DE2018517A1 - Semiconductor with passivating film of silica and tantalum - pentoxide having improved moisture resistance - Google Patents

Abstract

Composite passivating film, which has excellent moisture resistance and low surface charge density, is produced by contacting semiconductor platelets, having at least one PN-transition, with vapour of volatile organo-Si cpds., which can decompose below ca. 700 degrees C, to deposit SiO2 on free surface of platelets; forming Ta2O5 film on this by reactive spraying of Ta in O2 atm.; and subjecting platelets to thermal treatment at ca. 100-400 degrees in non-reducing atm. These semiconductors can be used for (planar) thyristors, diodes, transistors, etc. Conditions used in production of film are not detrimental to electrical properties of semiconductor material.

Description

Method of manufacturing a semiconductor device The invention relates to a method for manufacturing a semiconductor device which. outstanding Has stable electrical properties and especially with a composite Passivation film is provided, which provides excellent protection against moisture offers.

Because the electrical parameters of semiconductor devices are different the activity of their PN interfaces under atmospheric influences change non-reversibly, the dividing surfaces must protect against such atmospheric influences, such as moisture, isolated by applying a suitable passivation film become to the generation such passivation films are tooth-rich Methods and procedures have been developed.

In the case of a silicon dioxide film, this is a typical passivation film and generally by thenaic oxidization of the surface of the silicon semiconductor device is formed, the gradient of the concentration distribution at the PN junctions tends to be to change due to undesired diffusion of impurities, as a result, the electrical properties of the device deteriorate or are inadmissible to be changed.

To avoid the undesirable thermal influences during the thermal Avoiding oxidation are already some methods of forming the passivation film which can be run at relatively lower temperatures.

In one of the methods, the semiconductor chip becomes the lighter one Formation of silicon dioxide on the wafer surface in contact with a vapor brought containing hydrogen fluoride and nitric acid. With this procedure is however, it is difficult to make the oxide film sufficiently thick as a passivation film; rather, a significant number of tiny holes remain in the film.

Another method is to put the silicon dioxide film on the surface The platelet is formed by having silicon deposited as silicon dioxide is achieved by breaking down a suitable volatile organic silicon compound is produced. Since monosilane (SiH4) or disilane are both volatile organic Silicon compounds can decompose at temperatures below about 7000 C Formation of the passivation film take place at relatively lower temperatures. Of the silicon dioxide film formed by the chemical decomposition of the silicon compound however, is related to its poor resistance to moisture its passivation properties inadequate, so that at the transition surfaces a considerably high leakage current occurs in the device.

An object of the invention is therefore to provide a new method for Manufacture of a semiconductor device having a passivation film with improved moisture resistance. The passivation film should are formed under conditions that do not have any undesirable thermal influences to have. In particular, a composite passivation film should be provided, which has small paint flow properties.

According to the invention, this is done on a free surface of the semiconductor wafer a silicon dioxide film formed by chemical decomposition of a volatile organic silicon compound silicon dioxide is deposited; on the silicon dioxide film a tantalum pentoxide film is formed by cathodic sputtering of tantalum in an oxygen atmosphere educated; the chip is then subjected to a heat treatment for durability of the composite film against moisture parting. With another Embodiment is the chemical decomposition of the organic silicon compound formed silicon dioxide film is subjected to a preheating treatment before the formation of the tantalum pentoxide film. Further details of the invention result from the following description of exemplary embodiments in conjunction with the drawings, in which Fig. 1 is a diagram showing the relationship between the breakdown voltage of a semiconductor device according to the invention and the Represents the temperatures of the heat treatment; Fig. 2 is a graphical representation the surface charge densities of those provided with different passivation films Facilities shows; and Figure 3 is a graph showing surface charge densities on devices provided with different passivation films of treatment temperatures shows.

As already mentioned, the volatile used according to the invention organic silicon compound have a decomposition temperature below about 7000 C. If the formation has more than 700 ° C, it may be that the electrical parameters of the Thermal devices during the formation of the silicon dioxide film be changed inadmissibly. Therefore it is necessary to use a silicon compound to be used, which can be dismantled at low temperatures.

