Method and control system for depositing a layer
A method and control system are provided for depositing a layer in a sputter-deposition system having a target cathode. A first dependence relationship of a deposition rate of the layer on an operating parameter, selected from cathode voltage, cathode current, and cathode power, is provided prior to deposition of the layer. A second dependence relationship of the operating parameter on time is measured during deposition of the layer, while a different operating parameter, also selected from cathode voltage, cathode current, and cathode power, is held substantially constant. On the basis of the first and second dependence relationships, a deposition time for the layer is dynamically determined during deposition of the layer.
1. A method for depositing a layer to a deposition thickness substantially equal to a reference deposition thickness d r in a sputter-deposition system having a target cathode connected to a power supply, comprising ordered steps of:
a) providing to a controller a first parameter A, a second parameter B, and a third parameter C, selected from a group of operating parameters of the target cathode consisting of cathode voltage, cathode current, and cathode power, such that the first parameter A, the second parameter B, and the third parameter C are different operating parameters of the target cathode, by means of an interface;
b) providing to the controller a reference value of the second parameter B r , and a first dependence relationship r(A,C) of a deposition rate r of the layer on the first parameter A and the third parameter C of the form r(A,C)=kA x C y , wherein k is a reference constant, x is a first dependence exponent, and y is a second dependence exponent, wherein the reference constant k is not equal to 0, and wherein the first dependence exponent x is not equal to 0, by means of the interface;
c) controlling the power supply to start deposition of the layer, by means of the controller;
d) controlling the power supply to hold the second parameter B substantially constant at the reference value of the second parameter B r during deposition of the layer, by means of the controller, while allowing the first parameter A and the third parameter C to drift over time t, so that the deposition rate r is also allowed to drift over time t;
e) monitoring the power supply to continually measure a second dependence relationship A(t) of the first parameter A on time t during deposition of the layer, by means of the controller;
f) continually determining whether a deposition time t d for the layer, at which the layer has a deposition thickness substantially equal to the reference deposition thickness d r , has been reached by performing an integration over time t of the first dependence relationship r(A,C) using the second dependence relationship A(t) as the second dependence relationship A(t) is measured during deposition of the layer, by means of the controller; and
g) controlling the power supply to stop deposition of the layer once the deposition time t d has been reached, by means of the controller.
2. The method of claim 1 wherein the reference constant k, the first dependence exponent x, and the second dependence exponent y correspond to values determined from one or more previous depositions of layers carried out while holding the second parameter B substantially constant at the reference value of the second parameter B r .
3. The method of claim 1 wherein the second dependence exponent y is equal to 0; wherein the reference constant k is of the form
k
=
r
r
A
r
x
,
wherein r r is a reference deposition rate, A r is a corresponding reference value of the first parameter, and x is the first dependence exponent; and wherein the reference deposition rate r r and the reference value of the first parameter A r correspond to an average deposition rate r a and an average value of the first parameter A a , respectively, measured for one or more previous depositions of layers carried out while holding the second parameter B substantially constant at the reference value of the second parameter B r .
4. The method of claim 1 wherein the second dependence exponent y is equal to 0; and wherein the reference constant k is of the form
k
=
r
r
A
r
x
,
wherein r r is a reference deposition rate, A r is a corresponding reference value of the first parameter, and x is the first dependence exponent; further including a step of determining the reference value of the first parameter A r and the reference value of the second parameter B r by updating reference values of the first and second parameters of one or more previous depositions of layers to correct for a difference Δr between the reference deposition rate r r and an average deposition rate r a measured for the one or more previous depositions of the form Δr=r r −r a , prior to step (b).
5. The method of claim 1 wherein the second dependence exponent y is equal to 0, and wherein step (f) includes continually calculating an integral over time t of the second dependence relationship A(t) to a power of the first dependence exponent x of the form
∫
0
t
d
A
(
t
)
x
ⅆ
t
.
6. The method of claim 5 wherein in step (f) the integral
∫
0
t
d
A
(
t
)
x
ⅆ
t
is calculated by performing a summation over time t of the second dependence relationship A(t) to a power of the first dependence exponent x of the form
∑
0
t
d
A
(
t
)
x
Δ
t
.
