Method of micro-machining an integrated sensor on the surface of a silicon wafer

Claim 2

A method according to claim 1, in which the lateral etching step is conducted at a pressure of 13 Pa (100 mTorr) to about 133 Pa (1000 mTorr) and with the substrate (10) at a temperature of at least 35°C.

Claim 3

A method according to claim 1, which further comprises the step of sealing the trench (20) with a polysilicon film (36) such that the cavity (22) is sealed from the surface of the epitaxial silicon layer (14), the cavity (22) forming a sealed reference chamber for a pressure-sensing device (38)

Claim 4

A method according to claim 1, in which the etching step forms a second trench (20) through the epitaxial silicon layer (14) and into the N+ buried layer (12), and in which the method further comprises the step of sealing the second trench (20) with a polysilicon film (36) such that the micro-machined element (18) forms a membrane for a pressure-sensing device (38).

Claim 5

A method according to claim 1, in which the etching step forms the trench as an elongated trench (20b) which extends through the epitaxial silicon layer (14) and into the N+ buried layer (12) so as to form the micro-machined element (18) as a cantilevered beam which extends over the cavity, the cantilevered beam defining a suspended mass for a motion-sensing device (25).

Claim 6

A method according to claim 1, in which the etching step forms a second trench (20) through the epitaxial silicon layer (14) and into the N+ buried layer (12) such that the micro-machined element (18) is a bridge over the cavity (22)

Claim 7

A method according to claim 1, in which the etching step forms at least two elongated trenches (20b) which extend through the epitaxial silicon layer (14) and into the N+ buried layer (12), the elongated trenches (20b) defining the micro-machined element (18) as a mass which is suspended by at least two beams over the cavity (22)

Claim 8

A method according to claim 1, in which the etching and lateral etching steps form a capacitor (46) such that the trench (20b) defines opposing plates (47) of the capacitor (46); and the method further comprises the steps of: depositing a conductive film (36) on the opposing plates (47) of the capacitor (46) so as to reduce the distance between the opposing plates (47); and etching back the conductive film (36) so as to isolate the opposing plates from each other; whereby the capacitance value of the capacitor (46) is increased.

Claim 9

A method according to claim 1, which further comprises the steps of: forming an oxide layer (16) on the epitaxial silicon layer (14) prior to etching the trench (20a); applying a polysilicon layer (36) on a surface of the oxide layer (16) after etching the trench (20a); doping the polysilicon layer (36) with a dopant; masking a predetermined region of the polysilicon layer (36) with a masking material; etching exposed portions of the polysilicon layer (36) from the surface of the oxide layer (16) so as to leave at least one remaining polysilicon region on the oxide layer (16); removing the masking material; and activating the dopant in the remaining polysilicon region; whereby the remaining polysilicon region defines an active integrated circuit device (34)

Claim 10

A method according to claim 1, which further comprises the steps of: filling the cavity (22) and the trench (20) with polyimide (48) such that the micro-machined element (18) is substantially immobilised; depositing over the polyimide (48) a first layer of a material (50) selected from the group consisting of silicon nitride and silicon dioxide; annealing the first layer of material (50) at a temperature and for a duration which are sufficient to relieve stress in the first layer of material (50); forming at least one opening (52) in the first layer of material (50); etching the polyimide (48) through the opening (52) in the first layer of material (50) so as to release the micro-machined element (18); and depositing over the first layer of material (50) a second layer of a material (54) so as to seal the opening (52) in the first layer of material (50) and to form an encapsulating layer over the micro-machined element (18); whereby the micro-machined element (18) is free to respond to motion of the substrate (10) whilst being protected by the encapsulating layer (54)

Claim 11

A method according to claim 1, in which the N+ buried layer (12) is a first N+ buried layer formed by doping the substrate (10) with an n-type species which diffuses relatively slowly in silicon, and wherein the epitaxial silicon layer (14) is a first epitaxial silicon layer, and the method further comprises the steps of: forming a second N+ region (60) in the surface of the first epitaxial silicon layer (14) by doping a region of the first epitaxial silicon layer (14) with an n-type species which diffuses relatively slowly in silicon; forming a third N+ region (58) within a portion of the second N+ region (60) and above a portion of the first N+ buried layer (12), the third N+ region (58) being doped with an n-type species which diffuses relatively quickly in silicon; growing a second epitaxial silicon layer (56) over the surface of the first epitaxial silicon layer (14) so as to establish second and third N+ buried layers (58,60) beneath the surface of the second epitaxial silicon layer (56) and above the first N+ buried layer (12); heat-treating the substrate (10) sufficiently to diffuse a portion of the n-type species of the third N+ buried layer (58) into a portion of the first N+ buried layer (12), the heat treatment being insufficient to diffuse the n-type species of the first N+ buried layer (12) into any portion of the second N+ buried layer (60) and being insufficient to diffuse the n-type species of the second N+ buried layer (60) into any portion of the first N+ buried layer (12), so that a portion of the first epitaxial silicon layer (14) remains between a portion of the first N+ buried layer (12) and a portion of the second N+ buried layer (60); etching at least one trench (20) through the second epitaxial silicon layer (56) and into at least one of the first, second and third N+ buried layers (12,60,58); and laterally etching a cavity (22) beneath the surface of the second epitaxial silicon layer (56), the lateral etching step being conducted with a chlorine-containing gas at a predetermined pressure and with the substrate at a predetermined temperature so as to preferentially etch the first, second and third N+ buried layers (12,60,58); whereby a micro-machined element (18) is formed between an upper portion of the cavity (22) and a lower portion of the cavity (22), the micro-machined element (18) being a component of the semiconductor device.

