Etch rates of polymers

When it comes to etching, not all polymers are created equal. In a seminal work, it was found that the etch rate of polymers in an RIE process depends critically on the carbon and oxygen... 

Polymer sample temperature, measured with a thermocouple situated beneath a thin glass platform supporting the sample, depended on etch rate of the polymer the maximum temperature rise encountered in any run was 9 K, exhibited by TB after 20 min exposure to 0(3P). The... 

The 02 reactive ion etching rates of poly(disilanylenephenylene) 10 and 11, and polyimide (PIQ) were measured. As can be seen in Figure 4, the polymers 10 and 11 show very high etching resistance against the oxygen plasma, compared with the PIQ. 

We first experimented with the Quartz Crystal Microbalance (QCM) in order to measure the ablation rate in 1987 (12). The only technique used before was the stylus profilometer which revealed enough accuracy for etch rate of the order of 0.1 pm, but was unable to probe the region of the ablation threshold where the etch rate is expressed in a few A/pulse. Polymer surfaces are easily damaged by the probe tip and the meaning of these measurements are often questionable. Scanning electron microscopy (21) and more recently interferometry (22) were also used. The principle of the QCM was demonstrated in 1957 by Sauerbrey (22) and the technique was developed in thin film chemistiy. analytical and physical chemistry (24). The equipment used in this work is described in previous publications (25). When connected to an appropriate oscillating circuit, the basic vibration frequency (FQ) of the crystal is 5 MHz. When a film covers one of the electrodes, a negative shift <5F, proportional to its mass, is induced ... 

Figure 26, A comparison of the etch rates of thermal oxide, acrylate resist (PMMA) and AZ resist using DE-100 gas at 200W and 0,55 Torr, The shaded areas surrounding the acrylate and AZ curves represent the etch rates of typical aliphatic and aromatic polymers respectively.

PE etch rate measurements were made in either a IPC 4005 or legal 421 system. To determine the plasma etch rate of the polymer... 

Increased durability can be designed into polymer resists. For instance, for the relative etch rates of a variety of polymers in an 02 plasma, a high correlation exists between the structural properties of the polymer and their... 

Several years ago, Taylor et al. (2,3) showed that the oxygen plasma-etch resistance of carbon-based polymers could be markedly enhanced by incorporating certain atoms into the polymer chain. Particularly effective were those elements such as silicon or titanium that form a refractory oxide during oxygen RIE. The oxide is formed at the surface of the resist and greatly retards the subsequent etching rate of the remaining resist. 

Etch rate of metal-free polymers was reported to be inversely proportional to the carbon atom content in the polymer (. For organosilicon polymers, role of silicon atoms under O2-IBE is discussed as an analogy of that for the carbon atoms in carbonacious polymers. The number of silicon atoms in a unit volume is given by... 

A second method of local planarization involves spinning photoresist onto the SiOj ILD to obtain local planarity. The resist is then hard baked and etched with an RIE etch tailored to remove SiOz (or ILD) at the same rate as the photoresist. Because the etch rate of the two materials is equal, the planarity of the resist film transfers into the SiOz film. However, a precise match in SiOj and photoresist etch rates is difficult to maintain because the relative ratio of SiOj to photoresist exposed increases as the etch back proceeds. Loading effects then result in a decrease in the Si02 etch rate and increase in the photoresist etch rate. Furthermore, polymer deposits build up on the etch reactor chamber walls over time etching of this polymer depletes the chemicals used to etch the photoresist, which slows the photoresist etch rate. If the etch rates are not matched, the planarity of the photoresist layer will not transfer well to the SiOz. 

Fig. 4.32 Relative reaction ion etch rates of various photoresist polymer candidates.

Poly(trichloroethyl methacrylate) (PTCEM) is a polymer electron resist with a high glass transition temperature, Tg = 126° C. It is soluble in many common organic solvents. The plasma etch rate of the polymer is relatively high (8). In our PDE work, PTCEM has been used as the base polymer. Several monomer/PTCEM mixtures have been evaluated as a PDE. 

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