High-power pulsed magnetron sputtering process as well as a high-power electrical energy source

Abstract

A high-power pulsed magnetron sputtering process, wherein within a process chamber by means of an electrical energy source a sequence of complex discharge pulses is produced by applying an electrical voltage between an anode and a cathode in order to ionize a sputtering gas. The complex discharge pulse is applied for a complex pulse time. The cathode has a target comprising a material to be sputtered for the coating of a substrate, and the complex discharge pulse includes an electrical high-power sputtering pulse having a negative polarity with respect to the anode and being applied for a first pulse-time, the high-power sputtering pulse being followed by an electrical low-power charge cleaning pulse having a positive polarity with respect to the anode and being applied for a second pulse-time. The ratio .sub.1/.sub.2 of the first pulse-time (.sub.1) in proportion to the second pulse-time (.sub.2) is 0.5 at the most.

Claims

1. A high-power pulsed magnetron sputtering process, wherein: producing within a process chamber via an electrical energy source, a sequence of complex discharge pulses to apply an electrical voltage (V) between an anode and a cathode in order to ionize a sputtering gas; and coating a substrate with a ceramic material, wherein each complex discharge pulse is applied for a complex pulse time () and the cathode being a target comprising a material to be sputtered for the coating of the substrate; wherein the complex discharge pulse comprises an electrical high-power sputtering pulse having a negative polarity with respect to the anode that is applied for a first pulse-time (.sub.1) followed by an electrical low-power charge cleaning pulse having a positive polarity with respect to the anode that is applied throughout an entire second pulse-time (.sub.2), wherein a voltage of the high-power sputtering pulse is between 400V and 2000V, wherein a peak power density of the high-power sputtering pulse is between 1 and 20 KW/cm.sup.2, wherein a ratio .sub.1/.sub.2 of the first pulse-time (.sub.1) in proportion to the second pulse-time (.sub.2) is 0.5 at the most, and wherein subsequent to the low-power charge cleaning pulse and before another high-power sputtering pulse is applied, the process further comprises at least one of switching off and setting to zero the voltage (V) applied between the anode and the cathode for a third pulse-time (.sub.3), said third pulse-time (.sub.3) being less than the second pulse-time (.sub.2), and wherein at least one of: a peak current density of the high-power sputtering pulse is between 0.05 A/cm.sup.2 and 5 A/cm.sup.2, and a peak power of the high-power sputtering pulse is between 0.1 MW and 3 MW.

2. A process in accordance with claim 1, wherein the ratio .sub.1/.sub.2 of the first pulse-time (.sub.1) in proportion to the second pulse-time (.sub.2) is between 0.005 and 0.5.

3. A process in accordance with claim 1, wherein at least one of the high-power sputtering pulse and the low-power charge cleaning pulse is at least one of a low frequency AC-voltage, a rectified low frequency AC-voltage, and a DC-voltage pulse.

4. A process in accordance with claim 3, wherein the frequency of the at least one of the high-power sputtering pulse and the low-power charge cleaning pulse is between 0 Hz and 10 kHz.

5. A process in accordance with claim 1, wherein at least one of: the voltage of the high-power sputtering pulse is between 600V and 2000V, and a voltage of the low-power charge cleaning pulse is between 0V and 500V.

6. A process in accordance with claim 1, wherein the first pulse-time (.sub.1) of the high-power sputtering pulse is between 1 s and 5000 s.

7. A process in accordance with claim 1, wherein at least one of: the second pulse-time (.sub.2) of the low-power charge cleaning pulse is longer than 25 s, and the complex pulse time () is between 50 s and 1000 ms.

8. A process in accordance with claim 1, wherein an ionization degree of the sputtering gas is between 3% and 100%.

9. A process in accordance with claim 1, wherein at least one of: the sputtering method for coating the substrate is a reactive sputtering method or a non-reactive sputtering process.

