JPS63282274A - Chemical vapor growth device and method for using same - Google Patents

Abstract

PURPOSE:To deposit a smooth thin film with high reproducibility and uniformity and to improve selectivity during selective growth of a thin by holding a substrate between blocks placed opposite to each other at a narrow interval and heated to different temp. so that the surface of the substrate subjected to deposition confronts the block on the higher temp. side and by carrying out vapor growth. CONSTITUTION:An Si oxide film 42 si formed on an Si substrate 41, a resist mask pattern is formed on the film 42 and the film 42 is etched form an opening 43. Immediately before a metal such as Al is deposited, a naturally oxidized film 44 is removed by surface cleaning to obtain a wafer substrate 47, 8. This substrate 47, 8 is held with a holder 7 between block 10, 14 placed opposite to each other at a narrow interval and heated to different temps. so that the surface of the substrate subjected to deposition confronts the block 10 on the higher temp. side. A gaseous compd. contg. a metal such as Al is then introduced into a deposition chamber 1 and the metal such as Al 45 is selectively deposited only in the opening 43 in the substrate 47, 8. Since the gaseous compd. on the surface of the substrate 47, 8 can highly be supersatd., a smooth high quality film can be deposited.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a chemical vapor deposition apparatus for forming thin films and a method of using the same.

[Conventional technology]

Chemical vapor deposition (hereinafter referred to as rcVDJ) is a method of depositing a thin film on a substrate using a chemical reaction, and is one of the well-known thin film forming methods along with vapor deposition and sputtering. especially,
In the manufacturing process of semiconductor integrated circuit devices, it is widely used for forming silicon oxide films and polycrystalline silicon thin films. CVD is classified into various types depending on the heating method, gas pressure, type of chemical reaction, etc. for example,
Cold wall type, which heats only the deposition substrate, and hot wall type, which heats the entire reactor.Also, atmospheric pressure CVD, which performs the reaction under atmospheric pressure, and low pressure CVD, which performs the reaction under reduced pressure. Normal CVD using
In addition, plasma CVD, optical CVD, and the like are generally known.

The characteristics of C and VD as thin film forming means are that a thin film with excellent step coverage can be formed on an uneven substrate, that the composition ratio of the thin film can be controlled freely, and that it can be applied without contaminating or damaging the substrate. Examples include the ability to form a thin film.

On the other hand, CVD also has some drawbacks compared to vapor deposition and sputtering. The first drawback of CVD is that the temperature of the thin film deposition substrate is limited by the reaction temperature of the gas, and the substrate temperature cannot be changed freely.

This causes various problems in CVD, particularly in conventional CVD using heat.

In the case of CVD, the temperature at which deposition proceeds at a sufficient rate due to the chemical reaction of source gases is not necessarily the most suitable temperature for crystal growth of a thin film.

Generally, the reaction temperature of the source gas in CVD is usually considerably higher than the substrate temperature in other forming methods such as evaporation and sputtering. When thin films are deposited at high substrate temperatures in the manufacturing process of semiconductor integrated circuits, diffusion and reactions progress in the deposited films themselves and on the deposited substrates, often causing serious deterioration of device characteristics.

In addition, thermal CVD involves selective growth that takes advantage of differences in the surface materials of the substrate, that is, depositing a thin film only on a pattern of a specific material on the substrate surface, and not depositing a thin film on other materials. However, as the substrate temperature increases, the selectivity tends to decrease for reasons described later, making it difficult to achieve selective growth.

Furthermore, in cases where an alloy film of aluminum and silicon is deposited using two or more raw material gases with significantly different reaction temperatures, such as triisobutylaluminum gas and silane gas, conventional thermal CVD is not suitable for deposition. It is difficult to mix silicon into aluminum at the reaction temperature at which the surface of the film becomes smooth.

As one method for preventing such problems, plasma CVD methods and photoCVD methods that attempt to promote reactions using energy other than heat, such as plasma or light, are attracting attention. These CVD methods make it possible to lower the substrate temperature to a temperature close to that of other forming methods such as evaporation and sputtering, but many of the CVD methods Characteristics are sacrificed. Furthermore, since the selective growth described above uses only the thermal energy difference in film deposition as the selectivity mechanism, it becomes difficult to achieve this selective growth if other energies such as plasma are used.

A second drawback of CVD is that surface irregularities tend to become large. This is a problem in thermal CVD, especially when depositing crystalline thin films such as metals, and the degree of unevenness generally increases as the surface free energy of the thin film material increases and the substrate temperature rises ( According to the nuclear growth theory using the surface free energy model of Volmer et al., this can be explained as follows.References include "Condensation and Evaporation (Published by Macmillan) J (J, P,) firth and G, M
, Pound: Conden-sation and
Evaporation (Macmillan, New
York, 1963).

Atoms that reach the substrate undergo repeated collisions and re-evaporation, forming an aggregate called a cluster, in which a certain number of atoms are bonded together. The total free energy G of one cluster is the sum of the change in free energy during condensation from the gas and the surface free energy of the cluster formed,
It is expressed as the following formula.

G = (' o -' 4 πr ” + g v ・4
TCr 3/3) ・f (θ)・・・(
1) Here, r: radius of curvature θ of the cluster: contact angle f of the cluster with respect to the substrate (θ)=(2-3 cos θ+cos' θ)/4: deposition factor σ of the cluster. : Surface free energy per unit area between gas phase and cluster gv: Free energy change per unit volume when changing from gas phase to liquid phase, always negative. In the case of supersaturated vapor generation, if the vapor pressure at equilibrium is p, the actual vapor pressure is p, the volume of the evaporation source is Ω, the Boltzmann constant is 1, and the absolute temperature is T, then gv = - (kT/ Ω)In (p/p, ). Here, p/pe is the degree of supersaturation.

If r that gives the maximum value of G is set as r''', then dG/dr=
By setting it to 0, r*= 2σo/gv...(2) G"=(16π
σo3/ 3 gv3) ・f (θ) - (31 is obtained. Therefore, if the radius is larger than r"', G will become smaller as it grows, so it will continue to grow on average, and conversely, if the radius is larger than r"' If it is smaller, it disappears as an average. This value of r" is called the critical radius, the cluster with r=r" is called the critical nucleus, and the nucleus larger than the critical nucleus is called the stable nucleus.G
''' can be regarded as the activation energy required to generate stable nuclei. Also, the number density n'' of critical nuclei formed on the substrate is the number of adsorption positions per unit area n
If o, then Boltzmann's formula, n*=noexp (-G11/kT)...(4)
is given by

As is clear from equations (2), (3), and (4), the surface energy σ of the thin film material. The larger the value is, and the smaller the volume energy change Ig,l during cluster generation, the larger the critical radius r1 becomes, and the smaller the number density n1 of critical nuclei becomes. In addition to the surface energy and supersaturation degree of the thin film material, the number density n of critical nuclei is affected by the contact angle θ.When the surface free energy of the substrate material is small and the surface free energy of the thin film material is large, θ, that is, f (θ) increases, and the number density n''' of critical nuclei decreases. In this way, the critical nuclei stochastically generated on the substrate continue to grow as stable nuclei, and eventually these nuclei coalesce to form a thin film. Therefore, when focusing on the unevenness on the surface of the formed thin film, if the density of stable nuclei initially generated on the substrate is small, the radius of the nuclei when they coalesce becomes large.11 As a result, the unevenness on the surface of the thin film becomes large. It can be said that it will be.

To summarize the above discussion, when a thin film material with a high surface free energy is deposited on a substrate with a low surface free energy with a low degree of supersaturation, large nuclei are generated sparsely, and the surface roughness of the thin film becomes large. Surface free energy generally tends to be small for insulators such as oxides, and large for metals such as aluminum and silicon. Therefore, this tendency is most noticeable when a metal thin film is formed on an insulating substrate. In normal capping and sputtering, the degree of supersaturation is extremely large at 1010 to 102 degrees, so the critical radius is small at a few angstroms or less, and the density of critical nuclei is large enough to almost match the number of adsorption positions.

Therefore, in these deposition methods, the unevenness on the surface of the thin film is sufficiently small and usually does not pose a problem.

However, in the case of CVD, it is said that the degree of supersaturation is not very large.
Science and Technology 127 (1980)
194. , W., A., P., C1aassen and
J, Bloem: J, Electrochem, Soc.
,:5olid-St, Sci, & Tech, 127
(1980) 194. ), the number density of critical nuclei decreases to the extent that it affects the surface roughness.

In fact, surface irregularities often pose a specific problem in CVD of metal thin films. For example, when high melting point metals such as molybdenum and tungsten are formed by vapor deposition or sputtering, a thin film with a small crystal grain size of several hundred particles and a smooth surface tends to be formed, whereas when CVD is used, becomes stonewall-like crystal grains with a grain size of 1000 Å or more, and large irregularities are formed on the surface. This is because the substrate temperature during vapor deposition and sputtering of these metal thin films is usually 300°C.
~400°C, whereas CVD requires a high substrate temperature of 500 to 600°C, which is the decomposition temperature of the source gas, which facilitates crystal growth, and is caused by small supersaturation in CVD. It is thought that the number density of the sparse critical fluid is the main factor.

Surface irregularities are a particularly serious problem for aluminum thin films formed by CVD, and the substrate temperature is 25°C.
Although the temperature is 0 to 300°C, which is not so high compared to vapor deposition, etc., there are irregularities of about 10% of the film thickness, and for this reason, it has not been put to practical use. In this case as well, the cause of surface irregularities is explained based on the nuclear growth process. References for this include, for example, [Solid State Science and Technology 131 (1984)]
2175R, A, Revy, M, L, Green a
nd P, Ni, Gallagher: J, Elect-
rochem, Soc, :5olid-5t, Sci,
& Tech, 131 (1984) 2175.

