WO1997030001A1

WO1997030001A1 - Glass and glass-ceramic compositions; glass and glass-ceramic substrates

Info

Publication number: WO1997030001A1
Application number: PCT/GB1997/000248
Authority: WO
Inventors: Jürgen Werner; Ralf Bergmann; John George Darrant
Original assignee: Gec Alsthom Limited; MAX-PLANCK-Gesellschaft zur Förderung der Wissenschaften e.V.
Priority date: 1996-02-14
Filing date: 1997-01-29
Publication date: 1997-08-21
Also published as: GB2310314A; GB9603028D0

Abstract

A glass or glass-ceramic composition has thermal stability up to at least 700 °C: the composition is used for forming a substrate for an inorganic material or a semi-conducting material e.g. silicon and its coefficient of thermal expansion is substantially the same as that of the material.

Description

Glass and Glass-ceramic compositions: Glass and Glass-ceramic substrates

This invention relates to glass compositions and glass-ceramic compositions and their use as substrates.

Glass and Glass-ceramics have been used for many years as electrical and electronic substrates. The properties of these materials in these applications which make them attractive are their coefficients of thermal expansion and their thermal stability. Alumino or Borosilicate glasses are currently used as substrates for silicon in devices such as solar cells and thin film transistors for displays, due to their matched thermal expansion and stability up to about 600 °C and relatively low cost. The performance of such devices is limited by the maximum processing temperature at which the device can be produced, and this also affects the cost. An increase in the refractoriness (i.e. thermal stability) of the substrate would enable higher temperature processing with concomitant device performance enhancement and/or cost reduction.

Silicon is currently used as a substrate for silicon in microelectronic applications, e.g. silicon on insulator (SOI). The use of a lower cost substrate material in place of silicon would offer significant cost reduction.

An object of the present invention is to provide a refractory glass or glass-ceramic composition able to withstand high temperature processing and capable of being used as a substrate, which gives improved performance at lower cost. High temperature in this context refers to temperatures of 700°C and above.

Embodiments of the invention will be described which involve the selection of particular oxides which are mixed and heated to form a glass melt. Alternatively, chemical precursors to glass (e.g. sol-gel) are combined and reacted. The selected constituents and processing ensure a final substrate material which is either a glass or glass-ceramic with a coefficient of thermal expansion in the range 1-12 x lO^/K. The material may be used as a substrate for silicon for thin film solar cells (manufactured e.g. by deposition techniques such as chemical vapour deposition, solution growth, ion beam or ion beam assisted deposition, molecular or cluster beam deposition or sputter deposition assisted techniques) and the technology of thin film transistors in displays. In addition, the material may be used as a substrate or support for crystalline silicon in microelectronic or micromechanic applications, e.g. Silicon on Insulator (SOI) or bonding of silicon wafers.

Fine adjustment of the thermal expansion coefficient of the glass or glass-ceramic allows also use for other semiconductor materials such as germanium, silicon-germanium, gallium arsenide, silicon carbide, diamond, copper-indium-diselinide, gallium nitride, etc, and other inorganic or semi-conducting materials as appropriate.

From one aspect, the invention provides a glass or glass-ceramic composition having thermal stability up to at least 700° C and comprising at least 50 wt% SiO₂and at least 9 wt% Ai ₃.

From a further aspect, the invention provides a component comprising a substrate having a material applied thereto either directly or with at least one intermediate layer between the substrate and the material, said substrate being formed of a glass or glass-ceramic composition having a thermal stability (as hereinafter defined) up to at least 700^ and having a coefficient of thermal expansion which is substantially the same (as hereinafter defined) as that of the material.

From a still further aspect, the invention provides a method of manufacturing a component comprising a substrate having a material applied thereto either directly or with at least one intermediate layer between the substrate and the material, said method comprising forming the substrate of a glass or glass-ceramic composition having a thermal stability (as hereinafter defined) up to at least 700⁽C and having a coefficient of thermal expansion which is substantially the same (as hereinafter defined) as that of said material.

