question: How does UV light reset EPROM chips?
comment: You write to or program a EPROM memory not flash them. The word flash might be used for flash memory that is a type of EEPROM that is the one common today but for the old memory types it was not the the common expression. To quote the Wikipedia article ton EPROM > Photons of the UV light cause ionization within the silicon oxide, which allow the stored charge on the floating gate to dissipate So it work but making the isolator conductive. You need UV light because it have enough energy to ionization atom ie provide enough energy so electons can leave the atom. This is the same reason that UV light in sunlight or from other sources damages cells and can cancer. It might ionize the DNA or other parts of the cell so the molecules break apart. Plastic get damage by UV for the same reason it break apart the polymerers that plastic is made of. X-rays can do the same thing EPROM and you can erase circus that do not have a transparent windows in the packing. With a bit other material you can have a similar effect in semiconductor with visible light that is know as a solar cell. Solar cells is a photovoltaic effect instead of a photoelectric effect but it is almost the same thing.
passages: The programming process is not electrically reversible. To erase the data stored in the array of transistors, ultraviolet light is directed onto the die. Photons of the UV light cause ionization within the silicon oxide, which allow the stored charge on the floating gate to dissipate. Since the whole memory array is exposed, all the memory is erased at the same time. The process takes several minutes for UV lamps of convenient sizes; sunlight would erase a chip in weeks, and indoor fluorescent lighting over several years. Generally, the EPROMs must be removed from equipment to be erased, since it is not usually practical to build in a UV lamp to erase parts in-circuit. The Electrically Erasable Programmable Read-Only Memory (EEPROM) was developed to provide an electrical erase function and has now mostly displaced ultraviolet-erased parts.
   Section::::Enhancement opportunities for EUV patterning.:Phase shift masks.
   Section::::Enhancement opportunities for EUV patterning.:Source-mask optimization.
   EPROMs (Erasable Programmable Read-Only Memory) are erased by exposure to UV radiation. These modules have a transparent (quartz) window on the top of the chip that allows the UV radiation in.
  
  Section::::Applications.:Fluorescent dye uses.
  
  Colorless fluorescent dyes that emit blue light under UV are added as optical brighteners to paper and fabrics. The blue light emitted by these agents counteracts yellow tints that may be present and causes the colors and whites to appear whiter or more brightly colored.
   The first generation of PICs with EPROM storage are almost completely replaced by chips with Flash memory. Likewise, the original 12-bit instruction set of the PIC1650 and its direct descendants has been superseded by 14-bit and 16-bit instruction sets. Microchip still sells OTP (one-time-programmable) and windowed (UV-erasable) versions of some of its EPROM based PICs for legacy support or volume orders. The Microchip website lists PICs that are not electrically erasable as OTP. UV erasable windowed versions of these chips can be ordered.
  
  Section::::Hardware features.:Part number.
   BULLET::::- EPROM ("Erasable programmable read-only memory") In this type the data in it can be rewritten by removing the chip from the circuit board, exposing it to an ultraviolet light to erase the existing data, and plugging it into a PROM programmer. The IC package has a small transparent "window" in the top to admit the UV light. It is often used for prototypes and small production run devices, where the program in it may have to be changed at the factory.
   Section::::Enhancement opportunities for EUV patterning.:Optimum illumination vs. pitch.:Pitch-dependent focus windows.
   Section::::EUV-specific optical issues.:Mask absorber phase effects.
   Its UV transparency also finds uses in the semiconductor industry; an EPROM, or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off, but which can be erased by exposure to strong ultraviolet light. EPROMs are recognizable by the transparent fused quartz window which sits on top of the package, through which the silicon chip is visible, and which permits exposure to UV light during erasing.
  
  Due to the thermal stability and composition, it is used in semiconductor fabrication furnaces.
   Section::::Details.
  
  As the quartz window is expensive to make, OTP (one-time programmable) chips were introduced; here, the die is mounted in an opaque package so it cannot be erased after programming – this also eliminates the need to test the erase function, further reducing cost. OTP versions of both EPROMs and EPROM-based microcontrollers are manufactured. However, OTP EPROM (whether separate or part of a larger chip) is being increasingly replaced by EEPROM for small sizes, where the cell cost isn't too important, and flash for larger sizes.
   Section::::EUV-specific optical issues.:Reflective optics.:Pattern shift from defocus (non-telecentricity).
  
  Section::::EUV-specific optical issues.:Reflective optics.:Pattern shift from defocus (non-telecentricity).:Mask feature vertical placement.
   An EPROM cell is a MOS (metal-oxide-semiconductor) transistor that can be switched on by trapping an electric charge permanently on its gate electrode. This is done by a PAL programmer. The charge remains for many years and can only be removed by exposing the chip to strong ultraviolet light in a device called an EPROM eraser.
   In Intel's complementary lithography scheme at 20 nm half-pitch, EUV would be used only in a second line-cutting exposure after a first 193 nm line-printing exposure.
   Section::::Enhancement opportunities for EUV patterning.:Optimum illumination vs. pitch.:Illuminations for advanced nodes.
   Section::::Applications.:Triggers.
  