FIG. 12 shows a photograph of a typical metal structure of aluminum formed by CVD. There are irregularities due to crystal grains, and gaps are seen at some of the boundaries of the crystal grains.

Large irregularities on the surface of a thin film make it difficult to accurately form fine patterns using photolithography, and also cause variations in thin film properties such as electric abrasion resistance. Furthermore, even when another thin film is deposited on top of this thin film to form a multilayer structure, local variations in film thickness occur in the uneven portions, making it impossible to obtain an ideal multilayer structure. As a result,
This poses a major problem when used as a constituent material for semiconductor integrated circuits and the like. Semiconductor integrated circuits are required to be increasingly finer and more precise as they become faster and larger, and reducing the unevenness of such thin films is the most important issue for submicron and nanometer devices. It's coming.

To summarize the above problems, with conventional CVD, it is extremely difficult to form fl) a smooth thin film with small surface irregularities, especially a metal thin film.

(2) Furthermore, selective growth of thin films is difficult due to the high substrate temperature during thin film deposition, and it is difficult to avoid deterioration or failure of semiconductor elements due to changes in the physical and chemical states of the substrate and deposited film during film deposition. hard.

(3) Furthermore, it is impossible to mix silicon into aluminum at a reaction temperature that makes the surface of aluminum smooth by using two or more raw material gases, such as triisobutylaluminum gas and silane gas, which have different reaction temperatures. be.

The inventors of the present invention have invented a new CVD method that substantially solves the problems of the conventional CVD described above, and have already filed a patent application (Japanese Patent Application No. 190494/1982). This method deposits a thin film on the deposition surface of the substrate by placing the deposition surface of the substrate close to the heating block and introducing the raw material gas between the heating block and the deposition surface of the substrate. It is something to do. Further, the chemical vapor deposition apparatus of the above invention is an apparatus for carrying out the above chemical vapor deposition method, and includes a heating block and a substrate held so that the surface of the substrate is close to and faces the heating block. The deposition chamber is equipped with a substrate holder.

According to the chemical vapor deposition method of the invention, the source gas is first heated and activated by the heating block, and reaches the low-temperature deposition substrate in a state where it is easily decomposed, and film deposition progresses on the surface of the deposition substrate. do. That is, the film is deposited while the temperature of the source gas is always higher than the substrate temperature. For this reason, the source gas on the substrate is in a considerably supersaturated state compared to normal CVD. According to the nuclear growth theory, the volume energy change during cluster generation becomes large, (3),
As is clear from equation (4), the activation energy G''' for stable nucleation becomes smaller, and the number density n'' of the critical liquid becomes higher. Therefore, the average radius of the nuclei when they coalesce becomes smaller, and a smooth film with fewer irregularities is formed.

In this way, the first feature of the new CVD method is that it can produce a smooth and high-quality thin film, but there are also other advantages to the conventional CVD method.
This method has the advantage of reducing the second and third problems of the method. That is, even if the substrate temperature during deposition is kept low by heating the gas, the deposition may proceed at a sufficient speed, and deterioration of the film itself, the substrate, etc. due to reactions or the like can be reduced. Also,
Even in CVD that uses two or more raw material gases with different reaction temperatures, a high-temperature heating block is located near the substrate surface, so the gas with a high decomposition temperature also reacts and is deposited on the substrate. It becomes possible to do so.

[Problem that the invention seeks to solve]

Although the new CVD method has many excellent features as described above, when it is used as a practical device, it is inferior in terms of controllability of deposition conditions9. In the case of the above-mentioned CVD, in which a thin film is deposited by flowing a raw material gas at a predetermined pressure while the positional relationship between the heating block and the thin film deposition substrate is fixed, the relationship between the deposition substrate and the heating block is fixed. Both the temperature distribution of the gas and the temperature of the deposition substrate are determined only by the temperature of the heating block. That is, it is not possible to manually control the gas temperature and the substrate temperature independently. Moreover, the device structure on the back side of the deposition substrate, that is, the side not facing the heating block, is not clearly defined, and the chamber walls and the like are placed at arbitrary positions. For this reason, the wafer temperature varies from device to device depending on the chamber structure and the like, making it difficult to universally determine deposition conditions.

[Means for solving problems]

In order to solve these problems, the present invention provides two heating blocks facing each other whose temperatures are controlled independently, and a thin film deposition substrate placed between the two heating blocks at a distance from each of the two heating blocks. A substrate holder for holding a thin film deposition substrate is provided in the deposition chamber so as to be positioned at a distance from the substrate holder.

Further, in the method according to the present invention, a thin film deposition substrate is held between two closely facing heating blocks maintained at different temperatures, and the deposition surface of the thin film deposition substrate is placed between two heating blocks. The vapor phase growth is performed by facing the heating block on the high temperature side.

[Effect]

In the apparatus according to the invention, for example, a heating block facing the surface of the thin film deposition substrate to be deposited is maintained at a high temperature, and a heating block facing the back side of the substrate is maintained at a lower temperature.

The source gas is first heated to a high temperature and activated by a heating block facing the deposition surface of the substrate, and reaches the low-temperature deposition substrate surface in an easily decomposed state, and a film is deposited on the deposition substrate surface. That is, film deposition proceeds in a state where the temperature of the source gas is always higher than the substrate temperature.

For this reason, the state of the raw material gas on the substrate surface can be made highly supersaturated, and features such as being able to deposit a smooth and high-quality film can be obtained. Furthermore, when the geometric arrangement, gas type, pressure, etc. are fixed, the temperature of the deposition substrate is determined by the temperature of the two heating blocks that sandwich the substrate. It becomes possible to set the temperature and the substrate temperature to desired values.

〔Example〕

First, an embodiment of a chemical vapor deposition apparatus according to the present invention will be schematically described. FIG. 1 is a diagram showing the configuration of the entire CVD apparatus, and detailed parts, an exhaust system, and a control system are omitted. In FIG. 1, 1 is a deposition chamber, 2 is a wafer loading/unloading chamber, 3 is a raw material chamber, 4.5 is pulp, 6 is variable pulp, 7 is a substrate holder, 8 is a wafer substrate, 9 is a heater, 10.14 11 is a heating block, 11 is a cylindrical tube, 12 is an orifice, 13 is a stirring motor, and 15 is a triisobutylaluminum liquid.

The vacuum chamber of the apparatus shown in FIG. 1 is roughly divided into a deposition chamber 1, a wafer loading/unloading chamber 2, and a raw material chamber 303, each of which is independently evacuated. The ultimate pressure in any vacuum chamber is preferably a high vacuum of about 10-' Torr, but even if it is a low vacuum evacuated using only a low vacuum pump,
There is no fundamental effect on this embodiment. The deposition chamber 1 has a raw material chamber 3, a wafer loading/unloading chamber 2, and pulp 5, respectively.
Two heating blocks 10 and 14, which are connected to each other through a heating block 4 and capable of heating up to 500° C., are installed in close proximity to each other and facing each other. The substrate holder 7 can fix the wafer substrate 8 for deposition introduced from the wafer loading/unloading chamber 2 so as to face the heating block 10.14 at a predetermined distance.

At this time, the surface of the wafer to be deposited is placed on the high temperature heating block 10.
is facing.

Both of the two heating blocks 10.14 and the substrate holder 7 have moving mechanisms, and the distance between the two heating blocks and the distances DI and D2 between each heating block 10.14 and the wafer substrate 8 are freely variable. It is now possible to do so. The variable range of Di and D2 is approximately 2mm to 30mm.
It is mm.

A heater 9 is wound around the outer wall of the raw material chamber 3, and the liquid temperature of the raw material can be heated and controlled to a predetermined temperature. Further, a stirring motor 13 is installed in the raw material chamber 3 to keep the liquid temperature uniform. A cylindrical pipe 11 protrudes horizontally from the upper side wall of the raw material chamber 3
is introduced into the deposition chamber 1 via the pulp 5, and its expanded terminal end is pressed against the heating block 10.

A fine orifice 12 is opened in the side surface of the expanded cylindrical tube 11, and even when the pressure in the deposition chamber 1 is reduced to 0.01 Torr or less, the cylindrical tube 11 is
The interior can be maintained at a pressure close to that of the raw material chamber 3. The path of the raw material gas from the raw material chamber 3 to the deposition chamber 1 is heated to a temperature comparable to that of the raw material chamber 3 so that the once vaporized raw material does not liquefy again.

The first embodiment shown in FIG. 1 relates to the basic configuration. On the other hand, FIG. 2 shows a more specific mass production apparatus as a second embodiment, and FIG. 2 (al is a schematic plan view, and FIG. 2(b) is a configuration diagram.

In FIGS. 2(a) and (b), 21 is the main chamber;
22 to 24 are reactors, 25 is a load rotor chamber, 26 is a rotating disk, 27 is a motor, 28 is a wafer holding plate, 29 is a ring plate, 30 is a lower dome, 31 is a vacuum partition, 32 is a vacuum pump, 33 is a Pulp, 34 is leak pulp, 35 is upper matching box, 36 is lower matching box, 37 is spring, 38 is upper dome, 9a is heater, T
C is a temperature detector such as a thermocouple. In FIG. 2, the same or equivalent parts as in FIG. 1 are given the same reference numerals.