'Thermal stability' in the context refers to the ability of the composition to withstand processing without a significant degree of change in its surface characterisation as manifested by surface crystallisation, and its bulk characteristics. 'Substantially the same' refers to the coefficients of thermal expansion being sufficiently close so that the material applied to the substrate rrj intains its physical integrity eg it will not crack or peel. Thus the substrate will have a similar coefficient of thermal expansion as that of the materials applied thereto eg silicon, germanium, silicon-germanium, gallium arsenide, silicon carbide, diamond, copper-indium-diselenide, gallium nitride, etc (i.e. in the range 1-12 x 10 ^"VK).

The substrate may be either transparent, translucent or opaque.

The substrate material is normally made from oxides or chemical precursors to glasses or glass- ceramics including at least a selection of: SiO₂, Al₂O₃, As₂O₃, BaO, Cs₂O, CaO, CeO₂, MgO, P₂O₅, SrO, TiO₂, ZnO, ZrO₂ and lanthanide oxides.

The substrate may be produced via a glass melting route eg wherein a selection of given oxides are mixed and heated to a form of glass melt or via chemical routes (e.g. sol-gel).

The glass or glass-ceramic may be made from SiO₂, Al₂O₃ nucleating agents comprising one or more of P₂O₅, TiO₂ and ZrO₂ and other oxides including one or more of As₂O₃, BaO, CaO, Cs-O, CeO₂, MgO, SrO, ZnO and lanthanide oxides.

For example, such a material may comprise a glass or glass-ceramic made from silica 50.0 wt to 75.0 wt%; aluminium oxide 9.0 wt% to 40.0 wt%; arsenic oxide 0.1 wt% to 15.0 wt ; barium oxide 0.1 wt% to 45.0 wt%; calcium oxide 0.1 wt% to 25.0 wt%; caesium oxide 0.1 wt% to 45.0 wt ; cerium dioxide 0.1 wt% to 15.0 wt%; magnesium oxide 0.1 wt to 25.0 wt%; phosphorous pentoxide 0.1 wt% to 15.0 wt%; strontium oxide 0.1 wt% to 25.0 wt%; titanium dioxide 0.1 wt% to 15.0 wt%; zinc oxide 0.1 wt to 15.0 wt ; zirconium dioxide 0.1 wt% to 15.0 wt%, and lantiianide oxides 0.1 wt% to 15.0 wt% and other oxides to a total of 100 wt%.

Glass and glass-ceramic compositions within the scope of the invention may optionally comprise other constituents such as firing agents, colourants or other additives, used in minor proportions to modify melting characteristics, appearance and/or other glass properties.

The substrate may be formed to be flat , concave or convex and may be structured eg formed with intersecting grooves, or dimples.

The substrate may be used directly or with a passivation layer coating (e.g. SiO₂ , Si. N_y Al₂ O₃ or AIN) or a combination of suitable passivation layers; such passivation layer(s) may act for preventing the glass from crystallising and/or protecting the film from diffusion of impurities from the elass. The substrate (with or without a passivation layer) may be coated with or bonded to a semiconducting film consisting of silicon, germanium, silicon-germanium, gallium arsenide, silicon carbide, diamond, copper-indium-diselenide, gallium nitride, or other inorganic/semi¬ conducting materials. The semi-conducting material may be organic or inorganic.

Further, the semiconductor film may be fabricated into solar cells, thin film transistors, silicon on insulator structures , micromechanical devices, light emitting diodes, semiconductor lasers or optoelectronic devices or other solid state devices or circuits.

Still further, the substrate may be used as a mechanical support for the handling or processing of crystalline silicon or other semiconductors.

Embodiments of the invention are now given by way of example only.

Examples

1. In a first embodiment glass composed of all or a part of the components SiO ₂, Al ₂O ₃, BaO, MgO, ZnO, ZrOj, Cs Q is melted and cast to yield blocks for subsequent machining to desired substrate shape. Thin films of silicon or other semiconductors are deposited and /or subsequently treated in the temperature range of 700 - 1450 °C to yield solar cells, thin film transistors, micromechanical, optoelectronic or other solid state devices or circuits.

2. Table 1 give a series of ten glass compositions in accordance with the invention. The constituents are melted at 1650°C - 1800°C and annealed at e.g. 800°C for 1 h - 2 h. Subsequent treatment is as in Example 1.

