JPH04320332A - Thin film formation method - Google Patents

Abstract

PURPOSE:To form selectively a good quality of thin film on a substrate in a specified region. CONSTITUTION:In a thin film formation method which forms a thin film by introducing a raw gas and absorbing a compound on a substrate by chemical reaction, A CuN compound, which is electrically polarized as the compound, is used whereas Cu atoms of the CuN compound is selectively introduced to upper electrodes 17 and 19 on the substrate by means of electric power.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a thin film, and more particularly to an improvement in a method for forming a thin film using a CVD method.

0002

[Prior Art] Semiconductor devices such as VLSIs generally have a structure in which a conductive thin film for flowing charge and transmitting electrical signals and an insulating thin film for electrically insulating the conductive thin films are stacked. doing. The conductive thin film is usually made of Al・S
It is formed by patterning a thin film of i.Cu alloy, polycrystalline Si added with impurities such as As, WSi2, or the like.

High integration of semiconductor devices such as VLSIs has been achieved mainly by miniaturization of elements. For example, ultra large memory such as IMDRAM, 256KSRAM, etc.
SIs are manufactured with gate lengths reduced to 1 to 1.2 μm, and further attempts are being made at the laboratory level to create highly integrated ULSIs with gate lengths on the order of submicrons.

However, if an element with dimensions of this order is reduced in both the vertical and lateral directions according to the scaling law, the performance and reliability of the element will deteriorate, so miniaturization is mainly achieved by reducing the lateral dimension. It has been realized.

That is, since the wiring resistance is proportional to the cross-sectional area,
If the horizontal dimension is reduced, the resistance value will be smaller if the vertical dimension is not reduced, which is advantageous in terms of performance improvement. In addition, when the vertical dimension is reduced, the current density increases significantly, so when electrons flow in the wiring, the atoms that make up the wiring, for example, Al atoms in the case of Al wiring, are transported and the line width of the wiring becomes narrower. A phenomenon occurs in which the wiring becomes disconnected (electro migration). Because of this, in order to increase the cross-sectional area as much as possible, vertical reduction of the conductive thin film has generally not been actively carried out.

[0006] In the case of insulating thin films as well, thinning has not been actively pursued from the viewpoint of ensuring voltage resistance between multilayer interconnections and suppressing crosstalk.

[0007] As described above, from the viewpoint of maintaining the reliability and reliability of VLSIs, each thin film cannot be rapidly thinned.

As a result, the surface of a VLSI exhibits an uneven shape. For example, in a VLSI based on submicron design standards, wiring is formed at a pitch of 0.5 μm or less, and the spaces between them are filled with an insulating film. As a result, the surface shape becomes extremely uneven.

Furthermore, in order to increase the degree of integration of semiconductor devices,
A sharp rectangle is adopted as the shape of each wiring. When the shape of the wiring becomes steep in this way, the shape of the insulating film deposited on it also becomes steep.

When the next layer of conductive film is sputter-deposited on the surface of such a base insulating film, the conductive film becomes extremely thin at the bottom of the step, which is called a step cut.
In severe cases, it may break off and accumulate. This phenomenon is particularly noticeable at the bottom of the connection hole, and in extreme cases when the connection hole is narrow and deep, no conductive thin film is deposited at all at the bottom of the connection hole. For example, in a 16MDRAM, the opening diameter is expected to be 0.5 μm and the depth to be around 1.5 μm. In this case, the aspect ratio will be around 3, and with normal sputtering, the Al alloy film will be at the bottom of the connection hole. It has been confirmed through experiments that it does not accumulate.

The non-uniformity of the thickness of the conductive thin film at the bottom of the step or the bottom of the connection hole is caused by the fact that it is formed by sputtering. For sputtering, the film deposition rate is
It is approximately proportional to the viewing angle at that point. For this reason, the deposition rate becomes extremely slow at the bottom of a step or the bottom of a connection hole where the angle of view is extremely small, and a relatively thin conductive thin film is formed, resulting in an uneven film thickness.

Similar difficulties arise with insulating thin films. That is, it becomes difficult to uniformly create spaces between wirings using an insulating thin film, and an overhang phenomenon occurs. Once this phenomenon occurs, the reaction gas no longer enters the groove once the protruding insulating thin film at the top of the wiring is connected. As a result, a cavity called a "cavity" is created in the insulating thin film that has created the space.

[0013] When a thin film is further formed on the uneven surface of the thin film, such as the surface of the VLSI described above, uniformity of the film thickness becomes important. In order to solve the above-mentioned problems in forming thin films, the emergence of a technique for forming thin films with uniform thickness has been awaited.

[0014] In recent years, as a method for depositing a conductive thin film with a uniform thickness, research has been actively conducted on a method of depositing a metal film by low pressure chemical vapor deposition (LPCVD). According to this method, by reducing the pressure of the system, the so-called "wrap-around" effect of the source gas becomes noticeable, and the source gas is sufficiently supplied to the bottom of the step, making it possible to obtain a thin film with excellent step coverage. . For example, WSi2 thin films have been put into practical use to reduce the resistance of DRAM bit lines. That is, lower resistance can be achieved by using a WSi2 thin film formed by LPCVD instead of the impurity-doped Si film of the DRAM bit line, or by forming a WSi2 thin film on the Si film.

Conventionally, when forming a conductive thin film using the CVD method, there were problems in controlling the film quality, removing impurities, and oxidizing the surface, but recently, the purity of the raw material gas has been improved, and load lock has been achieved. CVD equipment with added mechanisms has also been developed, which has reduced the problem of surface oxidation.

However, with the CVD method, it is still difficult to form a thin film of uniform quality on the bottom of the groove, so when etching using dilute hydrofluoric acid, etc., the etching rate of the thin film on the bottom of the groove is lower than that of the thin film on the flat part. The problem was that it was difficult to etch uniformly.

