JPH0722129B2 - Wafer temperature control system in oxidation / diffusion device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a wafer temperature control system in an oxidation / diffusion apparatus, and is particularly generated when a wafer row is inserted into / drawn from an oxidation / diffusion apparatus in a heat treatment step of a semiconductor process. The present invention relates to a wafer temperature control system in an oxidation / diffusion apparatus suitable for reducing crystal defects due to variations in oxide film thickness and thermal stress.

[Background of the Invention]

2. Description of the Related Art Conventionally, in a heat treatment step of a semiconductor manufacturing process, an oxidation / diffusion process is performed by an oxidation / diffusion device. This oxidation / diffusion process puts a row of wafers on a boat and
The process is completed by inserting the wafer row into the reaction tube of the diffusion device, moving the inserted wafer row by the boat loader, and then withdrawing the wafer row. During the movement of the wafer row by the boat loader, the heat treatment is performed after the on / off control of the heater coil provided on the outer wall of the reaction tube.

In such an oxidation / diffusion process, the temperature change that occurs when the wafer row is inserted into or pulled out from the oxidation / diffusion device becomes non-uniform within the wafer, causing stress and causing crystal defects. When it becomes more significant, it eventually undergoes plastic deformation. Therefore, it is necessary to control the temperature of the wafer surface in order to reduce the temperature change. This temperature control is
Based on the empirical data obtained from the actual wafer manufacturing process, the speed pattern (wafer moving speed pattern) at the time of wafer row insertion / withdrawal and the heater coil on / off time determined by the reaction tube wall profile However, the velocity pattern at the time of wafer row insertion / withdrawal and the dynamic control of the reaction tube wall temperature profile were hardly performed. Furthermore, with the recent increase in the diameter of wafers (6 to 8 inches), it is expected that the temperature difference in the wafer surface that transiently occurs at the time of inserting and withdrawing the wafer row will become more remarkable. In addition, there is a problem that crystal defects are increased by thermal stress and the yield of semiconductor products is reduced.

[Object of the Invention]

An object of the present invention is to solve such a conventional problem and to eliminate an oxide film caused by a temperature difference in a wafer surface that transiently occurs at the time of inserting / drawing a wafer row in a heat treatment process by an oxidation / diffusion device in a semiconductor manufacturing process. It is an object of the present invention to provide a wafer temperature control system in an oxidation / diffusion device, which can reduce thickness variation and crystal defects due to thermal stress.

[Outline of Invention]

In order to achieve the above object, the wafer temperature control system in the oxidation / diffusion apparatus of the present invention comprehensively controls a semiconductor manufacturing process parameter such as a wafer diameter, a wafer interval, and a boat moving speed at the time of oxidation / diffusion of a wafer by a computer. In the wafer temperature control system that controls the wafer temperature in the oxidation / diffusion device, the wafer temperature data file fed back from the operating condition determination unit is used to calculate the in-plane thermal stress distribution and the oxide film thickness variation value using a computer. And the in-plane thermal stress distribution and the oxide film thickness variation value are extracted from the evaluation unit, and the condition values of the wafer diameter, the wafer interval, and the boat moving speed set therein are calculated. By substituting into the heat balance equation for the wafer, the boat, and the wall of the reaction tube, which mainly consist of the radiation in the reaction tube, the stain And the result determines the optimum combination of the tube wall temperature profile and the wafer movement speed pattern that achieves the wafer temperature transient characteristics that satisfy the upper limit of the maximum temperature difference in the wafer surface required in advance. A wafer temperature calculation result calculated by the simulation is stored in a wafer temperature data file and is fed back to the evaluation unit, and an operating condition determining unit, and a threshold value for boat movement, stop, and pipe wall temperature determined by the operating condition determining unit. The time-series data of the boat is set by the operating condition determining unit so that the boat moving speed pattern and the pipe wall temperature profile are provided to the oxidation / diffusion device based on the set data, and the controller Based on the wall temperature of the reaction tube and the moving speed pattern data, E Ha temperature, boats insertion and withdrawal speed is controlled, thereby being characterized by comprising an oxidation-diffusion apparatus for performing an oxidation-diffusion process the wafer column.

Example of Invention

An embodiment of the present invention will be described in detail below with reference to the drawings.

First, the principle of the present invention will be described.

