Chapter One  Abnormal membrane rupture（25strip）

§1.1 Glass substrate film cracking（4strip）

1.1.1 glass substrateARMembrane rupture

【abnormal phenomenon】Network or linear cracks appear on the surface of the glass substrate after coating，Peel off at the interface between the film layer and the substrate，Optical inspection reveals an increase in scattering。

【Root cause analysis】

(1) Mismatched coefficient of thermal expansion：SiO2(0.5×10⁻⁶/℃)with glass(9×10⁻⁶/℃)significant difference，Shear stress is generated during cooling

(2) Excessive internal stress in the film layer：Low particle energy in evaporation process，The film layer is in a state of compressive stress(-50~-200MPa)

(3) The substrate temperature is too high：Exceeding the glass transition temperature(Tgabout550-600℃)，Thermal relaxation stress generated during cooling

(4) Excessive film thickness：Single layer film thickness exceeding2μmWhen，Significant increase in stress accumulation

(5) The cooling rate is too fast：The cooling rate inside the cabin exceeds10℃/min，Causing temperature gradient stress

【solution】

Option One（Emergency diagnosis）：

→ use100Observation of crack morphology under a microscope，Mesh like structure is subjected to thermal stress，Straight lines represent mechanical stress

→ UV-3700Measure transmittance curve，The significant decrease in transmittance in the shortwave region is due to internal cracks in the film layer

→ Record the coating process parameters：substrate temperature、evaporativity、vacuum degree、Cooldown

→ Compare the differences in process parameters between cracked samples and normal samples

Option 2（Process adjustment）：

→ Reduce the substrate temperature to room temperature~80℃，Temperature rise control during evaporation coating50℃within

→ Thick film layer(>1μm)Split into multiple layers and thin layers，Thickness of each layer0.3-0.5μm

→ Add transition layer：glass/NiCr/SiO2system，NiCrlayer50-100Å

→ Electron beam evaporation rate from2-5Å/sdrop to0.5-1Å/s

→ When designing the membrane system, control the total membrane thickness not to exceed5μm

→ Charge during coolingN2，Control the cooling rate3-5℃/min

Option Three（settle sth. once and for all）：

→ Thermal stress testing：Muffle furnace5℃/minHeat up to300℃，thermal insulation30min，natural cooling

→ Replace the film material：useAl2O3(α=7×10⁻⁶/℃)substituteSiO2，Reduce thermal expansion differences

→ Add substrate water cooling system，Temperature control throughout the coating process

→ Establish stress testing standards：Tencor FLX-2320measurement，Control stress±50MPa

→ Optimizing membrane design software to simulate stress distribution，Perform finite element analysis before design

→ Establish a database for the thermal expansion coefficient of film materials，Perform matching calculations when selecting materials

【preventive measures】

• Calibrate thermocouples before each batch of coating，Ensure accurate display of substrate temperature

• Establish a database for the thermal expansion coefficient of film materials，Perform matching calculations when selecting materials

• Film thickness exceeds5μmTime division multiple evaporation，Every interval cooling2hthe above

• Establish a record table for coating process parameters，Trace the cause of the anomaly

【Precautions】

⚠ After coating the glass substrate24hDo not perform heat treatment or cleaning inside，Allow stress to relax naturally

⚠ Do not forcefully peel off the film layer of the cracked sample，May cause glass breakage

⚠ Do not use ultrasonic cleaning in the cracked area of the membrane

1.1.2 Glass substrate infrared film cracking

【abnormal phenomenon】mid-wave infrared(3-5μm)Or long wave infrared(8-14μm)Cracks appear on the glass substrate in the film system，Affects infrared transmittance。

【Root cause analysis】

(1) Infrared film materialGe、SiThe coefficient of thermal expansion differs greatly from that of glass，Ge(5.9×10⁻⁶/℃)、Si(2.5×10⁻⁶/℃)

(2) Infrared film is usually thicker(>10μm)，More severe stress accumulation

(3) Infrared coating requires a higher substrate temperature(150-250℃)，Large cooling temperature difference

(4) ZnS、ZnSeThe adhesion between the film material and the substrate is weak

(5) In the infrared film systemH/LAlternating layers，Different membrane materials have inconsistent stress directions

【solution】

Option One（Emergency diagnosis）：

→ FTIRSpectrometer measures transmittance，3-5μmperhaps8-14μmDecreased band transmittance

→ Infrared thermal imager detects the temperature distribution on the film surface，There may be cracks in uneven areas

→ Microscopic observation of crack direction，Determine whether it is thermal stress or mechanical stress

Option 2（Process adjustment）：

→ Reduce the substrate temperature to100-150℃，Using ion assisted deposition(IAD)

→ Add buffer layer：glass/SiO2(200nm)/Infrared film system

→ ZnSThe evaporation rate decreases2-3Å/s，Geevaporativity1-2Å/s

→ Adopting layered coating：Each plating2-3Shutdown cooling after layer30min

→ Using ion beam assisted deposition(IBAD)，Improve film density and adhesion

Option Three（settle sth. once and for all）：

→ Switching to a film material with a thermal expansion coefficient closer to glass：in compliance withCdTe(α=4.9×10⁻⁶/℃)

→ useGeReplacing glass substrates with substrates for infrared optical components

→ Design stress balance membrane system：Alternating between compressive stress layer and tensile stress layer

→ Introducing plasma pretreatment，Improve interface bonding strength

→ Establish stress testing standards for infrared films：After plating24hMeasure stress values

