JPH1020337A - Production of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a semiconductor element having high reliability by continuously executing a stage for irradiation with a laser beam and a stage for forming a protective insulating film while maintaining vacuum. SOLUTION: A ground surface insulating film is formed on the main surface of a glass substrate. In succession, an amorphous silicon (a-Si) film is formed within the same vacuum device and is irradiated with the pulse laser beams LASER to convert the a-Si film to a polycrystalline silicon(poly-Si) film 301. A gate insulating film and gate electrode are formed and are patterned to prescribed shapes. The poly-Si film 301 is irradiated with the ion beam IB contg. phosphorus with these patterns as a mask, by which poly-Si layers 31 of an N type are formed in a part of the poly-Sr film. The film is again irradiated with the pulse laser beams. In succession, the protective insulating film 21 covering the entire part of the element is formed within the same vacuum device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device used in an active matrix type liquid crystal display device used as a display device for image information and character information of OA equipment and the like.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display device using thin film transistors, high definition and high image quality are important issues as well as cost reduction. In order to solve these problems, it is indispensable to improve the performance of a thin film transistor (hereinafter referred to as TFT) as a key device. If a high-performance TFT can be formed on an inexpensive glass substrate, for example, the 1985 Conference Record of International Display Research Conference
arch Conference) As described on page 9, TFT
The peripheral drive circuit that drives the active matrix is also T
It is expected to be constructed with FT and integrated on the same substrate to reduce the cost.

For this reason, various techniques have been proposed for forming a high-performance TFT on a glass substrate. Above all, a technique for recrystallizing a silicon film using a high-intensity laser beam is the most promising technique and is being studied at various places. In the laser recrystallization technique, a high-quality polycrystalline silicon (hereinafter, referred to as poly-Si) film having a large crystal grain size is obtained, so that the carrier mobility of the transistor is generally greatly improved. A high-intensity laser beam is also used for impurity activation annealing after ion implantation for the purpose of lowering the manufacturing process temperature.

[0004]

Heretofore, the laser irradiation step in the above-described laser annealing process has been performed as an independent step using an apparatus that is separate from the film forming steps before and after annealing. That is, when recrystallizing a semiconductor film formed on an insulating substrate via a base insulating film, after the formation of the base insulating film and the semiconductor film, the substrate is once transferred to a laser irradiation apparatus while being exposed to the atmosphere. Laser annealing. In addition, after activation of impurities by laser irradiation, a manufacturing process has been adopted in which the substrate is once transferred to a film forming apparatus while being exposed to the atmosphere to form a protective insulating film.

When laser annealing is employed for recrystallization of semiconductor films or activation of impurities, the reliability of the device cannot be ensured by the above-described manufacturing method. That is, in the laser recrystallization step, the substrate is exposed to the air between the steps of forming the base insulating film, forming the semiconductor film, and laser recrystallization, so that the interface between the base insulating film and the semiconductor film or It is inevitable that the surface of the semiconductor film is contaminated by impurities such as carbon in the air and moisture. When laser irradiation is performed in such a state, these impurities are taken into the semiconductor film during melting and recrystallization, and a high-quality film cannot be obtained. Impurities taken into the interface between the base insulating film and the semiconductor film may cause deterioration of characteristics during the steady operation after the device is manufactured, specifically, an increase in leak current.

Further, when a laser is used for the impurity activation annealing, a region near the pn junction of the element immediately after the annealing is weakened by the thermal strain accompanying rapid cooling, where the bonds between the atoms are weakened and defects are easily generated. Is formed. When the element in such a state is exposed to the atmosphere, weak bonds are broken due to the presence of moisture in the atmosphere, and a defect occurs. Such a defect causes an increase in leak current and a decrease in transconductance gm. In the above-mentioned prior art, sufficient consideration has not been given to the point relating to the reliability of such an element, and a semiconductor element that can be put to practical use has not been obtained. The present invention is to solve such a problem, and an object of the present invention is to provide a method for manufacturing a semiconductor device having a laser recrystallization or laser impurity activation step, and a manufacturing method capable of manufacturing a highly reliable semiconductor element. To provide.