The silicon dioxide is deposited from a vapor that is the silicon compound as well as an inert gas as a carrier gas. Used monosilane as a silicon compound is used, the growth conditions for the film include a platelet temperature from about 300 to 4000 C, a steam flow rate of 5 liters per minute and a Sauersteff flow rate of 0.15 liters per minute, the film grows at a rate of about 0.5 to 1 µ per minute.

In forming a tantalum pentoxide film, it is preferable to use the following worked: a tantalum rod is connected to a cathode, and one to the silicon dioxide film provided semiconductor wafer is brought into electrical connection with an anode. In order to remove the remaining gas or water from a vacuum vessel, this evacuated to a pressure of about 10-5 to 10-6 mm Hg; then a satub and a water-free oxygen-argon gas mixture is fed into the vessel in order to generate a suitable Generate oxygen partial pressure. By applying a voltage between the cathode and anode are hit by the tantalum rod connected to the cathode of energetic ions tantalum atoms on the plate lying at anode potential sprayed so that a tantalum pentoxide film is formed on the silicon.

The preferred partial pressure to produce the desired tantalum pentoxide film of the oxygen is about 5 x 10-3 to 5 x 10-2 Torr. Is the partial pressure less than 5 x 10-3 Torr, so the film may be due to lack of oxygen does not become a complete insulating substance. On the other hand, if the partial pressure is higher than 5 x 10-2 Torr, a uniform film cannot be produced because the glow discharge is unstable between the electrodes at such a high partial pressure.

In the above description it was said that the films consist of silicon dioxide and tantalum pentoxide; it should be noted, however, that the chemical composition of these films is not necessarily stoichiometric Formula corresponds to SiO2 or Ta2O5.

Through numerous experiments it has been found that the formation of the Film on the interface of the semiconductor device necessarily increases the surface charge density. Even if the silicon dioxide film the Increased charge density, this tendency is in the practically usable films ag least. Because the increase in the density of the surface charges causing leakage currents is small, the silicon dioxide film on the wafer surface becomes preferable educated. Although this film has low surface land impermeability, one does exist great disadvantage in that it has poor resistance to moisture. In the device according to the invention, therefore, the film becomes the tantalum pentoxide film which has excellent resistance to moisture kit.

Nevertheless, it has been shown that the stability of the facilities those with a passivation film composed of silicon dioxide and tantalum pentoxide films are provided, are inadequate with regard to the passivation properties d. before above all, the surface charge density is significant, thereby increasing the leakage current and the breakdown voltage of the devices is lowered.

I) Experiments have shown that the above disadvantages are eliminated or let it decrease by adding, after the formation of the composite film suitable heat treatment is carried out. By giving the facility a heat treatment at temperatures of about 200 to 4000 C in a non-reducing atmosphere the surface charge density can be made so small that the Sufficiently reduce leakage current when the device is in a forward current blocking mode leaves. The reasons for the weighting of the film and the heat treatment are has not been analyzed; However, ian assumes that the heat treatment causes the oxygen vacancies remaining in the silicon oxide film are filled with oxygen thereby eliminating or reducing lattice defects in the silicon dioxide film and the increase in surface charge density is caused.

As can be seen from the above, the to Passivating devices are not exposed to high temperatures that affect the electrical Properties of the devices during the formation of the film and the heat treatment worsen. This is a very important advantage of the invention Suitable Film thicknesses have been found experimentally. For the silicon dioxide film, one is Thickness of about 0.4 to 1) 1 useful. If the thickness is less than 0.4 µ, stay tiny holes remaining in the film, and the contact between the platelet surface and the tantalum pentoxide film causes the surface charge density to increase. is on the other hand, if the film thickness is greater than 1 µ, when the film is formed, the heat treatment and the operation of the device as a result of the different Coefficients of thermal expansion of platelets and film cracks in the film.

