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CN-122025499-A - Plasma etching method

CN122025499ACN 122025499 ACN122025499 ACN 122025499ACN-122025499-A

Abstract

The present application relates to a plasma etching method. A method of inductively coupled plasma etching an aluminum nitride film containing an additive selected from scandium, yttrium, and erbium is provided. The method includes placing a workpiece on a susceptor assembly within a plasma etching chamber, the workpiece including a substrate having the additive-containing aluminum nitride film deposited thereon and a photoresist mask disposed on the film, powering the plasma etching chamber with an RF power source, applying bias power to the susceptor assembly, and bulk etching the additive-containing aluminum nitride film through the photoresist mask using a switching process.

Inventors

  • S. B. Kazimi

Assignees

  • SPTS科技有限公司

Dates

Publication Date
20260512
Application Date
20250609
Priority Date
20241107

Claims (17)

  1. 1. A method of inductively coupled plasma etching an aluminum nitride film containing an additive, wherein the additive is selected from scandium, yttrium, and erbium, the method comprising: Placing a workpiece on a susceptor assembly within a plasma etching chamber, the workpiece comprising a substrate having the additive-containing aluminum nitride film deposited thereon and a photoresist mask disposed over the film; Powering the plasma etch chamber with an RF power supply; applying bias power to the base assembly, and Bulk etching the additive-containing aluminum nitride film through the photoresist mask using a switching process by repeatedly and alternately performing the following steps: (i) Plasma etching the film by feeding a chlorinated etching gas and an inert diluent gas into the plasma etching chamber at a substantially equal flow rate at a target chamber pressure, and (Ii) The film is plasma etched using the same chlorinated etching gas and an inert diluent gas at the same target chamber pressure, wherein the inert diluent gas has a flow rate at least four times the flow rate of the chlorinated etching gas.
  2. 2. The method of claim 1, comprising increasing the bias power applied to the base assembly during step (i).
  3. 3. The method of claim 1 or 2, wherein the alternation between steps (i) and (ii) occurs every 2-6 seconds.
  4. 4. The method of claim 1 or 2, wherein the substrate comprises a silicon wafer carrying a molybdenum electrode layer between the wafer and the additive-containing aluminum nitride film.
  5. 5. The method of claim 1 or 2, wherein the chlorinated gas comprises chlorine.
  6. 6. The method of claim 1 or 2, wherein the inert diluent gas comprises argon.
  7. 7. The method of claim 1 or 2, wherein the plasma etch chamber is powered with RF power in the range of 600-1200W.
  8. 8. The method of claim 1 or 2, wherein a bias power of 800-1400W is applied to the base assembly.
  9. 9. A method according to claim 1 or 2, wherein the bias power is increased by 200-500W during step (i).
  10. 10. The method of claim 1 or 2, wherein the plasma etch chamber is maintained at a pressure in the range of 2-5 mtorr during the bulk etching of the additive-containing aluminum nitride film.
  11. 11. The method of claim 1 or 2, comprising introducing each of the chlorinated etching gas and inert diluent gas into the plasma etching chamber at a flow rate of approximately 30-70sccm during step (i).
  12. 12. The method of claim 1 or 2, comprising introducing the chlorinated etching gas into the plasma etching chamber at a flow rate of approximately 60-120 seem and introducing the inert dilution gas into the plasma etching chamber at a flow rate of approximately 5-25 seem during step (ii).
  13. 13. The method of claim 1 or 2, further comprising plasma etching the remaining additive-containing aluminum nitride film in a soft landing step using a chlorinated etching gas comprising boron trichloride and chlorine in a 1:1 ratio and an inert dilution gas comprising argon after the bulk etching, wherein the bulk etching produces micro-trenches that are removed by the soft landing step.
  14. 14. The method of claim 1 or 2, wherein the photoresist mask profile is less than 75 degrees.
  15. 15. The method of claim 1 or 2, wherein the additive-containing aluminum nitride film comprises scandium and is defined by formula AlxScyN, wherein x+y = 1, and wherein scandium content y is 0.25 or greater, optionally about 0.4.
  16. 16. The method of claim 1 or 2, wherein the additive-containing aluminum nitride film has a depth, and bulk etching the additive-containing aluminum nitride film comprises bulk etching at least 85% of the depth.
  17. 17. An inductively coupled plasma apparatus for plasma etching an aluminum nitride film containing an additive selected from scandium, yttrium, and erbium, the apparatus comprising: an ICP plasma etching chamber; a susceptor assembly disposed within the plasma etching chamber and configured to receive a workpiece comprising a substrate having the additive-containing aluminum nitride film deposited thereon and a photoresist mask disposed on the film; A gas delivery system for feeding a chlorinated etching gas and an inert diluent gas into the plasma etching chamber; A plasma generating device for maintaining a plasma in the plasma etching chamber to etch the additive-containing aluminum nitride film of the workpiece, and A controller configured to control the apparatus to perform bulk plasma etching of the additive-containing aluminum nitride film via the photoresist mask in a switching process by repeatedly and alternately performing a first step in which the chlorinated etching gas and the inert dilution gas are fed into the plasma etching chamber in substantially equal amounts and a second step in which at least twice as much of the inert dilution gas is fed into the plasma etching chamber as compared to the chlorinated etching gas.