[0007]

Means for Solving the Problems In order to solve the above problems, the present invention takes the following measures. That is, a method of manufacturing a semiconductor device, comprising: irradiating a semiconductor film formed on a substrate with a laser beam; and forming a protective insulating film covering at least a part or all of the semiconductor film. A manufacturing method in which the step of irradiating a laser beam and the step of forming the protective insulating film are continuously performed while maintaining a vacuum is adopted.

A method for manufacturing a semiconductor device, comprising the steps of: forming an insulating film on a substrate; forming a semiconductor film on the insulating film; and irradiating the semiconductor film with a laser beam. A manufacturing method is employed in which the step of forming an insulating film and the step of forming a semiconductor film on the insulating film are continuously performed while maintaining a vacuum.

A step of forming an insulating film on the substrate;
A method for manufacturing a semiconductor device, comprising: forming a semiconductor film on the insulating film; and irradiating the semiconductor film with a laser beam, forming an insulating film on the substrate, and forming a semiconductor on the insulating film. A method for manufacturing a semiconductor device, wherein a step of forming a film and a step of irradiating the laser beam are continuously performed while maintaining a vacuum.

A step of forming an insulating film on the substrate, a step of forming a semiconductor film on the insulating film, a step of irradiating the semiconductor film with a laser beam, and covering at least part or all of the semiconductor film Forming a protective insulating film, wherein the step of forming an insulating film on the substrate and the step of forming a semiconductor film on the insulating film are continuously performed while maintaining a vacuum. In addition, a manufacturing method is employed in which the step of irradiating the laser beam and the step of forming the protective insulating film are continuously performed while maintaining a vacuum.

A step of forming an insulating film on the substrate;
Forming a semiconductor film having a predetermined planar shape on the insulating film, irradiating the semiconductor film with a laser beam, and forming a gate insulating film and a gate electrode on a part of the semiconductor film; Patterning the gate electrode and the gate insulating film into substantially the same plane shape, patterning the first gate electrode and the gate insulating film into the substantially same plane shape, and using the pattern of the gate electrode and the gate insulating film as a mask. Introducing a P-type or N-type impurity into the semiconductor film in a region of the semiconductor where the pattern of the gate electrode and the gate insulating film is not formed;
Irradiating the semiconductor film with a laser beam to activate impurities in the semiconductor film, forming a protective insulating film over the entire surface of the substrate including the semiconductor film, and removing a part of the protective insulating film. A method of manufacturing a semiconductor device, comprising: a step of exposing a part of a surface of a semiconductor film into which the impurity is introduced; and a step of forming source and drain electrodes so as to contact the exposed surface of the semiconductor film. A manufacturing method is employed in which the step of activating impurities by a laser beam and the step of forming a second insulating film over the entire surface of the substrate are continuously performed while maintaining a vacuum.

A step of forming an insulating film on the substrate;
Forming a semiconductor film on the insulating film, irradiating the semiconductor film with a laser beam, forming a gate insulating film and a gate electrode on a part of the semiconductor film, Patterning an insulating film into a substantially same plane shape, patterning the first gate electrode and the gate insulating film into a substantially same plane shape, and using the pattern of the gate electrode and the gate insulating film as a mask; P-type or N-type is formed in the semiconductor film in a region where the pattern of the gate electrode and the gate insulating film is not formed.
Introducing a type impurity, irradiating the semiconductor film with a laser beam to activate impurities in the semiconductor film, forming a protective insulating film on the entire surface of the substrate including the semiconductor film, Removing a part of the protective insulating film and exposing a part of the semiconductor film surface into which the impurity is introduced;
Forming a source and a drain electrode so as to be in contact with the exposed surface of the semiconductor film, a method of manufacturing a semiconductor device, the method comprising: forming an insulating film on the substrate; and forming a semiconductor film on the insulating film. The manufacturing method of continuously performing the step of forming while maintaining the vacuum was adopted.

