DE10324551A1 - Determining thickness of layer grown on semiconductor substrate comprises forming periodic structure on surface of substrate, carrying out selective epitaxial growth, and carrying out scatterometric process - Google Patents

Abstract

Determining the layer thickness (h) of a layer (10) epitaxially grown on a semiconductor substrate (1) comprises forming a periodic structure on a surface of the substrate with protrusions (5') and intermediate chambers (5''), carrying out selective epitaxial growth to deposit the layer in the intermediate chambers, and carrying out a scatterometric process to determine the layer thickness of the layer.

Description

The The present invention relates to a method for determining the layer thickness an optically contrast-free epitaxial on a semiconductor substrate grown layer.

Even though principally applicable to any integrated circuits the present invention and the underlying problem in explained with reference to integrated circuits in silicon technology.

The Measuring the layer thickness of epitaxially grown layers so far has been very problematic in many cases, since there is little or no contrast to the semiconductor substrate in question is available. Therefore, the semiconductor substrate usually has to pretreated (e.g. by doping), or it is a preliminary measurement and a re-measurement by a measuring system is necessary. The measurements usually take a long time and often do not have good repeatability.

2 shows a schematic representation of one from the US 6,383,824 B1 Known scatterometry system to illustrate the problem of the invention.

In 2 denotes reference numerals 20 generally a scatterometry system, which serves a deposition process that takes place in a deposition chamber 26 is carried out to control.

The scatterometry system 20 includes in particular a scatterometry device 24 and a connected controller 28 which in turn separates out in the deposition chamber 26 controls. reference numeral 21 denotes a semiconductor wafer, on the surface of which a periodic lattice structure 22 is provided over which the process layer 24 in the deposition chamber 26 is deposited.

The scatterometry device 24 usually directs a light beam with a broad spectral distribution onto the surface of the wafer to be analyzed via a light source 21 with the periodic lattice structure 22 and the process layer deposited above it 24 and analyzes the reflected light beam with a detector. The detector signal can vary depending on the wavelength and / or the angle of incidence. The structure can be determined from these reflection data by means of predetermined evaluation algorithms.

It is the object of the present invention, a simple and reliably repeatable Method for determining the layer thickness of an optically contrastless epitaxially to a layer grown on a semiconductor substrate create.

According to the invention Problem by the method for determining specified in claim 1 the layer thickness of an optically contrast-free epitaxial on a semiconductor substrate grown layer solved.

By the procedure according to the invention can measure the layer thickness selectively grown epitaxially Layers are carried out on known scatterometry systems.

The inventive method is fast, experience has shown good repeatability and can be applied to all selectively epitaxially grown layers. Time-consuming pre- and post-measurement procedures are completely eliminated. The The method is not restricted to specific layer thickness ranges. The Use of different measuring systems for different types of layers and Layer thicknesses are eliminated.

The The idea underlying the present invention is to apply a periodic test structure to the semiconductor substrate, which on the one hand provides an optical contrast to the semiconductor substrate and offers to the epitaxial layer and on the other hand a selective epitaxy enables on the semiconductor substrate. Then allow the selective epitaxy that the epitaxial layer only in the spaces between periodic structure is grown on the semiconductor substrate. In the structure thus created, a scatterometry system is used the epitaxial layer thickness using predetermined scatterometry algorithms certainly.

In the subclaims there are advantageous developments and improvements to the Object of the invention.

According to one preferred development, the periodic structure has lines as surveys.

According to one Another preferred development is when performing the Scatterometry method for determining the layer thickness of the layer an intensity distribution in dependence of the wavelength and / or determined from the angle of incidence of the reflected light, after which this to predetermined intensity distributions is being fitted.

According to one The semiconductor substrate is a further preferred development and the layer of the same material, especially silicon, and the periodic structure from a different material, especially silicon oxide.

According to one Another preferred development is the periodic structure through a deposition process, a lithography process and a subsequent etching process generated.

On embodiment the invention is illustrated in the drawings and in the following Description closer explained.

1a -E show schematic representations of successive process stages of a process as an embodiment of the present invention; and

2 shows a schematic representation of one from the US 6,383,824 B1 Known scatterometry system to illustrate the problems according to the invention.

