Calvin T. Gabriel

A simple wafer-level measurement technique for predicting oxide reliability

A new wafer-level measurement technique, the differential gate antenna analysis, has been developed to detect weaknesses in sub-micrometer oxide. This simple technique involves the use of dual antenna structures with different gate oxide areas but the same antenna area ratio. The critical parameter is the difference in their failure levels. It is shown that such a differential measurement of antenna failures correlates with product failure during accelerated life testing. The differential antenna structures are thus proven useful for real-time wafer-level monitoring of oxide reliability.

Gate oxide damage reduction using a protective dielectric layer

Gate oxide damage from charge entering through the top surface of the gate electrode during plasma ashing, ion implantation, and LDD spacer oxide etching was measured using antenna structures. Significant charge damage to the 9.0 nm-thick gate oxide was detected for each of these processes. The damage was reduced by using a protective dielectric layer, in this case a thermally deposited TEOS oxide over the polycide gate electrode before gate definition. The dielectric appears to block charge penetration into the antenna. Damage can be reduced further by increasing the thickness of the dielectric layer; for a sufficiently thick layer (about 150 nm), charge entering through the top surface of the antenna was effectively eliminated.<<ETX>>

PERFORMANCE OF DIFFERENT ETCH CHEMISTRIES ON TITANIUM NITRIDE ANTIREFLECTIVE COATING LAYERS AND RELATED SELECTIVITY AND MICROLOADING IMPROVEMENTS FOR SUBMICRON GEOMETRIES OBTAINED WITH A HIGH-DENSITY METAL ETCHER

Different chemistries were evaluated in a metal etcher with a high-density plasma source that was used to etch a titanium nitride antireflective coating (ARC). A composite film structure consisting of aluminum (with 0.5%–1% Cu) as the underlying layer, a titanium nitride ARC layer, and titanium nitride as the barrier layer were used for the standard stack, while titanium nitride and aluminum layers alone were used for the initial characterizations of the process. Conventional BCl3/Cl2 chemistry was used initially to etch both the titanium nitride ARC layer and the underlying aluminum layer. The performance of BCl3/Cl2 chemistry on the titanium nitride ARC layer as well as on the composite stack was evaluated. Partial etch measurements were taken to calculate the composite microloading and resist selectivity values. Different etch chemistries were then employed for the ARC layer while keeping conventional BCl3/Cl2 chemistry for the aluminum layer, and the difference in process performances were evaluated. ...

Control of Plasma Damage to Gate Oxide during High Density Plasma Chemical Vapor Deposition

Gate oxide damage resulting from high density plasma chemical vapor deposition of silicon oxide was investigated using damage sensitive antenna structures with area ratios up to 200,000 :1. Significant damage was detected from an unoptimized oxide deposition process. A 2 4-1 fractional factorial experimental design was used to screen the effect of four parameters : radio frequency power, microwave power, electrostatic chuck potential, and magnetic field. RF power and electrostatic chuck potential made no contribution to oxide degradation. The main factor was microwave power, and further experiments with microwave power ranging from 1500 to 2500 W showed that gate charging damage increased with microwave power, with the extent and distribution of damage depending on the magnetic field shape.

Minimizing metal etch rate pattern sensitivity in a high density plasma etcher

The variation of metal etch rate with spacing between metal lines was measured from scanning electron microscopy micrographs of TiN/Al–0.5%Cu/TiN wafers etched in a high density inductively coupled plasma metal etcher. The metal etch rate was found to depend on the spacing between metal lines, with etch rate significantly decreasing in very narrow spaces for a conventional Cl2/BCl3 chemistry. The effect of several process parameters on this etch rate dependence was studied. It was found that the dependence could be reduced significantly, and the traditional rolloff of etch rate as spacing decreases could be eliminated, by the choice of process gases. Addition of 15% CHF3 to a BCl3/Cl2 mixture resulted in a 50% reduction of the effect, and addition of both CHF3 and Ar under certain process conditions resulted in almost complete reduction or even inversion of the effect. A mechanism is proposed for this improvement: sidewall passivants like CHF3 reduce the sticking coefficient of chlorine on aluminum, boost...

Integration of metal masking and etching for deep submicron patterning

Although copper damascene interconnects offer many advantages over conventional subtractive etched Al alloys, the challenges and costs associated with converting to copper have combined to extend the useful life of Al alloy etching into the deep submicron regime. As a result, metal masking and etching are facing new challenges. Deep ultraviolet (DUV) photolithography has replaced the conventional i-line technique for patterning fine metal pitches, but some DUV photoresists are less able to withstand the aggressive plasma environment than their i-line counterparts. Reflectivity increases at DUV wavelength, so dielectric antireflective films are added on top of the metal stack. The mask-open process, where the dielectric film is plasma etched prior to etching the metal stack, alters the photoresist further and influences the subsequent metal etch. Aspect ratio dependent etch effects increase when etching narrow spaces resulting from tightened metal pitches, and gas additives may be required to protect the m...

Gate oxide damage: Testing approaches and methodologies

The main types of gate oxide damage measurement techniques are examined and compared, leading to a selection of “application-specific” damage measurement techniques. Each technique has strengths and weaknesses, so no single measurement can completely characterize damage. Instead, a combination of measurement approaches is needed, each one targeted to provide a piece of the damage puzzle. It is helpful to understand the different damage mechanisms when selecting a measurement technique, so a survey of mechanisms is given. Damage proceeds by either direct exposure of the gate oxide (through ion bombardment or ultraviolet radiation) or by indirect exposure (by charging from a nonuniform plasma or from the presence of high aspect ratio structures on the wafer). The relative importance of each mechanism depends on process technology and other factors. The most useful combination of damage measurement techniques includes surface potential measurement, electrically erasable read-only memory transistors, direct m...

Gate antenna structures for monitoring oxide quality and reliability

Gate antenna structures have been developed to detect charge induced process damage to sub-micron gate oxide. For the first time, this damage is correlated with product failure due to gate oxide in accelerated life testing. These antenna structures are thus proven to be useful for wafer level gate oxide reliability screening.

Amorphous silicon anti-fuse for high-speed FPGA application

Amorphous silicon has been used as a programmable material for a metal-to-metal anti-fuse. A study on the characteristics of such an anti-fuse and the parameters that affect its programming characteristics is presented. In the unprogrammed state the resistance of the anti-fuse is greater than 1 G Omega and the capacitance is less than 1.3 fF. Programmed state resistances of less than 50 Omega have been achieved. This technology is in production for a 1.0- mu m CMOS-based 1000-gate field programmable gate array (FPGA).<<ETX>>

Application Of Damage Measurement Techniques To A Study Of Antenna Structure Charging

Several damage measurement techniques were used to study charging with a comprehensive set of antenna structures encompassing polycide, metal 1, metal 2, contact, and via layers. The measurement techniques included gate leakage, threshold voltage shift from a Fowler-Nordheim stress, and charge-to-breakdown. Threshold voltage shift was most sensitive to low levels of charging; however, at high levels of damage to the transistor gate oxide, a threshold voltage could not be measured. Gate leakage and charge-to-breakdown gave consistent results for both low and high levels of charging, with charge-to-breakdown a little more sensitive than gate leakage.