PPT ON WET ETCHING

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Wet Etching  Presentation Transcript

1.ETCHING

2.What is etching ? Etching is a process by which material is removed. Mechanism of etching: Chemical etch – also called Wet Etch because normally water is present in the etchant Physical etch - also called Dry Etch – no water Reactive ion etch – Dry Etch

3.Types of Etching Patterned etch - Removing materials selectively Blanket etch - Removing materials from the entire wafer Isotropic etch - Etch rate is equal in all directions Anisotropic etch - Etch rate is different in different directions

4.Wet Etch Processes Use chemical solution to dissolve the materials Byproducts are gases, liquids or solids that are soluble in the etchant solution or evaporate away

5.Process – Wet Chemical Etching Purpose- to remove material selectively Equipment- chemical bath, rinsing baths, dryer Method – Dip the wafers in the etchant for required time, rinse the wafers in rinsing chemicals and dry the wafers

6.Patterned etch

7.Materials To Be Etched Semiconductors Single-crystal silicon Poly Dielectric Oxide Nitride Metal silicides Tungsten silicide Cobalt silicide Platinum silicide Metal Aluminum Gold Titanium Tungsten copper Metal alloys aluminum-copper alloys

8.Wet Etch Processes Oxide wet etch SiO2 + 6 HF = H2SiF6 + 2 H2O Silicon etch Isotropic etch Si + HNO3 + 6 HF = H2SiF6 + HNO2 + 2 H2O Anisotropic etch 23.4 wt% KOH + 13.3 wt% Isopropyl alcohol (C3H8O) + 63.3 wt% H2O at 80 – 820 C etch rate for <100> is 100X that for <111>

9.Wet Etch Processes Nitride etch Si3N4 + 4 H3PO4 = Si3(PO4)4 + 4 NH3 Metal etch Mixture of phosphoric acid, acetic acid, nitric acid and water for metals e.g. Aluminum Hydrogen peroxide and sulfuric acid for titanium silicide

10.Etch Basics Etch rate Uniformity Selectivity Profile Loading effects Over etch Residue

11.Etch Rate Speed at which the material is removed Step Height – depth of the etched opening High etch rate for high throughput Determined by process and equipment variables material being etched reactor configuration etchant gases process parameters

12.Etch Rate Etch Uniformity

13.Should be repeatable From wafer to wafer With in a wafer Measured by wafer thickness mapping

14.Etch Selectivity It is the ability of the etchant or the etching system to attack the desired material layer while at the same time not attacking or affecting the other materials present on the wafer.

15.Etch Selectivity It is the ratio of the etch rates between the different materials S = ER1 / ER2 ER1 is the etch rate for the material to be etched and ER2 is the etch rate for the material NOT to be etched S should be high

16.Anisotropy It pertains to the ability of the etchant to attack the layer in a directed manner. Chemical etching is essentially isotropic. Ionic etching is in one direction and therefore anisotropic.

17.Uniformity Uniformity refers to the uniformity of etch rates on different parts of the wafer from wafer to wafer, in the same lot from lot to lot Etch rate should be the same

18.Throughput Throughput is the number of wafers processed per unit time, say per day. It indicates the time taken to process a lot of wafers