Patent ID: 6864466

Claim:
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.