Avoiding Oxygen Plasma Damage During Hard Mask Etching in Magnetic Tunnel Junction (MTJ) Fabrication Process
An etch process flow for forming magnetic tunnel junction (MTJ) cells with enhanced throughput that also increases the magnetoresistive ratio and decreases critical dimension (CD) variation is disclosed. A photoresist pattern is formed on a dielectric antireflective coating (DARC), which contacts a top surface of a hard mask (HM) that is an uppermost MTJ layer. After a first ion beam etch (IBE) or reactive ion etch (RIE) transfers the pattern through the DARC, a second etch is used to transfer the pattern through the HM. The second etch includes an oxidant to passivate the pattern sidewalls and completely removes the photoresist layer because of one or both of a thicker DARC and thicker HM than in conventional processing. Accordingly, an oxygen etch typically used to remove the photoresist after the HM etch is avoided and thereby provides improved MTJ performance, especially for CDs<60 nm.
1 . A method of etching a magnetic tunnel junction (MTJ) stack of layers, comprising:
providing a MTJ stack of layers on a first electrode wherein the MTJ stack of layers includes a hard mask (HM) on a first stack of layers, and forming a second stack of layers comprising a dielectric antireflective coating (DARC) with a first thickness on the HM, and a photoresist layer on the DARC;
forming a pattern with a critical dimension (CD) in the photoresist layer and transferring the pattern through the DARC with a first etch process that is an ion beam etch (IBE) or a reactive ion etch (RIE) wherein the pattern after the first etch process includes at least a sidewall that extends from a top surface of the DARC to a top surface of the HM;
performing a second etch that is an IBE or RIE wherein the pattern in the DARC is transferred through the HM, and wherein the first thickness is sufficiently large such that the photoresist layer is entirely removed before the end of the second etch, and the sidewall extends from a DARC top surface to a top surface of the first stack of layers, and wherein the second etch comprises one or more oxidants that passivate the sidewall; and
performing a third (MTJ) etch that is one or both of a RIE or IBE comprised of a noble gas and the one or more oxidants wherein the MTJ etch transfers the pattern through the first stack of layers, and stops at a top surface of the first electrode and thereby forms a plurality of MTJ cells.
2 . The method of claim 1 wherein the first and second etches and the MTJ etch are all RIE or all IBE, and are performed in a first process chamber.
3 . The method of claim 2 further comprised of a cleaning step that is an IBE or plasma etch performed after the MTJ etch, and wherein a plasma is generated from a gas mixture comprised of a noble gas and the one or more oxidants.
4 . The method of claim 1 wherein the one or more oxidants is selected from air, 0 2 , methanol, ethanol, H 2 0 2 , H 2 0, N 2 0, NH 3 , and CO.
5 . The method of claim 1 wherein the first etch is an IBE and comprises a noble gas that is Ar, Kr, Xe, or Ne.
6 . The method of claim 1 wherein the second etch is an IBE and comprises a noble gas that is Ar, Kr, Xe, or Ne.
7 . The method of claim 1 wherein the first etch is a RIE and comprises a fluorocarbon or chlorocarbon.
8 . The method of claim 1 wherein the second etch is a RIE and comprises a fluorocarbon or chlorocarbon.
9 . The method of claim 1 wherein the first etch further comprises oxygen in order to passivate the sidewall.
10 . The method of claim 1 wherein the MTJ stack of layers is formed in a magnetoresistive random access memory (MRAM), spin torque transfer (STT)-MRAM, spin torque oscillator (STO), sensor, or biosensor.
11 . The method of claim 1 wherein the first stack of layers comprises a free layer (FL), a reference layer (RL), and a tunnel barrier between the FL and RL.
12 . The method of claim 1 wherein the first thickness is substantially larger than a thickness of the hard mask.
13 . A method of etching a magnetic tunnel junction (MTJ) stack of layers, comprising:
providing a MTJ stack of layers on a first electrode wherein the MTJ stack of layers includes a hard mask (HM) on a first stack of layers, and forming a second stack of layers comprising a dielectric antireflective coating (DARC) on the HM, and a photoresist layer on the DARC wherein the HM is a metal, alloy, or metal nitride having a first thickness;
forming a pattern with a critical dimension (CD) in the photoresist layer and transferring the pattern through the DARC with a first etch process that is an ion beam etch (IBE) or a reactive ion etch (RIE) wherein the pattern after the first etch process has a sidewall that extends from a top surface of the photoresist layer to a top surface of the HM;
performing a second etch that is an IBE or RIE wherein the pattern in the DARC is transferred through the HM, and wherein the first thickness is sufficiently large such that the photoresist layer is entirely removed and the sidewall extends to a top surface of the first stack of layers, and wherein the second etch comprises one or more oxidants that passivate the sidewall; and
performing a third (MTJ) etch that is one or both of a RIE or IBE comprised of a noble gas and the one or more oxidants wherein the MTJ etch transfers the pattern through the first stack of layers, and extends the sidewall to a top surface of the first electrode and thereby forms a plurality of MTJ cells.
14 . The method of claim 13 wherein the first and second etches and the MTJ etch are all RIE or all IBE, and are performed in a first process chamber.
15 . The method of claim 14 further comprised of a cleaning step that is an IBE or plasma etch performed after the MTJ etch, and wherein a plasma is generated from a gas mixture comprised of a noble gas and the one or more oxidants.
16 . The method of claim 13 wherein the one or more oxidants is selected from air, 0 2 , methanol, ethanol, H 2 0 2 , H 2 0, N 2 0, NH 3 , and CO.
17 . The method of claim 13 wherein the first etch is an IBE and comprises a noble gas that is Ar, Kr, Xe, or Ne.
18 . The method of claim 13 wherein the second etch is an IBE and comprises a noble gas that is Ar, Kr, Xe, or Ne.
19 . The method of claim 13 wherein the first etch is a RIE and comprises a fluorocarbon or chlorocarbon.
20 . The method of claim 13 wherein the second etch is a RIE and comprises a fluorocarbon or chlorocarbon.
21 . The method of claim 13 wherein the first etch further comprises oxygen in order to passivate the sidewall.
22 . The method of claim 13 wherein the MTJ stack of layers is formed in a magnetoresistive random access memory (MRAM), spin torque transfer (STT)-MRAM, spin torque oscillator (STO), sensor, or biosensor.
23 . The method of claim 13 wherein the DARC has a thickness substantially greater than the first thickness.