SELECTIVE ETCHING PROCESS FOR SiGe AND DOPED EPITAXIAL SILICON

Abstract

The present disclosure relates to a fabricating procedure of a radio frequency device, in which a precursor wafer including active layers, SiGe layers, and a silicon handle substrate is firstly provided. Each active layer is formed from doped epitaxial silicon and underneath a corresponding SiGe layer. The silicon handle substrate is over each SiGe layer. Next, the silicon handle substrate is removed completely, and the SiGe layer is removed completely. An etch passivation film is then formed over each active layer. Herein, removing each SiGe layer and forming the etch passivation film over each active layer utilizes a same reactive chemistry combination, which reacts differently to the SiGe layer and the active layer. The reactive chemistry combination is capable of producing a variable performance, which is an etching performance of the SiGe layer or a forming performance of the etch passivation film over the active layer.

What is claimed is: 
     
         1 . A radio frequency (RF) device comprising:
 a mold device die comprising a device region, an etch passivation film, and a first mold compound, wherein:
 the device region includes a front-end-of-line (FEOL) portion and a back-end-of-line (BEOL) portion underneath the FEOL portion, wherein the FEOL portion comprises an active layer and isolation sections, which surround the active layer and extend vertically beyond a top surface of the active layer to define an opening within the isolation sections and over the active layer; 
 the etch passivation film resides over the top surface of the active layer and within the opening, wherein the etch passivation film is formed of boron nitride (BN) and boron chloride (BCl x , x=0-3); and 
 the first mold compound resides over the etch passivation film to fill the opening; and 
   a multilayer redistribution structure formed underneath the BEOL portion of the mold device die, wherein the multilayer redistribution structure comprises a plurality of bump structures, which are on a bottom surface of the multilayer redistribution structure and electrically coupled to the FEOL portion of the mold device die.   
     
     
         2 . The RF device of  claim 1  wherein:
 the BEOL portion comprises connecting layers; 
 the FEOL portion further comprises a contact layer, wherein the active layer and the isolation sections reside over the contact layer, and the BEOL portion resides underneath the contact layer; and 
 the multilayer redistribution structure further comprises redistribution interconnections, wherein the plurality of bump structures is electrically coupled to the FEOL portion of the mold device die via the redistribution interconnections within the multilayer redistribution structure and the connecting layers within the BEOL portion. 
 
     
     
         3 . The RF device of  claim 2  wherein the FEOL portion is configured to provide a switch field-effect transistor (FET). 
     
     
         4 . The RF device of  claim 3  wherein the active layer includes a source, a drain, and a channel of the FET, while the contact layer includes a gate structure of the FET, the gate structure extending horizontally underneath the channel. 
     
     
         5 . The RF device of  claim 1  wherein the first mold compound has a thermal conductivity greater than 1 W/m·K. 
     
     
         6 . The RF device of  claim 5  wherein the first mold compound has a thermal conductivity greater than 10 W/m·K. 
     
     
         7 . The RF device of  claim 1  wherein the first mold compound has a dielectric constant less than 8. 
     
     
         8 . The RF device of  claim 7  wherein the first mold compound has a dielectric constant between 3 and 5. 
     
     
         9 . The RF device of  claim 1  wherein a portion of the first mold compound resides over the isolation sections. 
     
     
         10 . The RF device of  claim 1  further comprising one or more device passivation layers, wherein:
 the one or more device passivation layers extend over an entire backside of the device region, such that the one or more device passivation layers continuously cover the etch passivation film and side surfaces of the isolation sections within the opening, and top surfaces of the isolation sections; and 
 the first mold compound resides over the one or more device passivation layers to fill the opening. 
 
     
     
         11 . The RF device of  claim 10  wherein the one or more device passivation layers are in contact with a top surface of the etch passivation film. 
     
     
         12 . The RF device of  claim 10  wherein the first mold compound is in contact with a top surface of the one or more device passivation layers. 
     
     
         13 . The RF device of  claim 10  wherein the one or more device passivation layers are formed of silicon composites. 
     
     
         14 . The RF device of  claim 13  wherein the one or more device passivation layers includes a first device passivation layer and a second device passivation layer, wherein:
 the first device passivation layer extends over the entire backside of the device region, such that the first device passivation layer continuously covers the etch passivation film and the side surfaces of the isolation sections within the opening, and the top surfaces of the isolation sections; 
 the second device passivation layer resides over the first device passivation layer, wherein the first device passivation layer and the second device passivation layer are formed from different silicon composites; and 
 the first mold compound resides over the second device passivation layer to fill the opening. 
 
     
     
         15 . The RF device of  claim 14  wherein:
 the first device passivation layer is configured to terminate surface bonds at the top surface of the active layer; and 
 the second device passivation layer is configured to provide a barrier to moisture and impurities attempting to diffuse into the active layer. 
 
     
     
         16 . The RF device of  claim 15  wherein:
 the first device passivation layer is formed of silicon dioxide; and 
 the second device passivation layer is formed of silicon nitride. 
 
     
     
         17 . The RF device of  claim 1  wherein the isolation sections are formed of silicon dioxide. 
     
     
         18 . The RF device of  claim 1  wherein the FEOL portion is configured to provide at least one of a switch FET, a diode, a capacitor, a resistor, or an inductor. 
     
     
         19 . The RF device of  claim 1  wherein the etch passivation film is in contact with the top surface of the active layer. 
     
     
         20 . The RF device of  claim 1  wherein no silicon crystal exists between the first mold compound and the top surface of the active layer, wherein the silicon crystal has no nitrogen or oxygen content.