Method of plasma etching

Abstract

To mitigate the problem of footing.SOLUTION: A method of plasma-etching an additive-containing aluminum nitride film, the additive-containing aluminum nitride film containing an additive element selected from scandium (Sc), yttrium (Y) and erbium (Er), comprises the steps of: placing a workpiece upon a substrate support within a plasma chamber, the workpiece comprising a substrate having an additive-containing aluminum nitride film deposited thereon and a mask disposed upon the film to define at least one trench; introducing BCl3 gas; introducing Cl2 gas; introducing an inert diluent gas; and establishing plasma within the chamber to plasma-etch the additive-containing aluminum nitride film exposed within the trench; where the ratio of the inert diluent gas flow rate to the sum of the BCl3 and Cl2 flow rates is in the range between 0.45:1 and 0.75:1 and the ratio of the BCl3 flow rate to the Cl2 flow rate is in the range between 0.75:1 and 1.25:1.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a plasma etching method, in particular to a method for plasma etching an additive-containing aluminum nitride film containing an additive element selected from among scandium (Sc), yttrium (Y) and erbium (Er), and also to an associated apparatus for plasma etching such an additive-containing aluminum nitride film. [Background technology]

[0002] Piezoelectric devices based on Aluminum Nitride (AlN) and Aluminum Scandium Nitride (AlScN) are widely used in a wide range of RF technologies, such as bulk acoustic wave (BAW) devices, piezoelectric micromachined ultrasonic transducers (PMUTs), Lamb wave contour mode resonators (CMRs), microphones and sensors. Mobile phones typically incorporate a large number of AlN and AlScN BAW devices, and there is a demand for thinner BAW devices to generate higher operating frequencies. Improving the piezoelectric performance in thinner devices is a great challenge, as the tolerances become tighter and their integration on circuit boards becomes more complex. The addition of Sc is known to improve the piezoelectric properties of BAW devices. However, there are a number of issues associated with etching AlScN, which become even more troublesome at higher scandium contents.

[0003] Standard Chlorine (Cl 2 When using a SiO2 / Argon (Ar) based chemistry, as the Sc percentage in the doped AlN increases, the etch rate typically decreases. This decrease can result in the mask (e.g., photoresist or SiO 2The selectivity of AlScN to the mask (pre-etch mask) decreases, which increases the critical dimension (CD) and results in shallower sidewall angles in the AlScN trenches. Common sidewall profile control methods include adjusting the slope of the pre-etch mask, changing the platen bias, etchant gas flow, or process pressure. These methods are generally effective for AlScN with lower Sc content, but at higher Sc percentages, the etch becomes increasingly physical, reducing the overall effectiveness of these methods. Similar phenomena have been observed with AlYN and AlErN films.

[0004] The slowing of the AlScN etch rate also reduces the selectivity to the metal underlayer, which leads to increased underlayer loss and may impair the performance of some devices, e.g., BAW filters. Because the bottom electrical contacts to BAW devices are typically molybdenum (Mo), tungsten (W) or platinum (Pt), if too much metal is removed due to the slowing of the AlScN etch rate, the electrical resistance of the contacts increases, resulting in reduced device performance. Typical modifications to increase the AlScN etch rate, e.g., increasing the platen bias or increasing Cl 2 Increasing the flow will ultimately have little or no effect on sidewall angle or underlayer selectivity, and in some cases may even exacerbate the problem.

[0005] An AlScN etch process typically has two etch steps. The first step is the main bulk etch process, which has a high etch rate, good selectivity to the mask material, steep sidewall profile, and minimal footing. Typically, 80-85% of the material is etched away by this type of etch. The second step is a soft etch step, which requires good selectivity to the underlying electrode. This is typically a low etch rate process. This process typically only etches away 15-20% of the material, so good selectivity can be obtained at the expense of etch rate and etch profile.