As long as it is possible to produce a film without holes, that is thinnest film most suitable, as the surface charge density becomes smaller, the lower the thickness of the silicon dioxide film.

The heat treatment takes place in a non-reducing atmosphere, for example from oxygen, oxygen-nitrogen, an inert gas or a mixture of an inert gas and nitrogen. An oxygen-containing atmosphere is suitable best, as the oxygen contributes to lattice defects or oxygen vacancies to reduce or eliminate in the film. One containing, for example, hydrogen A reducing atmosphere, on the other hand, cannot be used, since hydrogen is the oxygen deficiency increased in the film. The pressure for di. atmosphere used in the heat treatment is not limited.

The results of the experiments carried out by the inventor have shown that by forming a phosphate glass layer under the tantalum pentoxide film A semiconductor device can achieve solves that have very small surface charge density-and Has leakage current properties. The phosphate glass layer can thereby be formed that phosphorus pentoxide is deposited on the silicon dioxide film from an atmosphere the vapor of a phosphorus compound, such as phosphine (PH3) or phosphorus oxychloride (POCl3) contains, or indene a mixture of phosphorus pentoxide on the free platelet surface and silicon dioxide is deposited from an atmosphere that is volatile organic Contains silicon compound and the phosphorus compound.

As the phosphorus pentoxide as an oxidizing agent to oxidize the oxygen vacancies in which silicon dioxide acts, the film becomes stable to moisture, so so that the whole facility becomes stable. Because the phosphate glass has a high water absorption capacity the tantalum pentoxide film must be formed on the phosphate glass layer, to protect the facility against moisture.

The following examples are provided to provide a better understanding of the invention.

Example I Regarding the Effects of the Thickness of the Silica Film the following results were obtained when testing for minute or pinholes.

Table 1 Test No. Thickness (µ) Leakages in the film (%) 1 0.2 90 2 0.3 40 3 0.4 16 4 0.6 15 5 1.0 15 6 0.6 - 0.7 10 In this case the leaks were mediated by currents flowing between on the silicon dioxide film and the wafer formed metal films were applied; the percentage of leaks results from the ratio of those points at which electricity flowed to the total number the test points. From the results given in Table 1 it can be seen that that the number of pinholes in the film is sufficiently small when the felt thickness is larger than 0.4µ.

In order to achieve a sufficiently small number of pinholes, So the thickness can be made larger than 0.4µ.

The result obtained in connection with Test No. 6 in which the silicon dioxide film by thermal oxidation of the chip at a temperature above 1100 ° C is for comparison with that formed by chemical deposition the organic silicon compound formed silicon doioxidfilm shown.

Experiment II The results of heat crack tests on silicon dioxide films, formed by chemical deposition of the organic silicon compound, are reproduced in Table 2, Table 2 According to Heat m e a n d l u n g Thickness (µ) Film- Photo- at at at at at bildg. caustic. 300 ° C 400 ° C 600 ° C 800 ° C 1000 ° C 0.65 - 0.80 0 ° 0 0 0 0 0 0.80 - 0.95 0- 0 0 0 0 0 0 1.0 - 1.2 0 0 0 0 0x x 1.2 - 1.5 0 x - - - -> 1.5 x - - - - -In Table 2 is the occurrence of a crack represented in the movie by x. From the results according to Table 2 it can be seen that the thickness of the silicon dioxide film in view of the heat treatment to improve the properties of the film must be less than about 1µ. In particular, is a Thickness of less than 0.95 microns preferred.

Experiment III Pinhole tests were performed on the tantalum pentoxide film carried out. In this experiment, the number of needles per unit area is given calculated by converting the total number of pinholes in the film. The results are shown in Table 3.