As shown in the planar block diagram of FIG.
and one load lock chamber 25, and these four subchambers are vacuum isolated or differentially evacuated from the main chamber 21 during deposition and processing/notching operations.

As shown in FIG. 2(b), one large rotating disk 26 is held within the main chamber 21, and four wafers are simultaneously transferred by the rotation of the rotating disk 26 driven by a motor 27. Ru. During wafer transfer, all the main and sub-chambers 21 to 25 are temporarily connected to a vacuum to create a high vacuum.

Although the rotating disk 26 is of a horizontal type in FIG. 2, it may be of a vertical type rotating on a vertical plane. The vertical type is better in terms of reactor maintenance.

The wafer substrate 8 on which a thin film is to be deposited is placed in the substrate holder 7 in the wafer loading/unloading chamber 2 with the surface to be deposited facing downward. Installation is performed from above by moving the wafer holding plate 28 upward while the ring plate 29 is fixed by a cylinder. There are various methods for transferring wafers between the atmosphere and vacuum, and any method may be used. For example, as shown in FIG. A method can be used in which the atmosphere and vacuum are separated by crimping with an O-ring.

That is, a vacuum partition is formed around the substrate holder 7 using a wafer holding plate 28 that holds the wafer substrate 8 using a vacuum or an electrostatic chuck, and a ring plate 29 that moves up and down in conjunction with or independently of the wafer holding plate 28. 31, the main chamber 21 and the wafer loading/unloading chamber 2 are separated. After operating the vacuum pump 32 and pulp 33 in the crimped state to reduce the pressure in the wafer loading/unloading chamber 2, the wafer holding plate 2
8 and the ring plate 29 are moved upward in conjunction with each other, the wafer loading/unloading chamber 2 and the main chamber 21 are vacuum-connected, and at the same time, the spring 37 connecting the substrate holder 7 and the rotating disk 26 is compressed. , rotation of the rotating disk 26 becomes possible.

Conversely, when taking out the wafer substrate 8 from the main chamber 21 into the atmosphere, the wafer holding plate 28 and the ring plate 29 are moved downward in cooperation with each other to press the periphery of the substrate holder 7 and remove the wafer substrate 8 from the main chamber 21. After separating the wafer loading/unloading chamber 2 from the wafer loading/unloading chamber 2, the leak valve 34 is opened to bring the wafer loading/unloading chamber 2 to atmospheric pressure. The wafer substrate 8 can be taken out by moving only the wafer holding plate 28 upward while keeping the ring plate 29 fixed.

The operating mode of the reactor is shown in FIG. In FIG. 3, the same or equivalent parts as in FIG. 2 are given the same reference numerals. As shown in FIG. 3(a), when the wafer substrate 8 is transferred, the substrate holder 7, which is connected to the rotating disk 26 via the spring 37, is released from the pressure bonding of the reactor and freely rotates. become able to.

At this time, the two heating blocks 1 sandwiching the wafer substrate 8
0.14 has already been heated to a predetermined temperature.

After the wafer substrate 8 is placed in the reactor, the dome 38 at the top of the reactor presses around the substrate holder 7 to vacuum isolate the inside of the reactor from the main chamber 21, as shown in ('b). . At this time, the heating block 14 also moves and approaches the wafer substrate 8. Subsequently, a gas such as Ar is introduced into the reactor for surface cleaning before deposition, and R is applied to the wafer substrate 8 by the matching box 35 at the top.
F (high frequency) is applied to perform sputter etching. Next, the two heating blocks 10.14 sandwiching the wafer substrate 8 are moved and stopped at a predetermined position close to the wafer substrate 8, as shown in (C). In this state, triisobutylaluminum gas is introduced to selectively grow aluminum.

In addition to the above-mentioned modes, as shown in FIG. 3(d), a structure is adopted in which RF can be applied to the heating block 10 using the matching box 36 at the bottom, and plasma CVD is also possible. In addition, in both Fig. 3 (C) and (d),
By changing the raw material gas, W, Ti, Cr, Si
Metals other than /l such as /l can also be deposited.

Specific usage examples of the apparatus shown in FIGS. 2 and 3 are shown in the table.

Hole filling (3 substrates at the same time) uses all three reactors for selective growth of aluminum, and because it can deposit on three substrates at the same time, it has the feature of high throughput. Aluminum cladding can be used for etc.

Full-surface deposition (two layers at the same time) involves non-selective growth of metal in the reactor 3, that is, a thin layer of metal such as Ti-3i-W is deposited on the entire surface, and then selective growth of aluminum is performed in the reactor 23 and 24. Aluminum will be deposited over the entire surface, and the underlying metal can be used as a barrier between the aluminum and the base ViSi, etc. With the above full surface deposition, 2
The reason why A4 selective growth was performed twice at the same time was in consideration of the fact that the time for metal non-selective growth was shorter than the time for A1 selective growth.

Two-stage deposition (one layer at a time) is a combination of the above two cases, in which aluminum is selectively grown in reactor 22, then metal is non-selectively grown in reactor 23, and finally metal is grown in reactor 24. selective growth of aluminum. this is,
The through-holes are filled with the first selective growth, and then aluminum is deposited on the entire surface to obtain a flat surface.

In addition to the above example, there are variations such as performing non-selective metal growth in the same reactor following the aluminum deposition in the reactor 24. Substrate etching prior to deposition can be performed immediately prior to deposition after the wafer substrate has been moved into the reactor. It is also possible to use the reactor 22 as an etching-only chamber, and after etching the wafer there, transfer the wafer to the reactor 23 or 24 for deposition, but in this case, care must be taken not to lengthen the time between etching and deposition. There is a need.

Next, an example of selective growth of aluminum using such a CVD apparatus will be described with reference to FIG. Prior to CVD, a silicon oxide film 42 is first formed on a silicon substrate 41, as shown in FIG. 4(a). The silicon substrate 41 is p-type (100) 5Ωcm here.
However, there is no essential difference in surface orientation and resistivity even if other types are used. In addition, the silicon oxide film 42
In this embodiment, silicon is formed by thermally oxidizing silicon, but it may be deposited by other formation methods, such as vapor phase epitaxy or sputtering. Furthermore, even if other materials such as silicon oxide film or silicon nitride film doped with phosphorus or boron are used, there is no fundamental difference in effectiveness as long as the film is a so-called insulating thin film.

Next, as shown in FIG. 4(b), through holes 43 are formed using resist mask pattern formation using known photolithography technology and etching technology. There are several known lithography techniques and etching techniques for the silicon oxide film 42 in this process, and any method may be used; When etching is performed, a very slight polymerized film or altered film that is difficult to observe may be formed on the open silicon surface.Such slight changes in the surface condition may cause problems during the subsequent aluminum deposition process. In addition, when a clean silicon surface is obtained using normal wet etching using a buffered hydrofluoric acid solution instead of dry etching, the resist pattern used as an etching mask must be carefully considered. A thin natural oxide film and other contamination occur on the silicon surface due to the process of removing the oxide and the simple passage of time.The natural oxide film 44 shown in FIG. This is a general term for layers.

In order to remove such a natural oxide film layer 44, as shown in FIG. 4(C), a pretreatment for cleaning the silicon surface is required immediately before aluminum deposition.

The main purpose of this process is to remove the natural oxide film layer 44 formed on the silicon surface, ensure reproducibility of selective aluminum deposition in the next process, and at the same time obtain a continuous, smooth, and high-quality aluminum film. be. The usual pretreatment is
For example, after confirming the hydrophobicity of the silicon opening by lightly etching the silicon oxide film by immersing it in a 1.5% dilute hydrofluoric acid aqueous solution for about 10 seconds to several minutes, wash it with pure water for a few minutes to more than ten minutes. Just leave it to dry.

The etching rate of the natural oxide film 44 increases as the concentration of hydrofluoric acid increases, so when the concentration is high, the time required to obtain hydrophobicity becomes shorter. However, since the silicon oxide film 42 other than the openings is also etched, etching conditions must be selected appropriately depending on each case.

Furthermore, if the water washing time becomes longer, an oxide film will be formed on the silicon surface again and it will become water permeable, so the water washing should be finished before this happens. Even if the native oxide film 44 is etched, hydrophobicity may not be obtained, or even if hydrophobicity is obtained, it may be difficult to form a smooth continuous film even under normal deposition conditions when aluminum is deposited. this is,
This is seen when the silicon surface is contaminated or damaged by dry etching or other processes mentioned above. In such a case, after opening the through hole 43,
For example, tens to hundreds of silicon oxide films are formed in the openings by oxidizing the silicon surface in an oxygen atmosphere at around 900°C, and then this oxide film is removed using a dilute hydrofluoric acid solution, etc. By doing so to obtain hydrophobicity, a good aluminum film can be formed.