[0006] For the avoidance of doubt, footing is the unwanted deviation from an ideal flat bottom at the base of an etched feature. It is usually measured using SEM cross-sections of the etched feature. Footing is caused by etch rate differences between near-mask and far-mask regions at the base of the etched feature. Figure 2 illustrates the creation of an etched feature with and without footing. More specifically, the workpiece shown in Figure 2(a) is before etching. The workpiece comprises a silicon wafer 200 having an AlScN layer 201 deposited thereon. A mask 202 is formed on the AlScN layer 201 to leave an opening 203 through which the AlScN layer can be etched. The workpiece shown in Figure 2(b) is after etching the AlScN layer 201, where the created trench 204 has a flat base without footing. The workpiece shown in FIG. 2(c) is after etching of the AlScN layer 201, resulting in trenches 205 revealing footings in the form of concave base profiles. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2021-100104 A [Patent Document 2] Patent Publication No. 2021-090047 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention, in at least some of its embodiments, seeks to address at least some of the problems set forth above. [Means for solving the problem]

[0009] According to a first aspect of the present invention, there is provided a method for plasma etching an additive-containing aluminum nitride film, the additive-containing aluminum nitride film containing an additive element selected from the group consisting of scandium (Sc), yttrium (Y) and erbium (Er), comprising the steps of: placing a workpiece on a substrate support within a plasma chamber, the workpiece comprising a substrate having an additive-containing aluminum nitride film deposited thereon, and a mask disposed on the additive-containing aluminum nitride film, the mask defining at least one trench; BCl 3 Gas is pumped into the chamber at a rate of BCl in sccm (standard square centimeters per minute). 3 introducing the gas at a flow rate; Cl 2 Gas was introduced into the chamber at Cl2 in sccm. 2 introducing the gas at a flow rate; introducing an inert diluent gas into the chamber at an inert diluent gas flow rate in sccm; establishing a plasma in the chamber and plasma etching the doped aluminum nitride film exposed in the trench; BCl 3 Flow rate and Cl 2 The ratio of the inert dilution gas flow rate to the total flow rate is within the range of 0.45:1 to 0.75:1, and Cl 2 BCl vs. flow rate 3 Flow ratios within the range of 0.75:1 to 1.25:1 are provided. This can reduce footing problems.

[0010] BCl 3 Flow rate and Cl 2 The ratio of the inert diluent gas flow rate to the total flow rate may be within the range of 0.48:1 to 0.6:1.

[0011] Cl 2 BCl vs. flow rate 3The ratio of the flow rates may be in the range of 0.9:1 to 1.1:1, optionally in the range of 0.95:1 to 1.05:1, optionally about 1.0:1.

[0012] BCl 3 Flow rate and Cl 2 The flow rates each may be in the range of 20-30 sccm, optionally about 25 sccm.

[0013] The inert diluent gas flow rate may be in the range of 20-30 sccm, optionally about 25 sccm.

[0014] Plasma etching may also be performed with gas pressures in the chamber below 5 mTorr.

[0015] An inductively coupled plasma (ICP) may be established within the chamber using a power in the range of 750-1500 W.

[0016] An RF bias signal having a power in the range of 1000-1500 W may also be applied to the substrate support during the plasma establishing step in the chamber.

[0017] The method of the first aspect of the invention may be performed as a first main plasma etching step to etch away most of the doped aluminum nitride film exposed in the trench, followed by a second plasma etching step to etch away the remaining doped aluminum nitride film exposed in the trench. The second aspect of the invention describes a second plasma etching step that may be used in conjunction with the first aspect of the invention. In principle, it is not necessary to perform such a second plasma etching step in the first aspect of the invention.

