WO2022260509A1 - Glass frit compositions for semiconductor passivation applications - Google Patents

Glass frit compositions for semiconductor passivation applications Download PDF

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Publication number
WO2022260509A1
WO2022260509A1 PCT/NL2022/050276 NL2022050276W WO2022260509A1 WO 2022260509 A1 WO2022260509 A1 WO 2022260509A1 NL 2022050276 W NL2022050276 W NL 2022050276W WO 2022260509 A1 WO2022260509 A1 WO 2022260509A1
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WIPO (PCT)
Prior art keywords
glass
glass frit
ppm
passivation
lead
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PCT/NL2022/050276
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French (fr)
Inventor
Olivier Jean André DESANTE
Svetlana Nikolaevna EMELIANOVA
Hong Ren
Maxence VALLA
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Fenzi Agt Netherlands B.V.
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Publication of WO2022260509A1 publication Critical patent/WO2022260509A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02225—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer
    • H01L21/0226—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process
    • H01L21/02282—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process liquid deposition, e.g. spin-coating, sol-gel techniques, spray coating
    • H01L21/02288—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process liquid deposition, e.g. spin-coating, sol-gel techniques, spray coating printing, e.g. ink-jet printing
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C3/00—Glass compositions
    • C03C3/04—Glass compositions containing silica
    • C03C3/062—Glass compositions containing silica with less than 40% silica by weight
    • C03C3/064—Glass compositions containing silica with less than 40% silica by weight containing boron
    • C03C3/066—Glass compositions containing silica with less than 40% silica by weight containing boron containing zinc
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
    • C03C8/02—Frit compositions, i.e. in a powdered or comminuted form
    • C03C8/04—Frit compositions, i.e. in a powdered or comminuted form containing zinc
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02109—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates
    • H01L21/02112—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer
    • H01L21/02123—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer the material containing silicon
    • H01L21/02126—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer the material containing silicon the material containing Si, O, and at least one of H, N, C, F, or other non-metal elements, e.g. SiOC, SiOC:H or SiONC
    • H01L21/02129—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer the material containing silicon the material containing Si, O, and at least one of H, N, C, F, or other non-metal elements, e.g. SiOC, SiOC:H or SiONC the material being boron or phosphorus doped silicon oxides, e.g. BPSG, BSG or PSG

Definitions

  • the present specification relates to glass frit com positions for semiconductor passivation applications.
  • Lead containing glass frits are currently being used for their passivation properties in semiconductor devices.
  • the glass frits are deposited in an ink or paste formula tion comprising the glass frit and an organic carrier me dium.
  • the ink or paste is deposited over a semiconductor substrate and fired to form a glass passivation layer.
  • a two-stage firing process may be utilized including a pre firing stage to remove components of an organic carrier medium followed by a main firing step to melt and fuse the glass frit into a glass passivation layer.
  • the resultant glass passivation layer must exhibit good dielectric prop erties as well as excellent acid resistance (e.g. to HF).
  • W02018/026402 discloses a lead-free glass passivation coating composition for forming a fired glass passivation layer on a semiconductor substrate.
  • the pas sivation glass coating composition includes a glass compo nent that is lead-free, cadmium-free, and free of alkali metal oxides and coloured transition metal oxides (i.e. metal oxides of V, Fe, Co, Ni, Cr, Cu, Mn).
  • the glass com ponent is a bismuth based glass comprising: 5-56 mol% B ⁇ 2q3, ⁇ 15-60 mol% ZnO; 0.1-43 mole% B2O3; 0.1 -15 mol% AI2O3; 4-53 mol% S1O2; and 1.5-43 mol% total R2O3, wherein R represents trivalent ions selected from the group consist ing of B 3+ , Al 3+ , La 3+ , Y 3+ , Ga 3+ , ln 3+ , Sc 3+ , and lanthanide ions from Ce 3+ to Lu 3+ , and excluding colour producing transition metals Mn 3+ , Fe 3+ , Cr 3+ , V 3+ , Co 3+ .
  • R represents trivalent ions selected from the group consist ing of B 3+ , Al 3+ , La 3+ , Y 3+ , Ga 3+ , ln 3+ , Sc 3+ , and lanthanide ions from Ce 3+
  • a method of manufacturing a semiconduc tor component comprising: depositing a glass frit over a semiconductor layer; and firing the glass frit to form a passivation glass layer disposed over the semi conductor layer, wherein the glass frit is composed of a lead-free zinc borate silicate glass comprising ZnO, B 2 O 3 , and S1O 2 , less than 5 mol% B12O3, and less than 100 ppm by weight of each of Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li.
  • the glass frit comprises less than 4, 3, 2, 1, 0.1, or 0.01 mol% of B1 2 O 3 and is most preferably free, or at least substantially free, of bismuth.
  • the glass frit utilized to fabricate the passivation glass layer of a semiconductor component differs from the bismuth-based glasses described in W02018/026402.
  • the re duction or omission of bismuth reduces the cost of the passivation glass.
  • avoiding the requirement for a source of bismuth, usually in the form of B1 2 O 3 eliminates a source of contamination which can lead to a reduction in passivation performance in semiconductor de vice applications. It has been found that high perfor mance, lead-free passivation glass layers can be fabricat ed from lead-free zinc borate silicate glass frit which is free, or substantially free, of bismuth.
  • the glass frit also comprises less than 0.1 or 0.01 mol% of AI 2 O 3 and may be free, or at least sub stantially free, of aluminium.
  • Such glass frits are also distinguished over those of W02018/026402 which require AI 2 O 3 . Avoiding the requirement for a source of aluminium eliminates a source of contamination which can lead to a reduction in passivation performance in semiconductor de vice applications. It has been found that high perfor mance, lead-free passivation glass layers can be fabricat ed from lead-free zinc borate silicate glass frit which is free, or substantially free, of aluminium.
  • the glass frit may be deposited over the semiconduc tor in the form of a paste or ink comprising the glass frit in a liquid carrier, preferably an organic carrier medium.
  • the glass frit, and the subsequent paste or ink formulated using the glass frit should be prepared care fully to avoid contamination with impurities which can lead to a reduction in passivation performance in semicon ductor device applications.
  • the glass frit, paste or ink, and resultant passivation glass layer should comprises less than 100 ppm, 80 ppm, 60 ppm, 40 ppm, or 30 ppm by weight of each of Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li.
  • these elements represent com mon impurities from the alkali metals, alkaline earth met als and early (coloured) transition metals.
  • the materials used to fabricate the passivation layer should be free, or substantially free of alkali metals, alkaline earth met als, and early (coloured) transition metals as well as be ing lead-free.
  • the glass frit is advantageously formed without addition of a compound comprising any of Pb, Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li. Fur thermore, raw materials and preparation conditions are se lected to minimize contamination with these elements.
  • the glass frit may comprise less than 100 ppm, 80 ppm, 60 ppm, 40 ppm, or 30 ppm by weight of one, more, or all of Ba, Sr, Ti, Bi, and A1.
  • Such glass frits are formed without addition of one, more, or all of these elements or com pounds thereof.