In addition to the methods described above, methods for removing the natural oxide film 44 include:
After the wafer substrate 47 is placed in a CVD apparatus for aluminum deposition, it is effective to clean the surface of the substrate using dry etching or the like immediately before deposition. This is not so much of a problem when the substrate surface is single crystal silicon, but when aluminum is selectively deposited on a substrate made of polycrystalline silicon or aluminum, a natural oxide film layer 44 is formed using dilute hydrofluoric acid or the like. Even if aluminum is removed, a natural oxide film layer will be formed again in a very short period of time until aluminum is deposited, and good deposition may not be possible. In this case, R
A CVD apparatus equipped with F plasma and an etching mechanism is required. Of course, in addition to RF plasma, there is also electron cyclotron resonance (ECR).
Etching or the like may also be used. When the base substrate is made of aluminum, if the substrate is left in a vacuum for a long time after etching with RF plasma or the like, a natural oxide film will be formed, making it impossible to deposit the material well. When we investigated the range of standing time for depositing a good film, we found that the substrate temperature was 250°C.
If the pressure is 10-'T o r r, approximately 1 minute to 2
It was within minutes. When left for 3 to 5 minutes, an aluminum film with severe surface irregularities was deposited, and when left for 10 minutes, no aluminum film was deposited and only a few aluminum nuclei were formed. No deposition was observed when left for 30 minutes. From the above results, in order to deposit a good film, the removal of the natural oxide film layer shown in FIG. 4(C) is an extremely important step, and after the removal of the natural oxide film layer 44,
It can be seen that it is necessary to start the deposition immediately. If it takes a long time to deposit, the pressure in the deposition chamber should be kept as low as possible. Furthermore, the wafer substrate is
This is a general term that includes everything shown in FIGS. 4(a) to (e).

The wafer substrate 47 that has undergone the above processing is set in a reactor to deposit aluminum.
Before setting the CVD equipment, the following preparations are required. In the following description, the apparatus shown in FIG. 1 will be used. First, the raw material chamber 3, the deposition chamber 1, and the wafer loading/unloading chamber 2 are sufficiently evacuated in advance, and a triisobutylaluminum liquid 15 is introduced into the raw material chamber 3, and the stirring motor 13 is
Heat to the specified temperature while keeping the temperature uniform.

Although triisobutylaluminum has a sufficiently high vapor pressure even at room temperature without heating, it can generate vapor more efficiently by heating. However, it is known that when the heating temperature exceeds 50° C., it tends to change to diisobutylaluminum halide, which has a low vapor pressure, so it cannot be heated to such a high temperature.

Here, the temperature was mainly set at 45°C.

Regarding the raw material gas supply capacity, the raw material chamber 3 has a cylindrical shape with a diameter of about 10 cm and a height of about 22 cm, and with this level of liquid temperature and surface area, the evaporation rate of the raw material gas is sufficiently high. Even during normal gas consumption of several tens of cc/min, a vapor pressure close to that of the raw material gas can be maintained. Further, since the raw material chamber 3 is cylindrical, the surface area of the liquid does not change even if the amount of raw material gas changes, and the evaporation rate remains constant. Therefore, the flow rate of the raw material gas can be changed while keeping the pressure constant by changing the conductance of the orifice opened in the side surface of the cylindrical tube. In parallel with the heating of the source chamber 3 described above, the two heating blocks 10 and 14 in the deposition chamber 2 are also heated and controlled to maintain a constant temperature.

After the above preparatory work, the wafer substrate 47 (corresponding to the wafer substrate 8 in FIG. 1) that has been subjected to the pretreatment shown in FIG. 4(C) is placed in the wafer loading/unloading chamber 2, and is thoroughly evacuated. Subsequently, the wafer substrate 47 (8) is moved to the deposition chamber 1, and the wafer substrate 47 (8) is placed between the two opposing heating blocks 10.14 and held for several minutes. Bring the temperature to a near steady state. At this time, the wafer substrate 47 can be heated more effectively by flowing an inert gas such as argon around the wafer.

Subsequently, the valve 5 between the raw material chamber 3 and the deposition chamber 2 is opened to introduce the raw material gas into the deposition chamber 1, and the deposition of aluminum is started. In addition, in order to prevent the pressure in the deposition chamber 1 from fluctuating greatly immediately after opening the valve 5, the inside of the source chamber 3 may be evacuated at the same flow rate as during deposition for an appropriate period of time before the valve 5 is opened. desirable. After a predetermined deposition time has elapsed, the valve 5 between the raw material chamber 3 and the deposition chamber 1 is closed to complete the deposition. By performing the operations described above, aluminum 45 can be selectively deposited only in the opening 43 of the silicon substrate 41, as shown in FIG. 4 fd).

Aluminum 45 with excellent smoothness is not deposited on the silicon oxide film 42 and is selectively deposited only on the silicon in the opening 43.
It is necessary to carefully select the film deposition conditions in order to deposit the It is an important parameter.Dl-
D2-5mm, gas flow rate approximately 20-30 Cc
/min, and the pressure of the raw material gas inside the cylindrical tube 11 was set to 0.57.

FIG. 5 shows how an aluminum film is deposited on silicon when the pressure in the deposition chamber 1 is approximately 0.05 Torr. In FIG. 5, the horizontal axis represents the temperature TD of the heating block 10 facing the surface to be deposited, and the vertical axis represents the temperature TB of the heating block 14 facing the back side of the substrate. Aluminum deposition does not proceed until the temperature of the heating block reaches a certain level. Therefore, in FIG. 5, the boundary between the area where aluminum is not deposited and the area where aluminum is deposited will be named the "deposition boundary". As a result of experimental investigation of the deposition boundary, it has become clear that it is approximately represented by a straight line S1 of TD+TB=C. C becomes a constant when the distances Di, D2, the pressure of the source gas, etc. are fixed, and was approximately 460 to 480° C. under these conditions. In the region above the deposition boundary line in the figure, the deposition rate increases as the value of TD+TB increases, and at the same time, the film thickness distribution changes so that the periphery of the wafer substrate becomes thicker. Furthermore, as the TD+TBO value increases, the surface unevenness of the deposited aluminum film becomes more severe. At an even higher temperature, island-shaped aluminum nuclei begin to form on the silicon oxide film, and are deposited non-selectively, without distinguishing between silicon and silicon oxide films.

In FIG. 5, in the region on the straight line S2 of TB=TD, all the surrounding wall surfaces of the wafer substrate are heated to the same temperature, so it can be said that the state is the same as that of the conventional real wall type CVD. In the hot wall type, the entire quartz tube on which the deposition substrate is installed is heated by a heater, and in this case, the source gas is heated to the same temperature as the quartz tube while flowing inside the tube. Therefore, in the hot wall type, the source gas temperature is approximately equal to the substrate temperature. On the other hand, TB>
In the entire region of TD (above the boundary of the TB=TD straight line in the graph), the back surface of the wafer substrate is heated to a high temperature, and the wall surface facing the front surface is at a low temperature.
It can be considered to be the same as conventional cold wall CVD. In the cold wall type, the deposition substrate is fixed in close contact with a heated substrate heater, and a source gas having a temperature lower than that of the substrate is introduced.

The CVD in this device is
Unlike VD, TB≦TD (direct vA32 in the graph
A major feature is that a completely new area below the boundary can be used. Under these conditions, the temperature of the source gas is higher than the temperature of the substrate just before deposition, so the source gas on the substrate surface becomes more supersaturated, or it is possible to keep the substrate temperature low. Therefore, a smooth and high quality aluminum film can be obtained. The region S3 indicated by the broken line in the figure shows the region where a good quality aluminum film was actually obtained.
It is considered that the above situation has been realized.

The region S3 is also a region where the thickness of the aluminum film deposited on the wafer substrate is approximately uniform.

FIG. 6 shows a photograph of the metallographic structure of aluminum when TD=320°C and TB=200°C.

Until now, several reports have been made regarding the deposition of aluminum by CVD (however, it is not selective growth), but in all cases the surface state of the deposited film is a collection of small crystal grains, as shown in Figure 12. Yes, the unevenness is large.
In addition, gaps were partially observed between crystal grains. On the other hand, in the case of CVD using this apparatus, as can be seen from FIG. 6, the crystal grain size is large and the surface is smooth, with no gaps at the grain boundaries. The state of the metal structure changes depending on whether the material of the deposition substrate is silicon or aluminum.
For example, when deposited on a silicon substrate with a plane orientation of (111), the tortoise shell pattern shown in FIG. 6 was not observed. However, they all have a smooth surface and no gaps in the grain boundaries, and both form high-quality films.

Moreover, the region where such a film can be obtained is approximately TD+
It is a wide area along the line S1 of TB=C, and the temperature TD of the heating block 10 and the temperature TB of the heating block 14
By making variable , it is possible to obtain high-quality films with good controllability and reproducibility, and this method can be said to be highly practical even when applied to mass production equipment for thin film manufacturing.

All of the aluminum films deposited in areas other than the region S3 indicated by the broken line had problems such as large irregularities or poor uniformity. Further, for example, when TD+TB=600° C. or higher, it was difficult to obtain selectivity. However, the region S3 indicated by the broken line is not fixed quantitatively, but changes depending on the pressure, flow rate, and other conditions of the raw material gas, and therefore shows an approximate trend.

Let us now consider the meaning of the deposition boundary represented by the straight line S1 of approximately TD+TB=C. It is clear from the distance between the wafer substrate and the heating block, the pressure of the source gas, etc. that the flow of the source gas during deposition is in a viscous flow state. Therefore, the temperature distribution between the heating blocks in this case changes almost linearly, and for example, the temperature of the wafer substrate placed equidistantly from both blocks becomes (TD+TB)/2. On the other hand, the deposition boundary line shown in Fig. 5 is TD+TB
This indicates that film deposition starts when the value of C reaches a certain constant C, and the temperature of the wafer substrate is (TD+TB)/
2, it can be seen that the progress of film deposition is mainly determined by the wafer substrate temperature. However, in the region where TB<TD, the deposition boundary line is TD+TB
There was also a tendency for the slope to be slightly larger than the straight line =C, suggesting that in addition to the substrate temperature, the source gas temperature also had a secondary effect on the progress of film deposition.

