Effect of Annealing Temperature on Microstructure and Resistivity of TiC Thin Films

Round 1

Reviewer 1 Report

This article is devoted to a systemic study of the morphology (surface topography), atomic and electronic structure of titanium carbide films before and after annealing obtained by magnetron sputtering. 

In the text of the article, I found a number of typos and some errors. For example, when describing the peaks in Ti 2p, the authors did not indicate the position of the peak which correspond to Ti-Ti bonds for the Ti 2p1/2 line and described all peaks in a somewhat chaotic way. Changes need to be made on lines 183-186. Also, the deposition rate in one case is 30.7 nm / min, in the other 30.8 nm / min. Figure 3 needs to be corrected, since of very poor quality.
Questions:
1) In the introduction, the authors emphasized that titanium carbide films can be used as the metal gate material. They pointed to the need to reduce the threshold voltage as one of the important problems. However, in this work, they did not study the work function of the electron for the initial film and how it changes depending on the annealing temperature. Without these dimensions, the work seems incomplete.
2) In this work, the crystallite size was investigated by SEM, AFM and XRD. As you can see, the results of the analysis by the SEM and AFM methods have a good correlation. Considering that the AFM method is a direct measurement method, why present data on the crystallite size by the XRD method, for which the analysis for such films is apparently not entirely correct? Should the calculation of the crystallite size by XRD be removed from the article?
3) How was the C/Ti ratio estimated and why is it 0.74? If we consider the XPS data, this ratio changes from 0.89 to 0.46 (0.74 in the as-prepared film).
4) In the C 1s spectra (Fig. 3c), the authors distinguish a peak at 288.5 eV, which they attribute to single carbon-oxygen bonds. In fact, this peak corresponds to C = O bonds. In addition, a shoulder is observed in the carbon spectra at a binding energy of 286.3 eV. According to [https://doi.org/10.1016/j.nimb.2017.08.040] this state can be related to C-O bonds.
5) The TiO state in O 1s at an energy of 531.6 eV raises doubts, since in the Ti 2p spectra, this TiO state is not distinguished. According to https://srdata.nist.gov and http://www.xpsfitting.com/search/label/Titanium, the distance between TiO and TiO2 in the Ti2p line is about 3 eV. Consequently, TiO, if it really exists, could be well seen in the Ti 2p spectra. Most likely, the high-energy shoulder in the O 1s spectra is associated with carbon-oxygen bonds (C = O) [see https://doi.org/10.1016/j.nimb.2017.08.040].

Author Response

Response to Reviewer 1 Comments

We sincerely appreciate the editor’s letter and the reviewers’ comments regarding our manuscript. All the comments mentioned are invaluable and very useful for revising and improving our manuscript. We have carefully considered all comments carefully and have made corrections, which we hope to meet with the approval. We have also prepared a copy with the changes highlighted and marked it with different colors (deleted, revised and newly added). The replies to the comments are as follows:

Point 1: In the text of the article, I found a number of typos and some errors. For example, when describing the peaks in Ti 2p, the authors did not indicate the position of the peak which correspond to Ti-Ti bonds for the Ti 2p1/2 line and described all peaks in a somewhat chaotic way. Changes need to be made on lines 183-186. Also, the deposition rate in one case is 30.7 nm / min, in the other 30.8 nm / min. Figure 3 needs to be corrected, since of very poor quality.

Response 1:

• The position of Ti-Ti bonds for Ti 2P_1/2 indicated in the text.

Added: The position of Ti-Ti bonds at 454.12 eV.

• The chaotic description in line 183 is also modified.

Revision: Four peaks were observed for as-deposited thin film. They are Ti 2p_3/2 peaks of the 183 binding energies at 454.12 eV and 458.71 eV which was correspond to the Ti-Ti bond and TiO₂, and two weak peaks around at 460.79 eV and 464.36 eV for Ti 2p_1/2 which 185 related to TiC and TiO₂, respectively. For the as-deposited film, two doublets peaks Ti 2P_1/2 and Ti 2P_3/2 can be observed. The Ti 2p_1/2 peak exhibited two components of binding energies at 454.12 and 458.71 eV which correspond to the metallic Ti-Ti binding and TiO₂ phase, while the Ti 2p_1/2 peak included two components of binding energies centered at 460.79 and 464.36 eV which related to TiC and TiO₂ phase, respectively.

