCl3 flow rate to the H2 flow rate is in the range of 11: 1 to 2: 1.

Description

[0001] This invention relates to a method for plasma etching, and more particularly to a method for plasma etching of aluminum nitride films containing additives, wherein the additive-containing aluminum nitride films contain additive elements selected from scandium (Sc), yttrium (Y), or erbium (Er). The invention also relates to related equipment for plasma etching such additive-containing aluminum nitride films.

[0002] Aluminum nitride (AlN) and aluminum scandium nitride (AlScN) piezoelectric devices are widely used in a range of RF technologies, such as bulk acoustic wave (BAW) devices, piezoelectric micromechanical ultrasonic transducers (PMUTs), Lamb wave profile mode resonators (CMRs), microphones, and sensors. Mobile phones typically incorporate multiple AlN and AlScN BAW devices, and achieving higher operating frequencies requires the use of thinner BAW devices. Improving the piezoelectric performance of thinner devices is a significant challenge as tolerances become increasingly stringent and device integration on circuit boards becomes more complex. Adding scandium (ScN) is known to improve the piezoelectric performance of BAW devices. However, several etching issues associated with AlScN exist, which are particularly problematic with high scandium content.

[0003] When using standard chlorine (Cl2) / argon (Ar) based chemicals, the etching rate typically decreases as the percentage of Sc in doped AlN increases. This decrease leads to lower selectivity for AlScN masks (e.g., photoresist or SiO2 masks), increasing the critical dimension (CD) and thus resulting in shallower sidewall angles within the AlScN trenches. Common methods for controlling the sidewall profile include adjusting the slope of the pre-etched mask, varying the platen bias, etchant gas flow rate, or process pressure. These methods are generally effective for AlScN with lower Sc contents, but at higher Sc percentages, the physicality of the etching becomes more pronounced, reducing the overall effectiveness of these methods. Similar effects have been observed with AlYN and AlErN films.

[0004] The reduced AlScN etching rate also decreases selectivity for the metal substrate, leading to increased substrate losses, which can impair the performance of some devices, such as BAW filters. The lower electrical contacts of BAW devices are typically made of molybdenum (Mo), tungsten (W), or platinum (Pt), and if excessive metal is removed, the contact resistance will increase due to the reduced AlScN etching rate, resulting in degraded device performance. Typical variations in the AlScN etching rate (such as increased platen bias or increased Cl2 flow) may ultimately have little effect on sidewall corners or substrate selectivity, or in some cases may even exacerbate the problem.

[0005] AlScN etching processes typically consist of two etching steps. The first step is a primary overall etching process, characterized by a high etch rate, good selectivity for the mask material, steep sidewall profiles, and minimal footing (for clarity, footing refers to the non-ideal deviation from an ideal flat surface at the base of the etched feature). This primary etching typically removes 80-85% of the material. The second step is a soft-landing etch step, which should have good selectivity for the underlying electrode. This is typically a low etch rate process. Since this process usually only etches 15-20% of the material, good selectivity can be achieved by sacrificing etch rate and etch profile.

[0006] In at least some embodiments of the present invention, the present invention seeks to improve AlScN:Mo selectivity to minimize electrode loss.

[0007] According to a first aspect of the present invention, a method for plasma etching an aluminum nitride film containing additives is provided, the aluminum nitride film containing additives containing an additive element selected from scandium (Sc), yttrium (Y), or erbium (Er), the method comprising the following steps:

[0008] A workpiece is placed on a substrate support within a plasma chamber. The workpiece includes a substrate having a metal film disposed thereon, an aluminum nitride film containing additives deposited on the metal film, and a mask disposed on the aluminum nitride film containing additives, the mask defining at least one trench.

[0009] BCl3 gas is introduced into the chamber at a flow rate of BCl3 in sccm;

[0010] H2 gas is introduced into the chamber at an H2 flow rate of sccm;

[0011] An inert dilution gas flow rate, measured in sccm, is used to introduce inert dilution gas into the chamber; and

[0012] Plasma is established within the chamber to plasma etch the additive-containing aluminum nitride film exposed within the trench;

[0013] The ratio of the inert diluent gas flow rate to the BCl3 flow rate is in the range of 1:3 to 1:11, and the ratio of the BCl3 flow rate to the H2 flow rate is in the range of 11:1 to 2.25:1.