Although the experiment described above was conducted with D1=D2=5 mm, even if D1 and D2 change, the approximate deposition boundary can be predicted by calculating the wafer substrate temperature. When the distance between the two heating blocks is kept constant and the wafer M plate 47 (8) is brought closer to the heating block 10 at the temperature TD, the slope of the deposition boundary becomes steeper, and D1=Omm.
At the limit of , it becomes a vertical line (TD=C/2). Conversely, when the wafer substrate 47 is brought closer to the heating block 14 at the temperature TB, the slope of the deposition boundary becomes gentler, and D2=Om
At the limit of m, it becomes a horizontal line (TB=C/2). At this time, the center of rotation of the deposition boundary line is two straight lines TD + TB = C and T
B is the intersection of TD.

As the deposition boundary moves, the range of conditions under which a good quality film can be deposited also changes. In addition, as for the variable range of Di and D2, since a sufficiently high quality film was deposited within the range of about 3 mm or more and less than 15 mm, the realistic minimum interval is determined by the processing accuracy of the heating block and the accuracy of the position control of the wafer substrate. , the maximum spacing is thought to be limited by deterioration of uniformity of the deposited film due to fringe effects. The peripheral effect refers to the fact that when the distance between the two heating blocks 10 and 14 is large, gases other than those heated on the heating surface occur in the vicinity of the double-jaw heating blocks, and the deposited film around the wafer substrate is mixed. This is a phenomenon in which the thickness and film quality become non-uniform.

Patent applications already filed by the inventors of the present application (Japanese Patent Application No.
No. 190494) is a case where D2=Omm. In this case, the deposition boundary in FIG. 5 is TB=C/2=23
It becomes a straight line from 0 to 240°C, and the conditions for depositing a good quality film are also limited to when TB is around 250 to 260°C. It is extremely difficult to suppress the temperature distribution of the heater for heating the substrate (in this case, the heating block on the back side of the wafer substrate), and even if the heater temperature is uniform, the wafer temperature may vary depending on the degree of contact between the heater and the wafer substrate. Since a large temperature distribution occurs on the substrate, it is difficult to ensure uniformity in the thickness and quality of the deposited film using a conventional type of apparatus in which the heater and the wafer substrate are in contact with each other. When the heating block and wafer substrate are separated (D 2 >
Omm), the temperature of the wafer substrate is extremely uniform because the thermal conductivity within the wafer substrate is sufficiently higher than that of gas and because the wafer substrate is heated with a gas whose temperature is averaged.

When the pressure of the source gas becomes low and the gas flow becomes a molecular flow region, the wafer substrate temperature comes to be expressed as the geometric mean of the temperatures of the two heating blocks, and the spatial temperature distribution also changes over distance. However, since the wafer substrate temperature and the temperature distribution between heating blocks can be easily determined, the situation of polycrystals can be roughly predicted. can.

As mentioned above, the conditions for depositing a high-quality film vary depending on the distance between the heating block and the wafer substrate, the gas pressure, etc., and it is not possible to describe all of these conditions, but the basic idea is clear. Therefore, individual conditions can be determined accordingly.

In this example, as a result of measuring the wafer substrate temperature during deposition using a thermocouple, it was found that the substrate temperature rose at the same time as the source gas was flowed and deposition started, and the temperature remained almost constant for about 1 to 2 minutes. became clear. If an inert gas such as argon is flowed in advance before flowing the raw material gas, the temperature reaches a steady state more quickly.

The raw material gas is heated to a high temperature and activated in the heating block 10, and reaches the lower temperature substrate 8 in a state where it is easily decomposed. Although it is difficult to know in what process the raw material gas that reaches the substrate 8 decomposes into aluminum, it is clear that under these conditions the aluminum on the substrate 8 is considerably supersaturated compared to normal CVD. Conceivable. In this case, according to the nucleus growth theory, the volume energy change during cluster generation becomes large, +3), (As is clear from equation 41, the activation energy G* for stable nucleation
becomes smaller, and the number density n'' of critical nuclei becomes higher.

Therefore, the average radius of the nuclei when they coalesce becomes smaller, and a smooth film with fewer irregularities is formed.

The process of depositing a high-quality film by the deposition method of the present invention can be characterized by observation using a scanning electron microscope (SEM). Using the apparatus shown in Fig. 1, D1=D2=5
With the wafer substrate set at the center of two heating blocks, the Al film was deposited using the conditions at points A and B shown in FIG. Point A is the condition under which a good quality film is deposited, TD=320° C., TB=200° C., where the source gas temperature is higher than the substrate temperature. Point B, which is a condition for comparison, is a condition where TD=200° C., TB=320° C., and the source gas temperature is lower than the substrate temperature. Since the raw material gas is in a viscous flow state and the thermal conductivity of the wafer substrate is sufficiently higher than that of the gas, points A and B
It is thought that the substrate temperatures are almost the same, approximately 260°C.

10 and 11 are metallographic photographs showing the growth process of the Al film when depositing the Al film under these conditions, with FIG. 10 showing sample A and FIG. 11 showing sample B. 1st
As shown in Figure 0, for sample A deposited at point A where the source gas temperature is higher than the substrate temperature, the deposition start point 2
After a few minutes, high-density growth nuclei are generated (Fig. 10(b)).
). Because the distance between the nuclei is small, the nuclei progress to coalesce after 3 minutes (Fig. 10 (C1)), and after 5 minutes, a smooth continuous film is formed (Fig. 10 (d)). Note that FIG. 10 (al indicates the time 1 minute after the start of deposition).

On the other hand, for sample B deposited at point B where the gas temperature is low, the results are shown in Figure 11 (
As shown in a), (b), (C) and (dl),
Even when the deposition time becomes longer, the core density does not increase much, and only island growth progresses, and they do not coalesce even after a deposition time of 5 minutes. This results in an Af film with severe irregularities. In areas other than point B, where TB>TD, a similar tendency for island growth was observed.

From the above results, in the deposition method according to the present invention, the heated source gas reaches the substrate at a lower temperature, so the gas state on the substrate surface becomes highly saturated, and therefore a high density of nuclei is generated. It can be assumed that a smooth film can be obtained by using this method, and it was confirmed that the behavior is the same as the result of the nucleus growth theory using the surface free energy model of Wolff et al.

In addition to the above, this method has the following important features compared to other CVD methods. In the hot wall type, since the entire deposition atmosphere is heated to the same temperature as the substrate, a reaction occurs on the entire wall surface of the deposition chamber, and the raw material gas is wasted. In addition, periodic cleaning of wall surface deposits is required, making maintenance of the device troublesome. In this method, the raw material gas is introduced into the deposition chamber 1 at a low temperature, and is heated to a high temperature only when it reaches the vicinity of the deposition substrate 8.

Gas consumption in this case occurs only on the deposition substrate and on the surface of the heating block 10. The area of these heating parts is extremely small compared to the hot wall type, which is excellent in both prevention of waste of raw material gas and equipment maintenance.

Another feature of this method is that since the gas temperature can be made sufficiently high relative to the substrate temperature, deposition is possible even in the case of a source gas that is difficult to decompose in normal CVD. That is, by heating the raw material gas to a high temperature in the heating block 10, the gas itself is activated or converted into a highly reactive substance. This has the effect of accelerating the decomposition reaction on the low-temperature substrate 8, making it possible to deposit a thin film while keeping the substrate temperature low.

Triisobutylaluminum used as a raw material gas in this example decomposes into diisobutylaluminum halide having a low vapor pressure at temperatures above 50°C.

For this reason, if the gas is heated to 100 to 200°C in the gas transport path, it will condense and liquefy, making it impossible to sufficiently supply the raw material gas to the deposition substrate 8. In this embodiment, the raw material gas is Until then, it is supplied at a low temperature of about 50° C., and is only heated to a high deposition temperature near the surface of the heating block 10, which is heated to a high temperature. Therefore, liquefaction in the transport route of the raw material gas is prevented.

Further, the front side of the deposition substrate 8 faces the immediate vicinity of the heating block 10, and while the relatively low temperature raw material gas is in contact with the back side of the deposition substrate 8, the front side facing the heating block 10 Gas heated to a high temperature is incident.In practice, even if a good aluminum film is deposited on the surface of the deposition substrate 8, there are cases where no aluminum is deposited on the back side of the substrate.The temperature of the wafer itself is different from the front and back sides. Since there is not much difference, it can be understood that in this method, the reaction is promoted by gas heating, and gas heating is extremely important.

Furthermore, triisobutylaluminum introduced near the heating block 10 is heated and converted into diisobutylaluminum halide having a low vapor pressure, and a low-temperature wafer substrate 8 is placed immediately nearby. Therefore, in this respect as well, the wafer surface is extremely oversaturated, which is one of the reasons why a high quality aluminum film with high smoothness is formed in this example.

According to this embodiment, the raw material gas itself is heated by the two heating blocks 10.14 to have a constant spatial temperature distribution, and the deposition substrate placed between these heating blocks is heated by the raw material gas. has been done. Therefore, the reproducibility and uniformity of film deposition were significantly improved compared to the usual cold wall CVD method.