• In addition, the deposition rate of the thin film is 30.8 nm/min, and the deposition rate of wrong writing is corrected.

Revision: 30.7 nm / min, 30.8 nm / min

• Figue 3 had been corrected.

Point 2: In the introduction, the authors emphasized that titanium carbide films can be used as the metal gate material. They pointed to the need to reduce the threshold voltage as one of the important problems. However, in this work, they did not study the work function of the electron for the initial film and how it changes depending on the annealing temperature. Without these dimensions, the work seems incomplete.

Response 2:

• In the introduction, it is pointed to the need of reduce the threshold voltage variation from device to device, not to reduce the threshold voltages. A detailed discussion as below: When the gate dimension is comparable to the grain size of the metal gate, the gate of MOSFET device is only composed of several grains with different orientations (lead to different work function), this cause the threshold voltage vary from device to devices since the threshold voltage directly related to the gate work functions, which is called threshold voltage variations. Therefore, the variation of threshold voltage can be reduced by reducing the grain size. Because, in this case, when the grain size is much smaller than the gate size, so the gate electrode can cover a large number of grains, and the average work function of grains contained in each gate is almost equal, so the difference of threshold voltage between gates can be reduce. In order to clarify the main goal of this work, relevant contents have been added in the introduction (between line 75 and 76), as shown below:

Newly Added: The main goal of this study is prepares TiC thin films with small grain size which lead the reduction of the threshold voltage variation. On account of, when the gate dimension is comparable to the grain size of the metal gate, the gate of MOSFET device is only composed of several grains with different orientations (lead to different work function), this cause the threshold voltage vary from device to devices since the threshold voltage directly related to the gate work functions, which is called threshold voltage variations. Therefore, the variation of threshold voltage can be reduced by reducing the grain size. Because, in this case, when the grain size is much smaller than the gate size, so the gate electrode can cover a large number of grains, and the average work function of grains contained in each gate is almost equal, so the difference of threshold voltage between gates can be reduce. However, too small grain size will lead to the increase of metal gate resistivity, so it is very important to keep the balance between film resistivity and grain size by changing deposition methods and process parameters.

Point 3: In this work, the crystallite size was investigated by SEM, AFM and XRD. As you can see, the results of the analysis by the SEM and AFM methods have a good correlation. Considering that the AFM method is a direct measurement method, why present data on the crystallite size by the XRD method, for which the analysis for such films is apparently not entirely correct? Should the calculation of the crystallite size by XRD be removed from the article?

Response 3:

• AFM and SEM directly reflect the morphology and size of particles, however, these methods are the result of observation of local areas, and the measured surface particles may or may not be grains, so there are certain contingencies and statistical errors. However, what is measured by X-ray diffraction method is the average grain size of the sample, which can avoid contingency. Therefore, in this study, the grain size was measured by X-ray instead of AFM.

Point 4: How was the C/Ti ratio estimated and why is it 0.74? If we consider the XPS data, this ratio changes from 0.89 to 0.46 (0.74 in the as-prepared film).

Response 4:

• In this study, the C/Ti ratio is estimated by XPS data. The C/Ti ratio of the film is 0.74 for as-deposited film. As you said, this ratio varies from 0.89 to 0.49 depending on the annealing temperature. We sincerely admit the mistake of using the wrong atomic ratio in this paper, and have corrected or deleted the inappropriate Ti/C atomic ratio written in this paper.

Delete：deletate Ti to C ratio of 0.74  in thirteen places in the text.

Point 5: In the C 1s spectra (Fig. 3c), the authors distinguish a peak at 288.5 eV, which they attribute to single carbon-oxygen bonds. In fact, this peak corresponds to C = O bonds. In addition, a shoulder is observed in the carbon spectra at a binding energy of 286.3 eV. According to [https://doi.org/10.1016/j.nimb.2017.08.040] this state can be related to C-O bonds.

Response 5:

• As you said we confirm the peak at 288.5 eV is correspond to C=O, not attributed to the C-O bonds, and we corrected this. By the way, the reference you recommended is added. In addition, a C-O correlation peak at the position of 286.3 eV was added in Figure. 3 and a brief analysis was given.

