Irradiation of Biological Materials by High Energy Roentgen Rays and Cathode Rays

Trump, John G.; Graaff, R. J. Van de

doi:10.1063/1.1698178

Cited by 75 publications

(11 citation statements)

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“…Studies of energy loss as a function of penetration in polymers (15), water (16), and luminescent materials (17) show that the amount of energy transfer varies in essentially the same way in all media.…”

Section: Discussionmentioning

confidence: 99%

Exposure of Photoresists: Electron Beam Exposure of Negative Photoresists

Broyde

1969

J. Electrochem. Soc.

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A threshold flux is required to form an image in negative photoresists when they are exposed to kilovolt electron beams. This threshold is related to the gel point of the photoresist. Using the known number of crosslinks per molecule at the gel point, the G values for the crosslinking of KPR and KTFR, were calculated from the absorbed energy of 2.5 _+ 0.2 x 1020 ev/cm ~ at the threshold, to be 0.65 and 1.20, respectively. An energy transfer model based on Bethe's penetration range for an electron and on the distribution of energy with depth of penetration found by Charlesby describes the change in threshold flux with changes in accelerating potential. Electron fluxes above the threshold value fully insolubilize the resist. The efficiency of absorbed energy for total insolubilization is a function of the energy of the incident electrons. 5 keV electrons are 3.3 times more efficient than uv light, but 15 keV electrons are only as efficient as photons.During the manufacture of semiconductor devices, parts of the semiconductor substrate have to be protected against etchants. This is accomplished by exposing photosensitive etch-resistant polymers called photoresists to light through a mask. The desired pattern of etch resistant polymeric material is obtained after a development process, which removes the unexposed portions of negative resists and removes the exposed portions of positive resists (1). The use of light in patterning the photoresist through a mask, limits the narrowest line and the edge resolution that can be routinely made in the photoresist to be wider than 2 ~m and 0.3 ~m, respectively.On the other hand, lines only 0.25 ~m wide (2) with edge resolutions of 0.05 ~m (3) have been prepared by using an electron beam to expose photoresist. Thornley and Sun (4) showed that both 14 and 20 keV electron beams could expose negative resists so that the resists were able to protect SiO2 against etchants. They found that a threshold existed in the exposing electron flux, below which no protection was provided. Above the threshold the amount of protection increased with increasing flux until full protection resulted. Kanaya, Yamazaki, and Tanaka (3) also found a threshold when they studied the thickness of a developed negative resist as a function of electron flux, for electrons accelerated between 20 and 100 keV. Matta (5) showed that the flux required for optimum exposure depends on the energy of the electrons. He feels that backscattered electrons play a part in the exposure process, but Kanya et al. (3) indicate that backscattering should be negligibly small for energies below 20 keV.The electron beam exposure of two negative photoresists has been investigated here. The first resist, Kodak Photosensitive Resist (KPR), contains a polyvinyl cinnamate polymer, while the second Kodak Thin Film Resist (KTFR), contains a polymerized isoprene dimer.'This work assumes that the threshold flux found in the exposure of these resists is related to the gel point of the resist. If this is the case, then the threshold flux sho...

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Section: Discussionmentioning

confidence: 99%

Exposure of Photoresists: Electron Beam Exposure of Negative Photoresists

Broyde

1969

J. Electrochem. Soc.

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“…The absorbed dose varies with depth (18) and is about 60% of maximum at the surface with a steady increase to a maximum at about one-third of the total penetration depth. At about two-thirds of the total penetration, the dose is equivalent to that absorbed at the surface.…”

Section: Experimental Methodsmentioning

confidence: 97%

Radiation Modification of Poly(ethylene oxide)

King¹

1967

Advances in Chemistry

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The electron or gamma irradiation of high molecular weight poly(ethylene oxide) (Polyox) causes marked changes in solution properties, molecular-weight distribution, and mo lecular weight. Crosslinking and degradation both occur, but their relative importance is determined by experimental conditions such as dose rate, oxygen concentration, and particle size. At low dose rates and in the presence of air, the G (scission) value is about 200. Changes in molecular weight and molecular-weight distribution have been mea sured and related to the gross improvements observed in solution properties: lower viscosity, increased shear stability, and longer shelf life.The polymerization of ethylene oxide with heavy metal catalysts yields -*· a polyether ranging in molecular weight from about 10 5 to 10 7 . The trade name Polyox has been given to this class of water-soluble resins (9). Alternative polymerization methods produce low molecular weight (<10 5 ) materials called Carbowaxes. Although the two polymers are chemically identical, there are large differences in molecular weight and molecular-weight distribution and important differences in physical properties.Solutions of Polyox resins are less stable than the lower molecular weight Carbowax series. McGary studied the chemical degradation of Polyox (JO) and found that aqueous or organic solutions of Polyox degrade upon long term aging-i.e., the solution viscosity decreases. This degradation is "accelerated by strong acids, certain oxidizing agents, ultraviolet light, and certain heavy metal ions." He concluded that Polyox degrades primarily by a chain oxidation process.Mechanical agitation is also an important degradation method in the higher molecular weight series. In fact, care must be taken in preparing solutions of high molecular weight samples since rapid agitation often decreases the bulk viscosity greatly.

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“…A pressure-insulated, electrostatic generator ofthe Van de Graafftype, operating at 3,000,000V. and capable of producing a continuous supply of monoenergetic electrons, was used for the production of the cathode rays (Robinson, 1947;Trump & Cloud, 1943;Trump & Van de Graaff, 1948). The dosages of cathode rays are expressed in terms of rontgen-equivalent-physical (r.e.p.)…”

Section: Methodsmentioning

confidence: 99%