Further, in this embodiment, the deposition progresses on the wafer substrate 8 due to the surplus heating gas that is not consumed by the heating block 10. Therefore, as the material for the surface of the heating block 100, for example, a material such as silicon or aluminum, on which aluminum is easily deposited, or a material such as a silicon oxide film, on which aluminum is difficult to deposit, is used, or a material such as a silicon oxide film, etc., is used to deposit the material on the deposition substrate 8. The amount of aluminum varies. For example, if the surface of the heating block 10 is made up of a pattern of silicon and a silicon oxide film, and the deposition substrate 8 is a silicon wafer, the silicon oxide film pattern can be formed without depositing aluminum on the entire surface of the silicon wafer 8. It was also possible to deposit aluminum only on the parts facing the surface.

Therefore, from the viewpoint of raw material gas consumption efficiency, the material for the surface of the heating block 10 should be one that does not easily cause aluminum deposition, such as silicon dioxide, titanium dioxide, tantalum pentoxide, molybdenum oxide, vanadium pentoxide, etc., which has a low surface energy. Preferably, it is a material. However, even with such a material, once aluminum is deposited, the aluminum continues to be deposited and is not effective in preventing gas consumption. In this embodiment, heating block 1
Although aluminum is used as the material for the 0 surface, there is no problem with gas consumption efficiency in normal deposition.

The state of aluminum deposition also changes depending on deposition conditions other than the heating block temperature and substrate temperature, that is, the flow rate and pressure of the source gas.

The gas pressure can be controlled by changing the temperature of the raw material chamber 3 within a range of about 50° C. from room temperature, as described above. In the case of this method, the pressure control range within the temperature range of the raw material chamber 3 is approximately 0.2Torr~2To
Selective growth was possible for both r and r. At pressures below 0.2 Torr, deposition hardly progressed, and as the pressure increased, the deposition rate tended to increase somewhat.

Regarding the flow rate of the source gas, even if the flow rate is constant, the gas flow rate at the wafer surface is greatly affected by the structure of the deposition chamber, so it is highly dependent on the device and difficult to handle in general. The standard flow rate used in this method was about 20 to 30 Cc/min, but the flow rate was 50 Cc/min.
C/min or less had no significant effect on the state of film deposition. However, as the flow rate increased, the temperature of the gas at the wafer surface decreased, and there was a tendency for aluminum deposition to occur less easily.

For example, when the flow rate is increased, deposition may not occur unless the substrate temperature is 20 to 30° C. higher than in the case of a standard flow rate. This phenomenon is not observed when the gas flow rate is small, and in extreme cases, it is possible to deposit aluminum to a sufficient thickness even when the exhaust gas is stopped and the deposition chamber 1 connected to the raw material chamber 3 is sealed. there were. However, in this case, the pressure within the deposition chamber 1 increases over time due to diisobutylene and hydrogen gas generated by the decomposition reaction of triisobutylaluminum.

By the aluminum deposition operation described above, the fourth
As shown in Figure (d), aluminum can be selectively deposited only in the through holes 43, which are silicon openings. The deposition conditions of this example are D1=D2=5m
m, the gas flow rate is approximately 20 to 30 cc/min, the pressure of the source gas inside the cylindrical tube 11 is 0.5 Torr, the pressure in the deposition chamber 1 is approximately 0.05 Torr, and TD = 320°C.
, TB=200°C. The thickness of the aluminum film inside the through hole 43 is 5000 mm, and by making it the same thickness as the silicon oxide film, a flat shape can be obtained.

Aluminum films deposited by conventional cold wall CVD have no problems in terms of impurities in the film, which are below the limit of Auger analysis, but the resistivity is somewhat high at around 3.3 μΩCm, and as can be seen from Figure 12. The film surface has large irregularities, making it unsuitable for fine patterns. This is thought to be because island formation occurs at the initial stage of film growth, and then these islands are connected to form a film. The unevenness of the film surface is greatly influenced by the substrate heating temperature during deposition.
If the substrate temperature is lowered, the unevenness will be reduced.

However, in the conventional method, even when deposited under the best conditions, it is inferior to other deposition methods such as sputtering and vapor deposition in terms of unevenness of the film surface.

In this method, as described above, by using two opposing heating blocks, it is possible to form a smooth film. In addition, if the film thickness is about 1000 people or more, it is 2.9 μΩ.
cm, which is close to the bulk resistivity, and also has a resistivity of 50 cm.
It can be seen that even if it is as thin as 0, it exhibits conductivity and is a continuous aluminum film.

FIG. 4(e) shows a state in which aluminum 45 having the same thickness as the silicon oxide film 42 is selectively deposited in the silicon opening 43, and then an aluminum film 46 is deposited over the entire surface using a normal sputtering method. ing.

The figure also shows the cross-sectional shape of the silicon opening after further patterning to form an aluminum wiring pattern.

In this method, an example has been shown in which the through hole 43 on the silicon substrate 41 opened in the silicon oxide film 42 is filled with aluminum, but the same method can be performed using other materials other than the combination of the silicon oxide film 42 and the silicon substrate 41. . Aluminum wiring in semiconductor integrated circuits is often connected to an element portion or underlying wiring through an opening in an insulating film. The underlying material in the opening at this time is usually single crystal or polycrystalline silicon or aluminum containing various impurities. In addition, metals such as titanium, molybdenum, tungsten, and platinum, or titanium silicide,
Silicide materials such as tungsten silicide, molybdenum silicide, tantalum silicide, and platinum silicide, as well as compounds such as titanium nitride and molybdenum nitride, may be used.

In particular, when the base is silicon, the interface is likely to deteriorate due to reactions with aluminum, etc. Therefore, as shown in FIG. Alternatively, it may be better to selectively grow the aluminum 54 after forming the barrier layer 53 made of molybdenum, tungsten, their silicides, platinum silicide, or the like.

Both materials are conductive metals or semiconductors,
Selective growth of aluminum is possible on these materials. In particular, with regard to silicon, it has been experimentally confirmed that aluminum can be deposited on materials that contain impurities such as arsenic, phosphorous, and boron to the extent of solid solubility, and on high-resistance single-crystal silicon and polycrystalline silicon with low concentrations of these impurities. did it.

In addition, if the base is aluminum or an aluminum alloy such as silicon-containing aluminum, it goes without saying that aluminum can be deposited because they are the same material, but a thick alumina layer of several tens of angstroms or more may be formed on the surface. In such cases, as in the case of silicon, it is necessary to perform a light etching using dilute hydrofluoric acid or the like, and then to clean the surface by plasma etching or the like immediately before the deposition after placing the film in a vacuum chamber. Since aluminum surfaces are quickly oxidized even in vacuum, after cleaning,
It was necessary to start the deposition within 1 to 2 minutes in a vacuum of r.

On the other hand, silicon oxide film is the most commonly used material for insulating films used in semiconductor integrated circuits, but silicon nitride films are also used.

The silicon oxide film includes a silicon oxide film formed by thermally oxidizing silicon, a silicon oxide film deposited by other formation methods such as a vapor phase epitaxy method or a sputtering method, and a silicon oxide film added with phosphorus or boron. Under the conditions of selective growth of aluminum according to this method, aluminum is not deposited on these insulating films.

From the above, the formation of a flat aluminum wiring with no step in the opening as shown in FIG. 4(e) can be applied to all through holes in semiconductor integrated circuits. When depositing only by sputtering or evaporation without using selective growth, a step is formed on the surface of the aluminum film at the silicon opening above the through hole, and a microcrank is generated at the bottom of the step, resulting in a decrease in yield due to wire breakage, etc. It was the cause of sexual decline. According to this method, by selectively depositing aluminum of approximately the same thickness as the step of the through-hole, the through-hole portion of the semiconductor integrated circuit is flat and has no disconnections, resulting in aluminum wiring with excellent yield and reliability. can be formed.

As mentioned above, CVD using two heating blocks 10°14 has the major feature of being able to deposit an aluminum film with a smooth surface and large grain size with good reproducibility, uniformity, and excellent selectivity. have Therefore, through-holes can be filled, and flat multilayer wiring becomes possible.

In the above examples, only triisobutylaluminum was used as the raw material gas, but even if other organic compounds of aluminum such as trinotylaluminum or triethylaluminum are used as the raw material gas, their chemical properties are very similar. Therefore, it is possible to deposit aluminum on a substrate in the same manner as described above with some differences in deposition conditions.

Next, as a second example of the method of using the chemical vapor deposition apparatus according to the present invention, an example will be shown in which an aluminum alloy containing silicon is deposited using triisobutylaluminum and disilane as source gases.

A first embodiment of a method of using a chemical vapor deposition apparatus according to the present invention is shown in FIGS. It is something. However, as a general wiring material, aluminum containing 1 to 2% silicon is most often used. The first reason is to prevent junction leakage at the pn junction caused by the reaction between the silicon substrate and aluminum, and the second reason is to prevent interconnect reliability from deteriorating due to electromigration. be. When selective growth of aluminum is applied to wiring as in the first embodiment, thin aluminum of about 1,000 layers is used for bonding to a silicon substrate, and when used to fill through holes, it is mainly used for upper layers. Since it is used to connect the aluminum wiring pipes in the lower layer, there are no major problems such as the above reaction even if the aluminum does not contain silicon. It is also possible to prevent the reaction by sandwiching a barrier layer such as titanium. However, if silicon can be added into the aluminum film at the same time as aluminum is selectively grown, the range of applications can be further expanded.

