Coating processes – Direct application of electrical – magnetic – wave – or... – Plasma
Reexamination Certificate
1999-03-29
2001-12-04
Meeks, Timothy (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Plasma
C427S574000, C427S575000, C427S579000, C427S255180, C427S255170, C427S255370, C427S255393, C438S787000, C438S788000
Reexamination Certificate
active
06326064
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to plasma-enhanced chemical vapor deposition (PECVD) processes, and more particularly to a PECVD process for growing silicon dioxide on a substrate surface wherein the surface is simultaneously etched such that the grown silicon dioxide layer has a reduced level of intrinsic stress and/or a reduced hydrogen content.
DESCRIPTION OF RELATED TECHNOLOGY
Chemical vapor deposition (CVD) is a process for forming a material layer by the reaction of gas phase reactants at or near a substrate surface. Thermal CVD processes typically rely on heating of the surface in order to promote the reaction(s) which result in formation of compound(s) on the substrate surface. A problem with thermal CVD processes is that the thermal reaction occurs at high temperatures thus requiring heat resistant substrates and it is difficult to control characteristics of the film such as internal stress. Depending on the nature of the deposited material, the surface temperature required for deposition may be as high as about 1000° C. Under a variety of circumstances, it would be desirable to be able to perform such CVD processes at lower temperatures.
In order to reduce the required surface temperatures, a variation of CVD referred to as plasma-enhanced CVD (PECVD) is employed. In PECVD, a radio frequency (RF) discharge converts the gas phase reactants to more reactive free radical species resulting in a plasma. The higher reactivity of the free radical species reduces the energy required for reaction and thus lowers the substrate surface temperature which is necessary to carry out the process. In particular, the specimen chamber includes a radio frequency electrode arranged opposite to the specimen table. Gas is introduced into the specimen chamber which is typically at a pressure of 0.1 to 10 Torr and radio frequency power is supplied to the specimen chamber to produce plasma. To grow a film of silicon nitride, gaseous molecules of SiH
4
and NH
3
can be dissociated into plasma and silicon nitride can be grown on a surface of a specimen substrate on a specimen table heated to 300-500° C. However, dissociation of SiH
4
and NH
3
may not be sufficient, H may be incorporated into the silicon nitride film and/or the Si-N bond may not be sufficient.
In a particular form of PECVD, referred to as electron cyclotron resonance (ECR) CVD, the plasma is established in a separate plasma chamber by the application of microwave energy to reactant molecules maintained within a magnetic field. In an ECR CVD apparatus, plasma is generated by a microwave discharge through electron cyclotron resonance and a thin film can be formed on a specimen surface with the aid of a divergent magnetic field. In this case, molecules in the plasma are activated and reacted on a specimen substrate to form the thin film. The apparatus includes a specimen chamber in which a specimen table is located, a plasma formation chamber separated from the specimen chamber, a microwave introducing window at one end of the plasma chamber and a plasma extracting orifice at the other end of the plasma chamber facing the specimen chamber. A magnetic circuit at the periphery of the plasma formation chamber forms a magnetic flux density necessary to produce ECR. The divergent magnetic field reduces in intensity in a direction towards the specimen chamber. The plasma formation chamber can have a shape and dimensions suitable for forming a microwave cavity resonator and gases can be supplied to the plasma formation and specimen chambers.
Of particular concern to the present invention, PECVD and ECR CVD processes (also referred to hereinafter as plasma CVD processes) may be used for growing silicon dioxide on substrate surfaces, particularly over semiconductor wafers where the silicon dioxide usually forms a dielectric layer between adjacent metallization layers. The use of aluminum in the metallization layers greatly limits the maximum temperature to which the wafers can be exposed. Plasma CVD allows lower processing temperatures to be used compared to thermal CVD processes.