[0017] As a method for uniformly depositing a thin film on the bottom of the groove and the lower part of the connection hole, there is a method using selective growth of the thin film. Selective thin film growth refers to a phenomenon in which a desired thin film can be deposited only on a specific base surface by vapor phase growth using a specific material under specific conditions.Currently, the material used is tungsten, a high melting point metal. (W), molybdenum (Mo
), titanium silicide (TiSi2), tantalum silicide (TaSi2), aluminum (Al), copper (Cu), single crystal Si, etc. have been reported.

[0018] Such a vapor phase growth method is called a selective CVD method, and it is possible to uniformly deposit a thin film from the bottom to the top of the step portion and connection hole. It is possible to reduce the aspect ratio and flatten the substrate surface.

[0019] As the design rule becomes smaller, fine patterning and etching become difficult. Therefore, the selective CVD method, which deposits the required amount of thin film at the required location, is promising as a thin film forming technology for future VLSIs.

[0020] Furthermore, if the shape of the base is determined in some way, the selectively deposited film can be positioned with the base in a self-aligned manner to select the base, and so-called misalignment of the mask can be avoided. There is no need to think about it, and it is promising both from the viewpoint of increasing the degree of integration and from the viewpoint of increasing the reliability of the device.

However, the conventional selective CVD method utilizes a surface chemical reaction, which is difficult to control, and has not been put to practical use.

[0022] As a method for selectively forming a thin film without using the CVD method, there is a method using plating. In this method, a substrate is immersed in a solution containing a chemical species for depositing a thin film, and a thin film is selectively deposited on a specific underlying surface of the substrate by an electrochemical method. A thin film of Cu or the like has been realized by this method.

However, this method has not been put into practical use due to the purity of the plating solution, the purity of the deposited thin film, and the limited number of substrates on which the Cu film can be deposited.

[0024]

[Problems to be Solved by the Invention] As mentioned above, various conventional thin film forming methods have been observed to have certain effects and are considered promising, but their drawbacks have also become noticeable, and no method has yet been considered a favorite. .

The present invention has been made in consideration of the above circumstances, and its object is to provide a thin film forming method that can form a high quality thin film on a predetermined region of a substrate.

[0026]

The gist of the present invention is to guide predetermined atoms of an electrically polarized compound to a predetermined region on a substrate by electric force to grow a thin film.

That is, in order to achieve the above object, the thin film forming method of the present invention involves introducing a raw material gas and adsorbing a compound onto a substrate through a chemical reaction to form a thin film. It is characterized by using an electrically polarized compound as the compound and selectively guiding predetermined atoms of the compound to a predetermined region on the substrate by electric force.

[0028] In order to guide the predetermined atoms of the electrically polarized compound to a predetermined region on the substrate by electric force, it is desirable to conduct this by charging the predetermined region on the substrate.

Note that in order to guide predetermined atoms of the electrically polarized compound to a predetermined region on the substrate by electric force, it is preferable to place the substrate in an electric field.

[0030]

[Operation] Since the thin film forming method of the present invention uses an electrically polarized compound, it is possible to selectively guide predetermined atoms of the compound to a predetermined region on a substrate by electric force.

[0031] Therefore, a thin film having uniform thickness and quality can be easily deposited in a desired region.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below with reference to the drawings.

FIG. 1, FIG. 2, and FIG. 3 each illustrate the first aspect of the present invention.
A cross-sectional view in the thickness direction of a sample substrate 25 used in the method of forming a Cu thin film according to the embodiment, a cross-sectional view at the lower electrode part,
FIG. 3 is a cross-sectional view of the upper electrode section.

[0034] To explain this according to the forming process, first,
A thermal oxide film 3 having a thickness of approximately 0.2 μm is formed on a silicon substrate 1.

Next, after depositing an Al film with a thickness of about 0.5 μm on this thermal oxide film 3 using a sputtering method, this Al film is patterned to form a lower electrode 5 having a shape as shown in FIG. 7 and an external power source are formed, and a lower electrode part 13 is formed on the thermal oxide film 3.

Next, a silicon dioxide film 15 with a thickness of about 0.1 μm is formed on the entire surface using a plasma CVD method, and then an Al film with a thickness of about 0.5 μm is formed on this silicon dioxide film 15 using a sputtering method. and deposit. Then this Al
The film is patterned to form lower electrodes 5 and 7 as shown in FIG.
Upper electrodes 17 and 19 facing each other are formed, and an upper electrode portion 21 is formed on the silicon dioxide film 15.

Finally, the electrode extraction portion 9 of the lower electrode portion 13 is formed using photolithography and reactive sputtering.
, 11 are provided with connection holes 23 in the silicon dioxide film 15 to complete the sample substrate 25.

The sample substrate 25 formed as described above is carried into a CVD apparatus to form a film.

FIG. 5 is a schematic sectional view showing the structure of this CVD apparatus. A susceptor 31 on which a sample substrate 25 is placed is housed inside the film forming chamber 29, and the sample substrate 25 is placed on top of the susceptor 31. A heat source 33 made of, for example, a heater is provided inside the susceptor 31 to heat the sample substrate 25 .

At the upper part of the film forming chamber 29, there is a discharge electrode 35 made of stainless steel that faces the susceptor 31 and is movable up and down.
A charging member is inserted through the opening of the discharge electrode 35, moves up and down, contacts the electrode extraction parts 9 and 11 of the lower electrode part 13, and charges the electrode extraction parts 9 and 11 to different polarities. electrodes 37 and 39 are provided.

