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Back-end-of-line fabrication steps in Software Generate barcode 3/9 in Software Back-end-of-line fabrication steps

14.2.3 Back-end-of-line fabrication steps use software code 3 of 9 writer tocompose code-39 on software Microsoft Official Website n) First interlevel dielectr Software 3 of 9 barcode ic. A generous layer of silicon dioxide gets deposited with no intervention from any mask. Following another CMP planarization step, this insulating material is to become the rst interlevel dielectric (ILD) providing electrical separation between the bulk structures and the rst layer of metal.

o) Contact plug formation. Mask contact de nes those locations where metal1 shall connect to a di usion or polysilicon region underneath. Cuts are anisotropically etched open where indicated before tungsten is deposited to form plugs.

The excess tungsten is then removed and the surface planarized to prepare for the subsequent metallization step. p) Deposition and patterning of rst metal layer. A metal layer (300 nm or thicker) is deposited over the entire surface.

Much of this layer is then selectively removed so as to leave behind those parts that are de ned by the metal1 mask, which explains why this step is quali ed as subtractive metallization. More precisely, metal deposition includes a series of substeps to form a metal stack where aluminum, copper or tungsten is sandwiched between thin liners of metal nitrides or other materials that improve adhesion, abate the formation of hillocks, act as di usion barriers, or otherwise help suppress undesirable phenomena. Such details are abstracted from in the gure.

q) Second interlevel dielectric. The second interlevel dielectric is deposited and planarized. r) Via plug formation.

Mask via1 de nes those locations where a rst-layer-metal structure shall connect to the next metal above. Much as for contact formation, a cut is etched open, then lled with tungsten, and the excess material is removed and the surface planarized. s) Deposition and patterning of second metal layer.

The second layer of metal is obtained by way of subtractive metallization.. 14.2 BASIC CMOS FABRICATION FLOW t) Third interlevel dielectr 3 of 9 barcode for None ic followed by via plug formation. From this point on, the steps of dielectric deposition, planarization, plug formation, metal deposition, and metal patterning alternate for each additional metal layer. Note that two masks are required per metal layer.

The gure shows the situation after the via2 plugs have been formed. u) Deposition and patterning of third metal layer. The third metal layer which is the topmost one in the case shown is now complete.

As a rule, higher-level metals are fatter (up to 1 m) and must respect more important minimum widths and spacings than their lower-level counterparts. v) Overglass and bond pad openings. The entire wafer surface is covered by depositing a nal layer of silica.

The overglass is complemented by a nal passivation layer placed on top to better protect the stack from environmental attacks such as humidity, chemical agents, and scratching. To allow bonding and probing of the chip, generous openings get etched into the protective layers where indicated by the pad mask. Note that only the topmost metal can be contacted in this way.

Please keep in mind that there exist many variations to the basic CMOS process described in the above series of drawings. Most likely, the reader will have to make adaptations to account for departures in a speci c fabrication process at hand. Comprehensive and authoritative references on VLSI technology include [386] [387] [381] [388] [389].

What sets [219] apart from others is a comparison of CMOS and BiCMOS. Photographs and/or computer animation are available from websites such as [385]..

14.2.4 Process monitoring Between processing steps, wa Software USS Code 39 fers are subject to optical inspection and electrical tests. The electrical characteristics of MOSFETs of di erent sizes are measured and kept on record, and the same applies for an assortment of pn-junctions. Capacitance voltage characteristics are obtained from MOSCAPs.

Van der Pauw structures serve to determine the resistivities of all conductive layers while various shapes of capacitors are included to monitor the dielectric layers. Long interdigitated serpentines and chains of many series-connected contacts or vias help to check for electrical shorts and continuity. Such elementary test structures are collected into process control monitors (PCMs) along with inverters and ring oscillators.

Wafers that are found to su er from fatal defects or from excessive parameter variations are sorted out. Even more importantly, the data gathered are used to constantly monitor fabrication equipment and procedures..

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