【preventive measures】

• The substrate must be preheated before infrared film coating100℃the above，Remove surface moisture

• ZnSBefore using the film material, it is necessary to200℃prebake 2hremove moisture

• Vacuum degree required for infrared film coating chamber≤3×10⁻³Pa，Prevent oxidation

【Precautions】

⚠ Infrared film cannot be directly touched by hand，The oil in fingerprints will absorb infrared light

⚠ Infrared film samples need to be stored dry，humidity>60%Will cause hydrolysis of the membrane layer

1.1.3 Optical glass thick film cracking

【abnormal phenomenon】thickness>5mmEdge or center cracks appear on optical glass after coating，Large size glass(>200mm)More likely to occur。

【Root cause analysis】

(1) Thick glass has a large thermal capacity，Uneven heating generates temperature gradient stress

(2) Glass edges dissipate heat quickly，Slow central heat dissipation，Radial temperature difference can reach30-50℃

(3) Stress concentration at the contact point of the fixture，Difference in thermal expansion coefficient between glass and metal fixtures

(4) The self weight of thick glass causes the stress difference between the bottom and the top facial mask layer

(5) There are residual stresses inside the partially annealed glass，Overlay after coating

【solution】

Option One（Emergency diagnosis）：

→ Polarization stress meter for detecting stress distribution inside glass

→ Measure the starting point of the crack：The edge starts with a thermal gradient，The center starts from the stress of the fixture

→ Check if there are any indentations or damages at the contact points between the fixture and the glass

Option 2（Process adjustment）：

→ Using a circular heater，Ensure uniform temperature on the glass surface(temperature difference<5℃)

→ Replace the fixture with a material with an expansion coefficient close to glass(Like graphite、ceramics)

→ Add preheating stage：with2℃/minSlowly raise the temperature to the coating temperature

→ Add support at the bottom of the glass，Reduce self weight stress

→ Slowly cool after coating：with1-2℃/minCool down to100℃below

Option Three（settle sth. once and for all）：

→ Pre treatment of glass using an optical annealing furnace，Eliminate internal stress

→ Switching to low expansion glass(Like borosilicate glassα=3.3×10⁻⁶/℃)

→ Design specialized fixtures：Multi point flexible support，Avoid point contact

→ Establish temperature field simulation：ANSYSAnalyze temperature gradient distribution

→ For>300mmglass，Adopting zone heating technology

【preventive measures】

• Stress testing must be conducted before coating thick glass，σ>5MPaAnnealing treatment is required

• Fixture design needs to consider thermal expansion compensation，contact area>50%

• Add circulating air to the coating room，Improve temperature uniformity

【Precautions】

⚠ After thick glass coating, suction cups are required for transportation，Avoid edge stress

⚠ Thick glass with cracked film cannot be reworked，Stress has altered the internal structure

1.1.4 Mobile phone cover glass film cracked

【abnormal phenomenon】Mobile phone cover glass(Corning Gorilla、Xujianzi Longji and others)plateAF/ARHair like cracks appear behind the membrane。

【Root cause analysis】

(1) The cover glass has undergone chemical strengthening，There is a compressive stress layer on the surface(about100-200MPa)，Overlay after coating

(2) Thin glass thickness(0.5-1.1mm)，Low flexural strength

(3) Uneven glass surface after chemical strengthening，Uneven film thickness

(4) AFmembrane(fluoride)Poor adhesion with glass，Stress generated by membrane shrinkage

(5) Inconsistent film stress between silk screen ink area and transparent area

【solution】

Option One（Emergency diagnosis）：

→ Check the crack location：Stress concentration occurs at the edge of the ink，Randomly distributed as thermal stress

→ Measure the stress of the glass reinforcement layer：Surface stress gauge detectionCS>800MPaMaybe too high

→ checkAFfilm thickness：>20nmEasy to cause shrinkage cracks

→ Compare the cracking rates of glass from different suppliers

Option 2（Process adjustment）：

→ controlAFThe film thickness is8-15nmscope

→ Reduce the coating temperature to<80℃，Adopting low-temperature evaporation

→ AFMembrane evaporation in two stages，each time5-8nm，Intermediate interval cooling

→ Add bottom layer：SiO2(5nm)/AFmembrane，Improve adhesion

→ Control the humidity inside the coating room<30%，preventAFmembrane hydrolysis

→ Pre treatment of ink area：Plasma cleaning to remove organic matter

Option Three（settle sth. once and for all）：

→ Negotiate with glass suppliers，Control chemical strengthening stressCS<750MPa

→ Switching to physical vapor deposition(PVD)Alternative evaporation method，The film layer is denser and has lower stress

→ Develop specialized low stressAFFilm material

→ Design stress relief structure：Edge retention0.5mmNon coated area

→ Establish glass incoming inspection standards：Strengthening layer stress、surface roughness

【preventive measures】

• The incoming cover glass must be inspected for strengthening layer stress，Return of batches exceeding the standard

• Plasma cleaning parameters before coating：Arqi100sccm，power200W，time60s

• AFThe film material needs low temperature(-20℃)storage，Prevent volatilization

【Precautions】

⚠ AFAfter film plating24hDo not bend test inside，The film layer needs to be cured

⚠ AFThe membrane cannot come into contact with organic solvents，Will dissolve the film layer

§1.2 Sapphire substrate film cracking（4strip）

1.2.1 LEDSapphire substrate film cracking

【abnormal phenomenon】LEDUsing sapphire substrate(Al2O3)plateITOperhapsDBRCracks appear behind the membrane，Affects chip yield。

