Anisotropic etching methods

Detector elements 11 are formed on a ceramic substrate 1. Each detector element includes a photosensitive zone 9, an output terminal 4 and a common terminal S. The detector elements are arranged in an array protruding from a common metal line 3, which is connected to a terminal pad 6. The terminal electrodes and the common metal line are formed on a comb-like patterned photo-conductive layer 2. An aperture plate 7 of silicon or ZnS having apertures 8 formed therein by an anisotropic etching method is prepared. The purpose of the aperture plate is to restrict the field of view of the photosensitive zones. An auxiliary electrode 30 is formed on the aperture plate. When the aperture plate is assembled with the substrate using an adhesive, the auxiliary electrode is pressed against the common metal line and the common terminal, which together reduce the electrical resistance. 

The fabrication method generates functional elements via anisotropic etching of high-quality semiconductor wafers, referred to as mother wafers.13 17 25 The process begins with photolithographic definition of patterns... 

The limitations encountered with solution etching can be overcome by plasma-enhanced etching. Adhesion is not a major problem with dry-etch methods. Undercutting can be controlled by varying the plasma chemistry, gas pressure, and electrode potentials (2-6) and thereby generate directional or anisotropic profiles. 

Sputter or ion etching (IE) is also a physical etching method with inert ions (such as Ar+) from a plasma which are accelerated towards the substrate. In this case the substrate is in contact with the plasma. The etching profile is anisotropic, the selectivity is poor. 

Wet chemical anisotropic etching of monocrystalline silicon has been widely applied in microtechnology (18,20). This method is based on the dependence of etching velocity on crystal orientation, so only a few basic geometries can be... 

Precise microstructures with nearly any cross-sectional shape can be generated by means of anisotropic plasma-etching methods, where again silicon is the most important and proven material (18,20). Usually, a mask pattern is transferred into a thin layer consisting of a material resistant to plasma etching on a silicon... 

Laermer F, Schilp A (Robert Bosch GmbH). Method of Anisotropically Etching Silicon. U.S. Patent No. 5501893, 1996. 

To create liquid access, holes were punched through the replica. Then it was placed on another thin slab of PDMS for sealing. Because an anisotropic KOH-based etching method was employed to etch the Si master without corner compensation, the channel intersections in the replica were limited in shape by the <111> plane of the Si master [159]. 

In addition to the chemical etching method described above, other etching methods such as chemical anisotropic etching, and reactive plasma etching, may also be used to define the geometric configuration of the sensor element. These etching techniques are also established microelectronic processes and are extensively described elsewhere [6]. 

Fig. 2. (left) The subtractive method of patterning a thin film showing isotropic vs. anisotropic etching, (right) The additive method of patterning a thin film. 

A separation chip, according to the Lund-method, is most easily made by anisotropic etching of a (100>-oriented silicon wafer. The channel mask should be aligned 45° offset to the (110)-cut phase of the wafer. Figure 44.13a, to accomplish the desired rectangular channel cross-section. Figure 44.13b. 

Laermer F, Schilp A (1994) Method of anisotropically etching silicon. German Patent DE4241045, (USA Patents 5501893, 1996)... 

Silicon has a diamond cubic crystal structure. The Miller indices of the main crystallographic planes of silicon are (100), (110), and (111), respectively. In the wet bulk micromachining, there are two silicon etching methods isotropic (direction-independent) and anisotropic... 

The most common method of pattern transfer to the substrate is by wet chemical etching. However, all semiconductor wet etching processes exhibit the same basic limitation. This limitation is due to the isotropy of the process, which makes linewidth control difficult for features less than 2 pm when thick substrate layers are used. The need to transfer fine features in thick substrates has led to the development of anisotropic etching techniques such as plasma etching, reactive ion etching (RIE) and sputter etching. 

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