Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2001-01-19
2002-02-19
Ghyka, Alexander G. (Department: 2812)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S396000, C438S653000
Reexamination Certificate
active
06348376
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating semiconductor devices, and more particularly, to a method of forming a metal nitride film by chemical vapor deposition (CVD) where a metal source and a nitrogen source are used as a precursor, and a method of forming a metal contact and a capacitor of a semiconductor device using the above method.
2. Description of the Related Art
A barrier metal layer, which prevents mutual diffusion or chemical reaction between different materials, is indispensable to stabilize the contact interfaces of semiconductor devices. In general, a metal nitride such as TiN, TaN or WN has been widely used as the barrier metal layer of semiconductor devices. Here, TiN is a representative example among the above metal nitrides.
However, when the metal nitride film such as TiN is fabricated by sputtering, its application to highly integrated semiconductor devices is not appropriate, due to low step coverage. For an example,
FIGS. 9A and 9B
show the cross-section of a via contact for connection between metal wiring.
FIGS. 9A and 9B
show a simple via contact and an anchor via contact, respectively. The formation processes thereof are as follows. A first metal layer
30
composed of aluminum (Al) is formed on a semiconductor substrate
20
. A TiN film
40
is formed as a capping film on the resultant structure by sputtering, and then an interlayer insulative film
50
or
51
is deposited. A contact hole is formed by etching the interlayer insulative film
50
or
51
on the first metal layer
30
. In
FIG. 9B
, the step of forming an anchor A by wet etching is added. After Ti as an adhesive layer and TiN
60
or
61
as a barrier metal layer is deposited, a tungsten (W) plug
70
or
71
is formed to fill the contact hole, by CVD. Thereafter, tungsten at the upper portion is removed by chemical mechanical polishing or etch-back, and then a second metal layer is deposited on the resultant structure, thereby completing the connection between metal wiring. However, this last step is not shown.
Here, in a conventional method, the TiN film
60
or
61
, being the barrier metal layer, is deposited by sputtering, with inferior step coverage. Here, the thickness of a TiN film on the bottom, corner and anchor A of the contact hole is reduced, with an increase in the aspect ratio of the via. Accordingly, at a thin portion, Ti or Al combines with fluorine remaining in tungsten source gas WF
6
during tungsten deposition being a subsequent process, and thus an insulative film X is formed of TiF
x
or ALF
x
, leading to a contact failure.
When the contact failure is avoided by increasing the deposition time to increase the thickness of the TiN film
60
or
61
, the thickness of the TiN film increases only at the upper portion of the contact hole, and the upper portion of the contact hole is narrowed or blocked. Thus, voids are likely to be generated upon subsequent tungsten deposition. A process with improved step coverage is required to apply TiN to a contact with a high aspect ratio. Accordingly, a process for fabricating a metal nitride film using CVD (hereinafter called a CVD-metal nitride film) has been developed as a next generation process.
A general process for forming a CVD-metal nitride film uses a metal source containing chlorine (Cl), e.g., a precursor such as titanium chloride TiCl
4
. The CVD-metal nitride film using TiCl
4
as the precursor has a high step coverage of 95% or higher and is quickly deposited, but Cl remains in the metal nitride film as impurities. The Cl remaining as impurities in the metal nitride film causes corrosion of metal wiring such as Al and increases resistivity. Thus, the Cl content in the metal nitride film must be reduced and the resistivity must be lowered, by deposition at high temperature. That is, in the CVD-metal nitride film process using the metal source such as TiCl
4
, a deposition temperature of at least 675° C. is required to obtain resistivity of 200 &mgr;&OHgr;-cm or less. However, a deposition temperature of 600° C. or more exceeds thermal budget and thermal stress limits which an underlayer can withstand. In particular, when the metal nitride film is deposited on an Si contact or a via contact with an Al underlayer, a deposition temperature of 480° C. or lower is required, so that a high temperature CVD-metal nitride film process cannot be used.
A low temperature deposition CVD-metal nitride film process is possible, by adding MH (methylhydrazine, (CH
3
)HNNH
2
) to the metal source such as TiCl
4
, but this method has a defect in that step coverage is decreased to 70% or lower.
Another method capable of low temperature deposition is to form a MOCVD-metal nitride film using a metalorganic precursor such as TDEAT (tetrakis diethylamino Ti, Ti(N(CH
2
CH
3
)
2
)
4
), or TDMAT (tetrakis dimethylamino Ti, Ti(N(CH
3
)
2
)
4
). The MOCVD-metal nitride film has no problems due to Cl and can be deposited at low temperature. However, the MOCVD-metal nitride film contains a lot of carbon (C) as impurities, giving high resistivity, and has inferior step coverage of 70% or less.
A method of forming a metal nitride film using atomic layer epitaxy (ALE) has been tried as an alternative to deposition, in order to overcome the problems due to Cl. However, the ALE grows the metal nitride film in units of an atomic layer using only chemical absorption, and the deposition speed (0.25 A/cycle or less) is too slow to apply the ALE to mass production.
A TiN film is also used as the electrode of a semiconductor capacitor. In particular, the TiN film is usually used in a capacitor which uses tantalum oxide (Ta
2
O
5
) as a dielectric film. Semiconductor capacitors, which use the TiN film as an electrode, also have the above-described problems.
That is, in order for a semiconductor capacitor to have a high capacitance per unit area of a semiconductor substrate, its electrode is designed three-dimensionally, as in cylindrical capacitors. Hence, the shape of the semiconductor capacitor is so complicated that it is critical to guarantee step coverage of deposited materials as its electrode. Accordingly, a TiN electrode formed by CVD using a Cl-containing metal source having an excellent step coverage as a precursor has been used as the electrode of a capacitor. However, as described above, the CVDed TiN film provokes corrosion of metal wiring and gives high resistivity, due to a high concentration of Cl, resulting in a degradation in the leakage current characteristics of a capacitor.
SUMMARY OF THE INVENTION
To solve the above problems, an objective of the present invention is to provide a method of forming a metal nitride film, which gives excellent step coverage even at a high deposition speed and a low temperature, low impurity concentration, and low resistivity.
Another objective of the present invention is to provide a method of forming a metal contact having a barrier metal layer which has excellent step coverage even at a high deposition speed and a low temperature, low impurity concentration, and low resistivity, by applying the metal nitride film formation method to a metal contact of a semiconductor device.
Still another objective of the present invention is to provide a method of forming a capacitor which gives excellent step coverage, low impurity concentration and low resistivity, using the metal nitride film formation method.
Accordingly, to achieve the first objective, there is provided a method of forming a metal nitride film using chemical vapor deposition (CVD) in which a metal source and a nitrogen source are used as a precursor. In this method, first, a semiconductor substrate is introduced into a deposition chamber, and the metal source flows into the deposition chamber. After a predetermine time, the flow of the metal is stopped, and a purge gas is introduced into the deposition chamber. After a predetermined time, the purge gas is cut off and the nitrogen source gas flows into the deposition chamber to react with the metal source adsorbed on the semic
Choi Gil-Heyun
Jeon In-Sang
Kang Sang-Bom
Lim Hyun-Seok
Ghyka Alexander G.
Marger & Johnson & McCollom, P.C.
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