A method for manufacturing a semiconductor device, comprising: a step of irradiating a semiconductor film formed on a substrate with a laser beam; and a step of forming a protective insulating film covering at least a part or all of the semiconductor film. The process of irradiating and the process of forming a protective insulating film are continuously performed while maintaining a vacuum, so that a semiconductor layer in which defects are likely to be generated due to thermal strain or the like during laser irradiation is reduced. Since it is not exposed to the air, a highly reliable element can be manufactured without defects due to moisture in the air.

In particular, the step of forming a semiconductor film having a predetermined planar shape on a substrate, the step of forming a gate insulating film and a gate electrode on a part of the semiconductor film, and the step of forming the gate electrode and the gate insulating film substantially the same A step of patterning into a planar shape, a step of patterning the gate electrode and the gate insulating film into substantially the same planar shape, and a pattern of the gate electrode and the gate insulating film of the semiconductor using the pattern of the gate electrode and the gate insulating film as a mask. Introducing a P-type or N-type impurity into the semiconductor film in a region where the semiconductor film is not formed, irradiating the semiconductor film with a laser beam to activate the impurity in the semiconductor film, Forming a protective insulating film, removing a part of the protective insulating film and exposing a part of the semiconductor film surface into which impurities are introduced, and A method of manufacturing a semiconductor device having at least a step of forming source and drain electrodes so as to be in contact with each other. In the step of activating the impurities in the semiconductor film by irradiating a laser beam, the semiconductor layer, which is likely to have a defect formed near the drain junction, is exposed to the air by adopting a selective manufacturing method. Since no defects occur during bonding due to moisture in the air, a semiconductor element having good characteristics can be manufactured.

A step of forming an insulating film on the substrate;
A method of manufacturing a semiconductor device, including a step of forming a semiconductor film on an insulating film and a step of irradiating the semiconductor film with a laser beam; forming an insulating film on a substrate, and forming the semiconductor film on the insulating film; Process is continuously performed while maintaining a vacuum, so that the interface between the insulating film and the semiconductor film is not exposed to the atmosphere and there is no contamination by carbon and the like, so that high-quality recrystallization is performed. A semiconductor film is obtained.

Further, the method for manufacturing a semiconductor device includes a step of forming an insulating film on the substrate, a step of forming a semiconductor film on the insulating film, and a step of irradiating the semiconductor film with a laser beam. The step of forming an insulating film, the step of forming a semiconductor film on the insulating film, and the step of irradiating a laser beam are continuously performed while maintaining a vacuum, so that an interface between the insulating film and the semiconductor film is formed. Not only is the semiconductor film surface not exposed to the atmosphere, and there is no contamination by carbon etc.
A high-quality recrystallized semiconductor film can be obtained.

In particular, a step of forming an insulating film on the substrate;
A step of forming a semiconductor film over the insulating film, a step of irradiating the semiconductor film with a laser beam, a step of forming a gate insulating film and a gate electrode on part of the semiconductor film, A step of patterning the gate electrode and the gate insulating film into substantially the same plane shape; a step of patterning the gate electrode and the gate insulating film into a substantially same plane shape; Introducing a P-type or N-type impurity into the semiconductor film in a region where no pattern is formed, irradiating the semiconductor film with a laser beam to activate the impurity in the semiconductor film, Forming a protective insulating film on the substrate, removing a portion of the protective insulating film, exposing a portion of the semiconductor film surface into which impurities are introduced, and exposing the semiconductor film surface A method for manufacturing a semiconductor device, the method including at least forming a source and a drain electrode so as to be in contact with each other. By performing the process continuously, the interface between the insulating film and the semiconductor film is not exposed to the atmosphere, and there is no contamination by carbon or the like.
A high-quality recrystallized semiconductor film can be obtained, and a high-performance semiconductor element can be manufactured.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 7 are sectional views showing a method of manufacturing a semiconductor device according to a first embodiment of the present invention. First, plasma CVD as a base insulating film 2 on a main surface of a glass substrate 1 is performed.
A SiO ₂ film is formed to a thickness of 400 nm by the method. Subsequently, an amorphous silicon (a-Si) film 30 is formed to a thickness of 50 nm in the same vacuum apparatus without exposing the substrate to the atmosphere (FIG. 1).