[0018] According to a second aspect of the present invention, there is provided a method for plasma etching an additive-containing aluminum nitride film, the additive-containing aluminum nitride film containing an additive element selected from the group consisting of scandium (Sc), yttrium (Y) and erbium (Er), comprising the steps of: placing a workpiece on a substrate support within a plasma chamber, the workpiece comprising 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 defining at least one trench; BCl 3 Gas, Cl 2 performing a first main plasma etching step, introducing a gas and an inert diluent gas into the chamber to establish a plasma in the chamber thereby plasma etching a majority of the additive-containing aluminum nitride film exposed in the trench; BCl 3 Gas and an inert diluent gas are introduced into the chamber, but Cl 2 performing a second plasma etching step, where no gas is introduced into the chamber and a plasma is established in the chamber to plasma etch the remaining doped aluminum nitride film exposed in the trench to reveal the metal film; The present invention provides a method for producing a hologram having the following structure:

[0019] In this way, the selectivity to the metal underlayer can be improved, which can be defined as the etching rate of the additive-containing aluminum nitride film / the etching rate of the metal film.

[0020] In the second plasma etching process, BCl 3 Gas is in the range of 50-100 sccm, optionally in the range of 75-95 sccm of BCl 3 A flow rate can also be introduced into the chamber.

[0021] In the second plasma etching step, an inert diluent gas may be introduced into the chamber at an inert diluent gas flow rate in the range of 10 to 20 sccm.

[0022] In the second plasma etching step, an inductively coupled plasma (ICP) may be established in the chamber using a power in the range of 400-700 W.

[0023] In the second plasma etching step, an RF bias signal having a power in the range of 500-700 W may be applied to the substrate support.

[0024] The metal film may be a molybdenum film. Alternatively, the metal film may be a tungsten, ruthenium or platinum film.

[0025] The first plasma etch step and / or the second plasma etch step may be performed with a chamber gas pressure of 5 mTorr or less.

[0026] The first aspect of the present invention may also be used as the first plasma etching step.

[0027] The inert diluent gas may be argon. Other inert gases, such as other noble gases, may also be envisaged.

[0028] The substrate may be a semiconductor substrate, optionally a silicon substrate, for example a silicon wafer, which may be of any suitable diameter, for example 150 mm diameter or 200 mm diameter.

[0029] The additive-containing aluminum nitride film is represented by the formula Al x Sc yThe film may be an aluminum scandium nitride film defined by AlScN, where x+y=1. For the avoidance of doubt, the metal contents x and y in this formula are atomic contents. As can be appreciated, the atomic percentage of Al is 100x and the atomic percentage of Sc is 100y. The scandium content y may be 0.30 or greater. The scandium content y may be 0.35 or greater, optionally about 0.4. The scandium content y may be 0.50 or less, optionally 0.45 or less. Both aspects of the invention are particularly useful for etching AlScN films with a high Sc content.

[0030] The mask can be a photoresist mask. The mask can be a silicon oxide mask.

[0031] The plasma can also be an inductively coupled plasma (ICP).

[0032] According to a third aspect of the present invention, there is provided an apparatus for plasma etching an additive-containing aluminum nitride film containing an additive element selected from among scandium (Sc), yttrium (Y) and erbium (Er) through a mask, the apparatus comprising: A chamber; a substrate support disposed within the chamber; BCl 3 Gas in sccm is BCl 3 Flow rate, Cl 2 Gas in sccm is Cl 2 a gas delivery system for introducing into the chamber an inert diluent gas at a flow rate in sccm and an inert diluent gas at a flow rate in sccm; a plasma generating apparatus for maintaining a plasma in the chamber for etching a workpiece comprising a substrate having an additive-containing aluminum nitride film deposited thereon, and a mask disposed on the additive-containing aluminum nitride film, the mask defining at least one trench; a controller configured to control the apparatus such that a plasma etch is performed to etch away the doped aluminum nitride film exposed in the trench; and The controller is a BCl 3 Flow rate and Cl 2 The ratio of the inert dilution gas flow rate to the total flow rate is within the range of 0.45:1 to 0.75:1, Cl 2 BCl vs. flow rate 3 A control is provided for the gas distribution system such that the flow ratio is maintained within the range of 0.75:1 to 1.25:1.