The transient characteristics of the in-plane temperature distribution of the wafer, which transiently occurs at the time of inserting / drawing the wafer row into / from the oxidation / diffusion device, largely changes due to the difference in the reaction tube wall temperature profile and the wafer row moving speed. However, it is impossible at present to directly measure the wafer temperature in the reaction tube due to problems such as contamination of the silicon wafer surface. It is desirable to control the tube wall temperature profile and the wafer moving speed online with the wafer temperature measurement data. It was difficult to realize the wafer temperature transient characteristics. As a solution to this, in advance, an optimal combination of a tube wall temperature profile and a wafer moving speed pattern that realizes a wafer temperature transient characteristic that satisfies the required upper limit value of the in-wafer maximum temperature difference is calculated by using the reaction tube thermal phenomenon. Described physical model (wafer temperature control model)
Thus, the temperature of the wafer surface can be effectively controlled by simulating and determining the control history and reproducing the control history on an actual device.

FIG. 1 is an overall configuration diagram of an oxidation / diffusion system showing an embodiment of the present invention.

In FIG. 1, reference numeral 1 is an oxidation / diffusion device for performing oxidation / diffusion processing on a wafer row, 2 is an operating condition determination unit of the oxidation / diffusion device 1, and 3 is a model for calculating in-plane thermal stress of wafer and oxide film thickness variation calculation model. Evaluated part 4 is pipe wall temperature, boat insertion
PID (Proportional Integr) for setting the withdrawal speed
al and Derivative) controller.

In the oxidation / diffusion system having such a configuration, the operating condition determination unit 2 first extracts the stress distribution and the oxide film thickness variation value 31 from the thermal stress model and the oxide film thickness calculation model in the evaluation unit 3, and executes the simulation. Then, the operation conditions are determined, and the time series data 22 of the threshold temperature that gives the boat movement pattern and the pipe wall temperature profile is set in the PID controller 4. Next, the PID controller 4 controls the wafer temperature in the apparatus by the tube wall temperature and the moving speed pattern data 44 of the reaction tube of the oxidation / diffusion apparatus 1 and takes in the reaction tube wall temperature measurement data 11 to obtain a time series. Control can be performed.

FIG. 2 is an internal configuration diagram of the oxidation / diffusion device 1 of FIG.

In FIG. 2, 110 is a reaction tube, 120 is a boat loader used for inserting / drawing a wafer row, 130 is a wafer row to be heat-treated, 140 is a boat that carries the wafer row 130 and moves in the reaction tube 110, 150, 151, 152 Is a heater coil for heating the tube wall of the reaction tube 110, and 160, 161, 162 are representative points in the reaction tube 110 for measuring the tube wall temperature.

FIG. 3 is an internal configuration diagram of the operating condition determination unit 2 according to the present embodiment.

In FIG. 3, 210 is a simulation condition setting unit that determines the simulation conditions of the wafer temperature control model, 220 is a wafer temperature control model calculation unit that is a main part of the present invention, and 230 is a boat movement, stop, and pipe wall temperature. Wafer temperature control history file that stores time series data 221 of threshold value Tthu, 240 is a wafer temperature history file that stores the wafer temperature calculation result 222, and 250 is the oxide film thickness variation value 31 and the required oxide film thickness. This is a comparison unit that performs comparison with uniform accuracy.

FIG. 4 is a flowchart of internal functions of the wafer temperature control model calculation unit 220 shown in FIG.

Hereinafter, the wafer temperature control method according to this embodiment will be described with reference to FIGS. 1 to 4.

First, in the oxidation / diffusion apparatus 1 shown in FIG.
Optimal combination conditions of a three-zone tube wall temperature profile and a boat moving speed pattern for controlling the temperature distribution in the wafer surface that transiently occurs when inserting the wafer row 130 into the 110, in particular, the maximum temperature difference ΔTmax in the wafer surface. The operating condition determination unit 2
Determined by

Here, the operating condition determining method by the operating condition determining unit 2 will be described below (see FIG. 3). First, the simulation condition setting unit 210 sets the process parameters such as the wafer diameter, the wafer interval, the boat moving speed, and the required maximum temperature difference ΔTmaxth in the wafer surface. Next, the set data 211 is given to the wafer temperature control model calculation unit 220. In this control model calculation unit 220, as shown in FIG. 4, the maximum temperature difference ΔTmax in the wafer surface at each time step is updated by a physical model that gives a wafer temperature and a reaction tube wall temperature, which will be described later, and this value and ΔTmaxth The following control measures are determined by comparison with

(A) When ΔTmax ≧ ΔTmaxth In order to reduce the temperature difference, the movement of the boat (140) is stopped.