[0014] In this way, selective modification of the metal substrate can be achieved. Selectivity can be defined as the etching rate of the aluminum nitride film containing additives / the etching rate of the metal film.

[0015] The ratio of the inert dilution gas flow rate to the BCl3 flow rate can be in the range of 1:5 to 1:6.

[0016] The ratio of BCl3 flow rate to H2 flow rate can be in the range of 5.7:1 to 3.8:1.

[0017] The flow rate of BCl3 can be in the range of 90 to 110 sccm, the flow rate of inert dilution gas can be in the range of 10 to 30 sccm, and the flow rate of H2 gas can be in the range of 10 to 40 sccm.

[0018] During the plasma etching step, an RF bias signal with a power range of 500-700W can be applied to the substrate support.

[0019] According to a second aspect of the present invention, a method for plasma etching an aluminum nitride film containing additives is provided, the aluminum nitride film containing additives containing an additive element selected from scandium (Sc), yttrium (Y), or erbium (Er), the method comprising the following steps:

[0020] A workpiece is placed on a substrate support within a plasma chamber. The workpiece includes a substrate having a metal film disposed thereon, an aluminum nitride film containing additives deposited on the metal film, and a mask disposed on the aluminum nitride film containing additives, the mask defining at least one trench.

[0021] A first plasma etching step is performed, wherein BCl3 gas, Cl2 gas, and an inert dilution gas are introduced into the chamber, and plasma is established within the chamber to plasma etch most of the additive-containing aluminum nitride film exposed within the trench; and

[0022] Perform a second plasma etching step to plasma etch the remaining additive-containing aluminum nitride film exposed within the trench to reveal the metal film, the second plasma etching step comprising:

[0023] BCl3 gas is introduced into the chamber at a flow rate of BCl3 in sccm;

[0024] H2 gas is introduced into the chamber at an H2 flow rate of sccm;

[0025] An inert dilution gas flow rate, measured in sccm, is used to introduce inert dilution gas into the chamber; and

[0026] Plasma is established within the chamber to plasma etch the additive-containing aluminum nitride film exposed within the trench;

[0027] During the second plasma etching step, the ratio of the inert dilution gas flow rate to the BCl3 flow rate is in the range of 1:3 to 1:11, and the ratio of the BCl3 flow rate to the H2 flow rate is in the range of 11:1 to 2.25:1.

[0028] The second plasma etching step is performed separately from the first plasma etching step. In one embodiment, the second plasma etching step is performed immediately after the first plasma etching step. The second plasma etching step may include any features of the method of the first aspect of the present invention.

[0029] In one embodiment, Cl2 gas is not introduced into the chamber during the second plasma etching step.

[0030] The inert diluent gas can be argon, and the metal film can be a molybdenum film.

[0031] The mask may be a photoresist mask.

[0032] Plasma can be inductively coupled plasma (ICP).

[0033] The substrate can be a semiconductor substrate, such as a silicon substrate.

[0034] Aluminum nitride films containing additives can be made from Al x Sc y N is defined as an aluminum nitride scandium film, where x + y = 1; and where the scandium content y is at least 0.35.

[0035] According to a third aspect of the invention, an apparatus is provided for etching an additive-containing aluminum nitride film by mask plasma etching, the additive-containing aluminum nitride film containing an additive element selected from scandium (Sc), yttrium (Y), or erbium (Er), the apparatus comprising:

[0036] chamber;

[0037] A substrate support is disposed within the cavity;

[0038] A gas delivery system for introducing BCl3 gas with a flow rate of BCl3 in sccm, H2 gas with a flow rate of H2 in sccm, and inert dilution gas with a flow rate of inert dilution gas in sccm into the chamber.

