System and method to control radial delta temperature
View Patent ↗A system and method of minimizing stress related to the ramp rate of a variable by limiting the ramp rate as a function of the current value of the variable is provided. More specifically, the present invention provides a system and method of maintaining the radial delta temperature of a semiconductor substrate or other heated body below the crystal slip curve by dynamically controlling the temperature ramp rate during processing.
1. A method of changing the temperature of a body housed in a heating chamber of a temperature controlled furnace from a starting temperature to an ending temperature using a temperature control algorithm comprising the steps of:
providing temperature data from one or more temperature sensing devices in said heating chamber and a temperature set point as inputs to said temperature control algorithm which controls power delivery to one or more controllable heating elements in said furnace;
calculating a maximum allowable temperature ramp rate as a function of temperature comprising:
Δ
T
=
2
.4928
α
E
C
f
ɛ
1
n
f
t
ⅇ
(
U
nkT
)
(
1
)
where fε/ft is the strain rate, E is Young's modulus, α is the coefficient of thermal expansion of the body, C=4.5×10 4 N m −2 , n=2.9, k is Boltzmann's constant, and T is the absolute temperature of the edge of the body, and U is the activation energy for glide movement required for wafer slip;
accelerating said temperature set point from said starting temperature at a finite acceleration rate until said maximum allowable temperature ramp rate for the current temperature setpoint value is achieved; and
decelerating said temperature set point at a finite deceleration rate until said ending temperature is reached such that the temperature of said body reaches said ending set point temperature smoothly without substantially overshooting or oscillating about said ending temperature.
2. The method according to claim 1 wherein said controllable heating elements are selected from the group consisting of radiant heat lamps and heating coils.
3. The method according to claim 1 wherein said temperature sensing devices are one or more thermocouples providing one or more temperatures for each of said one or more controllable heating elements.
4. The method according to claim 3 wherein a control temperature which is a mathematical combination of said one or more thermocouple temperatures is an input to said temperature control algorithm.
5. The method according to claim 4 wherein said control temperature is further defined to have a known offset from said thermocouple temperatures.
6. The method according to claim 5 wherein said temperature offsets are static offsets that correct said control temperature for differences between the temperature of said body and said thermocouple temperatures.
7. The method according to claim 1 wherein said body is a semiconductor substrate.
8. A temperature controlled furnace for changing the temperature of a body comprising:
a heating chamber housing one or more controllable heating elements, and one or more temperature sensing devices; and
a temperature controller configured to carry out the method of claim 1 .