[0033] According to a fourth aspect of the present invention, there is provided an apparatus for plasma etching an additive-containing aluminum nitride film containing an additive element selected from among scandium (Sc), yttrium (Y) and erbium (Er) through a mask, comprising: A chamber; a substrate support disposed within the chamber; BCl 3 Gas, Cl 2 a gas delivery system for introducing gas and an inert diluent gas into the chamber; a plasma generating device for maintaining a plasma in the chamber for etching a workpiece comprising: 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 defining at least one trench; BCl 3 Gas, Cl 2 a first main plasma etch step in which a BCl gas and an inert diluent gas are introduced into the chamber to establish a plasma in the chamber thereby etching away a majority of the doped aluminum nitride film exposed in the trench; 3 Gas and an inert diluent gas are introduced into the chamber, but Cl 2a second plasma etching step of establishing a plasma in the chamber without introducing a gas into the chamber and thereby etching away the remaining doped aluminum nitride film exposed in the trench to reveal the metal film; and The present invention provides a method for producing

[0034] The plasma generating device may be an inductively coupled plasma (ICP) device.

[0035] For the avoidance of doubt, whenever this application refers to the words "comprising" or "having" and similar terms, it is understood that the invention also encompasses more restrictive terms such as "consisting solely of" and "consisting essentially of."

[0036] The invention has been described above and extends to any and all inventive combinations of the features set forth above or in the following description, drawings or claims, for example any feature disclosed in connection with one aspect of the invention may be combined with any feature disclosed in connection with any other aspect of the invention.

[0037] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0038] [Figure 1] FIG. 1 is a schematic depiction of a plasma etching apparatus for etching an additive-containing aluminum nitride film. [Diagram 2] 1A is a schematic cross-sectional view of a workpiece before etching, FIG. 1B is a schematic cross-sectional view of a workpiece after etching without a footing, and FIG. 1C is a schematic cross-sectional view of a workpiece before etching without a footing. [Diagram 3] FIG. 13 shows SEM images taken after etching using Ar flow rates varying from 10 sccm to 35 sccm. [Figure 4]FIG. 14 shows SEM images taken after etching with various BCl3 / Cl2 flow ratios. [Diagram 5] FIG. 1 is a schematic cross-sectional view of a workpiece having an underlying molybdenum film beneath an AlScN layer. [Figure 6] FIG. 13 is a diagram showing the change in selectivity with the change in platen power. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Referring to FIG. 1 of the drawings, there is shown a schematic representation of an apparatus 10 for plasma etching a workpiece 11, comprising a process chamber 12 within which plasma etching of the workpiece 11 is performed.

[0040] The apparatus 10 further includes a substrate support 13. The substrate support may be a platen assembly 13 and may be formed of a metal, such as aluminum, and is disposed within the chamber 12 while being electrically insulated from the chamber walls 12a by conventional means, such as a ceramic brake 14. The substrate support may also include an electrostatic chuck (ESC) that may be attached to a surface of the platen assembly. The platen assembly 13 includes a body 13a having a support surface 13b for receiving the workpiece 11 and is electrically biased using a radio frequency (RF) voltage generator. For example, application of a negative bias voltage to the platen assembly 13 may be useful in controlling the bombardment of positively charged ions from the plasma onto the surface of the workpiece 11.

[0041] The process chamber 12 includes a chamber wall 12a, which may be made of a metal such as aluminum, and which is typically electrically grounded. The chamber 12 further includes first, second and third gas inlets 15a, 15b and 15c, through which BCl 3 Gas, Cl 2Sources (not shown) of gas and inert diluent gas, such as argon, may each 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 by-products of the etching process may exit the chamber 12.

[0042] 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 disposed about the periphery of the chamber 12 and adjacent respective dielectric windows 12b formed in the chamber wall 12a. The antenna or antennas 18 may be, for example, a substantially planar spiral configuration, a helical coil configuration, or a toroidal configuration, and, as is common practice, the RF signal from the generator 17 may be impedance matched to the antenna 18 to minimize power reflection from the antenna 18. The antenna 18 is disposed about the periphery of the chamber 12, and power is inductively coupled into the chamber 12 through the dielectric windows 12b.