10. High-power electrical energy source for producing a complex discharge pulse for carrying out a process in accordance with claim 1.

11. A process in accordance with claim 9, wherein the ceramic material comprises at least one of a nitride, an oxide and a carbide.

12. A high-power pulsed magnetron sputtering process, said process comprising: producing within a process chamber via an electrical energy source, a sequence of complex discharge pulses to apply an electrical voltage (V) between an anode and a cathode in order to ionize a sputtering gas, said cathode comprising an oxide target material that is sputtered onto a substrate: applying each complex discharge pulse for a complex pulse time (), said complex discharge pulse comprising an electrical high-power sputtering pulse having a negative polarity with respect to the anode that is applied for a first pulse-time (.sub.1) followed by an electrical low-power charge cleaning pulse having a positive polarity with respect to the anode that is applied for a second pulse-time (.sub.2) that is longer than the first pulse time (.sub.1); subsequent to the electrical low-power charge cleaning pulse and before another electrical high-power sputtering pulse is applied, switching off and/or setting to zero the electrical voltage (V) applied between the anode and the cathode for a third pulse-time (.sub.3), said third pulse-time (.sub.3) being less than the second pulse-time (.sub.2): utilizing a voltage of the high-power sputtering pulse of between 600V and 2000V; and utilizing a peak power density of the high-power sputtering pulse of between 1 and 20 KW/cm.sup.2, wherein a ratio .sub.1/.sub.2 of the first pulse time (.sub.1) in proportion to the second pulse-time (.sub.2) is 0.5 at most, and wherein at least one of: a peak current density of the high-power sputtering pulse is between 0.05 A/cm.sup.2 and 5 A/cm, and a peak power of the high-power sputtering pulse is between 0.1 MW and 3 MW.

13. A high-power pulsed magnetron sputtering process, said process comprising: producing within a process chamber via an electrical energy source, a sequence of complex discharge pulses to apply an electrical voltage (V) between an anode and a cathode in order to ionize a sputtering gas, wherein said cathode is a target comprising a material to be sputtered for coating on a substrate; applying each complex discharge pulse for a complex pulse time (), said complex discharge pulse comprising an electrical high-power sputtering pulse having a negative polarity with respect to the anode that is applied for a first pulse-time (.sub.1) followed by an electrical low-power charge cleaning pulse having a positive polarity with respect to the anode that is applied for a second pulse-time (.sub.2); subsequent to the electrical low-power charge cleaning pulse and before another electrical high-power sputtering pulse is applied, switching off and/or setting to zero the electrical voltage (V) applied between the anode and the cathode for a third pulse-time (.sub.3), said third pulse-time (.sub.3) being greater than the first pulse-time (.sub.1) and less than the second pulse-time (.sub.2); utilizing a peak voltage of the high-power sputtering pulse of between 800V and 2000V; utilizing a peak power density of the high-power sputtering pulse of between 1 and 20 KW/cm.sup.2; and the coating on the substrate being a ceramic material, wherein a ratio .sub.1/.sub.2 of the first pulse-time (.sub.1) in proportion to the second pulse-time (.sub.2) is 0.5 at most, and wherein at least one of: a peak current density of the high-power sputtering pulse is between 0.05 A/cm.sup.2 and 5 A/cm.sup.2, and a peak power of the high-power sputtering pulse is between 0.1 MW and 3 MW.

14. A process in accordance with claim 13, wherein during the third pulse-time (.sub.3) time is provided in order to relax into a starting state.

15. A process in accordance with claim 1, wherein during the third pulse-time (.sub.3) time is provided in order to relax into a starting state.

16. A process in accordance with claim 12, wherein the third pulse-time (.sub.3) is less than the second pulse-time (.sub.2).

