Grid formed with silicon substrate

• US 6,018,566 A
• Filed: 10/24/1997
• Issued: 01/25/2000
• Est. Priority Date: 10/24/1997
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TRW Inc. (Northrop Grumman Corporation)
• Inventors: Eberhard, Carol D., Pinneo, George G., Sergant, Moshe
• Primary Examiner(s): Church, Craig E.
• Application Number:
  US08/957,541
• Time in Patent Office: 823 Days
• Field of Search: 378/154, 378/155, 378/145
• US Class Current: 378/154
• CPC Class Codes: G21K 1/025 using multiple collimators, e.g. Bucky screens; other devices for eliminating undesired or dispersed radiation

Abstract

An X-ray collimator grid is formed within a wafer of monocrystalline silicon material by forming a plurality of spaced parallel elongate slots within a planar surface of a silicon crystal wafer, and forming slats of heavy metal in situs within each of said slots, including squeegeeing the heavy metal into the slots, from particles of heavy metal, each said slat gripping the walls of an associated slot.

Claims

1. The process of fabricating an X-ray collimator grid in a silicon crystal wafer that contains a plurality of spaced parallel deep elongate slots of microscopic width depending from an upper surface of said wafer, which includes the steps of:

forming a sold slat of heavy metal in situs with n each of said slots to fill each slot, with each said s conforming to the walls of an associated slot and filling irregularities, whereby at least a frictional bond is created between the slat and the spaced side walls defining g respective slot;

said step of forming a slat including h steps of;

placing particles of heavy metal comprising pure gold on said upper surface; and

moving said particles of heavy metal alone said upper surface and into said slots by brushing particles of heavy metal into said slots; and

heating said silicon crystal wafer and said particles to the melting temperature of said pure gold to liquefy said particles within said slots and form a gold silicon eutectic alloy that chemically bonds to silicon.

2. The method of forming an ray collimator arid In a silicon crystal wafer, said wafer having planar surfaces taken along the <

110>

crystal plane, said latter plane being oriented perpendicular to the <

111>

crystal plane, comprising the steps of;

forming a plurality of spaced deep elongate slots of microscopic within the planar, 110>

surface of a silicon crystal, said slots depending from said planar surface to a predetermined depth into said crystal wafer and being oriented parallel to one another and to the <

111>

plane of said crystal; and

forming a solid slat of heavy metal in situs within each of said slots from heavy metal particles to produce a plurality of slats in said wafer filling said elongate slots including the steps of;

depositing heavy metal particles upon the surface of said silicon crystal comprising the steps of;

preparing a metal paste of heavy metal particles and an epoxy binder material, wherein said heavy metal particles are disposed in said paste, and

depositing said paste upon the surface of said silicon crystal, said metal particles being of a size small enough to fit within said slots;

moving a squeegee along said surface to force said heavy metal particles within said slots, said slats substantially filling aid respective slots and being at least mechanically linked to said silicon crystal; and

following said step of moving a squeegee along said surface,

heating said silicon crystal and said epoxy binder material to cure said binder material, whereby said metal paste softens and flows into available space at the lowermost available space within said respective slots to form said rigid slats and link said rigid slats to said silicon crystal.

3. The method as defined in claim 2, further comprising the step, prior to said step of heating said silicon crystal and said epoxy binder material, of degassing said silicon crystal to pull entrained air from said epoxy binder material.

4. The method as defined in claim 2, further comprising the steps, following said step of heating, of:

determining whether said slots are filled, and, only if such determination is negative, repeating said steps of depositing heavy metal particles on said surface of said silicon crystal, squeegeeing said heavy metal particles into said slots, reheating said silicon crystal and said epoxy binder material, and again determining whether said slots are filled, and repeating said last three named steps of depositing, squeegeeing and reheating until said slots are completely filled.

5. An X-ray collimator grid, comprising:

a monocrystalline silicon substrate;

said substrate having top and bottom planar surfaces, and said substrate including a plurality of straight narrow deep slots within a top planar surface and extending perpendicular thereto, said slots including right and left hand side walls;

a plurality of slats, each of said slats containing at least a predominant portion of heavy metal for rendering said slats impenetrable to X-radiation;

each of slats consisting of a core of Gold and right and left outer side walls to said core of a Gold Silicon alloy;

each of said slats being formed within a respective one of said plurality of slots;

said right and left outer side walls of said slats forming a bond to respective right and left hand side walls of said slots for preventing removal of said slats from said slots.

