Dry etching technique

Despite the fact that dry etching techniques have improved dramatically in recent decades, the manufacture of microelectromechanical systems (MEMS) is still a domain of wet etching and silicon electrochemistry. The multiplicity of structures that can be achieved with silicon, together with its excellent mechanical properties [Pe6], have led to an immense variety of micromechanical applications. 

Plasma etching has demonstrated viable solutions to essentially all the problems encountered with liquid etching. Adhesion does not appear to be critical with dry etching techniques. In addition, undercutting can be... 

Dry etching techniques permit etch processes to be carried out in various modes. These can be described as purely chemical, purely physical, and a mixture of chemical and physical. With plasma etching and RIE, we have concentrated on chemical and ion assisted processes. In this section, etching methods that depend either solely or primarily on physical processes (momentum transfer) will be discussed briefly. 

Three different dry etch techniques were investigated isotropic O2 plasma etching in a Tegal 200 reactor, R.I.E. in a parallel-plate in-house modified Tegal AOO reactor and R.I.M. in a Veeco, Model RG-830. The conditions of operation for each system were as follows where time is the time to etch 1.2 p of fully cured polyimide. 

A metal interconnect fabrication process is disclosed in US-A-5384267. A metal layer and a photoresist layer are formed on an array of HgCdTe detectors. The photoresist layer is patterned to form a positive mask and the metal interconnect is formed by using a dry etching technique. 

TABLE 1 Summary of etch rate results for GaN, AIN and InN from various dry etching techniques for some typical etchant gases. 

Alternative dry etching techniques have recently been developed for the nitrides for low-damage applications. Photoassisted dry etching is set up analogously to CAIBE except that the ion beam source is replaced with an ultraviolet laser. Leonard and Bedair [25] reported on the photoassisted dry etching characteristics of GaN using HC1 gas and a 193 ran ArF excimer laser (1400 mJ/cm2) with the substrate... 

In conclusion, the optical gain of quantum well GaN/AlGaN was estimated, based on the density-matrix theory. The introduction of GaN quantum wells as active regions in GaN-based surface emitting lasers can reduce the threshold current to lower than that of bulk GaN layers. Sub-milliampere operation can be expected by reducing the device diameter. Fabrication processes such as highly reflective mirrors and dry-etch techniques have been demonstrated. 

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). 

An alternative approach to the complicated photoresist systems could be the application of APD (ablative photodecomposition), where a strong absorbance at the irradiation wavelength is one of the conditions for successful ablation. A logical approach to the use of APD as a dry etching technique in microlithography is the development of polymers designed for APD. This is especially true for photolithographic applications that do not require a submicron resolution, such as thin film transistor (TFT) fabrication for liquid crystal displays (LCD) which require a resolution around 1 pm. 

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