Layer Addition during Photolithography

A brief review

Methods for layer addition include thermal oxidation, vapor deposition and electroplating. Layers needed to be adjoined after photolithography are the dielectric layer, electrical insulator, patterning mask and layer for metallization contracts. Thermal Oxidation intends to grow the oxide layers under the thickness of 1 micrometer. Usually the silicon dioxide layer is the layer where this process is done. Dry oxidation or wet oxidation can be used with this process where the dry method includes the usage of the oxygen under a high range of temperature such as 90-12000C. Furthermore the wet oxidation includes the process with the assistance of water. Film Deposition is another methof for layer addition and can be either assisted by chemicals or by physical means. The Physical Vapor Deposition can occur either by evaporation, sputtering or reactive sputtering method. The Chemical Vapor Deposition can occur in the low pressure mode or plasma enhanced. Step coverage is one of the biggest obstacles in the process of physical evaporation. This obstacle can be prevented by rotating the wafer, broadening the area of source’s deposition or elevating the temperature. On the other hand sputtering method usage eliminates this obstacle. This method uses he principle of plasma, the forth state of matter. In addition reactive sputtering uses non-inert gases such as oxygen, nitrogen, hydrogen. Radio Frequency Sputtering is a technique used by alternation of the electrical potential of the current at the radio frequencies in a vacuum and it disables the charge formation over the sputtering materials. On the other hand the chemical methods include the reaction of chemicals either thermally, electrically or optically. Atmospheric pressure vapor deposition method is perfect for depositing high rates, it is simple and enables high throughput. Its main disadvantage is that it has a poor uniformity and that is why it is more preferred for thick oxides. Low pressure CVD garantuees high rate of purity, but its rate of depositions are low and that is why it is mostly preferred for polysilicon or dielectric deposition. Plasma Enhance CVD on the other hand uses low temperature normally used for backend process but its disadvantage is because of plasma damage occuring usually in that process. Its main usage is in dielectrics coatings[1].

The most important concepts:

Planar Growth

Kinetics of Growth

Thermal Oxide

Oxidation Charts

Water Surface Colors

Film Deposition


Step Coverage



Paschen Curve

Reactive Sputtering

Radio Frequency Sputtering

Comparison of PVD methods

Chemical Vapor Deposition

CVD mechanism

PolySi Deposition

Growth Rate Dependance

Laser Assisted CVD


LIGA Process

Wafer Bonding Techniques


1- retrieved on 23.013.2018

Brief Introduction to Photolithography

Photolithography is the process performed in microfabrication about patterning the thin films of the substrate.ıt is highly important in the development of devices on batch. It consists of projection of a circuit into a mask due to light exposure and dissolution of the hard areas by usage of a solution bath such as acid (wet method)or oxygen ions (dry method) [1].The elements used in photolithography are usually: photoresist, mask, wafer, chip etc.The steps that are crucial about photolithography are: surface cleaning, barrier layer formation (oxidation), spin coating with photoresist, soft baking, mask alignment, exposure, development, hard baking and post process cleaning [3]. Other types of photolithography include: Extreme Ultraviolet Photolithography (EUV), e-beam Lithography, Ion Beam Lithography and X Ray Lithography. Those types of photolithograpy increase the resolution compared to the classic methods [4]. Photoresists play an important role in photolithography and the most widely used photoresists are the positive and the negative one. The positive photoresist when exposed to light becomes soluble in the photoresist developer while the negative one in the same conditions becomes insoluble[5].   




4- Jain, K. Excimer Laser Lithography, SPIE Press, Bellingham, WA, 1990.