U.S. patent application number 12/199124 was filed with the patent office on 2009-03-19 for process for cleaning a semiconductor wafer.
This patent application is currently assigned to SILTRONIC AG. Invention is credited to Thomas Buschhardt, Diego Feijoo, Guenter Schwab, Clemens Zapilko.
Application Number | 20090071507 12/199124 |
Document ID | / |
Family ID | 40384093 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090071507 |
Kind Code |
A1 |
Buschhardt; Thomas ; et
al. |
March 19, 2009 |
PROCESS FOR CLEANING A SEMICONDUCTOR WAFER
Abstract
Semiconductor wafers are cleaned by forming a first liquid film
on a surface of the semiconductor wafer to be cleaned, the first
liquid film containing hydrogen fluoride and ozone; replacing the
first liquid film with a second aqueous liquid film which contains
hydrogen fluoride and ozone, the concentration of hydrogen fluoride
in the second liquid film being lower than in the first liquid
film; and removing the second liquid film.
Inventors: |
Buschhardt; Thomas;
(Burghausen, DE) ; Zapilko; Clemens; (Burghausen,
DE) ; Feijoo; Diego; (Burghausen, DE) ;
Schwab; Guenter; (Neuoetting, DE) |
Correspondence
Address: |
BROOKS KUSHMAN P.C.
1000 TOWN CENTER, TWENTY-SECOND FLOOR
SOUTHFIELD
MI
48075
US
|
Assignee: |
SILTRONIC AG
Munich
DE
|
Family ID: |
40384093 |
Appl. No.: |
12/199124 |
Filed: |
August 27, 2008 |
Current U.S.
Class: |
134/3 |
Current CPC
Class: |
C11D 7/08 20130101; C11D
11/0047 20130101; H01L 21/02052 20130101; C11D 7/02 20130101; H01L
21/02057 20130101 |
Class at
Publication: |
134/3 |
International
Class: |
C23G 1/02 20060101
C23G001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2007 |
DE |
10 2007 044 787.8 |
Claims
1. A process for cleaning a semiconductor wafer surface, comprising
forming a first aqueous liquid film on the surface, the first
liquid film containing hydrogen fluoride and ozone; replacing the
first liquid film with a second aqueous liquid film which contains
hydrogen fluoride and ozone, the concentration of hydrogen fluoride
in the second liquid film being lower than in the first liquid
film; and removing the second liquid film.
2. The process of claim 1, wherein no more than 120 s elapse from
formation of the first liquid film until removal of the second
liquid film.
3. The process of claim 1, wherein no more than 60 s elapse from
formation of the first liquid film until replacement of the first
liquid film with the second liquid film.
4. The process of claim 1, wherein the concentration of hydrogen
fluoride in the first liquid film is from 0.1 to 10 wt %.
5. The process of claim 2, wherein the concentration of hydrogen
fluoride in the first liquid film is from 0.1 to 10 wt %.
6. The process of claim 1, wherein the concentration of hydrogen
fluoride in the second liquid film is from 0.001 to 0.1 wt %.
7. The process of claim 2, wherein the concentration of hydrogen
fluoride in the second liquid film is from 0.001 to 0.1 wt %.
8. The process of claim 4, wherein the concentration of hydrogen
fluoride in the second liquid film is from 0.001 to 0.1 wt %.
9. The process of claim 1, wherein the first liquid film is
replaced with the second liquid film through displacement of the
first liquid film by the second liquid film, and the surface
remains constantly wetted with liquid during the replacement.
10. The process of claim 1, wherein the semiconductor wafer is
rotated with a rotational speed in the range of from 100 to 2000
rpm during cleaning.
11. The process of claim 1, wherein the first or second liquid
film, or both liquid films, contain HCl in a concentration of from
0.2 to 2.0 wt %.
12. The process of claim 2, wherein the first or second liquid
film, or both liquid films, contain HCl in a concentration of from
0.2 to 2.0 wt %.
13. The process of claim 4, wherein the first or second liquid
film, or both liquid films, contain HCl in a concentration of from
0.2 to 2.0 wt %.
14. The process of claim 6, wherein the first or second liquid
film, or both liquid films, contain HCl in a concentration of from
0.2 to 2.0 wt %.
15. The process of claim 1, wherein the second liquid film is
displaced by ultrapure water, ultrapure water containing ozone, SC1
solution or dilute hydrochloric acid.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a process for cleaning a
semiconductor wafer with an aqueous liquid film, which contains
hydrogen fluoride and ozone.
[0003] 2. Background Art
[0004] Semiconductor wafers for use in the fabrication of
electronic components must generally be cleaned of particles and
metal contaminants. Such cleaning steps are customary both for the
fabricators of the electronic components and for their suppliers,
i.e. the manufacturers of the semiconductor wafers.
