US8558330 (Раздаточный материал), страница 2

The substrate further comprises a deep Well having ating the deep Well, resulting in a diaphragm structure thatoperates as a pieZoresistor con?gured to measure pressureWithin the cavity.second doping type (e.g., n-type) With a gradient dopingIn another embodiment, the present disclosure relates to apro?le. The deep Well is located Within a diaphragm (i.e., asubstrate section that is thinner than the surrounding substrate), Which abuts a cavity located Within the backside of theMEMs pressure sensor.

The MEMs pressure sensor comprises a substrate having a ?rst doping type. A deep Welllocated Within a top side of the substrate, Wherein the deepWell comprises a second doping type having a gradient doping pro?le. A cavity is disposed Within a backside of thesubstrate at a position opposing the deep Well, such that the65substrate. One or more pieZoresistors are located Within thedeep Well. The pieZoresistors are sensitive to deformations(e.g., bending) in the diaphragm caused by changes in theUS 8,558,330 B234pressure of the cavity. The resulting MEMs pressure sensorprovides for cheaper sensor production than equivalent sensors utilizing an epitaxial layer.tion than that of the one or more shalloW Wells 106.

ThemetalliZation layers 118 connect the pieZoresistors to one ormore integrated chip logic elements (not shoWn) con?guredFIG. 1 illustrates a cross sectional vieW of an embodimentto receive and translate an electrical signal corresponding toof a micromechanical systems (MEMs) pressure sensor 100,Which has a pieZoresistive element comprising a deep Wellthe resistive value of the diaphragm.104 formed Within a substrate 102.pressure sensor having a diaphragm 201 in various stages ofoperation. The MEMs pressure sensor is con?gured to meaFIG. 2 illustrates an exemplary embodiment of a MEMsThe substrate 102 has a ?rst doping type and the deep Well104 has a second doping type.

In some embodiments, the ?rstsure a pressure Within the cavity 110 based upon resistivedoping type comprises a p-type dopant and the second dopingchanges caused by a force that the pres sure Within the cavitytype comprises an n-type dopant, such that the MEMs pres110 exerts on the diaphragm 201.

Side vieW 200 illustrates aMEMs pressure sensor in Which the pressure Within the cavity110 is equal to the pressure on an opposite side of the diasure sensor 100 comprises a p-type substrate having an n-typedeep Well. The deep Well 104 is located Within a top surface122 (i.e., a frontside) of the substrate 102 and has a gradientphragm 201. As illustrated in side vieW 202, if the pressureWithin the cavity 110 is loWer than the pressure on the oppodoping pro?le that extends along doping cross section 126,Which is perpendicular to the top surface 122 of the substrate102. The doping pro?le along doping cross section 126 isillustrated in more detail beloW in FIG.

3. The deep Well 104has a bottom surface that is in contact With a cavity 110located Within a backside 124 of the substrate 102, such thatthe deep Well 104 extends from a top surface 122 of thesubstrate to the cavity 110.20The cavity 110 comprises a steep sideWall angle 0 formedby an electrochemically controlled etching (ECE) processthat stops at a PN junction 120 located betWeen the substrate102 and the deep Well 104. In some embodiments, the sideWall angle 0 has an angle of 54.70 With the backside 124 of theto push up on the diaphragm 201.

This force 208 acts as a25substrate 102. The cavity 110 results in a pliable diaphragmdeep Well corresponding to deep Well 104 in FIG. 1, in accor30dance With an embodiment. It Will be appreciated that since35the n-type deep Well (deep n-Well) is formed by an implantation process, the resulting doping pro?le 304 of the deepn-Well contains a gradient doping pro?le. The gradient doping pro?le extends perpendicular from the top surface of thesubstrate through the deep n-Well, as illustrated by dopingdescribed in more detail With reference to FIG. 2 beloW. InFIG.

1, the pliable diaphragm comprises the deep Well 104. Inan embodiment, the cavity 110 may be partially enclosed bya glass or silicon layer 112 located along the backside 124 ofthe substrate 102. The diaphragm is con?gured to react totensile force on the shalloW Wells 106, thereby increasing theresistance of the shalloW Wells 106.FIG. 3 illustrates a graph 300 shoWing a simulation of thedoping pro?le of a MEMs pressure sensor having an n-typecomprising a bendable substrate section that is thinner thanthe surrounding substrate section. The pliable diaphragm issite side of the diagram 201, the pressure difference causes aforce 204 to push doWn on the diaphragm 201. This force 204acts as a compressive force on the shalloW Wells 106, therebydecreasing the resistance of the shalloW Wells 106.

Altematively, as illustrated in side vieW 206, if the pressure Within thecavity 110 is greater than the pressure on the opposite side ofthe diaphragm 201, the pressure difference causes a force 208mechanical stress that is caused due to a pressure Within thecross section 126 in FIG. 1. Graph 300 of FIG. 3 illustrates acavity 110.logarithmic doping pro?le measured in cm“3 along the y-axis.In an embodiment, the diaphragm comprises one or morepressure sensing elements comprised Within the deep Well104 and con?gured to measure a pressure Within the cavity110. In some embodiments, the pressure sensing elementscomprise one or more pieZoresistors formed Within the deep40The depth from the Wafer surface measured in pm is shoWn onthe x-axis extending from the surface of the substrate 102 at 0pm.As illustrated in the graph 300, the doping pro?le 302 of ann-type epitaxial layer, Which is typically used in anotherWell 104.

In some embodiments, the one or more pieZoresisapproach of MEMs pressure sensing devices, is constant overtors comprise diffusion pieZoresistors comprising one ormore shalloW Wells 106 located Within the deep Well 104. Thethe depth of the epitaxial layer. In contrast, the doping pro?le45one or more pieZoresistors are con?gured to change resistivity based upon mechanical stress applied to the diaphragm.For example, a deformation in the crystal lattice of the diax-axis. The gradient pro?le comprises a dopant concentrationphragm causes a change in the band structure of the pieZoresistors in the diaphragm, leading to a change in the resistivity50of the one or more pieZoresistors.In some embodiments, the one or more shalloW Wells 106have a ?rst doping type having a higher doping concentrationthan that of the deep Well 104.

In various embodiments, suchdiffusion pieZoresistors comprise diffused n-Wells or p-Wellslocated Within a deep p-Well or a deep n-Well, respectively.304 of a deep n-Well comprises a gradient pro?le that extendsfrom the surface of the substrate through the deep Well to a PNjunction 306 located at the intersection of the substrate 102and deep Well, 104, Which is approximately 9.6 pm on the55that is inversely proportional to the distance from the substrate surface.

For example, the doping pro?le 304 of a deepn-Well decreases from approximately 1016 at the surface ofthe Wafer to approximately 1011 at the PN junction 306.The depth of the PN junction 306 can be varied to achievea desired diaphragm thickness depending on the processingparameters of the implantation, including, for example, theimplant dose and/or energy, a subsequent drive in time and/ortemperature, etc. In an embodiment, the depth of the PNFor example, in some embodiments, the one or more pieZoresistors comprise a silicon n-Well pieZoresistor having a ?rstand second shalloW p-Well formed Within a deep n-Well.junction 306 and doping pro?le is determined prior to proThe one or more shalloW Wells 106 are connected by Way 60 cessing through use of predictive simulations, such as shoWnof Well contacts 108 to one or more metalliZation layers 118.in FIG.

3. Such simulations provide for processing paramIn some embodiments, the metalliZation layers 118 areformed Within an interlevel dielectric (ILD) layer 114 up untilthe far back end metalliZation layers, Which Will extend outWard from the ILD layer 114 to a packaging comprising apassivation layer 116. In some embodiments, Well contacts108 have a ?rst doping type With a higher doping concentraeters that enable a precise PN junction depth and dopingpro?le to optimiZe performance of the MEMs pressure sensor.65In graph 300, the PN junction 306 is located at a depth ofapproximately 9.7 um from the Wafer surface.

At depthsgreater than that of the PN junction 306, such as greater thanUS 8,558,330 B2569.7 um, the doping pro?le changes from an n-type dopant toa p-type dopant, Which is the dopant type of the substrate.nents to form Within both n-type material and Within p-typematerial on the same substrate, thereby enabling monolithicintegration of the MEMs pressure sensor With a bulk isolatedIn an embodiment, the disclosed MEMs pressure sensorcomprises a monolithic MEMS pressure sensor having aMEMs pressure sensing device comprised Within a sameCMOS integrated chip.The semiconductor substrate is selectively masked byforming a ?rst masking layer that de?nes one or more deepintegrated chip (e.g., Within the same silicon die) as one ormore CMOS devices. The integration of the MEMs pressuresensing device along With the one or more CMOS devicesWithin a same integrated chip enables a relatively small dieWell regions.