Outside the film forming chamber 29, a gas supply section 41,
A gas exhaust section 43 is provided. The gas supply section 41 includes a stainless steel BCl3 cylinder, a copper nitride (CuN) cylinder, an N2 cylinder, and the like.

The BCl3 cylinder is connected to the film forming chamber 29 via a pipe 45. The BCl3 gas is introduced into the film forming chamber 29 through a valve 47 provided in the pipe 45.
Controlled by opening and closing. Similarly, pipes 49 and 53 and valves 51 and 55 are provided for the CuN cylinder and the N2 cylinder, respectively.

[0043] The gas exhaust section 43 consists of an exhaust pump, etc.
It is connected to the film forming chamber 29 via a gate valve 57.

Next, the CVD apparatus 27 configured as described above
A method for forming a Cu film using the following will be explained.

First, the gate valve 57 is opened and the gas in the film forming chamber 29 is exhausted by the gas exhaust section 43.
Reduce the pressure inside 9 to about 1 x 10-7 Torr or less.

Next, the valve 47 is opened and the gas supply section 41 is
Cl3 gas is introduced into the film forming chamber 29, and a high frequency voltage is applied between the discharge electrode 35 and the susceptor 31 to generate a discharge, thereby removing the surfaces of the upper electrodes 17 and 19. This is a process for removing the damaged layer and natural oxide film generated during patterning of the Al film. Note that for this purpose, for example, Ar plasma is generated and Ar
Other methods may be used, such as removing the surfaces of the upper electrodes 17 and 19 using ions.

Next, the valve 45 is closed and the gas in the film forming chamber 29 is exhausted again by the exhaust section 43, and after the pressure in the film forming chamber 29 is reduced to 1×10 −7 Torr or less, a voltage is applied to the heating source 33 . The sample substrate 25 is heated to bring the surface temperature of the sample substrate 25 to 350°C.

Next, after lowering the charging electrodes 37 and 39 and bringing them into contact with the electrode extraction parts 9 and 11 of the sample substrate 25, respectively, the charging electrodes 37 and 39 are removed by a DC power source (not shown). 39 +100V, -10 respectively
Apply a DC voltage of 0V. As a result, positive charges and negative charges are induced on the surfaces of the upper electrodes 17 and 19 of the sample substrate 25, respectively, due to electrostatic induction. Note that the state at this time can be represented by the electrical circuit diagram shown in FIG.

Next, the C in the CuN cylinder of the gas supply section 41
In order to increase the vapor pressure of uN and prevent recondensation in the pipe 49, the CuN cylinder and the pipe 49 are heated with a heater and maintained at 250°C, and the surface temperature of the sample substrate 25 is raised to 3.
After confirming that the temperature has stabilized at 50°C, open valve 51 and
CuN gas is introduced into the film forming chamber 29 using r as a carrier gas, and this state is maintained for 30 minutes to form a Cu thin film. At this time, the pressure inside the film forming chamber 29 is 1×10−
It was about 3 to 1×10 −2 Torr.

Next, after closing the valve 51 and stopping the supply of CuN/Ar gas, the gate valve 57 is opened and the gas in the film forming chamber 29 is exhausted by the gas exhaust section 43 to reduce the pressure in the film forming chamber 29. Maintain the pressure below 1×10 −7 Torr for 10 minutes.

Finally, after closing the gate valve 57, the valve 55 is opened to introduce dry N2 gas into the film forming chamber 29, and the pressure in the film forming chamber 29 is brought to about atmospheric pressure, thereby completing the formation of the Cu thin film.

When the sample substrate 25 that had undergone the above steps was taken out and looked at, it was confirmed visually that a thin film had been deposited on the upper electrodes 17 and 19 of the sample substrate 25 from a change in color.

Next, this Cu thin film was examined by quantitative analysis and qualitative analysis, and it was found that carbon was present on the upper electrodes 17 and 19.
A thin Cu film was deposited on the electrode plates 17 and 19, and the thicknesses of the Cu thin films on the electrode plates 17 and 19 were both approximately 0.5 μm, which coincided within experimental error.

However, the N content in the Cu thin film deposited on the upper electrode 17 (positively charged) is lower than the N content in the Cu thin film deposited on the upper electrode 19 (negatively charged). It was also 30 to 50 times more common.

Next, a method for forming a Cu thin film according to a second embodiment of the present invention will be described.

This embodiment differs from the first embodiment described above by changing the charging state of the upper electrodes 17 and 19.
The reason is that a u thin film was formed.

That is, only the charging electrode 39 is connected to the sample substrate 25.
After the upper electrode 19 was brought into contact with the electrode extraction part 11, a voltage of -100V was applied to the electrode extraction part 11 to charge the upper electrode 19 with a negative charge to form a film.

When the Cu thin film obtained in such a charged state was examined, a Cu thin film with a thickness of about 0.1 μm was formed on the upper electrode 17 (uncharged), and a Cu thin film with a thickness of about 0.1 μm was formed on the upper electrode 19 (negatively charged). ) A thin Cu film with a thickness of about 0.5 μm was formed on the top.

The facts shown in the first and second embodiments described above can be considered as follows. The electronegativities of Cu and N are 1.9 (Cu) and 3.0 (N), respectively, so in a CuN compound, the N atom is δ- and the Cu atom is δ+.
The CuN compound as a whole forms an electric dipole.

Therefore, when the upper electrode 17 is positively charged and the upper electrode 19 is negatively charged as in the first embodiment, the CuN compound becomes as shown in FIGS. 6(a) and 6(b). It is attached to the surfaces of the upper electrodes 17 and 19 in such a manner that it is exposed. That is, due to electrostatic attraction, Al atoms on the surface of the upper electrode 17 and C
The N atom of the uN compound is preferentially bonded to the upper electrode 19.
The Al atoms on the surface of the CuN compound bond preferentially to the Cu atoms of the CuN compound.