[0005] Aqueous solutions which contain hydrogen fluoride (HF) and
ozone (O.sub.3) have proven to be effective cleaning agents. U.S.
Pat. No. 5,759,971 describes a cleaning process in which a
plurality of semiconductor wafers are simultaneously immersed in an
aqueous bath which contains HF in a concentration of between 0.03
and 0.05 wt % and ozone dissolved to saturation. Modem processes
are designed for single-wafer treatment, inter alia because this
allows lower consumption of cleaning liquid. The cleaning liquid in
such a process is applied as a liquid film onto one or both major
surfaces of the semiconductor wafer. U.S. Pat. No. 7,037,842 B2
describes a process in which a surface of a rotating semiconductor
wafer is sprayed with an aqueous cleaning liquid which contains
hydrogen fluoride and ozone.
[0006] For economic reasons it is desirable to make the cleaning
cycle times as short as possible, i.e. to achieve the highest
possible throughput of semiconductor wafers. Conflicting with this
aim is the fact that, in general, cleaning is commensurately more
complete when it is carried out for a longer time. An obvious
solution to this problem might be supposed to involve increasing
the concentration of the hydrogen fluoride and ozone components
which exert the cleaning action. This strategy, however, has the
disadvantage that increasing the concentration of hydrogen fluoride
will also enhance the etching action of this component, which leads
to undesirable roughening of the cleaned surface.
SUMMARY OF THE INVENTION
[0007] It is an object of the invention to provide a process which
allows short cycle times and effective cleaning without
unacceptably increasing the roughness of the surface. These and
other objects are achieved by a process for cleaning a
semiconductor wafer, comprising forming a first aqueous liquid film
on a surface to be cleaned, the first liquid film containing
hydrogen fluoride and ozone; replacing the first liquid film with a
second aqueous liquid film which contains hydrogen fluoride and
ozone, the concentration of hydrogen fluoride in the second liquid
film being lower than in the first liquid film; and removing the
second liquid film.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0008] The advantages of the process are significant, particularly
in connection with the cleaning of silicon semiconductor wafers
which are still free of semiconductor components. Such
semiconductor wafers are typically cleaned after polishing, heat
treatment or after the deposition of an epitaxial layer. The
etching action of the cleaning liquid exposes COP defects (crystal
originated particles) and oxygen precipitates (BMD, bulk
microdefects). These are detected as particles by scattered-light
measuring instruments, and they are a cause of the increase in the
roughness of the surface. The invention makes it possible to
restrict this detrimental effect, but without having to abandon
rapid completion of the cleaning.
[0009] The cleaning process according to the invention, which is
based on the concept of single-wafer treatment of a rotating
semiconductor wafer, comprises two cleaning stages which differ
primarily by the concentration of hydrogen fluoride in the cleaning
liquid, the concentration in the cleaning liquid of the first stage
being higher than in the cleaning liquid of the subsequent stage.
The first stage extends from the formation of a first liquid film
on the semiconductor wafer's surface to be cleaned, until
replacement of the first liquid film with a second liquid film. The
second stage lasts from this time until the second liquid film is
removed from the semiconductor wafer's surface to be cleaned. Both
stages preferably last no longer than 60 s respectively, more
preferably no longer than 30 s respectively, so that cleaning
according to the invention can be carried out in preferably no more
than 120 s, more preferably in no more than 60 s.
[0010] The changeover from the first cleaning stage to the second
cleaning stage is preferably carried out through the first liquid
film being displaced by the second liquid film, and the
semiconductor wafer's surface to be cleaned remains constantly
wetted with liquid during this time.
[0011] The thickness of the first and second liquid films is
controlled via the speed with which the semiconductor wafer is
rotated about a rotation axis which perpendicularly intersects the
center of the surface to be cleaned. The rotation speed preferably
lies in a range of from 100 to 2000 rpm. The range of from 200 to
500 rpm is particularly preferred. The speed of the rotational
movement during the first cleaning stage may differ from the speed
of the rotational movement during the second cleaning stage. The
speed selected for the first cleaning stage will preferably not be
changed during the cleaning stage. Owing to the rotational movement
of the semiconductor wafer, used cleaning liquid flows off together
with particles and dissolved contaminants at the edge of the
semiconductor wafer. The loss of cleaning liquid due to this flow
is compensated continuously by applying a corresponding amount of
fresh liquid through one or more nozzles onto the semiconductor
wafer's surface to be cleaned.
[0012] The first cleaning stage is essentially intended to rapidly
dissolve native surface oxide and possibly polishing agent residues
containing silica sol, with the aid of a comparatively high
concentration of hydrogen fluoride. The adhesive base for insoluble
particles is also removed by this, so that they can continue to be
washed off from the surface of the semiconductor wafer. The second
stage is in essentially intended to sustain the washing process
under conditions which promote it, while simultaneously minimizing
the material erosion generated by the etching of semiconductor
material.
