Controlled Interlayer Between Titanium Carbon-Nitride and Aluminium Oxide

Home , Aluminium oxide, Titanium nitride

UPTEC K11 006 Examensarbete 30 hp Januari 2011

Controlled interlayer between titanium carbon-nitride and aluminium oxide

Sara Munktell von Fieandt Abstract Controlled interlayer between titanium carbon-nitride and aluminium oxide Sara Munktell von Fieandt

Teknisk- naturvetenskaplig fakultet UTH-enheten In the industry of metal cutting tools the conditions are extreme; the temperature can vary thousand degrees rapidly and the pressure can be tremendously high. To survive Besöksadress: this kind of stress the cutting tool must be both hard and tough. In order to obtain Ångströmlaboratoriet Lägerhyddsvägen 1 these properties different coatings are used on a base of cemented carbide, WC-Co. Hus 4, Plan 0 Common coatings are hard ceramics like titanium nitride and titanium carbon-nitride with an outer layer of aluminium oxide. Postadress: In this thesis the possibility of using titanium dioxide as an interlayer between titanium Box 536 751 21 Uppsala carbon-nitride and aluminium oxide to control the morphology and phase of aluminium oxide is investigated. Of the different aluminium oxide phases only the Telefon: alpha-Al2O3 is stable. The titanium carbon-nitride coatings are made by CVD 018 – 471 30 03 (chemical vapour deposition); also the alumina is deposited by CVD. The titanium Telefax: dioxide was deposited by atomic layer deposition (ALD) which is a sequential CVD 018 – 471 30 00 technique that allows a lower deposition temperature and better control of the film growth than CVD. The obtained thin films were analyzed using XRD, Raman Hemsida: spectroscopy, ESCA and SEM. To test the adhesion of the coatings the samples were http://www.teknat.uu.se/student sand blasted. A thin interlayer of titanium dioxide causes the aluminium oxide to grow as alpha-Al2O3, thinner TiO2 gave better adhesion.

Handledare: Tommy Larsson (Seco Tools AB) Mats Boman Ämnesgranskare: Mikael Ottoson Examinator: Gunnar Westin ISSN: 1650-8297, UPTEC 11 006 Sponsor: Seco Tools AB

Abstract

Controlled interlayer between titanium carbon-nitride and aluminium oxide.

In the industry of metal cutting tools the conditions are extreme; the temperature can vary thousand degrees rapidly and the pressure can be tremendously high.

To survive this kind of stress the cutting tool must be both hard and tough. In order to obtain these properties different coatings are used on a base of cemented carbide, WC-Co. Common coatings are hard ceramics like titanium nitride and titanium carbon-nitride with an outer layer of aluminium oxide.

In this thesis the possibility of using titanium dioxide as an interlayer between titanium carbon- nitride and aluminium oxide to control the morphology and phase of aluminium oxide is investigated. Of the different aluminium oxide phases only the α -Al 2O3 is stable. The titanium carbon-nitride coatings are made by CVD (chemical vapour deposition), also the alumina is deposited by CVD. The titanium dioxide was deposited by atomic layer deposition (ALD) which is a sequential CVD technique that allows a lower deposition temperature and better control of the film growth than CVD. The obtained thin films were analyzed using XRD, Raman spectroscopy, ESCA and SEM. To test the adhesion of the coatings the samples were sand blasted. A thin interlayer of titanium dioxide causes the aluminium oxide to grow as α-Al 2O3, thinner TiO 2 gave better adhesion.

Table of Contents Sammanfattning ...... 4 1 Aim ...... 5 2 Introduction ...... 6 3 Background ...... 6