[0039] A plasma generating apparatus for maintaining plasma within a chamber for etching a workpiece comprising a substrate having a metal film disposed thereon, an aluminum nitride film containing additives deposited on the metal film, and a mask disposed on the aluminum nitride film containing additives, the mask defining at least one trench; and

[0040] A controller configured to control the device to perform plasma etching to etch the additive-containing aluminum nitride film exposed within the trench, wherein the controller controls the gas delivery system to maintain the ratio of the inert dilution gas flow rate to the BCl3 flow rate in the range of 1:3 to 1:11, and the ratio of the BCl3 flow rate to the H2 flow rate in the range of 11:1 to 2:1.

[0041] According to a fourth aspect of the invention, an apparatus is provided for etching an additive-containing aluminum nitride film by mask plasma etching, the additive-containing aluminum nitride film containing an additive element selected from scandium (Sc), yttrium (Y), or erbium (Er), the apparatus comprising:

[0042] chamber;

[0043] A substrate support is disposed within the cavity;

[0044] A gas delivery system for introducing BCl3 gas, Cl2 gas, H2 gas and inert dilution gas into the chamber;

[0045] A plasma generating apparatus for maintaining plasma within a chamber for etching a workpiece comprising a substrate having a metal film disposed thereon, an aluminum nitride film containing additives deposited on the metal film, and a mask disposed on the aluminum nitride film containing additives, the mask defining at least one trench; and

[0046] A controller is configured to control the device to perform the following steps:

[0047] A first plasma etching step involves introducing BCl3 gas, Cl2 gas, and an inert dilution gas into the chamber, and establishing plasma within the chamber to plasma etch most of the additive-containing aluminum nitride film exposed within the trenches.

[0048] In the second plasma etching step, BCl3 gas, H2 gas, and an inert dilution gas are introduced into the chamber such that during the second plasma etching step, the ratio of the inert dilution gas flow rate to the BCl3 flow rate is in the range of 1:3 to 1:11, and the ratio of the BCl3 flow rate to the H2 flow rate is in the range of 11:1 to 2:1, and plasma is established in the chamber to etch the remaining additive-containing aluminum nitride film exposed in the trench to reveal the metal film.

[0049] While the invention has been described above, it encompasses any inventive combination of features set forth in the description, drawings, or claims above or below. For example, any feature disclosed with respect to one aspect of the invention may be combined with any feature disclosed with respect to any other aspect of the invention.

[0050] Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0051] Figure 1 This is a schematic diagram of a plasma etching apparatus used to etch aluminum nitride films containing additives.

[0052] Figure 2 This is a schematic diagram of the steps associated with a method according to an embodiment of the present invention; and

[0053] Figure 3 These are schematic cross-sectional views of the workpiece (a) before etching and (b) after etching.

[0054] Refer to the attached diagram. Figure 1 A schematic diagram of an apparatus 10 for plasma etching of a workpiece 11 is provided, and includes a processing chamber 12 in which plasma etching of the workpiece 11 is performed.

[0055] The device 10 further includes a substrate support 13. The substrate support may be a platen assembly 13, which may also be formed of a metal such as aluminum, and is disposed within the chamber 12, but electrically isolated from the chamber wall 12a by a conventional component such as a ceramic circuit breaker 14. The substrate support may also include an electrostatic chuck (ESC) that can be attached to the surface of the platen assembly. The platen assembly 13 includes a body 13a having a support surface 13b for receiving a workpiece 11, and is electrically biased using a radio frequency (RF) voltage generator 21. For example, providing a negative bias voltage to the platen assembly 13 can help control the positively charged ion bombardment of the plasma on the surface of the workpiece 11.

[0056] The processing chamber 12 includes a chamber wall 12a, which may be formed of a metal such as aluminum and is generally electrically grounded. The chamber 12 further includes a first gas inlet 15a, a second gas inlet 15b, a third gas inlet 15c, and a fourth gas inlet 15d, through which sources of BCl3 gas, Cl2 gas, an inert diluent gas (e.g., argon), and H2 gas (not shown) can be fluidly coupled to introduce the gases into the chamber 12. The chamber 12 further includes an outlet 16 through which the gases and any byproducts of the etching process can be discharged from the chamber 12.