However, the surface temperature of the sample substrate 25 (
350℃) is the decomposition temperature of the CuN compound (approximately 300℃)
Since it is higher, the CuN compound gradually decomposes. At this time, the N atoms on the upper electrode 17 whose surface is positively charged are sandwiched between the Al atoms and Cu atoms on the surface of the sample substrate 25 and are difficult to desorb. The content of N atoms in the Cu thin film deposited increases.

On the other hand, the upper electrode 1 whose surface is negatively charged
Since the N atoms on the upper electrode 9 face the vacuum side, the N atoms are likely to bond with each other and desorb, so that the content of N atoms in the Cu thin film deposited on the upper electrode 19 decreases.

Furthermore, as in the second embodiment, the upper electrode 17
When is uncharged and the upper electrode 19 is negatively charged, the thickness of the Cu film deposited on the upper electrode 17 is determined by the adhesion probability between the CuN compound and the Al atoms on the surface of the upper electrode 17, which is determined by the substrate temperature. Almost decided. That is, the CuN compound and the sample substrate 2
The effect of promoting Cu film deposition due to electrostatic attraction between the two surfaces disappears. Therefore, a Cu thin film with a thickness of about 0.5 μm is deposited on the upper electrode 19 whose surface is negatively charged, whereas a Cu thin film with a thickness of about 0.1 μm is deposited on the uncharged upper electrode 17.
Only the u thin film will be deposited.

Next, a method for forming a Cu thin film according to a third embodiment of the present invention will be described.

FIG. 7(a) shows a cross-sectional view of the sample substrate 25 used in this example. Note that the sample substrate 2 in FIG.
Portions corresponding to 5 are designated by the same reference numerals as in FIG. 1, and detailed description thereof will be omitted.

To explain the formation process of this sample substrate 25, first, a thermal oxide film 3 with a thickness of about 0.2 μm is formed on a silicon substrate 1. Next, an Al film is deposited on the thermal oxide film 3 using a sputtering method, and then a portion of the Al film around the substrate is removed to form an electrode plate 59 having a shape as shown in FIG. 7(b).

Next, the charging electrode 37 of the CVD device 27 is
The charging electrode 37a is replaced with a charging electrode 37a having a partially chipped disk-shaped electrode as shown in FIG. 8(a). This charging electrode 37a
The disc-shaped electrode part is made of stainless steel and has a thickness of approximately 100μ.
m silicon dioxide film is coated. Further, when the charging electrode 37a is lowered, it is placed so as to contact the electrode plate 59 as shown in FIG. 8(b).

Next, after placing the sample substrate 25 on the susceptor 31 of the CVD apparatus modified as described above, the gas in the film forming chamber 29 is evacuated as in the first embodiment, and the sample substrate is removed by plasma. The damaged layer and natural oxide film of the electrode 59 of No. 25 are removed. At this time, the charging electrode 37a is connected to the electrode plate 59 so that the plasma is not affected by the charging electrode 37a.
The electrode 59 is evacuated to a position where it does not overlap so that the entire surface of the electrode 59 is uniformly exposed to plasma.

Next, the sample substrate 25 is heated by the heat source 33 to bring the surface temperature of the sample substrate 25 to 350° C. Once the surface temperature is stabilized, the charging electrodes 37a and 39 are brought into contact with the electrode 59 of the sample substrate 25, and then +10 to charging electrode 37a
While applying a DC voltage of 0 V, the charging electrode 39 was lowered to the ground potential. As a result, negative charges appear on the surface of the electrode 59 facing the charging electrode 37a due to electrostatic induction. Note that the positive charge is transferred to the electrode 59 via the charging electrode 39.
It flows out and disappears.

Thereafter, the charging electrode 39 is separated from the electrode 59, and then the application of voltage to the charging electrode 37a is stopped, and the charging electrode 37a is separated from the electrode 59. As a result,
The electrode 59 is negatively charged.

Finally, a Cu thin film is deposited on the electrode 59 in the same manner as described in the first embodiment.

When the thickness of the Cu thin film on the electrode 59 (negatively charged) obtained by the above method was examined, it was approximately 0.3 μm.
It was confirmed that

FIG. 9(a) shows a cross-sectional view of a sample substrate 25 used in a method for forming a Cu thin film according to a fourth embodiment of the present invention. Note that portions corresponding to the sample substrate 25 in FIG. 1 are given the same reference numerals as in FIG. 1, and detailed description thereof will be omitted.

[0074] To explain this according to the forming process, first,
A thermal oxide film 3 with a thickness of about 0.2 μm is formed on the silicon substrate 1, and then an Al film with a thickness of about 0.5 μm is deposited on the thermal oxide film 3 by sputtering.

Next, the electrode 61 is formed by removing the Al film around the substrate, and then the electrode 61 is formed to a thickness of about 0 using the plasma CVD method.
．． A 2 μm silicon dioxide film 15 is deposited over the entire surface.

Finally, as shown in FIG. 9(b), a connection hole 23 for establishing electrical continuity is provided in the silicon dioxide film 15.

The sample substrate 25 thus obtained was
It is placed on the susceptor 31 of the VD device 27, and a Cu thin film is formed using the same procedure, method, and conditions as in the third embodiment (however, the substrate temperature is changed from 350° C. to 450° C.).

When the Cu thin film obtained by the above method was examined, it was found that the Cu thin film was also deposited on the silicon dioxide film 15, and its thickness was about 0.3 μm.

