TiCN having reduced growth defects by means of HiPIMS

Abstract

A method for applying a coating having at least one TiCN layer to a surface of a substrate to be coated by means of high power impulse magnetron sputtering (HIPIMS), wherein, to deposit the at least one TiCN layer, at least one Ti target is used as the Ti source for producing the TiCN layer, said target being sputtered in a reactive atmosphere by means of a HIPIMS process in a coating chamber, wherein the reactive atmosphere comprises at least one inert gas; preferably argon, and at least nitrogen gas as the reactive gas, wherein: the reactive atmosphere additionally contains, as a second reactive gas, a gas containing carbon, preferably CH4, used as the source of carbon to produce the TiCN layer wherein, while depositing the TiCN layer, a bipolar bias voltage is applied to the substrate to be coated, or at least one graphite target is used as the source of carbon for producing the TiCN layer, said target being used for sputtering in the coating chamber using a HIPIMS process with the reactive atmosphere having only nitrogen gas as the reactive gas, wherein the Ti targets are preferably operated by means of a first power supply device or a first power supply unit and the graphite targets are operated with pulsed power by means of a second power supply device or a second power supply unit.

Claims

1. A method for applying a coating to a surface of a substrate to be coated by means of high power impulse magnetron sputtering (HiPIMS), the coating having a titanium nitride (TiN) layer and a titanium carbonitride (TiCN) layer, wherein at least one target containing Ti is used as the Ti source for producing the coating, said target being sputtered in a reactive atmosphere by means of a HiPIMS process in a coating chamber with a bias voltage applied to the substrate, wherein the reactive atmosphere comprises an inert gas and nitrogen gas as a reactive gas, the method comprising the steps of: producing the TiN layer as undercoat for the TiCN layer, wherein the TiN layer is deposited on the surface of the substrate and the TiCN layer is applied immediately thereafter, wherein the bias voltage applied to the substrate for deposition of the TiN layer is changed after deposition of the TiN layer to bipolar pulsed operation for deposition of the TiCN layer, and producing the TiCN layer on the TiN layer, wherein to reduce growth defects during deposition of the TiCN layer, the reactive atmosphere additionally comprises, as a second reactive gas, a gas comprising carbon used as the source of carbon to produce the TiCN layer and, while depositing the TiCN layer, the bipolar bias voltage is applied to the substrate, including a negative bias voltage (−V) and a positive bias voltage (+V), wherein a maximum value of the negative bias voltage used is in a range from −20 V to −200 V, wherein bias voltage levels of the negative bias voltage and the positive bias voltage are adjusted to be asymmetric or symmetrical to one another, wherein a time ratio t.sub.neg:t.sub.pos of the negative bias voltage to the positive bias voltage is in a range from 5:1 to 1:2, and wherein the total pressure of the reactive atmosphere in the coating chamber is in a range of 0.02 Pa to 2 Pa.

2. The method according to claim 1, wherein the gas comprising carbon comprises CH.sub.4.

3. The method according to claim 1, wherein the gas comprising carbon comprises C.sub.2H.sub.2.

4. The method according to claim 1, wherein the gas comprising carbon consists of CH.sub.4.

5. The method according to claim 1, wherein the gas comprising carbon consists of C.sub.2H.sub.2.

6. The method according to claim 1, wherein the power density at the target is in a range of 0.1 kW/cm.sup.2 to 3 kW/cm.sup.2.

7. The method according to claim 1, wherein Ar is the inert gas, and a partial pressure ratio of Ar to N.sub.2 is in a range of 0.01 to 0.95.

8. The method according to claim 1, wherein the time ratio t.sub.neg:t.sub.pos of the negative bias voltage to the positive bias voltage is in a range from 2:1 to 1:1.

9. The method according to claim 1, wherein the bias voltage levels of the negative bias voltage and the positive bias voltage are adjusted to be asymmetric to one another.

10. The method according to claim 9, wherein the ion current and the electron current are set independent of one another.

