Gas Floating Disk Not Levitating? Susceptor Troubleshooting Guide

A gas floating disk that doesn't lift correctly may cause confusion and frustration, particularly in a process that relies on stable heating or exact weight balance. Many times the issue was not with the disk, but what is going on below the disk. Levitation can be affected by the surface of the Susceptor semiconductor , flow rate of the gas, and even slight changes in temperature. Some find that the disk is not floating or does float but wobbles or is too low. It's best to follow a checklist before jumping to the end that something's broken. In many cases subtle changes will make a significant difference to restoring smooth floating behavior.

Gas Flow Distribution Failure in Gas Floating Disk Systems

An uneven flow of gas across the susceptor surface is one common cause for a gas floating disk to fail to lift. If the gas is not distributed evenly, the disk will not have the same cushion needed for it to float. Can tilt or get stuck on one side or remain on the ground entirely. This typically indicates blockage, misalignment or wear in the gas delivery system. It may manifest in reality after regular intervals of use or maintenance. For instance, a technician could clean the chamber and replace parts, but if there is a small particle or a part not quite fitting inside a gas channel, the spreading of the flow will be altered. Even a slight change can cause areas of low pressure, thus making the disk lose its buoyancy. One easy test of starting a check is listening and feeling for uniformity of gas output from each line. If one side is weaker, it's a sure sign. Then check for dust, residues or buildup in the gas holes or gas channels. These minute deposits may gradually clog flow, but may not be immediately apparent. One other thing to look out for is the gas supply pressure stability. The disk may bounce up and down if the pressure varies during operation. This can be attributed to the regulator or aging supply lines. The surface itself may be a susceptor that is not capable of solving the flow behavior issue in some cases. Gas will not spread evenly on the surface if it has evenly coated or worn patches. Once a user reported that their system began to malfunction after a few months of stable operation, the problem was revealed to be uneven coating buildup towards the edge of the susceptor that caused gas flow in the system to be diverted.

Surface Roughness Impact of CVD SiC Coating on Levitation Stability

One important aspect that is often forgotten is the surface roughness of the CVD SiC coating on the susceptor. A rough surface or an uneven surface can even upset the floating stability of the disk in good gas system operation. The answer is quite simple-the gas film that carries the disk does require a smooth, even flow to distribute the load uniformly. If the surface is not smooth, but rather has very small peaks, pits or a texture to the coating, then the flow of gas will be disrupted before the cushion can be created. This translates to lack of stability in hovering flight. The disk may float, but it shakes slightly, drifts or can't maintain a steady height. Some operators call it breathing motion, in which the disk moves up and down but is not controlled. This sometimes causes people to think they may have a gas issue when in reality, there is an issue on the surface. An actual case study is from a line of long thermal cycles. Upon installation, the system functioned as expected, but after a couple of weeks the levitation was less stable. The SiC coating was inspected after the process, and a micro-roughness was observed as a result of uneven deposition of SiC in a part of the susceptor. This slight variation proved sufficient to cause non-uniform gas distribution. It's not always necessary to have cutting-edge equipment at the outset. But sometimes, the uneven surface gloss and texture differences can be seen with a simple visual inspection under angled light. Surface measurement tools can be used to verify roughness changes, which are not discernable by eye, in more sensitive cases.

Blockage, Leakage & Channel Design Issues in AMAT Centura5200

Another category of problems is related to blockage, gas leakage and internal channel design in systems such as AMAT Centura 5200. These subtle problems can subtly upset the gas cushion keeping the disk afloat even when everything else seems to be in perfect order. Typically, blockage begins gradually. It can be residual debris, flakes from coatings or even fine dust which gradually accumulates within the narrow gas paths. The system will initially continue to function, albeit weaker or with a little instability. The disk will float in some zones and not others, and/or may not float level over time. Once, a technician discovered that a blockage was partially present near one of the distribution ports and that one side of the disk was lower than the other. Once this section had been cleaned, the levitation was once again stable. Another issue that can go unnoticed is leakage. Reducing the amount of gas that escapes prior to it reaching the surface of the susceptor will reduce the pressure and the floating effect will also reduce. This is possible along the joints, seals or at some slightly worn fittings. Design is another major factor in channels. Gas channels in systems built by Applied Materials can be designed to evenly distribute flow, but wear, modification, or contamination can alter their flow characteristics. The channel path could be unbalanced, meaning that either an excess of gas is delivered to one area or a shortage to another. This is not even distribution, which directly impacts the stability of the levitation.

Diagnosing Wear and Damage: When to Consider AMAT Gas Float Disk Repair

Wear and damage on a gas float disk system typically are not all present at once, but rather develop over a period of time. The challenge is there are often very subtle clues that can be overlooked as minor performance fluctuations. However, as soon as the wear accumulates, simple adjustment or cleaning is not enough to recover levitation stability. One of the early indications is uneven floating levels. The disk could start up properly and slowly come back down while running. Another indication is vibration which did not exist before. When smooth operation was observed in the past, but no longer, it is usually a sign of surface wear or irregular contact between the susceptor components. There are also clues that can be found by physical inspection. The spread of the gas underneath the disk may be impacted by scratches, erosion of the coating, or color change on the surface of the susceptor. Damage, no matter how slight, can cause enough disruption of the gas cushion to lower the strength of the lift. Occasionally, edges of the disk will wear out more than the center, typically resulting in imbalanced pressure over time. This was evidenced from a real production line with an AMAT Centura 5200 system. After months of stable levitation, the tool began to lose its levitation. Initially, operators monitored gas flow and pressure, and things seemed to be ok. A follow-on inspection revealed that the surface of the susceptor was wearing away and affecting gas flow across the surface with the appearance of worn micro-grooves. Cleaning was no longer of much assistance and the only real repair was to make repairs to the surface area that was worn.

Interaction Between Susceptor Flatness and Gas Cushion Formation

If the surface of the susceptor is not smooth enough, the air layering created beneath the disk cannot be stable. Even small variations in the surface, such as flatness, will alter the gas propagation and pressure build-up. That pressure must be equal in all directions or the disk won't work. If there is a slight difference in height, then the gas will move quicker on one side and collect on the other, making things unbalanced. This is usually manifested in a slow tilt in real operation. The disk could still be floating but appears to be leaning to one side. In the steady state, some users observe the disk movement although the gas flow and pressure readings seem to be normal. The point where flatness works its magic is typically this one. A typical case is a system with long production cycles in which the susceptor had been subjected to multiple heating and cooling cycles. The surface shape has been altered over time by slight thermal deformation. Not obvious but the levitation began to become uneven. The center area was checked using a straightness gauge and was found to be slightly above the edges. A slight change in that was sufficient to dislodge the gas cushion. These problems with flatness also are complicated by coating layers. A thick or irregular CVD layer will cause the geometry of the surface to gradually change. The buildup of the coating can produce very slight slopes or waves, even if the base material is stable, which can impact gas behavior.