Revision and addition:  For as-deposited one can be observed three main peaks at 281.76 eV, 284.82 eV, 288.47 and 286.3 eV which is ascribed to Ti-C, C-C [17, 38] , C-O C=O [35] [44] and C-O [42] bonds, respectively.

Newly added references:

[42] Cao, H.; Qi, F.; Ouyang, X.; Zhao, N.; Zhou, Y.; Li, B.; Luo, W.; Liao, B.; Luo, J. Effect of Ti Transition Layer Thickness on the Structure, Mechanical and Adhesion Properties of Ti-DLC Coatings on Aluminum Alloys. Materials. 2018, 11 (9), 1742.

[44] Nesov, S.N.; Korusenko, P.M.; Povoroznyuk, S.N.; Bolotov, V.V.; Knyazev, E.V.; Smirnov, D.A. Effect of carbon nanotubes irradiation by argon ions on the formation of SnO_2-x /MWCNTs composite. NUCL INSTRUM METH B. 2017, 410, 222-229.

Point 6: The TiO state in O 1s at an energy of 531.6 eV raises doubts, since in the Ti 2p spectra, this TiO state is not distinguished. According to https://srdata.nist.gov and http://www.xpsfitting.com/search/label/Titanium, the distance between TiO and TiO2 in the Ti2p line is about 3 eV. Consequently, TiO, if it really exists, could be well seen in the Ti 2p spectra. Most likely, the high-energy shoulder in the O 1s spectra is associated with carbon-oxygen bonds (C = O) [see https://doi.org/10.1016/j.nimb.2017.08.040].

Response 6:

• Just you said, the high energy shoulder at a binding energy of 531.6 eV in the O 1s spectra is associated with C=O not with TiO phase, indeed. And we correct as requested:

Revision: Fig. 3 (d) shows the O 1s spectra of the TiC films for as-deposited and annealed ones. For as-deposited sample, there are only two peaks, one is probably related to TiO₂ (530.12 eV) and other weak peak is related with TiO C=O (531.62 eV) [39]. With the increase of annealing temperature TiO C=O related peak disappeared while TiO₂ related peak moves slightly towards the higher binding energy state. (line 200-204)

Author Response File: Author Response.docx

Reviewer 2 Report

The merit of the described TiC growth is the thorough and detailed material analysis. It contains enough information to understand the effect of heat treatment. The authors emphasize that the composition of the sputtered Ti / C layer has an atomic ratio of 0.74. This obviously depends on the 300W DC or RF power connected to the targets. What was their intention by using equal DC and RF power, resulting in a non-stoichiometric composition? Items in lines 96, 264 and 267 would need to be corrected. I don’t feel qualified to judge about the English language and style but I feel a few word phrases (e.g. "in a word" lines 19, 299) should be corrected.

Author Response

Response to Reviewer 2 Comments

We sincerely appreciate the editor’s letter and the reviewers’ comments regarding our manuscript. All the comments mentioned are invaluable and very useful for revising and improving our manuscript. We have carefully considered all comments carefully and have made corrections, which we hope to meet with the approval. We have also prepared a copy with the changes highlighted and marked it with different colors (deleted, revised and newly added). The replies to the comments are as follows:

Point 1: The authors emphasize that the composition of the sputtered Ti / C layer has an atomic ratio of 0.74. This obviously depends on the 300W DC or RF power connected to the targets. What was their intention by using equal DC and RF power, resulting in a non-stoichiometric composition?

Response 1:

• In order to improve the growth rate of thin films, higher deposition power of 300 W was applied to both Ti target and C targets. However, the power types applied to Ti target and C target are also different, in which DC power applied for Ti target while RF power applied for C target due to the difference electrical properties of these two materials. The stability range of TiC_x is very large which x was various in the range of 0.47-0.97 without any structural changes [11]. Therefore, in order to reduce the resistivity of TiC thin films, it is necessary to increase the content of metal (Ti) in the thin films, so the Ti/C atomic ratio is set at 0.74.

Point 2: Items in lines 96, 264 and 267 would need to be corrected. I don’t feel qualified to judge about the English language and style but I feel a few word phrases (e.g. "in a word" lines 19, 299) should be corrected.