Further, the substrate is moved in the same vacuum apparatus, and the a-Si film 30 is irradiated with a high-intensity ultraviolet pulsed laser light LASER to convert the a-Si film 30 into a polycrystalline silicon (poly-Si) film. Convert to 301 (FIG. 2). The wavelength of the laser light is 308n from a XeCl excimer laser.
m, pulse duty 30 ns, energy density 300 mJ
/ Cm ² pulse light was used.

Next, after the poly-Si film 301 is patterned into a predetermined planar shape by a well-known photolithography method, an SiO ₂ film is
An 80 nm thick film is formed by the VD method, and a 100 nm thick Al film is formed as the gate electrode 10 by the sputtering method (FIG. 3).

Next, the gate electrode 10 and the gate insulating film 20 are patterned into a predetermined planar shape by a well-known photolithography method, and an ion beam IB containing phosphorus is irradiated using the pattern of the gate electrode 10 and the gate insulating film 20 as a mask. The N-type poly-Si film 301
An Si layer 31 is formed. Here, in the case of forming a P-type transistor, an ion beam containing boron may be irradiated (FIG. 4). Next, the phosphorus atoms introduced by the ion beam IB are electrically activated to activate the N-type poly-Si layer 3.
In order to lower the resistance of the pulse laser light 1
Irradiate LASER (Fig. 5). Subsequently, the substrate is moved in the same vacuum apparatus without being exposed to the air, and a SiO ₂ film is formed to a thickness of 400 nm by a plasma CVD method as a protective insulating film 21 covering the entire device (FIG. 6).

Next, a contact hole is opened in the protective insulating film 21 by a known photolithography method, an Al film is formed to a thickness of 500 nm by a sputtering method, and is patterned into a predetermined shape by a known photolithography method.
As the source electrode 11 and the drain electrode 12, a thin film transistor on a glass substrate is completed.

In this embodiment, a base insulating film is formed and a-Si
Formation of film 30 Further, since the step of laser beam irradiation was performed in the same vacuum apparatus without exposing the substrate to the atmosphere, the interface between the base insulating film and the a-Si film and the a-
Since the surface of the Si film is not contaminated by impurities from the atmosphere, a high-quality poly-Si film is obtained, and the characteristics of the thin film transistor are improved. In particular, the base insulating film and a-S
Since the interface of the i film is not contaminated, a thin film transistor having a small leak current can be obtained.

In this embodiment, the step of irradiating the ion beam IB containing phosphorus or boron and then irradiating a pulsed laser beam to activate the introduced impurity atoms and the step of forming the protective insulating film 21 are described. Since the substrate was exposed in the same vacuum apparatus without being exposed to the air, the layer which is likely to have a defect formed in the poly-Si film after the irradiation of the pulsed laser beam is not exposed to the air. There is an effect that a highly reliable element can be manufactured without generating defects due to moisture in the atmosphere.

FIGS. 8 to 10 are sectional views showing a method for manufacturing a semiconductor device according to the second embodiment of the present invention. First, a plasma CV is formed on a main surface of a glass substrate 1 as a base insulating film 2.
A 400 nm thick SiO ₂ film is formed by Method D. Subsequently, an amorphous silicon (a-Si) film 30 is formed to a thickness of 50 nm in the same vacuum apparatus without exposing the substrate to the atmosphere, and is patterned into a predetermined shape by a known photolithography method (FIG. 8).

Next, the patterned a-Si film 30 is irradiated with a high-intensity ultraviolet region pulsed laser beam LASER to convert the a-Si film 30 into a polycrystalline silicon (poly-Si) film 301 (FIG. 9). ). Subsequently, the substrate is moved in the same vacuum apparatus without being exposed to the air, and an SiO ₂ film is formed as a gate insulating film 20 by plasma CVD.
0 nm is formed. Further, an Al film is formed to a thickness of 100 nm as a gate electrode 10 by a sputtering method (FIG. 1).
0).

Thereafter, a thin film transistor on a glass substrate is completed by the same steps as those described with reference to FIGS.