(B) When ΔTmax <ΔTmaxth (i) If the movement of the boat (140) is stopped, the movement of the boat (140) is restarted.

(Ii) If the boat (140) is moving, the threshold temperature on the pipe wall inlet side of the three-zone system is increased by ΔT to bring the pipe wall temperature profile close to the profile in the steady state.

The above processes (a) and (b) are repeated until the wafer movement is completed, and the boat movement, stop, and tube wall temperature threshold Tthu
The time series data 221 are sequentially stored in the wafer temperature control history file 230, and the wafer temperature calculation result 222 is stored in the wafer temperature history file 240. Based on this wafer temperature transient characteristic result, the evaluation unit 3 including the thermal stress model and the oxide film thickness calculation model shown in FIG. Thickness variation is calculated. This thermal stress distribution and the oxide film thickness variation value 31 are compared with the yield stress of the wafer and the oxide film thickness uniformity accuracy required in this processing step by the comparison unit 250, and if appropriate, the wafer temperature at this time. In order to reproduce the transient characteristics on an actual device, the boat movement pattern stored in the previous wafer temperature control history file 230 and the time series data 22 of the threshold value of the tube wall temperature are set in the PID controller 4. .

On the other hand, if the evaluation result of the comparison unit 250 is not valid,
The required maximum in-plane temperature difference ΔTmaxth is updated, and the simulation is performed again using the wafer temperature control model.

Regarding the thermal stress model and the oxide film thickness calculation model that form the evaluation unit 3, the planar stress state of a silicon wafer having a two-dimensional temperature distribution in the wafer plane is taken as a problem of the micro-deflection of the flat plate when there is a force in the wafer plane. A stress calculation model to be determined, a Deal-Grove oxide film thickness calculation formula, and the like may be used.

Now, regarding the physical model that gives the wafer temperature and the reaction tube wall temperature, which are the core of the wafer temperature control model calculation unit 220,
An example is shown below.

In the target oxidation / diffusion device, the wafers 130 arranged on the boat 140 made of silicon or quartz are
After being inserted into a reaction tube of a three-zone heating system heated to a high temperature of around 1000 ° C. and subjected to a predetermined heat treatment, the reaction tube 110
Be pulled out of. Therefore, the phenomenon is that the reaction tube 11
Ignoring the effect of the gas in 0, it can be described by the heat balance equation for the wafer, the boat, and the reaction tube wall, which mainly consist of radiation. It is assumed that the wafer thickness and boat thickness are sufficiently smaller than the size in the plane direction, that there is no temperature distribution in the thickness direction, and that the temperature distribution in the cylindrical reaction tube cross section is axially symmetric. Then, the following system of simultaneous partial differential equations can be derived.

Wafer; boat; Reaction tube; cfef ∂Tf (r, t) / ∂t = V ・ {Kf (Tf) ▽ Tf (, t)} + q (3) Boundary condition on reaction tube wall; Where T _WI (, t), Tb (, t), Tf (, t), Indicate the i-th wafer temperature, boat temperature, reaction tube temperature, and reaction tube wall surface temperature, respectively. Gnj
(, ′), Indicate the form factors for wafer to wafer, tube wall to wafer, boat to wafer, tube wall to boat, wafer to boat, wafer to tube wall, and tube wall to tube wall, respectively. Also,
l _W , lb is wafer, boat length, (C _W , Cb, Cf), (e _W , e
b, ef), (ε _W , εb, εf), (a _W , ab, af), (K _W , Kb, K
f) is the specific heat, density, emissivity, absorptivity, and thermal conductivity of the wafer, boat, and reaction tube, respectively. σ is the Stefan-Boltzmann constant, dS _W , dSb, dSf are wafers,
Area elements in boats and pipe walls, n in Σ represents the number of times of reflection of radiation, and ∇ represents a differential operator. Q in the second term on the right side of the equation (3) is the heating amount of the reaction tube.
Heater coils 150, 151, 15 are independent in the center and right
2 can be heated, and by comparing the set temperature (threshold temperature) Tthl, Tthc, Tthr of the representative points 160, 161, 162 of each part with the measured temperature, the heater current ON / OFF control can be performed independently for each part to achieve the desired reaction. The pipe wall temperature profile is realized. Therefore, also in the reaction tube temperature setting model given by the above equation (3), ON / OFF control of the heating amount q is performed by comparing the calculated reaction tube representative temperature with the threshold temperature.