Response 2:

• The sentences in line 96 had been corrected,

Revision: After deposition, some of the samples were annealed for 20 min in a high vacuum (~ 10^-3 pa) furnace at five different temperatures of 400 °C, 500 °C, 600 °C, 700 °C and 800 °C, respectively. After deposition, some samples were annealed at 400 °C, 500 °C, 600 °C, 700 °C and 800 °C for 20 min under high vacuum conditions (~10^-3pa).

• The sentences in line 264 had been corrected,

Revision: Where ρ_b is the bulk resistivity mainly determined by composition and phase, and ρ_i, ρ_g and ρ_s are the resistivity which related to impurities, grain boundary boundaries and surface scattering.

• The sentences in line 267 had been corrected,

Revision：Furthermore, the composition variation on the annealing is very small, so its effects on the total resistivity can be ignored, too. In addition, the change of atomic percentages with annealing temperature is also very small, so its influence on the total resistivity can be ignored.

• In lines 19 and 299, replace “In a word” with “In brief”.

Author Response File: Author Response.docx

Reviewer 3 Report

In this paper “Effect of Annealing Temperature on Microstructure and Resistivity of TiC Thin Films” Authors presents the influence of deposition method and annealing temperatures on microstructure, surface topography, bonding states and electrical resistivity of TiC films. This thin films were prepared by non-reactive simultaneously double magnetron sputtering.  All produced samples were annealed at different temperatures under high vacuum conditions after deposition. Investigations by XRD method show that TiC thin films was as form crystals - without annealing. The crystallinity of thin films is improved after annealing. Raman spectra confirm the formation of TiC crystal and amorphous states of carbon.

In my opinion this paper can be interesting to readers of Coatings journal. The paper is clearly presented. The paper contains 6 figures and 1 table – some figures are legible and good quality.

English of the paper is rather good – in my opinion the language of the paper should be a little improved. I am asking for corrections by a native speaker.

I find some mistakes for example:

• Experiment chapter – Please describe equipment used in the experiment – work development environment / work apparatus should be given – model of equipment (manufacturer, city, country).
• A literature review done in an interesting way supported by 61 literature items. Amount of references is also sufficient but some papers cited in the references 49 from all 61 are older then 5 years – these publications constitute over 80 % of all cited papers.
• Minimum 34 papers from all 61 (over 55 %) are wrote by authors from Asia – China, Japan and others. Are the topics covered in this article only by research centers from Asia? I ask for a reliable verification of global research in this field. I propose to add some new (from the last 5 years) publications on the production or properties of these type of materials. Authors should include several modern papers (also from Europe and America).
• Please prepare a literature review according to the guidelines of the Coatings journal.
• In my opinion Conclusions chapter should be a little changed. In this chapter there are no summary of all significant information obtained by the Authors and written in the Results and discussion
• References numbers [13], [41], [55] – please add or correct date of paper publication.
• There are some poor quality or illegible figures in the paper (too small descriptions, illegible legends) – for example figures: 2 and 4.
• Figure 5 should be decreased
• When the Authors mean – "… this work ..." (for example line 301) the phrase "… this research ..." or "… this investigations ..." should be used, but not the word "… work …".

The results obtained are interesting and promising. The manuscript can be accepted for publication in Coatings journal after MINOR corrections.

Author Response

Response to Reviewer 3 Comments

We sincerely appreciate the editor’s letter and the reviewers’ comments regarding our manuscript. All the comments mentioned are invaluable and very useful for revising and improving our manuscript. We have carefully considered all comments carefully and have made corrections, which we hope to meet with the approval. We have also prepared a copy with the changes highlighted and marked it with different colors (deleted, revised and newly added). The replies to the comments are as follows:

Point 1: English of the paper is rather good – in my opinion the language of the paper should be a little improved. I am asking for corrections by a native speaker.

