Plasma etching method

Abstract

The etching method for aluminum scandium nitride films is improved to minimize wear on the underlying electrode and eliminate the need for fitting. [Solution] An RF power source is used to supply power to the plasma etching chamber, bias power is applied to the platen assembly, and a switched process is used to bulk etch an additive-containing aluminum nitride film through a photoresist mask. The switched process consists of two steps: one in which the film is plasma-etched by supplying a chlorine-based etching gas and an inert diluent gas at equal flow rates to the plasma etching chamber at a target chamber pressure; and the other in which the film is plasma-etched using the same chlorine-based etching gas and inert diluent gas at the same target chamber pressure, with the flow rate of the inert diluent gas being at least four times that of the chlorine-based etching gas. These steps are repeated and alternated.

Description

Technical Field

[0001] The present invention relates to a plasma etching method, particularly a method for plasma etching an additive-containing aluminum nitride film. The present invention also relates to an apparatus for plasma etching an additive-containing aluminum nitride film.

Background Art

[0002] Aluminum scandium nitride (AlScN) is a piezoelectric material used in a wide range of applications, including bulk acoustic wave (BAW) filters, microphones, and sensors for communication (e.g., 5G). Improving the piezoelectric performance of devices (particularly thinning of the devices) is a major challenge due to tighter tolerances and more complex device integration on circuit boards.

[0003] One of the main processes in device manufacturing is etching the aluminum scandium nitride layer so that it stops on the lower molybdenum electrode while minimizing electrode loss. Generally, a two-stage etching process is used when landing (accreting) on ​​the molybdenum electrode. A bulk etching process, which is optimized in terms of aluminum scandium nitride etching rate and selectivity against the resist mask, is followed by a soft landing etching process that has high selectivity against molybdenum but a lower aluminum scandium nitride etching rate. Typically, 85-90% of the aluminum scandium nitride film is removed by bulk etching. Switching to the soft landing process reduces molybdenum loss throughout the etching process. Etching is usually performed through a mask that defines the etching area (i.e., trench). Ideally, etching should produce steep sidewalls within the aluminum scandium nitride layer with minimal footing (base formation) or microtrenching (fine groove formation) and without redeposition. When footing occurs, there is a difference in etching rate between the area near the mask and the area far from the mask, and it is necessary to eliminate the additional etching time that leads to unwanted molybdenum loss. The cause of foot formation is thought to be glung (low-angle incidence) of ions from the mask sidewall and / or delay in sputtering of etching byproducts from the sidewall. The cause of microtrenching is a localized increase in etching rate near the sidewall at the bottom of the trench due to ion reflection from the trench sidewall. Microtrenching results in uneven etching of the aluminum scandium nitride layer and can also lead to unwanted molybdenum loss.

[0004] While primary etching can be controlled to produce steep sidewalls without redeposition and avoid footing, soft-landing etching can lead to footing. Footing (i.e., caused by the etching depth lag between the vicinity of the mask and the area far from the mask) tends to become more pronounced as the scandium content and thickness of the aluminum scandium nitride layer increase. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-91411 [Overview of the project] [Problems that the invention aims to solve]

[0006] In this technical field, there is a need to improve the etching method for aluminum scandium nitride films to minimize wear on the underlying electrode and eliminate the need for footing, particularly when using a photoresist mask. While eliminating footing is necessary to ensure device performance, it has been found difficult to achieve this without additional etching, which tends to increase wear on the lower electrode and is therefore undesirable. [Means for solving the problem]

[0007] In a first aspect of the present invention, a method for inductively coupled plasma etching of an additive-containing aluminum nitride film is provided, wherein the additive is selected from scandium, yttrium, and erbium. The method involves placing a workpiece comprising a substrate on which the aluminum nitride film is deposited, and a photoresist mask disposed on the film, on a platen assembly in a plasma etching chamber, supplying power to the plasma etching chamber with an RF power source, applying bias power to the platen assembly, and bulk etching the additive-containing aluminum nitride film through the photoresist mask using a switched process, wherein the switched process involves repeatedly alternating between (i) plasma etching the film by supplying substantially equal flow rates of a chlorine-based etching gas and an inert diluent gas to the plasma etching chamber at a target chamber pressure, and (ii) plasma etching the film using the same chlorine-based etching gas and inert diluent gas at the same target chamber pressure, wherein the flow rate of the inert diluent gas is at least four times that of the chlorine-based etching gas.

[0008] Optionally, in this method, the bias power for the platen assembly is increased during process (i). Advantageously, this avoids redeposition buildup on the sides of the etched features.