[0043] A plasma is generated in a region 19 of the chamber 12 above the workpiece 11, thereby exposing the workpiece 11 to the plasma. Process gases are introduced into the chamber 12 via respective flow regulators 20a, 20b, 20c coupled to respective inlets 15a, 15b, 15c, and because the inlets 15a, 15b, 15c and the outlet 16 of the chamber 12 are located on opposite sides of the plasma region 19, etching gases are necessarily passed into the chamber 12, through region 19, above the workpiece 11, and out the outlet 16. One example of a suitable apparatus which may be used to practice the present invention is the Synapse™ module manufactured by the applicant's SPTS Technologies Limited of Newport, UK.

[0044] Although the methods of the present invention are presented in the context of AlScN films, the skilled reader will recognize that the methods are equally applicable to AlYN and AlErN films.

[0045] A workpiece 11 is placed on a platen 13 within a plasma chamber 12. The workpiece 11 comprises a substrate 11, e.g., a silicon wafer substrate, on which a piezoelectric AlScN film 11a has been deposited, e.g., using a pulsed DC sputtering technique. In one embodiment, the film is Al 0.6 Sc 0.4 The film is composed of AlScN, i.e., 60% aluminum and 40% scandium. This is a high scandium content film, and such high scandium content films are difficult to process using prior art methods. The present invention provides a significant improvement in the processing of high scandium content AlScN films. Film composition determination is typically accomplished through the use of energy dispersive x-ray analysis (EDAX). The workpiece 11 further includes a photoresist or SiO 2 film formed on the film 11a. 2 A mask 11b is provided in which a trench 11c of 5 μm to 100 μm is patterned using a hard mask.

[0046] With the workpiece 11 placed on the platen 13 in the chamber 12, BCl 3 , Cl 2 and argon gas are introduced into chamber 12 through respective inlets 15a-c using respective flow regulators 20a-c, and the pressure within chamber 12 is maintained at about 2-5 mTorr, or substantially 3 mTorr, by a pressure regulator (not shown). Once the chamber 12 has been suitably conditioned with the gases, an RF potential is applied to antenna 18 by generator 17 to inductively couple power (hereinafter referred to as "source power") into the etching gas, thus generating a plasma and emitting Al. 0.6 Sc 0.4Etching of the AlScN film begins. A bias voltage that also delivers bias power is applied to the platen assembly 13 through the use of a voltage generator 17 typically operating at 13.56 MHz, allowing etching of the AlScN film 11b.

[0047] By controlling the process parameters of the first main etch step, footing was reduced, and by controlling the process parameters of the second soft-etch step, improved selectivity was achieved.

[0048] [Footing reduction] Diluent gas, BCl 3 Gas and Cl 2 Gas flow was controlled to minimize etch footing. Experiments were performed using a workpiece of the type outlined in Figure 2. More specifically, to prepare the workpiece, a 350 nm thick Al 0.60 Sc 0.40 For this experiment, the wafers were 150 mm in diameter, but the same principles can be applied to wafers of other sizes, e.g., 200 mm diameter wafers. The wafers were fabricated using SiO 2 with an open area of ​​less than 14% and thicknesses between 1.7 and 3.5 μm. 2 Patterning was performed using a mask. The mask profile was less than 80°. A process was performed to create a 10 μm wide trench.

[0049] In this experiment, Ar was used as a diluent gas and the effect of varying the Ar flow rate into the chamber was investigated. An initial increase in Ar flow reduced the plasma loading, making the plasma more uniform and minimizing footing. The process used was physical in nature, with low pressure (2 mTorr), high bias power (1300 W) and low source power (1000 W), and Cl 2 The flow rate of BCl is 25sccm. 3 The flow rate of Ar was changed from 10 sccm to 35 sccm.