Description

(1) In the following, the invention will be explained in more detail with reference to the drawings. Shown are:

(2) FIG. 1a: a known unipolar high-power magnetron sputtering sequence;

(3) FIG. 1b: a high-power pulse according to FIG. 1a;

(4) FIG. 2a: time dependence of the voltage for a pulse sequence according to FIG. 1a;

(5) FIG. 2b: a known bipolar high-power magnetron sputtering sequence;

(6) FIG. 2c: a known superimposed high-power magnetron sputtering sequence;

(7) FIG. 2d: another superimposed high-power magnetron sputtering sequence;

(8) FIG. 3: a sputtering target having accumulated positive ions:

(9) FIG. 4: a process chamber for carrying out the invention;

(10) FIG. 5: a complex high-power discharge pulse according to the invention;

(11) FIG. 6: a second embodiment of a complex high-power pulse according to FIG. 5;

(12) FIG. 7: a third embodiment of a complex high-power pulse according to FIG. 5;

(13) FIG. 8: an embodiment combining the complex high-power pulses of FIG. 6 and FIG. 7.

(14) FIG. 1 to FIG. 3 which are related to pulse sequences or problems known from the state of the art, have already been discussed in great detail and thus, the discussion is continued with FIG. 4 and FIG. 5 showing both a process chamber for carrying out the present invention and schematically a high-power pulse according to the invention.

(15) By FIG. 4 a process chamber 2 for carrying out the invention is displayed which process chamber 2 is, apart from the electrical energy source 3, in principle well known from the state of the art. A similar process chamber is for example disclosed in WO 2006/049566 A1.

(16) A sputtering chamber 21 is formed in the interior of the process chamber 2 having walls 5 made of e.g. stainless steel plate, the walls of the housing thus being electrically conducting and acting as the anode 5. The housing has for example the shape of a circular cylinder. The target 8 is located in parallel to the flat end walls of the cylinder and is carried by a support 81 made of electrically conducting material. The target 8 is a circular plate of material, which is to be applied to a substrate in order to establish a coating in form of a film.

(17) At the rear end of the target 8, at a surface which is not directed towards the center of the chamber 2, a magnet assembly 800 is mounted so that the north pole or poles are arranged at the periphery of the target and the south pole or poles at the center of the support 81 and the target 8. Thus, the magnetic fiel lines 801 of the magnets 800 pass from the periphery of the support 81 to the center thereof. The magnetic field is most intense at the poles of magnets 800. It is understood that also other known configurations can also be advantageously used.

(18) The electric system of the sputtering device includes electrodes between which a voltage from the power supply 3 is applied for ionizing the sputtering gas 7 in the process chamber 2. In the illustrated embodiment, the anode 5 is formed by the electrically conducting walls 5 of the chamber 2, which e.g. can be grounded. Of course, alternatively e.g. a separate anode, not shown in FIG. 4, can be used. The cathode 6 is formed by the target 8 and is negatively biased in relation to the anode 5. The substrate 9 can have some suitable electrical potential.

(19) According to the invention, a high-power electrical energy source 3 is provided to establish a complex discharge pulse 4 as for example described in detail by FIG. 5 showing a very simple complex discharge pulse 4 according to the present invention.

(20) The special embodiment of a complex discharge pulse 4 according to the present invention displayed by FIG. 5, is produced by means of the electrical energy source 3 providing a sequence of complex discharge pulses 4 by applying an electrical voltage V between the anode 5 and the cathode 6 in order to ionize the sputtering gas 7 as shown in FIG. 4. The complex discharge pulse 4 is applied for a complex pulse time . The complex discharge pulse 4 includes an electrical high-power sputtering pulse 10 having a negative polarity with respect to the anode 5 and being applied for a first pulse-time .sub.1. The high-power sputtering pulse 10 und/or the low-power charge cleaning pulse 11 is preferably a DC-voltage pulse as in principle well known from the state of the art.