11. The method according to claim 1, wherein the coating consists of the TiN layer and the TiCN layer.

12. The method according to claim 1, wherein the target containing Ti is a metallic target consisting of Ti.

13. The method according to claim 1, wherein the target containing Ti is a ceramic target consisting of TiC.

Description

(1) The invention is completed in detail in the following and using figures and tables with examples.

(2) FIG. 1: Table with an overview of the properties of sample deposited TiCN layers that were deposited using a bipolar bias voltage according to Example 1 (see C, D, E) compared to TiCN layers that were deposited using a DC voltage according to prior art (see A, B)

(3) FIG. 2: Light-microscope pictures of TiCN layer surfaces according to Example 1 using different bias voltages

(4) FIG. 3: Table with an overview of the properties of sample deposited TiCN layers that were deposited using Ti and graphite targets according to Example 2 (see A, B, C, D, E) compared to TiCN layers that were deposited using only Ti targets and a DC voltage according to prior art (see REF))

(5) FIG. 4: Light-microscope pictures of TiCN layer surfaces according to Example 2 using different target or reactive gas configurations.

EXAMPLE 1 (ACCORDING TO A FIRST PREFERRED EMBODIMENT)

(6) All TiCN layers shown as examples for this first Example were produced with a thin TiN layer as the undercoat. First, the TiN undercoat was deposited on the surface to be coated using the following parameters: a pulse power, P.sub.pulse, of 60 kW, an average power on the target, Pay, of 9.0 kW with a t.sub.pulse of 25 ms, at a total pressure, p.sub.tot, of 0.81 Pa, with an N.sub.2 partial pressure of 0.01 Pa, an Ar partial pressure of 0.4 Pa and a constant bias voltage of −80 V at a coating temperature of 450° C.

(7) The TiCN layers were then applied immediately afterward with the same P.sub.pulse, the same P.sub.av, the same N.sub.2 partial pressure and Ar partial pressure but with an additionally constant CH.sub.4 flow of 50 sccm and a shorter t.sub.pulse of 1 ms.

(8) For the comparison examples A and B in the table of FIG. 1, there was a DC bias voltage both during deposition of the TiN undercoat and during the deposition of the TiCN layer.

(9) For the Examples C, D and E of the invention in Table 1 of FIG. 1, the bias voltage according to the invention was changed after the deposition of the TiN undercoat to bipolar pulsed operation for the deposition of the TiCN layers according to the invention.

(10) All layers had a layer thickness of about 4.0 μm and were then characterized as can be seen in the summary of layer properties in Table 1. The sample numbers A and B were deposited under identical conditions but in different batches with a constant DC bias voltage of −40 V. The sample numbers C, D and E were deposited using a bipolar pulsed voltage of −50 V, −80 V and −100 V, respectively. The duty cycle t.sub.neg:t.sub.pos of the negative bias voltage to the positive bias voltage was kept constant at 50:25 ms for the samples C, D and E.

(11) Surprisingly, a considerable reduction in the roughness factors Ra, Rz and Rmax was found using pulsed bias voltage according to the invention instead of a DC bias voltage when the bias voltage was comparable and even higher. FIG. 2 shows light-microscope pictures of the coated sample surfaces with sample B (constant −40 V-DC) being compared to the samples C, D and E. The optical impression of the black spots is produced by growth defects that disturb the otherwise very smooth surface structure under incident light. A lower density of black spots can clearly be seen in the samples C to E compared to sample B, something that agrees well with the measured roughness values. Interestingly, however, the measured carbon content of the layers, within the specified measuring accuracy, is independent of the method used to apply the bias voltage and was roughly constant at 10±2 at %.

(12) Surprisingly, considerably lower internal stress values were measured for the TiCN layers using pulsed bias voltage than for the comparison samples using DC bias voltage. As seen in Table 1, the internal stress level of −4.4 GPa that occurred when using −40 V of DC bias voltage was not reached until the pulsed bias voltage was −100 V.

(13) Furthermore, a moderate increase in the hardness was seen with the pulsed bias voltage, a situation that is becoming more desirable for the application.

