(Photo) Lithography for semiconductor applications

There are various vacuum deposition processes used to create thin film deposition (coatings) of metal, alloys and non-metals. This can be achieved through mechanical, electromechanical or thermodynamic means. Kamet’s mineral insulated heating elements have a broad range of applications in deposition systems. After thin-film deposition, the next step in semiconductor processing is etching and (photo)lithography is one means of doing this.

What is (photo)lithography for semiconductor applications?

Lithography refers to the transfer of a chip design to a photosensitive material by selective exposure to light. It is part of the chip manufacturing process and the process is comparable to darkroom photography, but instead of a negative for a picture, they use a mask or reticle to expose a geometric print onto a wafer using light. A mask that resembles the chip’s geometry is held above a pre-heated and photoresist-coated wafer. Extremely high intensity UV light is directed downward through the mask and onto the wafer. This causes a chemical change in the photoresist areas that are exposed to the light by the mask. Developer is then used to dissolve and wash away either the positive (most commonly) or negative areas of the photoresist. The next step is the etching process, in which a chemical agent removes the uppermost layer of the substrate in the areas that are not protected by the photoresist. Once the photoresist is no longer needed, it is chemically removed from the substrate.

Silicon dioxide is deposited onto all regions of the pre-heated wafer to coat any parts of the wafer that may have been altered in the cleaning process. Excess silicon dioxide that remains on top of the photoresist is removed and at this stage the first layer of the chip geometry is completed. This process is repeated to obtain different geometries in as many layers as necessary, in order to complete the chip’s circuit design. Lastly, a chemical agent removes all silicone dioxide from the wafer, leaving silicon as the only remaining element on the wafer.

Photolithography is developing at ever increasing resolutions, which allows for the application of ever smaller structures. This results in a higher density of transistors within an integrated circuit and, as such, higher capabilities of computer processing with smaller components.

It is evident that lithography plays a critical role in the continued advancement of Moore’s Law. Moore’s Law is an expectation that we innovate at a pace whereby we roughly double the number of transistors on a microchip every 2 years. As such, electronic devices are able to become smaller, more powerful and cheaper thus driving the demand for the overall industry.

There are different types of lithographic methods, depending on the radiation used for exposure:

• extreme ultraviolet lithography (as described above)
• electron beam lithography
• x-ray lithography
• ion beam lithography

Extreme ultraviolet (EUV) lithography is the main focus of this page as it makes use of the specialized mineral insulated heaters that Kamet can supply

What are the advantages and disadvantages of EUV lithography for semiconductor applications?

EUV Lithography allows for the production of ever smaller transistors thus allowing for a higher density of transistors within an integrated circuit. This follows the ongoing trend of increasingly higher computer processing capabilities with smaller components. A core dynamic that drives demand in the overall industry. At this point in time, EUV lithography is considered at the leading edge of circuit production and is said to hold the key to the future of microchip advancements.

For all the ground-breaking progress EUV lithography has brought to the industry, it does come with some disadvantages and/or limitations:

• Price: It is expensive, not only in operational costs but in the price of the machinery’s components.
• Complexity:It is a highly complex process and only one company is capable of producing these machines.
• Precision: absolute precision is essential and even small undetected defects on mirror surfaces can potentially result in the waste of millions of chips.
• Yields: the hourly yield of microchips is lower in EUV than in other methods, which makes it less suited to some high volume production applications

Which heating solutions does Kamet offer for Lithography for semiconductor applications?

There are multiple ways to heat up the processes for lithography, one of the most important and widely used is resistive heating. This is Kamet’s area of expertise, with a range of high quality mineral insulated heating elements well suited for lithography. A homogeneous temperature control over the entire area of the wafer is one of the main reasons for implementation.

At Kamet we have the know-how to design bespoke heating systems that meet the challenges of all the different stages in the Lithography processes. Any of our MI heaters (e.g. plate heaters, wafer heaters and heat tracing) can be customized to meet the specific conditions of the lithography process.

Vacuum soldering/brazing

One common way to integrate our heating elements in lithography processes (as well as deposition systems) is by vacuum soldering/brazing in panels. Vacuum soldering has several advantages:

• surface contaminants are removed from all the parts without any discoloration
• the entire product is heated with extreme precision
• uniform heating allows for good control over the whole process, which helps to limit undesirable distortions caused by localized heating
• It is possible to combine vacuum soldering with base material annealing or hardening processes.

Advantages of mineral insulated heating elements for lithography

• Our heaters can ensure temperatures of up to 1000°C
• Kamet’s range of specialized mineral insulation for the heating elements means they have:
  • Resistance to demanding atmospheres (vacuum, inert gasses)
  • Chemical resistance
  • Excellent dielectric endurance
• The customization of sheath materials guarantees mineral insulation that matches any environment
• Seamless transitions between the hot and cold sections of heaters
• Hot and cold sections have equal diameters
• Termination is simple due to cold ends which prevent overheating
• High power densities can be accommodated
• Uniformity of heat distribution to a source, wafer, target or substrate
• A large bending radius makes heating elements suited to intricate, curved applications
• Allows for highly accurate, precision heating for critical processes
• Thinner, low mass designs are possible
• Quick warming times
• Sealed heating elements prevent contamination
• Thermocouples can be included in the design