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Has anyone tried using PMMA as a mask when etching SiO2?
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Nancy Nichols
Has anyone tried using PMMA as a mask when etching SiO2?
If you continue to use PMMA, you need good heat-sinking, and you need to keep the dry etch power down and no oxygen. PMMA is Plexiglas plastic and has a low deformation temperature. It flows if it gets heated up. First thing you would need is a graph of etch rates for PMMA and for SiO2 over a range of dry etch powers, particularly the low end. Be careful if you try a prebake. You need to know the temperature at which it begins to flow and ruin the profile. It is low. This means low and long.
If you continue to use PMMA, you need good heat-sinking, and you need to keep the dry etch power down and no oxygen. PMMA is Plexiglas plastic and has a low deformation temperature. It flows if it gets heated up. First thing you would need is a graph of etch rates for PMMA and for SiO2 over a range of dry etch powers, particularly the low end. Be careful if you try a prebake. You need to know the temperature at which it begins to flow and ruin the profile. It is low. This means low and long.
Hello, Actually your reported 1:1 etch selectivity of SiO2/PMMA is one of best reported in the literature/internet. Typically people have less than 0.6:1 for this material:mask combination. Also from your description it looks like that this selectivity is enough for your final goal, why you need more PMMA left?
Hello, Actually your reported 1:1 etch selectivity of SiO2/PMMA is one of best reported in the literature/internet. Typically people have less than 0.6:1 for this material:mask combination. Also from your description it looks like that this selectivity is enough for your final goal, why you need more PMMA left?
I am keeping same parameter from resist to dry etching. I only change the baking temperature at 180 oC from 2 min to 15 min for PMMA A4 resist. Features are improving but not perfect.
I am keeping same parameter from resist to dry etching. I only change the baking temperature at 180 oC from 2 min to 15 min for PMMA A4 resist. Features are improving but not perfect.
In general, PMMA resist is poor etching selectivity. If you use another e-beam resist like ZEP520-A, you can basically obtain higher etch selectivity. And If you must certainly use a PMMA resist when SiO2 dry etching, you need to select fluorine-series gases like CHF2, C2F6, CF4, C4F8, Ar while excluding O2 gas. In case of using fluorine-series gases you can easily etch SiO2 layer using e-beam resist. As you mentioned, you have to bake finally after development, namely, Hard-bake. And add Ar gas (less than 10 sccm) to CHF3/CF4 gas. To improve more selectivity and to get fine pattern for e-beam lithography, you have to use ICP-RIE tool type than simple RIE type.
In general, PMMA resist is poor etching selectivity. If you use another e-beam resist like ZEP520-A, you can basically obtain higher etch selectivity. And If you must certainly use a PMMA resist when SiO2 dry etching, you need to select fluorine-series gases like CHF2, C2F6, CF4, C4F8, Ar while excluding O2 gas. In case of using fluorine-series gases you can easily etch SiO2 layer using e-beam resist. As you mentioned, you have to bake finally after development, namely, Hard-bake. And add Ar gas (less than 10 sccm) to CHF3/CF4 gas. To improve more selectivity and to get fine pattern for e-beam lithography, you have to use ICP-RIE tool type than simple RIE type.
In general, PMMA resist is poor etching selectivity. If you use another e-beam resist like ZEP520-A, you can basically obtain higher etch selectivity. And If you must certainly use a PMMA resist when SiO2 dry etching, you need to select fluorine-series gases like CHF2, C2F6, CF4, C4F8, Ar while excluding O2 gas. In case of using fluorine-series gases you can easily etch SiO2 layer using e-beam resist. As you mentioned, you have to bake finally after development, namely, Hard-bake. And add Ar gas (less than 10 sccm) to CHF3/CF4 gas. To improve more selectivity and to get fine pattern for e-beam lithography, you have to use ICP-RIE tool type than simple RIE type.
In general, PMMA resist is poor etching selectivity. If you use another e-beam resist like ZEP520-A, you can basically obtain higher etch selectivity. And If you must certainly use a PMMA resist when SiO2 dry etching, you need to select fluorine-series gases like CHF2, C2F6, CF4, C4F8, Ar while excluding O2 gas. In case of using fluorine-series gases you can easily etch SiO2 layer using e-beam resist. As you mentioned, you have to bake finally after development, namely, Hard-bake. And add Ar gas (less than 10 sccm) to CHF3/CF4 gas. To improve more selectivity and to get fine pattern for e-beam lithography, you have to use ICP-RIE tool type than simple RIE type.