  • Raw materials and preparation conditions can be selected to minimize contamination with these ele ments.
  • certain embodiments may consist essen tially of ZnO, B 2 O 3 , and S1O 2 and exclude other components including Ba, Sr, Ti, Bi, Al, V, Fe, Co, Ni, Cr, Cu, Mn, La, Y, Ga, In, Sc, and lanthanide ions from Ce to Lu.
  • the glass frit may comprise: 30 to 70, 40 to 65, or 50 to 60 mol% ZnO; 10 to 40, 20 to 40, or 30 to 40 mol% B 2 O 3 ; 2 to 35, 2 to 25, 2 to 20, or 5 to 15 mol% S1O 2 ; or any combination of the aforementioned lower and upper lim its.
  • the glass frit is amorphous prior to firing. Compositional ranges have been established to provide good glass formability, a homogenous amorphous glass frit material without phase separation or crystalli sation, and thus a starting glass frit material suitable for paste formulation offering good printability, while also providing compositions which can crystallize on fir ing to give advantageous properties such as acid re sistance.
  • the glass frit is advantageously fired at a tempera ture in excess of 800°C, e.g. in a range 800°C to 1000°C. It has been found that the lead-free zinc borate silicate glasses of the present specification have different crys talline phases present in different ratios according to firing temperature. At low temperatures between room temperature (nominally 25°C) and approximately 600°C, the lead-free zinc borate silicate glass is amorphous with the boron present in both BO 3 and BO 4 coordinate states in a ratio of approximately 70% BO 3 and 30% BO 4 .
  • the passivation glass layer may comprise greater than 50%, 60%, 70%, 80% or 90% of a total boron content in a BO 4 coordination state.
  • the present specification thus proposes the use of a lead-free zinc borate silicate glass as defined above for fabricating a passivation glass layer of a semiconductor component.
  • a resultant semiconductor component com prising a semiconductor layer; and a passivation glass layer disposed over the semiconductor layer, the pas sivation glass layer comprising a fired glass frit, the glass frit being composed of a lead-free zinc borate sili cate glass as defined above.
  • Figure 1 shows a heating profile for a variable- temperature (VT) X-ray diffraction (XRD) analysis of lead- free zinc borate silicate glass frit to establish a corre lation between phase structure and processing temperature and determine evolved phases and transition temperatures during heat treatment up to 860°C under air;
  • VT variable- temperature
  • XRD X-ray diffraction
  • Figure 2 shows the resultant VT-XRD data by imple menting the heating profile of Figure 1 on a sample of lead-free zinc borate silicate glass and illustrates the development of different crystal phases within the lead- free zinc borate silicate glass frit on increasing heat treatment temperature starting with an amorphous exhibit ing no XRD peaks at room temperature and moving through various phase transitions to a dominant Zh4q(Bq2)b crystal phase with BO4 coordination at temperatures in excess of 800°C;
  • Figure 3 shows a differential scanning calorimeter (DCS) plot for lead-free zinc borate silicate glass indi cating a major exothermal event at 791°C which corresponds to the formation of Zh4q(BO2)6 / the dominating crystalline phase in this material at high processing temperatures in excess of 800°C as confirmed by the VT-XRD analysis shown in Figure 2;
  • DCS differential scanning calorimeter
  • Figure 4 shows solid state NMR spectra for lead-free zinc borate silicate glass processed at different tempera tures indicating peaks associated with BO3 coordinated bo ron (d( 11 B) ⁇ 13 ppm) and BO4 coordinated boron (d( 11 B) ⁇ 0 ppm) within the glass material, the data indicating the development of a strong and sharp BO4 peak on heating above 800°C as a result of increased crystallinity com pared to the BO4 peak of materials heated at lower temper atures which are weak and broad, indicative of primarily amorphous material;
  • Figure 5 shows a plot of the BO 4 fraction of the total BO 4 + BO 3 coordinated boron within the lead-free zinc bo rate silicate glass as a function of temperature, clearly demonstrating that for the 840°C heat treated material, the BO 4 fraction is dominating at ⁇ 90%;
  • Figure 6 shows hot-stage microscopy data for lead- free zinc borate silicate glass heated to various tempera tures, the data showing five zones (I - Softening (600 - 650°C); II - First Crystallisation (650 - 700°C); II+III - Residual glass softening (650 - 750°C); IV - Second Crys tallisation plateau (750-950°C); and V - Melting (> 950°C)), the thermal behaviour of the 840°C heat treated material indicating high crystallinity and the heating mi croscopic data being consistent with the XRD, DSC, and NMR results of Figures 1 to 5;
  • Figures 7 to 12 show layer thickness profile results for layers of lead-free zinc borate silicate glass fired at two different temperatures (690°C and 840°C) and sub jected to three different acid treatments (HC1, H 2 SO 4 , and HF), results indicating that while the glass which is fired at 690°C is strongly affected by all of the acids, the glass fired at 840°C is resistant to all of the acids;
  • Figure 13 shows an XRD analysis of lead-free zinc bo rate silicate glass frit sintered at 840°C
  • Figure 14 shows an XRD analysis of a lead-free zinc borate silicate glass layer fired at 840°C on a silicon wafer.
  • Figure 15 show an XRD analysis of a lead-free zinc borate silicate glass layer fired at 840°C on a silicon wafer and after being subjected to three different types of acid treatment indicating that all the acids primary attack the willemite crystal phase, with H 2 SO 4 being the most aggressive followed by HC1 and HF.
  • the present specification provides a method of manufacturing a pas sivation glass layer in a semiconductor component using a lead-free zinc borate silicate glass frit comprising or consisting of ZnO, B2O3, and S1O2 with low, or substantial ly no, bismuth and with minimal other impurity elements which can detrimentally affect passivation performance.
  • the lead-free zinc borate silicate glass frit is fabricated so as to be amorphous, uniform, and of good printability in order to enhance deposition of a uni- form and consistent frit layer prior to firing.
  • the glass compositions are such that they develop a dominant crys talline Zh4B d O ⁇ 3 phase (BO4 coordination) at firing tempera tures over 800°C to provide a very acid resistant pas sivation layer.
  • glass materials are conven tionally defined in terms of equivalent oxide content, even if other compound types are used as the starting ma terials.
  • the boron con tent may be provided using H3BO3 as the starting raw mate rial in combination with ZnO and S1O2.
  • the powder mixture for glass melting was prepared using high purity raw materials: ZnO, H3BO3 and S1O2.
  • lOOg of the raw materi als powder mix was melted in a platinum crucible at a melting temperature of 1375°C and a melting time of 60 minutes.
  • the melting temperature of 1375°C when using high purity raw materials was significantly higher com pared to corresponding compositions made using standard grades of raw materials comprising more impurities.
  • the coefficient of thermal expansion (CTE) of the melted glass was measured as 48 x 10 6 /°C using a dilato- metric method.
  • the lead-free zinc borate silicate glass frits as de scribed herein can be used to form the passivation layer of power devices.
  • a glass frit-based paste suitable for screen printing is re quired and the substrate on which the paste is applied is silicon.