3.1 Aluminium oxide Al 2O3 ...... 7

3.2 Titanium dioxide TiO 2 ...... 7

4 Experimental ...... 8 4.1 Atomic Layer Deposition (ALD) ...... 8

4.1.1 Basic characteristics ...... 8

4.2 Chemical vapour deposition (CVD) ...... 11

4.2.1 Basic characteristics ...... 11

4.3 Analytical techniques ...... 13

4.3.1 X-ray diffraction (XRD) ...... 13

4.3.2 X-ray reflectivity (XRR) ...... 13

4.3.3 X-ray fluorescence (XRF) ...... 14

4.3.4 Raman spectroscopy ...... 14

4.3.5 Electron spectroscopy for chemical analysis (ESCA) ...... 14

4.3.6 Scanning electron microscopy (SEM) ...... 15

4.4 ALD of titanium dioxide ...... 16

4.5 CVD of aluminium oxide ...... 16

4.6 Film characterisation ...... 17

4.6.1 Film thickness ...... 17

4.1.2 Film adhesion ...... 17

5 Results ...... 18 5.1 XRD characterisation ...... 18

5.2 Raman characterisation ...... 21

5.3 ESCA on Al 2O3 ...... 23

5.4 Evaluation of the film thickness ...... 24

5.5 SEM ...... 25

5.6 XRF ...... 26

5.7 Film adhesion ...... 26

6 Discussion...... 27 7 Conclusions ...... 27 8 Acknowledgements ...... 28 9 References ...... 29

Sammanfattning Ett skär för metallbearbetning får utstå extrema påfrestningar, så som stora temperaturförändringar under kort tid och mycket höga tryck. För att erhålla verktyg som kan tåla dessa förhållanden pågår intensiv forskning. Marknaden är under konstant utveckling där maskiner med högre skärhastigheter och nya material att bearbeta driver efterfrågan på bättre skärverktyg.

Idag består de flesta skär för olika metaller av ett bulkmaterial av hårdmetall med olika typer av hårda keramiska beläggningar. I det här examensarbetet undersöks möjligheten att förbättra egenskaperna hos hårdmetallskär med en ytbeläggning bestående av ett innre lager av Ti(C,N) och ett yttre av Al 2O3.

Beläggningarna görs med CVD (Chemical Vapour Deposition). Al 2O3 finns i flera olika struckturer, de två vanligaste är termodynamisktstabila α -Al 2O3 och metastabila κ- Al 2O3. Den önskvärda fasen är α -

Al 2O3 men då man belägger Al 2O3 på Ti(C,N) så får man vanligen κ-Al 2O3. Syftet med projektet var att med ett mellanlager av titanoxid ska kunna styra fasinnehållet i Al 2O3. Titanoxiden belades med ALD (Atomic Layer Deposition) en beläggnings metod som kan ge mycket tunna och jämna filmer.

Filmerna analyserades med XRD, Raman spectroskopi, ESCA, SEM och XRF.

Ett tunt skikt av TiO 2 mellan Ti(C,N) och Al 2O3 resulterade i att α -Al 2O3 erhölls.

1 Aim The aim of this work was to test if the phase content of CVD aluminium oxide on cemented carbide cutting tools could be tailored by an interlayer of titanium dioxide. A more specific aim of this investigation was to determine if α -Al 2O3 could be phase selectively deposited. By selectively depositing α -Al 2O3 with a good adhesion the durability of the cutting tools can be enhanced.

2 Introduction To be able work with most metals and alloys tools that can withstand extreme conditions is essential. Much research is spent on developing new materials and new combinations of materials to optimize the properties of cutting tools. A common combination to create a cutting tool for steel is cemented carbide with multilayer coatings of different ceramics. The ceramics are often titanium nitride or titanium carbonitride and aluminium oxide. In this thesis the possibility of enhancing the properties of this kind of cemented carbide cutting tools by adding a titanium dioxide interlayer between the titanium carbon-nitride and the aluminium oxide is studied. The hope is that by adding the titanium dioxide interlayer we will be able to phase se lectively deposit α -Al 2O3.

Figure 1: Schematic cross-section of the coating before and after TiO 2 deposition

3 Background The industry of metal cutting is under constant development. New machines with higher cutting speed and new materials that require more advanced cutting tools are two reasons for this. A cutting tool needs to be tough, wear resistant, deformation resistant and stable at high temperatures.

Today most cutting tools for different kinds of steel and other types of metals are similarly constructed with a hard but tough bulk material and a multilayer coating of hard and stable ceramics.

The cutting tools that are studied in this thesis have a bulk material of cemented carbide and coatings of titanium carbon-nitride and aluminium oxide. The cemented carbide is made from a powder mixture that is pressed in the right shape and then sintered. To obtain the optimal shape the tool is treated with different types of grinding and polishing. To further enhance the properties multilayer coatings is deposited on the tool. There are two different techniques often used to create these kinds of hard coatings; chemical vapour deposition (CVD) and physical vapour deposition (PVD). CVD is the deposition method that is used for the titanium carbon- nitride and the aluminium oxide coatings in this study.