In in the figures, the same reference numerals designate the same or functionally the same Ingredients.

1a -E show schematic representations of successive process stages of a process as an embodiment of the present invention.

In 1a denotes reference numerals 1 a silicon semiconductor substrate. On the silicon semiconductor substrate 1 becomes a silicon oxide layer 5 for example deposited with a CVD process. A photolithographic process known per se then creates a periodic (in one or two dimensions) lattice structure in the silicon oxide layer 5 provided what lines 5 ' (one-dimensional periodicity) from silicon oxide and spaces 5 '' on which the surface of the semiconductor substrate 1 is exposed. For example, the lines point 5 ' and the gaps 5 '' a width of 200 nm, the height of the lines 5 ' Is 130 nm.

Instead of the lines 5 '' Cylinders (two-dimensional periodicity) could also be used in a further exemplary embodiment not shown in the figures.

The resulting periodic lattice structure is in 1b shown. It is important in this context that the lattice layer made of silicon oxide with an optical scatterometry method provides an optical contrast to the underlying semiconductor substrate 1 and for the later epitaxial layer 10 can offer. It is also important that the lattice layer makes it possible in the subsequent process step, which in 1c is shown, a selective epitaxial deposition of the epitaxial silicon layer 10 on the surface of the semiconductor substrate in the spaces 5 '' permit. In other words, the epitaxial silicon layer forms 10 not on the surface of the lines 5 ' or cylinders, but only in the spaces 5 '' on the semiconductor substrate 1 ,

The resulting structure according to 1c can be subjected to a scatterometry measurement either in situ or after the epitaxial growth process has ended. The values of the intensity determined as a function of the reflected wavelength can be used to determine the height h of the selectively epitaxially grown silicon layer 10 Begin at predetermined pattern curves I (λ, h1), I (λ, h2) etc., for example using the least squares algorithm.

On this way is a very accurate and reliably repeatable Layer thickness h of the epitaxial layer can be determined.

Even though the present invention above based on a preferred embodiment it is not limited to this, but in a variety of ways and modifiable.

In particular is the selection of the epilayer, substrate and lattice materials only by way of example and can be varied in many ways.

1

Silicon semiconductor substrate

5

silicon oxide

5 ', 5' '

lines, interspaces the periodic structure

door

10

epitaxial layer

S

light source

e

detector

h, h1, h2

height

I

intensity

λ

wavelength

Claims (5)

Method for determining the layer thickness (h) of an optically contrast-free epitaxial on a semiconductor substrate ( 1 ) grown up layer ( 10 ) with the steps: providing a periodic structure ( 5 ' . 5 '' ) on a surface of the semiconductor substrate ( 1 ) with surveys ( 5 ' ) and spaces ( 5 '' ) in which the surface of the semiconductor substrate ( 1 ) exposed; where the periodic structure ( 5 ' . 5 '' ) is such that it provides an optical contrast to the semiconductor substrate ( 1 ) and to the shift ( 10 ) with a scatterometry method and which offers a selective epitaxy process on the semiconductor substrate ( 1 ) permits; Performing the selective epitaxial process to deposit the layer ( 10 ) in the gaps ( 5 '' ); and performing the scatterometry method to determine the layer thickness (h) of the layer ( 10 ). A method according to claim 1, characterized in that the periodic structure ( 5 ' . 5 '' ) Lines ( 5 ' ) with one-dimensional periodicity or cylinders with two-dimensional periodicity as elevations. Method according to claim 1 or 2, characterized in that when performing the scatterometry method for determining the layer thickness (h) of the layer ( 10 ) an intensity distribution is determined as a function of the wavelength and / or the angle of incidence of the reflected light and is fitted to predetermined intensity distributions. A method according to claim 1, 2 or 3, characterized in that the semiconductor substrate ( 1 ) and the layer ( 10 ) made of the same material, especially silicon, and the periodic structure ( 5 ' . 5 '' ) consist of a different material, in particular silicon oxide. Method according to one of the preceding claims, characterized in that the periodic structure ( 5 ' . 5 '' ) is generated by a deposition process, a lithography process and a subsequent etching process.