The present invention relates to semiconductor processing, and more particularly, to a method for manufacturing isolating structures in a substrate. The substrate is particularly, but not exclusively, silicon carbide, and reference will be made throughout this description to this field of application for convenience of illustration.
Silicon carbide is an extremely resistant material to chemical etching, as is well known to those skilled in the art. Removing a portion of silicon carbide by ordinary etching techniques as used in standard silicon-integrated circuit manufacturing processes is difficult. A method for etching away such layers is based on the use of a fluorine solution utilizing an especially dense plasma.
While being advantageous on several counts, this method has certain drawbacks. In particular, a hard mask layer must be used to define the areas to be removed. Defining the hard mask layer involves some serious resolution problems, and complicates the silicon carbide etching process.
In view of the foregoing background, an object of the present invention is to provide a method for manufacturing isolating structures in silicon carbide layers. This method is compatible with standard microelectronic device manufacturing techniques and is effective to overcome the limitations of the prior methods.
The principle on which this invention is based is one of xe2x80x9cdamagingxe2x80x9d the areas of the silicon carbide layer to be removed by modifying the lattice structure of the silicon carbide layer using an ion implantation process, thereby making for faster and more efficient removal of such layers.
One aspect of the invention is directed to a method for forming isolating structures in a silicon carbide layer. The method comprises depositing a masking layer on first and second portions of a silicon carbide layer, forming openings through the masking layer to expose the first portions of the silicon carbide layer, and implanting ions into the first portions of the silicon carbide layer.
The silicon carbide layer is preferably heated to form an oxide layer thereon having first portions on the first portions of the silicon carbide layer, and having second portions on the second portions of the silicon carbide layer. The first portions of the oxide layer have a first thickness, and the second portions of the oxide layer have a second thickness less than the first thickness.
The method preferably further includes removing the oxide layer to form isolating regions in the first portions of the silicon carbide layer. Insulation material may be deposited in the isolating regions to form isolating structures. The masking layer may be removed before heating the silicon carbide layer. The ions may comprise heavy ions or a dopant.
Another aspect of the invention is directed to a method for forming isolating trenches for an epitaxially grown diode. The method preferably comprises forming a first epitaxial layer having a first type of conductivity on a silicon carbide layer, and forming a second epitaxial layer having a second type of conductivity on the first epitaxial layer. A masking layer is formed on the second epitaxial layer, and openings are formed through the masking layer to expose first portions of the second epitaxial layer.
The method preferably further comprises removing the first portions of the second epitaxial layer to expose first portions of the first epitaxial layer, and implanting ions into the first portions of the first epitaxial layer. The first and second epitaxial layers and the silicon carbide layer are heated to form an oxide layer having first portions on the first portions of the first epitaxial layer, and having second portions on the second epitaxial layer.
The first portions of the oxide layer have a first thickness, and the second portions of the oxide layer have a second thickness less than the first thickness. The oxide layer may be removed to form isolating trenches in the first portions of the first and second epitaxial layers. Insulation material may be deposited in the isolating trenches.
Yet another aspect of the invention is directed to a method for isolating an edge of an epitaxially grown diode. After the isolating trenches have been formed as discussed above for the epitaxially grown diode, a ring mask is formed on a peripheral portion of the isolating trenches. Ions are implanted into the isolating trenches to form an implanted region in the first epitaxial layer that extends across a bottom and sidewalls of the trench adjacent the ring mask for isolating the edge of the epitaxially grown diode.
The method preferably further includes removing the ring mask, and heating the first and second epitaxial layers and the silicon carbide layer to form a second oxide layer on the trench and on the second epitaxial layer. A portion of the second oxide layer on the second epitaxial layer may be removed.