FR2469467A1 - Metallisation of semiconductor with aluminium silicon alloy - by chemical vapour deposition from aluminium alkyl cpd. and silane - Google Patents

Abstract

Metallisation of semiconductor elements with Si/Al alloy is effected by exposure to an atmos. of Al alkyl (I) vapour contg. silane at reduced pressure (5.2 mu bar) and 250-500 (300-400) degrees C. (I) consists of i-Bu3Al and/or i-Bu2AlH. (I) and the silane are diluted with an inert gas, which is introduced into the heating chamber periodically, so that its pressure exceeds that of (I). The (I)/silane mixt. also contains H2. (I) can be supplied from a vaporiser or in liquid form from an atomiser. The Si wafers are cleaned before metallisation. The process is esp. useful for metallising Si elements, including integrated circuits. Special pretreatment of the semiconductor is unnecessary and deposition and tempering take place in one stage, at temps. similar to those used in later coating and assembly stages, so that difficulties due to the sepn. of Si on cooling from high temp. are avoided.

Description

 The present invention relates to the metallization of semiconductor devices, and more particularly methods for the deposition of aluminum on silicon devices. The term device as used herein is intended to include not only discrete devices but also integrated circuits.

 Conventional metallization processes for the fabrication of semiconductor integrated circuits require high-vacuum equipment knives in which electrically conductive material is evaporated or sprayed, usually aluminum, along a straight path from from a localized source. This technique has the disadvantage of a limited productivity of industrial metallization plants because the semiconductor washers usually have to be fed by charging into a network of cuvettes supported by a planetary motion mechanism. During a deposition hase, the front surface of each washer sees the source of steam and is coated with the conductive material.

 Another disadvantage of this method of "visually coating" is the poor quality of the coating on the vertical parts or other surface irregularities of the treated washers, due to the mask effect produced by these parts. It is necessary in the conventional vacuum treatment for rapid atomization of the conductive material by electron beam or spray evaporation techniques, with considerable disadvantage at the interface in the net-oxide-silicon devices (NOS).

 This disadvantage must be overcome by heating the devices to a relatively high temperature, for example 4700 C. At temperatures of this order, the solubility and the diffusion rate of the silicon in the aluminum are high enough to cause the formation of pits in the areas of the contact windows of the devices, thereby degrading the underlying junctions. This effect is particularly harmful in the case of large-scale integration where superficial junctions are used.

To remedy this situation, the semiconductor industry has generally adopted the silicon deposition technique in aluminum alloys to maintain the silicon saturated metallization when heated to the annealing temperature. This technique, however, poses other problems. For example,
because of difficulties in controlling the exhibition a film. of the
silicon-containing films far exceeding the limits of
solubility are deposited. Such films pose problems of attack
and because of the considerable reduction in the solubility of silicon
in aluminum when the temperature decreases, p-type silicon is precipitated particularly in the areas of the contact windows. This
precipitated silicon increases the height of the SCHOTTKY barrier
effective with the n-type material and therefore increases the resistance of
contact.

The object of the invention is to minimize if not overcome
these disadvantages.

French patent application NO 79 27649 filed on
November 9, 1979 describes a method of metallization of a device to
semiconductor with a coating made of an alloy of alumina and
silicon, comprising exposing the device to an atmosphere of
alkyl-aluminum vapor containing silane at a temperature of
between 250 and 5000 C and at a reduced pressure.

In the process of the aforementioned patent application
Slalkyl aluminum and silane decompose to deposit both
aluminum and silicon (co-deposition phenomenon "), forming
thus the alloy on a semiconductor surface. It has now been
recognized that the deposition conditions of the alloy may have a
starting point close to those envisaged in this patent application.

In particular it has now been discovered that the processes of
deposition of aluminum and silicon could occur either
separately or jointly.

According to one aspect of the present invention there is provided a method of metallizing a body or a device
semiconductor by a silicon-aluminum alloy, comprising
the simultaneous or successive exposure of the device to a vapor
of aluminum alkyl and silane at a reduced pressure and at a
high temperature or at temperatures sufficient to cause the
deposition and alloying of the elements.

According to another aspect of the invention there is provided a method
of metallization of a semiconductor body by a silicon alloy
and aluminum, comprising exposing said body to a vapor
of aluminum alkyl at a temperature of 200 to 3500 C so as to deposit
an aluminum coating on the body, and the exposure of the coated body
from Andean silane to a temperature of about 350 to 5500 C, which causes the aluminum film to be alloyed with silicon.

