Hard bake

Hard baked goods such as cookies and crackers have a relatively low water and high fat content. Water can be absorbed, and the product loses its desirable texture and becomes subject to Hpid rancidity. Packagiag for cookies and crackers includes polyolefin-coextmsion film pouches within paperboard carton sheUs, and polystyrene trays overwrapped with polyethylene or oriented polypropylene film. Soft cookies are packaged in high water-vapor-barrier laminations containing aluminum foil. 

The incorporation of PDMSX into conventional novolac resins has produced potential bilevel resist materials. Adequate silicon contents necessary for O2 RIE resistance can be achieved without sacrificing aqueous TMAH solubility. Positive resist formulations using an o-cresol novolac-PDMSX (510 g/mole) copolymer with a diazonaphthoquinone dissolution inhibitor have demonstrated a resolution of coded 0.5 pm L/S patterns at a dose of 156 mJ/cm2 upon deep-UV irradiation. A 1 18 O2 etching selectivity versus hard-baked photoresist allows dry pattern transfer into the bilevel structure. 

Figure 6. Scanning electron micrographs of hard-baked PMMA films before and after a 1.0-min oxygen-RIE treatment at the following conditions a, unetched and b, etched, 0.125 W/cm, 35 mTorr, -230 VDC, no thermal grease. Continued on next page.

AZ-1350 photoresist was used as a thick bottom layer polymer. AZ resist, thicker than 1.0 was spin-coated on silicon wafer (oxide coated) or substrate with topographic features. The resist was hard-baked for 1 hour at 200 C. SNR film was then spin-coated on a hard-baked AZ resist layer from 5 wt% solution in methylisobutylketone. 

The resolution of 2LR with SNR/AZ resist where SNR had Mw of 3.8 x 104 was evaluated as a well-resolved line and space width on the Si wafer. A 0.2 /an SNR layer was coated on a hard-baked AZ resist with 1.0 thickness and exposed with an electron beam, then developed. The obtained pattern of SNR is transferred to the AZ resist layer by 02 RIE. 

In a first step, the negative working photoresist SU-8 is spin-coated on to the disk and soft baked [110]. The disk is then UV-exposed to pattern the bottom layer. A silver thin metal layer is thereafter evaporated. The metal layer is spin-coated with an AZ-type photoresist, dried, exposed and developed. In this way, the metal layer can be developed independently from the patterning of the SU-8 layer underneath. The metal layer is patterned by wet-chemical etching. As a next step, a second SU-8 layer is deposited, soft-baked and exposed. Top and bottom layers are now developed. After a hard bake, a second CaF2 disk is attached to the stack and sealed by a light-curing epoxy resin. 

What are the purposes of soft bake and hard bake after photoresist is coated on a wafer [321] (4 marks)... 

Figure 8. Self developed submicron images produced in a film of poly(p-t-butylphenyl methylsilane) by irradiation at 248 nm (55 mJ/cm -pulse, 550 mJ total dose). The images were transferred into 2.0 /im of a hard baked AZ photoresist by O2-RIE.

Figure 9. 0.75 ixm features generated in a bilayer of 0.2 fxm of poly(cyclohexyl methylsilane) coated over 2.0 fitn of a hard baked AZ photoresist using mid UV projection lithography, 100 mJ/cm ... 

To measure the sensitivity, the resist solution was spin-coated onto a hard-baked (at 200 C) OFPR-800 resist layer or a baked (at 200 0 polyimide film (PIQ, Hitachi Chemical Co.). Irradiation was carried out using a high pressure mercury-xenon source (600W, Hanovia). 

Trilevel Schemes. Trilevel processing (6, 7) requires planarization of device topography with a thick layer of an organic polymer, such as polyimide or a positive photoresist that has been baked at elevated temperatures ( hard baked ) or otherwise treated to render it insoluble in most organic solvents. An intermediate RIE barrier, such as a silicon dioxide, is deposited, and finally, this structure is coated with the desired resist material. A pattern is delineated in the top resist layer and subsequently transferred to the substrate by dry-etching techniques (Figure 3). 

Brominated poly(l-trimethylsilylpropyne) is an example of a substituted polyacetylene that is suitable for bilevel-resist processes (34). Requiring both exposure and postexposure bake (PEB) steps, samples of the polypropyne having a mole fraction of bromine from 0.1 to 0.2 per monomer unit exhibit sensitivities in the order of 25 mj/cm. Submicrometer resolution has been demonstrated, and etching-rate ratios relative to hard-baked photoresist planarizing layers are —1 25. 

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