Table 3 Thickness (µ) Number of pinholes per cm² 0.1 300 0.2 140 0.3 100 0.4 96 0.5 95 In general, it is required that the number of pinholes per unit area (cm²) is less than is about 150. It can be seen from Table 3 that the thickness of the tantalum pentoxide film is added to this must be stronger than about 0.2 µ. Since when spraying, the rate of growth of the tantalum pentoxide film is only 0.1 to 0.3 µ per hour, a practical thickness may be around 0.2 to 0.7 µ are test IV Regarding the effects of the heat treatment, a Experiment carried out on a planar type thyristor, the one N emitter layer with a thickness of 15 μ a P base layer with a thickness of 20 µ, an N base layer with a thickness of 80 to 100 µ and a resistance of 20 ## cm, a P-emitter layer with a thickness of 40 to 50 µ and a composite A passivation film consisting of a silicon dioxide film of 0.8 to 0.9 µ thickness and a tantalum pentoxide film. The samples were kept for 1 to 5 hours 300 to 600 ° C heat treated.

In Fig. 1, curve A shows the reverse breakdown voltages and curve B shows the forward breakdown voltages of said thyristor. Though after the results from Fig.

1 a heat treatment above 300 ° C to improve the breakdown voltage contributes, it is likely to be unfavorable to use the thyristor at temperatures above about 400 ° C heat treat.

Another experiment showed that one of the Heat treatment carried out at around 200 ° C is not expected to have any effect, since the undesirable substances such as water included in the film are insufficient removed. The heat treatment should therefore be carried out between about 200 and 400 ° C will.

It should be noted that the effect of the heat treatment through Removal of the locking tension in the film, for example through the oiling effect of the treatment comes about.

Trial V An diodes with a breakdown voltage of 1500 volts was made Conducted another experiment to determine the effects of the heat treatment. Some of the diodes used in this experiment did not have a passivation film, some were provided with the composite passivation film.

The results of this experiment are shown in Table 4.

Table 4 Samples Forward Leakage Current (µA) at 500 V without Film 4.0 without heat treatment 6.5 after 2 hours of heat treatment at 350 ° C in a nitrogen atmosphere 9.1 after 2 hours of heat treatment at 350 ° C in an oxygen atmosphere 5.0 Da Doiden can change their electrical parameters during long periods of operation without a film, the passivation film is required, although the diodes without a film are the least Have leakage current properties.

According to the results in Table 4, the heat treatment is suitable in an oxygen atmosphere best to reduce leakage currents. Also oxygen atmosphere however, it can be used because the leakage current is still less than 10> 1A.

Experiment VI In Fig. 2, the relationship between the types of films and or surface charge density NFB shown. At this stitch, the thickness was of the silicon dioxide film, which is formed by the chQ-mixed deposition of silane (SiH4) as organic Silicon compound was formed, 0.8 to 0.9 µ, while the thickness of the tantalum pentoxide film (Ta2O5) has been changed. The samples No. 1, 2 and 3 had thicknesses of 0t2 p, 0.3 µ or 0.45 µ.

The heat treatment after the formation of the Ta2O5 film by reactive Spraying was carried out for 5 hours at 300 ° C. in an oxygen atmosphere. The comparative sample No. 4 of FIG. 2 is a device which only had a silicon dioxide film of 0.8 to 0.9) 1 thickness.

From Fig. 2 it can be seen that the surface charge density by Using the composite passivation film and appropriate heat treatment can be reduced.

In the case of a silicon dioxide film formed by thermal oxidation the surface charge density is considerably greater than that of the invention Device despite the superposition of the tantalum pentoxide film on the silicon dioxide film.

Therefore, only the combination of the films and heat treatment according to the invention advantageous, experiment VII The inventor has experimentally determined the following: Although the electrical properties of devices with a base resistance less than about 10 ## cm, which contributes to the breakdown voltage of the device, Can only be improved by the mentioned heat treatment is with facilities with a base resistance greater than about 10 #. cm a preheating treatment in conjunction with the silicon dioxide film to improve the properties very much cheap.

The preheating is done relatively before the tantalum pentoxide film is formed high temperatures of around 700 to 900 ° C for a short period of time ton 1 to 30 Minutes carried out.

