Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MANUFACTURING AN ALUMINIUM ALLOY PLATE
FOR VACUUM CHAMBER ELEMENTS
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of and priority to European Patent
Application No.
20179258.7, filed June 10, 2020, the contents of which are herein incorporated
by reference in
its entirety.
FIELD OF THE INVENTION
The invention relates to a method of manufacturing an aluminium alloy plate of
an Al-
Mg-Si alloy (also known as a 6XXX-series aluminium alloy) for forming elements
of the
vacuum chambers of apparatuses for manufacturing semiconductor devices and
liquid crystal
devices, such as CVD systems, PVD systems, ion-implanting systems, sputtering
systems and
dry etching systems, and those placed in the vacuum chambers. The invention
relates also to a
method of manufacturing vacuum chamber elements from the Al-Mg-Si alloy plate.
The
invention further relates to methods of manufacturing valves and total
assemblies from the
Al-Mg-Si alloy plate.
BACKGROUND TO THE INVENTION
Reactive gases, etching gases, and corrosive gases containing halogen as a
cleaning
gas are supplied into the vacuum chambers of apparatuses for manufacturing
semiconductor
devices and liquid crystal devices, such as CVD systems, PVD systems, ion-
implanting
systems, sputtering systems and dry etching systems. Therefore, the vacuum
chambers are
required to have corrosion resistance to corrosive gases (hereinafter,
referred to as "corrosive
gas resistance"). Since a halogen plasma is often produced in the vacuum
chamber, resistance
to plasmas (hereinafter, referred to as "plasma resistance") is also
important. Recently,
aluminium and aluminium alloy materials have been used for forming elements of
the
vacuum chamber because aluminium and aluminium alloy materials are light and
excellent in
thermal conductivity. Since aluminium and aluminium alloy materials are not
satisfactory in
corrosive gas resistance and plasma resistance, various surface quality
improving techniques
for improving those properties have been proposed. However, many of those
properties are
still unsatisfactory and further improvement of those properties is desired.
Coating an
aluminium or an aluminium alloy material with a hard anodic oxide film having
a high
hardness has been found to be effective in improving plasma resistance. The
hard anodic
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oxide film is resistant to the abrasion of a member by a plasma having high
physical energy
and hence is capable of improving plasma resistance. The vacuum chamber
elements require
also sufficiently high mechanical strength and elongation, and colour
uniformity and a high
breakdown voltage after anodization.
US patent document US-2012/0325381-A1 discloses a manufacturing process for a
block of aluminium at least 250 mm thick designed for manufacture of an
element for a
vacuum chamber, the method comprises casting a block of a given 6XXX-series
aluminium
alloy, optionally homogenizing said cast block, performing a solution heat
treatment directly
on the cast and optionally homogenized block, quenching the block, stress
relieving of the
quenched block by means of cold compression, followed by artificial ageing to
a T652
condition. A key element of the disclosed process is that prior to the
solution heat treatment
the block has not been hot or cold worked to reduce its thickness. The
resultant plate product
is a so-called "cast plate". A disadvantage of cast plate is that the
unavoidable phases
resulting from the combination and precipitation at grain boundaries of
elements like iron,
manganese, magnesium, and silicon, often in an eutectic form after
solidification, cannot be
fully dissolved in the subsequent processing steps like homogenization and
solution heat
treatment and remain as sites for crack initiation, thus significantly
lowering the mechanical
properties (e.g., ultimate tensile strength, elongation, toughness, and
others), or as initiators of
local corrosion (e.g. pitting corrosion) and are harmful also for final
treatments like
anodization which is of particular relevance for vacuum chamber elements. Any
oxide layer
present within the cast alloy will also remain in its original shape therefore
also lowering the
mechanical properties. Although cast plate products might be produced more
cost effective,
because substantially the as-cast microstructure is maintained, and strongly
depends on the
local cooling speed during the casting operation, there is much more variation
in mechanical
properties as function of the testing location as compared to rolled plate
products, rendering
cast plates less suitable for many critical applications.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a sample light microscope image for analysing the phases and
particles of
the aluminium alloy materials described herein.
DESCRIPTION OF THE INVENTION
As will be appreciated herein below, except as otherwise indicated, aluminium
alloy
designations and temper designations refer to the Aluminium Association
designations in
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Aluminium Standards and Data and the Registration Records, as published by the
Aluminium
Association in 2019 and are well known to the person skilled in the art. The
temper
designations are laid down also in European standard EN515.