Until now, a patent application has been filed claiming that silicon-containing aluminum can be deposited by simultaneously introducing silane gas and organic aluminum gas onto a substrate in CVD of aluminum (Japanese Patent Laid-Open No. 55-91119), but in practice, It is impossible to achieve this with normal thermal CVD and use it in the manufacturing process of semiconductor integrated circuits.
When aluminum is deposited using organic aluminum, the substrate temperature is at most 400 to 500°C. At temperatures higher than this, it is difficult to obtain a high-quality aluminum film, and even if it is obtained, the aluminum film and the underlying substrate silicon and silicon oxide film will react or interdiffuse, resulting in the desired structure. is not obtained. This situation is the same even when other semiconductors such as GaAs are used as the base substrate. On the other hand, the decomposition temperature of silane is said to be at least 600°C or higher, and silane does not decompose within the temperature range where aluminum can be deposited.
It turns out that it is not possible to dope silicon while depositing aluminum.

CV that decomposes raw material gas using energy other than heat
D. For example, by using plasma CVD or photo-CVD, it is possible to deposit aluminum while doping silicon with silane. However, such C
VD has the above-mentioned drawbacks, which results in the characteristics of CVD being halved.

By using this method, an aluminum film containing silicon can be effectively deposited using organic aluminum such as triisobutylaluminum and silane gas as raw materials. For example, if the apparatus shown in FIG. 1 is used and the temperature of the heating block 10 is set to about 600°C and the substrate temperature of the heating block 14 is set to about 200°C, then at the same time as the silane is decomposed, aluminum is decomposed without reacting with the substrate. Allows for film deposition. However, since the decomposition temperature of silane and the deposition temperature of aluminum are significantly different from each other, it is difficult to obtain deposition conditions with good uniformity. By using disilane instead of silane, these problems are solved and silicon-containing aluminum membranes can be easily deposited.

In the apparatus shown in FIG. 1, D1=D2=5 mm,
TD=360°C, TB=150°C.

Disilane was flowed at about 30 cc/min, and other conditions such as the flow rate of triisobutylaluminum were the same as in the first example. However, since the gas pressure in the deposition chamber 1 was the sum of the partial pressures of the two gases, it was a little high at 0.8 Torr. The concentration of silicon in aluminum under these conditions was about 2%. As a result of experiments, if only disilane is introduced and triisobutylaluminum is not completely flushed, in order to decompose disilane and deposit silicon on the substrate,
It was necessary to set the temperature TD of the heating block 10 to approximately 400° C. or higher. However, it has been revealed that when disilane and triisobutylaluminum are flowed simultaneously, silicon enters the aluminum film even at lower temperatures, and silicon is contained on the order of percent at temperatures above about 350°C. When the temperature TD is increased, the decomposition of disilane is promoted and the concentration of silicon in aluminum rapidly increases.

Therefore, the concentration of silicon can be freely varied depending on the temperature of the heating block or the flow rate of disilane.

As shown above, by using triisobutylaluminum and disilane as source gases in CVD using a heating block, it becomes possible to deposit aluminum containing an arbitrary amount of silicon.

In this method, aluminum containing silicon is selectively grown, but instead of selective growth, it is also possible to deposit the aluminum over the entire surface regardless of the material of the underlying substrate. There are several methods of such non-selective growth. For example, by increasing the temperature TD to about 380° C. and decreasing the flow rate of disilane, aluminum containing silicon can be deposited over the entire surface. However, it is somewhat difficult to obtain film thickness uniformity with this method.As another method, TD=40
With the heating block 10 at a high temperature of about 0° C., only disilane is flowed to deposit a thin layer of silicon over the entire surface. Aluminum is then deposited under standard selective growth conditions as in the first or second embodiments described above. In selective growth, aluminum is deposited only on silicon, but since the entire surface is covered with silicon, here aluminum is deposited on the entire surface. In this case, a film with excellent uniformity and film quality can be obtained. Further, since silicon deposited under aluminum diffuses into the aluminum film during aluminum deposition or during subsequent heat treatment, silicon does not need to be added during aluminum deposition.

In a similar sense, a thin film of titanium or the like may be deposited in advance and then aluminum may be deposited.

FIG. 8 shows a case where the first embodiment (see FIGS. 4(C) to (e)) of the method of using the chemical vapor deposition apparatus according to the present invention is applied, and the gate electrode and source of the MOSLSI are ,
This is an example in which aluminum is selectively deposited on the drain to lower the resistance. This figure shows the flow of the main manufacturing process, and parts that do not directly affect this method are omitted.

First, as shown in FIG. 8(a), a p-type silicon substrate 61 having an inter-element isolation region 62 formed using a silicon oxide film is prepared, and a gate oxide film is further formed in the region to become an active element. Form 63.

Next, as shown in FIG. 8(bl, (C)), a polycrystalline silicon thin film 64 doped with phosphorus is deposited, and the thin film is processed using lithography and etching techniques to form a gate electrode 65. In addition to phosphorus, the impurity of polycrystalline silicon may be arsenic, boron, etc., depending on the purpose.

Subsequently, as shown in FIG. 8(d), the area around the gate electrode is oxidized to form a polycrystalline silicon oxide film 66, and ions are implanted to form a source and drain 67 using the gate electrode as a mask. As the ion species, usually arsenic or phosphorus is used for n-channel devices, and boron is used for p-channel devices.

Thereafter, as shown in FIG. 8(e), a heat treatment is performed to activate the implanted ions, and a silicon oxide film 68 is deposited using a low pressure CVD method.

This silicon oxide film 68 is formed thickly on the side surfaces of the gate electrode 65, so by using directional dry etching, a side wall 69 is formed on the side surface of the gate electrode 65, as shown in FIG. 8(f). can be formed. The silicon oxide film 68 may be any insulating film that is thickly formed on the side surface of the gate electrode 65, such as reflowed PSG or BPSG, or a so-called bias sputtered silicon oxide film sputtered by applying a slight bias. Furthermore, a silicon nitride film or the like may be used.

After this, as shown in FIG. 8 (phantom), aluminum 70 is selectively grown on the exposed silicon surface of the gate electrode 65 and on the source and drain 67. This pretreatment is performed after dry etching, so a silicon oxide film of about 100 layers is first formed at about 800 to 900°C, and then etched with a dilute hydrofluoric acid solution. It is best to expose a clean silicon surface.For aluminum deposition, use the apparatus shown in Figure 1 and set D1=D2-5m.
m, TD=320°C, TB-200°C, and the pressure of source gas 0.5 Torr, and the deposition time was about 1.
Aluminum film with a thickness of approximately 1000 layers was formed in 0 minutes.

Next, as shown in FIG. 8(h), a glabellar insulating film 71 is deposited, and a through hole 72 is opened using known lamination and etching techniques.

After this, wiring is generally formed by depositing an aluminum film using a sputtering method or the like, but here, the method shown in FIG.
), the through holes are filled with a selectively grown aluminum film 73 formed by this method. As a pretreatment before depositing aluminum, only etching with a dilute hydrofluoric acid solution is performed, and deposition is performed using the same method as in the case of FIG. 8(g). However, alumina is removed by plasma cleaning in a vacuum immediately before deposition. By setting the thickness of the deposited film to 5000 mm, which is the same as the depth of the through hole, it is possible to reliably fill the inside of the through hole and obtain a flat surface.

Thereafter, an aluminum film is deposited on the entire surface using a sputtering method, etc., and an aluminum pattern a7 as shown in FIG.
Complete 4.

Note that at this time, the sputtering method was not used, and the C
Aluminum may be deposited over the entire surface using VD. For example, through-hole 7 can be selectively deposited with aluminum.
After burying the inside of 2, aluminum can be subsequently deposited on the entire surface under non-selective growth conditions. The method of non-selective growth is as described above, heating block 10.14
There are methods such as increasing the temperature of the film, and depositing aluminum after depositing silicon or the like on the entire surface.

As mentioned above, in the example shown in Figure 8, selectively grown aluminum is attached to polycrystalline silicon and the source and drain to lower the resistance of the gate electrode wiring, and selectively grown aluminum is used to fill the through holes to flatten them. It has been realized and is used for two different purposes. In particular, when applied to bonding technology, the resistivity of aluminum is 2.9.
Since it is μΩcm, which is close to that of bulk, it is possible to lower the resistance by one to two orders of magnitude compared to the case where tungsten or silicide is attached.

Furthermore, in the case of bonding to sources and drains, if the aluminum film is too thick, the aluminum will react with the substrate silicon, causing problems such as junction leakage. There is almost no problem in the following cases.

Furthermore, if necessary, as shown in FIG. 7, selective growth of aluminum may be performed after a barrier layer is pasted on the source and drain or on the polycrystalline silicon gate electrode. The thickness of this barrier layer may be, for example, on the order of 100 to 1000 thick. The resistance of a barrier layer of this thickness is several times to an order of magnitude higher than the resistance of selectively grown aluminum, and a sufficiently low resistance can only be achieved by pasting aluminum.

FIG. 9 is a sectional view showing an example in which this method is applied to electrode extraction of a bipolar LSI and formation of a resistor using polycrystalline silicon.

FIG. 9(a) shows npn in the separated silicon substrate 81.
) A transistor is formed and a polycrystalline silicon electrode pattern is further formed thereon. That is, 8
Reference numeral 2 designates an element isolation oxide film, 83 an n buried layer, 84 a collector, 85 a base, and 86 an emitter. The surface of the silicon substrate 81 in this state has a polycrystalline silicon electrode pattern 87 and a silicon oxide film 88 separating them.
A mask 89 for forming a resistor is formed on a polycrystalline silicon region that is to become a resistor.

As the material of this mask 89, an insulating material such as a silicon oxide film or a silicon nitride film is used.