(14) Preferably, a bias voltage in the range of −20 V to −200 V is used.

(15) Preferably, the duty cycle t.sub.neg:t.sub.pos of the negative bias voltage to the positive bias voltage is in a range from 10:1 to 1:5, preferred in 5:1 to 1:2 and particularly preferred in 2:1 to 1:1.

(16) The bias voltage level can be set such that it is symmetrical or asymmetrical. In the case of asymmetrical operation, it is possible to set the ion current and the electron current independent of one another,

(17) Preferably, acetylene (C.sub.2H.sub.2) or methane (CH.sub.4) is used as the gas containing carbon.

(18) According to another embodiment of the invention, ceramic TiC targets or targets made of Ti and TiC can be used in place of metallic titanium targets when depositing TiCN layers.

EXAMPLE 2 (ACCORDING TO A SECOND PREFERRED EMBODIMENT)

(19) All TiCN layers shown as examples for this second Example were produced with a thin TiN layer as the undercoat. First, the TiN undercoat was deposited on the surface to be coated using the following parameters: a pulse power, P.sub.pulse, of 60 kW, an average power on the target, P.sub.av, of 9.0 kW with a t.sub.pulse of 25 ms, at a total pressure, p.sub.tot, of 0.81 Pa, with an N.sub.2 partial pressure of 0.01 Pa, an Ar partial pressure of 0.4 Pa and a constant bias voltage of −80 V at a coating temperature of 450° C. During this, three titanium targets were operated in the manner specified above. The TiCN layers (A, B, C, D, E in the table of FIG. 3) were deposited in accordance with the invention immediately afterward wherein the three titanium targets were operated as before with the same settings but, in addition, three carbon targets were added.

(20) The three carbon targets were used for deposition in different sample processes with P.sub.pulse of 60 kW, a constant bias voltage of −50 V, but different t.sub.pulse values of 0.05, 0.1, 0.2, and 0.3 ms, respectively, with the resulting Pay of 0.4, 0.9, 1.8, and 2.8 kW, respectively. The associated samples are listed in the sequence as A, B, C and D, and the properties are specified in FIG. 3.

(21) As the reference sample (REF), a conventionally deposited TiCN layer was produced, again with the same TiN undercoat as described above wherein, however, only titanium targets were used for the TiCN layer and Ar was used as the process gas at a partial pressure of 0.40 Pa, N.sub.2 was used as the first reactive gas at a partial pressure of 0.01 Pa and additionally CH.sub.4 was used as the second reactive gas at 50 sccm, corresponding to a total pressure p.sub.tot of 0.47 Pa. A DC bias voltage was used both for deposition of the TiN undercoat and for deposition of the TiCN layer. These settings for the reference sample correspond to prior art as mentioned above in the introduction and serve for comparison purposes with regard to layer properties and process stability.

(22) A process with the TiN undercoat described above but using to process gases and two types of targets for the TiCN layer was used for the additional comparison sample E. In this case, the parameters for the three titanium targets were held constant as described above and the settings for the three carbon targets were comparable to those used for sample C, each with P.sub.pulse of 60 kW, a constant bias voltage of −50 V, t.sub.pulse of 0.2 ms, and the resulting P.sub.av of 1.8 kW, an Ar partial pressure of 0.4 Pa, an N.sub.2 partial pressure of 0.03 and a fixed CH.sub.4 flow of 10 sccm were used for deposition.

(23) All layers shown as examples had a layer thickness of about 4.0 μm and were then characterized as can be seen in the summary of layer properties in Table 1 of FIG. 1.

(24) FIG. 4 shows light-microscope pictures of the coated sample surfaces with sample REF being compared to the samples A, B, C and D. The optical impression of the black spots is produced by growth defects that disturb the otherwise very smooth surface structure under incident light. Surprisingly, the samples A to D exhibit a lower density of black spots in comparison to sample REF, something that agrees well with the measured roughness values. The amount of carbon increases with increasing power at the target.