For any description of alloy compositions or preferred alloy compositions, all
references to percentages are by weight percent unless otherwise indicated.
The term "up to" and "up to about", as employed herein, explicitly includes,
but is not
limited to, the possibility of zero weight-percent of the particular alloying
component to
which it refers. For example, up to 0.08% Zn may include an aluminium alloy
having no Zn.
It is an object of the invention to provide a method of manufacturing an
aluminium
alloy plate of an Al-Mg-Si aluminium alloy or 6XXX-series aluminium alloy for
forming
vacuum chamber elements. It is another object of the invention to provide a
method of
manufacturing vacuum chamber elements from an Al-Mg-Si aluminium alloy plate.
It is a
further object of the invention to provide a method of manufacturing valves
and total
assemblies from the Al-Mg-Si aluminium alloy plate.
These and other objects and further advantages are met or exceeded by the
present
invention and providing a method of manufacturing an aluminium alloy plate for
vacuum
chamber elements, the method comprising the steps of, in this order:
(a) providing a rolling feedstock material of an Al-Mg-Si aluminium alloy
having a
composition comprising of, in wt.%,
Mg 0.80% to 1.05%;
Si 0.70% to 1.0%;
Mn 0.70% to 0.90%;
Fe up to 0.20%;
Zn up to 0.08%, preferably up to 0.05%;
Cu up to 0.05%, preferably up to 0.03%;
Cr up to 0.03%, preferably up to 0.02%;
Ti up to 0.06%, preferably 0.01% to 0.06%;
unavoidable impurities each <0.03%, total <0.10%, balance aluminium;
(b) homogenizing of the rolling feedstock at a temperature in a range of
550 C to 595 C;
.. (c) hot-rolling of the homogenized rolling feedstock in one or more rolling
steps to a hot-
rolled plate having a thickness of at least 10 mm;
(d)
solution heat-treatment (SHT") of the hot rolled plate at a temperature in a
range of
540 C to 590 C;
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(e) rapid cooling or quenching of the SHT plate, preferably by one of spray
quenching or
immersion quenching in water or other quenching media;
(f) stretching of the cooled SHT plate to obtain a permanent elongation
from 1% to 5%;
(g) artificial ageing of the stretched plate, preferably to a T6 condition
(e.g., T651) or T7
condition (e.g., T7651).
By the careful control of narrow compositional ranges of the Al-Mg-Si alloy in
combination with the thermo-mechanical processing the resultant aluminium
alloy plate is
ideally suitable for manufacturing vacuum chamber elements. It is available in
a wide range
of thicknesses and is very good anodizable with a hard anodic coating. The
aluminium plate
material has high mechanical properties providing good shape stability of the
vacuum
chamber element. Several properties of an anodized element depend on the plate
material's
microstructure and composition. The plate product has a microstructure having
a uniform
distribution of phases within the plate leading to a less affected anodic
layer concerning e.g.
plate thickness and uniformity at the surface after anodization. The resultant
plate product
according to this invention provides a high corrosive gas resistance, e.g. as
tested in a bubble
test using 5% HC1; and has a high breakdown voltage (AC, DC) measured
according to ISO-
2376(2010).
In an embodiment the Al-Mg-Si alloy plate at thickness 55 mm in T651 condition
has
a tensile yield strength (YS) of at least 250 MPa, and even of at least 265
MPa, in the LT-
direction in accordance with the applicable norm ISO 6892-1 B.
In an embodiment the Al-Mg-Si alloy plate at thickness 55 mm in T651 condition
has
a tensile strength (UTS) of at least 300 MPa, and even of at least 310 MPa, in
the LT-
direction in accordance with the applicable norm ISO 6892-1 B.
In an embodiment the Al-Mg-Si alloy plate at thickness 55 mm in T651 condition
has
an elongation (Asomm) at least 8%, and even of at least 10%, in the LT-
direction in accordance
with the applicable norm ISO 6892-1 B.
Mg in combination with Si are the main alloying elements in the aluminium
alloy to
provide strength by the formation of Mg2Si phases. The Mg should be in a range
of 0.80% to
1.05%, and preferably in a range of 0.85% to 1.05%. A preferred upper-limit
for the Mg
.. content is 1.0%. A too high Mg content may lead to lead to the formation of
coarse Mg2Si
phases having an adverse effect of the quality of a subsequently applied
anodization coating.