3.1 Aluminium oxide Al 2O3 A material that has proven itself in the harsh environment of metal cutting is aluminium oxide. Aluminium oxide shows great properties in wear resistance, toughness and deformation resistance at high temperatures. There are two (of several more) common phases of aluminium oxide that usually obtained in the CVD coatings, α-Al 2O3 and κ -Al 2O3. The thermodynamically stable phase is α-Al 2O3. If a cutting tool is coated with κ -Al 2O3 the film may undergo phase transformation during the cutting process which could reduce the durability of the tool coating and therefore α-Al 2O3 is the desired phase[1-3]. Research has shown that the performance of the α-Al 2O3 can be enhanced even further by control of its texture[1].

Aluminium oxide is usually combined with layers of titanium carbonitrides. Ti(C,N) has complementary wear properties to aluminium oxide making it widely used on metal cutting tools[3].

It has proven to be a difficult task to deposit α -Al 2O3 on Ti(C,N) with CVD as the phase obtained is mainl y κ -Al 2O3. The hypothesis of this study is that a thin layer of titanium dioxide can control the growth of the aluminium oxide so that the obtained phase is α -Al 2O3[12-16].

3.2 Titanium dioxide TiO 2

TiO 2 crystallises in three different polymorphs, the thermodynamically stable rutile and two meta-stable phases; anatase and brookite. In the composition range TiO-TiO 2 there exists more than 60 phases called Magnéli phases and they are often very colourful. In the ALD process either rutile or anatase is formed. If the deposition is preformed at 300˚C as in this work anatse is the stable phase in thin films.

Titanium dioxide has a wide range of applications and many appealing properties. Some examples of these properties are good chemical resistance and a high dielectric constant and rutile has a high refractive index. Thin films of titanium dioxide the can, among other things, be used as photo-electrodes and photo-catalysts for water splitting as conductive films in solar cells. Rutile can also be used as a white pigment in paint and anatase is known to have self cleaning properties in UV-light.

4 Experimental

4.1 Atomic Layer Deposition (ALD) Atomic layer deposition is a thin film deposition method that was developed in the early 1970s by a Finnish researcher named Suntola and his team[6]. ALD is a chemical vapour deposition related technique. It is based on self-terminating reactions of a gas adsorbed on a surface, yielding a possibility to create films as thin as a few atomic layers with good control. ALD has unique properties regarding step coverage and growth control; conformal films can be deposited on surfaces that are extremely complex. Another advantage compared to CVD is the possibility to use more reactive precursors and therefore have lower deposition temperatures. The reason for this is that since the precursor gases are not mixed in the reactor you can avoid the risk of undesired gas phase reactions, some ALD reactions can even be used at room temperature depending on the precursors.

The technique is most suited to deposit ceramic materials but it can also be used to deposit thin films of pure elements. Materials commonly deposited by ALD are different types of oxides, nitrides and sulphides but there are plenty of other possible material combinations. The precursor types vary from water and simple halides to complex metalorganic compounds. A suitable precursor must be volatile but not have tendencies to decompose thermally at the process temperature. For the deposition of titanium dioxide the most common precursors are TiCl 4 and H2O. Other suitable precursors are TiI 4 and H 2O. O 2 can also be used as an oxygen source[6-10].

In this thesis an ALD reactor from Picosuns SUNALE R-series was used for the deposition of titanium dioxide[18,19].

4.1.1 Basic characteristics A simple ALD setup is based on the repetition of four steps, see Figure 2: two self terminating gas-solid reactions and two purge steps. The four steps are called an ALD cycle. In the first step the first precursor is pulsed through the reactor. The gas can chemisorb or react with the surface and form a monolayer. The second pulse is a purge step where an inert gas is pulsed through the reactor removing all residues of the first precursor. In the third step the second precursor is pulsed through the reactor and reacts with the monolayer of the first precursor. The fourth step is a second purge pulse where all reaction by-products and residual gases are removed [10].

Figure 2: ALD reaction cycle

Complex multilayer structures can be formed because of the ability to vary the precursors from cycle to cycle.