(21) The high-power sputtering pulse 10 is then followed by an electrical low-power charge cleaning pulse 11 having a positive polarity with respect to the anode 5 and being applied for a second pulse-time .sub.2. According to the invention, a ratio .sub.1/.sub.2 of the first pulse-time (.sub.1) in proportion to the second pulse-time (.sub.2) is 0.5 at the most. In the present example of FIG. 5 the ratio .sub.1/.sub.2 of the first pulse-time (.sub.1) in proportion to the second pulse-time (.sub.2) is about 0.17.

(22) Choosing a relatively low ratio .sub.1/.sub.2 which is much smaller than one, that is .sub.1/.sub.2<1 as e.g. schematically shown by FIG. 5, and at the same time applying a very low voltage of for example 1V-10V during the charge cleaning pulse time .sub.2, the target 8 is reliably cleaned from positive electrical charges, wherein at the same time a noticeable collecting of electrons is avoided so that in turn, a heating of the target 8 is also essentially avoided.

(23) Since the negative high-power pulse 10 is applied only for a comparatively short interval of time having a high voltage of about 600V up to 1000V or more than 1000V, the corresponding current 1000, which is for reasons of simplicity only shown for the first high-power sputtering pulse 10 by the dashed line 1000, does not show a smooth characteristic but has a sharp peak structure and is timely sharp correlated with the sharp and very short pulse 10 of the applied negative voltage. As a result, the applied electrical power is sharply concentrated and strong timely connected with the applied short voltage pulse 10 so that the entire electrical energy is applied in a very short interval of time leading to a very high ionization of the plasma.

(24) By FIG. 6 a second embodiment of a complex high-power pulse 4 according to the present invention is displayed which complex high-power pulse 4 is very important in practice. The complex high-power pulse 4 according to FIG. 6 is produced by means of the electrical energy source 3 providing a sequence of complex discharge pulses 4 by applying an electrical voltage V between the anode 5 and the cathode 6 in order to ionize the sputtering gas 7 as shown in FIG. 4. The complex discharge pulse 4 is applied for a complex pulse time . The complex discharge pulse 4 includes an electrical high-power sputtering pulse 10 having a negative polarity with respect to the anode 5 and being applied for a first pulse-time .sub.1. The high-power sputtering pulse 10 und/or the low-power charge cleaning pulse 11 according to FIG. 6 is a low frequency AC-voltage, in particular a rectified low frequency AC-voltage. Regarding the special embodiment of FIG. 6 the frequency of the high-power sputtering pulse 10 und/or of the low-power charge cleaning pulse 11 is about 1 kHz. The 1 kHz AC-pulse is also schematically displayed by FIG. 6. It is understood that the complex discharge pulse 4 can also be advantageously produced by using DC-voltage pulses 10, 11.

(25) The high-power sputtering pulse 10 according to FIG. 6 is then followed by an electrical low-power charge cleaning pulse 11 having a positive polarity with respect to the anode 5 and being applied for a second pulse-time .sub.2. According to the special embodiment of FIG. 6, subsequent to the low-power charge cleaning pulse 11 and before another high-power sputtering pulse 10 is applied, the voltage V between the anode 5 and the cathode 6 is switched off and/or is set to zero for a third pulse-time .sub.3.

(26) In addition to the advantages already described above, using the pulse sequence 4 according to FIG. 6, the electrical energy source 3 can be easily and properly switched from the positive voltage V for producing the low-power charge cleaning pulse 11 to the negative voltage V for producing the high-power negative sputtering pulse 10 without any problems.

(27) Regarding FIG. 7, a third embodiment of a complex high-power pulse 4 according to FIG. 5 is displayed. The complex high-power pulse 4 according to FIG. 7 is of course also produced by means of the electrical energy source 3 by applying an electrical voltage V between the anode 5 and the cathode 6 in order to ionize the sputtering gas 7 as shown in FIG. 4. The complex discharge pulse 4 is applied for a complex pulse time . The complex discharge pulse 4 includes an electrical high-power sputtering pulse 10 having a negative polarity with respect to the anode 5 and being applied for a first pulse-time .sub.1.