For comparison, a Cu thin film was formed without charging the electrode plate 61 with a negative charge, and the results were compared between the case where the electrode plate 61 was charged with a negative charge and the case where it was not charged with a negative charge.
Although there was no significant difference between the two in terms of deposition rate,
Regarding the adhesion and adhesion of the Cu thin film to the silicon dioxide film 15, the case where the Cu thin film was negatively charged was far superior.

Next, a method for forming a Cu thin film according to a fifth embodiment of the present invention will be described. This example is the first example described above.
The main difference from the fourth embodiment is that a Cu thin film is formed on the sample substrate 25 in an electric field.

First, a sample substrate 25 as shown in FIG. 10 is prepared.

To explain this according to the manufacturing process, element isolation is performed on the silicon substrate 63 according to the usual method, and MOS
After forming the transistor, a predetermined pattern of an insulating film, for example, an oxide film 65 with a thickness of about 1.4 μm, is placed on the silicon substrate 63.
Form on top.

Next, an Al alloy film is deposited over the entire surface using magnetron sputtering or the like, and then the Al alloy film is patterned using ordinary photolithography and reactive ion etching to form wiring 67 in a predetermined shape.

Finally, a silicon oxide film 69 is deposited as an interlayer insulating film over the entire surface using the plasma CVD method, and
The surface of the silicon oxide film 69 is planarized by resist etchback, lapping, or the like. Next, the interlayer connection hole 7 is formed using photolithography and reactive ion etching.
1 is formed to complete the sample substrate 25.

In the sample substrate 25 thus obtained, in the step of forming the interlayer connection hole 71, the Al alloy film surface 73 at the bottom of the interlayer connection hole 71 was exposed to an etching gas used for reactive ion etching, for example, fluorine. (F), carbon (C
), a damaged layer is formed on the surface 73 of this Al alloy film. Furthermore, the Al alloy film surface 73
Because it is oxidized by oxygen in the air, an oxide film is also formed on it.

Next, the discharge electrode 3 of the CVD apparatus 27 in FIG.
5 is replaced with an electrode that can be water-cooled, a so-called water-cooled electrode. However, one that can move up and down facing the susceptor 31 is used.

Next, the CVD apparatus 27 modified in this way
After placing the sample substrate 25 on the susceptor 31 , the gate valve 57 is opened and the pressure inside the film forming chamber 29 is reduced to 1×10 −7 Torr or less by the gas exhaust section 43 .

Next, after fixing the water-cooled electrode at a position approximately 150 mm away from the surface of the sample substrate 25, BCl3 plasma is generated in the same manner as in the first embodiment to etch the Al alloy film surface 73 and remove the damaged layer. , remove the oxide film.

Next, in order to exhaust plasma gas etc., the pressure inside the film forming chamber 29 is again reduced to 1×10 −7 Torr or less, and then a voltage is applied to the heating source 33 to remove the sample substrate 25 .
is heated to a surface temperature of 350°C.

Next, bring the water-cooled electrode close to the sample substrate 25 side,
After setting the distance between the sample substrate 25 and the water-cooled electrode to 30 mm,
A DC voltage of +1 kV was applied to the water-cooled electrode, and the film forming chamber 29 and susceptor 31 were lowered to earth potential. At this time, care must be taken to prevent discharge from occurring between the water-cooled electrode, the film forming chamber 29, and the susceptor 31.

The strength of the electric field generated in this way cannot be calculated accurately because the effective electrode area of the susceptor 31 cannot be accurately estimated, but it is approximately +300 V between the sample substrate 25 and the water-cooled electrode. A substantially uniform electric field of /cm is applied. In this case, electric lines of force flow from the water-cooled electrode to the sample substrate 25.
running in the direction of

Next, under the same conditions and procedures as in the first example, Cu
N/Ar gas is introduced into the film forming chamber 29, and the sample substrate 25 is
A Cu thin film is deposited on top. At this time, a thin layer of what appeared to be recondensed CuN was locally deposited on the surface of the water-cooled electrode.

FIG. 11 shows a Cu thin film 75 deposited in the region where the interlayer connection hole 71 is located.

The Cu thin film 75 was deposited on the entire surface of the silicon substrate 63, and its thickness was about 0.4 μm on the wiring 67.
Approximately 0.05 on the silicon oxide film 69, which is an interlayer insulating film.
It was μm. That is, the thickness of the Cu thin film 75 is dependent on the underlying layer, and the Cu thin film 75 is preferentially deposited from the exposed Al alloy film surface 73 of the interlayer connection hole 71, that is, from the groove portion.

Further, when the N content in the Cu thin film 75 was examined, it was found to be 8 atomic % or less.

Furthermore, the X-ray diffraction intensity of the Cu thin film 75 was also investigated. As a result, the diffraction intensity in the Miller index (111) direction was strong. That is, the Cu thin film 75 has a Miller index (11
1) was found to be strongly oriented in the direction. When the X-ray diffraction intensity of the bulk Cu thin film was examined, the diffraction intensity ratio in the Miller index (111), (200), and (220) directions was 1:0.46:0.20. In other words, the bulk Cu thin film was uniformly oriented in these directions.

As a comparative example, only the susceptor 31 was lowered to the ground potential, -1 kV was applied to the water-cooled electrode, and the direction in which the electric lines of force ran was reversed (from the sample substrate 25 to the water-cooled electrode). A Cu thin film deposition experiment was conducted in the same manner. As a result, the thickness of the Cu thin film did not show dependence on the underlying layer, and the deposition rate of the Cu thin film also became slow. Note that the thicknesses of the Cu thin films deposited on the wiring 67 and the silicon oxide film 69 were both about 0.1 μm. Further, the nitrogen content of the Cu thin film was also higher than that of the above example, and in some cases it was as high as 30 atomic%.

The results of the present example and comparative example described above can be considered as follows.