For the ALD process to work at optimal efficiency some conditions needs to be fulfilled. These terms can be summarised in a so called ALD window, see Figure 3. If the temperature is too low there can be insufficient activation energy or condensation of the precursor limiting the growth. On the other hand if the temperature is too high the precursor can de-compose or re-evaporate from the surface and thereby affect the growth rate of the film.

Figure 3: ALD-window

There are two common types of ALD- reactors: flow-through and the open and closed reactor. The open-closed reactor has a low efficiency but a good control of film growth. An open-closed reactor is optimal for complex surfaces i.e. substrates with a large surface area compared to size. The downside of the open-closed reactor is the risk for condensation. The flow-through reactor is efficient and rapid and most suited for more simple substrates. There are two different varieties of the flow-through reactor: the cold-wall, where the substrate is heated separately and the hot- wall where the entire reactor is heated. Today many other varieties of reactors are used with different types of complements and adaptations[20].

Today there are numerous applications for ALD from microelectronics to catalysts. In this thesis ALD is used to create thin films of titanium dioxide on cemented carbide cutting tools coated with Ti(C,N). The technique was chosen because of its capability to make so thin and conformal films[7,10].

4.2 Chemical vapour deposition (CVD) Chemical vapour deposition is one of the most established film deposition methods today both in the industry and for research. The technique has numerous applications in many different fields. In CVD a solid material is grown from a vapour phase. The CVD process has many interesting properties like good step coverage and high deposition rate compared to ALD. The down side is that you often need high deposition temperatures[12].

At Seco Tools the CVD methods are divided in to two categories HTCVD (High Temperature CVD), MTCVD (Moderate Temperature CVD). HTCVD has deposition temperatures above 900˚C and MTCVD has deposition temperatures between 750˚C and 900˚C.

4.2.1 Basic characteristics The reaction processes of CVD are very complex and have several steps, see Figure 4. First the precursor gases are carried to the reactor by a main gas flow, step 1, where they react homogeneously with each other to form secondary precursors, step 2. These precursors are carried to the surface, step 3, and when they are adsorbed, step 4, they diffuse to an energetically favourable growth site, step 5. On these sites the precursors react heterogeneously and begin to form a film, step 6 and 7. Residues from the reactions desorb from the surface and are carried away by the main gas flow, step 8 and 9 [12].

Figure 4: CVD reaction steps

There is a risk that reaction by-products are incorporated in the film. There are several factors influencing these kinds of contaminations. Optimising the deposition temperature is one way to minimize the contaminations.

Figure 5: CVD schematic overview of the gas flows

Figure 4 shows a schematic view of the CVD reactor and the gas flows in it. Different combinations of gases are used in the depositions of the Ti(C,N) and the aluminium oxide. The precursors used for the deposition of Ti(C,N) are TiCl 4 and CH 3CN, also present are N 2 and H 2. The general reaction formula can be described as follows:

TiCl 4 + yCH 3CN → Ti(C,N) + xHCl

For the deposition of Al 2O3 the precursors are AlCl 3 prepared in a separate reactor and CO 2. Other gases needed are H 2 and HCl. H2S is used as a catalyst. There are a number of different types of CVD reactors. The one used in this study is a hot-wall reactor. In a hot-wall reactor the entire reactor is heated, see Figure 5.

12 Figure 6: CVD-reactor after removal of the furnace .

4.3 Analytical techniques

4.3.1 X-ray diffraction ( XRD) X-ray diffraction is an established analytical technique that uses X-rays interactions with a material to characterise it. With XRD one can identify crystalline phases and their properties such as composition, grain size, unit cell parameters and much more. The X-ray interaction studied is a type of elastic scattering called diffraction occurring in materials having long range atomic order, meaning the material needs to be at least partly crystalline. Some diffraction in amorphous materials can occur caused by local order. Diffraction arises when the terms of Bragg’s law is fulfilled. nλ = 2dsin(θ) n is an integer, λ is the wavelength of the incoming radiation, d is the distance between the atomic planes and θ is the diffraction angle, see Figure 7.

Every crystalline material gives rise to a specific combination of diffracted beams depending on its symmetry, contents and spacing. The data obtained is often displayed in a diffractogram. X- ray diffraction is a non-destructive technique for a vast majority of materials.

