METHOD OF CHARACTERIZING A CHAMBER BASED UPON CONCURRENT BEHAVIOR OF SELECTED PLASMA PARAMETERS AS A FUNCTION OF SOURCE POWER, BIAS POWER AND CHAMBER PRESSURE

• US 20070080137A1
• Filed: 12/11/2006
• Published: 04/12/2007
• Est. Priority Date: 05/16/2003
• Status: Active Grant

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Gold, Ezra, HOFFMAN, DANIEL
• Granted Patent: US 7,470,626 B2
• Time in Patent Office: Days
• US Class Current: 216/59
• CPC Class Codes: H01J 37/32174 Circuits specially adapted for controlling the RF discharge
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

Abstract

The invention involves a method of characterizing a plasma reactor chamber through the behavior of plasma parameters selected from a group comprising ion density, wafer voltage, etch rate, wafer current, as functions of chamber parameters of source power, bias power and chamber pressure. The method begins by performing two steps for each one of the selected chamber parameters. The first step consists of ramping the level of the one chamber parameter while sampling RF electrical parameters at an RF bias power input to said wafer support pedestal and computing from each sample of said RF electrical parameters the values of the plasma parameters. These values are stored with the corresponding levels of the one chamber parameter as corresponding chamber parameter data. The second step consists of deducing, from the corresponding chamber parameter data, a single variable function for each of the plural plasma parameters having said one chamber parameter as an independent variable. The method continues with constructing combinations of these functions that are three variable functions having each of the chamber parameters as a variable. Then, from each three-variable function, the method constructs a set of surfaces, each individual surface corresponding to a respective constant value of the corresponding plasma parameter and defining simultaneous values of all of the selected chamber parameters. These surfaces are stored in memory for later use in controlling the chamber during wafer processing.

Claims

1. A method of operating a plasma reactor chamber with respect to plasma parameters selected from a group comprising ion density, wafer voltage, etch rate, wafer current, by controlling chamber parameters of source power, bias power and chamber pressure, said method comprising:

characterizing the reactor chamber by performing the steps of;

a. for each one of said selected chamber parameters, ramping the level of the one chamber parameter while sampling RF electrical parameters at an RF bias power input to said wafer support pedestal and computing from each sample of said RF electrical parameters the values of the plasma parameters, and storing said values with the corresponding levels of said one chamber parameter as corresponding chamber parameter data;

b. for each one of said selected chamber parameters, deducing, from the corresponding chamber parameter data, a single variable function for each of said plural plasma parameters having said one chamber parameter as an independent variable;

c. constructing combinations of said functions and from said combinations, constructing surfaces defining simultaneous values of all of said selected chamber parameters, each respective surface corresponding to a respective constant value of one of said plural plasma parameters, and storing said surfaces.

2. The method of claim 1 further compprising:

controlling a plasma in the chamber during processing of a production wafer in the chamber in accordance with user-selected values of each of said plural plasma parameters by performing the following steps;

a. for each one of said selected plasma parameters, fetching a relevant surface of constant value corresponding to the user-selected value of said one plasma parameter, and determining an intersection of the relevant surfaces, said intersection corresponding to a target value of source power, bias power and chamber pressure; and

b. setting said source power, bias power and the pressure in said chamber, respectively, to the respective target value.

3. The method of claim 2 wherein the number of said selected plasma parameters is three.

4. The method of claim 3 wherein said selected plasma parameters are ion density, wafer voltage and etch rate.

5. The method of claim 1 wherein the step of constructing surfaces defining simultaneous values of all of said chamber parameters comprises the following step carried out for each one of said selected plasma parameters:

combining the single variable functions dependent upon respective single variables of source power, bias power and chamber pressure into a single composite function dependent upon the following three variables;

source power, bias power and chamber pressure.

6. The method of claim 5 wherein the step of constructing surfaces defining simultaneous values of all of said selected chamber parameters further comprises the following step carried out for each one of said selected plasma parameters:

setting the composite function equal to a succession of values of the respective plasma parameter.

7. The method of claim 6 wherein the step of constructing surfaces defining simultaneous values of all of said chamber parameters further comprises the following step carried out for each one of said selected plasma parameters:

for each one of said succession of values, solving for a surface defining a set of simultaneous values of source power, bias power and chamber pressure for which the respective plasma parameter has the one value.

8. The method of claim 1 wherein the step of sampling RF electrical parameters at an RF bias power input to said wafer support pedestal comprises:

sensing an input impedance, an input current and an input voltage to a transmission line coupled between a bias power impedance match circuit and an electrode within the wafer pedestal.