 The co-deposition technique consists of a deposition and annealing operation in a single step, characterized in that the alumintum films saturated with silicon at the deposition temperature are deposited, preferably after an activation phase. from a mixture of an alkylaluminum and silane at a reduced pressure. The deposition temperature should be between 250 and 5000 C, preferably 300 to 4000 C, to provide both optimum annealing and alloy characteristics of the particular semiconductor device being processed. The hydrogen released during the decomposition of the alkylaluminum and silane increases the annealing efficiency of the process.

 In the other sequential deposition technique, use is made of a gas phase alloying operation in which, after a surface activation phase, aluminum films are deposited by thermal decomposition of an aluminum alkyl at a temperature of 50.degree. temperature of 200 to 3500 C, preferably between 240 and 3000 C, so as to obtain optimal characteristics of deposition with regard to the quality of the film and its uniformity. Immediately after the deposition phase of the aluminum is passed silane in the gaseous state in the deposition region and the temperature is raised to around 350 d 5500 C in order to saturate the aluminum with silicon at a desired level according to the subsequent treatment and to anneal the aluminum. MOS interface as well as ohmic contact formation. During this gas phase alloying step, it is assumed that silane is chemically absorbed on the aluminum film which has been deposited first and then decomposes to form silicon. The latter diffuses into the aluminum film until it is saturated. It appears that, unlike conventional deposition processes, no NOS interface is formed during chemical vapor deposition and that the temperature of this gas phase alloy step, which determines the silicon content of the film, can be chosen as low as possible while remaining compatible with ohmic contact formation and subsequent treatment of the semiconductor.

 In a modification of this method the deposition apparatus may have two different temperature zones, the semiconductor washers passing into the hottest zone for the gas phase alloy after the deposition has been performed. In another modification of the same process the aluminum films are deposited by conventional physical means, for example by evaporation or sputtering, followed by a silane annealing step at an elevated temperature.

 It has been established that the presence of silane saturates the aluminum films freshly deposited with silicon and avoids the formation of pits of attack in the contact windows, these pits, in the absence of silane, forming at temperatures of the order of 3400 C.

 In each of the simultaneous or sequential deposition techniques it was recognized that the adhesion and quality of the deposited films was enhanced by exposing the semiconductor washers to surface activation gas, usually titanium tetrachloride. before the deposition.

 The temperatures employed are chosen so as to be comparable to a subsequent treatment of the semiconductor intended to provide layers of protection against scratching and to be able to mount the chips. The process produces aluminum and silicon alloys which are saturated with silicon at such temperatures and thus are not damaged by subsequent processing.

 The invention will be better understood on reading the detailed description which follows, given by way of non-limiting example with reference to the single appended figure which is a schematic representation of a facility provided for the metallization of semiconductors. .

 The figure shows a semiconductor appearing, for example, in the form of silicon wafers 11 which dolent be subjected to metallization; they are placed on a nacelle or an inert support 12, for example made of silica, and then placed in an oven 13 hermetically closed by a door 14 and a gasket 15. The air of the oven 13 is pumped via a lateral inlet tube 16, heated to the required deposition temperature and purified by an inert gas, for example argon, introduced through a valve 17 and a flow meter 18 attached to a gas supply manifold 19 which feeds a tube 20 communicating with the oven 13. After purification the gas supply is stopped and the oven is pumped again.The washers 11 may in some applications be cleaned by passing for example hydrochloric acid vapor in the oven 13 through the manifold 19, after which the furnace is pumped again, although in most cases this cleaning step can be omitted.

 It is advantageous that the washers are again exposed to titanium tetrachloride vapor via the manifold 19 after which the furnace is again pumped.

 In the simultaneous deposition process, the deposition of a silicon and aluminum alloy on the washers is carried out by passing an alkyl aluminum vapor, for example tri-isobutyl aluminum (TIBA), or mixtures thereof. of aluminum alkyl from a temperature-controlled tank containing the liquid alkyls, through a valve 22 in the oven 13 and an simultaneously passing silane through the collector 19 into the oven 13.

