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Temperature Measured VS Actual 


Have you ever wondered how to properly measure temperature?  It is an elusive thing.  This article will try to explain temperature measurement as it relates to RTA processes.  It can be said that the actual temperature is not the same as the measured temperature.


What is Temperature?

Temperature is a measure of the average energy of motion, or kinetic energy, of particles in matter. When particles of matter, whether in solids, liquids, gases, or elementary plasmas, move faster or have greater mass, they have more kinetic energy, and the material appears warmer than a material with slower or less massive particles.  In the context of thermodynamics, kinetic energy is also referred to as thermal energy and the transfer of thermal energy is commonly referred to as heat. Heat always flows from regions of higher temperature to regions of lower temperature.  When matter is described as a collection of a large number of particles, it derives thermodynamic parameters as statistical averages of the microscopic parameters of the particles.


On the molecular level, temperature is the result of the motion of particles which make up a substance. Temperature increases as the energy of this motion increases.

Molecules, such as O2, have more degrees of freedom than single atoms: they can have rotational and vibrational motions as well as translational motion.  An increase in temperature will cause the average translational energy to increase.  It will also cause the energy associated with vibrational and rotational modes to increase.  Thus a diatomic gas, with extra degrees of freedom (rotation and vibration), will require a higher energy input to change the temperature by a certain amount, i.e. it will have a higher heat capacity than a monatomic gas.

The temperature of a system rises (kinetic energy increases) when it receives heat.  Similarly, a loss of heat from the system tends to decrease its temperature


When two systems are at the same temperature, no heat transfer occurs between them. When a temperature difference does exist, heat will tend to move from the higher-temperature system to the lower-temperature system, until they are at thermal equilibrium.


Temperature is the measure of the average kinetic energy of the molecules of a substance: the greater the kinetic energy the higher the temperature.


An increase in temperature is an increase of heat.  Also, an increase in temperature means the kinetic energy of the molecules is increasing.


Measuring the Temperature

Measuring the temperature of a substance changes its kinetic energy at the point of contact.  The point of contact transfers energy from the hotter material to the colder material.  This means heat is removed from the hotter material to increase the temperature of the colder material. 


If a thermocouple is positioned so it is touching a wafer, the thermocouple is exposed to the same heating source as the wafer.  Therefore, the thermocouple is also being heated.  Now, which one is hotter, the thermocouple or the wafer, or are they the same temperature? 


At the point of contact, the kinetic energy is the same.  The thermodynamics is at equilibrium at this point.  However, the point of contact is a very small area, usually a few thousands of an inch square.  The surrounding area is trying to become at equilibrium with the point of contact.  It is either removing energy from this point or transferring energy to this point.  Over a large area, the energy at this point is different by the induced heating or cooling of the thermocouple.


A thermocouple by its nature is constantly removing heat from a system.  It needs to generate electricity so external systems can measure the temperature.


Measuring the temperature also depends on the thermo conduction of the contact point.  A bare thermocouple touching a bare wafer is different than a thermocouple that is embedded into a wafer with a ceramic paste.  The embedded thermocouple does not touch the wafer directly.  There is a layer of ceramic between the thermocouple and the wafer material.  Also, the ceramic material is shielding the thermocouple from being directly heated by the heating source.


Therefore, measuring the temperature with a thermocouple is an approximate value.  There are many variables that affect the measuring of the temperature.  If multiple thermocouples are used at different places on the surface of the wafer, they will all measure different temperatures for the same amount of heating.


There are several other factors that have not been taken into account for the difference in temperature at different points, also known as the temperature uniformity of a wafer. 



Uniformity is the uneven temperature distribution within the surface of the wafer. 


The sheet resistivity measured on a wafer indirectly indicates the temperature uniformity.  It also tests the results of uniformity as an actual process.


ˇ¤         Maximum Non-uniformity:


?         ˇŔ5ˇăC across a 6" (150mm) wafer at 1150ˇăC. (This is a one sigma deviation 100 angstrom oxide.) For a titanium silicidation process, no more than 4% increase in non?uniformity during the first anneal at 650ˇăC to 700ˇăC.