【Root cause analysis】

(1) Sapphire thermal expansion coefficient(5.3×10⁻⁶/℃)giveITO(7×10⁻⁶/℃)There are differences

(2) Thin thickness of sapphire substrate(100-430μm)，Easy to bend and deform

(3) ITOHigh requirements for film resistivity(>1×10⁻⁴Ω·cm)，Film thickness required>200nm

(4) MOCVDThere is thermal stress on the substrate after high-temperature growth，Overlay after coating

(5) Sapphire has different crystal orientations on its surface(0001)、(11-20)，The growth stress of the film layer is different

【solution】

Option One（Emergency diagnosis）：

→ Microscopic observation of crack direction：Internal stress along the crystal direction，Random external stress

→ measurementITOsheet resistance，>15Ω/□Possible insufficient film thickness or cracking

→ XRDtestingITOcrystal orientation，(222)Low orientation stress

→ Check the sapphire crystal orientation markings，Adjustment process for different crystal orientations

Option 2（Process adjustment）：

→ ITOSedimentation temperature from300℃drop to200-250℃

→ Sputtering power from3W/cm²drop to1.5-2W/cm²

→ O2/ArThe ratio is from2:8adjust1:9，Reduce oxidative stress

→ increaseTiO2buffer layer(20nm)：sapphire/TiO2/ITO

→ ITOThickness is deposited in two stages：each time100nm，Intermediate annealing30min

→ Rapid annealing after sputtering(RTA)：600℃、N2atmosphere、30s

Option Three（settle sth. once and for all）：

→ switch toIZO(Indium zinc oxide)substituteITO，Lower stress

→ Using pulsed laser deposition(PLD)perhapsALDtechnology

→ Sapphire surface treatment：N2Plasma activation，increase dangling bonds

→ Design stress compensation layer：compressive stressTiO2+Tensile stressITOalternate

→ Establish wafer level stress mapping：Stress testing before plating on each substrate

【preventive measures】

• Sapphire incoming materials must be inspected for curvature，>30μmReject

• ITOTarget purity required>99.99%，Impurities cause uneven stress

• Sapphire needs to be coated before200℃bake30minRemove water vapor

【Precautions】

⚠ Sapphire substrates cannot be stacked，Edge contact can generate microcracks

⚠ Membrane crackingLEDThe chip cannot be reworked，The lattice has been damaged

1.2.2 Sapphire optical window film cracking

【abnormal phenomenon】Sapphire optical window(Watch surface、optical lens)plateARCracks or broken edges appear behind the membrane。

【Root cause analysis】

(1) Sapphire has high hardness but high brittleness，Micro cracks are prone to occur at the edges

(2) ARThe membrane is usually composed of multiple layers of oxides(SiO2/TiO2alternate)，total thickness2-5μm

(3) sapphirecface(0001)There is a significant difference in stress compared to other crystal surface coatings

(4) Sudden change in film thickness at the chamfer of the window edge，stress concentration

(5) Sapphire has good thermal conductivity，Fast edge cooling during coating，Uneven temperature

【solution】

Option One（Emergency diagnosis）：

→ Crack at the chamfered edge→Improper chamfering or excessive film thickness

→ Crack in the central area→Thermal stress or internal stress within the film layer

→ Edge collapse accompanied by cracks→mechanical damage，Non membrane issues

→ Comparison of different batches，Exclude the issue of sapphire incoming materials

Option 2（Process adjustment）：

→ Edge area occlusion coating：Using a mask plate，Not plated at the chamfer

→ Reduce the total film thickness：ARMembrane fromλ/4design changedλ/8Design

→ Using ion assisted deposition(IAD)：Increase membrane density and reduce stress

→ Sputtering replaces evaporation：The film layer is more uniform，Better stress distribution

→ Control the coating temperature<150℃，Reduce thermal stress

Option Three（settle sth. once and for all）：

→ Sapphire edge laser chamfering+chemical polishing，Eliminate microcracks

→ Develop specialized low stressARCoating System：SiO2/Al2O3substituteSiO2/TiO2

→ Adopting stress gradient design：Bottom layer low stress→Top level high stress

→ Using plasma cleaning to enhance interface bonding

→ Establish a dedicated coating process standard for sapphire windows

【preventive measures】

• Sapphire edges require laser chamfering+chemical polishing

• Acetone is used before coating+Ultrasonic cleaning with anhydrous ethanol5min

• Flexible support is required for the edges during window installation，Avoid hard contact

【Precautions】

⚠ Sapphire film cannot be repaired after cracking，Can only be replaced

⚠ Fragments may be generated at the edge of the cracked sample，Pay attention to protection

1.2.3 Sapphire decorative piece film cracking

【abnormal phenomenon】Sapphire decorative piece(Mobile camera protection cover、button)Decorative film plating(Color film)Later cracks appeared。

【Root cause analysis】

(1) Decorative film usually contains a metal layer(Cr、Ti)，There is a significant difference in thermal expansion coefficient between sapphire and sapphire

(2) Total thickness of decorative film>5μm，Far thicker thanARmembrane

(3) Decorative components have complex shapes，Uneven distribution of membrane stress at curved surfaces

(4) Volume expansion of metal layer after oxidation，Generate compressive stress

(5) multilayer metal/Oxide alternation，Accumulation of interface stress

【solution】

Option One（Emergency diagnosis）：

→ Cracks distributed along the curved surface→Shape causes stress concentration

→ Cracks in the metal layer area→Metal oxidation or excessive stress

→ Color change accompanied by cracks→The metal layer has been oxidized

→ Compare flat and curved samples，Determine the influence of shape

Option 2（Process adjustment）：

→ The thickness of the metal layer is controlled within<50nm，Reduce stress

→ useTisubstituteCr：TiBetter adhesion with sapphire

→ increaseSiO2protective layer：Covering above the metal layer50nm SiO2

→ Using arc-shaped fixtures：Match with the shape of decorative parts，Uniform support