6. The method of forming an X-ray collimator grid in a silicon crystal wafer, said wafer having planar surfaces taken log the <

110>

crystal plane, said latter plane being oriented perpendicular to the <

111>

crystal plane, comprising the steps of;

forming a plurality of spaced deep elongate slots of microscopic width within the planar <

110>

surface of a silicon crystal, said slots depending from said planar surface to a predetermined depth into said crystal wafer and being oriented parallel to one another and to the <

111>

plane of said crystal; and

forming a solid slat of heavy metal in situs within each of said slots from heavy metal particles to produce a plurality of slats in said wafer, said heavy metal particles being an eutectic alloy having a predetermined eutectic temperature and comprising an alloy of Gold and Tin, said heavy metal particles being of a size less than said microscopic width of said slots and said slats filling said respective slots and being at least mechanically linked to said silicon crystal;

said step of forming a slat of heavy metal including the steps of;

depositing said heavy metal particles upon the surface of said silicon crystal;

moving said heavy metal particles along said surface to deposit said heavy metal particles within said slots;

applying a solder flux to said slots over said hi metal particles;

heating said silicon crystal and said heavy metal particles at least to said predetermined eutectic temperature to change the state of said metal particles from a solid state to a liquid state without changing said silicon crystal from a solid state; and

terminating said heating to permit said heavy metal particles to change from said liquid state back to said solid state and thereby form said slats.

7. The method as defined in claim 6 wherein said slots are formed of a width in the range of fifteen microns and one-hundred microns and a depth no less than essentially 80 times said width.

8. The method of forming an X-ray collimator grid in a silicon crystal wafer, said wafer having planar surfaces taken along the <

110>

crystal plane, said latter Plane being oriented perpendicular to the <

111>

crystal plane, comprising the steps of;

forming a plurality of spaced dee elongate slots of microscopic width within the planar <

110>

surface of a silicon crystal, said slots depending from said planar surface to a predetermined depth into said crystal wafer and being oriented parallel to one another and to the <

111>

plane of said crystal; and

forming a solid slat of heavy metal in situs within each of said slots from heavy metal particles to produce a plurality of slats in said wafer, said heavy metal particles consisting of an eutectic alloy selected from the group consisting of;

(1) a Gold and Germanium alloy in the following composition;

88% Gold and 12% Germanium (by weight); and

(b) a Gold and Silicon alloy in the following composition;

96.4% Gold and 3.6% Silicon (by weight), said heavy metal particles being of a size less than said microscopic width of said slots and said slats Filling said respective slots and being at least mechanically linked to said silicon crystal;

said step of forming a slat of heavy metal including the steps of depositing said heavy metal particles upon the surface of said silicon crystal and moving said heavy metal particles along said surface to deposit said heavy metal particles within said slots.

9. An X-ray collimator grid, comprising:

a monocystalline silicon substrate;

said substrate having a top and bottom planar surfaces, and said substrate including a plurality of straight narrow slots within a top planar surface extending perpendicular thereto, said slots including right and left hand side walls;

said top and bottom planar surfaces being within <

110>

crystal plane; and

said slots extending parallel with a <

111>

crystal plane;

a plurality of slats, each of said slats including at least a predominant portion of heavy metal for rendering said slats impenetrable to X-radiation, said heavy metal comprising a eutectic metal alloy selected form the group consisting of (a) Gold and Germanium in the following composition;

88% Gold and 12% Germanium (by weight);

(b) Gold and Silicon in the following composition;

96.4% Gold and 3.6% Silicon (by weight); and

(c) Gold and Tin in the following composition;

80% Gold and 20% Tin (by weight), each of said slats being disposed within and filing a respective one of said plurality of slots and said slats having side walls intimately engaging said side walls of said slots for inhibiting removal of said slats from said slots.

10. The process of fabricating an X-ray collimator grid in a silicon crystal wafer that contains a plurality of spaced parallel deep elongate slots of microscopic width depending from an upper surface of said wafer, which includes the steps of:

forming a solid slat of heavy metal in situs within each of said slots to fill up each slot, with each said slat conforming to the walls of an associated slot and filling irregularities, whereby at least a frictional bond is created between the slat and the spaced side walls defining a respective slot

said step of forming a slat, including the steps of;

placing particles of heavy metal comprising an eutectic metal alloy on said upper surface; and

moving said particles of heavy metal along said upper surface and into said slots by brushing particles of heavy metal into said slot and

heating said silicon crystal wafer and said particles to the eutectic temperature of said eutectic metal alloy to liquify said particles within said slots.

11. The process defined in claim 10, wherein said eutectic metal alloy consists of a eutectic alloy selected from the group of (a) a gold and germanium alloy, (b) a gold and silicon alloy and (c) a gold and tin alloy.

12. The process defined in claim 10, further comprising the step, prior to said step of heating, of:

applying a solder flux to said slots over said particles.