Two types of XRD film analysis were used in this study , θ-2θ scans and gracing -incidence X-ray diffraction (GIXRD). With θ-2θ scans information about materials phase content and of its texture can be obtained. In GIXRD the incoming angle of the X-rays is very small, around 0.5 ˚. This type of XRD is suited for analyzing ultrathin films. The small incoming angle makes the X- rays travel a longer distance through the thin film and the signals from the film is enhanced[11].

Figure 7: XRD

4.3.2 X-ray reflectivity (XRR) X-ray reflectivity analyses the reflected X-rays and utilities the same type of equipment as XRD. From an XRR analysis you can obtain properties such as film density and film thickness. XRR only works with extremely smooth surfaces. It is also a non-destructive technique for most materials[11].

4.3.3 X-ray fluorescence (XRF) X-ray fluorescence is a non-invasive and fast technique that is often used to determine the elemental composition of a sample. When irradiated with X-rays an element can emit characteristic fluorescence. These photons are used to give a qualitative identification of the elements in the sample and they can also give a quantitative evaluation if compared to a reference sample [11].

4.3.4 Raman spectroscopy Light can interact with a material in many different ways, in Raman spectroscopy the inelastic scattering of an intense monochromatic light beam is used to characterise a sample. The scattering depends on the fact that some energy from the light is transferred to the vibration modes in the atoms and molecules. The energy losses are specific for the vibration frequencies of the sample, which gives a Raman spectrum and with it you can, among other things, identify your sample. Raman spectroscopy can be used on most non-metallic samples from gases to solids. The technique is non-destructive to most materials[5,9,11].

4.3.5 Electron spectroscopy for chemical analysis (ESCA) ESCA or X-ray photoelectron spectroscopy (XPS) is a surface analysis technique that is based on the photoelectric process. The sample is irradiated with X-rays and the emitted electrons are analysed. Each element has a unique spectrum. Depending on the bonding in the material and its composition the spectrum changes, peaks can shift position or/and split, giving unique analysing opportunities. ESCA can also give quantitative information. The analysed electrons have a short mean free path through the material making ESCA a surface sensitive technique. If combined with an ion-sputter removing layer by layer displaying new surfaces, ESCA can give an extremely detailed analysis of the bulk of a material as well. When the sputter is used the sample is damaged, otherwise the technique is non destructive. To be able to detect the photoelectrons vacuum is essential[11].

4.3.6 Scanning electron microscopy (SEM) SEM is a versatile technique that is very common in the industries and research facilities since a couple of decades. It can generate high resolution images at magnifications far beyond the capability of light optical microscopes.

The instrument generates a picture by a focused electron beam that is scanned over the surface of the sample; each scanning point represents a pixel in the created image. When the beam hits the sample a number of different interactions occur. In SEM the backscattered electrons or the secondary electrons are usually analysed. The backscattered image gives more chemical information, the contrast in the image depends among other things on the atomic number of the elements in the sample. Secondary electron gives better and more comprehensible images of the surface; it is easier to see topography and it provides a higher resolution.

An SEM is often equipped with an EDS (Energy dispersive X-ray spectrograph) detector that analyse the X-rays that also arise from the electron beam interactions. With this you gain a good elemental analysis and some quantitative information.

The analysis usually requires vacuum. Some samples can be damaged by the electron beam but in general it does not destroy the sample. No sample preparation is needed if the sample is an electrical conductor. A non-conducting sample is more difficult to study because it becomes charged by the electron beam[11].

4.4 ALD of titanium dioxide The equipment used to deposit the titanium dioxide films was a hot wall ALD reactor from Picosun. Different thicknesses were tested to determine how thick the titanium dioxide needed to be to be able to affect the aluminium oxide. The same settings were used in all the depositions except for the number of cycles which for the most part controls the thickness of the films. The pulse schedule was tested on beforehand to obtain suitable parameters. Before the samples were put in the reactor they were cleaned in ethanol in an ultra-sonic bath for ten minutes and then dried with nitrogen gas. The deposition temperature was 300˚C.

The precursors that were used to deposit titanium dioxide were TiCl 4 and H 2O.

