Method and test structure for determining resistances at a plurality of interconnected resistors in an integrated circuit
A method for determining resistances at a plurality of interconnected resistors in an integrated circuit and a resistor configuration in which the resistors are interconnected to form a ring structure. Two measurement pads are in each case provided at the nodes between two resistors. The measurement pads can be used for feeding in current and for measuring voltage according to the known four-point measurement method. The effect of the ring structure is that fewer measurement pads are required, in contrast to the customary series circuit of resistors. By way of example, in the case of a ring structure with four resistors, two measurement pads are advantageously saved. The consequently reduced chip area required for the ring structure is advantageous particularly in the case of test circuits, which can be arranged for example in the narrow sawing frame between two chips.
1. A method for determining resistances in a test structure for integrated circuits with a four-point measurement, wherein at least four resistors are interconnected and the resistors have measurement pads for impressing a measurement current and for measuring a voltage drop, the method which comprises:
providing a plurality of resistors, interconnected in a ring structure with each two resistors connected to one another via a node, and with each of four nodes having two measurement pads for impressing current and measuring a voltage;
in a first measurement step, impressing a first measurement current via one measurement pad at a first node, the current being divided between two mutually parallel resistor branches each having at least two series-connected resistors, measuring first, second and third voltages at a second measurement pad of the first node and a respective measurement pad of the two nodes adjacent the first node, while the measurement pads of a remaining node serve as a zero point;
in a second measurement step, impressing a second measurement current via one measurement pad at a second node, the current being divided between two mutually parallel resistor branches each having at least two series-connected resistors, measuring fourth, fifth and sixth voltages at a second measurement pad of the second node and a respective measurement pad of the two nodes adjacent the second node, while the measurement pads of a remaining node serve as a zero point; and
determining the resistances of the four resistors from the measured voltages and from the measurement currents.
2. A test structure for integrated circuits for determining resistances of at least four interconnected resistors with a four-point measurement, comprising:
a plurality of measurement pads respectively connected to the resistors for impressing measurement current and measuring a voltage drop;
a ring structure interconnecting the resistors, said ring structure forming at least two mutually parallel resistor branches, each said resistor branch having at least two resistors connected in series, each two interconnected resistors of said ring structure being connected at a node, each said node having two measurement pads for impressing a current and for measuring a voltage.
3. The test structure according to claim 2 disposed on a wafer in a kerf between two integrated memory circuits.
4. The test structure according to claim 2 disposed on a wafer in a kerf between two DRAM memory circuits.