[0057] In one embodiment, the plasma is inductively coupled plasma (ICP) generated by applying an RF voltage from an RF voltage generator 17 to one or more antennas 18 disposed around a chamber 12 and near corresponding dielectric window segments 12b formed in the chamber wall 12a. The one or more antennas 18 may comprise, for example, a generally planar helical configuration, a helical coil configuration, or a ring configuration, and, as in standard practice, impedance matching of the RF signal from the generator 17 with the antennas 18 is performed to minimize reflections of electrical power from the antennas 18. The antennas 18 are positioned around the chamber 12, and electrical power is inductively coupled into the chamber 12 through the dielectric window segments 12b. However, in an alternative embodiment not shown, the plasma may be generated using a so-called immersion ICP coil comprising an antenna formed in a helical configuration extending within and around a ring-shaped ceramic housing, which is “immersed” within the plasma chamber 12.

[0058] Plasma is generated in zone 19 of chamber 12, positioned above workpiece 11, thus exposing workpiece 11 to the plasma. The flow rate of process gas into chamber 12 is controlled via corresponding flow regulators or mass flow controllers 20a, 20b, 20c, 20d coupled to corresponding inlets 15a, 15b, 15c, 15d, and the inlets 15a, 15b, 15c, 15d and outlet 16 of chamber 12 are positioned on opposite sides of plasma zone 19, such that the etching gas required to pass through chamber 12, through zone 19, and over workpiece 11 to outlet 16. An example of a suitable apparatus for carrying out the invention is the Synapse (RTM) module manufactured by the applicant, SPTS Technologies Limited.

[0059] Refer to the attached diagram. Figure 2 A flowchart is shown, outlining the steps associated with a method 100 for plasma etching of an additive-containing aluminum nitride film according to an embodiment of the present invention. The method will be described with reference to AlScN films, but those skilled in the art will recognize that the method is equally applicable to AlYN and AlErN films.

[0060] The method includes placing the workpiece 11 on a pressure plate 13 within the plasma chamber 12 at step 101. (Refer to the accompanying drawings.) Figure 3 The workpiece 11 includes a substrate 11a, such as a silicon wafer substrate, on which a metal film layer 11b, such as a molybdenum film, is deposited. For example, a piezoelectric AlScN film 11c is deposited on the metal film layer 11b using pulsed DC sputtering technology. In one embodiment, the film contains Al 0.65 Sc 0.35N, meaning the film contains 65% aluminum and 35% scandium. The film composition is typically determined using energy-dispersive X-ray analysis (EDAX). The workpiece 11 further includes a mask 11d, which is patterned using a 4-4.4 mm photoresist to form 5 μm-100 μm trenches 11e on the film 11c.

[0061] With the workpiece 11 positioned on the pressure plate 13 within the chamber 12, at step 102, BCl3 gas, Cl2 gas, and inert dilution gas are introduced into the chamber 12 via the corresponding inlets 15a-c using appropriate flow regulators 20a-c, and the pressure within the chamber 12 is maintained at approximately 2-5 mTorr or approximately 2 mTorr by a pressure regulator (not shown). Once the chamber 12 is properly conditioned with gas, at step 103, an RF potential is applied to the antenna 18 via generator 17 to inductively couple electrical power into the gas, thereby initiating plasma and initiating Al... 0.65 Sc 0.35 Etching of the N film. At step 104, a bias voltage is also applied to the platen assembly 13 using a voltage generator 21 (typically operating at 13.56 MHz) to provide a bias voltage to the Al film at step 105. 0.65 Sc 0.35 Etching of N-film 11c.