Table 2 below illustrates the results of thermal stability trials with some of the glass compositions as set out in Table 1 such compositions being identified as NK2/(4297, 4298, 4300-4303)

KEY No surface crystallisation visible.

Very Umited amount of surface crystallisation.

Very significant degree of surface crystallisation.

Severe surface crystallisation.

Table 2: Thermal stability trials on example glasses and glass-ceramics

As indicated above, 'thermal stability' refers to the ability of the composition to withstand processing without any or without a significant degree of change in its surface characteristics as manifested by surface crystallisation, and its bulk characteristics.

The table. Table 3, below illustrates the thermal behaviour of the glasses designated 4297, 4298 4300-4303 in accordance with the invention, in comparison with known glasses. (Pyrex is a trade mark).

Material Linear thermal expansion coefficient Transformation Softening α l0-* (25 - T°C) temperature temperature

200 400 600 800 1000 Ts

Polycrystalline 3.13 3.55 3.79 3.82 3.87 - • Silicon

Fused Quartz 1.29 1.11 1.03 0.79 0.61 - -

Pyrex Glass 4.10 3 S7 3.94 - - 551 602

Schott 3.94 3.73 3.96 - - 556 612 float glass

4297 4.49 4.51 4.58 4.52 _m 794 847

4298 4.13 4.61 4.80 4.65 820 850

4300 3.12 3.37 3.52 3.40 . 826 870

4301 3.38 3.58 3.72 3.65 _β 833 896

4302 3.50 3.74 3.88 3.72 837 879

4303 3.29 3.66 3.85 3.86 _β 822 874

Table 3: Thermal expansion of polycrystalline silicon, fused quartz, Pyrex glass, Schott float glass and example glasses and glass-ceramics.

The accompanying Figure 1 illustrates the percentage linear change in dimensions of the glasses NK2/4300-4303 versus temperature in comparison with silicon.

A glass composition is prepared as per any one of the examples in Table 1 but in addition amoφhous silicon is deposited e.g. by low pressure chemical vapour deposition or plasma enhanced chemical vapour deposition at temperatures below 600°C and subsequently crystallized by a furnace anneal at temperatures around 600 °C for periods of 2 to 48 h, by rapid thermal annealing at temperatures in the range of approx. 750 - 1300°C for fractions of seconds to several minutes or a combination of both or by laser annealing or zone melt crystallisation processes using a variety of heat sources.

4. Glass is prepared as per Example 1 or 2 above but in addition silicon is deposited at temperatures around 1000°C by chemical vapour deposition using a trichlorosilane process.

5. As per Example 3 except that the polycrystalline Si layer created in Example 3 is further thickened by a silicon - liquid phase epitaxy process from various metal solutions (e.g. In, Sn Bi, Ga) at temperatures around 900°C, or a vapour phase epitaxy process from trichlorosilane at temperatures around lOOO'C.

6. As Example 5, except that the silicon film is fabricated into a solar cell using standard microelectronic cleaning techniques (e.g. RCA cleaning sequence with or without HF etching or other standard cleaning procedures used in microelectronic device fabrication like cleaning solutions using organic cleaning ingredients), solid state or other means of dopant diffusion at temperatures around 850 °C and an optional thermal Si surface oxidation at temperatures around 1100 °C. The RCA cleaning sequence consists of two cleaning steps: first a mixture of ammonia, hydrogen peroxide and water, heated to about 70-80°C and applied for approximately 10 - 15 min followed by a water rinse and a mixmre of hydrochloric acid, hydrogen peroxide and water, again at the same temperature and time. Alternatively, a mixture of sulphuric acid and hydrogen peroxide is used. There are a lot of varieties like boiling in HCl or HNO₃or dipping in HF or combinations. On the other hand, organic cleaning solvents like 'Mucasol' (TM) may be utilised.

7. As Example 3, except that the silicon film is fabricated into thin film transistor devices or circuits using standard cleaning techniques, solid state diffusion or other means of dopant incorporation (e.g. ion implantation) and other electronic device production sequences.

8. As in any previous example except that sheet glass is either drawn or cast from the melt. The glass may be polished if necessary - this will not always be essential.