[0009] Optionally, the alternation between processes (i) and (ii) can occur every 2 to 6 seconds.

[0010] Optionally, the substrate comprises a silicon wafer, the silicon wafer supports a molybdenum electrode layer, and the molybdenum electrode layer lies between the wafer and an additive-containing aluminum nitride film.

[0011] Optionally, the chlorine-based gas may be one that contains chlorine.

[0012] Optionally, the inert diluent gas may contain argon.

[0013] Optionally, the plasma etching chamber can be powered with RF power in the range of 600 to 1200 W.

[0014] Optionally, a bias power of 800-1400W is applied to the platen assembly.

[0015] Optionally, increase the bias power by 200-500W during process (i).

[0016] Optionally, the plasma etching chamber can be kept at a pressure within the range of 2-5 mTorr during the bulk etching of the additive-containing aluminum nitride film.

[0017] Optionally, in this method, during step (i), a chlorine-based etching gas and an inert diluent gas are introduced into the plasma etching chamber at a flow rate of approximately 30 to 70 sccm.

[0018] Optionally, in this method, during step (ii), a chlorine-based etching gas is introduced into the plasma etching chamber at a flow rate of approximately 60 to 120 sccm, and an inert diluent gas is introduced into the plasma etching chamber at a flow rate of approximately 5 to 25 sccm.

[0019] Optionally, in this method, after bulk etching, a chlorine-based etching gas containing boron trichloride and chlorine in a 1:1 ratio, and an inert diluent gas containing argon are used in a soft-landing process to plasma etch the remaining additive-containing aluminum nitride film, thereby removing the microtrenches (fine grooves) created by bulk etching in this soft-landing process.

[0020] Optionally, the profile of the photoresist mask can be set to less than 75 degrees.

[0021] Optionally, the additive-containing aluminum nitride film contains scandium and is formulated as Al x Sc y N is defined by x+y=1, and its scandium component ratio y is set to 0.25 or higher, optionally approximately 0.4 (this indicates that the amount of scandium in the film is 25-40% or more).

[0022] Optionally, the aluminum nitride film may have depth, and when bulk etching the additive-containing aluminum nitride film, bulk etching may be performed over at least 85% of its depth.

[0023] In a second aspect of the present invention, an inductively coupled plasma apparatus for plasma etching an additive-containing aluminum nitride film, wherein the additive is selected from scandium, yttrium, and erbium, comprising an ICP plasma etching chamber, a platen assembly disposed within the plasma etching chamber and configured to receive a workpiece comprising a substrate on which the aluminum nitride film is deposited, and a photoresist mask disposed on the film, and a gas supply system for supplying a chlorine-based etching gas and an inert diluent gas into the plasma etching chamber, and the aluminum nitride film of the workpiece The present invention provides a device comprising: a plasma generator that maintains plasma within its plasma etching chamber for etching a material film; and a controller configured to control the device to perform bulk plasma etching of an aluminum nitride film through a photoresist mask according to a switched process, wherein the switched process involves repeatedly alternating between a first step of supplying substantially equal amounts of chlorine-based etching gas and inert diluent gas into the plasma etching chamber, and a second step of supplying at least twice the amount of inert diluent gas compared to the chlorine-based etching gas into the plasma etching chamber.

[0024] Hereinafter, exemplary embodiments of the present invention will be described solely by way of example with reference to the accompanying drawings below.

Brief Description of the Drawings

[0025] [Figure 1] It is a figure which shows the apparatus for plasma-etching an aluminum scandium nitride film. [Figure 2] It is a workpiece provided with an aluminum scandium nitride film and shows the state before etching. [Figure 3] It is a figure which shows the workpiece of FIG. 2 after being etched and having a footing. [Figure 4] It is a figure which shows the workpiece of FIG. 2 after being etched and having a microtrench. [Figure 5] It is a figure which shows the workpiece of FIG. 2 after being etched without any footing or microtrench. [Figure 6] It is a flowchart of a method for etching an aluminum scandium nitride film.

Mode for Carrying Out the Invention

[0026] Of the drawings, FIG. 1 provides a schematic depiction of an apparatus 10 for plasma-etching a workpiece 11. The apparatus 10 is an inductively coupled plasma (ICP) etching apparatus and includes a plasma etching chamber 12 inside which plasma etching of the workpiece 11 is performed.

[0027] The apparatus 10 further includes a substrate support 13. The substrate support can be a platen assembly 13, which can be further made of a metal such as aluminum and disposed inside the chamber 12, but is electrically separated from the chamber wall 12a by a conventional means such as a ceramic break 14.