9. The method of claim 8 wherein the step of computing from each sample of said RF electrical parameters the values of plural plasma parameters is carried out separately for plasma parameters of ion density, wafer voltage and etch rate.

10. The method of claim 9 wherein the step of computing from each sample of said RF electrical parameters the values of plural plasma parameters comprises:

computing a junction admittance of a junction between said transmission line and the electrode within the wafer pedestal from said input impedance, input current and input voltage and from parameters of the transmission line.

11. The method of claim 10 wherein the step of computing from each sample of said RF electrical parameters the values of plural plasma parameters further comprises:

providing shunt electrical quantities of a shunt capacitance between the electrode and a ground plane;

providing load electrical quantities of a load capacitance between the electrode and a wafer on the pedestal.

12. The method of claim 11 wherein the step of computing from each sample of said RF electrical parameters the values of plural plasma parameters further comprises:

computing said etch rate, plasma ion density and wafer voltage from said junction admittance, said shunt electrical quantities, said load electrical quantities and a frequency of RF bias power applied to said electrode.

13. The method of claim 12 wherein said parameters of said transmission line comprise a length of said transmission line, a characteristic impedance of said transmission line and a complex loss factor of said transmission line.

14. The method of claim 13 wherein said said shunt electrical quantities are computed from the size of an electrode-to-ground gap length, an area of said wafer, an electrode-to-ground dielectric constant and an electrode-to-ground conductive loss component.

15. The method of claim 14 wherein said load electrical quantities are computed from an electrode-to-wafer gap length, an area of the wafer, an electrode-to-wafer dielectric constant and an electrode-to-wafer conductive loss component.

16. The method of claim 15 wherein the step of computing said etch rate, plasma ion density and wafer voltage comprises:

first computing said wafer voltage and an imaginary part of a plasma admittance comprising a plasma susceptance, and computing said ion density and etch rate from said wafer voltage and said plasma susceptance.

17. The method of claim 1, wherein the number of said selected plasma parameters is less than three, said method further comprising further comprising:

controlling a plasma in the chamber during processing of a production wafer in the chamber in accordance with user-selected values of each of said selected plasma parameters by performing the following steps;

a. for each one of said selected plasma parameters, fetching a relevant surface of constant value corresponding to the user-selected value of said one plasma parameter, and determining an intersection of the relevant surfaces which defines a line in a 3-dimensional space whose dimensions are source power, bias power and chamber pressure; and

b. varying said source power, bias power and the pressure in said chamber, respectively, along said line.

18. The method of claim 1 wherein the combination of said functions for wafer voltage, V_wafer, having the variables of source power P_source, bias power P_bias, and chamber pressure p, is:

V_wafer(P_source, P_bias, p)=
V₀(P_bias/P_b0)^a[(P_source/P_s0)K₁(p/p₀)<sup>−

1</sup>+(p/p₀)^b]^c

where V₀ is a reference voltage, P_b0 is a maximum bias power, P_s0 is a maximum source power, p₀ is a minimum chamber pressure and K₁ is a constant and a, b and c are real numbers.

19. The method of claim 18 further comprising:

determining V₀ by applying zero plasma source power and maximum plasma bias power and setting chamber pressure at the minimum p=p₀ and measuring the wafer voltage; and

determining K₁ by increasing the source power to the maximum value while measuring wafer voltage and adjusting K₁ until the expression yields the measured value for wafer voltage.

20. The method of claim 18 wherein other plasma parameters comprising ion density and etch rate are functions of (i) V_Wafer(P_source, P_bias, p) and (ii) plasma susceptance S, and

$\begin{array}{c}S\end{array}$

( P source , P bias , p ) = ⁢

S 0 ⁡

( P bias / P b ⁢

 

⁢

0 ) e ⁡

[ ( P source / P s ⁢

 

⁢

0 ) ⁢

( p / p 0 ) f ] ⁢

[ K 2 ⁡

( P bias / P b ⁢

 

⁢

0 ) g ⁢

( p / p 0 ) h + ( p / p 0 ) i ]

where S₀ is a reference susceptance and K₂ is a constant and e, f, g, h and i are real numbers.

21. The method of claim 20 further comprising:

determining S₀ by applying maximum bias power and zero source power while holding the chamber at minimum pressure and measuring susceptance;

determining K₂ by increasing source power to the maximum value, measuring susceptance and changing K₂ until the expression yields the measured value of susceptance.

22. The method of claim 21 wherein plasma ion density η

is a function of susceptance and wafer voltage as follows;

η

=S²V_wafer².

23. The method of claim 22 wherein etch rate ER is a function of susceptance and wafer voltage as follows:

ER=kS²V_wafer^3/2.