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Pressure controlled vertical probing

IP.com Disclosure Number: IPCOM000203488D
Publication Date: 2011-Jan-26
Document File: 4 page(s) / 45K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a probe system for protecting the Cu pad and dielectric from probe-induced damage as well as reducing probe scratches and induced debris on a wafer. The system incorporates contact sensing and probe driver control and prevents probe overdrive while increasing the lifetime and cleaning cycle of probe tips.

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Pressure controlled vertical probing

For a traditional wafer electrical test, two types of probe cards have been used: vertical and cantilever. To ensure good contact of probes and probing pads on a silicon wafer, adjusting the "preset overdrive" of the wafer chuck is the method applied for both types of probe card. Now, with the introduction of Ultra Low K (ULK) dielectrics, the "preset overdrive" method can introduce too much downward pressure, inevitably causing probing damage. The probes not only dig into and damage the tiled Cu pads, they also damage the enclosed dielectric. It may cause either a direct shorting between the metal pads next to the probed metal pads, or possibly moisture ingress through poorly capped/sealed damaged dielectric that causes via opens in neighboring structures due to an incomplete via etch process.

A solution is needed to:
• Prevent probe overdrive which induces scratches and debris on the wafer surface and damages the dielectric layer

• Increase the lifetime and cleaning cycle of the probe tips

One approach in prior art to reduce the damage from in line probing is to design a spring structure of the probe tip which can reduce probe pressure on probing pads from direct overdrive. Another approach describes a feedback control system of which sensor and motor are both mounted on stage supporter. This can only achieve global adjustment without precision scale

A common solution to this problem is to use probe cards built with a Low Down Force specification. This is accomplished by the probe supplier modifying the physical dimensions of the probe needle to obtain a lower Balance Contact Force (BCF). A typical example would be to order a card with a 1 gram per mil BCF rating (versus 2 grams per mil BCF). One disadvantage of reducing the BCF is that it increases in CRES due to the fact that less force is available to break through any oxide coating on the Al/Cu pads. It may influence the transistor characteristic readout.

The disclosed invention is a probe system with contact sensing and probe driver control which protects the Cu pad and dielectric from probe-induced damage and reduces probe scratches and induced debris on a wafer. The system contains three main parts and a feedback loop:
1. Pressure-controlled Probe with Pressure-Sensing Unit (PSU)
2. Piezoelectric Driver Unit (PDU)
3. Wafer stage Driving Motor
4. A control system with a feed...