?         Post-anneal sheet resistivity measured on a 150mm wafer annealed at 1100ˇăC for 10 seconds. R&D models optimized for slip control.


Check uniformity. Run a test wafer and measure the resistivity. Compare the values with those obtained on the wafer measured when the unit was first installed. 




With the implant conditions, ramp rate, steady step time and other parameters held fixed, the correct process temperature can be adjusted to give the desired resistivity.  To determine the correct temperature, several runs with slightly different temperatures will need to be done.  If the resistivity increases as the temperature decreases, then the correct temperature needs to be increased.  However, if the resistivity decreases as the temperature decreases, then the correct temperature needs to be decreased.

Temperature Control Check Procedure

This check verifies the proper operation of the AccuThermo temperature control system. It is accomplished by annealing implanted wafers and measuring the uniformity and sheet resistivity. The following test wafers will be needed:


ˇ¤         Wafer Specifications: Test, monitor or prime, p-type <100> 10 to 40ohm/sq. Wafers should be from a single batch with identical backside surface conditions.

ˇ¤         Implant Conditions: 5E15 arsenic cm-2 at 80 KeV with no screen oxide present.


Step 1.        Install one of the unannealed wafers on the tray inside the oven so that it rests squarely on the quartz pins.

Step 2.        Close and lock the heating chamber door.

Step 3.        Use the software to create a recipe with the same parameters as those shown on figure Optimize this recipe before testing.




Step #































 Recipe for Temperature Control


Step 4.        Run the recipe. After 60 seconds, the lamps should turn on and the temperature should start to rise within 5 seconds. The temperature should rise to 1100ˇăC, and then the lamps should turn off after 10 seconds.

Step 5.        Return to the Main Menu screen.

Step 6.        Wait until the temperature falls below 300ˇăC, and then open the oven door.

Step 7.        Allow the wafer to cool to room temperature.

Step 8.        Etch the wafer in a Buffered Oxide Etch (BOE) prior to resistivity mapping.

Step 9.        Use a 45-point probe to measure wafer sheet resistivity. The process specifications for Ion Implant Activation are listed below.


ˇ¤         Uniformity: Within one wafer, ˇÜ1% one sigma, as measured on a sheet resistivity mapping system using 45 or more measurement points. This assumes that the inherent implant uniformity (as measured after a furnace anneal at 1000ˇăC for 20 minutes) is <.4% one sigma.

ˇ¤         Repeatability: ˇÜ2% wafer-to-wafer repeatability.


Run the temperature tests on several wafers to verify the temperature accuracy. 


Uniformity Troubleshooting

There are several factors that can affect uniformity.


?      The heat absorption over the entire surface of the wafer may not be uniform.

?      The heat conduction throughout the wafer may not be uniform.

?      The quartzware may be dirty.

ˇ¤         Clean the quartzware according to the section ˇ°Quartzware Cleaningˇ±.

ˇ¤         Level the quartz tray.

?      There may be one or more bad lamps.

ˇ¤         Check the lamps according to the section ˇ°Identifying a Bad Lampˇ±.

ˇ¤         Visually check the condition of the lamps.  A yellow or white deposit inside the lamp envelope will reduce the amount of light energy escaping from the lamp to heat the wafer.  Changing the lamp may be required.

ˇ¤         Check if a triac is bad.  Refer to section ˇ°Intensity is Higher than Normalˇ± or ˇ°Lamps Flickerˇ±.

?      There could be insufficient air cooling.

ˇ¤         The CDA cooling flow rate could be insufficient.  Refer to the Installation chapter.

?      The process gas may have a problem.

ˇ¤         Low process gas flow ¨C The process gas source may be getting low.

ˇ¤         Process gas pressure may be too high ¨C If the process gas pressure is too high, the MFC may not be able to control it properly.

ˇ¤         Contaminated process gas.


If the uniformity is not acceptable, try moving the lamps around until the uniformity is desirable.


Consider using the PSum parameter in the recipe.  Use this parameter only if the same type of production wafers are being processed using the same recipe.  Refer to section ˇ°Process Control Alarmsˇ± for a discussion on how to use PSum.  Run several wafers with clean quartzware to determine the proper PSum values.



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