[0050] Figure 3 shows SEM images obtained after etching using Ar flow rates of (a) 10 sccm, (b) 20 sccm, (c) 25 sccm, and (d) 35 sccm. A decrease in footing from 41 nm to 7 nm was observed as the Ar flow rate was increased from 10 to 25 sccm. The sidewall angles of the etched AlScN trenches are also shown in Figures 4(a)-(d). Table 1 summarizes these results. Further increases in the Ar flow rate resulted in a slight increase in footing.

[0051] Without being bound by any particular theory or speculation, it is believed that increasing the Ar flow rate dilutes the plasma, making it more uniform, thus reducing the loading effect near the mask. 3 It is also believed that sputtering of the base by-products can be promoted.

[0052] [Table 1]

[0053] Significant footing improvements can be obtained when the argon flow is controlled in combination with the reactant gas flow.

[0054] There are two main chlorine-based reactive gases for etching AlScN: 2 and BCl 3 ) was used. 3 and Cl 2 Using both results in a steeper etch profile for AlScN. Boron has a larger sputter mass and promotes sputtering of Sc-based etch by-products from the sidewalls, which makes the profile steeper. It turns out that the optimal Cl etch profile results in a flat etch front, thereby minimizing footing. 2 :BCl 3 There is a ratio: BCl 3At low levels, uneven sputtering of etch by-products from the sidewalls results in uneven footing. 3 :Cl 2 The smallest footing was observed in the ratio BCl 3 Further increasing the ratio of BCl increases footing. It is believed that excess Cl ions are available in the plasma environment, which favors chemical etching rather than physical etching, where by-product removal by physical sputtering may occur. Figure 4 shows the results of the etching of various BCl 3 / Cl 2 SEM images obtained after etching with flow ratios of 0.47 and 0.50 are shown in Fig. 4(a) and (b), respectively. 3 :Cl 2 4(c) and (d) show the left and right walls of a trench etched using BCl ratios of 1.0 and 2.13, respectively. 3 :Cl 2 The results were obtained using the ratio. Table 2 summarizes these results.

[0055] [Table 2]

[0056] Surprisingly, when etching AlScN, which has a high Sc content, BCl 3 A relatively low flow rate may be beneficial. 3 does not generate much free Cl, but B, B-Cl, and B-Cl 2 This promotes sputtering because BCl 3 The higher flow is expected to make the etch more physical, which will aid in the etching of AlScN with higher Sc content. The larger sputter mass of boron helps in the removal of etch by-products, which is the best for achieving a flat etch front. 3 :Cl 2A ratio may be necessary.

[0057] [Improvement of selection ratio in soft-adhesion process] Experiments were carried out using a workpiece of the type generally shown in Figure 5; the illustrated workpiece comprises a silicon wafer 50 having a molybdenum layer 51 formed thereon. An AlScN layer 52 is deposited on the molybdenum layer 51. A photoresist mask 53 is formed on the AlScN layer 52 to leave an opening 54 through which the AlScN layer can be etched. More specifically, in preparing the workpiece, a 200 nm thick Al 0.60 Sc 0.40 The N and Mo layers were deposited and patterned using a 4 μm thick photoresist mask. For this experiment the wafers were 200 mm in diameter, but the same principles can be applied to wafers of other sizes, e.g. 150 mm diameter. The process is 0.60 Sc 0.40 The process was developed specifically for AlScN wafers. The process conditions can be readily adapted for AlScN films with different Sc contents. The selectivity to the underlying Mo layer was calculated for trenches with 5 μm CD and 100 μm CD.

[0058] The selectivity to the underlying electrode is BCl 3 Without being bound by any particular theory or speculation, the improvement was achieved by using only BCl 3 is absorbed into the surface of AlScN and BCl 2 BCl, Cl and B are separated. 3 Gas is Cl 2 It is thought that it does not generate much free Cl compared to BCl. 3 In this case, it is considered that the presence of B increases the sputtering of Sc-based by-products and increases the etching rate of AlScN, but the presence of less active Cl decreases the etching rate of Mo.