In the second embodiment, as in the first embodiment, the steps of forming the base insulating film and forming the a-Si film 30 were performed in the same vacuum apparatus without exposing the substrate to the atmosphere. Since the interface between the insulating film and the a-Si film is not contaminated, a thin film transistor having a small leakage current can be obtained. After irradiation with an ion beam IB containing phosphorus or boron, a pulse laser is used to activate the introduced impurity atoms. Since the step of irradiating the light and the step of forming the protective insulating film 21 were performed in the same vacuum apparatus without exposing the substrate to the atmosphere, defects formed in the poly-Si film after the irradiation of the pulse laser light were generated. In addition to the effect that the layer which is easy to be exposed is not exposed to the air, and there is no defect caused by moisture in the air and a highly reliable element can be manufactured, the patterned poly-Si
Since the step of irradiating the film 30 with the laser beam and the step of forming the gate insulating film 20 were performed in the same vacuum apparatus without exposing the substrate to the atmosphere, the poly-Si film and the gate insulating film that determine the performance of the transistor Interface is not contaminated, so that a high-performance thin film transistor can be manufactured.

FIG. 11 is a schematic diagram of a vacuum apparatus for performing such a laser irradiation step and a film forming step without exposing the substrate to the atmosphere. The apparatus includes a transfer chamber L0, a transfer chamber L0 having a robot arm RM for transferring a substrate SUB.
Load chamber L1 for unloading the substrate, unload chamber L2 for unloading the substrate, film forming chamber C1 for forming the Si film, and film forming chambers C2 and C4 for forming the SiO ₂ film. And a laser irradiation chamber C3 for irradiating a laser beam. The laser light is emitted from an external laser oscillation source OSC, is reflected by a mirror M, and passes through a quartz window QW to a laser irradiation chamber C.
3 is introduced.

In order to carry out, for example, the steps described with reference to FIGS. 1 and 2 using this apparatus, the substrate is moved from L1 (substrate introduction) to
C1 (SiO ₂ film) → C2 (a-Si film) → C3
(Laser irradiation) → L2 (substrate removal) may be moved in this order.

In order to carry out the steps described with reference to FIGS. 5 and 6, the substrate is moved from L1 (substrate introduction) to C3 (laser irradiation).
It may be moved in the order of → C1 (SiO ₂ film formation) → L2 (substrate removal).

In order to carry out the steps described with reference to FIGS. 9 and 10, the substrate is placed in the order of L1 (substrate introduction) → C3 (laser irradiation) → C4 (SiO ₂ film formation) → L2 (substrate removal). Just move it.

As described above, the manufacturing method of the present invention can be carried out by using the apparatus as shown in FIG. In addition, by using such an apparatus, the film formation and the laser irradiation step, which have been conventionally performed as separate processes, can be continuously and efficiently performed.

[0035]

According to the present invention, since the substrate is not exposed to the air before and after the laser irradiation step, there is no contamination due to undesired impurities or occurrence of defects in the device due to moisture in the air, and high performance and reliability are achieved. A highly reliable semiconductor device can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first step showing a method for manufacturing a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a second step showing the method for manufacturing the semiconductor device of the first embodiment of the present invention.

FIG. 3 is a sectional view showing a third step in the method for manufacturing the semiconductor device according to the first embodiment of the present invention;

FIG. 4 is a sectional view showing a fourth step in the method for manufacturing the semiconductor device according to the first embodiment of the present invention;

FIG. 5 is a sectional view of a fifth step showing the method for manufacturing the semiconductor device of the first embodiment of the present invention.

FIG. 6 is a sectional view of a sixth step showing the method for manufacturing the semiconductor device of the first embodiment of the present invention.

FIG. 7 is a sectional view of a seventh step showing the method for manufacturing the semiconductor device of the first embodiment of the present invention.

FIG. 8 is a sectional view of a first step showing a method for manufacturing a semiconductor device according to a second embodiment of the present invention.

FIG. 9 is a sectional view of a second step showing the method for manufacturing the semiconductor device of the second embodiment of the present invention.

FIG. 10 is a sectional view of a third step showing the method for manufacturing the semiconductor device of the second embodiment of the present invention.