Response 1:

The language of the paper had improved. We point out each sentence revision one by one, the modification details are as follows:

• After deposition, some of the samples were annealed for 20 min in a high vacuum (~ 10-3 pa) furnace at five different temperatures of at 400 °C, 500 °C, 600 °C, 700 °C and 800 °C for 20 min under high vacuum conditions (~10^-3pa)., respectively. (line 95-97)
• Four peaks were observed for as-deposited thin film. They are Ti 2p_3/2 peaks of the binding energies at 454.12 eV and 458.71 eV which was correspond to the Ti-Ti bond [16] and TiO₂ [17] , and two weak peaks around at 460.79 eV and 464.36 eV for Ti 2p1/2 which related to TiC [31]and TiO₂ [37] , respectively. For the as-deposited film, two doublets peaks Ti 2P_1/2 and Ti 2P_3/2 can be observed. The Ti 2p_1/2 peak exhibited two components of binding energies at 454.12 and 458.71 eV which correspond to the metallic Ti-Ti binding [17] and TiO₂ phase [19], while the Ti 2p_1/2 peak included two components of binding energies centered at 460.79 and 464.36 eV which related to TiC [34] and TiO₂ [41, 42] phase, respectively. (line 183-186)
• where ρb is the bulk resistivity mainly determined by composition and phase, and ρ_i, ρ_g and ρ_s are the resistivity which related to impurities, grain boundary boundaries and surface scattering [65]. (line 264-66)
• Furthermore, the composition variation on the annealing is very small, so its effects on the total resistivity can be ignored, too. In addition, the change of atomic percentages with annealing temperature is also very small, so its influence on the total resistivity can be ignored. (line 267-269)

Point 2: Experiment chapter – Please describe equipment used in the experiment – work development environment / work apparatus should be given – model of equipment (manufacturer, city, country).

Response 2:

• In the experimental part, we added the corresponding information of the instruments used in this study. The details are as follows:

Equipment Addition Information: Magnetron sputtering (JGP450, Shenyang Zhongke Instrument, Shenyang, China); Grazing incident X-ray diffractometer (GIXRD, D8 ADVANCE, Bruker, Karlsruhe, Germany); Scanning electron microscope equipped with energy dispersion spectra (SEM/EDS, SU8010, Hitachi, Tokyo, Japan); Atomic force microscopy (AFM, Bruker Dimension ICON, Bruker, Madison, America); X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi, Thermo Fisher, Chicago, America); Raman spectrometer (Raman, LabRAM HR Evolution, HORIBA Scientific, Paris, France); Four Point Probe (RTS-8, Suzhou Lattice Electronics Co., Ltd, Suzhou, China).

Point 3: A literature review done in an interesting way supported by 61 literature items. Amount of references is also sufficient but some papers cited in the references 49 from all 61 are older than 5 years – these publications constitute over 80 % of all cited papers. Minimum 34 papers from all 61 (over 55 %) are wrote by authors from Asia – China, Japan and others. Are the topics covered in this article only by research centers from Asia? I ask for a reliable verification of global research in this field. I propose to add some new (from the last 5 years) publications on the production or properties of these type of materials. Authors should include several modern papers (also from Europe and America).

Response 3:

• The authors did not notice that more than 80% of the references cited in this paper were wrote by authors from Asia ( China, Japan and others older) and are older than 5 years. We found some new related references (include from Europe and America) and added them to the references, such as:

Newly added references:

12. De Bonis, A.; Santagata, A.; Galasso, A.; Laurita, A.; Teghil, R. Formation of Titanium Carbide (TiC) and TiC@C core-shell nanostructures by ultra-short laser ablation of titanium carbide and metallic titanium in liquid. J. Colloid Interface Sci. 2017, 489, 76-84.
13. Dev, V. Lithium intercalation studies in cubic titanium carbide thin films. Appl. Surf. Sci. 2018, 449, 537-541.
14. Roger, J.; Gardiola, B.; Andrieux, J.; Viala, J.C.; Dezellus, O. Synthesis of Ti matrix composites reinforced with TiC particles: thermodynamic equilibrium and change in microstructure. J Mater Sci Mater Med. 2016, 52 (7), 4129-4141.
15. Létiche, M.; Brousse, K.; Demortière, A.; Huang, P.; Daffos, B.; Pinaud, S.; Respaud, M.; Chaudret, B.; Roussel, P.; Buchaillot, L.; Taberna, P. L.; Simon, P.; Lethien, C. Sputtered Titanium Carbide Thick Film for High Areal Energy on Chip Carbon-Based Micro-Supercapacitors. ADV FUNCT MATER. 2017, 27 (20), 1606813.
16. Cao, H.; Qi, F.; Ouyang, X.; Zhao, N.; Zhou, Y.; Li, B.; Luo, W.; Liao, B.; Luo, J. Effect of Ti Transition Layer Thickness on the Structure, Mechanical and Adhesion Properties of Ti-DLC Coatings on Aluminum Alloys. Materials. 2018, 11 (9), 1742.
17. Nesov, S.N.; Korusenko, P.M.; Povoroznyuk, S.N.; Bolotov, V.V.; Knyazev, E.V.; Smirnov, D.A. Effect of carbon nanotubes irradiation by argon ions on the formation of SnO_2-x /MWCNTs composite. NUCL INSTRUM METH B. 2017, 410, 222-229.

