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Stress measurement and stress balance in films

Stress measurement and stress balance in films description/claims

The history of light-emitting diodes (“LEDs”) is sometimes characterized as a “crawl up the spectrum.” This is because the first commercial LEDs produced light in the infrared portion of the spectrum, followed by the development of red LEDs that used GaAsP on a GaAs substrate. This was, in turn, followed by the use of GaP LEDs with improved efficiency that permitted the production of both brighter red LEDs and orange LEDs. Refinements in the use of GaP then permitted the development of green LEDs, with dual GaP chips (one in red and one in green) permitting the generation of yellow light. Further improvements in efficiency in this portion of the spectrum were later enabled through the use of GaAlAsP and InGaAlP materials.

This evolution towards the production of LEDs that provide light at progressively shorter wavelengths has generally been desirable not only for its ability to provide broad spectral coverage but because diode production of short-wavelength light may improve the information storage capacity of optical devices like CD-ROMs. The production of LEDs in the blue, violet, and ultraviolet portions of the spectrum was largely enabled by the development of nitride-based LEDs, particularly through the use of GaN. While some modestly successful efforts had previously been made in the production of blue LEDs using SiC materials, such devices suffered from poor luminescence as a consequence of the fact that their electronic structure has an indirect bandgap.

While the feasibility of using GaN to create photoluminescence in the blue region of the spectrum has been known for decades, there were numerous barriers that impeded their practical fabrication. These included the lack of a suitable substrate on which to grow the GaN structures, generally high thermal requirements for growing GaN that resulted in various thermal-convection problems, and a variety of difficulties in efficient p-doping such materials. The use of sapphire as a substrate was not completely satisfactory because it provides approximately a 15% lattice mismatch with the GaN. Progress has subsequently been made in addressing many aspects of these barriers. For example, the use of a buffer layer of AlN or GaN formed from a metalorganic vapor has been helpful in accommodating the lattice mismatch. Further refinements in the production of Ga—N-based structures has included the use of AlGaN materials to form heterojunctions with GaN and particularly the use of InGaN, which causes the creation of defects that act as quantum wells to emit light efficiently at short wavelengths. Indium-rich regions have a smaller bandgap than surrounding material, and may be distributed throughout the material to provide efficient emission centers.

While some improvements have thus been made in the manufacture of such compound nitride semiconductor devices, it is widely recognized that a number of deficiencies yet exist in current manufacturing processes. Moreover, the high utility of devices that generate light at such wavelengths has caused the production of such devices to be an area of intense interest and activity. In view of these considerations, there is a general need in the art for improved methods and systems for fabricating compound nitride semiconductor devices.

Embodiments of the invention provide methods and systems for fabricating structures. Some embodiments of the invention are specifically directed at fabrication of compound nitride semiconductor structures, but other types of structures may be fabricated in different embodiments.

In a first set of embodiments, methods are provided of fabricating a compound nitride semiconductor structure. A substrate is disposed within a first processing chamber. A first group-III precursor and a first nitrogen precursor are flowed into the first processing chamber. The first group-III precursor comprises a first group-III element. A first layer is deposited over the substrate with a thermal chemical-vapor-deposition process within the first processing chamber using the first group-III precursor and the first nitrogen precursor. The first layer comprises nitrogen and the first group-III element. The substrate is transferred from the first processing chamber to a transfer chamber different from the first processing chamber. A temperature of the first layer is measured within the transfer chamber. A curvature of the first layer is also measured within the transfer chamber. The substrate is transferred to a second processing chamber different from the first processing chamber and different from the transfer chamber. A second layer is deposited over the first layer within the second processing chamber.

In some embodiments, the transfer chamber provides optical access between an interior of the transfer chamber and an exterior of the transfer chamber. In such embodiments, the curvature of the first layer may be measured by directing light to a surface of the first layer and receiving light reflected from the surface. The curvature is then determined from the reflected light. For instance, a plurality of light beams may be directed to the surface of the layer and light spots corresponding to reflections of the light beams from the surface may be received. The curvature is determined from positions of the received light spots.