  • the thermal expansion of the frit is preferably between 2.6 to 4.1 c 10 6 /°C.
  • the glass transition tempera ture of the frit Tg is ideally > 450°C and the glass sof tening temperature T f is ⁇ 1000°C, while the operating temperature in a semiconductor device is typically ⁇ 200°C.
  • High purity is one of the most critical requirements for this passivation application.
  • a dielectric per spective acceptable elements in the glass composition in clude Ba, Sr, Al, B, Ti, Zn, and Bi while elements which are not acceptable from a dielectric perspective include Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li.
  • a zinc borate silicate glass system has been explored and successfully developed as the suitable material system.
  • Acid durability is an other critical product requirement and it is required that the passivation layer should be resistant to HF etching.
  • the zinc borate silicate glass system has been found to provide such acid durability when suitably processed (e.g. fired at a temperature over 800°C).
  • the actual levels of all the inclusive elements such as Zn, B and Si in the obtained frit powder are close to the nominal values. More importantly, all the impurities are suitably controlled below the acceptable levels, satisfying the stringent application specifica tion.
  • the exemplary glass frit material as defined above was subjected to analysis by variable-temperature X-ray diffraction (VT-XRD), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and hot-stage mi croscopy.
  • VT-XRD variable-temperature X-ray diffraction
  • DSC differential scanning calorimetry
  • NMR nuclear magnetic resonance
  • hot-stage mi croscopy The analyses and results are summarized below.
  • the frit material is amorphous at room temperature. However, upon heating, it undergoes several different crystallisations. To establish the exact correlation be tween its phase structure and temperature, the as-made frit material was studied by variable-temperature (VT) X- ray diffraction (XRD) to precisely determine its evolved phases and transition temperatures during heat treatment up to 860°C under air conditions.
  • VT variable-temperature
  • XRD X- ray diffraction
  • a powder sample of the glass frit material was packed into a sample holder and mounted in a heating chamber un- der flowing air (20% O2 / N2).
  • An initial long data set was measured at room temperature for reference (RT pre-VT da ta) between 10 - 130° 2Q with a step size of 0.02°, ls/step.
  • the VT Data was collected between 23-70°2q, step size of 0.020° with a collection time of 0.43s/step.
  • a ramp rate of 12°C/min from room temperature up to 860°C was applied with data collected in 20°C increments from 500°C as shown by the heating profile in Figure 1.
  • the sample was then cooled from 860 to 30°C at 12°C/min and a final room temperature reference dataset collected.
  • a fi nal long dataset 'post-calcination' measured between 10- 130°2Q with a step size of 0.02°, ls/step was collected at room temperature following the heat treatment experiment (RT post-VT data), again for reference
  • Figure 2 is a contour plot of the results of the var iable temperature XRD experiment. It is evident from Fig ure 2 that the starting material at room temperature (RT- start) was amorphous exhibiting no obvious XRD peaks. The sample was expected to remain amorphous between room tem perature and 500°C, hence no data collection was performed during this heating range. On further heating, this sample remained amorphous up to at least 680°.
  • a third crystalline phase was first detected as a trace phase in the 740°C dataset. This phase was cubic in structure and closely matches the following documented isostructural phases: Zinc Borate, Zh4q(Bq2)b - PDF 01-076- 0917 in Figure 2; and/or Zinc Borate, Zn(B0 2)2 - PDF 00- 039-1126 in Figure 2.
  • RT end in Figure 2 was the long dataset collected at room temperature post cooling. This dataset confirmed the pre- dominant phase present post heating/cooling to be cubic, closely matching the isostructural phases indicated above such as Zh4q(BO2)6 ⁇ Relatively minor amounts of crystalline Zinc Borate, Zn3(603)2 and Willemite, Z ⁇ SiCg were also evi dent in the final cooled material.
  • the as-made glass frit powder was analysed using a simultaneous thermogravimetric analyser (Netzsch STA449F3) and differential scanning calorimeter with coupled mass spectrometer (Netzsch Aelous) for evolved gas analysis.
  • the heating procedure adopted was from 40 to 1000°C with a heating rate of 10°C /min. Measurement was blank corrected and the measurement pan used was graphite with no lid. The measurement atmosphere used was Argon.
  • the system was cal ibrated with metal standards for temperature and sensitiv ity accuracy.
  • the probe was tuned to 192.57 MHz and referenced to NaBH4 at -42.06 ppm.
  • Powdered samples were packed into zirconia MAS rotors with Kel-F caps, with before and after weighing providing the sample mass. The rotors were spun using room-temperature purified compressed air. The rotor diameter was 4 mm and the frequency used for measuring 11 B was 10000 Hz.
  • the glass material (for the heat treatment £ 700°C) was mainly amorphous (indictive by the observed broad peaks) consisting of both BO 3 and BO 4 environments.
  • the 840°C heat treated material however showed a sharp BO 4 peak (with little BO 3 ), which revealed the high crystallinity of the material after the high temperature heat treatment, consistent with tetrahedral boron sites in the Zh4q(Bq2)b crystalline phase as determined by XRD.
  • the processed spectra are shown in Figure 4.
  • the sintered sample treated at 840°C showed a strong and sharp BO4 peak indicative of a crys talline environment.
  • the sintered samples also exhibit a well-structured BO3 peak indicative of a crystalline envi ronment.
  • the BO 4 fraction of the total (BO 4 + BO 3 ) was plotted as a function of temperature as shown in Figure 5. This clearly demonstrates that the 840°C heat treated material comprises a BO 4 fraction which is dominating at ⁇ 90%.
  • the thermal behaviour of the 840°C heat treated mate rial suggests its high crystallinity.
  • the heating micro scopic data is consistent with the XRD, DSC, and NMR re sults described previously.
  • Acid resistance testing Lead-free zinc borate silicate glass frit was pre pared as previously described.
  • the glass frit powder was mixed with a liquid carrier media (80% glass powder; 20% media) to form a paste.
  • the paste was then screen printed on a silicon wafer, dried at 150°C, and fired in a fur nace. One set of samples was fired at 690°C for 4 minutes while another set of samples was fired at 840°C for 4 minutes.
  • the layer thickness of the fired plates was measured on a profilometer (NANOFOCUS USCAN).
  • the fired plates were tested to determine the effect of three acids on the layer thickness: HC1 (3.7%); H 2 SO 4 (5%); and HF (10%).
  • the layer thickness was measured be fore and after acid attack.
  • Figures 7 to 12 show layer thickness profile results for layers of lead-free zinc borate silicate glass fired at the two different temperatures (690°C and 840°C) and subjected to the three different acid treatments (HC1, H 2 SO 4 , and HF).
  • Figure 7 shows the results for the 690°C fired sample treated with HC1 (3.7%).
  • the left-hand profile in Figure 7 is before acid application while the right-hand profile is after acid application. It is clear that HC1 has a significant effect on the glass layer.
  • Figure 8 shows the results for the 690°C fired sample treated with H 2 SO 4 ( 5%).
  • the left-hand profile in Figure 8 is before acid application while the right-hand profile is after acid application. It is clear that H 2 SO 4 has a sig nificant effect on the glass layer.
