Shallow trench isolation (STI), also known as box isolation technique, is an integrated circuit feature which prevents

electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The movin ...

leakage between adjacent

semiconductor device A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivit ...

components. STI is generally used on CMOS process technology nodes of

250 nanometer The 250 nanometer (250 nm or 0.25 µm) process refers to a level of semiconductor process technology that was reached by most manufacturers in the 1997–1998 timeframe. Products featuring 250 nm manufacturing process *The DE ...

s and smaller. Older CMOS technologies and non-MOS technologies commonly use isolation based on LOCOS. STI is created early during the

semiconductor device fabrication Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically integrated circuit (IC) chips such as modern computer processors, microcontrollers, and memory chips such as NAND flash and DRAM that are pres ...

process, before transistors are formed. The key steps of the STI process involve

etching Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other type ...

a pattern of trenches in the silicon, depositing one or more

dielectric In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the m ...

materials (such as

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

) to fill the trenches, and removing the excess dielectric using a technique such as

chemical-mechanical planarization Chemical mechanical polishing (CMP) or planarization is a process of smoothing surfaces with the combination of chemical and mechanical forces. It can be thought of as a hybrid of chemical etching and free abrasive polishing. Description The pro ...

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Certain semiconductor fabrication technologies also include deep trench isolation, a related feature often found in analog integrated circuits. The effect of the trench edge has given rise to what has recently been termed the "reverse narrow channel effect" or "inverse narrow width effect". Basically, due to the electric field enhancement at the edge, it is easier to form a conducting channel (by inversion) at a lower voltage. The

threshold voltage The threshold voltage, commonly abbreviated as Vth or VGS(th), of a field-effect transistor (FET) is the minimum gate-to-source voltage (VGS) that is needed to create a conducting path between the source and drain terminals. It is an important ...

is effectively reduced for a narrower transistor width. The main concern for electronic devices is the resulting

subthreshold leakage Subthreshold conduction or subthreshold leakage or subthreshold drain current is the current between the source and drain of a MOSFET when the transistor is in subthreshold region, or weak-inversion region, that is, for gate-to-source voltages b ...

current, which is substantially larger after the threshold voltage reduction.

Process flow

*Stack deposition (oxide + protective nitride) *

Lithography Lithography () is a planographic method of printing originally based on the immiscibility of oil and water. The printing is from a stone ( lithographic limestone) or a metal plate with a smooth surface. It was invented in 1796 by the German ...

print *Dry etch (

Reactive-ion etching Reactive-ion etching (RIE) is an etching technology used in microfabrication. RIE is a type of dry etching which has different characteristics than wet etching. RIE uses chemically reactive plasma to remove material deposited on wafers. The ...

) *Trench fill with oxide *

Chemical-mechanical polishing Chemical mechanical polishing (CMP) or planarization is a process of smoothing surfaces with the combination of chemical and mechanical forces. It can be thought of as a hybrid of chemical etching and free abrasive polishing. Description The pro ...

of the oxide *Removal of the protective nitride *Adjusting the oxide height to Si

References

External links

Clarycon: Shallow trench isolationN and K Technologies: Shallow trench isolationDow Corning: Spin on Dielectrics - Spin-on Shallow Trench Isolation
Semiconductor device fabrication Semiconductor structures {{Electronics-stub

Process flow

See also

References

External links