Use Of Photoresist Research Articles

A micromachined chip-based electrospray source for mass spectrometry.

A micromachining process is described for fabricating a mass spectrometry electrospray source on a silicon chip. The process utilizes polymer (parylene) layers to form a system of chambers, filters, channels, and hollow needle structures (electrospray emitters) that extend more than a millimeter beyond the edge of the silicon substrate. The use of photoresist as the sacrificial layer facilitates the creation of long channels. Access to the channel structures on the chip is through a port etched through the silicon substrate that also serves as a sample reservoir. A reusable chip holder consisting of two plastic plates and an elastomer gasket provides the means to mount the chip in front of the mass spectrometer inlet and make electrical and gas connections. The electrospray emitters have tapered tips with 5 microns x 10 microns rectangular openings. The shape of the tip can be varied depending on the shape of the mask used to protect the parylene structures during the final plasma etch. The parylene emitters are physically robust and require only a high electric field to achieve stable electrospray operation over a period of a few hours. Direct comparisons with conventional glass or fused silica emitters indicated very similar performance with respect to signal strength and stability, spectral quality, and endurance. The automated MS/MS analysis of a mixture of tryptic peptides was no more difficult and yielded nearly identical results as the analysis of the same sample using a conventional nanospray device. This work demonstrates that an efficient electrospray interface to mass spectrometry can be integrated with other on-chip structures and mass-produced using a batch process.

Selective growth on facets and in situ mask removal for regrowth

A variety of unique processing capabilities can be achieved if the use of photoresist can be avoided during wafer patterning. Two such processes are reported here, based on the resistless patterning technique in which ultra-violet light is used to modify the surface native oxide on GaAs into a more stable gallium oxide suitable for use as a mask. First, we report the easy, in situ removal of the masking gallium oxide after selective growth and then regrowth to form embedded structures without additional process steps. Second, a non-planar GaAs wafer was exposed to ultra-violet light at an angle so that the gallium oxide is formed everywhere except in the shadowed sidewall areas where the native oxide remains intact. Upon thermal desorption of the native oxide, selective growth of InAs was achieved on the previously shadowed sidewalls only.

Ultraviolet laser fabrication of ultrastrong optical fiber gratings and of germania-doped channel waveguides

We report the fabrication of low loss (<0.2 dB) fiber Bragg gratings of 10 nm reflection bandwidth, and of 19 nm bandwidth lossy gratings. With this technology we also demonstrate the direct writing of channel waveguides in commercial germania-doped wafers without the use of photoresist and etching.

Maskless etching of ion modified chromium films

Thin chromium films have been implanted with 40 keV Xe +, Sb + and Bi + ions at various doses. A considerable reduction of the etch rates of the modified Cr films in chlorine-based plasma and during chemical etching has been found. Furthermore, a substantial reduction of the reflection coefficient in the uv optical range has also been found. Test structures of micron dimensions have been obtained by this technique avoiding the use of photoresist during etching.

Masking Considerations in Chemically Assisted Ion Beam Etching of GaAs / AlGaAs Laser Structures

The use of photoresist, Cr, and as etch masks for structures in chemically assisted ion beam etching is reported. The optimized etch with a photoresist mask results in a high degree of anisotropy and smooth sidewalls. However, the etched surface contains undesirable features. The etch with a Cr mask is also highly anisotropic, and the etched surface is free of features. The drawback with Cr masks is that the sidewalls are rough. Vertical and smooth sidewalls as well as a featureless surface are obtained with a mask. The mask has been employed to etch the facets of monolithic laser structures.

Wafer cooling in ion implantation

Recent years have seen a marked increase in the use of ion implantation in semiconductor manufacture. A key element in this rapid growth has been the use of photoresist for masking during implantation. The greatest resolution is achieved with positive photoresists, that is, with resists in which the area exposed in lithography is removed during development. Positive photoresists are generally quite sensitive to temperature. Excessive temperature during implantation can blister resist, alter critical dimensions and render the resist difficult to remove during subsequent processing. Most photoresists are unaffected by temperatures below 100°C. Few positive resists will survive temperatures above 150°C during implantation.

Ion beam etching GaAs for integrated optical applications

Stripe waveguides fabricated in the III–V semiconductors are required if the possibility of monolithic integration of optical devices and components is to be realized. A technique that is able to define micron and sub-micron features is essential to produce low loss waveguides. Ion beam etching has been demonstrated to be a possible method for the fabrication of guides with good wall edges. A comparison of etch rates, using argon and freon 12 has been made, as a function of the beam energy. Ion beam etching of GaAs grown on Al xGa 1−As layers has been examined for utilization in integrated optical applications. Results of etch rates, edge definition and wall profiles are presented. The influence of beam angle relative to the sample surface is reported and problems relating to the use of photoresist masks are also discussed. Rib type waveguides have been fabricated and light guiding demonstrated at 1.15 ωm.

Material-selective etching of InP and an InGaAsP alloy

Wet chemical etchants are inexpensive and can be employed easily in device fabrication. Material-selective etchants extend the design flexibility for devices with heterostructures. Several etchants on (100) InP and LPE-grown (100) InGaAsP are studied with emphasis on smooth crystal surfaces and well-defined mesa-structures by use of photoresist. The best results are obtained with the system glycerine: HCl ∶ HClO4 for preferential attack of InP and with the system H2O ∶ H2SO4 ∶ H2O2 for preferential etching of InGaAsP. Detailed information is given on the etching solutions investigated, on the etching conditions and the etching rates of the most useful etchants.

Photolithography in Integrated Circuit Mask Metrology

Photoresist technology is shown to have important advantages over the use of high-resolution silver halide films in dimensional metrology for integrated circuit masks. Experimental techniques are shown for the use of photoresist and chrome images in the study of image quality and uniformity and in analysis of the causes of image degradation. This method is applied to in situ lens evaluation and to the measurement of the precision of photorepeater stepping tables used in mask fabrication. In additiont, he value of 0.3 µm is established as the practical limit of dimensional tolerance in the present photolithographic technology, and its significance to the advancement of the state of the art in mask manufacture is discussed.

The Use of Photoresist as a Holographic Recording Medium

A technique is described for recording holograms and forming diffraction gratings in Shipley AZ1350 photoresist using the 4579-A output from an argon laser. A pre-exposure technique is described that not only reduces exposure times but increases the signal-to-noise ratio of the image. It is also shown that the effects of the variable characteristic of the resist can be alleviated by monitoring diffraction efficiency during development.