  • Figure 9 shows the results for the 690°C fired sample treated with HF (10%).
  • the left-hand profile in Figure 9 is before acid application while the right-hand profile is after acid application. It is clear that HF has a signif icant effect on the glass layer.
  • Figure 10 shows the results for the 840°C fired sample treated with HC1 (3.7%).
  • the left-hand profile in Figure 10 is before acid application while the right-hand profile is after acid application. It is clear that HC1 has lit tle or no effect on the glass layer.
  • Figure 11 shows the results for the 840°C fired sample treated with H 2 SO 4 (5%).
  • the left-hand profile in Figure 11 is before acid application while the right-hand profile is after acid application. It is clear that H2SO4 has lit tle or no effect on the glass layer.
  • Figure 12 shows the results for the 840°C fired sample treated with HF (10%).
  • the left-hand profile in Figure 12 is before acid application while the right-hand profile is after acid application. It is clear that HF has little or no effect on the glass layer.
  • Figure 13 shows an XRD analysis of lead-free zinc bo rate silicate glass frit sintered at 840°C.
  • the glass frit powder was sintered in a furnace at a heating rate of 15°C/min to a temperature of 840°C and for a dwell time of 30 min in corundum crucible.
  • the CTE of the sintered glass material was measured as 42.6 x 10 6 /°C.
  • the XRD in dicates the main crystal phases are tetra-zinc-borate (4Zn0*E> 2 0 3) and willemite (2ZnO* S1O 2) ⁇
  • Figure 14 shows an XRD analysis of a lead-free zinc borate silicate glass layer fired at 840°C on a silicon wafer.
  • the main crystal phases of the 840°C fired enamel are tetra-zinc-borate (4Zn0*E> 2 0 3) , willemite (2ZnO*SiC> 2) and tri-zinc-borate (3ZnO* B2O3).
  • Figure 15 show an XRD analysis of a lead-free zinc borate silicate glass layer fired at 840°C on a silicon wafer and subjected to three different types of acid treatment indicating that all the acids primary attack the willemite crystal phase, with H2SO4 being the most aggres sive followed by HC1 and HF.
  • the HF testing data revealed that only the lead-free zinc borate silicate glass materials which were heat treated at above 800°C showed the satisfactory HF re sistance, while those materials which were either un-heat- treated or heat-treated at temperatures ⁇ 800°C exhibited inferior/unsatisfactory HF durability.
  • the acid test re sults confirmed that there is a strong correlation between HF durability and the presence of highly crystalline phase Zh4q(Bq2) d where B is in BO4 coordination.
  • a suitable glass system has been developed for use as a passivation layer in power devices. It has been discov ered that in order to satisfy acid durability requirements for certain applications, achieving the correct crystal phase and 11 B environment structure (BO 4 ) is essential. This correct phase assembly may be achieved by the appro priate heat treatment on the as-made lead-free zinc borate silicate glass frit materials. All impurity levels were appropriately controlled ensuring stringent product re quirements to be met. Furthermore, a compositional range has been established with good glass formability for ob taining a homogenous amorphous glass (without phase sepa ration or crystallisation) as a starting material suitable for paste formulation offering good printability. Benefits of the invention include: environmentally friendly lead- free frit and enamel; high firing temperature (above 800°C); low coefficient of thermal expansion; high acid resistance when fired at or above 800°C; and suitable for deposition on semiconductor wafers.
  • the glass frit materials described herein have been developed for use in semiconductor device passivation applications, it is also envisaged that the glass frit materials may be useful in other applications, particularly those which require an acid resistant glass enamel coating. Accordingly, other applications may comprise depositing the glass frit on a substrate (e.g. glass, metal, ceramic, or other substrate requiring an acid resistant coating) and firing the glass frit to form a glass layer disposed on the substrate.
  • a substrate e.g. glass, metal, ceramic, or other substrate requiring an acid resistant coating

Abstract

A method of manufacturing a semiconductor component, the method comprising: depositing a glass frit over a semiconductor layer; and firing the glass frit to form a passivation glass layer disposed over the semiconductor layer, wherein the glass frit is composed of a lead-free zinc borate silicate glass comprising ZnO, B2O3, and SiO2, less than 5 mol % Bi2O3, and less than 100 ppm by weight of each of Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li.

Description

GLASS FRIT COMPOSITIONS FOR SEMICONDUCTOR PASSIVATION AP PLICATIONS
Field
The present specification relates to glass frit com positions for semiconductor passivation applications.
Background
Lead containing glass frits are currently being used for their passivation properties in semiconductor devices. The glass frits are deposited in an ink or paste formula tion comprising the glass frit and an organic carrier me dium. The ink or paste is deposited over a semiconductor substrate and fired to form a glass passivation layer. A two-stage firing process may be utilized including a pre firing stage to remove components of an organic carrier medium followed by a main firing step to melt and fuse the glass frit into a glass passivation layer. The resultant glass passivation layer must exhibit good dielectric prop erties as well as excellent acid resistance (e.g. to HF).
There is a need for large (micro) electronics compa nies to move away from using lead-based glass materials. As such, lead-free alternatives are being investigated. In this regard, W02018/026402 discloses a lead-free glass passivation coating composition for forming a fired glass passivation layer on a semiconductor substrate. The pas sivation glass coating composition includes a glass compo nent that is lead-free, cadmium-free, and free of alkali metal oxides and coloured transition metal oxides (i.e. metal oxides of V, Fe, Co, Ni, Cr, Cu, Mn). The glass com ponent is a bismuth based glass comprising: 5-56 mol% Bΐ2q3,· 15-60 mol% ZnO; 0.1-43 mole% B2O3; 0.1 -15 mol% AI2O3; 4-53 mol% S1O2; and 1.5-43 mol% total R2O3, wherein R represents trivalent ions selected from the group consist ing of B3+, Al3+, La3+, Y3+, Ga3+, ln3+, Sc3+, and lanthanide ions from Ce3+ to Lu3+, and excluding colour producing transition metals Mn3+, Fe3+, Cr3+, V3+, Co3+. There is still a need for improved lead-free, pas sivation glass materials for semiconductor device applica tions. The present specification is intended to address this need.
Summary
According to an aspect of the present specification there is provided a method of manufacturing a semiconduc tor component, the method comprising: depositing a glass frit over a semiconductor layer; and firing the glass frit to form a passivation glass layer disposed over the semi conductor layer, wherein the glass frit is composed of a lead-free zinc borate silicate glass comprising ZnO, B2O3, and S1O2, less than 5 mol% B12O3, and less than 100 ppm by weight of each of Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li.
Preferably, the glass frit comprises less than 4, 3, 2, 1, 0.1, or 0.01 mol% of B12O3 and is most preferably free, or at least substantially free, of bismuth. As such, the glass frit utilized to fabricate the passivation glass layer of a semiconductor component differs from the bismuth-based glasses described in W02018/026402. The re duction or omission of bismuth reduces the cost of the passivation glass. Furthermore, avoiding the requirement for a source of bismuth, usually in the form of B12O3, eliminates a source of contamination which can lead to a reduction in passivation performance in semiconductor de vice applications. It has been found that high perfor mance, lead-free passivation glass layers can be fabricat ed from lead-free zinc borate silicate glass frit which is free, or substantially free, of bismuth.