 The alloy is deposited spontaneously on the washers li by a thermal decomposition process. It seems that the silicon incorporation process in the alloy film is self restrictive with respect to the solubility limit of silicon in aluminum at the temperature of # e-pos-ition. Thus, the concentration of the silane is not critical enough, although obviously, if the silane concentration far exceeds that required to saturate the aluminum, the deposition rate of the film is greatly reduced and films are obtained. mediocre quality.

 When the deposition is complete, the supply of silane and alkylaluminum is stopped, and the oven is brought to atmospheric pressure with the inert purification gas. The coated washers are then protected for the etching of the metal layer and it is not necessary to resort to an annealing or an additional alloy. The concentration of the silane in the steam mixture does not seem to be critical and However, it is preferable to employ a partial pressure of silane in the range of from about 20 to about 260 Pa.

 In the other sequential deposition process, the washers 11, preferably surface-activated with titanium tetrachloride vapor, are exposed to TIBA vapor from the temperature-controlled tank 21 while maintaining the oven temperature. The deposition should preferably be carried out in a temperature range between 240 and 300 C. After the deposition of aluminum, the TIBA steam supply is removed, the furnace is again pumped and the its temperature is raised to about 350 to 5000 C. Silane is passed during the warming cycle through the manifold 19, which deposes silicon and a subsequent alloy of the deposited silicon with the aluminum.

 When the deposition is complete, the furnace is once more pumped, refreshed, and previously treated.

 The sequential method allows independent optimization of the film deposition and alloying conditions, while the simultaneous process has the advantage of simplicity due to a compromise between the deposition and alloy requirements.

 The process can use different alkyls. Thus, for example, tri-ethyl aluminum can be employed: tri-isopropyl aluminum, tri-isobutyl aluminum (TIB), di-isobutyl aluminum hydride (HYDIBA) or mixtures thereof. TIBA, MDIBA or mixtures of these products should be of high quality The temperature at which the alkyl reservoir is maintained depends on the rate of evaporation of the alkyl or alkyl mixture. In addition, the alkyl silane mixture can in certain applications be diluted for example in argon and / or hydrogen, the latter improving the efficiency of the process with regard to annealing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A characteristic encapsulation of the simultaneous method of metallization of silicon wafers using the apparatus represented by the attached FIG. 1 will be described. Loading washers 11 on a support 12 and insertion into a
heated oven 13.

2. Pumping the oven to a pressure of less than 1.33 Pa.

3. Optional cleaning of the washers 11 for example with acid
chlorhydride and new pumping (usually this step will be
deleted).

4. Surface activation with TICL4 steam and new pumping.

5. Deposition made by passing silane and
the aluminum alkyl in the oven 13.

6. Completion of the deposition and new pumping of the oven.

7. Increase oven pressure to pressure
atmospheric nitrogen injection.

8. Unloading washers treated with nitrogen rinsing.

 In such a deposition process characterized in that the oven was maintained at 3500 C and that the deposition was carried out from silane and TIBA which was passed at a speed of 200 ml / min and at a pressure of 533 Pa, it was recognized that a deposition period of 4 minutes produced an alloy film with a thickness of one micrometer.

We will also describe a sequence characteristic of the sequential process 1. Loading washers on a support 12 and insertion in an oven
heated 13.

2. Pumping the furnace to a pressure of less than 1.33 Pa.

3. Optional cleaning of the washers with hydrochloric acid and
new pumping.

4. Surface activation of washers with TICL4 steam and
new pumping.

5. Maintain the oven at a temperature between 200 and 3500 C and
TIBA vapor passage to make a deposition
of aluminum.

6. Completion of the deposition and new pumping of the oven.

7. Pass silane to start the gas phase alloy.

8. Increase oven temperature to around
300 to 5500 C.

9. Completion of the alloy and new pumping.

10. Increase oven pressure to pressure
temospheric with nitrogen and unloading washers with
rinsing with nitrogen.

11. Refresh the oven to the deposition temperature of
aluminum and reloading with another batch of washers.

 In such a sequential deposition process, the furnace temperature was first maintained at 2700 C for an aluminum deposition period of 4 min, with a TIBA flow rate of 200 r / min and at a pressure of of about 133 Pa. Then silane was passed and the temperature was raised to 3900 C to effect a gas phase alloy with a silane flow rate of 150 ml / min and a pressure of 40 This produced an alloy film one micron thick and containing 0.4% atomic silicon. No pitting was observed in the contact windows of the washers. These processes were treated by this process, while it was recognized that omission of silane during the warm-up step resulted in severe pickling of the aluminum films in all cases.

