INCOMING MATERIAL
PHOTOLITHOGRAPHY
ETCH
IMPLANT
DIFFUSION
METAL
PASSIVATION
PROBE
TO ASSEMBLY
All starting material is verified for cleanliness, uniformity and compliance with Micron
specifications. Each silicon wafer receives a unique laser scribe for total product
traceability.
Wafers are coated with a layer of light-sensitive photoresist. Specified sections of the
wafer are exposed by projecting ultraviolet light onto the wafer through a mask. A
photoresist pattern, which will protect an underlying film from a subsequent etch step,
is produced.
The areas of the wafer not protected by the exposed photoresist are removed by either
plasma (dry etch) or acid (wet etch). The result is the definition of a given feature(s),
such as a hole or line. The photoresist is then cleaned or "stripped" off the wafer,
leaving a pattern in the exact design of the mask.
Wafers are bombarded with positively or negatively charged dopant ions, which are
implanted into the silicon. This process, called "doping," changes the electrical
characteristics in selected areas of the silicon and forms conductive regions on the
wafer.
Silicon dioxide, nitride and polysilicon layers are formed on the wafer during a number
of high-temperature furnace processes. The wafers are exposed to various gases,
which either react with the silicon, causing it to oxidize and form an SiO2 layer, or react
with each other to form poly and nitride deposits. These layers are patterned using
photolithography and form the layers of the diodes, transistors, and capacitors of the
circuit. High-temperature furnaces are also used to introduce and diffuse dopants into
the wafers.
A thin layer of aluminum or other metal is deposited and patterned, forming
interconnections between various regions of the die.
The fabrication process is completed by depositing a final glass layer on the wafer.
This layer protects the circuits from contamination or damage during the testing and
packaging process flows.
When the fabrication process is complete, each wafer consists of many discrete
integrated circuits or "die." Each die on the wafer is electrically tested using tiny probes
that connect the metalized pads on the die to the test station computer. This probe
testing produces wafer maps that store data on each functioning die. The wafer maps
are used later during the assembly process to ensure that only good die are
packaged.
Assembly (see next page).