While the influence on devices with a low base resistance the surface charge density is not so noticeable on the leakage current, should be Devices with a relatively high base resistance use silicon dioxide in this way are heat treated that removes the oxygen voids in the film or be reduced. This preheating treatment is carried out at about 700 to 900 ° C a short period of time, say 3 to 5 minutes, to get the one Desired influencing of the contaminant gradient at the PN Transition point as well as the occurrence of cracks in the film.

As the experiment showed, the preheating in an atmosphere of an inert gas such as argon or helium. In particular, a nitrogen atmosphere does not provide any advantages in terms of a Improvement of the electrical properties of the facility. On the other hand is a Unsuitable oxygen atmosphere as the silicon under the silicon dioxide film oxidizes.

After the preheating treatment, the tantalum pentoxide film is through said reactive spray is formed on the silicon dioxide film. Who aimed so The composite passivation film is subjected to the heat treatment at 200 to 400 ° C.

Fig. 3 shows a relationship between the types of the passivation film and the surface charge density NFB, the results being obtained from facilities with a silicon dioxide film formed by chemical deposition from a vapor of organic Silicon compound has been formed, represented by a, while the results of devices with the composite passivation film created by the Procedure has been made with the following steps is: training the silicon dioxide film by chemical deposition on the wafer; 5 minutes long preheating of the plate at the temperatures indicated in FIG. 3 in Argon atmosphere; Forming the tantalum pentoxide film by said relative spraying on the silicon dioxide film; and heat treatment of the chip at 300 ° C. in an oxygen atmosphere.

The thickness of the silica and tantalum pentoxide films are 0.8 to 0.9 µ or 0.3 µ.

From Fig. 3 it can be seen that the preheating treatment for Reduction of the surface charge density of the device is used, so that the The breakdown voltage of the device can be increased. By preheating the Processes employing silicon dioxide film can be used for devices with high breakdown voltages - compared to the process that only includes heat treatment - certainly fabricate.

It should be noted that the present invention applies to diodes, Transistors, thyristors and the like.

is applicable.

Claims

Claims (8)

Claims 1. A method for manufacturing a semiconductor device with a composite passivation film, the excellent resistance has against moisture and small surface charge density, thereby g e It is not noted that a semiconductor die has at least one PN junction brought into contact with vapor of a volatile organic silicon compound which can be decomposed at temperatures below about 7000 C to convert silicon dioxide from the steam deposit on a free surface of the wafer; that on the silicon dioxide film a tantalum pentoxide film by reactive spraying of tantalum in an oxygen atmosphere is formed; and that the chip is subjected to a heat treatment at about 200 to 400 ° C is subjected in a non-reducing atmosphere. 2. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that the non-reducing atmosphere is oxygen, nitrogen, argon, or helium contains a combination of these gases. 3. The method according to claim 1, characterized in that g e k e n n k z e i c h n e t that the precipitation of the silicon dioxide continues until the silicon dioxide film has reached a thickness of about 0.4 to 1μ. 4. The method according to claim 1, characterized g e L e n n -z e i c h n e t that the spraying of the tantalum pentoxide continues until this film has a Has reached a thickness of more than about 0.2 µ. 5. The method according to claim 1, characterized in that g e k e n nz e i c h n e z, that the silicon compound is monosilane (SiH4), disilane (Si2H6) or a combination of which is. 6. The method according to claim 1, characterized in that g e k e n n z ei c h n e t, that a phosphor glass layer is also formed under the tantalum pentoxide film, which consists of a mixture of silicon dioxide and phosphorus pentoxide. 7. The method according to claim 1, characterized in that g e k e n n z e i c h n e t, that the silicon dioxide film is subjected to a preheating treatment before the tantalum pentoxide film is formed at a temperature of about 700 to 900 ° C. 8. The method according to claim 6, characterized in that g e k e n n -z e i c h n e t that the phosphor glass layer is subjected to a preheating treatment before the tantalum pentoxide film is formed is subjected to at about 700 to 900 ° C.