Optionally, the glass frit also comprises less than 0.1 or 0.01 mol% of AI2O3 and may be free, or at least sub stantially free, of aluminium. Such glass frits are also distinguished over those of W02018/026402 which require AI2O3. Avoiding the requirement for a source of aluminium eliminates a source of contamination which can lead to a reduction in passivation performance in semiconductor de vice applications. It has been found that high perfor mance, lead-free passivation glass layers can be fabricat ed from lead-free zinc borate silicate glass frit which is free, or substantially free, of aluminium.
The glass frit may be deposited over the semiconduc tor in the form of a paste or ink comprising the glass frit in a liquid carrier, preferably an organic carrier medium. The glass frit, and the subsequent paste or ink formulated using the glass frit, should be prepared care fully to avoid contamination with impurities which can lead to a reduction in passivation performance in semicon ductor device applications. As such, the glass frit, paste or ink, and resultant passivation glass layer, should comprises less than 100 ppm, 80 ppm, 60 ppm, 40 ppm, or 30 ppm by weight of each of Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li. These elements represent com mon impurities from the alkali metals, alkaline earth met als and early (coloured) transition metals. The materials used to fabricate the passivation layer should be free, or substantially free of alkali metals, alkaline earth met als, and early (coloured) transition metals as well as be ing lead-free. As such, the glass frit is advantageously formed without addition of a compound comprising any of Pb, Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li. Fur thermore, raw materials and preparation conditions are se lected to minimize contamination with these elements.
Furthermore, while in principle the presence of Ba, Sr, Al, B, Ti, Zn, and Bi in a glass material would be ac ceptable from a passivation perspective, the more raw ma terials which are utilized to fabricate the glass frit, the more sources of contamination are introduced into the passivation glass. As such, it has been found to be ad vantageous to minimize the number of components in the glass material which are required to meet performance re quirements. In this regard, it has been found that high performance passivation glass materials can be fabricated using a lead-free zinc borate silicate glass frit in which Ba, Sr, Ti, Bi, and A1 are excluded. Accordingly, the glass frit may comprise less than 100 ppm, 80 ppm, 60 ppm, 40 ppm, or 30 ppm by weight of one, more, or all of Ba, Sr, Ti, Bi, and A1. Such glass frits are formed without addition of one, more, or all of these elements or com pounds thereof. Raw materials and preparation conditions can be selected to minimize contamination with these ele ments. As such, certain embodiments may consist essen tially of ZnO, B2O3, and S1O2 and exclude other components including Ba, Sr, Ti, Bi, Al, V, Fe, Co, Ni, Cr, Cu, Mn, La, Y, Ga, In, Sc, and lanthanide ions from Ce to Lu.
The glass frit may comprise: 30 to 70, 40 to 65, or 50 to 60 mol% ZnO; 10 to 40, 20 to 40, or 30 to 40 mol% B2O3; 2 to 35, 2 to 25, 2 to 20, or 5 to 15 mol% S1O2; or any combination of the aforementioned lower and upper lim its. Advantageously, the glass frit is amorphous prior to firing. Compositional ranges have been established to provide good glass formability, a homogenous amorphous glass frit material without phase separation or crystalli sation, and thus a starting glass frit material suitable for paste formulation offering good printability, while also providing compositions which can crystallize on fir ing to give advantageous properties such as acid re sistance.
The glass frit is advantageously fired at a tempera ture in excess of 800°C, e.g. in a range 800°C to 1000°C. It has been found that the lead-free zinc borate silicate glasses of the present specification have different crys talline phases present in different ratios according to firing temperature. At low temperatures between room temperature (nominally 25°C) and approximately 600°C, the lead-free zinc borate silicate glass is amorphous with the boron present in both BO3 and BO4 coordinate states in a ratio of approximately 70% BO3 and 30% BO4. Above approxi mately 600°C to 700°C both ZhB4q7 (BO3 coordination) & Zh4BdOΐ3 (BO4 coordination) crystallise out from the amor- phous matrix (the precise temperature of the phase transi tions being dependent on the specific composition of the lead-free zinc borate silicate glass). As the firing tem perature is increased the proportion of ZhBdOΐ (BCg coor dination) increases and at firing temperatures over 800°C the crystalline Zh4BdOΐ3 phase ( BO4 ) is dominant over the crystalline ZnB4C>7 phase ( BO3 coordination). Acid re sistance tests have found that there is a strong correla tion between acid durability of a passivation glass layer and the presence of the highly crystalline phase ZhBdOΐ where B is in the BO4 coordination state. As such, advan tageously after firing the passivation glass layer com prises crystalline ZhBdOΐ . Furthermore, the passivation glass layer may comprise greater than 50%, 60%, 70%, 80% or 90% of a total boron content in a BO4 coordination state.
The present specification thus proposes the use of a lead-free zinc borate silicate glass as defined above for fabricating a passivation glass layer of a semiconductor component. Following the methodology as described above, there is provided a resultant semiconductor component com prising: a semiconductor layer; and a passivation glass layer disposed over the semiconductor layer, the pas sivation glass layer comprising a fired glass frit, the glass frit being composed of a lead-free zinc borate sili cate glass as defined above.
Brief Description of the Drawings
For a better understanding of the present invention and to show how the same may be carried into effect, cer tain embodiments of the present invention will now be de scribed by way of example only with reference to the ac companying drawings, in which:
Figure 1 shows a heating profile for a variable- temperature (VT) X-ray diffraction (XRD) analysis of lead- free zinc borate silicate glass frit to establish a corre lation between phase structure and processing temperature and determine evolved phases and transition temperatures during heat treatment up to 860°C under air;
Figure 2 shows the resultant VT-XRD data by imple menting the heating profile of Figure 1 on a sample of lead-free zinc borate silicate glass and illustrates the development of different crystal phases within the lead- free zinc borate silicate glass frit on increasing heat treatment temperature starting with an amorphous exhibit ing no XRD peaks at room temperature and moving through various phase transitions to a dominant Zh4q(Bq2)b crystal phase with BO4 coordination at temperatures in excess of 800°C;
Figure 3 shows a differential scanning calorimeter (DCS) plot for lead-free zinc borate silicate glass indi cating a major exothermal event at 791°C which corresponds to the formation of Zh4q(BO2)6/ the dominating crystalline phase in this material at high processing temperatures in excess of 800°C as confirmed by the VT-XRD analysis shown in Figure 2;
Figure 4 shows solid state NMR spectra for lead-free zinc borate silicate glass processed at different tempera tures indicating peaks associated with BO3 coordinated bo ron (d(11B) ~ 13 ppm) and BO4 coordinated boron (d(11B) ~ 0 ppm) within the glass material, the data indicating the development of a strong and sharp BO4 peak on heating above 800°C as a result of increased crystallinity com pared to the BO4 peak of materials heated at lower temper atures which are weak and broad, indicative of primarily amorphous material;
Figure 5 shows a plot of the BO4 fraction of the total BO4 + BO3 coordinated boron within the lead-free zinc bo rate silicate glass as a function of temperature, clearly demonstrating that for the 840°C heat treated material, the BO4 fraction is dominating at ~ 90%;
Figure 6 shows hot-stage microscopy data for lead- free zinc borate silicate glass heated to various tempera tures, the data showing five zones (I - Softening (600 - 650°C); II - First Crystallisation (650 - 700°C); II+III - Residual glass softening (650 - 750°C); IV - Second Crys tallisation plateau (750-950°C); and V - Melting (> 950°C)), the thermal behaviour of the 840°C heat treated material indicating high crystallinity and the heating mi croscopic data being consistent with the XRD, DSC, and NMR results of Figures 1 to 5;
Figures 7 to 12 show layer thickness profile results for layers of lead-free zinc borate silicate glass fired at two different temperatures (690°C and 840°C) and sub jected to three different acid treatments (HC1, H2SO4, and HF), results indicating that while the glass which is fired at 690°C is strongly affected by all of the acids, the glass fired at 840°C is resistant to all of the acids;
Figure 13 shows an XRD analysis of lead-free zinc bo rate silicate glass frit sintered at 840°C;
Figure 14 shows an XRD analysis of a lead-free zinc borate silicate glass layer fired at 840°C on a silicon wafer; and
Figure 15 show an XRD analysis of a lead-free zinc borate silicate glass layer fired at 840°C on a silicon wafer and after being subjected to three different types of acid treatment indicating that all the acids primary attack the willemite crystal phase, with H2SO4 being the most aggressive followed by HC1 and HF.