Claim 12

A method according to claim 1, for micro-machining a surface of said silicon layer (14) so as to form a sensing device (38) in the same layer (14) as at least one semiconductor device (40), the method comprising the steps of: etching a plurality of trenches (20a) through the layer (14) so as to laterally etch said cavity (22) beneath the surface of the layer (14); forming an oxide layer (42) on the layer (14) and on the surfaces defined by the trenches (20a) and the cavity (22); and depositing a polysilicon layer (36) over the oxide layer (42) so as to seal the trenches (20a), such that the cavity (22) is a sealed cavity beneath the surface of the layer (14); whereby the micro-machined element is formed between the sealed cavity (22) and the surface of the layer (14), the micro-machined element being a component of the sensing device (38).

Claim 13

A method according to claim 12, in which the semiconductor device (40) is formed on the layer (14) after the sensing device (38) has been formed.

Claim 14

A method according to claim 12, in which the semiconductor device (40) is formed on the layer (14) prior to the sensing device (38) being formed.

Claim 15

A method according to claim 12, in which the lateral etching step forms at least two cavities (22) beneath the surface of the layer (14)

Claim 16

A method according to claim 15, in which the step of depositing the polysilicon layer (36) seals at least one of the cavities (22) to form a sealed reference chamber beneath the surface of the layer (14), so that at least another one of the cavities (22) remains vented to a surface of the substrate (10), each one of the cavities (22) forming pressure-reference chambers for the sensing device (38a,38b)

Claim 17

A method according to claim 16, in which the sealed reference chamber (22) is sealed under a vacuum.

Claim 18

A method according to claim 15, in which the step of depositing the polysilicon layer (36) seals each of the two cavities (22) so as to form two sealed reference chambers for the pressure-sensing device (38).

Claim 19

A method according to claim 15, in which the step of depositing the polysilicon layer (36) seals each of the two cavities (22) at the surface of the layer (14), the method further comprising the step of: masking an opposite surface of the substrate (10); etching the opposite surface of the substrate (10) so as to etch the substrate (10) to the oxide layer (42) formed on a first of the two cavities (22); etching through the oxide layer (42) of the first of the two cavities (22) to the polysilicon layer (36) deposited on the first of the two cavities (22); and etching the polysilicon layer (36) of the first of the two cavities (22) so as to vent the first of the two cavities (22) to the opposite surface of the substrate (10); whereby the first of the two cavities forms a first sensing device (38a) for sensing pressure at the opposite surface of the substrate (10) and the other of the two cavities forms a second sensing device (38b) for sensing pressure at the surface of the layer (14), such that the first and second sensing devices (38a,38b) serve as pressure-references to each other.

Claim 20

A method according to claim 19, in which the step of etching the opposite surface of the substrate (10) is a wet silicon etch.

Claim 21

A method according to claim 19, in which the step of etching the opposite surface of the substrate (10) is an anisotropic etch.

Claim 22

A method according to claim 11, in which the first and second N+ buried layers (12,60) are each doped with arsenic and the third N+ buried layer (58) is doped with phosphorus.

Claim 23

A pressure-sensing device (38a,38b) formed in a substrate (10,14) having at least one semiconductor device (40) formed thereon for monitoring the pressure-sensing device (38a,38b), the pressure-sensing device (38a,38b) comprising: a first cavity (22) formed beneath a first surface of the substrate (10,14); first pressure-sensing means (38b) formed between the first cavity and the first surface of the substrate (10,14) so as to sense the pressure at the first surface of the substrate; a second cavity (22) formed beneath the first surface of the substrate (10,14) so as to be adjacent the first cavity, the second cavity being vented to a second surface of the substrate; and second pressure-sensing means (38a) formed between the second cavity (22) and the first surface of the substrate (10,14) so as to sense the pressure at the second surface of the substrate; whereby the first and second pressure-sensing means (38a,38b) serve as pressure references to each other.

Claim 24

A pressure-sensing device (38a,38b) according to claim 23, in which the first surface is a front side of the substrate (10,14) and the second surface is a rearside of the substrate (10,14)

Claim 25

A pressure-sensing device (38a,38b) according to claim 23, in which the first and second cavities (22) each comprise: an oxide layer (42) formed on the interior surface of the respective cavity (22); and a polysilicon layer (36) formed over the oxide layer (42) so as to seal the respective cavity (22) from the first surface of the substrate (10,14).

Claim 26

A pressure-sensing device (38a,38b) according to claim 23, in which a portion of the first surface of the substrate is exposed to atmospheric pressure whilst a portion of the second surface of the substrate is exposed within a manifold of an internal combustion engine, so that the first pressure-sensing means (38b) senses atmospheric pressure and the second pressure-sensing means (38a) senses manifold pressure within the internal combustion engine.