9. As in any previous example except that sheet glass is formed by the float method. 10. As Examples 8 or 9 where the sheet glass is mechanically structured on either one or both faces.

1 1. A glass composed of silica 64 wt%, aluminium oxide 21 wt%, barium oxide 7 wt%, and magnesium oxide 8 wt% and processed as in any previous example.

12. As Example 1 1 except that sheet glass is either drawn or cast from the melt.

13. As Example 11 except that sheet glass is formed by the float method.

14. As in Example 12 or 13 where the glass is mechanically structured on either one or both faces.

15. As in any of the previous Examples except that the glass is heat-treated in the range 600 - 1500°C to develop a polycrystalline microstructure (i.e. formation of a glass-ceramic).

16. As in any previous example except that thin film transistors, solar cell materials or semiconductor lasers or light emitting diodes or other solid state devices or circuits are deposited on the substrate material.

17. As in any of examples 1 - 16 except that the glass or glass-ceramic is combined with a silicon superstrate for subsequent production of a silicon on insulator device or solar cell or micromechanical or optoelectronic devices or circuits.

18. As in any previous example except that the substrate is treated with a surface passivation layer (e.g. SiO^.

19. As in any previous example except the glass or glass-ceramic is used as a mechanical support for the handling and processing of crystalline silicon.

20. As in any of examples 1 - 18 except the glass or glass-ceramic sheet is bonded to crystalline silicon.

21. A glass composed of SiO₂, Al₂O₃, BaO and MgO is prepared from chemical precursors (e.g. sol-gel). Thin sheets are cast onto a suitable substrate and heat-treated at temperamres up to 1500°C. Silicon is deposited in the temperature range 700 - 1450°C to yield thin films for solar cells or other solid state devices such as thin film transistors or micromechanical devices.

22. As example 21 except that thin sheets are prepared by extrusion.

23. As in either of examples 21 or 22 except that the glass is heat-treated in the range 600- 1500°C to develop a polycrystalline microstructure.

24. As in any of examples 21 - 23 except thin film transistors, solar cells, micromechanical devices or other solid state devices are fabricated on the substrate.

25. As in any of examples 21 - 24 except the glass or glass-ceramic is combined with a silicon superstrate for subsequent production of silicon on insulator or micromechanical devices.

26. As in any of examples 21 - 25 except that the substrate is treated with a surface passivation layer (e.g. SiO₂, Si_xN_y, AIN, Al_jO_j).

Claims

Ciaims

1. A component comprising a substrate having a material applied thereto either directly or with at least one intermediate layer between the substrate and the material, said substrate being formed of a glass or glass-ceramic composition having a thermal stability (as hereinbefore defined) up to at least 700°C and having a coefficient of thermal expansion which is substantially the same (as hereinbefore defined) as that of the material.

2. A component as claimed in Claim 1 wherein the glass or glass-ceramic composition is transparent or translucent or opaque.

3. A component as claimed in Claim 1 or Claim 2 wherein the glass or glass-ceramic composition is made from oxides or chemical precursors to glasses or glass-ceramics including at least two of the following:-SiO₂, Al₂O₃, As₂O₃, BaO, Cs-O, CaO, CeO₂ MgO, P₂O_s, SrO, TiO₂, ZnO, ZrO₂ , lanthanide oxides.

4. A component as claimed in any preceding claim, said substrate being produced via a glass melting route, wherein a selection of given oxides is mixed and heated to a form of glass melt.

5. A component as claimed in any one of Claims 1 - 3, said substrate being made using a chemical process eg sol-gel.

6. A component as claimed in any one of Claims 1 - 5, said substrate comprising at least 50 wt% SiO₂ and at least 9 wt% Al₂O₃

7. A component as claimed in any one of claims 1 - 5 said substrate being made from SiO₂, Al₂O₃, nucleating agents comprising one or more of P₂O₅ , TiO₂ and ZrO₂ , and other oxides including one or more of As₂O₃, BaO, CaO, Cs₂O , CeO₂, MgO, SrO, ZnO, lanthanide oxides.