In some instances, a plurality of temperature measurements of the first layer are obtained over a period of time while the substrate cools in the transfer chamber and plurality of curvature measurements of the first layer are obtained over the period of time. A relationship may then be derived between the measured curvature and the measured temperature over the period of time. This permits determination of a balanced-stress temperature of the first layer at which the first layer is substantially flat. Deposition of the second layer may be performed at substantially this balanced-stress temperature.

The second layer may be deposited by flowing a second group-III precursor and a second nitrogen precursor into the second processing chamber. The second group-III precursor comprises a second group-III element. A thermal chemical-vapor-deposition process is then used within the second processing chamber to deposit the second layer with the second group-III precursor and the second nitrogen precursor. In some cases, the second group-III precursor is not comprised by the first group-III precursor. Deposition of the second layer may be performed at a temperature within the second processing chamber where the first layer is substantially flat.

There are a number of different combinations of materials that may be used. For example, in one embodiment, the first group-III element is gallium, the second group-III element is aluminum, the first layer comprises a GaN layer, and the second layer comprises an AlGaN layer. In another embodiment, the first group-III element is gallium, the second group-III element is indium, the first layer comprises a GaN layer, and the second layer comprises an InGaN layer. In a further embodiment, the first group-III element is gallium, the second group-III element includes aluminum and indium, the first layer comprises a GaN layer, and the second layer comprises an AlInGaN layer.

In a second set of embodiments, a method is provided of fabricating a structure. A first layer is deposited over a substrate within a first processing chamber. The substrate is transferred from the first processing chamber to a transfer chamber different from the first processing chamber. A temperature of the first layer within the transfer chamber is measured, as is a curvature of the first layer. The substrate is transferred to a second processing chamber different from the first processing chamber and different from the transfer chamber. A second layer is deposited over the first layer within the second processing chamber at a temperature at which the first layer is substantially flat.

The transfer chamber may provide optical access between an interior of the transfer chamber and an exterior of the transfer chamber, permitting the curvature of the first layer to be measured by using light reflections as described above. In addition, temperature and curvature measurements may be made over a period of time while the substrate cools in the transfer chamber as described above, permitting derivation of a relationship between the measured curvature and the measured temperature over the period of time.

In a third set of embodiments, a cluster tool is provided. The cluster tool comprises a plurality of processing chambers, each of which includes a substrate holder. A gas-delivery system is configured to introduce gases into the plurality of processing chambers. A pressure-control system maintains selected pressures within the processing chambers. A temperature-control system maintains selected temperatures within the processing chambers. A transfer chamber is interfaced with each of the plurality of processing chambers. The transfer chamber provides optical access between an interior of the transfer chamber and an exterior of the transfer chamber. A robotic transfer system is adapted to transfer substrates between the transfer chamber and each of the plurality of processing chambers. A light source, a light detector, and an optical train are provided. The optical train directs light from the light source through the optical access to a surface of a substrate disposed within the transfer chamber and directs light reflected from the surface to the light detector.

A controller may additionally be provided in communication with the light detector. The controller comprises instructions to determine a curvature of the substrate from respective positions of a plurality of light spots reflected from the surface of the substrate and detected by the light detector.

A temperature monitor may also be disposed within the transfer chamber. In such instances, the controller may have instructions to obtain a plurality of temperature measurements of the substrate over a period of time while the substrate cools in the transfer chamber. A plurality of curvature measurements may similarly be obtained over the period of time. The controller may include instructions to derive a relationship between the curvature and temperature of the substrate over the period of time. Instructions comprised by the controller may determine the balanced-stress temperature at which the substrate is substantially flat from the determined relationship.

The controller may also be in communication with the temperature-control system and the robotic transfer system. In such cases, the controller may have instructions to maintain a temperature in one of the plurality of processing chambers substantially equal to the balanced-stress temperature and to transfer the substrate from the transfer chamber to the one of the processing chambers with the robotic transfer system.

A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings wherein like reference numerals are used throughout the several drawings to refer to similar components. In some instances, a sublabel is associated with a reference numeral and follows a hyphen to denote one of multiple similar components. When reference is made to a reference numeral without specification to an existing sublabel, it is intended to refer to all such multiple similar components.

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