Method for reducing an unevenness of a surface and method for making a semiconductor device

Embodiments of the invention relate to methods for reducing an unevenness of a surface of a body and to methods for making a semiconductor device.

Fabrication steps during semiconductor fabrication may result in uneven top surfaces of semiconductor wafers or other substrates. In order to improve further processing of such top surfaces of the semiconductor wafer or the substrate, it may be desirable to planarize the top surface prior to further processing same.

There is a need in the art for methods which permit for reducing an unevenness of a surface of a body in a controllable manner.

Embodiments of the invention provide for a method for reducing an unevenness of a surface of a body. In one example, a sacrificial layer is applied to the surface. A chemical/mechanical polishing is performed on the sacrificial layer and material of the body to reduce the unevenness of the surface.

Many aspects of this disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessary to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

In the cross-sectional views hatchings are omitted were appropriate in order to improve clarity of the drawings.

FIGS. 1 a to 1 d are schematic views of a body in cross-section, showing the process flow of an embodiment of the invention;

FIG. 1 e is a schematic view of a body in cross-section, showing an alternative structure that could utilize aspects of the invention; and

FIGS. 2 a to 2 f are schematic views of a semiconductor structure in cross-section, showing the process flow of an embodiment of the invention.

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

FIG. 1 a shows a body 10 comprising a surface 12 . The surface comprises an unevenness 14 . The unevenness may be in the shape of an elevation as shown in FIG. 1 a or may be in the form of a depression (as shown in FIG. 1 e ). While aspects of the invention will be described with respect to the embodiment of FIG. 1 a , similar process steps could be applied with the starting point shown in FIG. 1 e.

As shown in FIG. 1 b , a sacrificial layer 16 is applied to the surface 12 . In embodiments of the invention, the sacrificial layer 16 may be applied all-over the surface 12 or all-over at least a portion of the surface 12 .

Upon applying the sacrificial layer 16 , chemical-mechanical polishing of the sacrificial layer 16 and material of the body 12 is performed to reduce the unevenness 14 of the surface 12 . The result is shown in FIG. 1 c . To be more specific, in the embodiment shown, chemical-mechanical polishing from the top results in a planarized unevenness 14 a since the height of the elevation 14 is reduced. If there is a remainder 16 a of the sacrificial layer 16 after chemical-mechanical polishing, in embodiments of the invention it may be removed, as shown in FIG. 1 d.

In embodiments of the invention, the body 12 and the sacrificial layer 16 may comprise any conceivable material suitable for chemical-mechanical polishing. In embodiments, the body and the sacrificial layer may be formed of materials suitable for semiconductor fabrication. In embodiments of the invention, the body may comprise an oxide, such as silicon oxide, and the sacrificial layer may comprise nitride, such as silicon nitride.

In embodiments of the invention, in the chemical-mechanical polishing, a polishing rate of a material of the sacrificial layer is lower than a polishing rate of the material of the body. In embodiments of the invention, this allows for control of the overall polishing rate. In embodiments of the invention, the polishing duration and, therefore, the amount of removed material can be selected such that a substantial planar surface of the body is obtained. In embodiments of the invention, the sacrificial layer may be removed completely during chemical-mechanical polishing thereof. In embodiments of the invention, the material of the body, the material of the sacrificial layer and parameters of the chemical-mechanical polishing process, such as the chemicals in the slurry used in chemical-mechanical polishing, may be such that the selectivity between the sacrificial layer and the material of the body is adjusted in a way that the polishing rate of the sacrificial layer is lower than the polishing rate of the body.

In the following, an embodiment of the invention is explained referring to a semiconductor fabrication process. In the semiconductor fabrication process, a substrate portion may be oxidized making use of a patterned masking layer. An example is a so-called LOCOS (local oxidation of silicon) process, typically using a patterned nitride layer as a masking layer. Standard bird heads, which are also referred to as bird beaks, i.e., elevations or protrusions, may be observed at the edges of the patterned masking layer. The height of the bird heads may increase with increased oxidation thickness. The resulting topology may affect subsequent process steps, such as resist coating or lithography. Embodiments of the invention may be directed to a reduction of an unevenness, e.g., a topology, resulting from such bird's heads.

FIG. 2 a shows a silicon body 20 and a silicon oxide layer 22 , such as a SiO 2 layer, formed on a top surface of the silicon layer 20 . The silicon oxide layer 22 is optional and may or may not be provided.

