Process for polishing silicon wafers

Abstract

A process for the chemical-mechanical polishing of silicon wafers is by rotational movement of the silicon surface which is to be polished on a polishing plate which is covered with polishing cloth, with a continuous supply of an alkaline polishing agent which contains abrasives, at least 2 mum of material being removed from the polished silicon surface during the polishing. Immediately after the polishing has finished, and while maintaining the rotational movement, instead of the polishing agent at least two different stopping agents are supplied in succession, each removing less than 0.5 mum of material from the polished silicon surface.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a polishing process for semiconductor wafers made from silicon, which are used in particular in industry for the fabrication of microelectronic components.[0003] 2. The Prior Art[0004] Semiconductor wafers made from silicon, which are used as substrates for the fabrication of modern microelectronic components have to fulfill a wide range of properties. These properties are often specified within relatively narrow limits. A number of these quality parameters are only determined in the final processing step of the wafers, generally involving polishing followed by cleaning. Properties of this type include, for example, the planarity of the silicon wafers, their surface roughness and the extent of surface defects, such as scratches, spots and localized light scatterers.[0005] The polishing is generally carried out as a chemical-mechanical process. Here the silicon surface which is to be polished, while an alkaline p...

AI Technical Summary

Benefits of technology

[0014] The starting product for the process is silicon wafers with rounded edges which are produced by sawing a silicon single crystal and have been subjected to one or more of the process steps of lapping, grinding, etching and polishing. The end product of the process is silicon wafers with a polished front surface and an unpolished back surface or a polished front surface and a polished back surface, at least one polished side having a low roughness and a low defect rate.

[0016] The silicon wafers which are produced by sawing a silicon single crystal and rounding the edges may be subjected to one or more abrasive process steps before the polishing process according to the invention is carried out. The inventive process has the object of improving the wafer geometry and of removing flawed surface layers and contaminations. Suitable processes are, for example, lapping, grinding and etching. Wafers with polished surfaces can also be subjected to the process according to the invention. This is done for example in order to rework wafers which have already been polished but do not comply with specifications, so as to transform them into a state in which they do comply with the relevant specifications.

Problems solved by technology

However, incomplete rinsing away of alkaline polishing agent residues may lead to spots being formed on the wafer surface.

There are a number of drawbacks associated with this process.

Firstly, the roughness of the polished silicon surface which is produced does not allow direct further processing.

For example deposition of an epitaxial coating is not allowed or the fabrication of components is not allowed, without following the process with an expensive smoothing touch polishing step.

Thirdly the considerable drop in pH is caused by the addition of the acidic stopping agent, particularly when using large polishing machines which enable 12 or more silicon wafers to be polished simultaneously.

This leads to the formation of hard SiO.sub.2 crystallites, leading to scratches being formed on the polished surfaces.

The fact that a sequence of steps of this nature allows silicon wafers with improved surfaces to be produced was unexpected, was surprising and was impossible to foresee.

If the diameters were considerably smaller, the quantity to be polished at the same time would generally be excessively high to allow speedy loading and unloading.

But the preferred configuration with at least twelve wafers to be polished at the same time leads to polishing machine dimensions which have not yet been feasible to produce.

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