In this state, as shown in FIG. 9('b), aluminum 90 is selectively grown on the exposed polycrystalline silicon. Prior to aluminum deposition, a pretreatment is performed to remove the natural oxide film layer, but in this case, since dry etching is performed, it is first heated at about 800 to 900°C for 10 minutes.
It is preferable to form a silicon oxide film with a thickness of about 0.0 mm, and then to expose a clean silicon surface by etching with a dilute hydrofluoric acid solution.

Aluminum deposition was performed using the apparatus shown in FIG. 1, with D1=
The process was carried out under standard conditions of D2-5 mm, TD=320 DEG C., TB=200 DEG C., and source gas pressure of 0.5 Torr, and an aluminum film having a thickness of about 1000 mm was formed in a deposition time of about 10 minutes. This aluminum 90 lowers the resistance of the polycrystalline silicon electrode pattern, and at the same time, the polycrystalline silicon under the resistor formation mask 89 becomes a polycrystalline silicon resistor 91 whose dimensions are determined in a self-aligned manner.

Next, as shown in FIG. 9C, a glabellar insulating film 92 is deposited, and a through hole 93 is opened using known lamination and etching techniques.

After this, wiring is generally formed by depositing an aluminum film using a sputtering method or the like, but here, the method shown in FIG.
), a second selectively grown aluminum film 94 according to the present method is used to fill the through holes. As a pretreatment before aluminum deposition, only etching with a dilute hydrofluoric acid solution is performed, and deposition is performed using the same method as in the case of FIG. 9(b). However, alumina is removed by plasma cleaning in a vacuum immediately before deposition. By setting the thickness of the deposited film to be the same as the depth of the through hole, the inside of the through hole can be reliably filled and a flat surface can be obtained.

Thereafter, an aluminum film is deposited on the entire surface using a sputtering method, etc., and an aluminum wiring 95 is formed using known lithography and etching techniques as shown in FIG. 9(e).
complete.

As described above, in the example shown in FIG. 9, selectively grown aluminum is attached to the polycrystalline silicon electrode to lower the resistance, and at the same time, it is also used to form a resistor. Furthermore, selectively grown aluminum is used to fill the through holes to achieve planarization.

In particular, when applying bonding to technology, the resistivity of aluminum is 2.9 μΩcm, which is close to that of bulk, so compared to attaching tungsten or silicide,
It is possible to lower the resistance by orders of magnitude to two orders of magnitude. If the thickness of the aluminum film is large, the aluminum reacts with polycrystalline silicon, causing deterioration of device characteristics, but this is hardly a problem when the thickness of the aluminum film is about 1000 or less, as in the present method. If necessary, selective growth of aluminum may be performed after a barrier layer is pasted on the polycrystalline silicon electrode, as shown in FIG. The thickness of this barrier layer may be, for example, on the order of 100 to 1000 layers. The resistance of a barrier layer of this thickness is several times to an order of magnitude higher than the resistance of selectively grown aluminum, and a sufficiently low resistance can only be achieved by pasting aluminum.

The manufacturing example shown in FIG. 8 is an example in which the first embodiment of the method of using the chemical vapor deposition apparatus according to the present invention is applied to the deposition of aluminum, but it can also be applied to the vapor phase growth of metals other than aluminum and semiconductors. It is valid.

For example, for the deposition of tungsten or molybdenum, particularly for selective growth, this method enables the deposition of smooth, high-quality films. In the case of tungsten, tungsten hexafluoride is used as the raw material gas, and hydrogen, helium, argon, etc. are used as the carrier gas. The deposition device shown in Fig. 1 was used, with Di-3 to 10 mm and D
2=3~lQmm, TD 300~700℃, TB 2
00~600℃, total gas pressure 0.1~5Torr
It was changed to Selective growth of tungsten occurs through a silicon reduction reaction at the initial stage of growth, but as the film becomes thicker, it progresses through a hydrogen reduction reaction. Therefore, in order to deposit a thick film, it is necessary to use hydrogen as a carrier gas.

Typical deposition conditions are, for example, D1=D2=5mm, T
D=450℃, TB=300℃, total gas pressure 0.
5 Torr, partial pressure of tungsten hexafluoride 0.05 Torr
It was r. Depending on the purpose of use, tungsten may be deposited selectively, or conversely, tungsten may be deposited non-selectively over the entire surface of the wafer. The degree of selectivity depends on the adsorption energy of the raw material gas or the activation energy of nucleation based on the degree of supersaturation. Therefore, using the apparatus shown in FIG.
By arbitrarily selecting the temperature of the two heating blocks, it is possible to deposit a highly selective film or to deposit it on the entire surface.

Molybdenum can be deposited under almost the same conditions as tungsten, except that molybdenum hexafluoride is used as the source gas. Further, molybdenum pentachloride or the like may be used as another raw material gas.

For deposition of silicide such as tungsten silicide and molybdenum silicide, silane gas may be mixed under the above-mentioned deposition conditions for pure metal.

As for polycrystalline silicon, TD and TB can be deposited at 400 to 1100° C. using silane gas or the like as a raw material gas. When depositing amorphous silicon, it is desirable to lower the temperature of the heating block. If necessary, if disilane is used as the raw material gas, TD=400℃
However, deposition is possible. Amorphous silicon is generally used in many applications such as solar cells, and in such applications it is desirable that the film contains a large amount of hydrogen. In this method, the substrate temperature can be kept low, and amorphous silicon with high hydrogen content and good properties can be deposited.

As described above, thin films with excellent smoothness can be achieved by applying the method of using the chemical vapor deposition apparatus according to the present invention to the deposition of not only aluminum but also all kinds of metal and semiconductor thin films. It becomes possible. In addition, it is easier to increase the selectivity depending on the application of thin film formation, or conversely, to lower the selectivity (depositing on the entire surface).Furthermore, it is easy to control the process by increasing the hydrogen content, etc. It can also be applied to

〔Effect of the invention〕

As explained above, the present invention includes two heating blocks that face each other and whose temperatures are controlled independently, and a substrate holder that holds a thin film deposition substrate at a distance from the heating blocks between the two heating blocks. By installing it inside the deposition chamber,
The source gas can be heated to a high temperature by the heating block facing the surface to be deposited on the substrate, and the temperature of the substrate can be controlled by the temperature of the two heating blocks that sandwich the substrate, so the temperature of the source gas and the temperature of the substrate can be adjusted to the desired temperature. There are effects that can be set to values.

In addition, there are two
By holding a substrate for thin film deposition between two heating blocks and performing vapor phase growth with the surface of the substrate facing the heating block on the high temperature side, the temperature of the source gas is lowered to the substrate temperature immediately before film deposition. Since it is possible to advance film deposition at a higher temperature than the above, the state of the raw material gas on the substrate surface can be highly supersaturated, and a smooth thin film with small surface irregularities can be deposited with good reproducibility and uniformity. effective.

Furthermore, since the substrate temperature during thin film deposition can be kept low, selectivity in selective growth of thin films is improved, and reactions and diffusion in the film and underlying substrate during film deposition can be reduced. be.

Furthermore, by using two or more raw material gases having different reaction temperatures, it is possible to deposit an alloy thin film with good film quality controllability such as composition.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing one embodiment of the chemical vapor deposition apparatus according to the present invention, Fig. 2 is a block diagram showing another embodiment of the apparatus, and Fig. 3 is a reactor in the apparatus shown in Fig. 2. 4 is a cross-sectional view illustrating an embodiment of the chemical vapor deposition method according to the present invention, and FIG. 5 is a graph showing the state of aluminum deposition in the method according to the present invention. , Fig. 6 is a photograph of the metal structure of aluminum deposited on a silicon substrate using the method according to the present invention, Fig. 7 is a cross-sectional view showing a through hole when aluminum is selectively grown on a barrier layer, and Fig. 8 9 is a cross-sectional view showing an example of application of the method according to the present invention, FIGS. 10 and 11 are photographs of metal structure showing the initial stage of aluminum growth, and FIG.
Figure 2 is a photograph of the metal structure of aluminum deposited on a silicon substrate using a conventional method. 1...Deposition chamber, 2...Wafer loading/unloading chamber, 3...
Raw material chamber, 4.5... Valve, 6... Variable valve,
7... Substrate holder, 8... Wafer substrate, 9... Heater, 10° 14... Heating block, 11... Cylindrical tube, 12... Orifice, 13... Stirring motor, 1
5... Triisobutylaluminum.

Claims (3)

[Claims] (1) Two heating blocks facing each other whose temperature is controlled independently, and the thin film deposition substrate being positioned between the two heating blocks at a distance from each of the two heating blocks. A chemical vapor deposition apparatus comprising a substrate holder for holding a deposition substrate in a deposition chamber. (2) A step of cleaning the semiconductor surface or conductor surface of a substrate having a semiconductor surface or conductor surface and an insulator surface; Between two heating blocks facing each other, the semiconductor surface or conductor surface side is placed between the two heating blocks facing each other.
holding the heating block facing the higher temperature side of the two heating blocks, and introducing a compound gas containing at least metal to selectively deposit a metal film only on the semiconductor surface or the conductor surface. A method of using a chemical vapor deposition apparatus characterized by: (3) A substrate for thin film deposition is held between two closely facing heating blocks that are maintained at different temperatures so that its thin film deposition surface faces the higher temperature side of the two heating blocks. A method of using a chemical vapor deposition apparatus, characterized in that an aluminum film containing silicon is deposited on the surface of the substrate for thin film deposition by simultaneously introducing at least an organic aluminum compound gas and a silicon hydride gas.