A too low Mg content has an adverse effect on the tensile properties of the
aluminium plate.
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The Si should be in a range of 0.70% to 1.0%. In an embodiment the Si content
is at
least 0.75%, preferably at least 0.80%, and most preferably at least 0.84%. In
an embodiment
the upper-limit for the Si-content is 0.95%.
In an embodiment the ratio of Mg/Si, in wt.% is more than 0.9, and preferably
more
than 1.0, and most preferably more than 1.05. Reducing the amount of free Si
in the
aluminium alloy favours an increased elongation in the aluminium plate after
SHT at relative
high temperatures as done in accordance with the invention.
Another important alloying element is Mn and should be in a range of 0.70% to
0.90%
to increase the strength in the aluminium plate and to control the grain
structure and leads
recrystallisation after solution heat treatment and quenching. A preferred
lower limit is
0.75%. A preferred upper-limit is 0.85%.
Fe is an impurity element which should not exceed 0.20%. To control grain size
and to
achieve high mechanical strength and good corrosion resistance after
anodization the Fe level
is preferably up to 0.12%. However, it is preferred that at least 0.03% is
present, and more
preferably at least 0.04%. A too low Fe content may lead to undesirable
recrystallized grain
coarsening and makes the aluminium alloy too expensive. A too high Fe content
results in
reduced tensile properties and has an adverse effect on for example the
breakdown voltage
after anodization due to the formation of amongst others AlFeSi phases and has
also an
adverse effect on the corrosive gas resistance.
Zn up to about 0.08%, Cu up to about 0.05%, and Cr up to about 0.03% are
tolerable
impurities and have an adverse effect on the quality of a subsequently applied
anodization
coating, e.g. reduced corrosive gas resistance. In an embodiment the Zn is up
to about 0.05%,
and preferably up to about 0.03%. In an embodiment the Cu is up to about
0.03%, and
preferably up to about 0.02%. In an embodiment the Cr is up to about 0.02%.
Ti up to 0.06% is added as a grain refiner of the as-cast microstructure. In
an
embodiment it is present in a range of about 0.01% to 0.06%, and preferably in
a range of
about 0.01% to 0.04%.
Balance is made by aluminium and unavoidable impurities. Impurities are
present up
to 0.03% each and up to 0.10% total.
In an embodiment the Al-Mg-Si aluminium alloy has a composition consisting of,
in
wt.%, Mg 0.80% to 1.05%, Si 0.70% to 1.0%, Mn 0.70% to 0.90%, Fe up to 0.20%,
Zn up to
0.08%, Cu up to 0.05%, Cr up to 0.03%, Ti up to 0.06%, unavoidable impurities
each up to
0.03%, total up to 0.10%, balance aluminium, and with preferred narrower
ranges as herein
described and claimed.
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In an embodiment, the Al-Mg-Si aluminium alloy has a composition comprising,
in
wt.%,
Mg 0.70% to 1.05%;
Si 0.70% to 1.0%;
Mn 0.60% to 1.0%, preferably up to 0.95%;
Fe up to 0.20%;
Zn up to 0.2%;
Cu up to 0.10%;
Cr up to 0.05%, preferably up to 0.04%;
Ti up to 0.1%, preferably 0.01% to 0.08%;
Ni up to 0.06%;
unavoidable impurities each <0.05%, total <0.15%, balance aluminium.
The Al-Mg-Si-Mn aluminium alloy is provided as an ingot or slab for
fabrication into
a hot rolled plate product by casting techniques regular in the art for cast
products, e.g. Direct-
Chill (DC)-casting, Electro-Magnetic-Casting (EMC)-casting, Electro-Magnetic-
Stirring
(EMS)-casting, and preferably having an ingot thickness in a range of about
220 mm or more,
e.g. 400 mm, 500 mm or 600 mm. After casting the rolling feedstock, the as-
cast ingot is
commonly scalped to remove segregation zones near the cast surface of the
ingot. Grain
refiners such as those containing titanium and boron, or titanium and carbon,
are used as is
.. well-known in the art to obtain a fine as-cast grain structure.