Table 1: ALD settings

Precursor Pulse time (s) Samples Number of cycles TiCl 4 0,2 A 5,10,25,50,100,200,300,400 B 5,10,25,50,100,200,300,400 H2O 0,5 C 5,10,25,50,100,200,300,400 Purge (N ) 4 2 Silicon 100,200,300,400 Pulse Schedule 0,2 - 4 - 0,5 - 4

Three types of CVD coated substrates were used as samples. Sample A and B consists of an MTCVD Ti(C,N). In sample A the Ti(C,N) is fine-grained, and in Sample B it is coarse grained. Sample C has a very fine-grained HTCVD Ti(C,N) coating. In all cases the precursors used for coating were TiCl 4, CH3CN, N 2, and H2.

4.5 CVD of aluminium oxide Aluminium oxide was deposited by CVD at Seco Tools. The equipment used was a production scale IonBond system. Three recipes were tested: SM-o001 and SM-o002 where Al 2O3 coatings with different thicknesses. SM-o003 used an oxidizing step prior to Al 2O3 deposition. The deposition temperature for aluminium oxide was 10 00˚C.

For the deposition of Al 2O3 the precursors are AlCl 3 and CO 2. Other gases needed are H 2 and HCl. H 2S is used as a catalyst. The reaction can be described by the following coupled reactions:

CO 2 + H 2 → CO + H 2O

2AlCl 3 + 3H2O → Al 2O3 + 6HCl

4.6 Film characterisation GIXRD was used to identify the phase content of the titanium dioxide films. To confirm the result the samples were analysed with Raman spectroscopy. The aluminium oxide films were analysed with θ -2θ scan (Bragg -Brentano geometry) to find out which phase it contained. To create good overview and get a better understanding of the films structure the samples were analysed using SEM. To obtain an insight of what happened during the CVD process an ESCA was performed on the samples. Sputtering aluminium oxide requires a high acceleration voltage of the beam and in the experiment the voltage used was 4 kV.

In both ALD and CVD there is a risk that residues from the precursor reactions becomes incorporated in the film and contaminates it. In this case chlorine is most likely to contaminate the films. If the chlorine content is higher in the ALD films then in the CVD films the adhesion deteriorates. By analysing the samples with XRF the amount of chlorine in the films could be determined.

4.6.1 Film thickness One of the first obstacles encountered in the experimental procedure was how to determine the thickness of the titanium dioxide films. The most common and simplest way is to analyse the film with XRF or XRR, but since the underlying layer also contains tit anium that wasn’t possible.

The solution was to use a combination of XRR and ESCA. Silicon wafers, with a native SiO 2, samples were ALD coated at the same time as Samples A, B, and C for 100, 200, 300, and 400 cycles. The silicon samples were analysed using XRR to determine the film thicknesses.

When the thickness was known the silicon samples were analysed with ESCA. The acceleration voltage used to sputter the titanium dioxide was 2 kV. From the data obtained the sputter rate for titanium dioxide was calculated. The cutting tool samples were analysed with the same settings in the ESCA and with the sputter rate known the film thickness could be calculated.

SEM was also used as an alternative method to determine the film thickness. First and foremost the thickness of the aluminium oxide and titanium carbonitride films was studied in SEM.

4.1.2 Film adhesion Good film adhesion is crucial for the survivability of a cutting tool; therefore the aluminium oxide coated samples were tested by sand blasting. The adhesion was then determined by studying the resulting damage in a light optical microscope, LOM.

5 Results

5.1 XRD characterisation The GIXRD analysis of the samples with titanium dioxide films thicker than 100 cycles showed only anatase even though the purple colour of the A sample indicated the presences of Magnéli phases. No traces of rutile were observed. The titanium dioxide films with fewer than 100 cycles were difficult to analyse because their peak intensity was too low. The main anatase peak is at 25 degrees the other peaks visible are from the underlying Ti(C,N), see Figure 8. (1,1,1) (2,2,0) (2,0,0) (3,1,1) (1,0,1) (2,2,2) (2,0,0)

20 30 40 50 60 70 80

Figure 8: Diffractograms of TiO 2 on sample C (upper curve) and reference sample C.