[0059] Cl 2 +BCl3 The selectivity ratio achievable by the base soft etch is estimated to be 0.97:1. It was found that the reactive gas was BCl 3 The selectivity ratio increased to 1.6:1 by changing the platen power to 450 W. Further process refinements were found to improve the selectivity even further. Notably, the selectivity to the underlying Mo electrode was found to increase with increasing platen power. Increasing the platen power from 450 W to 600 W increased the selectivity to Mo from 1.65 to 2.58 for 5 μm CD features. For 100 μm features, the selectivity increased up to a platen power of 550 W. Further increases in platen power resulted in a decrease in the selectivity. Figure 6 shows the change in selectivity with platen power. Very low pressure (5 mT) and low source power (500 W) were used in this process.

[0060] For the soft etch, an AlScN:Mo selectivity of 2.5:1 was achieved using the process conditions shown in Table 3, which also shows the preferred conditions for the main etch.

[0061] [Table 3]

[0062] The performance of AlScN-based devices depends on the bottom electrode thickness. With higher scandium content, footing and Mo loss are more difficult to control. The present invention can provide lower electrode loss, which in turn can provide improved device performance in a wide range of applications, such as bulk acoustic wave (BAW) filters for communications (including 5G), microphones and sensors.

Claims

1. A method for plasma etching an additive-containing aluminum nitride film, wherein the additive-containing aluminum nitride film contains an additive element selected from scandium (Sc), yttrium (Y), and erbium (Er), The step of placing a workpiece on a substrate support in a plasma chamber, wherein the workpiece comprises a substrate having an additive-containing aluminum nitride film deposited thereon, and a mask disposed on the additive-containing aluminum nitride film and defining at least one trench, BCl ３ The gas is introduced into the chamber in units of sccm of BCl ３ Steps to introduce by flow rate, Cl ２ The gas is introduced into the chamber in sccm units of Cl ２ Steps to introduce by flow rate, The steps include introducing an inert diluent gas into the chamber at a certain inert diluent gas flow rate in sccm units, The steps include establishing a plasma in the chamber and thereby plasma etching the additive-containing aluminum nitride film exposed in the trench, It has the BCl ３ Flow rate and the Cl ２ The ratio of the inert diluent gas flow rate to the total flow rate is set to within the range of 0.45:1 to 0.75:1, and the Cl ２ BCl in relation to flow rate ３ A method of setting the flow rate ratio within the range of 0.75:1 to 1.25:

1.

2. The method according to claim 1, wherein the ratio of the flow rate of the inert dilution gas to the total of the flow rate of the BCl ３ and the flow rate of the Cl ２ is in the range of 0.48:1 to 0.6:

1.

3. A method according to claim 1 or 2, wherein the Cl ２ BCl in relation to flow rate ３ A method of setting the flow rate ratio within the range of 0.9:1 to 1.1:

1.

4. The method according to claim 1, wherein the BCl ３ Flow rate and the Cl ２ A method in which each flow rate is set within the range of 20 to 30 sccm.

5. A method according to claim 1, wherein the flow rate of the inert dilution gas is within the range of 20 to 30 sccm.

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

7. A method according to claim 1, wherein a first main plasma etching step is performed to etch off most of the additive-containing aluminum nitride film exposed in the trench, and a second plasma etching step is performed to etch off the remaining additive-containing aluminum nitride film exposed in the trench.

8. A method for plasma etching an additive-containing aluminum nitride film, wherein the additive-containing aluminum nitride film contains an additive element selected from scandium (Sc), yttrium (Y), and erbium (Er), The step of placing a workpiece on a substrate support in a plasma chamber, wherein the workpiece comprises 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 and defining at least one trench, BCl ３ Gas, Cl ２ The first main plasma etching step involves introducing a gas and an inert diluent gas into the chamber to establish a plasma within the chamber, thereby plasma etching most of the additive-containing aluminum nitride film exposed in the trench. BCl ３ The gas and inert diluent gas are introduced into the chamber, but Cl ２ The steps include: performing a second plasma etching process, in which a plasma is established in the chamber without introducing gas into the chamber, thereby etching away the remaining additive-containing aluminum nitride film exposed in the trench and exposing the metal film; A method of having.