→ Reduce the coating temperature to room temperature，Using electron beam evaporation

→ Step by step coating：Metal layer+Protective layers are plated separately

Option Three（settle sth. once and for all）：

→ Develop a specialized decorative film system：TiN/Si3N4Alternative metals/oxide

→ Using physical vapor deposition(PVD)Sputtering technology

→ Design stress relief groove：Slot on the back of decorative parts

→ Pre treatment using plasma nitriding，Enhance binding strength

→ Establish a specialized coating process library for decorative parts

【preventive measures】

• Before coating decorative parts, plasma cleaning is required：Ar 100sccm、200W、60s

• Purity of metal target material>99.9%，Impurities cause uneven film layer

• Decorative film color monitoring：Real time detection of online photometer

【Precautions】

⚠ Decorative film non scratch test，The metal layer is easily scratched

⚠ After the decorative film cracks, the color will change，Need to be replaced as a whole

1.2.4 Sapphire epitaxial film cracking

【abnormal phenomenon】sAPPHIrE wAFEr (GaN on sapphire)Cracks appear when plating current extension layer or passivation layer。

【Root cause analysis】

(1) GaNMismatch with sapphire lattice13.8%，There is already a high dislocation density after epitaxy

(2) Large warpage of epitaxial wafers(>100μm)，Local stress concentration during coating

(3) Current expansion layer(ITO/Ag)High temperature annealing is required，Thermal stress superposition

(4) passivation layer(SiN)Surface defects caused by plasma damage

(5) Thin thickness of epitaxial wafer(2-4μm)，Low mechanical strength

【solution】

Option One（Emergency diagnosis）：

→ PLspectral detection：The luminescence intensity at the crack decreases

→ Warpage measurement：>150μmHigh risk of membrane rupture

→ microscope observation：Cracking along the dislocation line is due to internal stress

→ Compare the film cracking rate of epitaxial wafers with different warpage degrees

Option 2（Process adjustment）：

→ ITOThe sedimentation temperature drops to200℃，Sputtering power reduced to1W/cm²

→ AgThe layer thickness is controlled within<100nm，Reduce stress

→ SiNUse of passivation layerPECVDsubstituteICP，Reduce plasma damage

→ increaseTi/Al/Tibuffer layer：Improve interface stress

→ Fixed epitaxial wafers using vacuum adsorption，Avoid mechanical clamping stress

→ Annealing before coating：300℃、N2atmosphere、10min

Option Three（settle sth. once and for all）：

→ Adopting stress matching epitaxial technology：AlNBuffer layer optimization

→ Developing low-temperature processes：ALDdepositionITO(150℃)

→ Using flexible electrodes：Graphene replacementITO

→ Design stress relief structure：Etching grooves on the back of epitaxial wafers

→ Establish the warpage of epitaxial wafers-Model of membrane rupture rate relationship

【preventive measures】

• Incoming warpage of epitaxial wafers<80μm，Exceeding the standard requires annealing treatment

• ITOTarget density>99%，Ensure uniform film layer

• Before coatingGaNSurface needsN2Plasma cleaning

【Precautions】

⚠ Epitaxial wafers are extremely brittle，Vacuum suction pen must be used for retrieval and placement

⚠ Epitaxial wafers with cracked film cannot be reworked，Dislocation has expanded

§1.3 silicon wafer/Germanium substrate film cracking（4strip）

1.3.1 Silicon wafer infrared film cracking

【abnormal phenomenon】Silicon wafer coated with infrared anti reflective film(3-5μmperhaps8-14μm)Later cracks appeared，Affects the performance of infrared detectors。

【Root cause analysis】

(1) Silicon thermal expansion coefficient(2.5×10⁻⁶/℃)giveZnS(7.5×10⁻⁶/℃)significant difference

(2) Thin silicon wafer thickness(300-500μm)，Easy to bend

(3) Infrared film is usually thicker(>5μm)，Significant stress accumulation

(4) Silicon wafer surface oxide layer(SiO2)Poor adhesion with infrared film

(5) Coating temperature>200℃When，Silicon wafer experiences slip deformation

【solution】

Option One（Emergency diagnosis）：

→ FTIRmeasurement3-5μmperhaps8-14μmTransmittance，<90%Possible membrane rupture

→ Microscopic observation of crack direction：Along the crystal direction(110)For internal stress

→ Warpage measurement：>50μmThe film layer has cracked

→ Electrical testing：Abnormal resistance at the membrane rupture site

Option 2（Process adjustment）：

→ Reduce the coating temperature to100-150℃，adoptIADassistant

→ ZnSevaporativity2-3Å/s，Geevaporativity1Å/s

→ increaseSiO2buffer layer(100nm)：silicon/SiO2/Infrared film

→ adoptGe/ZnSAlternating membrane system，Reduce single-layer thickness

→ Slowly cool after coating：with2℃/mincool down

→ Silicon wafer fixation using vacuum adsorption，Avoid clamping stress

Option Three（settle sth. once and for all）：

→ Surface pretreatment of silicon wafer：HF溶液(1%)soak30s，Remove the oxide layer

→ Develop a dedicated low stress infrared film system：Si/SiGeGradient layer

→ Using molecular beam epitaxy(MBE)Technology replaces evaporation

→ Design stress balance membrane system：Compressive stress layer+Alternating tensile stress layers

