Buffered oxide etch
Encyclopedia
Buffered oxide etch also known as buffered HF or BHF, is a wet etchant
used in microfabrication
. Its primary use is in etching thin film
s of silicon dioxide
(SiO2) or silicon nitride
(Si3N4). It is a mixture of a buffering agent
, such as ammonium fluoride
(NH4F), and hydrofluoric acid
(HF). Concentrated HF (typically 49% water) etches silicon dioxide too quickly for good process control. Buffered oxide etch is commonly used for more controllable etching.
Some oxides produce insoluble products in HF solutions. Thus, HCl is often added to BHF solutions in order to dissolve these insoluble products and produce a higher quality etch.
A common buffered oxide etch solution comprises a 6:1 volume ratio of 40% NH4F in water to 49% HF in water. This solution will etch thermally grown oxide at approximately 2 nanometres per second at 25 degrees Celsius.
Etching (microfabrication)
Etching is used in microfabrication to chemically remove layers from the surface of a wafer during manufacturing. Etching is a critically important process module, and every wafer undergoes many etching steps before it is complete....
used in microfabrication
Microfabrication
Microfabrication is the term that describes processes of fabrication of miniature structures, of micrometre sizes and smaller. Historically the earliest microfabrication processes were used for integrated circuit fabrication, also known as "semiconductor manufacturing" or "semiconductor device...
. Its primary use is in etching thin film
Thin film
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
s of silicon dioxide
Silicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
(SiO2) or silicon nitride
Silicon nitride
Silicon nitride is a chemical compound of silicon and nitrogen. If powdered silicon is heated between 1300° and 1400°C in an atmosphere of nitrogen, trisilicon tetranitride, Si3N4, is formed. The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen...
(Si3N4). It is a mixture of a buffering agent
Buffering agent
A buffering agent is a weak acid or base used to maintain the acidity of a solution at a chosen value. The function of a buffering agent is to prevent a rapid change in pH when acids or bases are added to the solution. Buffering agents have variable properties—some are more soluble than others;...
, such as ammonium fluoride
Ammonium fluoride
Ammonium fluoride is the inorganic compound with the formula NH4F. It crystallizes as small colourless prisms, having a sharp saline taste, and is exceedingly soluble in water.-Crystal structure:...
(NH4F), and hydrofluoric acid
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
(HF). Concentrated HF (typically 49% water) etches silicon dioxide too quickly for good process control. Buffered oxide etch is commonly used for more controllable etching.
Some oxides produce insoluble products in HF solutions. Thus, HCl is often added to BHF solutions in order to dissolve these insoluble products and produce a higher quality etch.
A common buffered oxide etch solution comprises a 6:1 volume ratio of 40% NH4F in water to 49% HF in water. This solution will etch thermally grown oxide at approximately 2 nanometres per second at 25 degrees Celsius.