Layered semiconductor wafer with low warp and bow, and process for producing it

Abstract

Semiconductor wafers with a diameter of at least 200 mm comprise a silicon carrier wafer, an electrically insulating layer and a semiconductor layer located thereon, the semiconductor wafer having been produced by means of a layer transfer process comprising at least one RTA step, wherein the semiconductor wafer has a warp of less than 30 μm, a DeltaWarp of less than 30 μm, a bow of less than 10 μm and a DeltaBow of less than 10 μm. Processes for the production of a semiconductor wafer of this type require specific heat treatment regimens.

Description

BACKGROUND OF THE INVENTION [0001] 1 Field of the Invention [0002] The invention relates to a semiconductor wafer with a diameter of at least 200 mm produced by a layer transfer process including at least one RTA step, and comprising a carrier wafer of silicon, an electrically insulating layer, and a semiconductor layer located thereon, the semiconductor wafer having low warp and bow, both in the unprocessed state and after any desired component fabrication process. Moreover, the invention relates to a process for producing such wafers. [0003] 2. Background Art [0004] SOI (silicon on insulator) wafers are generally produced by transferring a silicon layer from a donor wafer to a carrier wafer, also known as a handle wafer or a base wafer. Processes for producing SOI wafers by transferring a silicon layer (layer transfer) are described, for example, in EP533551A1, WO98 / 52216A1, and WO03 / 003430A2. SOI wafers comprise a carrier wafer and a single-crystal silicon covering layer, also kn...

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Benefits of technology

[0034] Another advantage of the invention is that the required changes to the heat treatment of the SOI wafer are simple to implement and have no harmful side effects on other important parameters of the finished SOI wafer.

[0035] The prior art has not disclosed a valid model which takes into account all the variables influencing the mechanical properties, in particular the deformation resistance of silicon wafers, simultaneously. This applies to an even greater extent in particular to semiconductor wafers with a layer structure which are produced by transferring a silicon layer and comprise a carrier wafer, an electrically insulating layer and a semiconductor layer.

[0036] The SOI wafers referred to have a specific thermal history behind them, leading to a specific BMD formation. FIG. 1 shows a typical BMD distribution in prior art SOI wafer of this type. The distribution is highly inhomogeneous, with a relatively low BMD density in the vicinity of the wafer back surface 3 but a BMD density which is higher by a multiple in the vicinity of the wafer front surface 1. The wafer front surface bears the thin film of silicon which is intended for the fabrication of electronic components. Overall, the BMD density decreases from the wafer front surface 1 to the center of the wafer 2 and then decreases further toward the wafer back surface 3. By contrast, the distribution of the BMD density in a conventional CZ silicon wafer (FIG. 2), i.e. a silicon wafer without a layer structure produced from a silicon single crystal pulled using the Czochralski method, is relatively homogeneous and has a different profile: the BMD density decreases from the center of the wafer 5 both toward the wafer front surface 4 and toward the wafer back surface 6.

[0037] Furthermore, the SOI wafer has a layer structure which leads to layer stresses similar to those in wafers with an epitaxial layer, a polycrystalline silicon layer or a silicon oxide layer.

[0038] The combination of the two effects, namely the incorporated layer stresses and the inhomogeneous defect distribution, leads to a complicated behavior on the part of the global shape, which differs significantly from the behavior of conventional CZ silicon wafers.

[0039] The RTA treatment of the prior art is employed only in order to sufficiently smooth the surface of the transferred silicon layer, which has a certain roughness as a result of being separated from the remainder of the donor wafer. According to prior art, this RTA treatment has no further objectives (cf. EP1158581A1). It was therefore not obvious to solve the photolithography problem by modifying this RTA treatment in accordance with the thermal treatment regimens described herein. EXAMPLES

Problems solved by technology

However, SOI wafers which are produced by this process have the drawback of being deformed during this heat treatment, as well as during subsequent heat treatments associated with the fabrication of electronic components.

This deformation can lead to serious complications in the fabrication of electronic components.

If the wafer is deformed, it cannot be completely “sucked” onto the vacuum wafer holder, with the result that the surface is not planar during exposure.

In this case, sharply defined imaging of the mask pattern on the surface is not possible in all regions of the SOI wafer.

Moreover, this can lead to a lateral offset in the mask pattern transferred to the SOI wafer, with the result that adjacent components overlap and therefore cannot function.

During the fabrication of electronic components comprising the application of complicated layer structures with the aid of a large number of heat treatment steps, deformation occurs for two reasons, manifesting itself in a deterioration in the warp and bow parameters: firstly, the layer structure of the SOI wafers e.g. silicon carrier wafer, insulating layer of silicon oxide, silicon layer, which inevitably entails certain stresses, leads to the increased formation of warp and bow.

This change in the plastic properties in turn leads to an increase in warp and bow.

However, the prior art RTC processes failed to produce wafers which have low initial deformation.

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