The important position of lithography technology in the semiconductor industry (3)
Mar 17, 2021
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The important position of lithography technology in the semiconductor industry (3)
●The composition and key points of lithography technology
The basic principle of photolithography is to use photoresist (or photoresist) to form the characteristics of corrosion resistance due to photochemical reaction after exposure, and to engrave the pattern on the mask onto the processed surface.
The main steps of lithography semiconductor chip silicon dioxide are:
1. Coat photoresist;
2. Register the mask and expose;
3. Dissolve the non-sensitized photoresist layer with a developing solution;
4. Use an etching solution to dissolve the unprotected photoresist The silicon dioxide layer;
5. Remove the photosensitive photoresist layer.
The continuous development of lithography technology provides a guarantee for the advancement of integrated circuit technology from three aspects: one is large-area uniform exposure, and a large number of devices and chips are made on the same silicon wafer at the same time, ensuring the mass production level; The second is that the line width of graphics has been continuously reduced, the integration of the use rights has been continuously improved, and the production cost has continued to decline; third, due to the shrinking of the line width, the operation speed of the device has become faster and faster, and the performance of the use rights of integrated circuits has been continuously improved. With the improvement of integration, the difficulties faced by lithography technology are also increasing.
Difficulties and challenges faced by lithography technology | |
≥32nm | abstract |
Research and development of image resolution enhancement technology for optical masks and manufacturing of post-optical imaging technology masks | Control pattern alignment, line width and defects, use sub-resolution assisted pattern technology; master the occurrence of defects in the exposure process; formulate the magnification of the mask required for the 193nm process platform to achieve less than 45nm half-pitch linewidth process patterns , And develop a compensation mode based on the use of small image fields; manufacture 1x five-defect film plates for post-optical imaging technology |
Cost control and return on investment | Control the input-output ratio of equipment and process, manufacture cost-acceptable and applicable optical masks and masks used in post-optical imaging technology; rationally allocate resources, eliminate waste, and develop 450mm silicon wafer production equipment |
Process control | Control the line width change of the gate electrode < 4nm, develop a new pattern alignment technology <11nm; control the line width edge roughness performance; control the measurement of the introduction of line width changes and defects <50nm; adopt a more accurate photoresist model, and use more Accurate OPC model and confirm its performance based on optical polarization effect; control and correct the light scattering of lithography equipment, especially for extreme ultraviolet lithography equipment; adopt design schemes that are conducive to the design of lithography process and the optimization of production requirements |
Immersive Lithography | Control the defects generated in the production of immersion lithography technology, develop and optimize the composition of the photoresist, so that it has good compatibility with the liquid and the top hydrophobic layer, and develop the photoresist with refractive index> 1.8; refractive index> 1.65 Immersion liquid and optical lens material with refractive index ＞1.65 |
Extreme ultraviolet lithography | Manufacture of mask substrates with low defect density; research and development of light source systems with power> 115 watts and long-life and low-loss optical components; research and development of line width edge roughness <3nm, sensitivity <10ml/cm 2 ; resolution <40nm half pitch Line width process pattern photoresist; manufacture optical components with <0.01nm root mean square error and less than 10% intrinsic light scattering; control the pollution of optical components, study the mask protection without organic protective film; research and optics Compatibility of imaging process production equipment |
●The composition of the lithography system:
The lithography machine is an exposure tool, which is the core part of the lithography project. It is expensive to build and is known as the most precise instrument in the world. At present, the world has a lithography machine with a cost of 70 million US dollars. The lithography machine can be called the flower of the modern optical industry, and its manufacturing is so difficult that only two or three companies in the world can manufacture it.
Mask
Photoresist (often along with the development of photolithography machines, and to a certain extent it also restricts the development of photolithography process)
ASML-XT1950i-EUV lithography machine
The main indicators of lithography technology:
Resolution W (resolution) -> the minimum line size that can be resolved and processed by the lithography system and the
depth of focus (DOF-DepthOf Focus) -> the scale range that the projection optical system can clearly image the
critical dimension (CD-Critical Dimension) to control the
alignment Alignment and Overlay (Alignment and Overlay)
Production Rate (Throughout)
Price
Among them, W is the most important index that determines the lithography system, and it is also the reason for determining the minimum feature size of the chip.
It is determined by Rayleigh's law: R = k1r/NA, where r is the wavelength of the lithography wave.
Ways to improve the resolution of lithography:
Reduce the wavelength r, where the lithography processing limit value: r/2, that is, the half-wavelength resolution
increases, the numerical aperture
optimization system design (resolution enhancement technology)
decreases k1
Mainstream lithography technology:
248nm DUV technology (KrF excimer laser) -> 0.10um feature size
193nm DUV technology (ArF excimer laser) -> 90nm feature size
193nm immersion technology (ArF excimer laser) -> 65nm feature size
The continuous progress of semiconductor technology is determined by the photolithography process
A new generation of alternative lithography technology:
157nmF2
EUV lithography, ultraviolet lithography,
electron beam projection lithography,
X-ray lithography,
ion beam lithography, nanoprinting
lithography
Optical lens
Transmissive lens (248nm, 193nm)
reflective lens (157nm)
The mask is
composed of a transparent substrate material (quartz glass) and an opaque metal absorption layer material (mainly metal Cr).
It is usually necessary to deposit a layer of anti-deep ultraviolet light damage on the surface of the bright-enhanced protective coating
Nikon recently launched a new 193nm immersion lithography machine
Resolution enhancement techniques (the RET):
the Step Scan-art
off-axis illumination (OAI)
proximity effect correction (OPC)
phase shift mask (PSM)
having a chemically amplified resist photosensitive rapid amplification
photoresist trimming (ResistTrimming)
anti Multi-layer photoresist with reflective function and surface exposure