[0062] In the first plasma etching step or the main etching step, antenna 18 is powered at approximately 1000 W, and pressure plate 13 is powered at approximately 1300 W. Flow regulator 20a is arranged to deliver BCl3 into chamber 12 at a flow rate of approximately 25 sccm, and Cl2 gas into chamber 12 at a rate of approximately 25 sccm, as determined by flow regulator 20b. Similarly, an inert dilution gas is introduced into chamber 12 at a rate of approximately 25 sccm, as determined by flow regulator 20c. In this respect, the flow rate ratio of BCl3 gas to Cl2 gas entering chamber 12 is approximately 1:1, and the flow rate ratio of BCl3 gas to Ar gas entering chamber 12 is approximately 1:1. Using these process conditions, most of the Al can be easily etched during the main etching step 100. 0.65 Sc 0.35 N-film 11c is used to provide suitable productivity. This main step provides good selectivity for the mask and steep trench sidewalls. However, once most of the Al... 0.65 Sc 0.35 If the N-film 11c has been etched, it is beneficial to stop the main etching step 100 and begin the second etching step, or so-called "soft landing" step 200, in order to minimize any unwanted etching of the underlying metal film layer 11b. The soft landing step is typically a low etching rate process.

[0063] The soft landing step 200 typically utilizes a lower platen bias to reduce the etch rate of the underlying layer and the subsequent loss of the metal film layer 11b. Referring to Table 1 (below), it is clear that during the main etching, the electrical power supplied to the plasma generation device 17 is approximately twice that during the soft landing etching. Similarly, during the soft landing etching, the platen 13 is supplied with approximately 50% of the electrical power compared to the main etching.

[0064] parameter Main Etching soft landing Pressure (mTorr) 2 3 Source power (W) 1000 500 Pressure plate power (W) 1300 550 <![CDATA[BCl3 flow rate (sccm)]]> 25 102 <![CDATA[Cl2 flow rate (sccm)]]> 25 0 Ar flow rate (sccm) 25 18 <![CDATA[Flow rate of H2 (sccm)]]> 0 See Table 2

[0065] Table 1

[0066] During the soft landing step of the method according to an embodiment of the invention, inlet 15b is closed at step 201 to prevent Cl2 gas from entering the chamber, and inlets 15a and 15c-d are opened at step 202 to introduce BCl3, a diluted inert gas (e.g., argon), and H2 gas into chamber 12, respectively. The pressure within chamber 12 is maintained at approximately 2-5 mTorr or generally 3 mTorr by a pressure regulator (not shown). Once chamber 12 is properly conditioned with gas, an RF potential is applied to antenna 18 via generator 17 at step 203 to inductively couple electrical power into the gas, thereby initiating plasma and beginning the etching of residual Al within trench 11e. 0.65 Sc 0.35 N film. Similar to the main etching steps, at step 204, a bias voltage is also applied to the platen assembly 13 using a voltage generator 21 (typically operating at 13.56 MHz) to provide a bias voltage to the residual Al at step 205. 0.65 Sc 0.35 Etching of N-film 11c.

[0067] Flow regulator 20a is configured to deliver BCl3 into chamber 12 at a flow rate of approximately 102 sccm, and argon gas into chamber 12 at a rate of approximately 18 sccm, as determined by flow regulator 20c. To demonstrate the effect of H2 gas on the selectivity of AlScN:Mo, a soft-landing procedure was performed using regulator 20d with three different H2 flow rates entering the chamber, as shown in Table 2 below.

[0068]

[0069] Table 2

[0070] During the first process (process 1), which serves as a control, no H2 is introduced into the chamber. During this process, the AlScN etching rate is approximately 107 nm / min, and the Mo etching rate is approximately 35 nm / min. During process 2, H2 gas is introduced at a flow rate of approximately 18 sccm, resulting in a reduced AlScN etching rate of approximately 97 nm / min and a reduced Mo etching rate of approximately 24 nm / min. As the H2 flow rate is further increased to 27 sccm in process 3, the AlScN etching rate further decreases to approximately 87 nm / min, and the Mo etching rate further decreases to 20 nm / min.