A patterned nitride mask 24 is provided over the silicon oxide layer 22 (or over the substrate 20 if the silicon oxide layer 22 is not provided) as shown in FIG. 2 b . The patterned nitride mask 24 comprises a recess 26 exposing a portion 22 a of the silicon oxide layer 22 (or of the substrate 20 if the silicon oxide layer is not provided).

The structure shown in FIG. 2 b is subjected to an oxidation process to form a thick oxide 22 b in a region where the nitride 24 is not provided. In a LOCOS process, the thick oxide 22 b may be called “field oxide.” In embodiments of the invention, the oxidation process may comprise a thermal oxidation process. The resulting structure is shown in FIG. 2 c . As can be seen in FIG. 2 c , an elevation 28 is formed in the region of the border 34 a of the nitride mask 24 , which is known in the art as a so-called bird head.

In embodiments of the invention, depending on the thickness of the thick oxide 22 b , oxidation may take place on top of the nitride mask 24 during generation of the thick oxide 22 b . Thus, upon generation of the thick oxide 22 b , a deglazing process may be performed to remove oxide material from the top of the nitride mask 24 . In embodiments of the invention, the deglazing process may comprise a wet-chemical etching process.

After oxidation and optionally deglazing, an additional sacrificial layer 30 is applied to the top surface of the structure shown in FIG. 2 c . In embodiments of the invention, the sacrificial layer is a nitride layer. In embodiments of the invention, the sacrificial layer is applied all-over the top surface of the structure shown in FIG. 2 c . In embodiments of the invention, the patterned nitride layer 24 may be removed prior to applying the sacrificial layer 30 .

In embodiments of the invention, the nitride layer 30 is applied using a low pressure chemical vapor deposition (LPCVD) or a plasma enhanced chemical vapor deposition (PECVD).

Subsequently, the top surface of the structure shown in FIG. 2 d is subjected to a chemical-mechanical polishing process, during which the sacrificial layer 30 is at least partially removed and during which material is removed from the elevation 28 and from the patterned nitride mask 24 . The resulting structure is shown in FIG. 2 e . In this chemical-mechanical polishing process, the selectivity between the nitride layer 30 and the thermal oxide may be adjusted in a way that the polishing rate of the nitride layer 30 is lower than the polishing rate of the oxide.

In the embodiment shown in FIGS. 2 a to 2 f , remainders 24 a and 30 a of the nitride layers 24 and 30 may remain after the chemical-mechanical polishing process. An unevenness 28 a having a reduced height when compared to the elevation 28 results from the chemical-mechanical polishing process.

Subsequently, the remaining portions 24 a and 30 a of the nitride layers may be removed and a surface having a reduced unevenness when compared to the oxide surface shown in FIG. 2 c is obtained. The resulting structure having the reduced unevenness is shown in FIG. 2 f . In embodiments of the invention, the remaining portions 24 a and 30 a are removed using a common wet-chemical etching process. In embodiments of the invention, this wet-chemical etching process may correspond to a nitride wet strip process of a LOCOS process.

In embodiments of the invention, the duration of the chemical-mechanical polishing process may be adapted, e.g., increased, to remove the whole topology, such that a substantially planar surface is obtained. In embodiments of the invention, the polishing duration may be adjusted such that the whole sacrificial layer is removed during the polishing process, so that the step of removing the remainder of the nitride layer may be omitted.

In embodiments of the invention, an optional cleaning, such as an RCA cleaning may be performed after the chemical-mechanical polishing process. In embodiments of the invention, an additional deglazing process may be performed prior to removing the remaining portions 24 a and 30 a . Subsequently, in embodiments of the invention, an oxidation process may be performed in order to oxidize residual nitride (so called white ribbons) at the edge of the thick oxide (LOCOS edge). Such an oxidation process is generally known as “KOOI oxidation” according to the name of the person who introduced this process.

Compared to bird head planarization using an additional resist etch back technique, in embodiments of the invention, processes of resist coating, etching and resist removal may be replaced by processes of deglazing, applying a nitride layer and chemical-mechanical polishing.

Although, the present application has been described referring to specific embodiments, it is clear for a person skilled in the art that embodiments of the inventive methods are applicable to planarize the top surface of semiconductor wafers or other substrates in any conceivable fabrication stage, where a planarized surface may be helpful for further processing.

Many variations and modifications may be made to the above-described embodiments. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.