John E. Heidenreich

Particle trapping phenomena in radio frequency plasmas

Particles generated in an argon plasma and suspended at the plasma/sheath boundary are localized by lateral trapping fields. In the commercial rf etching reactor used in this work, the particles and their motion in real time are observed by laser light scattering with the laser beam rapidly rastered in a plane parallel to the rf electrode. Repulsion between individual, relatively large particles is observed, verifying that there is significant negative charge on the particles. Two types of trapping regions are commonly seen: rings of particles around the outside edge of silicon wafers, and domes of particles over the centers of the wafers. It is shown that these effects are influenced by the topography of the electrode. In addition, particle densities >107 cm−3 for particles of diameter 0.2 μm are inferred from transmission studies for certain plasma conditions.

Rastered laser light scattering studies during plasma processing: Particle contamination trapping phenomena

The distribution and transport of particles in materials processing plasmas has been studied with a rastered laser light scattering technique. Contrary to expectation, the distribution of particles in a plasma processing tool is rarely random. Instead, structured clouds of particles form at the plasma/sheath boundary. The effect is attributed to trapping of the particles by weak electric field nonuniformities and the characteristic negative charge of isolated particles in a plasma. Field nonuniformities appear to be influenced by the topography and material design of the tool. For example, the presence of a Si wafer often induces significant particle trapping. Examples of particle trapping in a laboratory system are given, and similar phenomena are also verified in a manufacturing sputter deposition tool operating in a class 100 cleanroom. The implications of particle trapping in plasma processing are discussed.

X‐ray photoelectron and infrared spectroscopy of microwave plasma etched polyimide surfaces

In situ x‐ray photoelectron spectroscopy (XPS) and thermal desorption measurements indicate that etching of polyimide (PI) in a microwave oxygen plasma results in increased carbonyl (C–O) bonds on the etched surfaces, which can be removed by heating. Addition of CF4 to oxygen plasma enhances the etch rate, but also gives rise to fluorine coverages which appear to scale with the atomic F concentration in the gas mixture. XPS study of selected fluorinated model compounds shows that changes in the C 1s spectra of PI surfaces, etched in plasmas with different CF4 concentrations can be interpreted either as formation of Teflon‐like passivation layers or as simply fluorinated benzenes. Exposure to x‐ray irradiation at a constant flux or isothermal heating in vacuum caused the fluorine coverage to desorb in two stages, suggestive of two different fluorine‐containing desorbing species. Experimental evidence obtained by multiple internal reflectance and transmission Fourier transform infrared spectroscopy indicate...

Influence of the applied field frequency (27–2450 MHz) in high‐frequency sustained plasmas used to etch polyimide

The effect of the plasma stimulating frequency upon the etching of polyimide is reported. For the first time, a system has been developed which generates, over a large frequency domain (27–2450 MHz), a high‐frequency (HF) produced plasma by identical means (surface wave propagation) in a fixed plasma volume. It is found that the addition of CF4 to an O2 plasma affects the etch rate of polyimide in a manner which depends upon the operating frequency of the HF plasma. In particular, a maximum of etch rate per watt is observed around 50 MHz.

Chemical And Physical Aspects Of Multilayer Resist Processing

A multilayer resist structure is typically composed of at least two materials, an oxygen plasma resistant layer and a planarising layer which is eroded in an oxygen based plasma. This structure is then subjected to a variety of excited and ground state species generated in the plasma. To understand the final etched profile produced by such a system, it is necessary to characterise both the chemical nature of the plasma, and its impact upon the structure subjected to the etching process. This paper will discuss the effect of the intrinsic plasma properties such as composition, density, potential and electron energy distribution upon the processes which produce etching of both the planarising and etch resistant layers. The effect of the chemical composition of organometallic etch barriers based on silicon, germanium and iron and the process by which they resist these plasmas will also be presented and compared with the properties of the planarising layers. The etching properties of the planarising layer will be shown to depend strongly upon the plasma excitation frequency.

Damascene copper integration

The increase in ratio of wiring RC delay to the intrinsic transistor RC delay is motivating the IC industry to move from subtractive-aluminum to damascene-copper wiring. In addition to having 40% lower sheet resistance, damascene copper has significantly lower resistance and capacitance variability than subtractive-aluminum wiring due to improved reactive ion etch bias control. Damascene copper causes less plasma charging than subtractive-aluminum wiring in wire/via antenna devices and the charging can be modulated by electron shadowing during via RIE.