Currently available commercial model-based OPC tools do not always generate layouts which are mask rule compliant. Additional processing is required to remove mask rule violations, which are often too numerous for manual patching. Although physical verification tools can be used to remove simple mask rule violations, the results are often unsatisfactory for more complicated geometrical configurations. The subject of this paper is the development and application of a geometrical processing engine that automatically enforces mask rule compliance of the OPC'ed layout. It is designed as an add-on to a physical verification tool. The engine constructs patches, which remove mask rule violations such as notches or width violations. By employing a Mixed Integer Programming (MIP) optimization method, the edges of each patch are placed in a way that avoids secondary violations while modifying the OPC'ed layout as little as possible. A sequence of enforcement steps is applied to the layout to remove all types of mask rule violations. This approach of locally confined minimal layout modifications retains OPC corrections to a maximum amount. This method has been used successfully in production on a variety of DRAM designs for the non-array regions.
3D model calculation on the basis of Finite Elements were carried out to simulate the heat distribution under IR laser ablation. The physical constant of dentin were used for heat capacity, heat conductivity etc. Already for a single pulse the results show the temperature distribution at various times after the laser pulse as well as the temperature gradient and the mechanical stress. The time resolution of a single pulse into 80 equal time step showed the heat deposition during the laser pulse Even more exciting data were obtained for pulse trains. It is clearly obvious that after 10 pulses the system reached a dynamical equilibrium. The amount of heat left over in the tissue by the previous pulse away by the following pulse by removing heated tissue.
Mechanical effects that amy damage tissue were measured by laser doppler vibrometry. The results on the recoil momentum illustrate the laser parameters under which laser survey of organs with delicate structures becomes dangerous. One example is the acceleration of the tiny middle ear bones. In the case of an intact ossicular chain, the motion of a middle ear bone is transferred to the inner ear. The second topic is related to eye surgery. Removing or cutting of membranes, the lens or the vitreous body by pulsed lasers is often associated with the formation of laser induced cavitation bubbles. The collapse of these bubbles generates pressure shock waves propagation through the eye. Laser Doppler vibrometry was used to monitor the shock wave induced velocity of the sclera.
Laser ablated material escapes from the surface with high velocities up to the speed of sound. Due to the conservation of momentum, the same amount of momentum which is in the ablated material is also transferred to the remaining tissue. The effect of this recoil momentum is like a force which accelerates the tissue. In the case of the tiny middle ear bones, the acceleration may be so large that it harms structures of the inner ear. Laser Doppler vibrometry was used to measure the recoil momentum induced by infrared lasers like Holmium, Erbium and CO2 laser. This paper focuses on the effect of repetitive laser pulses of a short pulse CO2 laser.
Cranial rat bone was irradiated by 2.1 micrometers Holmium YAG laser radiation. Quantitative edge rates were calculated. Histologic sections were investigated by light and electron microscopy. 18 cases of hard fibrous or calcified spinal and cranial meningiomas and neurinomas were operated upon using pulsed laser beam. In rat cranial bone ablation rate ranged between 3 - 5/10 mm per pulse. Perifocal thermal damage was observed in a zone of 20 - 90 micrometers around the lesion. In all human cases tumors could be removed totally without additional neurological deficit. In vivo heat development was measured by an IR-camera.
A laser Doppler vibrometer was used in a pendulum experiment to measure the recoil momentum induced in hard tissue by pulsed infrared laser exposure. A Holmium:YAG laser was irradiated at bone and a superpulsed CO2 laser irradiated at dentin. Since the masses of the samples were known and the ablated masses were measured, this method allowed an indirect determination of the velocity of the ablated particles. In a second experiment performed with the CO2 laser the velocities of the ablated particles were measured directly by the time of flight detected by the laser beam of the vibrometer. The results of both methods are in good agreement; at a mean power of 0.5 Watt of the CO2 laser the velocity was 50 - 60 m/s increasing at higher mean powers.
