Methods to pattern contacts using chromeless phase shift masks
View Patent ↗Method for using chromeless phase shift lithography (CPL) masks to pattern contacts on semiconductor substrates and corresponding CPL masks for performing the method. The method for patterning contacts includes illuminating a CPL mask comprising a reticle having a plurality of phase-shifting features interspersed with non-phase-shifting areas using a short wavelength UV light source, wherein the phase-shifting features are configured in a pattern corresponding to a target pattern of the contacts on the semiconductor substrate. Phase-shifted and non-phase-shifted light passing through the reticle are projected as an aerial image onto a layer of a negative tone resist applied over the semiconductor substrate to pattern the contacts in the resist. The phase-shifting features are recesses which cause light passing therethrough to be phase-shifted by approximately 180 ° from light passing through non-phase-shifting areas of the mask. Each recess in the CPL mask is used to pattern a separate contact on the semiconductor substrate.
1. A method for patterning contacts, comprising;
illuminating a chromeless phase shift lithography (CPL) mask, the mask comprising a quartz reticle having a pattern of a plurality of phase-shifting features comprising recesses interspersed with non-phase-shifting areas, wherein each recess is to pattern a separate contact wherein the phase-shifting features are to pattern contacts, wherein the CPL mask is illuminated with a deep ultra-violet (DUV) wavelength light source, wherein light passing through the phase-shifting features is phase-shifted one hundred eighty degrees relative to light passing through the non-phase-shifted areas of the CPL mask; and
passing the phase-shifted and non-phase-shifted light through projection optics to project an aerial image onto a layer of a negative tone resist applied over a semiconductor substrate to pattern the contacts in the negative tone resist,
wherein the contacts are patterned using a single exposure of the DUV wavelength light source.
2. The method of claim 1 , wherein the phase-shifting features are arranged in a pattern to produce an array of contacts having a pitch of approximately 200 nanometers or less.
3. The method of claim 1 , wherein the phase-shifting features are arranged in a pattern to produce contacts having a critical dimension of approximately 100 nanometers or less.
4. The method of claim 1 , wherein the DUV wavelength light source produces light having a wavelength of one of 248, 193, or 157 nanometers.
5. The method of claim 1 , further comprising the operations of:
developing the negative tone resist;
removing portions of the negative tone resist not exposed by the aerial image; and
etching a plurality of contact holes in the semiconductor substrate in areas of the semiconductor substrate surface having the negative tone resist removed.
6. The method of claim 1 , wherein the phase-shifting features comprise a plurality of squares configured in a substantially square grid, and the contacts formed in the negative resist are substantially circular in shape.
7. A method for patterning contacts in a semiconductor substrate, comprising;
off-axis illuminating a chromeless phase shift lithography (CPL) mask, the mask comprising a quartz reticle having a pattern of a plurality of phase-shifting features comprising recesses interspersed with non-phase-shifting areas, wherein each recess is to pattern a separate contact, wherein the phase-shifting features are to pattern contact, wherein the CPL mask is illuminated with a deep ultra-violet (DUV) wavelength light source, wherein light passing through the phase-shifting features is phase-shifted one hundred eighty degrees relative to light passing through the non-phase-shifted areas of the CPL mask, said phase-shifting features arranged in a pattern; and
projecting phase-shifted and non-phase-shifted light passing through the CPL mask onto a layer of negative tone resist applied over the semiconductor substrate to pattern the contacts in the resist,
wherein the contacts are patterned using a single exposure of the DUV wavelength light source.
8. The method of claim 7 , wherein a quadrupole illumination source is employed to produce the off-axis illumination.
9. The method of claim 7 , wherein the DUV wavelength light source produces light having a wavelength of one of 248, 193, or 157 nanometers.
10. The method of claim 7 , wherein the phase-shifting features comprise a plurality of squares configured in a substantially square grid, and the contacts formed in the negative resist are substantially circular in shape.