[0071] The results show that the AlScN:Mo selectivity increases with increasing H2 gas flow rate into the chamber. It is believed that BCl3 gas dissociates into BCl2, BCl, Cl, and B, and H2 reacts with Cl to form HCl, which reduces the amount of available Cl and significantly decreases the Mo etching rate. On the other hand, the reduction in the AlScN etching rate is less than that of the Mo etching rate because, in this process, the abundant sputtering of boron contributes to the AlCl-based... x The sputtering of ScCl3 byproducts maintains the AlScN etching rate. For the electrode, i.e. the underlayer 11b formed on the bottom side of the piezoelectric film 11c, which is easily etched in chlorine-based chemicals (e.g., Mo), it was found that reducing the presence of Cl2 and introducing H2 gas into the chamber reduces the underlayer etching rate.

[0072] Therefore, the process of etching workpiece 11 (which comprises an AlScN film 11c deposited on a Mo film 11b) includes a main etching step 100 and a soft-landing etching step 200. The main etching step is used to etch trenches through most of the AlScN film 11c, while the soft-landing etching step occurs immediately after the main etching step 100 and begins before the trenches extend from the AlScN layer 11c. Since H2 gas is introduced into chamber 12 during the soft-landing step, it has been demonstrated above that improved selectivity of the lower electrode metal film can be achieved.

Claims

1. A method for plasma etching an aluminum nitride film containing additives, wherein the aluminum nitride film containing additives contains an additive element selected from scandium (Sc), yttrium (Y), or erbium (Er), the method comprising the following steps: A workpiece is placed on a substrate support within a plasma chamber. The workpiece includes a substrate having a metal film disposed thereon, an aluminum nitride film containing additives deposited on the metal film, and a mask disposed on the aluminum nitride film containing additives, the mask defining at least one trench. BCl3 gas is introduced into the chamber at a flow rate of BCl3 in sccm; H2 gas is introduced into the chamber at an H2 flow rate of sccm; An inert dilution gas flow rate, measured in sccm, is used to introduce inert dilution gas into the chamber; and Plasma is established within the chamber to plasma etch the additive-containing aluminum nitride film exposed within the trench; The ratio of the inert diluent gas flow rate to the BCl3 flow rate is in the range of 1:3 to 1:11, and the ratio of the BCl3 flow rate to the H2 flow rate is in the range of 11:1 to 2:

1.

2. The method according to claim 1, wherein the ratio of the inert diluent gas flow rate to the BCl3 flow rate is in the range of 1:5 to 1:

6.

3. The method according to claim 1 or claim 2, wherein the ratio of the BCl3 flow rate to the H2 flow rate is in the range of 5.7:1 to 3.8:

1.

4. The method according to any one of claims 1 to 3, wherein the BCl3 flow rate is in the range of 90 to 110 sccm.

5. The method according to any one of claims 1 to 4, wherein the inert diluent gas flow rate is in the range of 10 to 30 sccm.

6. The method according to any one of claims 1 to 4, wherein the H2 gas flow rate is in the range of 10 to 40 sccm.

7. The method according to any of the preceding claims, wherein during the plasma etching step, an RF bias signal with a power in the range of 500-700W is applied to the substrate support.

8. A method for plasma etching an aluminum nitride film containing additives, wherein the aluminum nitride film containing additives contains an additive element selected from scandium (Sc), yttrium (Y), or erbium (Er), the method comprising the following steps: A workpiece is placed on a substrate support within a plasma chamber. The workpiece includes a substrate having a metal film disposed thereon, an aluminum nitride film containing additives deposited on the metal film, and a mask disposed on the aluminum nitride film containing additives, the mask defining at least one trench. A first plasma etching step is performed, wherein BCl3 gas, Cl2 gas, and an inert dilution gas are introduced into the chamber, and plasma is established within the chamber to plasma etch most of the additive-containing aluminum nitride film exposed within the trench; and Perform a second plasma etching step to plasma etch the remaining additive-containing aluminum nitride film exposed within the trench to reveal the metal film, the second plasma etching step comprising: BCl3 gas is introduced into the chamber at a flow rate of BCl3 in sccm; H2 gas is introduced into the chamber at an H2 flow rate of sccm; An inert dilution gas flow rate, measured in sccm, is used to introduce inert dilution gas into the chamber; and Plasma is established within the chamber to plasma etch the additive-containing aluminum nitride film exposed within the trench; During the second plasma etching step, the ratio of the inert dilution gas flow rate to the BCl3 flow rate is in the range of 1:3 to 1:11, and the ratio of the BCl3 flow rate to the H2 flow rate is in the range of 11:1 to 2.25:

1.