Detailed Description
As described in the summary section, the present specification provides a method of manufacturing a pas sivation glass layer in a semiconductor component using a lead-free zinc borate silicate glass frit comprising or consisting of ZnO, B2O3, and S1O2 with low, or substantial ly no, bismuth and with minimal other impurity elements which can detrimentally affect passivation performance. Advantageously, the lead-free zinc borate silicate glass frit is fabricated so as to be amorphous, uniform, and of good printability in order to enhance deposition of a uni- form and consistent frit layer prior to firing. The glass compositions are such that they develop a dominant crys talline Zh4BdOΐ3 phase (BO4 coordination) at firing tempera tures over 800°C to provide a very acid resistant pas sivation layer.
An example of a lead-free zinc borate silicate glass frit composition consisting of ZnO, B2O3, and S1O2 is given below.
Figure imgf000010_0001
It should be noted that glass materials are conven tionally defined in terms of equivalent oxide content, even if other compound types are used as the starting ma terials. For example, in the present case the boron con tent may be provided using H3BO3 as the starting raw mate rial in combination with ZnO and S1O2.
To fabricate the glass frit material a powder mixture of the metal compound starting materials is prepared and then melted to form the glass. In this case, the powder mixture for glass melting was prepared using high purity raw materials: ZnO, H3BO3 and S1O2. lOOg of the raw materi als powder mix was melted in a platinum crucible at a melting temperature of 1375°C and a melting time of 60 minutes. Subsequently the molten glass was quenched in water, dried, and then jet milled to form a powdered frit material with a particle size distribution having a d(50) = 1.9 micrometres and a d(90) = 4.7 micrometres. It was noted that the melting temperature of 1375°C when using high purity raw materials was significantly higher com pared to corresponding compositions made using standard grades of raw materials comprising more impurities.
It is important that the frit is melted in a platinum crucible to avoid contamination. It is particularly im- portant to avoid alkali metal, alkaline earth metal, and any early transition metal contamination to achieve good dielectric properties in semiconductor passivation appli cations . The coefficient of thermal expansion (CTE) of the melted glass was measured as 48 x 106/°C using a dilato- metric method. The glass was measured to have a glass transition temperature Tg = 575°C and a glass softening temperature Tf = 620°C. Through different characterization techniques (de scribed later in this specification) it has been shown that after firing above 800°C the glass develops a unique crystal phase which allows a very high resistance against hydrofluoric acid. Furthermore, after firing at such tem- peratures, the glass also exhibits good dielectric proper ties.
Following on from the above, a range of twenty dif ferent lead-free zinc borate silicate glass frits have been fabricated as summarized in the tables below. All of these glass frits comprise 30 to 70 mol% ZnO, 10 to 40 mol% B2O3 and 2 to 35 mol% SiCb- Several examples also in clude one or more of AI2O3, ZrC>2, SnC>2, and BaO.
Figure imgf000011_0001
Figure imgf000012_0001
Figure imgf000012_0002
Figure imgf000012_0003
The lead-free zinc borate silicate glass frits as de scribed herein can be used to form the passivation layer of power devices. For this particular application, a glass frit-based paste suitable for screen printing is re quired and the substrate on which the paste is applied is silicon. The thermal expansion of the frit is preferably between 2.6 to 4.1 c 106/°C. The glass transition tempera ture of the frit Tg is ideally > 450°C and the glass sof tening temperature Tf is < 1000°C, while the operating temperature in a semiconductor device is typically < 200°C.
High purity is one of the most critical requirements for this passivation application. From a dielectric per spective acceptable elements in the glass composition in clude Ba, Sr, Al, B, Ti, Zn, and Bi while elements which are not acceptable from a dielectric perspective include Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li. Limited by the elements that can be used, a zinc borate silicate glass system has been explored and successfully developed as the suitable material system. Acid durability is an other critical product requirement and it is required that the passivation layer should be resistant to HF etching. The zinc borate silicate glass system has been found to provide such acid durability when suitably processed (e.g. fired at a temperature over 800°C).
Chemical analysis has been performed on the as-made frit powder to ensure composition and impurity content. An example of a chemical analysis of a glass frit accord ing to the present specification is set out in the table below. The as-made frit powder material was determined for the component elements Zn, B, and Si as well as the level of impurities.
Figure imgf000014_0001
Due to the precise control of the melting and the milling conditions, the actual levels of all the inclusive elements such as Zn, B and Si in the obtained frit powder are close to the nominal values. More importantly, all the impurities are suitably controlled below the acceptable levels, satisfying the stringent application specifica tion.
The exemplary glass frit material as defined above was subjected to analysis by variable-temperature X-ray diffraction (VT-XRD), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and hot-stage mi croscopy. The analyses and results are summarized below.
XRD Analysis
The frit material is amorphous at room temperature. However, upon heating, it undergoes several different crystallisations. To establish the exact correlation be tween its phase structure and temperature, the as-made frit material was studied by variable-temperature (VT) X- ray diffraction (XRD) to precisely determine its evolved phases and transition temperatures during heat treatment up to 860°C under air conditions.
A powder sample of the glass frit material was packed into a sample holder and mounted in a heating chamber un- der flowing air (20% O2 / N2). An initial long data set was measured at room temperature for reference (RT pre-VT da ta) between 10 - 130° 2Q with a step size of 0.02°, ls/step. The VT Data was collected between 23-70°2q, step size of 0.020° with a collection time of 0.43s/step. A ramp rate of 12°C/min from room temperature up to 860°C was applied with data collected in 20°C increments from 500°C as shown by the heating profile in Figure 1. The sample was then cooled from 860 to 30°C at 12°C/min and a final room temperature reference dataset collected. A fi nal long dataset 'post-calcination' measured between 10- 130°2Q with a step size of 0.02°, ls/step was collected at room temperature following the heat treatment experiment (RT post-VT data), again for reference.