The recoil momentum of hard tissue induced by pulsed IR laser exposure was measured in a pendulum experiment using laser Doppler vibrometry. For the experiments bone was irradiated by holmium:YAG laser radiation and dentin by a superpulsed CO2 laser. Since the initial masses of the samples were known and the ablated masses were measured, this method allowed also an indirect determination of the velocity of the ablated particles. In a second experiment performed with the CO2 laser the velocities of the ablated particles were measured directly by the time of flight detected by the laser beam of the vibrometer. The technical realization as well as the limitations of the method is discussed; furthermore laser parameters are pointed out which induce critical acceleration risking serious damage to sensitive organs.
Using the pendulum method the recoil momentum on dentin samples after pulsed irradiation (pulselength 80 - 100 microsecond(s) ) with a medical CO2-laser (Sharplan 40C, 10.6 micrometers ) was measured. Therefore a Laser-Doppler-vibrometer was used to deliver the velocity and the direction of movement. Because of known masses of the samples and measurement of the ablated masses the velocity of the ablated particles was calculated. As a second method to measure the velocity of the ablated particles the vibrometer was used in a time of flight experiment. Both methods delivered the same results at a mean power of 0.5 Watt. The velocity of the ablated particles was 50 - 60 m/s. At higher mean powers the thermal behavior of the tooth material leads to higher velocities.
Cranial rat bone was irradiated by 2,1 micrometers Holmium Yag laser radiation. Quantitative edge rates were calculated. Histologic sections were investigated by light and electron microscopy. 20 cases of hard fibrous or calcified spinal and cranial meningeomas and neurinomas were operated upon using pulsed laser beam. In rat cranial bone ablation rate ranged between 3-5/10 mm per pulse. Perifocal thermal damage was observed in a zone of 20-90 micrometers around the lesion. In all human cases tumors could be removed totally without additional neurological deficit. In vivo heat development was measured by an IR-camera.
Ablation of dentin and tartar was studied under carbon dioxide-laser irradiation in cw and pulse mode with pulse length down to 150 microseconds. The specimens had been cut by a diamant blade to slices of thicknesses between 0.8 and 2.8 mm. The laser induced temperature rise was measured by an infrared camera monitoring the backside of the samples. The specimens shape and structure at the laser spot was analyzed by electron microscopy. Of special interest was the testing of the SwiftLaseTM to reducing the heat. The experimental results show the necessity of a water cooling in all application modes. The origin of the cracks which had been observed in many of the samples, is currently under investigation.
An infrared camera was used to measure the temperature rise which takes place in endotracheal tubes under laser irradiation. It was seen that a metallic tube was heated up within a second to temperatures of 200 degrees to 300 degrees Celsius which was very destructive to the PVC conduits inside of the tube. A compound tube, on the other hand, reached temperatures of only 38 degrees Celsius at its inner surface. The thermal induced destruction of the conduits inside of the metallic tube is seen as the reason for complications like airway blocking. Furthermore preliminary results of a randomized clinical study are presented, showing that the metallic tube needed higher pressure levels than the compound tube.
The ablation of joint cartilage by Holmium laser radiation is followed by the creation of an unexpected large avital cell area below of the irradiated spot. To examine the reasons for the tissue destruction the effect of shockwaves as well as the temporal development of temperature due to the laser absorption was investigated. The temperature raise was observed by an infrared-camera. The creation of cell destroying temperatures below the irradiated area is explained by the absorption of the Holmium laser light and the spread out of heat from the absorption area, whereby the effects due to shockwave seem to be neglible. To reduce the development of high temperatures a method is presented that allows a local coding of the irradiated area.
The combination of the short penetration length in water and the delivery through flexible quartz fibers made the radiation of the Holmium laser very promising for minimal invasive surgery. Furthermore the available power density of 106 W/cm2 overcomes the threshold for ablation, which opens the way for cutting and removal of bone and cartilage, which is important for surgery especially in ENT. In contradiction, recently warning had been brought up that particularly in cartilage the damage zone can exceed the ablation zone by orders of magnitude and one should be restrictive using the Holmium laser for joint surgery. We found that the effect of Holmium laser radiation on tissue cannot be described by a pure absorption and ablation process. Experimental data showed that in the case of bone scattering has to be considered, and in the case of cartilage a remarkable heating of the remaining tissue occurred. This amount of heating could be reduced significantly by a new designed fiber mount, which cooled the tissue.