The Imprio 300 stepper uses a field-by-field alignment process in which alignment marks, typically located at the four corners of the field on both the wafer and mask, form a set of moire interferometric fringes. The detection of these fringes and the subsequent alignment corrections are achieved using three critical and separate sub-systems as follows:
Interferometric Moire Alignment Technique (i-MAT): The moire alignment approach used in the IMPRIO stepper is adapted from a similar approach developed for x-ray lithography and is capable of single point alignment accuracy well below 1nm. In operation, the i-MAT sub-system cameras view real-time moire signals that provide relative displacement errors between grating marks on the imprint mask and corresponding grating marks on the wafer. Figure one schematically illustrates field-by-field alignment based on eight alignment cameras and eight sets of grating patterns on the imprint mask and wafer.
Figure One: Interferometric Moire Alignment Technique.
While the alignment process begins before the mask touches the resist, critical alignment corrections occur while the mask is in contact with the liquid (resist), as illustrated in Figure Two:
Figure Two: Critical Alignment Corrections in Liquid
Using real-time data obtained from the iMAT camera system, the Imprio 300 stepper calculates and then makes adjustments to the relative positions of the mask and wafer multiple times per second, using the following sub-systems:
- Magnification Actuator System: An array of actuators mounted around the imprint mask periphery to make elastic, in-plane deformations to the mask to correct X and Y scaling, orthogonality, and higher order distortions.
- Wafer Stage: Corrects for rigid body alignment errors, such as displacement in X and Y and rotation (Ө). The low viscosity resist acts as a highly effective damping agent for any nanometer-scale noise, allowing excellent alignment performance to be obtained.
Performance
Overlay performance capability in mix-and match mode with 193i scanners has been validated in a number of ways with the Imprio 300. Mix-and-match overlay data collected at SEMATECH-Albany on a representative wafer reports <20nm (µ+3σ) overlay accuracy over a 26mm x 32mm field:
Source: SPIE Advanced Lithography Conference
At the Toshiba installation site in Japan, a 13mm x 13mm field size was used and the resulting overlay accuracy approached 10nm µ+3σ (see Figure):
Source: SPIE Advanced Lithography Conference
The value of a lithography technology is in its capability to fabricate working devices. In a device demonstration with IBM, Jet and Flash™ Imprint Lithography (J-FIL™) was used to pattern a FinFET storage class memory device’s gate layer with minimum features down to ~20nm:
Source: 2007 EIPBN Conference