Point 4: In my opinion Conclusions chapter should be a little changed. In this chapter there are no summary of all significant information obtained by the Authors and written in the Results and discussion.

Response 4:

• The conclusion chapter has been revised completely, as follows:

Revised conclusion chaper: In conclusion, the deposition method and annealing temperature have great influence on the microstructure and resistivity of TiC thin films. The TiC thin films have been crystallized even before annealing, and crystallinity of films have been improved with annealing. The grain size of the film is relatively small (8.5 - 14.7 nm) due to no heat treatment applied during depositions, but it can be adjusted by annealing. The growth rate of the TiC film is relatively high, about 30.7 nm / min. The surface of the film is composed of nanoparticles with irregular shape, and with annealing, the shape of the particles becomes regular and dense, which is beneficial to reduce the resistivity of films. The formation of TiC can be further confirmed by XPS and Raman spectra. But a certain amount of oxygen element can be detected by XPS, which may be oxygen molecules absorbed when the film exposed to air. And the non-reactive amorphous carbon phase can also be observed from the Raman spectrum. The surface of the film is smooth (Ra = 1.49 ~ 3.23 nm, Rq = 1.90 ~ 4.59 nm), and the roughness changes randomly with the change of annealing temperature. The resistivity of the thin film is small. With the increase of annealing temperature, the resistivity of the thin film decreases monotonously from 666.73 cm to 86.01 cm. In a word In brief, the prepared TiC film has excellent properties such as small grain size, good crystallinity and low resistivity, which can meet the requirements of metal gate.

Point 5: References numbers [13], [41], [55] – please add or correct date of paper publication.

Response 5:

• The date of references [13], [41], [55] have been added:

Corrected References:

[13] Grubbs, M.E.; Zhang, X.; Deal, M.; Nishi, Y.; Clemens, B.M. Development and characterization of high temperature stable Ta–W–Si–C amorphous metal gates. Appl. Phys. Lett. 2010, 97 (22), 1266-406.

[41] Lee, Y.C.; Hu, S.Y.; Water, W.; Tiong, K.K.; Feng, Z.C.; Chen, Y.T.; Huang, J.C.; Lee, J.W.; Huang, C.C. Rapid thermal annealing effects on the structural and optical properties of ZnO films deposited on Si substrates. J LUMIN. 2009, 129 (2), 148-152.

[55] Liu, H.D.; Chen, Y.M.; Yousaf, M.I.; Luo, C.; Wan, Q.; Hu, L.W.; Fu, D.J.; Ren, F.; Li, Z.G. In situ synthesized TiC–DLC nanocomposite coatings on titanium surface in acetylene ambient. Appl. Surf. Sci. 2015, 349, 93-100.

Point 6: There are some poor quality or illegible figures in the paper (too small descriptions, illegible legends) – for example figures: 2 and 4. Figure 5 should be decreased. When the Authors mean – "… this work ..." (for example line 301) the phrase "… this research ..." or "… this investigations ..." should be used, but not the word "… work …".

Response 6:

• The quality of the figures 2 and 4 is improved.
• Figure 5 has been decreased.
• Replace “work” with “research”

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Several errors need to be fixed:
1) in line 198 the titanium peaks are indicated as Ti 2P. It needs to be replaced with Ti 2p.
2) There is no indication of the position of the peak (dash-dotted line showing the position) for Ti-Ti (titanium in the metallic state) in the Ti 2p1/2 region (see Figure 3b).
3) On line 198 there is no space between the words "ones.For"