Figure 2 is a contour plot of the results of the var iable temperature XRD experiment. It is evident from Fig ure 2 that the starting material at room temperature (RT- start) was amorphous exhibiting no obvious XRD peaks. The sample was expected to remain amorphous between room tem perature and 500°C, hence no data collection was performed during this heating range. On further heating, this sample remained amorphous up to at least 680°.
Evidence of trace crystalline phase formation was first detected in the 700°C dataset, where the observed phases detected were: Zinc Borate, Zn3(B03)2 - PDF 04-011- 5158 in Figure 2; and Willemite, Zn2Si04 - PDF 00-037-1485 in Figure 2.
A third crystalline phase was first detected as a trace phase in the 740°C dataset. This phase was cubic in structure and closely matches the following documented isostructural phases: Zinc Borate, Zh4q(Bq2)b - PDF 01-076- 0917 in Figure 2; and/or Zinc Borate, Zn(B02)2 - PDF 00- 039-1126 in Figure 2.
All three trace phases increased in crystallinity and concentration on further heating to 860°C and above.
RT end in Figure 2 was the long dataset collected at room temperature post cooling. This dataset confirmed the pre- dominant phase present post heating/cooling to be cubic, closely matching the isostructural phases indicated above such as Zh4q(BO2)6· Relatively minor amounts of crystalline Zinc Borate, Zn3(603)2 and Willemite, Z^SiCg were also evi dent in the final cooled material.
DSC Analysis
The as-made glass frit powder was analysed using a simultaneous thermogravimetric analyser (Netzsch STA449F3) and differential scanning calorimeter with coupled mass spectrometer (Netzsch Aelous) for evolved gas analysis. The heating procedure adopted was from 40 to 1000°C with a heating rate of 10°C /min. Measurement was blank corrected and the measurement pan used was graphite with no lid. The measurement atmosphere used was Argon. The system was cal ibrated with metal standards for temperature and sensitiv ity accuracy.
The obtained DSC curve is shown in Figure 3. It is clear that a major exothermal event is peaked at 791°C, corresponding to the formation of Zh4q(BO2)6/ the dominat ing crystalline phase in this material as confirmed by the XRD analysis. In addition, a major glass transition is observed at ~645°C and the melting takes place at ~968°C.
NMR Analysis
Solid State NMR spectra were acquired at a static magnetic field strength of 14.IT ( 0(1H) =600 MHz) on a Bruker Avance Neo console using TopSpin 4.0 software. For 11B, the probe was tuned to 192.57 MHz and referenced to NaBH4 at -42.06 ppm. Powdered samples were packed into zirconia MAS rotors with Kel-F caps, with before and after weighing providing the sample mass. The rotors were spun using room-temperature purified compressed air. The rotor diameter was 4 mm and the frequency used for measuring 11B was 10000 Hz.
The glass material (for the heat treatment £ 700°C) was mainly amorphous (indictive by the observed broad peaks) consisting of both BO3 and BO4 environments. The 840°C heat treated material however showed a sharp BO4 peak (with little BO3), which revealed the high crystallinity of the material after the high temperature heat treatment, consistent with tetrahedral boron sites in the Zh4q(Bq2)b crystalline phase as determined by XRD.
The processed spectra are shown in Figure 4. For all the samples treated up to 700°C there are typical BO3 and BO4 environments. The sintered sample treated at 840°C, showed a strong and sharp BO4 peak indicative of a crys talline environment. The sintered samples also exhibit a well-structured BO3 peak indicative of a crystalline envi ronment.
The BO4 fraction of the total (BO4 + BO3) was plotted as a function of temperature as shown in Figure 5. This clearly demonstrates that the 840°C heat treated material comprises a BO4 fraction which is dominating at ~ 90%.
Hot-stage microscopy analysis
The above-mentioned series of powder samples which were heat treated at various temperatures respectively were also studied by a Misura hot-stage microscope (HSM, Expert System Solutions) and the results are shown in Fig ure 6. It is clear from Figure 6 that in total five zones may be assigned:
I: Softening (600 - 650°C)
II: First Crystallisation (650 - 700°C)
II+III: Residual glass further Softening (650 - 750°C)
IV: Second Crystallisation plateau (750-950°C)
V: Melting (> 950°C)
The thermal behaviour of the 840°C heat treated mate rial suggests its high crystallinity. The heating micro scopic data is consistent with the XRD, DSC, and NMR re sults described previously.
Acid resistance testing Lead-free zinc borate silicate glass frit was pre pared as previously described. The glass frit powder was mixed with a liquid carrier media (80% glass powder; 20% media) to form a paste. The paste was then screen printed on a silicon wafer, dried at 150°C, and fired in a fur nace. One set of samples was fired at 690°C for 4 minutes while another set of samples was fired at 840°C for 4 minutes. The layer thickness of the fired plates was measured on a profilometer (NANOFOCUS USCAN).
The fired plates were tested to determine the effect of three acids on the layer thickness: HC1 (3.7%); H2SO4 (5%); and HF (10%). The layer thickness was measured be fore and after acid attack.
Figures 7 to 12 show layer thickness profile results for layers of lead-free zinc borate silicate glass fired at the two different temperatures (690°C and 840°C) and subjected to the three different acid treatments (HC1, H2SO4, and HF).
Figure 7 shows the results for the 690°C fired sample treated with HC1 (3.7%). The left-hand profile in Figure 7 is before acid application while the right-hand profile is after acid application. It is clear that HC1 has a significant effect on the glass layer.
Figure 8 shows the results for the 690°C fired sample treated with H2SO4 (5%). The left-hand profile in Figure 8 is before acid application while the right-hand profile is after acid application. It is clear that H2SO4 has a sig nificant effect on the glass layer.
Figure 9 shows the results for the 690°C fired sample treated with HF (10%). The left-hand profile in Figure 9 is before acid application while the right-hand profile is after acid application. It is clear that HF has a signif icant effect on the glass layer.
Figure 10 shows the results for the 840°C fired sample treated with HC1 (3.7%). The left-hand profile in Figure 10 is before acid application while the right-hand profile is after acid application. It is clear that HC1 has lit tle or no effect on the glass layer.
Figure 11 shows the results for the 840°C fired sample treated with H2SO4 (5%). The left-hand profile in Figure 11 is before acid application while the right-hand profile is after acid application. It is clear that H2SO4 has lit tle or no effect on the glass layer.
Figure 12 shows the results for the 840°C fired sample treated with HF (10%). The left-hand profile in Figure 12 is before acid application while the right-hand profile is after acid application. It is clear that HF has little or no effect on the glass layer.
