3D ICs and CapacitanceThree-dimensional (3D) integrated circuits (ICs) feature silicon wafers and dies that are stacked vertically for improved device performance. By using the Z-axis, 3D ICs can overcome the power and footprint limitations associated with two-dimensional (2D) integrated circuits. Yet 3D ICs need coplanar surfaces to contact all of the pads, pins, and pillars.

To determine coplanarity, semiconductor manufacturers measure the angle and gap between two planes. Bonding tool actuators use these measurements to adjust components and ensure that all device pins and solder balls reside on the same geometric plane. This process, active parallelism compensation, promotes proper bonding without residual stress.

Unfortunately, active parallelism compensation is both challenging and expensive – especially when the required resolution for 3D ICs is in the sub-micron range. Capacitance-based sensing from MTI Instruments provides an accurate, cost-effective alternative for ensuring coplanarity and minimizing the risk of field failure.

Capacitive Sensing and High-Resolution Position Control for 3D ICs

MTI’s solution uses ASP-50-ILA capacitive displacement probes, a D-300 digital Accumeasure™ capacitive amplifier, and an actuator/control system. Working together, these components monitor and adjust the gap/angle between the bonding plane of the die bonding tool and the ground plane of the die or substrate.   With 3D ICs, setup is as simple as mounting the probes to the die bonding tool.

Establishing the planar surface requires at least three capacitance probes. Ensuring coplanarity with the die bonding tool requires three actuators for adjusting the die or substrate. To meet the needs of the semiconductor industry, these probes are cylindrical, flat, or threaded. They’re made of materials with negligible outgassing levels and operate under vacuum pressure and at elevated temperatures.

MTI’s D-300 Digital Accumeasure™ capacitive amplifer processes gap measurements and interfaces with the control system via 1000 base Ethernet or USB. Accumeasure™ technology monitors coplanarity and provides position control to the actuators. With less than 100 PPM drift, digital Accumeasure™ technology rivals interferometers for stability and accuracy.

To learn more, contact MTI Instruments.