Today I found out nearly same selectivity (1:1) while etching SiNx with C9 (PMMA) mask. I used CHF3 15 sccm and SF6 30 sccm.... I want to etch 200 nm of SiNx. Any suggestion on which gas should I use to increase the selectivity?
Today I found out nearly same selectivity (1:1) while etching SiNx with C9 (PMMA) mask. I used CHF3 15 sccm and SF6 30 sccm.... I want to etch 200 nm of SiNx. Any suggestion on which gas should I use to increase the selectivity?
Thanks a lot Mohamed and Harry. Sorry for the late notice as I was busy with something else. But I will keep in touch with you guys as soon as I get some interesting results.
Thanks a lot Mohamed and Harry. Sorry for the late notice as I was busy with something else. But I will keep in touch with you guys as soon as I get some interesting results.
I have had similar problems and it seems that the pre-bake of the PMMA matters. What is you protocol before the lithography? How is your prebaking? Try baking at 155°C for at least 30 min. You can play with the times, it seems that the longer the better, but it could affect your ebeam resolution. You need to characterize it.
I have had similar problems and it seems that the pre-bake of the PMMA matters. What is you protocol before the lithography? How is your prebaking? Try baking at 155°C for at least 30 min. You can play with the times, it seems that the longer the better, but it could affect your ebeam resolution. You need to characterize it.
If you continue to use PMMA, you need good heat-sinking, and you need to keep the dry etch power down and no oxygen. PMMA is Plexiglas plastic and has a low deformation temperature. It flows if it gets heated up. First thing you would need is a graph of etch rates for PMMA and for SiO2 over a range of dry etch powers, particularly the low end.
Be careful if you try a prebake. You need to know the temperature at which it begins to flow and ruin the profile. It is low. This means low and long.
If you continue to use PMMA, you need good heat-sinking, and you need to keep the dry etch power down and no oxygen. PMMA is Plexiglas plastic and has a low deformation temperature. It flows if it gets heated up. First thing you would need is a graph of etch rates for PMMA and for SiO2 over a range of dry etch powers, particularly the low end.
Be careful if you try a prebake. You need to know the temperature at which it begins to flow and ruin the profile. It is low. This means low and long.
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I use CHF3/Ar chemistry to etch SiO2 through the PMMA with very good selectivity in RIE tool. If you can, try to сool the table to minus temperatures.
I use CHF3/Ar chemistry to etch SiO2 through the PMMA with very good selectivity in RIE tool. If you can, try to сool the table to minus temperatures.
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HI Abdul,
I am also trying kind of similar thing. Did you finally found any optimized recipe?
Thanks in advance,
Salahuddin
HI Abdul,
I am also trying kind of similar thing. Did you finally found any optimized recipe?
Thanks in advance,
Salahuddin
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Hello,
Actually your reported 1:1 etch selectivity of SiO2/PMMA is one of best reported in the literature/internet. Typically people have less than 0.6:1 for this material:mask combination.
Also from your description it looks like that this selectivity is enough for your final goal, why you need more PMMA left?
Hello,
Actually your reported 1:1 etch selectivity of SiO2/PMMA is one of best reported in the literature/internet. Typically people have less than 0.6:1 for this material:mask combination.
Also from your description it looks like that this selectivity is enough for your final goal, why you need more PMMA left?
More
VOTE
I am keeping same parameter from resist to dry etching. I only change the baking temperature at 180 oC from 2 min to 15 min for PMMA A4 resist. Features are improving but not perfect.
I am keeping same parameter from resist to dry etching. I only change the baking temperature at 180 oC from 2 min to 15 min for PMMA A4 resist. Features are improving but not perfect.
More
VOTE
In general, PMMA resist is poor etching selectivity. If you use another e-beam resist like ZEP520-A, you can basically obtain higher etch selectivity. And If you must certainly use a PMMA resist when SiO2 dry etching, you need to select fluorine-series gases like CHF2, C2F6, CF4, C4F8, Ar while excluding O2 gas. In case of using fluorine-series gases you can easily etch SiO2 layer using e-beam resist. As you mentioned, you have to bake finally after development, namely, Hard-bake. And add Ar gas (less than 10 sccm) to CHF3/CF4 gas. To improve more selectivity and to get fine pattern for e-beam lithography, you have to use ICP-RIE tool type than simple RIE type.
