Semiconductor eutectic alloy metal (SEAM) technology for fabrication of compliant composite substrates and integration of materials

• US 6,199,748 B1
• Filed: 08/20/1999
• Issued: 03/13/2001
• Est. Priority Date: 08/20/1999
• Status: Expired due to Fees

• Current Assignee: Gemfire Corp. (Medtronic Plc)
• Original Assignee: Nova Crystals Inc. (Medtronic Plc)
• Inventors: Ng, Tuoh-Bin, Lo, Yu-Hwa, Zhu, Zuhua
• Primary Examiner(s): Ryan, Patrick
• Assistant Examiner(s): STONER, KILEY SHAWN
• Application Number:
  US09/378,769
• Time in Patent Office: 571 Days
• Field of Search: 228/121, 228/122.1, 228/123.1, 228/124.1, 228/124.5
• US Class Current: 228/121
• CPC Class Codes: B23K 20/023 Thermo-compression bonding

Abstract

A method of semiconductor eutectic alloy metal (SEAM) technology for integration of heterogeneous materials and fabrication of compliant composite substrates takes advantage of eutectic properties of alloys. Sub1 and Sub2 are used to represent the two heterogeneous materials to be bonded or composed into a compliant composite substrate. For the purpose of fabricating compliant composite substrate, the first substrate material (Sub1) combines with the second substrate material (Sub2) to form a composite substrate that controls the stress in the epitaxial layers during cooling. The second substrate material (Sub2) controls the stress in the epitaxial layer grown thereon so that it is compressive during annealing. A joint metal (JM) with a melting point of T_m is chosen to offer variable joint stiffness at different temperatures. JM and Sub1 form a first eutectic alloy at a first eutectic temperature T_eu1 while JM and Sub2 form a second eutectic alloy at a second eutectic temperature T_eu2. T_m1 and T_m2 are the melting points of Sub1 and Sub2, respectively. The following condition should be met: T_m1, T_m2>T_m>T_eu1, T_eu2. After cleaning of Sub1 and Sub2, JM is deposited on the bonding sides of Sub1 and Sub2. After preliminary bonding by applying force to press the bonding surfaces together at room temperature, high temperature bonding is subsequently performed, during which the temperature is ramped up to a temperature equal to or higher than T_m. During cooling, JM solidifies first, after which two eutectic alloys solidify.

Claims

1. A method for forming a wafer of a compliant composite substrate, comprising the steps of:

a) selecting a first substrate material having a melting point of T_m1;

b) selecting a second substrate material having a melting point of T_m2;

c) selecting a joint metal with a melting point of T_m;

wherein

i) said joint metal and said first substrate material form a first eutectic alloy at a first eutectic temperature T_eu1 while said joint metal and said second substrate material form a second eutectic alloy at a second eutectic temperature T_eu2; and

ii) T_m1 and T_m2>

T_m>

T_eu1 and T_eu2;

d) depositing said joint metal on a side of said first substrate material to form a first intermediate substrate;

e) depositing said joint metal on a side of said second substrate material to form a second intermediate substrate;

f) forming a substrate pair by combining said first and second intermediate substrates such that said sides of said first substrate material and said second substrate material having said joint metal on them are against each other;

g) ramping a temperature of said substrate pair up to at least T_m, whereby said temperature passes through T_eu1 and T_eu2; and

h) cooling, after step (g), said substrate pair to form said compliant composite substrate.

2. A method according to claim 1, further comprising enhancing adhesion between said first and second intermediate substrates by preliminarily bonding said substrate pair.

3. A method according to claim 1, wherein the steps of ramping and cooling are conducted in a high vacuum.

4. A method according to claim 1, further comprising soaking said substrate pair, after step (g) and before step (h), for a specified period of time at a temperature equal to or greater than T_m.

5. A method according to claim 1, further comprising forming a protective layer, before step (d), on said second substrate material on which epitaxial layers are to be grown.

6. A method according to claim 1, wherein said first substrate material is Ge and said second substrate material is Si.

7. A method according to claim 6, wherein said joint metal is Al+1% Si.

8. A method according to claim 1, further comprising selecting a first thickness of said joint metal deposited in step (d) and a second thickness of said joint metal deposited in step (e) such that a total thickness (t) of said joint metal is the sum of said first thickness and said second thickness, and said total thickness (t) satisfies an equation t≧

D Δ

α

/α

×

10<sup>−

4</sup>, where D is a dimension of said wafer, and Δ

α

/α

is a ratio of a thermal mismatch between Sub1 and Sub2 which equals |(α

₁−

α

₂)|/½

(α

₁+α

₂).

9. A method according to claim 8, further comprising selecting α

_eff such that α

_eff is approximately equal to a thermal expansion coefficient of an epitaxial layer to be grown on said composite substrate.

10. A method according to claim 1, further comprising selecting a first thickness of said first substrate material and a second thickness of said second substrate material such that:

11. A method according to claim 10, further comprising selecting α

_eff such that α

_eff is approximately equal to a thermal expansion coefficient of an epitaxial layer to be grown on said composite substrate.

12. A method according to claim 1, further comprising selecting said first substrate material and said second substrate material such that:

13. A method according to claim 12, further comprising selecting α

_eff such that α

_eff is approximately equal to a thermal expansion coefficient of an epitaxial layer to be grown on said composite substrate.

14. A method for forming a wafer of a compliant composite substrate, comprising the steps of:

a) selecting as a first substrate material Ge having a melting point of T_Ge;

b) selecting as a second substrate material Si having a melting point of T_Si;

c) selecting a joint metal with a melting point of T_m;

wherein

i) said joint metal and said first substrate material form a first eutectic alloy at a first eutectic temperature T_eu1 while said joint metal and said second substrate material form a second eutectic alloy at a second eutectic temperature T_eu2; and

ii) T_Ge and T_Si>

T_m>

T_eu1 and T_eu2;

d) depositing said joint metal on a side of said first substrate material to form a first intermediate substrate;

e) depositing said joint metal on a side of said second substrate material to form a second intermediate substrate;

f) forming a substrate pair by combining said first and second intermediate substrates such that said sides of said first substrate material and said second substrate material having said joint metal on them are against each other;

g) ramping a temperature of said substrate pair up to at least T_m, whereby said temperature passes through T_eu1 and T_eu2; and

h) cooling, after step (g), said substrate pair to form said compliant composite substrate.

15. A method according to claim 14, wherein said joint metal is Al+1% Si.

16. A method for forming a wafer of a compliant composite substrate, comprising the steps of:

a) selecting a first substrate material having a melting point of T_m1;

b) selecting a second substrate material having a melting point of T_m2;

c) selecting a joint metal with a melting point of T_m;

wherein

i) said joint metal and said first substrate material form a first eutectic alloy at a first eutectic temperature T_eu1 while said joint metal and said second substrate material form a second eutectic alloy at a second eutectic temperature T_eu2; and

ii) T_m1 and T_m2>

T_m>

T_eu1 and T_eu2;

d) depositing said joint metal on a side of said first substrate material to form a first intermediate substrate;

e) depositing said joint metal on a side of said second substrate material to form a second intermediate substrate;

f) forming a substrate pair by combining said first and second intermediate substrates such that said sides of said first substrate material and said second substrate material having said joint metal on them are against each other;

g) ramping a temperature of said substrate pair up to at least T_m, whereby said temperature passes through T_eu1 and T_eu2; and

h) cooling, after step (g), said substrate pair to form said compliant composite substrate,

wherein said first substrate material and said second substrate material are selected such that;