4.7. Metal Sheet Resistor (VDP), Structure 3.20 Metal sheet resistor (VDP), structure 3.20, is a four-terminal resistor arranged in a van der Pauw (VDP) configuration [12] and consists of metal deposited over the collector oxide. The discussion for structure 3.22, section 4.1, is applicable to structure 3.20. The arms on this structure have a width of 0.25 mil (6.4 um) which requires tight control of the metal etch step to prevent the arms from being etched away.

4.8. Metal-to-Base Contact Resistor, Structure 3.24

Metal-to-base contact resistor, structure 3.24, is a four-terminal resistor which consists of a base diffused into the collector and metal which touches the base at a square window 1.00 mil (25.4 μm) on a side; see figure 4. effective contact resistance for a unit area, Re, as given by this structure is calculated from

The

(8)

where the potential, V, is V1-V2 for a current, I, passed into I1 and out of I2 and A is the area of the contact. For a square contact window of 1.00 mil (25.4 μm) on a side, A = 6.45 x 10-6 cm-2. This structure is intended to serve as a process control monitor. It is not intended to yield absolute values for the specific contact resistance for the effective contact resistance determined by this structure is influenced by over-etch of the contact window and by current crowding effects since only a fraction of the contact carries a significant current [18]. Over-etch of a contact window occurs because the contact window is etched at the same time as the scribe lines. Etching the scribe lines requires removal of the collector oxide which is thicker than the base oxide.

4.9.

Metal-to-Emitter Contact Resistor, Structure 3.23

Metal-to-emitter contact resistor, structure 3.23, is a four-terminal resistor which consists of an emitter diffused into a base and metal which touches the emitter at a square window 1.00 mil (25.4 μm) on a side. The discussion for structure 3.24, section 4.8, is applicable to structure 3.23.

12

M

V2

4.10 Metal Step-Coverage Resistor, Structure 3.33

Metal step-coverage resistor, structure 3.33, is a two-terminal resistor which consists of a serpentine metal path 0.50 mil (12.7 um) wide which crosses 18 oxide steps etched by the CONTACT mask. Two resistors are combined into one structure. In one resistor the serpentine path crosses the oxide steps in a direction perpendicular to the other resistor. This allow a check of shadowing effects during metal deposition. This structure is us to check for metal continuity [19]. As shown below, the left-hand resistor is 31 squares long and the right-hand resistor is 35 squares long.

Collector resistor (FP, CS), structure 3.1, is a three-terminal resistor which consists of an emitter diffused into the collector. A metal field plate (FP) over the collector oxide controls the surface currents between the emitter and the channel stop (CS). The resistance is determined from the voltage drop between E1 and the backside for a current between E2 and the backside. In operation the field plate is biased so as to invert the collector surface. The collector resistivity is calculated with use of an expression which appropriately models the peripheral spreading resistance. Various expressions are available [20], [21]. This structure is intended for use on epitaxial layers deposited on more heavily doped substrates of the same conductivity type. The thickness of the layers must be small compared to the width of the field plate, 4.0 mil (102 um), so that the peripheral current spreading is easily modeled. Since the backside contact resistance is in series with the collector, it must be negligibly small compared with the collector resistance in order to determine the collector resistivity accurately.

4.9.

Metal-to-Emitter Contact Resistor, Structure 3.23

Metal-to-emitter contact resistor, structure 3.23, is a four-terminal resistor which consists of an emitter diffused into a base and metal which touches the emitter at a square window 1.00 mil (25.4 μm) on a side. The discussion for structure 3.24, section 4.8, is applicable to structure 3.23.

Metal step-coverage resistor, structure 3.33, is a two-terminal resistor which consists of a serpentine metal path 0.50 mil (12.7 um) wide which crosses 18 oxide steps etched by the CONTACT mask. Two resistors are combined into one structure. In one resistor the serpentine path crosses the oxide steps in a direction perpendicular to the other resistor. This allow a check of shadowing effects during metal deposition. This structure is u to check for metal continuity [19]. As shown below, the left-hand resiste is 31 squares long and the right-hand resistor is 35 squares long.