Method for manufacturing baw resonators on a semiconductor wafer

Abstract

A method for manufacturing a wafer on which are formed resonators, each resonator including, above a semiconductor substrate, a stack of layers including, in the following order from the substrate surface: a Bragg mirror; a compensation layer made of a material having a temperature coefficient of the acoustic velocity of a sign opposite to that of all the other stack layers; and a piezoelectric resonator, the method including the successive steps of: a) depositing the compensation layer; and b) decreasing thickness inequalities of the compensation layer due to the deposition method, so that this layer has a same thickness to within better than 2%, and preferably to within better than 1%, at the level of each resonator.

1 . A method, comprising:
 forming a stack of layers on a semiconductor substrate, the forming including:   forming a Bragg mirror on the substrate, the Bragg mirror including a conductive layer having a temperature coefficient of acoustic velocity (TCV) of a first sign;   depositing a compensation layer on the Bragg mirror, the compensation layer having a TCV of a second sign that is opposite to that of the first sign; and   decreasing thickness inequalities of the compensation layer at least until the compensation layer has a thickness variation less than 2%; and   forming a piezoelectric resonator on the compensation layer.   
     
     
         2 . The method of  claim 1  wherein decreasing thickness inequalities includes decreasing the thickness inequalities until at least the compensation layer has less than a 1% variation in thickness. 
     
     
         3 . The method of  claim 1  wherein decreasing thickness inequalities includes decreasing by ion etching of overthicknesses of the compensation layer caused by the depositing. 
     
     
         4 . The method of  claim 1 , wherein an upper layer of the Bragg mirror and the compensation layer are a single layer of a same material. 
     
     
         5 . The method of  claim 1  wherein the compensation layer includes silicon oxide. 
     
     
         6 . The method of  claim 1  wherein forming the piezoelectric resonator includes forming a lower electrode on the compensation layer, forming a layer of a piezoelectric material on the lower electrode, and forming an upper electrode on the layer of the piezoelectric material. 
     
     
         7 . The method of  claim 6  wherein the lower and upper electrodes includes molybdenum. 
     
     
         8 . The method of  claim 6  wherein the layer of piezoelectric material includes aluminum nitride. 
     
     
         9 . The method of  claim 1  wherein forming the Bragg mirror includes forming an alternating stack of layers of a material having a first acoustic impedance and of a material having a second acoustic impedance smaller than the first acoustic impedance. 
     
     
         10 . The method of  claim 9  wherein the material having the first acoustic impedance is tungsten and the material having the second acoustic impedance is silicon oxide. 
     
     
         11 . The method of  claim 1 , further comprising forming a frequency adjustment layer on the resonator, the frequency adjustment layer having a thickness capable of compensating for a frequency shift due to manufacturing dispersions. 
     
     
         12 . A device, comprising:
 a substrate;   a Bragg mirror on the substrate, the Bragg mirror comprising a plurality of conductive layers alternating with a plurality of dielectric layers;   a temperature compensation layer on the Bragg mirror, the compensation layer having less than a 2% variation in a thickness; and   a piezoelectric resonator on the temperature compensation layer, the piezoelectric resonator having a first electrode on the temperature compensation layer, a piezoelectric material layer on the first electrode, and a second electrode on the piezoelectric material layer.   
     
     
         13 . The device of  claim 12  wherein the temperature compensation layer includes silicon dioxide. 
     
     
         14 . The device of  claim 12  wherein the Bragg mirror includes a first dielectric layer on the substrate and a first conductive layer on the first dielectric layer, the temperature compensation layer being on the first conductive layer. 
     
     
         15 . The device of  claim 12  wherein the temperature compensation layer has a temperature coefficient of acoustic velocity (TCV) of a first sign and the plurality of conductive layers have a TCV of a second sign that is opposite to the first sign. 
     
     
         16 . The device of  claim 12  wherein the piezoelectric material layer is aluminum nitride. 
     
     
         17 . A method, comprising:
 forming a Bragg mirror, including:
 forming a first dielectric layer on a substrate; 
 forming a first conductive layer on the first dielectric layer; 
 forming a second dielectric layer on the first conductive layer; and 
 forming a second conductive layer on the second dielectric layer; 
   forming a temperature compensation layer on the second conductive layer of the Bragg mirror; and   forming a piezoelectric resonator on the temperature compensation layer, the forming the piezoelectric resonator including:
 forming a first electrode on the temperature compensation layer; 
 forming a piezoelectric material layer on the first electrode; and 
 forming a second electrode on the piezoelectric material layer. 
   
     
     
         18 . The method of  claim 17  further comprising forming a frequency adjustment layer on the second electrode of the piezoelectric resonator. 
     
     
         19 . The method of  claim 17  wherein forming the temperature compensation layer includes decreasing thickness inequalities of the compensation layer at least until the compensation layer has a thickness variation less than 2%. 
     
     
         20 . The method of  claim 17  wherein the temperature compensation layer has a temperature coefficient of acoustic velocity (TCV) of a first sign and the first and second conductive layers of the Bragg mirror have a TCV of a second sign that is opposite to the first sign.