  Series connection of an LED and a low-resistance photoresistor make the RO a trigger (memory cell) which can be controlled by current pulses. In transparent ROs, the state of such cell can be monitored visually by the LED emission.
  
  Section::::Applications.:Radio communication.
   Section::::EPROM generations, sizes and types.
  
  The first generation 1702 devices were fabricated with the p-MOS technology. They were powered with V = V = +5 V and V = V = -9 V in Read mode, and with V = V = -47 V in Programming mode.
  
  The second generation 2704/2708 devices switched to n-MOS technology and to three-rail V = +5 V, V = -5 V, V = +12 V power supply with V = 12 V and a +25 V pulse in Programming mode. 
   BULLET::::1. Two UvrA proteins form a dimer and they both have ATPase/GTPase activity.
  
  BULLET::::2. The UvrA dimer binds with a UvrB dimer and forms a complex that is able to detect DNA damage. The UvrA dimer functions as the unit responsible for the detection of DNA damage, probably through a mechanism of detecting distortions in the DNA double helix.
  
  BULLET::::3. Upon binding of the UvrAB complex to a putative damaged site, the DNA wraps around UvrB
  
  BULLET::::4. The UvrA dimer leaves and a UvrC protein comes in and binds to the UvrB and, hence, forms a new UvrBC complex.
   Erasure of the EPROM begins to occur with wavelengths shorter than 400 nm. Exposure time for sunlight of one week or three years for room fluorescent lighting may cause erasure. The recommended erasure procedure is exposure to UV light at 253.7 nm of at least 15 Ws/cm, usually achieved in 20 to 30 minutes with the lamp at a distance of about 2.5 cm.
  
  Erasure can also be accomplished with X-rays:
   Generally, a photomask is purchased/generated, which consists of opaque Chromium patterns on a transparent glass plate. A sample (or "substrate") is coated with a thin film of UV-sensitive photoresist. The sample is then placed underneath the photomask, and pressed into "contact" against it. The sample is "exposed", during which UV light is then shone from the top side of the photomask. Photoresist lying beneath transparent glass is exposed, and becomes able to be dissolved by a developer, while photoresist lying under Chrome did not receive any UV exposure and will remain intact after developing.
   Photolithography is used in the manufacture of semiconductors, integrated circuit components, and printed circuit boards. Photolithography processes used to fabricate electronic integrated circuits presently use 193 nm UV and are experimentally using 13.5 nm UV for extreme ultraviolet lithography.
  
  Section::::Applications.:Material science uses.:Polymers.
  
  Electronic components that require clear transparency for light to exit or enter (photovoltaic panels and sensors) can be potted using acrylic resins that are cured using UV energy. The advantages are low VOC emissions and rapid curing.
   Section::::EUV-specific optical issues.:Reflective optics.
  
  A fundamental aspect of EUVL tools, resulting from the use of reflective optics, is the off-axis illumination (at an angle of 6 degrees, in different direction at different positions within the illumination slit) on a multilayer mask. This leads to shadowing effects resulting in asymmetry in the diffraction pattern that degrade pattern fidelity in various ways as described below.
  
  Section::::EUV-specific optical issues.:Reflective optics.:Thick mask shadowing effects.
   BULLET::::- Interference UV Blockers are usually built into anti-reflective interference thin film stacks, and focus on maximizing the UV "reflection" below the visible light boundary. Industrially-available sol-gel processes offer up to 84% UV block, while magnetron-sputtered AR/UV-Blocking layers can block up to ~92% with no adverse effects on the transmission or absorption of visible light.
   When a device's firmware is stored in mask ROM or one-time programmable PROM, it cannot be modified without physically replacing the integrated circuit, so such a device cannot be field-programmable in the modern sense. Erasable PROM-based firmware can be erased and reprogrammed, but only after lengthy exposure to a high-intensity ultraviolet light source.
   A programmed EPROM retains its data for a minimum of ten to twenty years, with many still retaining data after 35 or more years, and can be read an unlimited number of times without affecting the lifetime. The erasing window must be kept covered with an opaque label to prevent accidental erasure by the UV found in sunlight or camera flashes. Old PC BIOS chips were often EPROMs, and the erasing window was often covered with an adhesive label containing the BIOS publisher's name, the BIOS revision, and a copyright notice. Often this label was foil-backed to ensure its opacity to UV.
   Section::::EUV-specific optical issues.:Reflective optics.:Pattern shift from defocus (non-telecentricity).:Wafer defocus.
  