[0028] Furthermore, the substrate support can be equipped with an electrostatic chuck (ESC) and mounted on the surface of the platen assembly. The platen assembly 13 has a body 13a with a support surface 13b for receiving the workpiece 11 and is electrically biased using a radio frequency (RF) voltage generator. For example, supplying a negative bias voltage to the platen assembly 13 can be used to control the emission of positively charged ions from the plasma onto the surface of the workpiece 11.

[0029] The plasma etching chamber 12 is equipped with a chamber wall 12a, which may be made of a metal such as aluminum and is usually electrically grounded. The chamber 12 is further equipped with first, second, and third gas inlets 15a, 15b, and 15c through which a corresponding chlorine (Cl) gas source, boron trichloride (BCl3) gas source, or inert diluent gas source such as argon gas source can be fluid-coupled and introduced into the chamber 12. Some or all of these gases can be used at various stages of the process. The chamber 12 is further equipped with an outlet 16 through which these gases and any byproducts of the etching process can be released from the chamber 12.

[0030] In one embodiment, the plasma is an ICP plasma generated by applying an RF voltage from an RF voltage generator 17 to one or more antennas 18, the antennas 18 being arranged around a chamber 12 and located near individual dielectric windows 12b formed within the chamber wall 12a. The one or more antennas 18 can have, for example, a substantially flat spiral configuration, a helical coil configuration, or a toroidal configuration, and reflection of power from the antennas 18 can be minimized by impedance matching of the RF signal from the generator 17 to the antennas 18 according to standard practice. The antennas 18 are positioned around the chamber 12, and their power is inductively coupled into the chamber 12 through the dielectric windows 12b.

[0031] Since the plasma is generated in region 19 of the chamber 12, i.e., the region above the workpiece 11, the workpiece 11 is exposed to the plasma. Some or all of the process gas is introduced into the chamber 12 through individual flow regulators 20a, 20b, and 20c coupled to individual inlets 15a, 15b, and 15c, and since the inlets 15a, 15b, and 15c of the chamber 12 and the outlet 16 are on opposite sides of the plasma region 19, the etching gas inevitably passes through region 19 and over the workpiece 11 to the outlet 16 as it passes through the chamber 12.

[0032] An alternative device used to carry out the present invention is the Synapse® module, manufactured by the applicant, SPTS Technologies Limited (Newport, UK).

[0033] In this exemplary embodiment, the workpiece 11 (see Figure 2) comprises a 200 mm silicon wafer 101, the wafer 101 supporting a 200 nm thick molybdenum electrode layer 103, on which a 1000 nm thick aluminum scandium nitride film 105 is deposited. The molybdenum and aluminum scandium nitride films in this exemplary embodiment were deposited using a Sigma® fxP® physical vapor deposition (PVD) tool. The workpiece is patterned with a photoresist mask 107, which defines etching trenches 109. In this exemplary embodiment, the photoresist mask defines approximately 15% of the aperture area (however, in other examples, a narrower or wider aperture area may be defined). The mask is adjusted by known means to achieve a mask profile of less than 75° (i.e., a shallow angle) to prevent etching byproduct buildup on the sidewalls of the etched features. In other examples, the workpiece may include wafers of other sizes, substrates other than silicon, electrodes other than molybdenum, layers of different depths, or additional layers. In this exemplary embodiment, the scandium content in the aluminum scandium nitride layer is approximately 35%, but as can be seen, the principles of the present invention are equally applicable to other component ratio levels, for example, those with a scandium content of 25% to 45%.

[0034] The effect of footing in this type of workpiece is shown in Figure 3. In some conventional etching methods, footing occurs because buildup 111 occurs near the trench sidewalls 113 due to the difference in etching rate between the area near the mask and the area far from the mask.

[0035] The effect of microtrenching in such workpieces is shown in Figure 4. In some conventional etching methods, microtrenches 115 are formed near the trench sidewalls due to ion reflection from the trench sidewalls at the trench bottom. The aim of the present invention is to eliminate the effects of fitting and microtrenching during etching of aluminum scandium nitride films.

[0036] According to the method of the present invention, a trench with a flat bottom is formed by etching, as shown in Figure 5, and fitting and micro-trenching are completely eliminated.

[0037] Although the methods according to the present invention will be demonstrated with reference to aluminum scandium nitride films, as will be apparent to the experienced reader, these methods are equally applicable to aluminum yttrium nitride (AlYN) films and aluminum erbium nitride (AlErN) films.