A simulation analysis example based on the wafer temperature control model described above is performed when the tube wall temperature profile is kept constant and the wafer insertion speed is set to be low (method A), and the tube wall temperature profile is set to a low value so that the wafer row can be quickly moved. FIG. 5 shows the results of the wafer temperature transient characteristics when the temperature was raised to the tube wall temperature profile in the case of method A (method B) after the movement. Further, FIG. 6 shows the tube wall temperature profile in each system and the threshold temperatures Tthl, Tthc, Tthr in the left, center and right portions of the reaction tube in the three zone heating system, respectively.

As described above, in the present embodiment, variations in oxide film thickness,
Optimizing the pipe wall temperature profile and the boat movement pattern that can control the temperature difference in the wafer surface that transiently occurs when inserting / drawing the wafer row into / out of the oxidation / diffusion device, which causes crystal defects due to thermal stress Since the combination can be realized on an actual device, variations in oxide film thickness and crystal defects can be reduced.

〔The invention's effect〕

As described above, according to the present invention, in the heat treatment process by the semiconductor process oxidation / diffusion device, the variation in the oxide film thickness caused by the temperature difference in the wafer surface occurring at the time of wafer insertion / extraction and the crystal defect due to the thermal stress are caused. It is possible to reduce the yield, and it is possible to improve the yield of manufactured semiconductor elements.

[Brief description of drawings]

1 is an oxidation / diffusion system configuration diagram showing an embodiment of the present invention, FIG. 2 is an internal configuration diagram of the oxidation / diffusion device of FIG. 1,
FIG. 3 is an internal block diagram of the operating condition determination unit of FIG. 1, FIG. 4 is a flowchart of the internal function of the wafer temperature control model calculation unit of FIG. 3, and FIG. 5 is a wafer temperature transient characteristic result of this embodiment. FIG. 6 and FIG. 6 are views showing the reaction tube wall temperature profile according to this example. 1: Oxidation / diffusion device, 2: Operating condition determination part, 3: Thermal stress model, evaluation part composed of oxide film thickness calculation model, 4: PID
Controller, 11: Reaction tube temperature measurement data, 22: Boat movement pattern determined by wafer temperature control model, and time series data of threshold temperature that gives tube wall temperature profile, 21: Model calculation result of wafer temperature transient characteristics .

Claims (2)

[Claims] 1. A wafer temperature control for controlling a wafer temperature in an oxidation / diffusion apparatus by comprehensively controlling a semiconductor manufacturing process parameter such as a wafer diameter, a wafer interval, a boat moving speed, etc. at the time of oxidation / diffusion of a wafer by a computer. In the system, the wafer temperature data file fed back from the operating condition determination unit is used to calculate the in-plane thermal stress distribution and the oxide film thickness variation value by solving the equations in the computer, and The in-plane thermal stress distribution and the oxide film thickness variation value are extracted, and the wafer diameter, the wafer interval, and the condition value of the boat moving speed that are set internally are used for the wafer mainly composed of radiation in the reaction tube, the boat, and the reaction tube wall. A simulation is performed by substituting it into the heat balance equation, and the results show that the maximum wafer surface The optimum combination of the tube wall temperature profile and the wafer movement speed pattern that achieves the wafer temperature transient characteristics that satisfy the upper limit of the temperature difference is determined, and the wafer temperature calculation result calculated by the above simulation is stored in the wafer temperature data file. The operating condition determining unit that stores and feeds back to the evaluating unit, and the time series data of the threshold values of boat movement, stop, and pipe wall temperature determined by the operating condition determining unit are set by the operating condition determining unit. Thereby, based on the set data, a controller that gives a boat moving speed pattern and a tube wall temperature profile to the oxidation / diffusion device, and the controller, based on the tube wall temperature and moving speed pattern data of the reaction tube, The wafer temperature and the boat insertion / extraction speed are controlled, which allows the wafer Column oxidation and diffusion device wafer temperature control system characterized by comprising an oxidation-diffusion apparatus for performing an oxidation-diffusion process. 2. The wafer temperature control system in the oxidation / diffusion apparatus according to claim 1, wherein the operating condition determination unit sets an upper limit value of the wafer surface temperature.