 In a modification of the process described herein, an inert gas, for example argon or nitrogen, is passed from a reservoir 24 and a valve 23 into the furnace 13 at regular intervals during the deposition process. The pressure in the furnace 13 is temporarily raised above the pressure of the TIBA vapor or of the TIBAIRYDIBA mixture contained in the evaporator, which reduces for a certain time the supply of alkyl. This allows periodic removal of the reaction products from the furnace 13, which are entrained with an inert gas in the pump. In other embodiments of the alkyl-aluminum process or the mixture of alkyls may be injected into the furnace 13 via an atomizing device. Alternatively, the liquid alkyl or alkyl mixture can be passed through. through a measuring apparatus in an instantaneous or continuous evaporation device.

 In another embodiment, a sequential process can be employed, characterized in that the aluminum coating is deposited using techniques other than chemical vapor deposition. For example, evaporation under vacuum or spraying can be used. The aluminum film and the silicon are then subjected to exposure to silane while the temperature is raised to around 350 to 5500.degree. C. as in the above description.

 The term semiconductor device as used herein is meant to apply to both discrete devices and integrated circuits.

 It is obvious that the foregoing description has been made by way of non-limiting example, and that other variants can be envisaged without departing from the scope of the invention.

Claims (15)

 Process for metallizing a semiconductor body with a silicon-aluminum alloy, characterized in that the body is exposed sequentially or simultaneously to an aluminum alkyl vapor and to silane at a reduced pressure and at a high temperature or at temperatures sufficient to effect deposition and alloying of the elements.  2. Process for metallizing a semiconductor body with an alloy of silicon and silicon, characterized in that the body is exposed to an alkyl aluminum vapor at a temperature of 200 to 3500 C in order to deposit an aluminum coating on the body, then expose the aluminum-coated body to silane while raising its temperature to around 350 to 5500 C allowing the alloy aluminum film with silicon.  3. Method according to claim 1 or 2, characterized in that the surface of the semiconductor body is activated by exposure to titanium tetrachloride vapor before the alloy deposition.  4. Method according to any one of claims 1, 2 or 3, characterized in that the deposition of aluminum is carried out at a temperature of 240 to 3000 C after which the alloy is made with silicon raising the temperature to around 350 to 5500 C.  5. Process according to any one of claims 1 to 4, characterized in that the aluminum alkyl comprises tri-iso-butyl aluminum (TIBA), di-isobutyl aluminum hydride (# YDIB), or mixtures thereof.  5. Process according to any one of claims 1 to 5, characterized in that the reactive vapors are diluted in an inert gas.  7. Process according to claim 6, characterized in that the inert gas is passed through the region surrounding the semiconductor body in order to disperse the reaction products in the vapor phase, the pressure of the gas being higher. that the pressure of the steam reacts.  8. Process according to any one of the preceding claims, characterized in that the reactive gas contains hydrogen.  9. Process according to any one ~ ~ e-e claims i to 8, characterized in that the alkyl-aluminum vapor is provided by evaporation of a certain amount of the alkyl liquid.  10. Process according to any one of claims 1 to 8, characterized in that the alkyl aluminum is dispersed in liquid form from an atomization device.  11. Method according to any one of claims 1 to 8, characterized in that the alkyl aluminum is dispersed from an evaporator.  12. Process according to any one of the preceding claims, characterized in that the semiconductor is silicon.  13. Method of metallizing a semiconductor body with an alloy of aluminum and silicon, characterized in that the body is exposed to an atmosphere of TIBA a pressure of 133 Palet B a temperature of 2700 C ce which allows deposition of an aluminius layer, and exposing the body to silane at a pressure of 40 while increasing the temperature to 3900 C to effect a gas phase alloy of aluminum with silicon.  14. A process for metallizing a semiconductor body, characterized in that it comprises depositing an aluminum coating on the body, and alloying the aluminum with silicon by exposing the coated body. aluminum has steam-silane while raising the body temperature to around 350 to 5500 C.  15. Process according to claim 14, characterized in that the aluminum coating is deposited by evaporation under vacuum or by spraying.  16. Process according to claim 14 or 15, characterized in that said silane vapor is passed at a pressure of 40 ° F.