The aluminium oxide coate d samples were analysed with θ -2θ scans to determine the phase content of the coatings. The analysis of the samples from the SM-o001 and SM-o002 recipes showed that a film with α-Al 2O3 as the predominant phase had formed on all thicknesses of titanium dioxide, see Figure 9. The unmarked peaks are from underlying layers. (1,1,3) (1,1,6) (3,0,0) (1,0,4) (0,1,2) (1,2,2) (1,1,9) (1,1,0) (0,0,6) (2,1,4) (0,2,4) (0,1,8) (1,0,10) (2,1,1) (2,0,8) (1,2,5) (2,0,2)

20 30 40 50 60 70

Figure 9: Diffractogram of α-Al 2O3 from SM-o002 on sample C with 400 cycles of TiO 2.

SM-o003 gave κ -Al 2O3 on all samples, see Figure 10. k (a 1,1,3) k k (a 1,2,2) k (a 3,0,0) (a 1,1,6) (a 1,0,4) (a 0,1,8) (a 0,1,2) (a 1,1,0) (a 0,0,6) k (a 2,1,4) (a 0,2,4) (a 1,0,10) k k (a 1,2,5) k (a 2,0,8) k k k k k k k k k k k k k k (a 2,1,1) (a 1,1,9) (a 2,0,2) k k k k k k k k k

20 30 40 50 60 70 80

Figure 10: Diffractograms of α-Al 2O3 from SM-o002 (lower curve) and κ - Al 2O3 from SM-o003 (upper curve), on sample C

5.2 Raman characterisation The Raman spectrum, Figure 11, confirmed the results from the GIXRD that the films contained titanium dioxide in the form of anatase on all samples. The characteristic anatase peaks are at ~146 cm-1 and ~238 cm -1[17] . The peak at 238 isn’t visible because the peaks from the underlying Ti(C,N) is in the same range, Figure 12.

Raman spectrum of TiO 300 cycles 2

146,2

Intensity (a.u.)

0 200 400 600 800 1000 Raman shift (cm -1 )

Figure 11: Raman spectrum for TiO 2 300 cycles on sample C

Raman spectrum of Ti(C,N) referens

Intensity (a.u.)

0 200 400 600 800 1000 Raman shift (cm -1 )

Figure 12: Raman spectrum for Ti(C,N) reference, sample C

The Raman spectrum of the aluminium oxide films showed weak α-Al 2O3 peaks on the samples from the SM-o001, Figure 13. The analysis of the films made with the SM-o003 recipe showed

α-Al 2O3 peaks but also peaks that differed from the typical α -Al 2O3 peaks, Figure 14. There are -1 seven characteristic α-Al 2O3 peaks ~ 378, 419, 431, 445, 492, 600, 748 cm [21].

Raman spectrum SM-o001

Intensity (a.u.)

0 200 400 600 800 1000 1200 Raman shift (cm -1 )

Figure 13: Raman spectrum from SM-o001 on sample A with 400 cycles of TiO 2, α marks the α-Al 2O3 peaks.

Raman spectrum SM-o003

Intensity (a.u.)

0 200 400 600 800 1000 1200 Raman shift (cm -1 )

Figure 14: Raman spectrum from SM-o003 on sample A with 400 cycles of TiO 2, * marks the atypical peaks

5.3 ESCA on Al 2O3 The ESCA results from after the CVD were inconclusive and it was difficult to determine whether the film reached was titanium dioxide or titanium carbonitride. The sample displayed in figure 15 is Sample C with 400 cycles of TiO 2 and Al 2O3 from the SM-o001 recipe.

40 Carbon Nitrogen 30 Atomic % Atomic Oxygen 20 Aluminium 10 Titanium 0 25 30 35 40 45 Sputter time (min)

Figure 15: ESCA cross-section of the Al 2O3 and the transition to the Ti(C,N)

5.4 Evaluation of the film thickness The silicon samples coated with 200, 300 and 400 cycles were analysed with XRR to determine the thickness of the titanium dioxide film.

Table 2: XRR and ESCA analysis on TiO 2 on silicon

Number of cycles Thickness (nm) Sputter time (min) 200 8 <0,1 300 13 <0,5 400 19 1

From the ESCA analysis of the silicon samples the sputter rate of titanium dioxide was calculated.

The sputter rate for titanium dioxide was 13-19 nm/min.