Plasma CVD processes for growing silicon dioxide are very useful because of their low temperature characteristics. However, there are certain limitations on growing silicon dioxide by plasma CVD compared to thermal CVD silicon dioxide deposition. Plasma CVD silicon dioxide films are usually less stable than thermal CVD silicon dioxide films, i.e., the atoms in the plasma CVD films will be present in higher free energy configurations than in the thermal CVD films. Such “high stress” films are undesirable since they can cause wafer deformation, i.e., bowing, which adversely affects subsequent processing steps. Also, plasma CVD silicon dioxide films will typically have higher levels of incorporated hydrogen (as hydroxyl) when hydrogen is present in one of the reactant gases compared to thermal CVD films. Higher hydrogen incorporation is undesirable because it is associated with poor film properties and a high dielectric constant.
The level of stress in plasma CVD films can be reduced by RF sputtering which appears to preferentially remove those atoms in the film that are bound in higher free energy states (least strongly bound) and thus contribute to film stress. Such sputtering, however, cannot be adjusted independently of other process parameters to reduce stress to optimally low levels. Moreover, such sputtering has no significant effect on lowering hydrogen incorporation into the silicon dioxide films.
PECVD processes for growing silicon nitride using feed mixtures containing nitrogen trifluoride (NF
3
), silane (SiH
4
), and nitrogen gas (N
2
) are described in publications such as Chorng-Ping et al. (1988), Journal of Vacuum Science and Technology B, Vol. 6, No. 2, pp. 524-532; Flamm et al. (1987), Solid State Technology, March, pp. 43-44; Fujita et al. (1985), J. Appl. Phys. 57:426-432; Livengood and Hess (1987) Appl. Phys. Lett. 50:560-562; Livengood et al. (1988), J. Appl. Phys. 63:2651-2659; Chang et al. (1987), J. Appl. Phys. 62:1406 et seq.; and Pai et al. (1990), J. Appl. Phys. 68:2442-2449. These processes generally result in the deposition of fluorinated silicon nitride.
Processes for periodically plasma etching a growing PECVD film have been proposed. The etching step(s) would be performed only after the PECVD process has been stopped and the deposition reactants removed.
U.S. Pat. No. 4,401,054 (“Matsuo”) discloses an ECR CVD apparatus wherein gaseous material and microwave power are introduced into a plasma formation chamber to generate plasma by microwave discharge through electron cyclotron resonance. Matsuo discloses that the apparatus can be used to form a thin film of Si, Si
3
N
4
, SiO
2
, MoSi
2
and WSi
2
.
Matsuo discloses several ECR CVD processes for forming thin films. For instance, a Si
3
N
4
film can be formed by introducing N
2
into the plasma formation chamber and SiH
4
into the specimen chamber. Instead of introducing only N
2
into the plasma formation chamber, Ar can be introduced to form a Si film or a mixture of Ar+20% N
2
can be introduced to form a Si
3
N
4
film. A SiO
2
film can be formed by introducing O
2
into the plasma formation chamber and SiH
4
into the specimen chamber. Phosphorus-silicate glass (“PSG”) films can be formed by introducing O
2
into the plasma formation chamber and SiH
4
+PH
3
into the specimen chamber. Molybdenum silicide (MoSi
2
) films can be formed by introducing MoF
6
into the plasma formation chamber and SiH
4
into the specimen chamber. Matsuo also discloses that the ECR CVD apparatus can also be used for plasma etching by introducing gases such as CF
4
.
U.S. Pat. No. 4,481,229 (“Suzuki”) discloses a method of growing a silicon-including film by using a halogenide silicon gas. Suzuki discloses that when Si—N or a-Si films are formed in conventional CVD apparatus of the D.C. glow discharge type and RF discharge type, hydrogen is contained in the deposited film. However, to avoid hydrogen in the Si including film, halogenide silicon gas such as
Denison Dean R.
Weise Mark
Burns Doane , Swecker, Mathis LLP
Lam Research Corporation
Meeks Timothy
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