Mikio Hongo

Laser Diffusion Connection Technology for VLSI Programming

Summary A laser diffusion technology to connect poly-silicon conductors for programming VLSI memories is developed. It is based on the fact that a Nitrogen laser pumped dye laser of 510 nm wavelength irradiated on an intrinsic poly-silicon film in a VLSI, having 10 10 2 resistivity, decreases the film resistivity to 10 3 Ω. The mechanism of resistivity reduction is due to the laser heat diffusion of impurity into the intrinsic poly-silicon film. It is also clarified that the passivation film thick-ness on the intrinsic poly-silicon film changes laser reflectivity from zero to over 50%, affecting the condition of the process. The practical processing condition of laser diffusion connection for VLSI programming to enhance chip yield without damage is obtained.

Evaluation of Molybdenum Conductors Formed by Laser-induced CVD.

This paper describes the evaluation results of molybdenum conductors formed by laser-induced CVD using thermal decomposition of molybdenum hexacarbonyl as a material gas. In order to apply this technique to LSI products, it is very important that the conductors deposited on LSI chips have sufficient reliability. From the fusing test, the applicable current density was found to be about 3 × 106 A/cm2 which is sufficiently high compared with the maximum current density, 1-3 × 105 A/cm2, for practical use. Molybdenum conductors, after laser annealing. endured a heat cycle test 70 times without a change of resistance. And, these conductors did not change resistance for 1 000 hours when a current density of 1.3 × 106 A/cm2was applied in a 125°C atmosphere. These results suggest the possibility of application in LSI products.

High-speed Forming of Low-resistivity Interconnects Using Laser-induced CVD.

Experimental investigations concerning formation of metal interconnects on LSI chips using laser-induced CVD are described. Molybdenum conductors were deposited by pyrolytic decomposition of molybdenum hexacarbonyl using argon ion-laser irradiation. Increasing molybdenum hexacarbonyl pressure, increasing laser power and decreasing writing speed were accompanied by increasing width and thickness of molybdenum conductors. Decomposition efficiency is 20 to 30% which is higher than conventional thermal CVD. Increased width and thickness diminished the resistance of the conductors, but the resistivity was almost independent of the forming conditions and higher than that of bulk molybdenum. Auger electron spectroscopy revealed that the high resistivity of the as-deposited films was due to the presence of carbon and oxygen as impurities. These impurities are removable by laser annealing in a vacuum, whereby the resistivity can be reduced to 10 μΩ·cm. These low-resistivity conductors can be applied to fault analysis or repair of not only MOS devices but also linear and bipolar devices.

Laser microformation of thin film on glass substrate for repair of transparent defects on high-density masks

Summary A new technique is developed for repairing transparent defects on high density masks for VLSI. A thin Ag-Ta organometallic film is first spin-coated onto a photomask and baked. Then an Ar laser microspot is applied to a small area on this film. After rinsing the mask with a solvent, an opaque layer remains at the laser-irradiated spot and the rest of the organometallic material is washed away. The opaque film formed locally by laser irradiation is dense enough to prevent light transmission and durable enough to withstand repeated washing with strong alkali and acid solutions.

Reduction of Contact Resistance in Interconnections Formed by Laser-Induced CVD.

Reduction of Contact Resistance in Interconnections Formed by Laser-Induced CVD Mikio HONGO, Takashi KAMIMURA, Shuzo SANO and Katsuro MIZUKOSHI This paper reports the experimental results of the reduction in contact resistance between aluminum conductors in a semiconductor device and molybdenum conductors deposited by laser-induced CVD. The contact holes are formed by focused ion beam through a passivation layer on the chip surface, and irradiated with an argon ion laser in a molybdenum-hexacarbonyl atmosphere. The holes can be filled with molybdenum, however, aluminummolybdenum contact resistance is very high. Even after sufficient removal of natural oxide, the contact resistivity with the molybdenum line formed cross on the aluminum line without a passivation layer is high. The high-resistive contact is caused by the formation of high-resistive alloy diffused aluminum into molybdenum. To prevent alloying, chrominum film was adopted as a barrier layer at the aluminum-molybdenum interface. As a result, the contact resistivity was reduced to 1/100. Automatic positioning using a pattern matching technique and an end-point monitor using a detection in change of the intensity of reflective light can realize low-resistive contact and good outward shape with good reappearance.

Mo Conductor Forming Technique with Laser Chemical Vapor Deposition (CVD)

A reduction in resistivity and an improvement in reliability of Mo conductors formed by laser CVD from Mo(CO)6 gas have been achieved using laser annealing. By establishing a standard of 10 μ Ω • cm, the reduction in resistivity was analyzed by AES (Auger Electron Spectrometry) and XRD (X‐ray Diffractometry) methods. Reliability has been confirmed by the stability of resistance when subjected to a heat cycle of −50 – 150°C for more than 70 times.

High performance conductor forming technique with laser chemical vapor deposition (CVD)

A reduction in resistivity and an improvement in reliability of Mo conductors formed by laser CVD from Mo (CO)6 gas have been achieved using laser annealing. By establishing a standard of 10 μ Ω · cm, the reduction in resistivity was analyzed by AES (Auger Electron Spectrometry) and XRD (X-ray Diffractometry) methods. Reliability has been confirmed by the stability of resistance when subjected to a heat cycle of −50 – 150°C for more than 70 times.A reduction in resistivity and an improvement in reliability of Mo conductors formed by laser CVD from Mo (CO)6 gas have been achieved using laser annealing. By establishing a standard of 10 μ Ω · cm, the reduction in resistivity was analyzed by AES (Auger Electron Spectrometry) and XRD (X-ray Diffractometry) methods. Reliability has been confirmed by the stability of resistance when subjected to a heat cycle of −50 – 150°C for more than 70 times.