→ Establish the curvature of silicon wafers-Membrane cracking rate database

【preventive measures】

• Warping degree of incoming silicon wafers<30μm，Excessive annealing treatment

• Before coating, the silicon wafer needs toHFhandle+DIwater rinse

• ZnSBefore using the film material200℃bake2h

【Precautions】

⚠ Silicon wafers cannot be touched by hand，Na+Pollution affects device performance

⚠ Film cracked silicon wafers cannot be reworked，The lattice has been damaged

1.3.2 Germanium infrared film cracking

【abnormal phenomenon】Germanium sheet(Ge)Red coated outer film(8-14μmanti-reflection)Later cracks appeared，GeIt is a commonly used substrate for long wave infrared。

【Root cause analysis】

(1) Gecoefficient of thermal expansion(5.9×10⁻⁶/℃)giveZnSe(7.0×10⁻⁶/℃)Close but still have differences

(2) GeLow hardness(Mohs 6)，Easy to scratch and generate stress concentration points

(3) GeSurface is prone to oxidation and formationGeO2，Poor adhesion with the membrane layer

(4) Long wave infrared film system has multiple layers(>20layer)，total thickness>10μm

(5) Gestay>100℃When the intrinsic carrier concentration increases，Temperature limitation of coating

【solution】

Option One（Emergency diagnosis）：

→ FTIRmeasurement8-14μmTransmittance，GeDouble sided coating should be applied>95%

→ microscope observation：Priority cracking at the scratch site→Surface damage is the main cause

→ Resistivity measurement：Abnormal resistivity at the membrane rupture site(Intrinsic excitation)

→ Comparing different surface roughnessGeFilm cracking rate

Option 2（Process adjustment）：

→ Reduce the coating temperature to80-100℃，Using ion beam assistance

→ GeSurface pretreatment：HCl(10%)soak1minRemove oxides

→ ZnSeevaporativity1-2Å/s，Low rate stress reduction

→ increaseBaF2buffer layer：Ge/BaF2(50nm)/ZnSe

→ Membrane design：Reduce the number of layers，Replace multiple thin layers with thick layers

→ After coating, chargeN2cooling，avoid oxidation

Option Three（settle sth. once and for all）：

→ GeSurface ion implantation：N+Inject to enhance surface hardness

→ developmentGeON(Germanium oxynitride)passivation layer

→ Switching to sputtering technology：The membrane layer is denser，Lower stress

→ DesignGe/GeO2Gradient layer：Reduce interface mutations

→ establishGeSurface treatment standards for films：roughness、cleanliness

【preventive measures】

• GeTablets need to be stored dryN2atmosphere，humidity>40%surface oxidation

• Before coatingGeThe film mustHClhandle+DIwater rinse+N2blow-dry

• ZnSePurity of membrane material>99.99%，Impurities absorb infrared light

【Precautions】

⚠ GeThe film should not come into contact with hard objects，Extremely easy to scratch

⚠ Membrane ruptureGeThe piece cannot be reworked，GeO2The layer has been damaged

1.3.3 Silicon wafer laser film cracking

【abnormal phenomenon】Laser damage threshold film for silicon wafer plating(1064nmaltitude sickness/High Transparency)Later cracks appeared。

【Root cause analysis】

(1) There are many laser film layers(>30layer)，total thickness>15μm

(2) SiO2/Ta2O5In the membrane systemTa2O5High stress(>100MPa)

(3) Laser film requires high-temperature annealing(>300℃)Raise the damage threshold，Thermal stress superposition

(4) Silicon wafer has high thermal conductivity(148W/m·K)，Fast edge heat dissipation

(5) Instantaneous increase in thermal stress of the film layer during high-power laser irradiation

【solution】

Option One（Emergency diagnosis）：

→ 1064nmLaser damage threshold testing：1-on-1test

→ Surface morphology of film layer：SEMObserving microcracks

→ Measurement of membrane stress：Curvature method calculation

→ Compare the damage threshold and film cracking rate at different annealing temperatures

Option 2（Process adjustment）：

→ Ta2O5Sputtering replaces electron beam evaporation，Reduce stress

→ Annealing temperature from400℃drop to250℃，Time extended to2h

→ increaseSiO2protective layer：top level200nm SiO2

→ adoptHfO2substituteTa2O5：HfO2Less stress

→ Membrane design：Reduce the thickness of the high refractive index layer

→ Laser film is deposited in two stages：Half thickness each time，Intermediate annealing

Option Three（settle sth. once and for all）：

→ Developing ion beam sputtering(IBS)Laser film：The highest density、Minimum stress

→ Using picosecond laser annealing：Local annealing，Reduce thermal stress

→ Design stress gradient membrane system：Bottom layer low stress→Top level high stress

→ Coarsening of silicon wafer backside：Increase heat dissipation area

→ Establish laser film damage threshold-Model of membrane rupture rate relationship

【preventive measures】

• The annealing of silicon wafer laser film must be carried out beforeN2atmosphere，Prevent oxidation

• Ta2O5Target purity>99.99%，Impurities reduce damage threshold

• Cleanliness of laser film plating room100level，Dust causes damage

【Precautions】

⚠ Laser film testing must start from low power，Prevent instantaneous damage

⚠ Laser film with membrane cracking cannot be used for high-power systems

1.3.4 SOI/SiCWaiting for special silicon film cracking

【abnormal phenomenon】SOI(Silicon on insulator)perhapsSiC(silicon carbide)Cracks appear after coating，forMEMSOr power devices。

