PLASMA RESIST IMAGE STABILIZATION TECHNIQUE (PRIST)
`
`W. n-L. Ma
`
`IBM Data Systems Division, East Fishkill
`Hopewell Junction, New York 12533
`
`ABSTRACT
`
`RESULTS AND DISCUSSION
`
`Figures 1 and 2 show micrographs of a resist
`PRIST, using a fluorocarbon plasma, effectively
`image after a 21OOC post bake without and with
`stabilizes the developed resist image in the produc-
`PRIST, respectively. Without PRIST, the resist
`tion of integrated circuits. This plasma treatment,
`lines flowed and merged after the post bake, and
`which is done at low power for a short time, allows
`the pattern is no longer recognizable. On the
`the resist to be baked in excess of 21OOC with no
`other hand, the PRIST-treated resist retained its
`measurable change in dimensions. This phenomenon
`integrity after the high temperature bake.
`is attributed to the change in thermal properties
`of the resist surface effected by the active
`fluorine and fluorocarbon species generated in the
`plasma.
`
`INTRODUCTION
`
`PRIST has a relatively wide process window.
`However, since fluorocarbon plasma also etches
`oxide, nitride, and silicon, it is advisable to
`minimize both rf power and treatment time. Both
`CF4 and DE 100 produce satisfactory results.
`However, DE 100 is less desirable because a small
`amount of oxygen in CF4 (i.e., DE 100) can increase
`A fluorocarbon plasma treatment allows wafers
`etch rates of the substrate materials.
`to be processed at high temperature without resist
`image and profile degradation.
`
`This technique can also be exercised in other
`plasma systems, such as reactive ion parallel
`Many integrated circuit fabrication operations,
`plate reactor and inductively coupled barrier
`such as ion implantation, reactive ion etching, and
`reactor.
`lift-off metallization, frequently encounter high
`temperature during the process. Such extreme heat
`We hypothesize that the fluorination of the
`may be detrimental when a resist mask is used.
`resist surface is responsible for the stabilization
`Also, deformation of the developed resist can occur
`of the resist image under a high processing temper-
`during post baking. Thus, the possible change in
`ature. The active fluorine and fluorocarbon
`image size constrains the minimum dimension
`of the
`species in the plasma react with the resist and
`mask geometry.
`fluorinates the surface. The treated surface has
`a higher softening temperature, and thus serves as
`a casting for the bulk resist, which maintains the
`developed resist image during the bake.
`The plasma reactor used in this experiment
`is
`a low-pressure barrier type rf discharge system with
`a 20.3 cm (8") diameter and 33 cm (13") long
`quartz chamber. The chamber is evacuated by a
`roughing pump; the 13.56 MHz power is capacitively
`coupled to the chamber through a pair of metal
`electrodes.
`
`EXPERIMENT
`
`SUMMARY
`
`PRIST is very effective in stabilizing the
`developed resist image. This technique, using
`fluorocarbon plasma, can prevent resist image
`deterioration even after a high temperature (21OOC)
`post bake. This phenomenon is attributed to the
`change in the resist surface property due to
`chemical reactions which occur during the treatment.
`
`The gases used are of fluorocarbon type, such
`as CF4 and DE 100 @ (CF + small amount of oxygen).
`4
`
`An AZ type positive resist is coated onto the
`S i wafer with or without the dielectric layers
`(oxide or nitride). After the image is developed
`
`on the resist, the wafers are briefly treated in a
`fluorocarbon plasma, followed by a 210'C post bake
`on a hot plate in an oven for 30 min.
`
`'Registered
`
`trademark of LFE Corp.
`
`22.6
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`574
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`CH1616-2/80/0000-0574 W . 7 5 0 1980 IEEE
`
`SAMSUNG-1010.001
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`

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`Fig. 1. Micrograph of a r e s i s t p a t t e r n a f t e r
`PRIST (320X)
`2 1 O O C post bake without
`
`a r e s i s t p a t t e r n a f t e r
`Fig. 2 . Micrograph of
`PRIST (800X)
`210OC post bake with
`
`22.6
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`575
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`SAMSUNG-1010.002
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`

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