9. A method according to claim 8, wherein in the second plasma etching step, the BCl ３ The gas is in the range of 50-100 sccm of BCl ３ A method of introducing the substance into the chamber by flow rate.

10. A method according to claim 9, wherein in the second plasma etching step, the BCl ３ The gas is in the range of 75-95 sccm of BCl ３ A method of introducing the substance into the chamber by flow rate.

11. A method according to any one of claims 8 to 9, wherein in the second plasma etching step, the inert diluent gas is introduced into the chamber at an inert diluent gas flow rate in the range of 10 to 20 sccm.

12. A method according to claim 8, wherein in the second plasma etching step, an RF bias signal having a power in the range of 500 to 700 W is applied to the substrate support.

13. The method according to claim 8, wherein the inert diluent gas is argon.

14. The method according to claim 8, wherein the metal film is a molybdenum film.

15. A method according to any one of claims 1, 8, wherein the mask is a photoresist mask.

16. A method according to any one of claims 1, 8, wherein the plasma is inductively coupled plasma (ICP).

17. A method according to any one of claims 1 or 8, wherein the substrate is a semiconductor substrate, and optionally a silicon substrate.

18. A method according to any one of claims 1 or 8, wherein the additive-containing aluminum nitride film is of the formula Al ｘ Sc ｙ A method for an aluminum scandium nitride film defined by N, where x + y = 1, wherein the scandium content y is 0.35 or more, optionally approximately 0.

4.

19. An apparatus for plasma etching an additive-containing aluminum nitride film containing an additive element selected from scandium (Sc), yttrium (Y), and erbium (Er) through a mask, Chamber and, A substrate support arranged within the chamber, BCl ３ BCl ３ In terms of flow rate, Cl ２ A gas with a sccm unit of Cl ２ A gas distribution system that introduces an inert diluent gas into the chamber at a flow rate and at an inert diluent gas flow rate in sccm units, A plasma generating apparatus for maintaining plasma in a chamber is used to etch a workpiece comprising a substrate having an additive-containing aluminum nitride film deposited thereon, and a mask disposed on the additive-containing aluminum nitride film and defining at least one trench, A controller is configured to control the apparatus so that plasma etching is performed and the additive-containing aluminum nitride film exposed in the trench is etched off. The controller controls the gas distribution system, and the BCl ３ Flow rate and the Cl ２ The ratio of the inert diluent gas flow rate to the total flow rate is within the range of 0.45:1 to 0.75:1, and the Cl ２ BCl in relation to flow rate ３ A device that maintains the flow rate ratio within the range of 0.75:1 to 1.25:

1.

20. An apparatus for plasma etching an additive-containing aluminum nitride film containing an additive element selected from scandium (Sc), yttrium (Y), and erbium (Er) through a mask, Chamber and, A substrate support arranged within the chamber, BCl ３ Gas, Cl ２ A gas supply system for introducing gas and inert diluent gas into the chamber, A plasma generating apparatus for maintaining plasma in a chamber is used to etch a workpiece comprising a substrate having a metal film placed thereon, an additive-containing aluminum nitride film deposited on the metal film, and a mask placed on the additive-containing aluminum nitride film and defining at least one trench, BCl ３ Gas, Cl ２ A first main plasma etching step involves introducing a gas and an inert diluent gas into the chamber to establish a plasma within the chamber, thereby etching away most of the additive-containing aluminum nitride film exposed in the trench, and BCl ３ The gas and inert diluent gas are introduced into the chamber, but Cl ２ A controller configured to control the apparatus so that a second plasma etching step is performed, which involves establishing a plasma in the chamber without introducing gas into the chamber, thereby etching away the remaining additive-containing aluminum nitride film exposed in the trench and exposing the metal film; A device equipped with the following features.

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