9. The method of claim 8, wherein the second plasma etching step further comprises the method of any one of claims 2 to 7.

10. The method of claim 8 or 9, wherein the second plasma etching step is performed separately from the first plasma etching step.

11. The method according to any one of claims 8 to 10, wherein the second plasma etching step is performed immediately after the first plasma etching step.

12. The method according to any one of claims 8 to 11, wherein Cl2 gas is not introduced into the chamber during the second plasma etching step.

13. The method according to any of the preceding claims, wherein the inert diluent gas is argon.

14. The method according to any of the preceding claims, wherein the metal film is a molybdenum film.

15. The method according to any of the preceding claims, wherein the mask is a photoresist mask.

16. The method according to any of the preceding claims, wherein the plasma is inductively coupled plasma (ICP).

17. The method according to any of the preceding claims, wherein during the plasma etching of the additive-containing aluminum nitride film exposed in the trench, the pressure within the plasma chamber is in the range of 2-5 millitors.

18. The method according to any of the preceding claims, wherein the substrate is a semiconductor substrate, optionally a silicon substrate.

19. The method according to any preceding claim, wherein the aluminum nitride film containing the additive is made of formula Al x Sc y N is defined as an aluminum scandium nitride film, where x + y = 1; and where the scandium content y is at least 0.

35.

20. An apparatus for etching an additive-containing aluminum nitride film by mask plasma etching, the additive-containing aluminum nitride film containing an additive element selected from scandium (Sc), yttrium (Y), or erbium (Er), the apparatus comprising: chamber; A substrate support is disposed within the cavity; A gas delivery system for introducing BCl3 gas with a flow rate of BCl3 in sccm, H2 gas with a flow rate of H2 in sccm, and inert dilution gas with a flow rate of inert dilution gas in sccm into the chamber. A plasma generating apparatus for maintaining plasma within a chamber for etching a workpiece comprising a substrate having a metal film disposed thereon, an aluminum nitride film containing additives deposited on the metal film, and a mask disposed on the aluminum nitride film containing additives, the mask defining at least one trench; and A controller configured to control the device to perform plasma etching to etch the additive-containing aluminum nitride film exposed within the trench, wherein the ratio of the inert dilution gas flow rate to the BCl3 flow rate is in the range of 1:3 to 1:11, and the ratio of the BCl3 flow rate to the H2 flow rate is in the range of 11:1 to 2.25:

1.

21. An apparatus for etching an additive-containing aluminum nitride film by mask plasma etching, the additive-containing aluminum nitride film containing an additive element selected from scandium (Sc), yttrium (Y), or erbium (Er), the apparatus comprising: chamber; A substrate support is disposed within the cavity; A gas delivery system for introducing BCl3 gas, Cl2 gas, H2 gas and inert dilution gas into the chamber; A plasma generating apparatus for maintaining plasma within a chamber for etching a workpiece comprising a substrate having a metal film disposed thereon, an aluminum nitride film containing additives deposited on the metal film, and a mask disposed on the aluminum nitride film containing additives, the mask defining at least one trench; and A controller is configured to control the device to perform the following steps: A first plasma etching step involves introducing BCl3 gas, Cl2 gas, and an inert dilution gas into the chamber, and establishing plasma within the chamber to plasma etch most of the additive-containing aluminum nitride film exposed within the trenches. In the second plasma etching step, BCl3 gas, H2 gas, and an inert dilution gas are introduced into the chamber such that the ratio of the inert dilution gas flow rate to the BCl3 flow rate is in the range of 1:3 to 1:11, and the ratio of the BCl3 flow rate to the H2 flow rate is maintained in the range of 11:1 to 2.25:

1. Plasma is established in the chamber to etch the remaining additive-containing aluminum nitride film exposed in the trench to reveal the metal film.

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