# NEGATIVE RESIST FORMULATION FOR PRODUCING UNDERCUT PATTERN PROFILES 

[0001] The field of the invention pertains to a negative radiation-sensitive aqueous base soluble photoresist compo› sition used for making integrated circuit (IC) and light emitting diode (LED) Devices 

[0002] Photoresist compositions are used in microlitho› graphic processes for making miniaturized electronic com› ponents such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate solvent in the photoresist composition and to fix the coating onto the substrate. The baked, coated surface of the substrate is next subjected to an image-wise exposure to imaging radiation. 

[0003] This radiation exposure causes a chemical trans› formation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are imaging radiation types commonly used today in microlithographic processes. After this image-wise expo› sure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the coated surface of the substrate. 

[0004] There are two types of photoresist compositions, negative-working and positive-working. When negative› working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to such a solution. Thus, treatment of an exposed negative› working resist with a developer causes removal of the non-exposed areas of the photoresist coating and the cre› ation of a negative image in the coating, thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited. 

[0005] The use of a negative-working, acid-sensitive pho› toresist composition is known in the prior art. Most of such prior art photoresist compositions use a crosslinking agent that reacts with the polymeric binder resin to form an insoluble film comprising a higher molecular weight poly› mer 

[0006] The major development in resist products and chemistry has been devoted to the silicon integrated circuit (IC) chip industry. This technology moved from i-line lithography to shorter wave length ( deep UV) lithographies, such as 248 nm, 193 nm and 157 nm in quest for higher resolution. Several generations of advanced deep UV resist materials have been developed. Critical dimensions (CD) well below 0.2 µmare achieved in production, applying 248 and 193 nm lithography based on chemically amplified resists. 

[0007] However, applications, such as processing of GaAs or compound III-V substrates, light emitting diodes (LED), high powered LED and organic light emitting diodes (OLED), on the other hand, largely are still employing 

## FIELD OF INVENTION 

## BACKGROUND 

conventional i-line lithography and i-line resist materials which are not chemically amplified. For these applications Deposition of metal ( a.k.a. metallization) on semiconductor substrates covered with a pattered photoresist is frequently done by chemical vapor deposition (CVD) technologies such as LPCVD. Sputtering metal deposition may also be employed to deposit thick, uniform metal layers. Another technique employed for metallization is Vacuum Deposition (VD), in particular as induced bye-beam (EBPVD). 

[0008] Electron beam physical vapor deposition, or EBPVD, is a form of physical vapor deposition in which a target anode is bombarded with an electron beam given off by a charged tungsten filament under high vacuum. The electron beam causes atoms from the target to transform into the gaseous phase. These atoms then precipitate into solid form, coating everything in the vacuum chamber (within line of sight) with a thin layer of the anode material. 

[0009] Sputtering metal deposition is done in a vacuum chamber where an electrically grounded metallic target wafer is bombarded with electrically charged Argon gas, sputtering away the metal atoms and depositing them on a target wafer. 

[0010] CVD metal deposition occurs by reaction of a reactive gas under reduced pressure with a either the semi› conductor substrate, itself or by reaction with a second reactive gas producing in both scenarios a metal deposit. For instance, as non-limiting examples, in the first scenario WF $_{6 }$ may affect deposition on a Silicon substrate by reaction with Si to produce a metallic W deposits and producing as a reaction product gaseous SiF $_{6 }$ which is pumped away. An example of the second scenario is the gaseous reaction of WF $_{6 }$ with H$_{2 }$ to deposit metallic W and producing as a reaction product gaseous HF which is pumped away. 

[0011] Using a pattered resist, either CVD or sputtering metal may be employed to metalize areas of substrate not covered by resist. However, subsequent to this step the remaining resist can be removed by either employing a chemical etchant or an adhesive tape applied to the surface of the resist to remove it. In either situation removal may be facilitated by employing a lift-off process is employed where the resist patterns were initially produced prior to metalli› zation have an undercut at the resist substrate interface. In the case where a chemical etchant is employed, such as a stripper, removal of remaining resist is made easier because the undercut portion of the resist is not metallized allowing the stripper to attack the resist and remove it. Straight wall, resist profiles, and profiles with a poor undercut have significant metallization at the sidewalls of these profiles making removal of the resist with a stripper much more difficult or impossible. Similarly, when using a sticky tape approach to affect removal of the resist, the more pro› nounced the undercut of the profiles the easier these are to remove without leaving large amount of residual resist on the substrate. The minimization of this residue, in tum, allows for a faster removal of this residue in subsequent stripping operation. Traditional, approaches to getting sloped profiles which have some undercut resist character› istics for lift-off application, have depended upon the manipulation of optical conditions during exposure such as exposure tool defocus. Such "optical" approaches are inher› ently limited by the optical physics itself, in the extent of undercut which is possible. 

[0012] There is a need for a high sensitivity i-line chemi› cally amplified negative resist which gives, during imaging, 