[0038] In this exemplary embodiment of the plasma etching method for an aluminum scandium nitride film 105 (Figure 6), at 201, a workpiece 11 is placed on a platen assembly 13 in a plasma etching chamber 12. In this method, at 203, the plasma etching chamber is powered by an RF power source, and plasma is generated from the gas supplied to the plasma etching chamber. In this method, at 205, bias power is applied to the platen assembly. In this method, at 207, the aluminum scandium nitride film is bulk etched through a photoresist mask using a switched process; the switched process consists of repeatedly alternating between a step of plasma etching the film by supplying substantially equal amounts of chlorine-based etching gas and inert diluent gas to the plasma etching chamber, and a step of plasma etching the film using the same chlorine-based etching gas and inert diluent gas, but with at least twice the amount of inert diluent gas compared to the chlorine-based etching gas.

[0039] In this exemplary embodiment of the present invention, power is supplied to the plasma etching chamber at approximately 1000 W during the first etching step and at 800-1000 W during the second etching step. Switching occurs every 3-5 seconds between each etching step. The process continues for approximately 70 loops (each etching step is performed once in each loop); the number of loops is determined by the depth of the aluminum scandium nitride layer. During the process, the plasma etching chamber is maintained at a pressure of 2-5 mTorr. In this exemplary embodiment, the chlorine-based etching gas contains chlorine and the inert diluent gas contains argon (however, as can be inferred, other chlorine-based etching gases and inert diluent gases may also be suitable). A typical etching rate is 85-142 nm / min.

[0040] The individual amounts of etching gas and diluent gas entering the chamber can be controlled by changing the gas flow rate into the plasma etching chamber. In the first etching step, argon gas is supplied to the plasma etching chamber at a gas flow rate of approximately 45-50 sccm. Simultaneously, chlorine gas is supplied to the plasma etching chamber at a gas flow rate of approximately 45-50 sccm. In other words, since the flow rates of the etching gas and diluent gas are substantially the same, approximately equal amounts of gas are supplied to the plasma etching chamber in the first etching step. However, as can be inferred, it is also possible to change the gas pressure and flow rate while ensuring that approximately equal amounts of gas continue to be supplied to the plasma etching chamber. By changing the flow rate or pressure, the amount of gas supplied can be changed. The platen power in the first etching step (i.e., the bias power applied to the platen assembly 13) is set within the range of 1000-1350 W. In practice, a pressure of 2-5 mTorr is targeted, and the flow rate is established within the desired range using a flow regulator.

[0041] In the second etching step, argon gas is supplied to the plasma etching chamber at a gas flow rate of approximately 85-95 sccm. Simultaneously, chlorine gas is supplied to the plasma etching chamber at a gas flow rate of approximately 5-15 sccm. The plasma etching chamber is maintained at a pressure of 2-5 mTorr. In other words, in the second etching step, the diluent gas flow rate is at least twice, for example, more than four times, the etching gas flow rate, and thus at least twice as much diluent gas as etching gas is supplied to the plasma etching chamber. As can be inferred, these flow rates may differ if the gas pressure changes, but the overall effect of supplying a larger amount of diluent gas to the plasma etching chamber remains the same. The platen power in the second etching step (i.e., the bias power applied to the platen assembly 13) is in the range of 1000-1200 W. The second etching step can be called the "sputtering step". Because the diluent has a large sputtering mass, this periodic etching process, accompanied by high-speed switching, results in increased sputtering of etching byproducts in the form of ScCl3 on the trench sidewalls compared to conventional methods. The etching depth lag between the vicinity of the mask and the area far from the mask is reduced, leading to a reduction in foot formation. The low process pressure ensures uniformity, which supports the sputtering. The high bias power applied to the platen assembly and the moderate power supply also support the sputtering.

[0042] In this exemplary embodiment, approximately 85% of the aluminum scandium nitride film is etched during bulk etching. The remaining aluminum scandium nitride can be etched in a soft-landing process.

[0043] Ultimately, after all AlScN has been etched with minimal molybdenum loss, there will be no fitting at all. As can be seen in Figure 4, the soft landing process can be further optimized by minimizing fitting in bulk etching or by enabling micro-trenching to a controlled depth. In a typical soft landing process exhibiting high molybdenum selectivity of approximately 4:1, only slight fitting occurs. By adjusting the bulk etching process so that a small amount of micro-trenching occurs in the soft landing process, which would normally result in some fitting, fitting can be eliminated and electrode loss minimized. Typically, in the soft landing process, BCl3 / Cl2 and Ar or BCl2 / Ar is used at approximately 2-5 mTorr, and an example process is described in GB2412922.3. [Explanation of symbols]

[0044] 11 Workpiece, 12 Chamber, 13 Substrate support, 15a, 15b, 15c Inlet, 17 RF voltage generator, 18 Antenna, 20a, 20b, 20c Flow regulator.