The purpose of a homogenisation heat treatment has at least the following
objectives:
(i) to dissolve as much as possible coarse soluble phases formed during
solidification, and (ii)
to reduce concentration gradients to facilitate the dissolution step. A
preheat treatment
achieves also some of these objectives. The homogenisation process is done a
temperature
range of 550 C to 595 C. In an embodiment the homogenization temperature is at
least
555 C, and more preferably at least 565 C. The soaking time at the
homogenisation
temperature is in the range of about 1 to 20 hours, and preferably does not
exceed about 15
hours, and is more preferably in a range of about 5 to 15 hours. The heat-up
rates that can be
applied are those which are regular in the art.
The hot rolling is performed to a hot rolling plate thickness of 10 mm or
more. In an
embodiment the upper-limit is about 230 mm, preferably about 200 mm and more
preferably
about 180 mm.
A next important process step is solution heat treating ("SHT") of the hot
rolled plate
material. The plate product should be heated to bring as much as possible all
or substantially
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all portions of the soluble alloying elements into solution. The SHT is
preferably carried out
at a temperature in the temperature range of about 540 C to 590 C. A higher
SHT
temperature provides more favourable mechanical properties, e.g. an increased
R. In an
embodiment the lower-limit for the SHT temperature is 545 C, preferably it is
550 C. In an
embodiment the upper-limit for the SHT temperature is about 580 C, and more
preferably
about 575 C. A low SHT temperature reduces the strength of the aluminium plate
and some
large Mg2Si phases main remain undissolved and may create so called "hot
spots" and
reducing the corrosion resistance after anodization and reduce the breakdown
voltage. It is
believed that shorter soaking times are very useful, for example in the range
of about 10 to
180 minutes, preferably in a range of 10 to 40 minutes, and more preferably in
a range of 10
to 35 minutes, for example for plate thicknesses up to 50 mm. A too long
soaking time at a
relative high SHT temperature results in the growth of several phases
adversely affecting the
ductility of the aluminium plate. The SHT is typically carried out in a batch
or a continuous
furnace. After SHT, it is important that the plate material be cooled with a
high cooling rate to
a temperature of 100 C or lower, preferably to below 40 C, to prevent or
minimise the
uncontrolled precipitation of secondary phases. On the other hand cooling
rates should
preferably not be too high to allow for a sufficient flatness and low level of
residual stresses
in the plate product. Suitable cooling rates can be achieved with the use of
water, e.g. water
immersion or water jets.
The SHT and quenched plate material is further cold worked, preferably by
means of
stretching in the range of about 1% to 5% of its original length to relieve
residual stresses
therein and to improve the flatness of the plate product. Preferably the
stretching is in the
range of about 1.5% to 4%, more preferably of about 2% to 3.5%.
After cooling the stretched plate material is aged, preferably artificially
aged, more
preferably to provide a T6 condition, more preferably a T651 condition. In an
embodiment the
artificial ageing is performed at a temperature in the range of 150 C to 190
C, and preferably
for a time of 5 to 60 hours.
In an embodiment the stretch plate material is aged to an over-aged T7
condition,
preferably to a T74 or T76 condition, and more preferably to an T7651
condition.
In a further aspect of the invention it relates to a method of manufacturing a
vacuum
chamber element, the method comprising the steps of manufacturing the Al-Mg-Si
alloy plate
having a thickness of at least 10 mm as herein set forth and claimed, and
further comprising
the subsequent steps of:
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(h) machining said aged plate, e.g. in T6, T651, T7, T74, T76, or T7651
condition, into a
vacuum chamber element of predetermined shape and dimensions;
(i) surface treating of the vacuum chamber element, preferably by means of
anodization;
preferably to provide an anode layer or anode coating layer thickness of at
least 20p.m, and
preferably a thickness of at least 30p.m;
optionally the product thus anodized is hydrated or sealed in deionised water
at a
temperature of at least 80 C and preferably of at least 98 C, preferably for a
duration of at
least about 1 hour. In an embodiment the hydration is performed in two steps,
a first steps
with a duration of at least 10 minutes at a temperature of 30 C to 70 C, and a
second step
with a duration of at least about 1 hour at a temperature of at least 98 C.
