End-point detection for fib circuit modification

Abstract

A Focused Ion Beam (FIB) milling end-point detection system uses a constant current power supply to energize an Integrated Circuit (IC) that is to be modified. The FIB is cycled over a conductive trace that is to be accessed during the milling process. The input power, or voltage to the IC is monitored during the milling process. The end-point can be detected when the FIB reaches the conductive trace. The FIB can inject charge onto the conductive trace when the FIB reaches the level of the conductive trace. An active device coupled to the conductive trace can amplify the charge injected by the FIB. The active device can operate as a current amplifier. The change in IC current can result in an amplified change in device input voltage. The end-point can be detected by monitoring the change in input voltage from the constant current power supply.

Description

[0001] This application claims the benefit of provisional U.S. Application Serial No. 60 / 560,134, entitled “End-Point Detection For FIB Circuit Modification,” filed Apr. 6, 2004.BACKGROUND OF THE DISCLOSURE [0002] Focused Ion Beam (FIB) milling can be used during the course of Integrated Circuit (IC) development to modify circuits embodied within one or more layers of a semiconductor device. The FIB can be used to physically alter traces within the IC. In a FIB IC modification, very small holes, also referred to as vias, can be milled into the IC in order to expose conductive layers or traces that are buried under the surface of the IC. The depth of the vias may only be on the order of microns. Thus, knowing when the FIB milling process has reached the conductive layers or traces can be critical to the success of the modification. Undermilling, or completing a via before the conductive layer or trace is reached can result in a poor electrical connection. Additionally, overmilling, o...

AI Technical Summary

Benefits of technology

This method ensures precise detection of the end-point, preventing damage to conductive layers and ensuring accurate modification by halting the milling process when the desired conductor is reached, thereby improving the reliability of FIB milling for high aspect ratio vias.

Problems solved by technology

Undermilling, or completing a via before the conductive layer or trace is reached can result in a poor electrical connection.

Additionally, overmilling, or continuing to mill after the conductive layer or trace has been reached, can destroy the conductor and defeat the intended modification.

However, visual inspection does not perform acceptably for high aspect ratio holes.

In very high aspect ratio vias, where the depth of the hole is greater than or equal to approximately ten times the diameter of the hole, the depth of the hole may not allow an operator to see the bottom of the hole, or there may be insufficient contrast at the bottom of the hole for the operator to determine if the desired layer has been reached.

The numerous characteristic curves do not ensure accurate milling of a desired device because milling by time and current assumes a consistent milling process across multiple devices.

The level of uniformity among devices may not always be sufficient to predict a milling depth based on characteristic curves.

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