Semiconductor device

Abstract: An embodiment of the instant invention is a method of controlling the grain size of a deposited material formed over a substrate to a first thickness, the method comprising the steps of: forming a first layer of the material to a second thickness which is less than the first thickness; forming a thin intermediate layer on the first layer, the intermediate layer having a grain structure which is different than the grain structure of the first layer; forming a second layer of the material on the thin intermediate layer to a third thickness which is less than the first thickness such that the first thickness is equal to the sum of the second and third thicknesses. Preferably, the intermediate layer is an interstitial layer. Preferably, the steps of forming the first layer, the thin intermediate layer on the first layer, and the second layer on the thin intermediate layer is repeated at least one time. Preferably, the first and the second layers are comprised of a material selected from the group consisting of: CVD metals, CVD dielectric films and CVD semiconductor films; more specifically, the first and the second layers are comprised of a material selected from the group consisting of. CVD aluminum and CVD polysilicon.

Description: FIELD OF THE INVENTION The instant invention pertains to semiconductor device fabrication and processing and more specifically to controlling grain growth in chemical vapor deposition processing. BACKGROUND OF THE INVENTION In many chemical vapor deposition (CVD) processes, grain size increases with increasing film thickness. This increase in grain size may be problematic since it enhances surface roughness. Enhanced surface roughness is a problem if the film is to be patterned (because errors are introduced in optical patterning) or if the film is being used for contact/via/trench fill (because voids will most likely be formed in small regions to be filled because of the large grain size). In addition, rough films exhibit higher resistivity due to surface roughness induced scattering, and the properties of films deposited on rough films may also be degraded. While many deposition techniques other than CVD (such as plasma assisted deposition and physical vapor deposition) produce films with smaller grain sizes, they do not provide the conformality and stoichiometric control that CVD processes provide. In addition, even though there are some disadvantages to large grain sizes, there are also some benefits. Films with larger grain sizes have lower bulk resistivity and superior electromigration resistance. EP-A-372 861 describes the inhibition of grain growth in metal film formation by CVD by the deposition of an auxiliary layer which causes renucleation of the metal on further deposition. U.S. Patent No. 4 726 983 suppresses electromigration in a sputtered aluminum layer by oxidizing the surface of the growing layer, a procedure that at the same time inhibits grain growth. The procedure is stated to be applicable also to an aluminum layer formed by CVD, but no details are given. There remains a need, however, for a process in which a film's grain size can be controlled, thereby controlling the electromigration resistance of the film, the ability to fill a small structure with the deposited film, and the overall morphology and resistivity of the film. SUMMARY OF THE INVENTION The present invention provides a method of forming an aluminum- or polysilicon-containing coating of a controlled grain size on a substrate which comprises forming on the substrate by chemical vapor deposition (CVD) a first aluminum or polysilicon layer, forming a thin intermediate layer, differing in grain structure from that of the first layer, on the first layer, and forming by CVD on the intermediate layer a second layer of the same material as the first layer, characterized in that the intermediate layer is formed by amorphizing the surface of the first layer or by depositing the same material that forms the first layer by plasma-assisted deposition or by physical vapor deposition. Preferably, the intermediate layer is an interstitial layer. Preferably, the steps of forming the first layer, the thin intermediate layer on the first layer, and the second layer on the thin intermediate layer are repeated at least once. Preferably, the first and second layers are formed to a thickness of 100 to 200 (1000 to 2000 Å ) nm, the intermediate layer being 5 to 50 nm (50 to 500 Å) thick. DETAILED DESCRIPTION OF THE DRAWINGS As was stated above, in many CVD processes grain size of films increases with increasing film thickness. In one embodiment of this invention the grain size of the deposited CVD Al or CVD polysilicon film is controlled by interrupting the CVD process when the grain size becomes unacceptably large, forming (preferably depositing) an intermediate layer (preferably an amorphous/microcrystalline layer) which has a different grain pattern than the CVD film, and then continuing with the CVD process. This may be done a plurality of times to ensure that the grains do not grow too large, and thereby achieve the desired grain size distribution. The intervening film may be formed by amorphizing the surface of the CVD film with a low energy moderate dose implant, or it can be amorphized by physical treatment. Alternatively, the intermediate layer may simply be deposited by plasma assisted deposition or physical vapor deposition (PVD). For example, to control the grain structure of a CVD Al film, the thermal CVD process can be interrupted approximately every 100 nm and a thin (preferably between 5 and 50 nm) Al film, formed by PVD or plasma assisted deposition, may be deposited. The advantage of a plasma-assisted CVD Al film instead of a PVD Al film is that the plasma assisted process can be performed in the same chamber as the CVD Al process, and is, therefore, less likely to affect throughput. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a graph illustrating the reflectance of a CVD Al film (the x-axis represents the thickness of the top layer in a stack and the y-axis represents the reflectance of the CVD Al film). In FIGURE 1, plot 104 illustrates the reflectance of a CVD Al film (whose thickness is given on the x-axis in Å, 10Å being 1 nm) which is formed on top of a 500Å thick TiN film. Plot 102 illustrates the reflectance of a CVD Al film (whose thickness is given on the x-axis in Å) which is formed on a 3000Å CVD Al layer with a microcrystalline material formed between the two CVD Al layers. As can be seen from point 106, the reflectance of a stack which is comprised of a 3000Å thick CVD Al layer, a microcrystalline thin layer, and a 1500Å CVD Al is approximately 185%. Referring to point 108, the reflectance of a 4500Å CVD Al film formed on a 500Å TiN film is approximately 145%. In reference to these two reflectance values, it is apparent that the stack which includes an intermediate layer has a smaller grain size when it is a total of 4500Å thick than a CVD Al layer which is 4500Å thick and which does not utilize the intermediate layer. The forming of a CVD Al layer on top of a TiN film, as shown in plot 104 of Figure 1, is not part of the present invention.

Claims: A method of forming an aluminum- or polysilicon-containing coating of a controlled grain size on a substrate which comprises forming on the substrate by chemical vapor deposition (CVD) a first aluminum or polysilicon layer, forming a thin intermediate layer, differing in grain structure from that of the first layer, on the first layer, and forming by CVD on the intermediate layer a second layer of the same material as the first layer, characterized in that the intermediate layer is formed by amorphizing the surface of the first layer or by depositing the same material that forms the first layer by plasma-assisted deposition or by physical vapor deposition. A method as claimed in claim 1, wherein the intermediate layer is formed by amorphization, and wherein amorphization is carried out by low energy moderate dose implant or by physical treatment. The method of claim 1 or claim 2, further comprising repeating the steps of forming said first layer, said intermediate layer on said first layer, and said second layer on said intermediate layer at least once. The method of any preceding claim, wherein said step of forming said first and second layers comprises forming said first and second layers to a thickness of 100 to 200 (1000 to 2000 Å) nm and said intermediate layer to a thickness of 5 to 50 (50 to 500 Å ) nm.

Inventors: PARANJPE AJIT P, PARANJPE, AJIT P.
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1997
Main classification: C23C16
IPC codes: C23C16, H01L21