7. The method of claim 1 wherein the second dependence exponent y is equal to 0; wherein the reference constant k is of the form
k
=
r
r
A
r
x
,
wherein r r is a reference deposition rate, A r , is a corresponding reference value of the first parameter, and x is the first dependence exponent; and wherein step (f) includes calculating a reference deposition time t r for the layer on the basis of the reference deposition rate r r , and the reference deposition thickness d r , continually calculating an integral over time t of the second dependence relationship A(t) to a power of the first dependence exponent x of the form
∫
0
t
d
A
(
t
)
x
ⅆ
t
,
continually comparing the integral
∫
0
t
d
A
(
t
)
x
ⅆ
t
to a product of the reference deposition time t r and the reference value of the first parameter A r to a power of the first dependence exponent x of the form A r x t r , and determining that the deposition time t d has been reached if the integral
∫
0
t
d
A
(
t
)
x
ⅆ
t
has a value greater than or equal to that of the product A r x t r .
8. The method of claim 1 wherein the second dependence exponent y is equal to 0; wherein the reference constant k is of the form
k
=
r
r
A
r
x
,
wherein r r is a reference deposition rate, A r is a corresponding reference value of the first parameter, and x is the first dependence exponent; and wherein step (f) includes calculating a reference deposition time t r for the layer on the basis of the reference deposition rate r r , and the reference deposition thickness d r , continually comparing the second dependence relationship A(t) to the reference value of the first parameter A r , and continually adjusting the deposition time t d from the reference deposition time t r accordingly.
9. The method of claim 1 wherein the second dependence exponent y is not equal to 0; wherein step (e) further includes monitoring the power supply to continually measure a third dependence relationship C(t) of the third parameter C on time t during deposition of the layer, by means of the controller; and wherein in step (f) the integration over time of the first dependence relationship r(A,C) is performed using the third dependence relationship C(t), as well as the first dependence relationship A(t), as the first dependence relationship A(t) and the third dependence relationship C(t) are measured during deposition of the layer.
10. The method of claim 9 wherein the reference constant k is of the form
k
=
r
r
A
r
x
,
wherein r r is a reference deposition rate, A r is a corresponding reference value of the first parameter, C r is a corresponding reference value of the third parameter, x is the first dependence exponent, and y is the second dependence exponent; and wherein the reference deposition rate r r the reference value of the first parameter A r and the reference value of the third parameter C r correspond to an average deposition rate r a , an average value of the first parameter A a , and an average value of the third parameter C a , respectively, measured for one or more previous depositions of layers carried out while holding the second parameter B substantially constant at the reference value of the second parameter B r .
11. The method of claim 9 wherein step (f) includes continually calculating an integral over time t of the second dependence relationship A(t) to a power of the first dependence exponent x and the third dependence relationship C(t) to a power of the second dependence exponent y of the form
∫
0
t
d
A
(
t
)
x
C
(
t
)
y
ⅆ
t
.
12. The method of claim 9 wherein the reference constant k is of the form
k
=
r
r
A
r
x
,
wherein r r is a reference deposition rate, A r is a corresponding reference value of the first parameter, C r is a corresponding reference value of the third parameter, x is the first dependence exponent, and y is the second dependence exponent; and wherein step (f) includes calculating a reference deposition time t r for the layer on the basis of the reference deposition rate r r and the reference deposition thickness d r , continually calculating an integral over time t of the second dependence relationship A(t) to a power of the first dependence exponent x and the third dependence relationship C(t) to a power of the second dependence exponent y of the form
∫
0
t
d
A
(
t
)
x
C
(
t
)
y
ⅆ
t
,
continually comparing the integral
∫
0
t
d
A
(
t
)
x
C
(
t
)
y
ⅆ
t
to a product of the reference deposition time t r , the reference value of the first parameter A r to a power of the first dependence exponent x, and the reference value of the third parameter C r to a power of the second dependence exponent y of the form A r x C r y t r , and determining that the deposition time t d has been reached if the integral
∫
0
t
d
A
(
t
)
x
C
(
t
)
y
ⅆ
t
has a value greater than or equal to that of the product A r x C r y t r .