[0099] The CuN compound basically flows along the region from the high pressure to the low pressure from the outlet of the pipe 51 to the exhaust hole of the exhaust section 43. However, in the sample substrate 25, since the sample substrate 25 is heated and a voltage is applied to the water-cooled electrode, in addition to the pressure difference, there is a diffusion phenomenon based on the concentration difference, the intensity of the electric field, and the electric polarization of the CuN compound. The CuN compound flows toward the surface of the sample substrate 25 according to a force proportional to the product of the strength and the force.

As explained above, in the CuN compound, the N atoms are polarized to δ- and the Cu atoms are polarized to δ+. For this reason, as in this example, lines of electric force flow from the water-cooled electrode to the sample substrate 2.
5, the CuN compound is oriented so that the Cu atoms face the sample substrate 25 side and the N atoms face the vacuum side, so atoms of the CuN compound preferentially appear on the surface of the sample substrate 25. adsorbs to.

[0101] Therefore, when thermal decomposition of the CuN compound occurs, N atoms easily become N2 gas and separate from the sample substrate 25, so it is thought that the N content in the Cu thin film 75 decreases. Furthermore, since a voltage is applied between the water-cooled electrode and the susceptor 31, negative charges are generated on the wiring 67 by electrostatic induction, which is considered to have an additional effect of promoting the deposition of the Cu thin film 75.

[0102] The reason why the Cu thin film 75 with strong orientation was obtained is considered to be because the CuN compound was oriented in an orderly manner and adsorbed to the surface of the sample substrate 25.

On the other hand, in a comparative example experiment in which a Cu thin film was formed with the electric lines of force reversed in direction, the CuN compound was formed so that the N atoms faced the sample substrate 25 side and the Cu atoms faced the vacuum side. Because of the orientation, N atoms preferentially adhere to the surface of the sample substrate 25. Therefore, in this state, even if CuN undergoes thermal decomposition, the N atoms are sandwiched between the Cu atoms and the atoms on the surface of the sample substrate 25.
It is thought that the N atoms became N2 gas and became difficult to separate from the sample substrate 25, and a large number of N atoms came to be included in the Cu thin film.

[0104] Furthermore, the reason why the deposition rate became slower is thought to be because, as mentioned above, N atoms become difficult to separate from the sample substrate 25 as N2 compounds, so N atoms accumulate on the substrate surface and thermal decomposition is suppressed. .

[0105] Also, the reason why a Cu thin film with stronger orientation than a bulk Cu thin film could not be obtained is thought to be because N atoms always exist between Cu atoms and atoms on the surface of the sample substrate 25. It will be done.

Although CuN was used as the source gas in the first to fifth embodiments, similar effects can be obtained by using other source gases, such as copper azide (CuN3).

[0107] Furthermore, although the above first to fifth embodiments have described the case of forming a Cu thin film, the present invention is also applicable to the formation of other thin films, such as titanium hydride (TiH2), titanium bromide (TiBr2), etc. ), tungsten hexafluoride (WF6), tungsten chloride (W
Cl2, WCl4, WCl5, WCl6), tungsten bromide (WBr2, WBr5, WBr6)
), tungsten iodide (WI2, WI3), etc. can also be applied to the formation of a W thin film.

Note that when using titanium or tungsten compounds as the raw material gas, the raw material gas is passed through the film forming chamber 29.
If the sample substrate 25 is partially decomposed by passing it through a high-temperature gas reservoir to form an intermediate whose structure is not symmetrical before being introduced into the sample substrate 25, the charging effect on the surface of the sample substrate 25 and the effect of applying an electric field will be more pronounced.

Further, although aluminum and silicon dioxide are used as the base, other bases such as silicon may be used.

Next, a method for forming a thin film according to a sixth embodiment of the present invention will be explained. This is an application of the present invention to the formation of a titanium silicide film.

First, the CuN cylinder attached to the pipe 49 of the CVD apparatus shown in FIG. 5 is replaced with a stainless steel TiH2 cylinder, and the N2 cylinder attached to the pipe 53 is replaced with a stainless steel SiCl4 cylinder. Further, a water-cooled electrode is used as in the fifth embodiment. Then TiH2
The entire cylinder and piping 49 are heated to 200°C with SiCl4
The entire cylinder and piping 53 are heated to 100°C to
This increases the vapor pressure of H2 gas and SiCl4 gas, and prevents TiH2 gas and SiCl4 gas from recondensing in the piping section.

Next, after placing the sample substrate 25 having the structure shown in FIG. 10 on the susceptor 31, BCl3 plasma is generated using Ar gas as a carrier gas to remove the damaged layer and natural oxide film layer on the surface of the wiring 67. Remove. Next, the heating source 33 was turned on and the sample substrate 25 was heated to a surface temperature of 450°C. At this time, the water-cooled electrode is retracted to a position approximately 20 mm above the sample substrate 25 to prevent the water-cooled electrode from overheating.

Next, a low frequency rectangular voltage as shown in FIG. 12(a) is continued to be applied between the water-cooled electrode and the susceptor 31, and in this state, the valves 51 and 55 are opened to
2 gas and SiCl4 gas are introduced into the film forming chamber 29. Thereafter, the valves 51 and 55 are closed to stop the introduction of TiH2 gas and SiCl4 gas. Furthermore, the application of the rectangular voltage is also stopped.

Finally, the heating source 33 is turned off and the surface temperature of the sample substrate 25 is lowered to room temperature.

[0115] The sample substrate 25 that underwent the above steps was examined using an X-ray diffraction measurement method. As a result, the thickness is approximately 0.5μ
It was confirmed that the titanium silicide film of m was selectively deposited only on the surface of the wiring 67.

Furthermore, when the surface temperature of the sample substrate 25 was set to a higher temperature to form a titanium silicide film, it was confirmed that the titanium silicide film was deposited on the entire surface of the sample substrate 25.