[0013] In the first liquid film, the concentration of hydrogen
fluoride is preferably from 0.1 to 10 wt %, and it more preferably
lies in a range of from 0.1 to 2.0 wt %. In the second liquid film,
the concentration of hydrogen fluoride is lower, preferably from
0.001 to 0.1 wt %, and it more preferably lies in a range of from
0.02 to 0.05 wt %. The concentration of ozone may be the same in
both liquid films, or it may be lower in the second liquid film
than in the first liquid film. In any event, however, it should be
selected so that it is high enough to leave behind a hydrophilic
wafer surface. Ozone may already be contained in the cleaning
liquid when the liquid film is applied onto the semiconductor
wafer. A preferred process, however, is one in which the liquid
film is enriched with ozone by diffusion-driven transport from the
surrounding gas phase. Such a process is described, for example, in
U.S. 2002/0050279 A1. In this case, ozone is introduced into the
process chamber as a mixture with oxygen. The concentration of
ozone in oxygen is preferably from 3 to 20 wt %.
[0014] It is furthermore preferable for the first and/or second
liquid film to contain hydrogen chloride (HCl) in a concentration
of from 0.2 to 2.0 wt %. This addition promotes the removal of
metallic contaminants such as ions of the metals copper, iron and
nickel.
[0015] The first and second liquid films are preferably at room
temperature (25.degree. C.). The temperature may however be lower
or higher than this, and it may be up to 95.degree. C. The
temperatures of the first and second liquid films may be the same
or different.
[0016] The second liquid film is preferably removed by displacing
it with a washing agent, for example ultrapure water, ultrapure
water containing ozone, SC1 solution or dilute hydrochloric acid.
The semiconductor wafer may subsequently be dried, for example by
spinning the washing agent off from the semiconductor wafer at a
high rotational speed with an influx of nitrogen, or by carrying
out a drying method known as Marangoni drying.
EXAMPLE
[0017] Silicon semiconductor wafers with a diameter of 300 mm were
cleaned after chemical-mechanical polishing (CMP). Coarse polishing
agent residues were removed beforehand with the aid of rollers.
Between 200 and 500 particles with an average size of more than 65
nm were detected on the polished surface of the semiconductor
wafers pretreated in this way. Some of these semiconductor wafers
were subjected according to the invention to two-stage cleaning
with a cleaning liquid containing HF and O.sub.3. During the first
cleaning stage, the polished surface of the semiconductor wafers
was sprayed in a single-wafer treatment device with an aqueous
solution which contained hydrogen fluoride in a concentration of
0.1 wt %. At the same time, an oxygen/ozone mixture with 230 g of
ozone/Nm.sup.3(stp) was passed through the gas space of the device.
A liquid film containing ozone, with an HF concentration of 0.1 wt
%, was formed on the surface of the semiconductor wafer treated in
this way. After 30 s had elapsed, the semiconductor wafer was
sprayed in a second cleaning stage with an aqueous solution which
contained hydrogen fluoride in a concentration of 0.05 wt %. The
ozone supply was not changed in any way so that a liquid film
containing ozone, with an HF concentration of 0.05 wt %, was formed
on the polished surface. After a further 30 s had elapsed, the
cleaned semiconductor wafer was washed with ultrapure water and
dried. The entire cleaning (first and second cleaning stages)
lasted 60 s, and was carried out by rotating the semiconductor
wafer with a constant speed of 300 rpm.
[0018] For comparison, semiconductor wafers which had been
pretreated as indicated above were subjected to merely one-stage
cleaning in the same device. The polished surface of the
semiconductor wafer to be cleaned was sprayed with an aqueous
solution which contained hydrogen fluoride in a concentration of
0.05 wt %. At the same time, an oxygen/ozone mixture with 230 g of
ozone/Nm.sup.3(stp) was passed through the gas space of the device.
A liquid film containing ozone, with an HF concentration of 0.05 wt
%, was formed on the surface of the semiconductor wafer treated in
this way. During the cleaning, the semiconductor wafer was rotated
with a constant speed of 300 rpm. After 60 s had elapsed, the
cleaned semiconductor wafer was washed with ultrapure water and
dried. For some of the semiconductor wafers, the duration of the
cleaning was extended to 240 s, and for others the concentration of
hydrogen fluoride was increased to 0.1 wt %.
[0019] Examining the efficiency of the cleaning revealed that on
average 80% fewer particles were found after the cleaning on the
semiconductor wafers cleaned according to the invention. With the
one-stage cleaning, 45% of the particles were removed in the best
case. The effect of extending the cleaning time was that the number
of detectable particles increased owing to etching effects, which
reduced the efficiency of the cleaning.
[0020] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *