DE3628399A1 - METHOD FOR PRODUCING A DIELECTRIC FILM ON A SEMICONDUCTOR BODY AND A SEMICONDUCTOR COMPONENT PRODUCED THEREOF - Google Patents

Description

The invention relates to a method for producing a dielectric film on a silicon body. It affects furthermore a semiconductor component produced by the method as well as a semiconductor component with a semiconductor body, an electrode and a semiconductor body and dielectric film separating the electrode.

Dielectric materials, e.g. B. silicon oxide (SiO _x with 1 ≦ ωτ x ≦ ωτ 2) are still used in semiconductor manufacturing. These materials are not only used as final passivation coatings for finished components, but also as intermediate insulation layers for multi-layer components. Thermally grown oxides, e.g. As silicon oxide, are typically used as dielectric films, for. B. as a gate insulator, in semiconductor devices, for. B. in an EAROM (Electrically Alterable Read Only Memory, electrically changeable ROM) or in a MOS field effect transistor (MOSFET), or as capacitors or the like.

Thermal oxidation methods, through which the best silicon oxide films are generally to be produced carried out that the silicon in question in an oxidizing Environment with temperatures between 800 and 1200 ° C brought. In many cases these are temperatures too high for the substrate. If, for example, the one to be manufactured dielectric film part of one over a glass substrate is to be manufactured semiconductor device requires lower process temperatures. Especially on the Field of liquid crystal display (LCD = Liquid Crystal Display) become thin film transistors on glass substrates made with a softening point of about 650 ° C. Around  hence an oxide on silicon on glass growing up thermally is the temperature of the substrate kept at about 600 ° C in the oxygen environment with the Result that about 120 hours to grow up from 60 to 70 nm silicon oxide are required.

Silicon oxide (SiO _x ), aluminum oxide and silicon nitride can be applied using glow discharge or chemical vapor deposition (CVD) techniques in a fraction of the time required for thermal growth, e.g. B. in a few hours or less at temperatures below 600 ° C. However, the dielectric quality of films formed in this way is poor in relation to that of thermally grown material.

In particular, the transistor turn-on voltage is used deposited silicon dioxide films unstable. It is believed that charge traps appear in the film and / or a collection at the silicon / dielectric interface of charge in the film when voltage is initially applied have as a consequence. The next time voltage is applied the switch-on voltage or threshold voltage migrates by 5 to 10 V or more, while transistors with thermal grown oxide the threshold voltage little or doesn't hike at all.

Furthermore, it is in the manufacture of dielectric films on hydrogenated, amorphous silicon, the process temperatures are desirable keep below about 400 ° C. These conditions apply because of the semiconductor properties of amorphous silicon at temperatures above 400 ° C - probably as  Result of a loss of hydrogen from the film above of this value - change.

The invention has for its object a method for Make a dielectric film at one temperature below 600 ° C, preferably below 400 ° C, at which the rate of growth of the film over that thermally grown in the same temperature range Film is considerably higher. At the same time, the dielectric Stability of a thermally grown film in the are essentially preserved. The solution according to the invention exists for the manufacturing process mentioned at the beginning of a dielectric film on a silicon body in the steps specified in the main claim.

According to this method, the dielectric oxide film can be one semiconductor device requiring such a film will.

Furthermore, the solution according to the invention for a semiconductor component exists with a semiconductor body and an electrode and an intermediate dielectric film in particular in the features of claim 9.

Improvements and further refinements are made in the Subclaims specified.

The invention provides a method for manufacturing of a three layer dielectric film on silicon and a semiconductor device using such a film created. Here, silicon is first in an oxygen  containing oxidized environment. When oxidizing a first layer of silicon oxide is formed. As soon as The oxidation has started to become reactive sputtering of aluminum started in an oxygen plasma. This creates a mixture of silicon and aluminum oxides containing second layer of dielectric Film formed. An essentially containing alumina third layer is by continuing the reactive Atomizing formed by aluminum.

A semiconductor device that the three-layer dielectric film between an electrode and a semiconductor body contains, has little or no Threshold voltage hike so that good stability is obtained becomes; in addition, such a semiconductor device with considerably less time and / or at lower Temperatures than according to comparable known processes getting produced.

Using the schematic drawings, details of the Invention explained. Show it:

Fig. 1 is a cross-sectional view of an apparatus for producing the dielectric film for a semiconductor device;

Fig. 2 is a cross section of a three-layer dielectric film having semiconductor device;

. 3 is a diagram Schwellspannungswanderung a semiconductor device with a dielectric film whose first layer is grown Fig plasma; and

Fig. 4 is a diagram Schwellspannungswanderung a semiconductor body with a dielectric film, the first zone is thermally grown.

The method according to the invention forms a three-layer dielectric film over a film or a substrate made of silicon (amorphous, polycrystalline or monocrystalline) by combining oxidation techniques and reactive spraying or sputtering techniques. A first layer containing silicon oxide (SiO _x with 1 ≦ ωτ x ≦ ωτ 2) is formed on the silicon either by plasma oxidation or thermal oxidation. Plasma oxidation can be carried out at temperatures between 25 and 300 ° C, while the thermal process is to be used where temperatures of 600 ° C or more can be tolerated. A second zone containing a mixture of silicon and aluminum oxides is formed by sputtering aluminum in an oxygen plasma. The continuation of the reactive sputtering finally leads to the third layer essentially containing aluminum oxide.

A device suitable for carrying out the described method is explained with reference to FIG. 1. The device 10 contains a vacuum chamber 12 , which can be designed as a glass bell. In the vacuum chamber 12 there is an electrode 14 , which can consist of a material with good electrical conductivity, such as aluminum, as a screen, a coil or a plate. The electrode 14 is connected to a mains connection 16 , which can be direct current, alternating current or high frequency for generating a voltage potential. Behind the electrode 14 there is a magnet 18 which is electrically isolated from the electrode 14 and which helps to concentrate the plasma in the region of the electrode. An aluminum target 20 may also be provided if the electrode 14 is made of a material other than aluminum. A magnet 22 is to be arranged behind the target 20 . An outlet 24 of the vacuum chamber 12 , which is intended to enable the system to be evacuated, is connected to a pump, not shown. Furthermore, a first inlet 26 and a second inlet 28 of the vacuum chamber 12 are provided and connected to gas extraction systems, not shown, which are intended to deliver the appropriate gas or gases. The device also includes a heat source, not shown, for heating the environment (in chamber 12 ) to a desired temperature.

If the first layer is to be thermally grown, the vacuum chamber 12 is first evacuated and then via the first inlet 26 to an oxygen source, e.g. B. CO ₂ , N ₂ O, O ₂ or H ₂ O, connected. The temperature in chamber 12 is then raised to about 600 ° C and the desired thickness of SiO _{2 is} grown on the silicon surface.

Alternatively, the first layer can be grown at a lower temperature by plasma oxidation in accordance with US Pat. No. 4,576,829. In this method, a substrate 30 consisting of or surrounded by silicon (amorphous, polycrystalline or single-crystal) is placed in front of the electrode 14 . The substrate 30 lies on a mounting plate 32 at a typical distance of approximately 2.5 cm from the electrode 14 . The mounting plate 32 is to be made of a material that can serve as a heat sink during the plasma oxidation in order to control the temperature of the substrate 30 . Such an arrangement with a heat sink is described in US Pat. No. 4,361,595. The reason for this is that the plasma could heat the substrate 30 well above 300 ° C, but the substrate temperature should be kept below 300 ° C. Other common methods of maintaining the temperature of the substrate 30 can also be used.

The vacuum chamber 12 is then evacuated through the outlet 24 to a pressure of about 25 to 140 Pa (about 0.2 to 1.0 x 10 ^-6 torr). Oxygen-containing gaseous intermediate is then admitted through inlet 26 to a pressure of about 6.5 to 7 Pa (about 50 m Torr). Suitable oxygen-containing gases in this connection include oxygen, carbon dioxide, nitrogen oxide and the like. To initiate the oxygen plasma, a high frequency of 13.56 MHz and about 300 to 600 W is applied to the electrode 14 , so that an effective power density between about 1 and 15 W / cm ² , preferably between about 5 and 7 W / cm ² , pending.

The production of the second layer of the dielectric film according to the invention also comprises the use of an oxygen-containing plasma. Therefore, when the first layer has grown thermally, the vacuum chamber is evacuated, cooled, and the plasma is initiated as indicated above. On the other hand, if the first layer was grown using the plasma oxidation technique, the plasma is only maintained. The second layer is created by reactive sputtering of the aluminum of the electrode 40 or the target 20 . This means that the oxygen plasma oxidizes the aluminum and then sprays the aluminum oxide away from the electrode 14 (or the target). At the same time, it is believed that the plasma sputtered some of the grown silicon oxide of the first layer and deposited again along with the aluminum oxide deposited by the reactive sputtering. In this way, the second layer contains a mixture of silicon and aluminum oxide. The concentration of the silicon oxide decreases with increasing distance from the first layer, while conversely the concentration of aluminum oxide increases with the distance from the first layer.

As soon as the dielectric film has grown to a thickness at which silicon oxide can no longer be sputtered from the first layer and deposited again together with the aluminum oxide, the sputtering of the electrode 14 or the target 20 by the oxygen plasma is continued essentially formed of aluminum oxide third layer. This reactive sputtering can be maintained until the desired final film thickness is reached.

It should be noted that in the case of plasma growth the first layer the plasma oxidation into that Silicon also in the growth of the second layer  continues until the thickness of the accumulating Dielectric further diffuses through Prevents oxygen. When the first zone grew thermally is some further oxidation when forming the second layer, but this is less probably when the thermally grown first layer has a thickness of more than about 10 nm.

The first layer, when plasma grown, has generally a thickness of between about 5 nm and 20 nm; when thermally grown, it can be larger Thickness, e.g. B. about 100 nm.

The second layer generally has a thickness between about 2 nm and 30 nm.

The third layer containing Al ₂ O ₃ can have any desired thickness and is generally kept between about 10 nm and 100 nm.

The entire thickness of the three layer film can be any desired depending on the application, for example layer thicknesses of about 100 nm are used considered suitable by thin-layer transistors.

Fig. 2 shows an embodiment with a metal-oxide semiconductor field effect transistor (MOSFET) from 40. It is pointed out that any semiconductor component which requires a high-quality dielectric thin film can advantageously be produced using the method according to the invention.

The transistor 40 is manufactured in part by methods according to the prior art. A silicon layer 44 is deposited on a glass substrate 42 . Then, a dielectric film 46 according to the invention, which consists of a first layer 48 , a second layer 50 on the first layer and a third layer 52 on the second layer, is deposited on the silicon layer 44 according to the method detailed above. An electrode serving as the gate of the component, which as a conductor z. B. made of metal, a silicide or polycrystalline silicon is deposited on the dielectric film 46 using conventional photolithographic methods. With the aid of self-aligning ion implantation methods, a source zone 56 and a drain zone 58 of one conduction type with a channel zone 60 of the other conduction type lying in between can be produced in the silicon layer 44 .

While making dielectric films with the help usual low-temperature techniques (below 500 ° C), e.g. B. by glow discharge or CVD, generally unstable MOSFETs with threshold voltage fluctuations of 5 to 10 V or have more, according to the present process manufactured components an improved stability. Furthermore the rate of growth of the film is essential higher compared to those working at a comparable temperature thermal oxidation techniques.

FIGS. 3 and 4 illustrate the stability of manufactured using the method according to the invention semiconductor devices. In the diagrams shown in FIGS. 3 and 4, the drain current I (in A) of the transistor of FIG. 2 is plotted on the gate electrode 54 as a function of the gate voltage U (in V). The solid line represents the current for the first application of -5 V to the source zone 56 with the drain zone 58 grounded. The dashed line represents the drain current for a subsequent -5 V application to source zone 56 after a + 10 V bias has been applied to gate electrode 54 at 150 ° C for 30 minutes. Specifically, Fig. 3 shows the improved stability of a three-layer dielectric film in a MOSFET, in which the first layer was grown plasma, assuming that the entire dielectric was formed at about 130 ° C. Fig. 3 shows for such a device has a threshold voltage of about 2 V migration after a 30 minute test with a bias voltage of +10 V at 150 ° C; this result is a significant improvement in stability over the prior art.

Figure 4 shows the results for another MOSFET made using the invention. In this case, the first layer contained about 6 nm of SiO ₂ , which had been thermally grown at about 600 ° C. in about 8 hours. The second and third layers had been deposited at about 130 ° C in about 0.5 hours, so that a total film thickness of about 7.5 nm was formed in 8.5 hours. The threshold voltage hike was negligible after a 30-minute test at 150 ° C with +10 V bias. This stability is comparable to that of a layer thermally grown at 600 ° C. in about 120 hours.

Claims (15)

1. A method for producing a dielectric film ( 46 ) on a silicon body ( 44 ), characterized by the following steps:
a) Forming a silicon oxide-containing first layer ( 48 ) of the film ( 46 ) by oxidizing the surface of the silicon body ( 44 ) in an oxygen-containing environment:
b) forming a second layer ( 50 ) containing a mixture of silicon and aluminum oxides over the first layer ( 48 ) by spraying on aluminum; and
c) forming a third layer ( 52 ) consisting essentially of aluminum oxide over the second layer ( 50 ) by reactive sputtering or spraying on of aluminum. 2. The method according to claim 1, characterized in that that step a) in an oxygen-containing Plasma is running and that plasma during the Steps b) and c) for the reactive atomization of Aluminum is maintained. 3. The method according to claim 1 or 2, characterized in that the ambient temperature is below a value about 300 ° C is maintained. 4. The method according to one or more of claims 1 to 3, characterized in that step a) is initiated by forming a silicon dioxide layer on the silicon body ( 44 ) by means of thermal oxidation. 5. The method according to one or more of claims 1 to 4, characterized in that a plasma with an effective power density of between about 1 and 15 W / cm ² is used. 6. The method according to claim 1, characterized in that the first layer ( 48 ) in step a) is produced by thermal oxidation. 7. The method according to claim 6, characterized in that that the thermal oxidation at a temperature of about 600 ° C is executed. 8. Semiconductors with a dielectric oxide film, characterized in that the dielectric  Oxide film according to the method according to one or more of claims 1 to 7 is made. 9. Semiconductor component ( 40 ) with a semiconductor body ( 44 ), an electrode ( 54 ) and an electrical film ( 46 ) lying in between, characterized in that the dielectric film ( 46 )
a) a first layer ( 48 ) made of silicon oxide;
b) a second layer ( 50 ) containing a mixture of silicon and aluminum oxides and lying on the first layer ( 48 ), in which the concentration of the silicon oxide decreases with increasing distance from the first layer ( 48 ) and in which the concentration of the aluminum oxide increases with the distance from the first layer ( 48 ); and
c) a third layer ( 52 ) containing aluminum oxide on the second layer ( 50 )
contains. 10. A semiconductor device according to claim 8 or 9, characterized in that the first zone ( 48 ) has a thickness between about 5 and 100 nm. 11. The semiconductor component according to claim 8 or 9, characterized by a plasma-grown first layer ( 48 ) with a thickness between about 5 and 20 nm. 12. Semiconductor component according to one or more of claims 8 to 11, characterized in that the second layer ( 50 ) has a thickness between about 2 and 30 nm. 13. Semiconductor component according to one or more of claims 8 to 12, characterized in that the third layer ( 52 ) has a thickness between about 10 and 100 nm. 14. Semiconductor component according to one or more of the claims 8 to 13, characterized by the training as a metal oxide semiconductor field effect transistor (MOSFET). 15. Semiconductor component according to one or more of claims 8 to 14, characterized in that the first layer ( 48 ) has a thickness of about 6 nm of thermally grown silicon dioxide.