(28) The high-power sputtering pulse 10 according to FIG. 7 is then followed by the time period .sub.3 in which the voltage V between the anode 5 and the cathode 6 is switched off and/or is set to zero for the third pulse-time .sub.3.

(29) Subsequent to the time period .sub.3 in which the voltage V is switched off or set to zero, the electrical low-power charge cleaning pulse 11 having a positive polarity with respect to the anode 5 is applied for the second pulse-time .sub.2.

(30) The complex high-power sequence 4 according to FIG. 7 is particularly suitable in case that the current 1000 has a relatively broad die-out region 1001 as can be exemplarily seen by FIG. 7. As well known by the person skilled in the art, the current 1000 associated with the high-power sputtering pulse 10 will not immediately go to zero after having switched of the high-power pulse 10 but it takes some time until the current has died out. Thus, as clearly shown by FIG. 7, after the high-power pulse 10 there will arise a more or less broad die-out region 1001 in which the current 1000 is still considerably different from zero.

(31) As a consequence, in case that the low-power cleaning pulse 11 is immediately applied after having switched off the high-power sputtering pulse 10, as for example showed by FIG. 6, depending on the concrete boundary conditions of an actual sputtering process, electrons can be accelerated to the target 8 due to the still existing current 1000 during the die-out period 1001 which can lead to a considerable heating of the target 8.

(32) This problem can be easily avoided by using a special complex discharge pulse 4 according to FIG. 7.

(33) Finally, FIG. 8 shows a very important embodiment of the present invention combining the advantages of the complex high-power pulses of both FIG. 6 and FIG. 7. The voltage V between the anode 5 and the cathode 6 is switched off and/or is set to zero for a second additional third pulse-time .sub.3, that is the voltage is brought to zero before the low-power cleaning pulse 11 is applied as well as after the low-power cleaning pulse 11 and before the next high-power sputtering pulse 11 is applied.

(34) Thus, using a complex discharge pulse according to FIG. 8, a heating of the target due to the die-out period 1001 of the current 1000 is avoided and, at the same time, the electrical energy source 3 can be easily switched from the negative voltage V for producing the high-power negative pulse 10 to the positive voltage V for producing the low-power charge cleaning pulse 11 without any problems.

(35) It is understood that the invention is not only related to the special embodiments discussed above but, of course, further embodiments are included, too. In particular, the invention relates to all advantageous combinations of the discussed embodiments.

(36) Summarizing the discussion of the present invention, since the negative high-power pulse is applied only for a comparatively short interval of time having a high voltage of up to 1000V or more than 1000V, the corresponding current does not show a smooth characteristic but has a sharp peak structure and is timely sharp correlated with the sharp and very short pulse of the applied voltage. As a result, the applied electrical power is sharply concentrated and strong timely connected with the applied short voltage pulse so that the entire electrical energy is applied in a very short interval of time leading to a very high ionization of the plasma. A degree of ionization of nearly 100% can easily be achieved by using the process of the present invention.

(37) In a special embodiment, subsequent to the negative high-power sputtering pulse a positive low-power charge cleaning pulse is applied. Since during the charge cleaning pulse a very low voltage of for example 1V is applied, on the one hand, the target is reliably cleaned from positive electrical charges, wherein at the same time a noticeable collecting of electrons is avoided so that in turn, a heating of the target is essentially avoided.

(38) During the third pulse-time when the voltage applied to the target is switched off or set to zero, time is provided to the system to relax into a starting state so that during each single complex pulse essentially identical sputtering conditions are provided leading in connection with the high degree of ionization and the very effective charge cleaning procedure of the target to a film being coated onto the substrate which film has a high denseness and a significantly improved uniformity, and thus, significantly improved physical and chemical properties compared with the films sputtered by the methods known from the state of the art.

(39) Further advantageous embodiments of the invention are presented.