In an embodiment the anodization is performed using an electrolytic solution
comprising at least sulfuric acid at a temperature about 15 C to 30 C and a
current density
from about 1.0 Aidm2 to about 2 Aidm2. The acid concentration in the anodizing
bath is
typically in a range of about 5 to 20 vol.%. The process takes from about 0.5
to 60 minutes,
.. depending on the desired oxide layer thickness. The sulfuric anodizing
generally yields an
oxide layer with a thickness from about 8 microns to about 40 microns.
In an embodiment the anodization is performed in an electrolytic solution
comprising
at least sulfuric acid at a temperature from about 0 C to about 10 C and a
current density
from about 3 Aidm2 to about 4.5 Aidm2. The process generally takes from about
20 minutes
to about 120 minutes. This hardcoat anodizing generally yields an oxide layer
with a
thickness from about 30 microns to about 80 microns, or even thicker.
In some embodiments, the material described herein can have a density of
phases and
particles having a size greater than 10 p.m2 of less than 400 phases per mm2.
For example, the
material can have a density of phases and particles having a size greater than
10 pm2 ranging
from 100 to 400 phases per mm2 or from 250 to 350 phases per mm2. The phases
and
particles can include AlFeSi-type phases and particles and Mg2Si phases and
particles.
The following example will serve to further illustrate the present invention
without,
however, constituting any limitation thereof On the contrary, it is to be
clearly understood
that resort may be had to various embodiments, modifications, and equivalents
thereof which,
.. after reading the description herein, may suggest themselves to those of
ordinary skill in the
art without departing from the spirit of the invention.
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EXAMPLE
Phase analysis experiments were performed on aluminium alloy samples for
anodizing
as described herein. Three samples of varying thicknesses were investigated,
including a
sample having a thickness of 130 mm (referred to herein as "Sample 1"), a
sample having a
thickness of 40 mm (referred to herein as "Sample 2"), and a sample having a
thickness of 14
mm (referred to herein as "Sample 3"). Each of the samples was analyzed at
three positions,
including the near surface position ("surface"), quarter thickness position
("s/4"), and half
thickness position ("s/2"). Seven images were captured per position at 1280 x
1024 pixel2
(0.382 um/pixel). As 0.191 mm2/image was analyzed for seven images,
approximately 1.34
mm2 for each position was investigated, amounting to 12.05 mm2 in total. Thus,
the samples
were extensively studied.
The images were taken using a light microscope at a magnification of 200x. The
samples were prepared in the same manner. No etching was performed. Grinding
and
polishing was performed for each sample, with special attention paid to avoid
any impact on
the data due to the preparation method, such as, for example, pores or
scratches that could
potentially be misinterpreted due to the use of greyscale analyzing tools.
The phases and particles analyzed were mainly AlFeSi-type phases and particles
along
with Mg2Si phases and particles. The detection was performed using ImageJ
software, and
the analysis was performed in grayscale. A sample image is shown in Figure 1.
A filter was
used to only count particles having an area of greater than 10 um2. The
results are shown
below in Table 1. The density for each position is shown in the column labeled
"Density
(phases/mm2)," the average density for each sample (calculated by taking the
average of the
three positions for each sample) is shown in the column labeled "Average
Density
(phases/mm2)", and the total average density calculated by taking the average
of the nine
measurements (three samples and three positions per sample) is shown in the
column labeled
"Total Average Density for All Samples (phases/mm2)." As shown in Table 1, the
densities
ranged from 250 to 320 phases/mm2.
Table 1
Sample Position Thickness Density Average Total
(mm) (phases/mm2) Density Average
(phases/mm2) Density for
All Samples
(phases/mm2)
Sample 1 surface 130 277.85 276.35 275.86
Sample 1 s/4 130 283.82
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Sample 1 s/2 130 267.39
Sample 2 surface 40 253.20 257.68
Sample 2 s/4 40 269.63
Sample 2 s/2 40 250.21
Sample 3 surface 14 270.38 293.53
Sample 3 s/4 14 318.93
Sample 3 s/2 14 291.29
All patents, publications and abstracts cited above are incorporated herein by
reference
in their entireties. Various embodiments of the invention have been described
in fulfilment of
the various objectives of the invention. It should be recognized that these
embodiments are
merely illustrative of the principles of the present invention. Numerous
modifications and
adaptions thereof will be readily apparent to those skilled in the art without
departing from the
spirit and scope of the present invention as defined in the following claims.
