Sailesh Mansinh Merchant

Noncontact ultrasonic ULSI process metrology using ultrafast lasers

Subpicosecond laser ultrasonic techniques have been used for nearly a decade to study the physical and chemical properties of thin films and multilayers. Recent advances in computational methods, optical design and laser technology have made it possible to develop further related techniques for thin film process metrology. In this paper we describe the principles and applications of picosecond ultrasonics, with an emphasis on in-line characterization of metal and dielectric films used in ULSI chip manufacturing. Topics to be discussed include measurements of simple metal films ranging from 50 A to 2 microns thick, and opaque multilayers consisting of up to six sequentially deposited metal films.

Alignment Mark Detection In CMOS Materials With SCALPEL E-Beam Lithography

A manufacturable process for fabricating alignment marks that are compatible the SCALPEL lithography system is described. The marks were fabricated in a SiO2/WSi2 structure using SCALPEL lithography and plasma processing. The positions of the marks were detected through e-beam resist in the SCALPEL proof of lithography (SPOL) tool by scanning the image of the corresponding mask mark over the wafer mark and detecting the backscattered electron (BSE) signal. Scans of 1 micrometers line-space patterns yielded mark positions that were repeatable within 20 nm 3(sigma) with a dose of 4 (mu) C/cm2 and signal-to-noise of 32 dB. An analysis shows that the measured repeatability is consistent with a random noise limited response combined with SPOL machine factors. By using a digitally sequenced mark pattern, the capture range of the mark detection was increased to 13 micrometers while maintaining 35 nm 3(sigma) precision. Further improvements in mark detection repeatability are expected when the SCALPEL electron optics is fully optimized.

Marks for SCALPEL® tool optics optimization

A method for optimizing the electron optics of the SCALPEL exposure tool is described. The method uses the SCALPEL mark detection method with a grating mark as an aerial image monitor. The root-mean-square deviation of the recorded backscattered electron signal from an ideal triangle waveform was used as a measure of the image fidelity, scale and orientation. The resolution of the technique is limited only by signal-to-noise and the fidelity of the marks. Experiments were performed using 2 @mm period grating marks that were fabricated in a SiO2/WSi2 structure using SCALPEL lithography and plasma processing. The projector lenses and magnification/rotation coils were optimized. For these experiments the measured resolutions for determining focus (@df), magnification (@dM), and rotation (@d@q) of a 250 @mm X 250 @mm field were @df ~ +/-1 @mm, @dM ~ +/-15 ppm and @d@q ~ +/- 0.1 mrad. A straightforward path to improving these results is described.

Recent progress in picosecond ultrasonic process metrology

We discuss the use of the picosecond ultrasonics technique for characterizing several challenging processes which are common in sub-0.18 micron processes. Specific processes considered are reactive TaN, RTP-CoSi2, and damascene copper. We describe the transition from one- to two- dimensional acoustical excitations in damascene copper lines, and show how picosecond ultrasonics measurements can be used in to make high throughput, all-optical copper line CD measurements.

Semiconductor Layering Processes

The sections in this article are n n n1 nSemiconductor: Poly-Silicon n n2 nOxides: Gate Dielectrics n n3 nNitrides n n4 nMultilevel Interconnects n n n nKeywords: n nmultilayered processes; noxides; ndielectrics; ninterconnects; nmetallization; npoly-silicon; namorphous silicon; nsilicides; nthermal budget

Low-pressure aluminum planarization for sub-0.5-um contact and via holes

A novel Al-0.5%Cu planarization technology for interconnects is presented using a low pressure Al physical vapor deposition process (or MaxFillTM), capable of filling high aspect ratio (A/R >= 3) via holes at wafer temperatures of less than or equal to 400 degree(s)C. Excellent Al film reflectivity and surface smoothness are achieved due to hardware modifications to the sputter tool and a modified process flow. A high level of vacuum integrity and cleanliness of the system dramatically reduces the time required to fill 0.35 micrometers via holes with aspect ratios of 3, resulting in a throughput in the excess of 24 wafers per hour. In the present work, a comparison of the film morphology between the traditional Two Step Planarization and MaxFillTM processes is presented, which shows the improved grain orientation, reflectivity and film roughness of the MaxFillTM process. The smooth surface morphology of the MaxFillTM process allows easier alignment during subsequent photolithography. In addition to the film properties, electrical results are presented that show that this new deposition technique can planarize 0.35 micrometers structures with A/Rs >= 3 with via resistance values that are lower by a factor of 2.5 than comparable chemically vapor deposited W plug vias.