【Root cause analysis】

(1) SOIThere is a buried oxygen layer in the structure(BOX)，The difference in thermal expansion coefficient leads to interface stress

(2) SiCExtremely high hardness(Mohs 9.2)，But it is brittle

(3) SiCHigh surface roughness(Ra>1nm)，Incomplete membrane coverage

(4) SOITop layer silicon thin(<100nm)，Low mechanical strength

(5) SiCGood thermal conductivity(490W/m·K)，Low temperature gradient stress but fast cooling

【solution】

Option One（Emergency diagnosis）：

→ Crack passes throughBOXlayer→SOIProblems with the structure itself

→ Cracks in the top layer of silicon→Coating stress or process issues

→ AFMmeasurementSiCsurface roughness，Ra>2nmPolishing is required

→ contrastSOIMembrane cracking rate of bulk silicon samples

Option 2（Process adjustment）：

→ SOICoating temperature<150℃，avoidBOXLayer stress

→ SiCSurface pretreatment：Chemical mechanical polishing(CMP)toRa<0.5nm

→ SiCPlasma cleaning before coating：SF6/O2，Remove surface carbon

→ adoptALDtechnology：low temperature(<200℃)、Good shape retention

→ SOIFixed use of vacuum adsorption，Avoid clamping

Option Three（settle sth. once and for all）：

→ developmentSOISpecialized low stress film system：Polycrystalline silicon gradient layer

→ SiCSurface nitriding treatment：Si3N4passivation layer

→ adoptFCVA(Filter cathode vacuum arc)technology

→ Design stress relief structure：SOIBackside etching

→ establishSOI/SiCSpecialized Coating Process Standards

【preventive measures】

• SOIIncoming materials must be inspectedBOXlayer quality，bubble-free

• SiCBefore coating, it is necessary toCMPPolish toRa<0.5nm

• ALDPrecursor purity>99.999%

【Precautions】

⚠ SOINot suitable for ultrasonic cleaning，BOXLayer may peel off

⚠ SiCThe cracked sample cannot be reworked，Surface has been damaged

§1.4 Metal substrate film cracking（3strip）

1.4.1 Copper substrate film cracking

【abnormal phenomenon】copper(Cu)Cracks appear after the substrate is coated with decorative or functional film，bronze mirror、Common problems with copper radiators and other products。

【Root cause analysis】

(1) Cucoefficient of thermal expansion(16.5×10⁻⁶/℃)extremely high，Significant difference from most film materials

(2) CuSurface is prone to oxidation and formationCu2O/CuO，Poor adhesion between film layer and oxide

(3) CuLow hardness(Mohs 3)，Easy to suffer mechanical damage after coating

(4) CuExcellent thermal conductivity(401W/m·K)，Small temperature gradient but extremely fast cooling

(5) CugiveNi、CrThe film material is prone to diffusion，Formation of brittle intermetallic compounds

【solution】

Option One（Emergency diagnosis）：

→ Cracks distributed along grain boundaries→Cucoarse grain ，Annealing treatment is required

→ Cracks in the oxide layer→CuSevere surface oxidation

→ Priority cracking at the scratch site→Surface mechanical damage

→ Compare polished and unpolishedCuThe membrane cracking rate of the sample

Option 2（Process adjustment）：

→ CuSurface pretreatment：rareH2SO4(10%)Soak to remove oxides

→ increaseNibottom layer(50-100nm)：Cu/Ni/Functional film

→ Reduce the coating temperature to room temperature，Using electron beam evaporation

→ Adopting electroplating+Vacuum plating composite process

→ CuSurface roughening：sandblastingRa=0.5-1μmIncrease adhesion

→ Control cooling rate：chargeN2slow cooling

Option Three（settle sth. once and for all）：

→ CuSurface chemical platingNi-P(5-10μm)：Complete isolationCuCompared to the membrane layer

→ developmentCuSpecialized low stress film system

→ Replacing vacuum plating with thermal spraying：Thicker film layer、Less stress

→ CuSubstrate annealing treatment：600℃、H2atmosphere、1h

→ establishCuSurface treatment standards：polishing、Passivation、roughness

【preventive measures】

• CuThe incoming materials must be inspected for the thickness of the oxide layer，>10nmAcid washing is required

• CuBefore coating, it is necessary toH2SO4handle+DIwater rinse

• CuStorage needs to be dry，humidity>50%Accelerated surface oxidation

【Precautions】

⚠ CuThe cracked sample cannot be reworked，Cu2OThe layer has been damaged

⚠ CuNot suitable for high temperatures(>200℃)Coating environment

1.4.2 Aluminum substrate film cracking

【abnormal phenomenon】aluminium(Al)Cracks appear on the substrate after coating，aluminum alloy doors and windows、Common problems with car wheels and other products。

【Root cause analysis】

(1) Alcoefficient of thermal expansion(23×10⁻⁶/℃)It is the highest among all metals

(2) AlSurface oxide layer(Al2O3)Dense and thick(2-5nm)，Poor adhesion with the membrane layer

(3) AlLow hardness(Mohs 2.75)，Easy to deform and generate stress

(4) AlReacts with many film materials to generate brittle compounds

(5) In aluminum alloyMg、SiInfluence of elements on film growth

【solution】

Option One（Emergency diagnosis）：

→ Cracks along the processing pattern→Mechanical stress is predominant

→ Random distribution of cracks→Thermal stress or internal stress within the film layer

