Method of micromachining an integrated sensor on the surface of a silicon wafer
First Claim
1. A method for micromachining a surface of a silicon substrate so as to form therein a micromachined element of a semiconductor device, the method comprising the steps of:
- forming an N+ region in the surface of the substrate;
growing an epitaxial silicon layer over the surface of the substrate so as to form an N+ buried layer beneath the epitaxial silicon layer;
etching at least one trench through the epitaxial silicon layer and into the N+ buried layer; and
laterally etching a cavity beneath the epitaxial silicon layer, the lateral etching step being conducted with chlorine gas at a pressure of about 100 to about 1000 mTorr and with the substrate at a temperature of at least about 35°
C. so as to preferentially etch the N+ buried layerand thereby form the micromachined element between the cavity and the epitaxial silicon layer, the micromachined element being a component of the semiconductor device.
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Abstract
A method for micromachining the surface of a silicon substrate which encompasses a minimal number of processing steps. The method involves a preferential etching process in which a chlorine plasma etch is capable of laterally etching an N+ buried layer beneath the surface of the bulk substrate. Such a method is particularly suitable for forming sensing devices which include a small micromachined element, such as a bridge, cantilevered beam, membrane, suspended mass or capacitive element, which is supported over a cavity formed in a bulk silicon substrate. The method also permits the formation of such sensing devices on the same substrate as their controlling integrated circuits. This invention also provides novel methods by which such structures can be improved, such as through optimizing the dimensional characteristics of the micromachined element or by encapsulating the micromachined element.
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Citations
31 Claims
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1. A method for micromachining a surface of a silicon substrate so as to form therein a micromachined element of a semiconductor device, the method comprising the steps of:
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forming an N+ region in the surface of the substrate; growing an epitaxial silicon layer over the surface of the substrate so as to form an N+ buried layer beneath the epitaxial silicon layer; etching at least one trench through the epitaxial silicon layer and into the N+ buried layer; and laterally etching a cavity beneath the epitaxial silicon layer, the lateral etching step being conducted with chlorine gas at a pressure of about 100 to about 1000 mTorr and with the substrate at a temperature of at least about 35°
C. so as to preferentially etch the N+ buried layerand thereby form the micromachined element between the cavity and the epitaxial silicon layer, the micromachined element being a component of the semiconductor device. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for micromachining a surface of a silicon substrate so as to form a sensing device in the same substrate as at least one semiconductor device, the method comprising the steps of:
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forming an N+ region in the surface of the substrate; forming a silicon layer over the surface of the substrate so as to form an N+ buried layer beneath the silicon layer; forming an etch mask on the silicon layer; etching a plurality of trenches into the substrate and into the N+ buried layer; laterally etching the N+ buried layer so as to form a cavity beneath the silicon layer, the lateral etching step being conducted with chlorine gas at a pressure of about 100 to about 1000 mTorr and with the substrate at a temperature of at least about 35°
C. so as to preferentially etch the N+ buried layer;forming an oxide layer on the substrate and on the surfaces defined by the trenches and the cavity; and depositing a polysilicon layer over the oxide layer so as to seal the trenches, such that the cavity is a sealed cavity beneath the surface of the substrate; whereby a micromachined element is formed between the sealed cavity and the surface of the substrate, the micromachined element being a component of the sensing device. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for micromachining a surface of a silicon substrate so as to form a sensing device therein, the method comprising the steps of:
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forming a first N+ region in the surface of the substrate by doping the substrate with a first n-type species; growing a first epitaxial silicon layer over the surface of the substrate so as to form a first N+ buried layer beneath the first epitaxial silicon layer; forming a second N+ region in the first epitaxial silicon layer by doping a region of the first epitaxial silicon layer with a second n-type species which diffuses relatively slowly in silicon as compared to the first n-type species; forming a third N+ region within a portion of the second N+ region and above a portion of the first N+ buried layer, the third N+ region being doped with an n-type species which diffuses relatively quickly in silicon as compared to the second n-type species; growing a second epitaxial silicon layer over the first epitaxial silicon layer so as to form second and third N+ buried layers beneath the second epitaxial silicon layer and above the first N+ buried layer; heat treating the substrate sufficiently to diffuse a portion of the n-type species of the third N+ buried layer into a portion of the first N+ buried layer, the heat treatment being insufficient to diffuse the first n-type species of the first N+ buried layer into any portion of the second N+ buried layer and being insufficient to diffuse the second n-type species of the second N+ buried layer into any portion of the first N+ buried layer, such that a portion of the first epitaxial silicon layer remains between a portion of the first N+ buried layer and a portion of the second N+ buried layer; etching at least one trench through the second epitaxial silicon layer and into at least one of the first, second and third N+ buried layers; and laterally etching a cavity beneath the second epitaxial silicon layer, the lateral etching step being conducted with a chlorine-containing gas so as to preferentially etch the first, second and third N+ buried layers; whereby a micromachined element is formed between an upper portion of the cavity and a lower portion of the cavity, the micromachined element being a component of the sensing device. - View Dependent Claims (22, 23, 24, 25)
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26. A method for encapsulating a structure formed on a surface of a semiconductor material, the method comprising the steps of:
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selectively patterning polyimide on the surface of the semiconductor material so as to cover the structure; depositing over the polyimide a first layer of material selected from the group consisting of silicon nitride and silicon dioxide; annealing the first layer of material at a temperature and for a duration which are sufficient to relieve stress in the first layer of material; forming at least one opening in the first layer of material; etching the polyimide through the opening in the first layer of material such that at least a portion of the first layer of material is suspended over the structure on the surface of the semiconductor material; and depositing over the first layer of material a second layer of material, the second layer of material sealing the opening in the first layer of material so as to form an encapsulating layer over the structure. - View Dependent Claims (27, 28, 29)
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30. A method for micromachining a surface of a silicon substrate so as to form a capacitor therein, the method comprising the steps of:
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forming an N+ region in the surface of the substrate; growing an epitaxial silicon layer over the surface of the substrate so as to form an N+ buried layer beneath the epitaxial silicon layer; masking the epitaxial silicon layer; etching at least one trench through the epitaxial silicon layer and into the N+ buried layer, the trench defining opposing plates of the capacitor; laterally etching a cavity beneath the epitaxial silicon layer, the lateral etching step being conducted with chlorine-containing gas such that the N+ buried layer is preferentially etched; depositing a conductive film on the opposing plates of the capacitor so as to reduce the distance between the opposing plates; and etching back the conductive film so as to isolate the opposing plates from each other. - View Dependent Claims (31)
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Specification