The Neverending Challenge of Finding the Ideal Lens
Advanced optical technologies and precision engineering contributed greatly in the quest of Canon's founders to realize their dream of producing the best camera in the world. Of these, optical technologies such as those used in lenses are a combination on a variety of technologies such as lens design, material selection, and processing technologies such as lens grinding and polishing.
The aim of a lens is to form an image of a subject as clearly and accurately as possible, but there is also problem that light does not focus on a single point because the refractive index of the glass varies depending on the wavelength of light. This is called chromatic aberration. Other aberrations include spherical aberration and coma aberration, and it is thus necessary to create lenses by combining concave and convex lenses made of varieties of glass having different wavelength dispersion in order to eliminate aberrations. Lenses are designed using between several and several dozen varied concave and convex lenses combined with over 100 glass materials, but selecting the optimal solution from countless combinations requires not only design know-how, but also an artistic sense similar to that needed to draw a picture. Canon's engineers constantly push the envelope, working hard to accumulate know-how and refine their senses through the design of a variety of lenses.
In order to design superior lenses, engineers must experience designing many lenses themselves, but referencing high quality lenses designed by other engineers is also important. When Canon designs a new lens, it holds an unveiling called a "review" providing an opportunity for information to be shared not only by the engineers responsible for design information, but also many other engineers. The strength of Canon's optical technologies is in the shared experience and accumulation of design information on numerous lenses by engineers.
Canon also developed its own computer software for lens design in the early 1960s, and has been developing a variety of software since. Canon's excellent design tools mark another strength of the company's optical technologies.
The company will continue to proactively undertake challenges in the pursuit of lenses that correct aberrations to the ideal degree.
High-Performance Lens Achieved by Embracing the Impossible
To date, Canon has produced literally hundreds of masterpiece lenses.
One such example is the fluorite lens, which had long been considered impossible to implement practically. Fluorite is characterized by extremely low levels of chromatic aberration, making it ideal for capturing vivid, detailed images that cannot be achieved using conventional optical glass. Fueled therefore by a burning desire to use this material in their lenses, the company's engineers ultimately succeeded in synthesizing fluorite crystals. Canon also developed special processing technologies for such delicate materials, which could not be polished in the same way as normal optical glass, quadrupling the amount of time used during the polishing process. In 1969, Canon launched the world's first lens incorporating fluorite.
However, fluorite is extremely expensive, so Canon developed glass with characteristics such as a refractive index and dispersive properties similar to fluorite in order to correct chromatic aberrations in more lenses. In the late 1970s, Canon succeeded in the practical application of a UD lens using this glass.
The company also began development of aspherical lenses. In theory, with conventional spherical lenses, the focal point for the central portion of the lens does not coincide with the focal point for the peripheral area. This discrepancy, however, can be eliminated with an aspherical lens. Aiming to achieve a level of precision within 0.1 μm (1 μm = one millionth of a meter), Canon engineers repeatedly measured and shaped the lenses, and established the necessary design, processing, and precision measurement technologies. In 1971, Canon became the world's first company to commercially produce an SLR camera lens incorporating aspherical lens elements. Today, the company manufactures aspherical lenses with a degree of processing accuracy of 0.02 μm.
Raw Fluorite, Artificial Crystal, and Lenses
Development of Japan's First Semiconductor Lithography Tool
In 1965, Canon began to apply its core optical technologies in the development of the U-series of lenses for use in the production of semiconductors. Three years later, these efforts culminated in the U170mmF1.8 — a lens that earned many plaudits for its technical superiority.
As work continued on new U-series lenses, Canon made the decision to expand into the development of semiconductor lithography devices in recognition of the prosperity of the global semiconductor industry. This marked a bold step into an industry of which the company had no previous experience.
Semiconductor integrated circuits are created by taking a circuit pattern drawn on a photomask and optically transferring it onto a wafer. In 1970, the company introduced a semiconductor production lens in the PPC-1 — a 1:1 projection mask aligner for 2-inch wafers that marked the first semiconductor lithography tool to be produced in Japan. However, as the system employed a manual alignment process and 3-inch wafers were to be introduced, this approach advanced no further.
PPC-1: Japan's First Semiconductor Lithography Tool
Onward to Become an Industry Recognized Producer of Lithography Equipment
In 1974, Canon introduced the PLA-300F, a proximity mask aligner in which the mask and wafer were separated by 10 to 20 μm and exposure was performed using collimated light. This method, capable of processing line widths of approximately 4 μm, facilitated high levels of productivity through its automatic wafer feed capability for wafer sizes up to 3 inches. The company subsequently launched the world's first mask aligner with a laser-based automatic alignment system, the PLA-500FA, in 1977. The machine became a best seller, enabling Canon to make a name for itself, both inside and outside the company, as a producer of semiconductor lithography equipment a mere decade after entering the field.
Subsequently, Canon introduced the MPA-500FA, which used the mirror projection method to achieve high-resolution, 2-μm line-width circuits on wafers of up to 5 inches in diameter, followed by the MPA-600FA, which added support for 6-inch wafers. This model contributed greatly to the mass production of 64 to 256 KB DRAM during the 1980s.
Since 1984, light-source wavelengths have been continually reduced in order to satisfy the need for narrower circuit line widths of semiconductor devices. These wavelengths transitioned from the 436 nm (1 nm = one billionth of a meter) of the mercury lamp g-line, to the 365 nm of the lamp's i-line, the 248 nm of the krypton fluoride laser (KrF laser), and the 193 nm of the argon fluoride laser (ArF laser). Advances were also made in optical systems with the development of new glass materials for light sources giving rise to higher levels of resolution. With these advancements demand grew for improvements in alignment precision, and masks (reticles) and stage control of wafers were also made extremely precise.
In 1984, Canon introduced its first stepper (reduction projection lithography tool) with the FPA-1500FA, which used the g-line as its light source. The FPA-2000i1, which utilized the i-line, was launched in 1990, followed in 1997 by the FPA-3000EX4 — a stepper that employed a Krf excimer laser as its light source. Canon has since gone on to further enhance its line up of lithography equipment.
Canon's First Stepper, the FPA-1500FA