Silicon Technology

1) Property chemistries to the base of the happened one of the system â " SiO₂ :

to)       Using idrofluorico acid the silicon can be dissolved silicon dioxide and be left intact

b)       silicon dioxide can be used in order to shield a silicon crystal from bombed ionizzanti atoms

 

2) Process to glide down:

The production of the integrated circuit happens through the following steps:

to)       Creation of the polisilicio

Dioxide of silicon and Carbon comes scaldati to 2000°C in a furnace, is obtained of the pure silicon to 90%, it comes then converted in triclorosilano that then comes distilled obtaining silicon to the polisilicio said solid state in how much constituted from small crystals with randomica direction.

b)       Production of a single crystal having diameter of approximately 10cm

b1) Technical of Czochralski

The polisilicio comes carried to a temperature of 1412°C correspondent to the melting point of the silicon, after which a seed of silicon with the intentional direction comes immesso ruotando in the fusion while the crucible wheel in the opposite direction, the crystal comes little to the time extracted from the fusion, and it is cooled off creating a cylinder of pure semiconductor and correctly oriented.

b2) Technical of Float Zones

The polisilicio cylinder comes made to ruotare and heated with a source RF to leave from the bottom where there is the seed in order then to go up towards the high.

c)       Production of the Wafer

After that the single crystal has been created it comes mannered by means of diamond creating of the said slices wafer

d)       Oxidation of the wafer

The silicon comes oxidized in way that can be shielded laddove is not desired is drug addict, the methods in order to oxidize it is following:

d1) thermal Oxidation

The wafer place in a quartz tube comes place to the inside of a furnace that produces a temperature comprised between 850°C and 1000°C, in the tube comes blown oxygen

d2) Deposition

It is had that oxygen and silicon come convogliati on the surface of the wafer and react them

in order to increase the speed of the oxidation to the temperature or the pressure can be increased

and)       Litografia

After that the wafer has been oxidized it is necessary to remove oxide from the regions that must be drug addicts, to such aim the wafer is covered with a called polymer Resist and on it a mask aligned through the microscope is placed, in the case of a resist positive, the areas masked not subiranno the attack of the ultraviolet beams which break off the ties between molecules and therefore it is dissolved using a dissolvent. To this point the regions protect from the resist do not come disciolte in acid HF which the silicon in those zones eliminates oxide bringing back to the light in which it must endure the drogaggio.

f)        Drogaggio

Before the impiantazione of the Ionian ones happens that consists in the strafing of the areas discovered of the wafer with of the Ionian ones accelerates from an electric field to you comprised between the 25keV and 200keV the Ionian ones in such a way penetrate for 1mm in the silicon altering heavy the regular structure of the same one that but it comes restored by means of a heating to 1000°C that the spread of the Ionian ones concurs.

g)       CVD

Draft of a procedure that concurs to create of the layers of silicon or insulator over to the wafer which comes place to the inside of a furnace heated to 1000°C by means of RF in which it comes blown a gas SiCL₄ that it is decomposed on the surface of the wafer creating the wished layer, the process is said epitassiale and is able to create a layer with smaller drogaggio of the below or for particular applications one can be deposited oxide layer or polisilicio.

h)       Metalization

It is before necessary to remove silicon oxide from the points in which the metallic contact with the silicon is demanded, after which one is deposited aluminum layer vaporizzando one solid source by means of Electron-Beam or Sputtering. The aluminum layer comes therefore eliminated laddove is not demanded by means of photolitograph and finally the wafer place in a furnace to 450°C comes where a good ohmmico contact happens the fusion of the aluminum on the silicon guaranteeing.

i)         Testing and impacchettamento

A preliminary test is carried out before on the wafer after which it is subdivided in Chips whose back is fixed to the covering and the contacts metalize to you come connect to you to the piedini after which the chip it comes isolated with plastic, metal or ceramics.

 

3) Litografia with loaded particles:

to)       Electronic

An electron source is had that generates a having bundle diameter much small, it goes to record an electronic Resist that acts as from mask, however in the Resist for via of the spread shape like a pear which turns out optimal in how much the metal that comes subsequently deposited does not arrive to contact with the Resist that otherwise when it comes eliminated would carry via also the metal to contact.

The procedure is the much slow in how much computer must guide the electronic bundle and eliminate the Resist point for point, however the precision that is obtained is much elevating and exactly concurs to realize masks that then come used in the photolitograph.

b) ionic

 

4) Litografia Tunnelling:

It is come true by means of one heads of tungsten that comes mail to a distance of approximately 10A° from the Resist, for Tunnell effect slides one current that records the Resist. It is one precise technology much but slow one.

 

5) Realization of the ohmic contacts towards the piedini external:

to)       thermal welding

A spout is had in which the wrapped wire on a spool slides, through a fiammella of oxygen creates a little ball which then comes crushed on the die carried to the temperature of 400°C, subsequently the spout is moved on the piedino and realizes the other logon.

b)       welding to ultrasounds

The spout with the pit is put to contact after which they begin the ultrasounds (100kHz) which let out the air from the space comprised between the two superficial ones, it is come therefore to create an optimal contact.