[0117] The composition of the titanium silicide film is determined by the surface temperature of the sample substrate 25, the source gas TiH2 gas,
This could be controlled by changing the flow rate of the SiCl4 gas and the amplitude and period of the rectangular voltage applied between the water-cooled electrode and the susceptor 31.

The reason why the titanium silicide film was selectively formed on the wiring 67 by the above method is considered to be as follows.

[0119] The electronegativity of Ti, H, Si, and Cl is 1.5 (Ti), 2.1 (H), and 1.8 (Si), respectively.
, 3.0 (Cl). Therefore, although covalent bonds are mainly involved in the bonding between atoms of the TiH2 compound and the SiCl4 compound, ionic bonds also make a small contribution. Therefore, TiH2 compound and SiCl4 compound are (δ-)H-Ti(
δ+ )-H(δ-), (δ-)Cl4-Si(
It is polarized like δ+).

By the way, the structure of the SiCl4 compound is Si
Since it has a tetrahedral structure centered on , the electric dipole moment of the SiCl4 compound is small. However, S
The melting point and boiling point of iCl4 are -70℃ and 57.6, respectively.
Both temperatures are low, and some decomposition begins at 100°C, so
When the surface temperature (450° C.) of the sample substrate 25 is set as described above, the bond between the Si atom and the Cl atom of the SiCl4 compound is broken, and a SiCl2 compound having a high polarization effect is formed. This is because the π orbital of the Si atom in the SiCl2 compound is no longer screened by the orbital of the Cl atom, so that the effect of Si(δ+) comes into play.

Therefore, the surface potential of the sample substrate 25 is +
In this case, as shown in FIG. 13(a), the Cl atom of the SiCl2 compound and the H atom of the TiH2 compound form the wiring 6.
selectively adsorbs to 7. However, since the electric dipole moment of the SiCl2 compound is larger than that of the TiH2 compound, the SiCl2 compound is preferentially adsorbed to the wiring 67, and the surface of the wiring 67 is covered with Si atoms (δ+) of the SiCl2 compound. It turns out.

Next, the surface potential on the sample substrate 25 side changes from + to 0.
When the adsorption state of the SiCl2 compound on the wiring 67 remains unchanged, the TiH2 compound and SiCl2
The compounds tend to be adsorbed onto the sample substrate 25 in random orientations. However, due to the influence of Si atoms (δ+) on the surface of the sample substrate 25, the Ti atoms of the TiH2 compound and the Si atoms of the SiCl2 compound are preferentially adsorbed to the wiring 67, as shown in FIG. 13(b). These compounds react with each other because the surface temperature of the sample substrate 25 is as high as 450°C. At this time, the H atoms of the TiH2 compound face the vacuum side. Furthermore, when the surface potential of the wiring 67 is changed from 0 to + again, the Cl atoms of the SiCl2 compound
The Cl atoms are adsorbed toward the surface of 7, and these Cl atoms react with the H atoms and are desorbed in the form of HCl. As a result, SiCl
2. The Si atom of the compound is directly bonded to the Ti atom. By repeating the above mechanism, the wiring 67
A TiSix film is selectively formed thereon.

Next, a method for forming a thin film according to a seventh embodiment of the present invention will be described.

This embodiment differs from the previously described sixth embodiment in that the voltage applied between the water-cooled electrode and the susceptor 31 was changed.

That is, as shown in FIG. 12(b), a rectangular voltage ranging from + to - is applied between the water-cooled electrode and the susceptor 31.

As shown in FIG. 14(a), when the surface potential of the wiring 67 is -, the SiCl2 compound which is the raw material gas has an orientation such that the Si atoms are on the surface side of the wiring 67 and the Cl atoms are on the vacuum side. It approaches the surface of the wiring 67 and is attracted to it. Further, the TiH2 compound, which is another source gas, approaches the surface of the wiring 67 and is adsorbed with an orientation such that the Ti atoms are on the surface side of the wiring 67 and the H atoms are on the vacuum side. however,
The electric dipole moment of the SiCl2 compound is higher than that of Ti.
Since it is larger than that of the H2 compound, the SiCl2 compound is preferentially adsorbed to the surface of the wiring 67. As a result, the surface of the wiring 67 is mainly covered with Cl atoms of SiCl2.

Then, as shown in FIG. 14(b), the wiring 67
When the surface potential of is changed from - to +, the SiCl2 compound approaches the surface of the wiring 67 with an orientation such that Cl atoms are on the surface side of the wiring 67 and Si atoms are on the vacuum side. At this time,
The adsorption state of the SiCl2 compound on the wiring 67 does not change. The SiCl2 compound that approaches the surface of the wiring 67 receives a repulsive force from Cl (δ-) on the surface of the wiring 67, so that adsorption to the wiring 67 is suppressed.

On the other hand, the TiH2 compound approaches the surface of the wiring 67 with an orientation such that the H atoms are on the surface side of the wiring 67 and the Ti atoms are on the vacuum side. When the TiH2 compound approaches the surface of the wiring 67, Cl atoms (δ-) on the surface of the wiring 67
is combined with the H atom (δ+) of the TiH2 compound to form H
The Ti atoms escape from the wiring 67 in the form of Cl, and as a result, the Ti atoms come to be directly bonded to the Si atoms. Furthermore, wiring 6
When the surface potential of the wiring 67 is changed from + to - again, Si (δ+) of the SiCl2 compound is adsorbed toward the surface of the wiring 67, and this Si atom is directly bonded to the Ti atom. By repeating the above mechanism, a high quality titanium silicide film (TiSix) with a low Cl content is selectively formed on the surface of the wiring 67. This titanium silicide film has a lower chlorine content and is of better quality than the titanium silicide film formed in the sixth embodiment.