In general, PMMA resist is poor etching selectivity. If you use another e-beam resist like ZEP520-A, you can basically obtain higher etch selectivity. And If you must certainly use a PMMA resist when SiO2 dry etching, you need to select fluorine-series gases like CHF2, C2F6, CF4, C4F8, Ar while excluding O2 gas. In case of using fluorine-series gases you can easily etch SiO2 layer using e-beam resist. As you mentioned, you have to bake finally after development, namely, Hard-bake. And add Ar gas (less than 10 sccm) to CHF3/CF4 gas. To improve more selectivity and to get fine pattern for e-beam lithography, you have to use ICP-RIE tool type than simple RIE type.
More
VOTE
Dear Avijit,
For SiNx etching the selectivity could be much better. Please try a mixture of CHF3:O2:Ar with flow ratios 9:1:1.5 . Hope they are all available.
Low power levels of both ICP (~100 Watts) and RIE (~10W) are favorable, as well as low chamber pressures (~3 mTorr).
Please keep updated about your results.
Good luck.
Dear Avijit,
For SiNx etching the selectivity could be much better. Please try a mixture of CHF3:O2:Ar with flow ratios 9:1:1.5 . Hope they are all available.
Low power levels of both ICP (~100 Watts) and RIE (~10W) are favorable, as well as low chamber pressures (~3 mTorr).
Please keep updated about your results.
Good luck.
More
VOTE
In general, PMMA resist is poor etching selectivity. If you use another e-beam resist like ZEP520-A, you can basically obtain higher etch selectivity. And If you must certainly use a PMMA resist when SiO2 dry etching, you need to select fluorine-series gases like CHF2, C2F6, CF4, C4F8, Ar while excluding O2 gas. In case of using fluorine-series gases you can easily etch SiO2 layer using e-beam resist. As you mentioned, you have to bake finally after development, namely, Hard-bake. And add Ar gas (less than 10 sccm) to CHF3/CF4 gas. To improve more selectivity and to get fine pattern for e-beam lithography, you have to use ICP-RIE tool type than simple RIE type.
In general, PMMA resist is poor etching selectivity. If you use another e-beam resist like ZEP520-A, you can basically obtain higher etch selectivity. And If you must certainly use a PMMA resist when SiO2 dry etching, you need to select fluorine-series gases like CHF2, C2F6, CF4, C4F8, Ar while excluding O2 gas. In case of using fluorine-series gases you can easily etch SiO2 layer using e-beam resist. As you mentioned, you have to bake finally after development, namely, Hard-bake. And add Ar gas (less than 10 sccm) to CHF3/CF4 gas. To improve more selectivity and to get fine pattern for e-beam lithography, you have to use ICP-RIE tool type than simple RIE type.
More
VOTE
Today I found out nearly same selectivity (1:1) while etching SiNx with C9 (PMMA) mask. I used CHF3 15 sccm and SF6 30 sccm.... I want to etch 200 nm of SiNx. Any suggestion on which gas should I use to increase the selectivity?
Today I found out nearly same selectivity (1:1) while etching SiNx with C9 (PMMA) mask. I used CHF3 15 sccm and SF6 30 sccm.... I want to etch 200 nm of SiNx. Any suggestion on which gas should I use to increase the selectivity?
More
VOTE
Thanks a lot Mohamed and Harry. Sorry for the late notice as I was busy with something else. But I will keep in touch with you guys as soon as I get some interesting results.
Thanks a lot Mohamed and Harry. Sorry for the late notice as I was busy with something else. But I will keep in touch with you guys as soon as I get some interesting results.
More
VOTE
I have had similar problems and it seems that the pre-bake of the PMMA matters. What is you protocol before the lithography? How is your prebaking? Try baking at 155°C for at least 30 min. You can play with the times, it seems that the longer the better, but it could affect your ebeam resolution. You need to characterize it.
I have had similar problems and it seems that the pre-bake of the PMMA matters. What is you protocol before the lithography? How is your prebaking? Try baking at 155°C for at least 30 min. You can play with the times, it seems that the longer the better, but it could affect your ebeam resolution. You need to characterize it.
More
VOTE