Closed-loop control of composition and temperature during the growth of InGaAs lattice matched to InP

Abstract

Articles you may be interested in͑Received 5 October 1998; accepted 27 November 1998͒ Spectroscopic ellipsometry ͑SE͒ and diffuse reflection spectroscopy ͑DRS͒ are used to control the Ga mole fraction and substrate temperature, respectively, during the growth of InGaAs lattice matched to InP. Ga mole fraction is controlled to within Ϯ0.002 of its target value and substrate temperature is controlled to within Ϯ2°C of its target value. The same growth under constant thermocouple control would result in a 50°C rise in real substrate temperature and a Ga composition 1% above its target value. In both cases, feedback control is achieved using a nested proportional-integral-derivative ͑PID͒ control loop, where, the inner loop consists of the conventional Eurotherm-thermocouple feedback loop and the outer loop updates the thermocouple setpoint using a PID control loop implemented in the control software. For composition control, the Ga cell thermocouple setpoint is increased ͑decreased͒ 0.2°C for every 0.002 that the Ga mole fraction, given by the SE sensor, deviates below ͑above͒ the target value. During substrate temperature control, the thermocouple setpoint is updated based on the temperature difference between the DRS sensor and the user setpoint. Frequency loop shaping, based on a dynamical model of the system obtained from an identification experiment, is used to tune the outer PID loop.

Optical Diagnostics for Thin Film Processing

“…Diffuse reflectance spectroscopy (DRS) measures the temperature-dependent change in near-bandgap light transmitted through a wafer, diffusely reflected by the wafer backside and transmitted through the top of the wafer, and has been used to measure and control temperature as precisely as ±0.5 • C during the growth of several ternary III-V semiconductors (77,234,262,263). An algorithm has been developed that corrects for the distortions in the band-edge profile from interference and/or absorption in the growing epilayer (264).…”

Real-time composition control of InAlAs grown on InP using spectroscopic ellipsometry

“…We chose to begin feedback control of the Al cell temperature after 8 min of growth using a PID approach. 20 The full squares of Fig. 4 again show the composition value controlled under feedback control by GMan against the subsequent ex situ composition measured by HRXRD.…”

“…[6][7][8][9][10][11][12][13][14][15] Following the work of Aspnes, 16,17 great effort has been devoted to the use of spectroscopic ellipsometry ͑SE͒ for in situ monitoring and real-time control of growth. It has been used with success to control, in a feedback loop, the thickness 18 and alloy composition [19][20][21] of the growing films. Moreover, in conjunction with other sensors, it has been proven to yield improved reproducibility in the growths of devices.…”

“…For the composition control of ternary compounds, such as AlGaAs, InGaAs or InAlAs, one of the group III effusion cells is kept at constant temperature during the entire growth, while the difference between the target and measured compositions is used to change the temperature of the other cell. 7,20 Hence, the accuracy of the control depends on the accuracy of the database of optical constants against which the growing film is compared. Since SE is surface sensitive, it has been found that the optical constants of a growing layer, which we call the ''dynamic'' OC, actually differ from those of an ''identical'' layer just sitting at the growth temperature ͑under group-V overpressure͒ and which we refer to as ''static'' OC.…”