→ Measurement of oxide layer thickness：EDXtestingOcontent

→ Compared to pureAlFilm cracking rate of aluminum alloy

Option 2（Process adjustment）：

→ AlSurface anodizing：generate10-20μm Al2O3layer

→ Reduce the coating temperature to<80℃，Using evaporation method

→ increaseTibottom layer(20nm)：Al/Ti/Functional film

→ Using magnetron sputtering instead of evaporation：Better adhesion of film layer

→ AlSurface sandblasting：Ra=1-2μmAdd mechanical locking

→ Control cooling rate<5℃/min

Option Three（settle sth. once and for all）：

→ AlSurface micro arc oxidation(MAO)：Generate ceramic layer

→ developmentAlSpecialized conversion film：Chromates or zirconates

→ adoptPVD-Albottom layer：Sputtering firstAlLayer by layer functional film

→ DesignAl/Al2O3Gradient layer：Reduce interface mutations

→ establishAlSurface treatment process library

【preventive measures】

• AlThe incoming materials must be inspected for the oxide layer，Thick oxide layer requires acid washing

• AlAnodizing or chemical conversion treatment must be carried out before coating

• AlNot suitable for long-term exposure to humid environments

【Precautions】

⚠ AlThe cracked sample cannot be reworked，The oxide layer has been damaged

⚠ AlCoating temperature is not acceptable>150℃，Will soften

1.4.3 Stainless steel substrate film cracking

【abnormal phenomenon】stainless steel(SUS304/316)Cracks appear after plating decorative or functional films。

【Root cause analysis】

(1) Thermal expansion coefficient of stainless steel(17×10⁻⁶/℃)There is a significant difference compared to oxide film materials

(2) Passivation film on stainless steel surface(Cr2O3)dense，Poor adhesion with vacuum coating

(3) Residual stress exists after stainless steel processing，Overlay after coating

(4) Stainless steelNi、CrReaction between elements and membrane materials

(5) Low surface roughness of stainless steel，Weak mechanical locking force

【solution】

Option One（Emergency diagnosis）：

→ Cracks along the processing pattern→Mechanical residual stress

→ Crack at the weld seam→Welding stress concentration

→ Surface passivation film detection：XPStestingCr2O3thickness

→ Compare the membrane cracking rates of polished and brushed stainless steel

Option 2（Process adjustment）：

→ Surface pretreatment of stainless steel：HCl(15%)+HNO3(5%)pickling

→ increaseCrbottom layer(50nm)：stainless steel/Cr/Functional film

→ Using magnetron sputtering：Ion bombardment to remove passivation film

→ Before coatingArplasma cleaning：500W、10min

→ Control the coating temperature<200℃

→ Surface roughening：sandblastingRa=0.3-0.8μm

Option Three（settle sth. once and for all）：

→ Nitriding treatment on stainless steel surface：generateCrNlayer

→ Develop a specialized stainless steel base coating process

→ Adopting multi arc ion plating：High energy ion cleaning surface

→ Design stress gradient membrane system

→ Establish surface treatment standards for stainless steel

【preventive measures】

• Stainless steel incoming materials must have the passivation film removed

• Plasma cleaning is necessary before stainless steel coating

• Stainless steel cannot be used for high temperatures(>300℃)Coating

【Precautions】

⚠ Stainless steel film cracked samples can be reworked，But it needs to be pickled again

⚠ Stainless steel welded parts must be annealed to relieve stress before coating

§1.5 Plastic/Organic substrate film cracking（4strip）

1.5.1 PMMA(acrylic)Membrane rupture

【abnormal phenomenon】PMMA(Polymethyl methacrylate)plateAR/AFCracks appear behind the membrane，optical lens、Display supplies, etc。

【Root cause analysis】

(1) PMMAcoefficient of thermal expansion(70×10⁻⁶/℃)extremely high，It's glass7times

(2) PMMALow glass transition temperature(Tg≈105℃)，Temperature limitation of coating

(3) PMMAStrong hygroscopicity(water absorption rate0.3%)，Moisture causes membrane stress

(4) PMMALow surface energy(about40mN/m)，Poor adhesion of film layer

(5) PMMALow hardness(Mohs 2-3)，Easy to scratch

【solution】

Option One（Emergency diagnosis）：

→ Cracks form a network like pattern→Thermal stress is predominant

→ Scratches along the crack edge→mechanical damage

→ Bubbling of the film layer accompanied by cracks→Substrate contains water

→ Compare dried and undriedPMMAMembrane rupture rate

Option 2（Process adjustment）：

→ PMMAPreprocessing：60℃vacuum drying24hremove moisture

→ Reduce the coating temperature to room temperature，Using electron beam evaporation

→ Increase plasma cleaning：O2plasma，Increase surface energy

→ increaseSiO2bottom layer(50nm)：PMMA/SiO2/Functional film

→ Using ion assisted deposition(IAD)：Improve membrane density

→ Control film thickness<500nm，Reduce stress

Option Three（settle sth. once and for all）：

→ PMMAsurfaceUVCuring treatment：Increase cross-linking density

→ developmentPMMASpecialized low stress film system

→ Using plasma polymerization as a base material：Improve adhesion

→ Using wet method+Vacuum plating composite process

→ establishPMMACoating process standards

【preventive measures】

• PMMAThe incoming materials must be vacuum dried，water content<0.1%

• PMMACoating temperature is not acceptable>80℃

• PMMAStorage needs to be dry，relative humidity<40%

【Precautions】

⚠ PMMAThe cracked sample cannot be reworked，Surface has been damaged

⚠ PMMADo not use organic solvents for cleaning

1.5.2 PC(polycarbonate)Membrane rupture

【abnormal phenomenon】PC(polycarbonate)Cracks appear after coating，eyeglass lens、protective face shield、Car lampshades, etc。