Description

Plasma etching method Technical Field The present invention relates to a plasma etching (PLASMA ETCHING) method, in particular to a method for plasma etching an aluminum nitride film containing an additive. The invention also relates to an apparatus for plasma etching an aluminum nitride film containing an additive. Background Aluminum scandium nitride (AlScN) is a piezoelectric material used in a range of applications including Bulk Acoustic Wave (BAW) filters, microphones and sensors for communications (e.g., 5G). As tolerances become tighter and integration of devices on circuit boards becomes more complex, improving the piezoelectric performance of devices (especially thinner devices) is a significant challenge. A key step in device fabrication is etching the aluminum scandium nitride layer until it ends in the molybdenum bottom electrode while minimizing electrode loss. Generally, if landed on a molybdenum electrode, a two-step etching process is used. Bulk etching (bulk etch) optimized for aluminum scandium nitride etch rate and selectivity relative to the resist mask is followed by a soft-landing etch step (soft-LANDING ETCH STEP) that has high selectivity to molybdenum, but its aluminum scandium nitride etch rate is lower. Typically, bulk etching will remove 85% -90% of the aluminum scandium nitride film. By switching to a soft landing process, the loss of molybdenum during overetch is reduced. Etching is typically performed through a mask that defines etched regions (i.e., trenches). Ideally, the etch will produce steep sidewalls in the aluminum scandium nitride layer without any redeposition and with very little foot residue (deposition) or micro-trenches (micro-trenching). Pin residue occurs when there is a difference between the etch rate close to the mask and the etch rate far from the mask and additional etch time is required to eliminate the pin residue, resulting in undesirable molybdenum loss. The reason for the formation of foot residues is believed to be ion glancing from the mask sidewalls and/or sputter delay from the etch byproducts of the sidewalls. The micro-trenches are caused by ion reflection from the trench sidewalls, which results in a localized increase in etch rate at the bottom of the trench adjacent the sidewalls. The micro-trenches lead to non-uniform etching of the aluminum scandium nitride layer and may also lead to undesirable molybdenum loss. Although the main etch may be controlled to provide steep sidewalls where no redeposition occurs and pin residue is avoided, the soft landing etch still results in pin residue. The foot-print (i.e., caused by etch depth hysteresis between the close-to-mask and far-from-mask regions) tends to be more pronounced as the scandium content and thickness of the aluminum scandium nitride layer increases. There is a need in the art for improved methods of etching aluminum scandium nitride films that minimize bottom electrode loss and eliminate pin residue, especially when using photoresist masks. To ensure device performance, it is necessary to eliminate pin residue, but it has proven difficult to achieve this without additional etching, which is undesirable because it tends to result in increased bottom electrode loss. Disclosure of Invention In a first aspect of the invention, a method of inductively coupled plasma etching an aluminum nitride film containing an additive selected from scandium, yttrium, and erbium is provided. The method includes placing a workpiece on a susceptor assembly within a plasma etching chamber, the workpiece including a substrate having an aluminum nitride film deposited thereon and a photoresist mask disposed on the film, powering the plasma etching chamber with an RF power source, applying bias power to the susceptor assembly, and etching the aluminum nitride film containing additives through the photoresist mask body using a switching process by repeatedly alternating (i) plasma etching the film by feeding a chlorinated etching gas and an inert diluent gas into the plasma etching chamber at substantially equal flow rates at a target chamber pressure, and (ii) plasma etching the film using the same chlorinated 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 the flow rate of the chlorinated etching gas. Optionally, the method comprises increasing the bias power applied to the base assembly during step (i). Advantageously, this avoids redeposition build-up on the sides of the etched feature. Optionally, the alternation between steps (i) and (ii) occurs every 2-6 seconds. Optionally, the substrate comprises a silicon wafer carrying a molybdenum electrode layer between the wafer and the additive-containing aluminum nitride film. Optionally, the chlorinated gas comprises chlorine. Optionally, the inert diluent gas comprises argon. Optionally, the plasma etch chamber is powered with RF power in the range of 600-1200W. Option