METHOD FOR MANUFACTURING BAW RESONATORS ON A SEMICONDUCTOR WAFER
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.