(25) Interestingly, however, it was found that, when comparing samples REF and C, they both have roughly the same carbon content but a considerably higher layer hardness was measured for sample C with the deposition performed in accordance with the invention. This means that using two target materials, one being titanium and the second, in this example, being carbon, has a positive effect on the layer properties and, in addition, permits a stable process.

(26) The comparison sample E that used the two different target materials of titanium and carbon, and N.sub.2 and CH.sub.4 as the reactive gases, exhibits a considerably higher surface roughness, a fact that, however, in comparison to the linear correlation of carbon content or roughness of the samples A, B, C and D that used the deposition process of the invention, may have something to do with the high carbon content in sample E.

(27) Within the scope of the invention, it is conceivable that a fine adjustment of the carbon content can be achieved by using targets made of a compound material containing carbon. This could be a compound, for example, that consists of one or a plurality of metals and one or a plurality of carbides, for example, a target made of TiC or Ti+TiC.

(28) It is just as conceivable that other metals such as Cr, Zr, Ta or Nb be used for the method according to the invention.

(29) Preferably, a bias voltage in the range of −20 V to −200 V, a total pressure ranging from 10.sup.−4 mbar (0.02 Pa) to 10.sup.−2 mbar (2 Pa), a power density in the range of 0.1 kw/cm.sup.2 to 3.0 kW/cm.sup.2 and/or an average power Pay in the range of 0.05 to 10 kW are used. The partial pressure ratio of Ar to N.sub.2 can vary within the range of 0.01 to 0.95.

(30) Preferably, acetylene (C.sub.2H.sub.2) or methane (CH.sub.4) is used as the gas containing carbon.

(31) According to another embodiment of the invention, ceramic TiC targets or targets made of Ti and TiC can be used in place of metallic titanium targets when depositing TiCN layers.

(32) Specifically, the present invention discloses a method of applying a coating having at least one TiCN layer to a surface of a substrate to be coated by means of HiPIMS, wherein, to deposit the at least one TiCN layer, at least one target containing Ti is used as the Ti source for producing the TiCN layer, said target being sputtered in a reactive atmosphere by means of a HiPIMS process in a coating chamber, wherein, to reduce growth defects during the deposition of the at least one TiCN layer, the reactive atmosphere comprises one inert gas, preferably argon, and at least nitrogen gas as the reactive gas, wherein, to reduce growth defects during deposition of the at least one TiCN layer, the reactive atmosphere additionally contains, as a second reactive gas, a gas containing carbon used as the source of carbon to produce the TiCN layer wherein, while depositing the TiCN layer, a bipolar bias voltage is applied to the substrate to be coated, or at least one target containing carbon is used as the source of carbon for producing the TiCN layer, said target being used for sputtering in the coating chamber using a HiPIMS process with the reactive atmosphere having only nitrogen gas as the reactive gas.

(33) Preferably, the method can be executed such that, if a gas containing carbon is used as the source of carbon, the gas containing carbon comprises CH.sub.4 or is made of CH.sub.4, or comprises C.sub.2H.sub.2 or is made of C.sub.2H.sub.2.

(34) Preferably, the method can be executed such that, if one target containing carbon is used as the source of carbon, one or a plurality of targets containing Ti are operated by means of a first power supply device or a first power supply unit and one or a plurality of targets containing carbon are operated with pulsed power by means of a second power supply device or a second power supply unit.

(35) In accordance with one preferred version of the methods described above, one or a plurality of targets containing Ti are metallic targets made of Ti.

(36) In accordance with another preferred version of the methods described above, one or a plurality of targets containing Ti are ceramic targets made of TiC.

(37) In accordance with another preferred version of the method described above in which at least one target containing carbon is used, one or a plurality of targets containing carbon are made of graphite.

(38) In accordance with another preferred version of the method described above in which at least one target containing carbon is used, one or a plurality of targets containing carbon are made of a compound material wherein the compound material, for example, comprises a metal or a plurality of metals and a carbide or a plurality of carbides.