FIG. 11 is an explanatory view of a vacuum device for performing the method of manufacturing a semiconductor device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Base insulating film, 301 ... Polycrystalline silicon film.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location H01L 29/78 627F (72) Inventor Shoichi Nagai 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture In Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Akio Mimura 1-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture In Hitachi Research Laboratory, Hitachi, Ltd.

Claims (8)

[Claims] 1. A method for manufacturing a semiconductor device, comprising: irradiating a semiconductor film formed on a substrate with a laser beam; and forming a protective insulating film covering at least a part or all of the semiconductor film. And a step of irradiating the laser beam and forming the protective insulating film continuously while maintaining a vacuum. 2. A method of manufacturing a semiconductor device, comprising: forming an insulating film on a substrate; forming a semiconductor film on the insulating film; and irradiating the semiconductor film with a laser beam. A method of manufacturing a semiconductor device, comprising: a step of forming an insulating film on a substrate; and a step of forming a semiconductor film on the insulating film, while continuously maintaining a vacuum. 3. The method according to claim 2, wherein the step of forming an insulating film on the substrate, the step of forming a semiconductor film on the insulating film, and the step of irradiating the laser beam are continuously performed while maintaining a vacuum. Semiconductor device manufacturing method. 4. A step of forming an insulating film on a substrate, a step of forming a semiconductor film on the insulating film, a step of irradiating the semiconductor film with a laser beam, and forming at least a part or all of the semiconductor film. Forming a protective insulating film to cover the semiconductor device, wherein the step of forming an insulating film on the substrate and the step of forming a semiconductor film on the insulating film are continuously performed while maintaining a vacuum. And a step of irradiating the laser beam and the step of forming the protective insulating film continuously while maintaining a vacuum. 5. A step of forming a semiconductor film having a predetermined planar shape on a substrate; a step of forming a gate insulating film and a gate electrode on a part of the semiconductor film; Patterning substantially the same planar shape, patterning the first gate electrode and the gate insulating film substantially in the same planar shape, and using the gate electrode and the gate insulating film pattern as a mask,
Introducing a P-type or N-type impurity into the semiconductor film in a region where the pattern of the gate electrode and the gate insulating film is not formed; and irradiating the semiconductor film with a laser beam to activate the impurities in the semiconductor film. And a step of forming a protective insulating film over the entire surface of the substrate including the semiconductor film, removing a part of the protective insulating film, and exposing a part of the semiconductor film surface into which the impurity is introduced, Forming a source and a drain electrode so as to be in contact with the exposed semiconductor film surface, wherein a step of activating impurities by the laser beam and forming a protective insulating film on the entire surface of the substrate The method of manufacturing a semiconductor device, wherein the step of performing is continuously performed while maintaining a vacuum. 6. A step of forming an insulating film on a substrate, a step of forming a semiconductor film on the insulating film, a step of irradiating the semiconductor film with a laser beam, and a step of forming a gate on a part of the semiconductor film. Forming an insulating film and a gate electrode; patterning the gate electrode and the gate insulating film into substantially the same plane shape; patterning the gate electrode and the gate insulating film into a substantially same plane shape; Using a pattern of an electrode and a gate insulating film as a mask, introducing a P-type or N-type impurity into the semiconductor film in a region of the semiconductor where the gate electrode and the gate insulating film pattern are not formed; Irradiating the film with a laser beam to activate impurities in the semiconductor film;
Forming a protective insulating film on the entire surface of the substrate including the semiconductor film; removing a part of the protective insulating film to expose a part of the semiconductor film surface into which the impurity is introduced; A method of manufacturing a semiconductor device having at least a step of forming source and drain electrodes so as to be in contact with a film surface, wherein a step of forming an insulating film on the substrate and a step of forming a semiconductor film on the insulating film A method for manufacturing a semiconductor device, wherein the method is performed continuously while maintaining a vacuum. 7. The method of manufacturing a semiconductor device according to claim 5, wherein a step of forming an insulating film on the substrate and a step of forming a semiconductor film on the insulating film are continuously performed while maintaining a vacuum. 8. The semiconductor device according to claim 5, wherein the step of irradiating the semiconductor film with a laser beam and the step of forming a gate insulating film on the semiconductor film are continuously performed while maintaining a vacuum. Manufacturing method.