Note that the valves 51 and 55 may be replaced with piezo valves, and the source gas may be introduced intermittently by opening and closing the piezo valves in synchronization with the frequency of the voltage applied between the water-cooled electrode and the susceptor 31.

That is, when the voltage is negative, only SiCl2 gas is introduced to prevent the adsorption of Ti(δ+) atoms in TiH2 gas, and when the voltage is positive, only TiH2 gas is introduced to prevent the adsorption of Ti(δ+) atoms in SiCl2 gas. By preventing adsorption of δ−) atoms, impurities contained in the titanium silicide film can be drastically reduced.

In the sixth and seventh embodiments, SiCl4 was used as the source gas for Si and TiH2 was used as the source gas for Ti, but similar effects can be obtained by using other source gases. For example, monosilane, disilane, and their halides may be used instead of SiCl4.

[0132] Also, instead of TiH2, tungsten fluoride (WF6), tungsten chloride (WCl2, W
A tungsten silicide film is formed by using tungsten bromide (WBr2, WBr5, WBr6), tungsten iodide (WI2, WI3), etc., and monosilane, disilane, and their halides. can do. In this case as well, the same effects as in the case of forming a titanium silicide film can be obtained.

Furthermore, copper nitride (CuN) and copper azide (CuN)
After depositing a Cu film using N3) etc., titanium hydride (
A Ti film could be deposited using TiH2), titanium bromide (TiBr2), etc., and the same effect as in the above-mentioned example of depositing a Cu thin film was obtained.

In particular, when these titanium or tungsten compounds are used as raw material gases, the raw material gases are partially decomposed by passing them through a high temperature gas reservoir before being introduced into the film forming chamber 29, so that they have a structure like SiCl2. When an intermediate with broken upper symmetry was formed, the effect of electric field application was more pronounced.

Furthermore, in the above embodiment, the waveform of the voltage applied between the water-cooled electrode and the susceptor 31 was rectangular;
Other shapes may be used as long as a predetermined electric field is generated. Note that the electric field referred to here is an electric field of a magnitude that does not cause discharge between the electrodes, and is different from the electric field generated in a normal plasma film forming apparatus.

[0136] In addition, various modifications can be made without departing from the gist of the present invention.

[0137]

As described above, according to the thin film forming method of the present invention, a compound can be easily guided to a predetermined region on a substrate in a predetermined orientation, so that a high quality thin film with few impurities can be formed on the substrate. It can be deposited in a predetermined area.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a sample substrate according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the shape of a lower electrode part.

FIG. 3 is a diagram showing the shape of an upper electrode part.

FIG. 4 is a diagram showing a state in which the upper electrode is charged with electric charge due to electrostatic induction.

FIG. 5 is a schematic configuration diagram of a CVD apparatus according to a first embodiment of the present invention.

FIG. 6 is a diagram showing how a CuN compound is attached to the upper electrode.

FIG. 7 is a diagram showing a sample substrate used in a third embodiment of the present invention.

FIG. 8 is a diagram showing a charging electrode used in a third embodiment of the present invention.

FIG. 9 is a diagram showing a sample substrate used in a fourth embodiment of the present invention.

FIG. 10 is a diagram showing a sample substrate used in a fifth embodiment of the present invention.

FIG. 11 is a diagram showing the deposition state of a Cu thin film.

FIG. 12 is a diagram showing a waveform of a voltage applied between a water-cooled electrode and a susceptor.

FIG. 13 is a diagram showing how TiH2 compounds and SiCl2 compounds are adsorbed onto the wiring surface in the sixth embodiment of the present invention.

FIG. 14 is a diagram showing how TiH2 compounds and SiCl2 compounds are adsorbed onto the wiring surface in the seventh embodiment of the present invention.

[Explanation of symbols]

1... Silicon substrate, 3... Thermal oxide film, 5, 7... Lower electrode,
9, 11... Electrode extraction part, 13... Lower electrode part, 15...
Silicon dioxide film, 17, 19... Upper electrode, 21... Upper electrode part, 23... Connection hole, 25... Sample substrate, 27... CVD
Apparatus, 29... Film formation chamber, 31... Susceptor, 33... Heat source, 35... Electrode for discharge, 37, 37a, 39... Electrode for charging, 41... Gas supply section, 43... Gas exhaust section, 45, 49,
53... Piping, 47, 51, 55... Valve, 57... Gate valve, 59, 61... Electrode, 63... Silicon substrate, 65
...Oxide film, 67...Wiring, 69...Silicon oxide film, 71...
Interlayer connection hole, 73...Al alloy film surface, 75...Cu thin film.

Claims (3)

[Claims] 1. A method for forming a thin film in which a raw material gas is introduced and a compound is adsorbed onto a substrate through a chemical reaction to form a thin film, in which an electrically polarized compound is used as the compound, and a predetermined polarization of the compound is performed by electric force. A method for forming a thin film, the method comprising selectively guiding atoms of to a predetermined region on the substrate. 2. A method for forming a thin film in which a raw material gas is introduced and a compound is adsorbed onto a substrate through a chemical reaction to form a thin film, in which an electrically polarized compound is used as the compound, and a predetermined area on the substrate is A method for forming a thin film, comprising selectively guiding predetermined atoms of the compound to a predetermined region on the substrate by charging the compound. 3. A method for forming a thin film in which a material gas is introduced and a compound is adsorbed onto a substrate by a chemical reaction to form a thin film, in which an electrically polarized compound is used as the compound, and the substrate is placed in an electric field to form a thin film. A method for forming a thin film, comprising selectively guiding predetermined atoms of a compound to a predetermined region on the substrate.