Junji Tamano

Plasma polymerized methyl‐methacrylate as an electron‐beam resist

Plasma polymerized methyl‐methacrylate thin film was formed on a glass substrate coated with chromium as a resist for electron‐beam lithography. The polymerizations were conducted at two discharge frequencies of 13.56 MHz and 5 KHz using a capacitively coupled discharge electrode system in a bell‐jar‐type reactor. Delineations were carried out using an electron beam whose diameter and acceleration voltage were 0.5 μm and 20 kV, respectively. As a test pattern, 25 pairs of parallel lines and spaces each having a 10‐μm width were delineated in a rectangular area of 0.5×0.5 mm2. Each line of 10‐μm width was depicted by sweeping over using the electron beam with 20 repetitions. The patterns were developed on the chromium by CCl4 plasma etching.

Vacuum lithography—A completely dry lithography using plasma processing

The purpose of this paper is to describe a thoroughly dry lithography using plasma polymerization and plasma etching. The new lithography is named vacuum lithography because all processes are performed at reduced pressures. Resist films were formed in bell-jar-type and argon-flow-type reactors. The controllability of plasma polymerization is discussed with respect to the type of reactor and gas mixture. A pattern was delineated in the resist using an electron beam, and it was developed by plasma etching with a mixture of argon and oxygen. It was found that the quality of the plasma-polymerized resist depends strongly on the polymer structure and on the plasma etching conditions. In this experiment, the recorded values of sensitivity and γ value of plasma-polymerized methyl methacrylate were 700 µC/cm2 and 1, respectively.

Vacuum lithography using plasma polymerization and plasma development

Abstract A completely dry lithography has been proposed which involves plasma polymerization of methyl methacrylate (MMA) and plasma development with CCl 4 . It was called vacuum lithography because all processes were performed in a vacuum. However, the developed pattern had a lower resolution than patterns produced by conventional lithography with a wet process. After several technical refinements, the quality of the resist and the developed pattern was markedly improved. In this paper, recent results will be reported. A gas-flow-type reactor was used instead of a bell-jar-type reactor because the morphology of plasma-polymerized MMA (PPMMA) varied with each experimental run which was performed with the same gas and discharge parameters. The monomer vapour was introduced downstream of the argon discharge, and the polymerized film was formed on the substrate placed further downstream in the mixed gas. The development of pattern was performed by etching with an Ar-O 2 mixture and with hydrogen gas instead of CCl 4 gas, because the etching rate of the resist was too high in a CCl 4 plasma and a clear pattern was not obtained. The evaluated sensitivity and γ value of PPMMA were 1000 μC cm −2 and 1 respectively. MMA containing 5% tetramethyltin was also used as a monomer gas for plasma polymerization downstream of the argon discharge. In this case the sensitivity and γ value were 10 μC cm −2 and 2 respectively.

A transparent boron-nitrogen thin film formed by plasma CVD out of the discharge region

A transparent boron-nitrogen thin film of thickness 550 nm was successfully deposited out of the discharge region by rf plasma CVD. The deposition was performed with diborane (4.8 vol % in N2) as the reactant gas and argon as the carrier gas by an inductively coupled reactor at a frequency of 13.56 MHz. The transparent films could be obtained at a low pressure of about 30 Pa, at a discharge power level of 30 W, and at room temperature without heating the substrate. The thin films obtained by rf plasma are compared with those obtained by microwave plasma. Both the refractive index and the deposition rate for the films deposited by microwave plasma are discussed according to the deposition conditions.