【Root cause analysis】

(1) PCcoefficient of thermal expansion(65×10⁻⁶/℃)givePMMAapproach，extremely high

(2) PCTemperature resistance ratioPMMAGood(Tg≈145℃)，But it is still prone to cracking after coating

(3) PCHigh internal stress，Residual stress exists after injection molding

(4) PCLow surface polarity，Poor adhesion of film layer

(5) PCrightUVsensitive，UVCuring may lead to degradation

【solution】

Option One（Emergency diagnosis）：

→ Cracks along injection flow marks→Residual stress in injection molding

→ Crack at the sprue→stress concentration

→ Polarization stress meter detection：<10nmDouble refraction is qualified

→ Compare annealed and unannealedPCMembrane rupture rate

Option 2（Process adjustment）：

→ PCannealing treatment：120℃、4h，Relieve internal stress

→ Reduce the coating temperature to<100℃

→ Increase plasma cleaning：Ar/O2Mixed plasma

→ Using magnetron sputtering：Low temperature process

→ increaseSiO2bottom layer(30nm)

→ Control film thickness<300nm

Option Three（settle sth. once and for all）：

→ PCSurface plasmon polymerization：generateSiOxCylayer

→ developmentPCSpecialized low stress hard coating

→ Using sol-gel+Vacuum plating composite

→ Optimize injection molding process：Reduce injection speed

→ establishPCCoating process standards

【preventive measures】

• PCIncoming materials must undergo annealing treatment，Relieve internal stress

• PCCoating temperature is not acceptable>120℃

• PCInjection molded parts need to be inspected for birefringence

【Precautions】

⚠ PCThe cracked sample cannot be reworked

⚠ PCDo not come into contact with strong solvents such as acetone

1.5.3 PET/PIWaiting for the flexible substrate film to crack

【abnormal phenomenon】PET(Polyethylene terephthalate)、PI(polyimide)Cracking after coating the flexible substrate。

【Root cause analysis】

(1) PETcoefficient of thermal expansion(20-30×10⁻⁶/℃)，Stress generated during stretching

(2) PETThin film thickness(12-250μm)，deformable

(3) Roll to roll(R2R)Improper tension control during coating

(4) PETLow surface roughness，poor adhesion

(5) PIGood temperature resistance but expensive price，Low surface energy

【solution】

Option One（Emergency diagnosis）：

→ Cracks along the tensile direction→Excessive tension

→ Crack at the winding point→Concentration of winding stress

→ Measure substrate tension：R2REquipment tension meter

→ Compare membrane cracking rates under different tensions

Option 2（Process adjustment）：

→ controlR2RZhang Li：PET 50-100N/m，PI 80-150N/m

→ Reduce the coating temperature to room temperature

→ Increase plasma cleaning：Arplasma

→ Using sputtering instead of evaporation：Better adhesion of film layer

→ Control the winding tension<unwinding tension

→ Add guide rollers：Reduce wrinkle stress

Option Three（settle sth. once and for all）：

→ PETSurface corona treatment：Increase surface energy to50mN/m

→ developmentR2RSpecialized low stress film system

→ adoptALDtechnology：Good shape retention、Low stress

→ Design stress relief structure：Grid like coating

→ establishR2RCoating process standards

【preventive measures】

• PETThe surface energy of incoming materials must be inspected，<40mN/mNeed corona treatment

• R2REquipment tension must be calibrated

• PETStorage should avoid wrinkles

【Precautions】

⚠ PETThe cracked sample cannot be reworked

⚠ PETThe roll should not be too tight，can transform

1.5.4 COC/COPIsocyclic olefin membrane cracking

【abnormal phenomenon】COC(Cyclic olefin copolymer)、COP(Cyclic olefin polymer)Cracking after optical plastic coating。

【Root cause analysis】

(1) COCcoefficient of thermal expansion(60×10⁻⁶/℃)tall，Optical grade requires low birefringence

(2) COCExtremely low water absorption rate(<0.01%)，But the surface energy is low

(3) COCPoor temperature resistance(Tg≈80-170℃)，Temperature limitation of coating

(4) COCHigh price，Membrane cracking leads to high scrap costs

(5) COCSensitive to solvents，Restricted cleaning

【solution】

Option One（Emergency diagnosis）：

→ Analysis of crack morphology：Determine the type of stress

→ Birefringence detection：<5nmTo be qualified

→ Comparing DifferentTgofCOCMembrane rupture rate

→ Check if the coating temperature exceeds the standard

Option 2（Process adjustment）：

→ Reduce the coating temperature to<60℃

→ Using electron beam evaporation or sputtering

→ increaseO2plasma cleaning

→ Control film thickness<200nm

→ Use special fixtures to avoid stress

Option Three（settle sth. once and for all）：

→ COCsurfaceUV/O3handle

→ developmentCOCSpecialized low stress film system

→ Using wet hard coating as the base

→ establishCOCCoating process standards

【preventive measures】

• COCIncoming materials must be inspectedTgAnd birefringence

• COCCoating temperature is not acceptable>Tg-20℃

• COCDo not come into contact with organic solvents

【Precautions】

⚠ COCThe cracked sample cannot be reworked

⚠ COCexpensive，Strict control of the process is required