8. A component as claimed in any one of Claims 1 - 5, said substrate being made from silica 50.0 wt% to 75.0 wt% and aluminium oxide 9.0 wt% to 40.0 wt% and also including one or more of the following in the wt% as specified:- arsenic oxide 0.1 wt% to 15.0 wt%; barium oxide 0.1 wt to 45.0 wt%; calcium oxide 0.1 wt% to 25.0 wt%; caesium oxide 0.1 wt% to 45.0 wt ; cerium dioxide 0.1 wt to 15.0 wt%; magnesium oxide 0.1 wt% to 25.0 wt%; phosphorous pentoxide 0.1 wt% to 15.0 wt ; strontium oxide 0.1 wt% to 25.0 wt%; titanium dioxide 0.1 wt% to 15.0 wt ; zinc oxide 0.1 wt% to 15.0 wt%; zirconium dioxide 0.1 wt% to 15.0 wt%; lanthanide oxides 0.1 wt% to 15.0 wt%; other oxides.

9. A component as claimed in any preceding claim wherein said substrate comprises constituents such as firing agents, colourants or other additives, used in minor proportions to modify melting characteristics, appearance and/or other glass properties.

10. A component as claimed in any proceding claim wherein the material is an inorganic material.

11. A component as claimed in any proceding claim wherein the material is a semi - conducting material.

12. A component as claimed in any preceding claim, said material being silicon.

13. A component as claimed in any proceding claim wherein the material is applied as a film to the substrate.

14. A component as claimed in any preceding claim, being a micro-electronic component.

15. A component as claimed in any preceding claim wherein the substrate has a passivation layer coating.

16. A component as claimed in any preceding claim wherein the substrate has a plurality of passivation layers applied thereto.

17. A component as claimed in either of Claims 15 or 16 wherein the or each passivation layer comprises SiO₂ and/or Si_N_y and/or Al₂O₃ and or AIN.

18. A component as claimed in any one of claims 15 - 17 wherein the substrate is coated with or bonded to a semiconducting film comprising silicon or germanium or silicon germanium or gallium arsenide or silicon carbide or diamond or copper- indium- diselenide or gallium nitride.

19. A method of manufacturing a component comprising a substrate having a material applied thereto either directly or with at least one intermediate layer between the substrate and the material, said method comprising forming the substrate of a glass or glass-ceramic composition having a thermal stability (as hereinbefore defined) up to at least 700°C and having a coefficient of thermal expansion which is substantially the same (as hereinbefore defined) as that of said material.

20. A glass or glass-ceramic composition having thermal stability up to at least 700° C and comprising at least 50 wt% SiO₂ and at least 9 wt% Al₂O ₃ .

21. A glass or glass-ceramic composition as claimed in Claim 20 which additionally comprises at least 0.1 wt% BaO and or at least 0.1 wt% Cs₂O.

22. A glass or glass-ceramic composition as claimed in Claim 20 being formed of SiO ₂, Al₂O₃ , nucleating agents comprising one or more of P O , TiO nd ZrO juid other oxides including one or more of As₂O₃, BaO, CaO, Cs₂O , CeO₂, MgO, SrO, ZnO and lanthanide oxides.

23. A glass or glass-ceramic composition as claimed in Claim 20 being made from silica 50.0 wt to 75.0 wt% and aluminium oxide 9.0 wt% to 40.0 wt% and also including one or more of the following in the wt% as specified:- arsenic oxide 0.1 wt% to 15.0 wt ; barium oxide 0.1 wt% to 45.0 wt%; calcium oxide 0.1 wt% to 25.0 wt%; caesium oxide 0.1 wt% to 45.0 wt%; cerium dioxide 0.1 wt% to 15.0 wt ; magnesium oxide 0.1 wt% to 25.0 wt%; phosphorous pentoxide 0.1 wt% to 15.0 wt%; strontium oxide 0.1 wt% to 25.0 wt ; titanium dioxide 0.1 wt to 15.0 wt%; zinc oxide 0.1 wt% to 15.0 wt%; zirconium dioxide 0.1 wt% to 15.0 wt%; lanthanide oxides 0.1 wt% to 15.0 wt%; other oxides.

24. A glass or glass-ceramic composition substantially as herein before described with reference to any of examples 1 - 26.

25. A component substantially as herein before described with reference to any of examples

1 - 26.