Claims

1. A method for inductively coupled plasma etching of an additive-containing aluminum nitride film, wherein the additive is selected from scandium, yttrium, and erbium. A workpiece is placed on a platen assembly within a plasma etching chamber, wherein the workpiece comprises a substrate on which the additive-containing aluminum nitride film is deposited, and a photoresist mask disposed on the film. The plasma etching chamber is powered by an RF power source. A bias power is applied to the platen assembly, and A method for bulk etching the additive-containing aluminum nitride film through the photoresist mask using a switched process, wherein the switched process is (i) A step of plasma etching the film by supplying a chlorine-based etching gas and an inert diluent gas at substantially equal flow rates to the plasma etching chamber at a target chamber pressure, (ii) A step of plasma etching the film using the same chlorine-based etching gas and inert diluent gas as described above at the same target chamber pressure, wherein the flow rate of the inert diluent gas is at least four times the flow rate of the chlorine-based etching gas, A method that involves repeatedly alternating between two things.

2. A method according to claim 1, comprising increasing the bias power for the platen assembly during step (i).

3. A method according to claim 1, wherein the alternation between process (i) and (ii) occurs every 2 to 6 seconds.

4. A method according to claim 1, wherein the substrate comprises a silicon wafer, the silicon wafer supports a molybdenum electrode layer, and the molybdenum electrode layer is located between the wafer and the additive-containing aluminum nitride film.

5. The method according to claim 1, wherein the chlorine-based gas contains chlorine.

6. The method according to claim 1, wherein the inert diluent gas contains argon.

7. A method according to claim 1, comprising supplying RF power in the range of 600 to 1200 W to the plasma etching chamber.

8. A method according to claim 1, comprising applying a bias power of 800 to 1400 W to the platen assembly.

9. A method according to claim 1, wherein the bias power is increased by 200 to 500 W during step (i).

10. A method according to claim 1, wherein the plasma etching chamber is maintained at a pressure in the range of 2 to 5 mTorr during bulk etching of the additive-containing aluminum nitride film.

11. A method according to claim 1, wherein during step (i), the chlorine-based etching gas and the inert diluent gas are each introduced into the plasma etching chamber at a flow rate of approximately 30 to 70 sccm.

12. A method according to claim 1, wherein during step (ii), the chlorine-based etching gas is introduced into the plasma etching chamber at a flow rate of approximately 60 to 120 sccm, and the inert diluent gas is introduced into the plasma etching chamber at a flow rate of approximately 5 to 25 sccm.

13. A method according to claim 1, further comprising a soft landing step in which, after the bulk etching, the remaining additive-containing aluminum nitride film is plasma-etched using a chlorine-based etching gas containing boron trichloride and chlorine in a 1:1 ratio and an inert diluent gas containing argon, and the microtrenches created by the bulk etching are removed by the soft landing step.

14. The method according to claim 1, wherein the profile of the photoresist mask is less than 75 degrees.

15. The method according to claim 1, wherein the additive-containing aluminum nitride film contains scandium and is of the formula Al ｘ Sc ｙ A method defined by N, where x + y = 1, where the scandium component ratio y is 0.25 or greater, and optionally approximately 0.

4.

16. A method according to claim 1, wherein the additive-containing aluminum nitride film has depth, and the bulk etching of the additive-containing aluminum nitride film is performed over at least 85% of its depth.

17. An inductively coupled plasma apparatus for plasma etching an additive-containing aluminum nitride film, wherein the additive is selected from scandium, yttrium, and erbium. ICP plasma etching chamber and The plasma etching chamber is configured to receive a workpiece comprising a substrate on which the additive-containing aluminum nitride film is deposited, and a photoresist mask disposed on the film, and the platen assembly disposed within the plasma etching chamber, A gas supply system for supplying chlorine-based etching gas and inert diluent gas into the plasma etching chamber, A plasma generating device for maintaining plasma in the plasma etching chamber in order to etch the additive-containing aluminum nitride film of the workpiece, A controller configured to control the apparatus to perform bulk plasma etching of the additive-containing aluminum nitride film through the photoresist mask according to a switched process, wherein the switched process involves repeatedly alternating between a first step of supplying substantially equal amounts of the chlorine-based etching gas and the inert diluent gas into the plasma etching chamber, and a second step of supplying at least twice the amount of the inert diluent gas compared to the chlorine-based etching gas into the plasma etching chamber. A device equipped with the following features.

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