Results indicating that while the glass which is fired at 690°C is strongly affected by all of the acids, the glass fired at 840°C is resistant to all of the acids. An XRD analysis has also been performed on untreated and acid treated samples to determine which phases within the glass material are susceptible to acid degradation.
Figure 13 shows an XRD analysis of lead-free zinc bo rate silicate glass frit sintered at 840°C. The glass frit powder was sintered in a furnace at a heating rate of 15°C/min to a temperature of 840°C and for a dwell time of 30 min in corundum crucible. The CTE of the sintered glass material was measured as 42.6 x 106/°C. The XRD in dicates the main crystal phases are tetra-zinc-borate (4Zn0*E>203) and willemite (2ZnO* S1O2) ·
Figure 14 shows an XRD analysis of a lead-free zinc borate silicate glass layer fired at 840°C on a silicon wafer. The main crystal phases of the 840°C fired enamel are tetra-zinc-borate (4Zn0*E>203) , willemite (2ZnO*SiC>2) and tri-zinc-borate (3ZnO* B2O3).
Figure 15 show an XRD analysis of a lead-free zinc borate silicate glass layer fired at 840°C on a silicon wafer and subjected to three different types of acid treatment indicating that all the acids primary attack the willemite crystal phase, with H2SO4 being the most aggres sive followed by HC1 and HF. The HF testing data revealed that only the lead-free zinc borate silicate glass materials which were heat treated at above 800°C showed the satisfactory HF re sistance, while those materials which were either un-heat- treated or heat-treated at temperatures < 800°C exhibited inferior/unsatisfactory HF durability. The acid test re sults confirmed that there is a strong correlation between HF durability and the presence of highly crystalline phase Zh4q(Bq2)d where B is in BO4 coordination.
Summary
A suitable glass system has been developed for use as a passivation layer in power devices. It has been discov ered that in order to satisfy acid durability requirements for certain applications, achieving the correct crystal phase and 11B environment structure (BO4) is essential. This correct phase assembly may be achieved by the appro priate heat treatment on the as-made lead-free zinc borate silicate glass frit materials. All impurity levels were appropriately controlled ensuring stringent product re quirements to be met. Furthermore, a compositional range has been established with good glass formability for ob taining a homogenous amorphous glass (without phase sepa ration or crystallisation) as a starting material suitable for paste formulation offering good printability. Benefits of the invention include: environmentally friendly lead- free frit and enamel; high firing temperature (above 800°C); low coefficient of thermal expansion; high acid resistance when fired at or above 800°C; and suitable for deposition on semiconductor wafers.
While the lead-free zinc borate silicate glass frit materials described herein have been developed for use in semiconductor device passivation applications, it is also envisaged that the glass frit materials may be useful in other applications, particularly those which require an acid resistant glass enamel coating. Accordingly, other applications may comprise depositing the glass frit on a substrate (e.g. glass, metal, ceramic, or other substrate requiring an acid resistant coating) and firing the glass frit to form a glass layer disposed on the substrate.
While this invention has been particularly shown and de- scribed with reference to certain examples, it will be un derstood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

Claims
1. A method of manufacturing a semiconductor component, the method comprising: depositing a glass frit over a semiconductor layer; and firing the glass frit to form a passivation glass layer disposed over the semiconductor layer, wherein the glass frit is composed of a lead-free zinc borate silicate glass comprising ZnO, B2O3, and S1O2, less than 5 mol% B12O3, and less than 100 ppm by weight of each of Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li.
2. A method according to claim 1, wherein the glass frit comprises less than 4, 3, 2, 1, 0.1, or 0.01 mol% of B12O3.
3. A method according to claim 1 or 2, wherein the glass frit comprises less than 0.1 or less than 0.01 mol% AI2O3.
4. A method according to any preceding claim, wherein the glass frit comprises less than 80 ppm, 60 ppm, 40 ppm, or 30 ppm by weight of each of Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li.
5. A method according to any preceding claim, wherein the glass frit is formed without addition of a compound comprising any of Pb, Cu, Cr, Co, Mn, Mo, Mg, Fe, Na, Ca, K, and Li.
6. A method according to any preceding claim, wherein the glass frit comprises less than 100 ppm, 80 ppm, 60 ppm, 40 ppm, or 30 ppm by weight of one or more of Ba, Sr, Ti, Bi, and A1.
7. A method according to any preceding claim, wherein the glass frit is formed without addition of a compound comprising one or more of Ba, Sr, Ti, Bi, and A1.
8. A method according to any preceding claim, wherein the glass frit comprises 30 to 70, 40 to 65, or 50 to 60 mol% ZnO.
9. A method according to any preceding claim, wherein the glass frit comprises 10 to 40, 20 to 40, or 30 to 40 mol% B2O3.
10. A method according to any preceding claim, wherein the glass frit comprises 2 to 35, 2 to 25, 2 to 20, or 5 to 15 mol% SiC>2.
11. A method according to any preceding claim, wherein the glass frit is amorphous prior to firing.
12. A method according to any preceding claim, wherein the glass frit is fired at a temperature in excess of 800°C.
13. A method according to any preceding claim, wherein after firing the passivation glass layer comprises crys talline Zn4B60i3.
14. A method according to any preceding claim, wherein after firing the passivation glass layer comprises greater than 50%, 60%, 70%, 80% or 90% of a total boron content in a BO4 coordination state.
15. A semiconductor component comprising: a semiconductor layer; and a passivation glass layer disposed over the semicon ductor layer, the passivation glass layer comprising a fired glass frit, the glass frit being composed of a lead-free zinc bo- rate silicate glass as defined in any preceding claim.
16. Use of a glass frit as defined in any preceding claim for fabricating a passivation glass layer of a semiconduc tor component.
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PCT/NL2022/050276 2021-06-08 2022-05-20 Glass frit compositions for semiconductor passivation applications WO2022260509A1 (en)

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US20140261662A1 (en) * 2013-03-18 2014-09-18 E I Du Pont De Nemours And Company Method of manufacturing a solar cell electrode
CN106448802A (en) * 2015-08-07 2017-02-22 E.I.内穆尔杜邦公司 Conductive paste composition and semiconductor devices made therewith
WO2018026402A1 (en) 2016-08-03 2018-02-08 Ferro Corporation Passivation glasses for semiconductor devices
EP3480179A1 (en) * 2017-11-07 2019-05-08 Ferro Corporation Low k dielectric compositions for high frequency applications
GB2587074A (en) * 2019-07-15 2021-03-17 Johnson Matthey Plc Composition, paste and methods

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140261662A1 (en) * 2013-03-18 2014-09-18 E I Du Pont De Nemours And Company Method of manufacturing a solar cell electrode
CN106448802A (en) * 2015-08-07 2017-02-22 E.I.内穆尔杜邦公司 Conductive paste composition and semiconductor devices made therewith
WO2018026402A1 (en) 2016-08-03 2018-02-08 Ferro Corporation Passivation glasses for semiconductor devices
EP3480179A1 (en) * 2017-11-07 2019-05-08 Ferro Corporation Low k dielectric compositions for high frequency applications
GB2587074A (en) * 2019-07-15 2021-03-17 Johnson Matthey Plc Composition, paste and methods

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