The sputter rate was used to calculate the film thickness on the cutting tool samples. The film thicknesses obtained were rough approximations and the growth rate on the thicker films was questionable.

Table 3: Thickness of TiO 2 on step 9 samples

Number of cycles Thickness (nm) Sputter time (min) 200 13 -19 1 300 39 - 57 3 400 65 - 95 5

100 90 80 70 60 carbon 50 nitrogen

Atomic % Atomic 40 oxygen 30 chlorine 20 10 titanium 0 1 2 3 4 5 6 7 8 9 10 11 12 Sputter time (min)

Figure 16: ESCA cross-section of the TiO 2 film and the transition to the Ti(C,N) on Sample C with 400 cycles of TiO 2

5.5 SEM In the SEM analysis it was impossible to see the titanium dioxide and therefore the film thickness of it couldn’t be determ ined by this method. The SEM pictures gave on the other hand a good overview of the multilayer structure on the samples and the thickness of the aluminium oxide and the titanium carbonitride could be determined.

Figure17 : α -Al 2O3 on 400 cycles of TiO 2 on Sample C Figure 18 : α -Al 2O3 on 5 cycles of TiO 2 on Sample C

Figure 19 : α -Al 2O3 with bad adhesion on Sample B Figure 20 : κ -Al 2O3 from the SM-o003 recipe

5.6 XRF The XRF analysis showed no direct contaminations of chlorine in the films. The chlorine content was the same before and after the deposition of the titanium dioxide.

5.7 Film adhesion The adhesion of the aluminium oxide film varied from different film thicknesses of the titanium dioxide and from different types of samples. Best adhesion had the 5 and 10 cycle thick films on Sample C.

Figure 21: LOM picture of SM-o001 on Sample B Figure 22: LOM picture of SM-o001 on Sample C with 400 cycles of TiO 2 with 50 cycles of TiO 2

Figure 21 displays a sample with poor adhesion, the coating is flaking from the sample surface. Figure 22 displays a sample with good adhesion.

6 Discussion The aims of the thesis were achieved; the aluminium oxide films deposited on titanium dioxide had the desired phase content, α-Al 2O3. The thinnest titanium dioxide films gave the best properties of the α -Al 2O3 and good adhesion. On the samples with thicker titanium dioxide films the adhesion was poor and the SEM analyses on some of the samples showed that the interface was porous. Sample C had the best adhesion. No increase in the chlorine content was detected.

The deposited titanium dioxide films contained mostly anatase but also some Magnéli phases which gave Sample A a purple colour. This was interesting in itself, apart from the original aim of the thesis because new colours are always popular on the market.

After the aluminium oxide was deposited the TiO 2 could no longer be detected. The ESCA probably could have given more answers but the analysis becomes too time-consuming when thick aluminium oxides films are analysed. To understand what happened with the titanium dioxide more analyses are required, for example transmission electron microscopy (TEM). One suggestion is that some of the oxygen in the TiO 2 was consumed during the Al 2O3 deposition and Magnéli phases were formed instead. Another proposition is that phases with Ti-Al-O have formed in the interlayer.

7 Conclusions

α-Al 2O3 was successfully deposited on a thin layer of titanium dioxide. Thinner titanium dioxide films gave better adhesion, thicker films also gave α -Al 2O3 but with poor adhesion. Further research on the subject of what happens to the titanium dioxide during the aluminium oxide deposition is needed. It would be interesting to investigate even thinner titanium dioxide films to determine how much is needed. Is only one cycle enough?

If the technique is to be used in industrial scale more research is required on how to adapt the process.

8 Acknowledgements First and foremost I would like to thank my supervisors Tommy Larsson and Mats Boman for making this project possible and for their valuable guidance and advises throughout the entire time. I would also like to thank Oscar Alm for all the good advises and the help at Seco Tools. I would like to thank Mattis Fondell for teaching me how to handle Picosun, helping me with many of the analyses and for always answering my more stupid questions.

Thanks to Mikael Ottoson, for reviewing my report and helping me with the XRD analysis. Special thanks to all my co-workers at the material chemistry department and Seco Tools for making me feel like home and for all of the fun discussions and memorable moments. David Rehnlund and Jonas Ångström it would not have been the same without you, thanks for all your help and support.

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