We describe a newly developed technique that uses optical projection lithography with a liquid crystal display (LCD) in place of a conventional reticle, in order to minimize turn-around-time and production cost. Circuit pattern data, generated by a computer aided design (CAD) system, is transferred directly to a control computer. The control computer converts the data into an equivalent dot matrix representation of the design for use on a LCD. The LCD is placed in a conventional optical stepper. One feature of this system is the simplicity of the data management scheme which permits the data to be handled by a computer file directly; without any of the manual assistance normally needed in conventional reticle fabrication. It is a very convenient method to reverse reticle tone by changing the LCD mode; easy compared to a conventional reticle manufacturing process. The minimum resolution of this proposed system is very similar to conventional systems that use optical reticles. We have demonstrated that this LCD Reticle-Free Exposure Method has the potential of replacing conventional reticles in optical stepper lithography. This method is applicable for manufacturing devices with relatively large fabrication rules and low production quantities, such as System-in-Package applications.
Liquid crystal display (LCD) in place of the conventional reticles for optical projection lithography is proposed, in order to minimize the turn-around-time and production cost. The transmittance ratio between the two modes of the LCD, such as transparent and opaque ones, is approximately a several dozen depending on the wave length of the light source. In this study, the Nikon g-line stepper was modified to apply the LCD on its reticle stage. The minimum resolution of this proposal projection system is quite similar to the one of the conventional reticle method. The exposure time is approximately 10 times longer compared to the conventional method. It has been proven that the LCD has the potential to be replaced for the conventional reticles in the optical stepper lithography that is applicable for devices with relatively large fabrication rules and low production amount.
Lithography is one of the most important techniques in the IC fabrication and has been extensively used in processing. The high resolution and accuracy of electron beam lithography is most appropriate for making mask of optical and X-ray lithography as well as direct writing on wafer. Two types of resist, ZEP-520 positive resist and SAL-601 negative resist, were prepared for used in the electron beam lithography. Three different patterns, which include isolated line, contact hole and line and space patterns were exposed on the tungsten, oxide, and metal substrates, respectively. The 0.15 micrometers resolution of lithography patterns was achieved. For the etching of polysilicon and oxide, well defined profile of polysilicon gate with 0.1 micrometers width and well-defined tapered profiles of oxide contact hole have been obtained successfully.
The mix-and-match method is an effective method to meet the requirements of minimizing the exposure time and the feature size, in which only the critical gate layer is exposed by electron beam lithography system, and the other ones by conventional g-line stepper. The negative type chemically amplified resist SAL601, made by Shipley, has been used for gate fabrication. The optimum conditions for the electron beam lithography including mark dimension, resist process and etching process have been investigated. The accelerating voltage and the beam current were fixed to be 40 kV and 0.25 nA, respectively. The mark of the electron beam lithography has the trench cross shape of 0.5 micrometers in depth, 20 micrometers in length and 3 micrometers in width. The sensitivity of SAL601 resist has been 20 (mu) C/cm2 for 0.1 micrometers patterning at 40 kV accelerating voltage. The polysilicon gate was etched by electron cyclotron resonance with SiO2 thin mask in HBr/O2 gas, for the appropriate anisotropy of etching and for the polysilicon-to-oxide selectivity of HBr/O2 gas plasma. The well defined profile of polysilicon gate with 0.1 micrometers width has been obtained successfully.
In this paper, a metrology for micro- and nanofabrication process has been implemented using an atomic force microscope (AFM). Deep submicron patterning on wafer and chromium photomask were done using well established e-beam direct write technology and evaluated using AFM. A fine pitch control method was proposed to fabricate grating pitch mask for the pitch measurement of AFM. It can finely control the grating pitch to 1 nm, less than the most pattern data unit (5 nm) used in electron beam lithography. AFM is a powerful metrology tool for deep submicron process. AFM was employed as an inspection tool for the evidence of the existence of quantum dots on the GaAs substrate, the quantum dots or islands can be inspected clearly. Good performance is obtained.
This work describes the mix-and-match lithography technology for 0.1 micrometer device fabrication including a resist patterning process using a G-line stepper and an e-beam lithography system on 6 inch wafers, device pattern layout and device fabrication. A high resolution positive type e-beam resist combined with a high throughput G-line stepper is found to be ideally suitable for fabricating a device with nanometer scale.
A high precision electron beam lithography systems which can be used to make reticles for 0.3 micrometers devices has been developed. This system is an enhanced model of the Hitachi electron beam lithography system, HL-700M. Key technologies used in this system are (1) the minimum address unit (0.0125 micrometers ) and the stage-positioning measurement unit (0.005 micrometers ) to correspond with higher precision specifications, (2) the refined beam correction functions and (3) the efficient environmental controls. The items of improvement on environmental controls are to design an anti-vibration column and to adopt a reticle temperature control system. The main specifications of this system are (1) the positioning accuracy: 0.06 micrometers , (2) stitching accuracy: 0.05 micrometers , (3) pattern width accuracy: 0.05 micrometers and (4) throughput: 0.5 reticle/hr. The system enables one to write phase shift masks using the direct writing mode in HL-700D.
Reticle specifications (line width accuracy, pattern stitching accuracy, overlay accuracy) required for 64M-DRAM are 0.05 for individual items. It is very hard for current Electron Beam Lithography systems (EBL) to produce high quality reticles and keep through-put the same as the current EBL. In order to satisfy 64M-DRAM application the HL-700M has thoroughly been
evaluated and modified to meet 0.05 ?m specification. A highly accurate electron beam correction program and a bordering exposure program were developed in order to improve line width accuracy. A rigid stage chamber construction and temperature control units have been developed in order to improve stitching and overlay accuracy. Line width accuracy (0.05 ?m) was confirmed. Stitching accuracy (0. 05 ?m) and overlay accuracy (0. 06 ?m) were obtained, which is 2 times the accuracy of the current HL-700M. The advanced HL-700M is under development for improvements.