Abstract:
The present invention provides an improved semiconductor device of a Silicon/Amorphous Silicon/Metal Structure (SASM) and a method of making an improved semiconductor device by a salicide process by using an anneal to form a thick silicide film on shallow source/drain regions and a chemical-mechanical polish (CMP) step is then performed to remove the silicide over the top of the spacers at the gate, thus breaking the continuity of the silicide film extending from the gate to the source drain region.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates generally to semiconductor devices and to an improved method of making a semiconductor device. More particularly, the present invention relates to a method to form silicide utilizing a silicon/ amorphous silicon/metal (SASM) structure, and laser annealing. 
     2. Description of Prior Art 
     Semiconductor devices are well known in the art. Conventional semiconductor structure often includes self-aligned suicides that are formed by Rapid Thermal Annealing (RTA) process. However, this process may result in suicides with poor uniformity, and has a tendency to consume source/drain junctions during silicidation as junction depths continue to decrease to less than 100 nm. In addition the process always has a silicide etch-back step after the first silicidation step to prevent bridging of the gate to the source/drain regions, which the current invention avoids. 
     For Example, U.S. Pat. No. 6,060,392 (Essaian et al.) discloses a laser anneal silicide process, however this process does not teach a key last CMP step of the current invention. U.S. Pat. No. 5,940,693 (Maekawa), U.S. Pat. No. 5,988,272 (Ishida et al.), and U.S. Pat. No. 6,074,900 (Yamazaki et al.), all show other laser anneal silicide processes. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an improved semiconductor device and method of making an improved semiconductor device using a SASM structure. Another purpose of the present invention is to use laser annealing for the formation of thick (low sheet resistance) silicide film on shallow source/drain regions. The extremely high ramp-up rate which is near zero thermal budget of the laser anneal allows melting and intermixing of the metal and silicon atoms. A Chemical Mechanical Polishing (CMP) step is used to break the continuity of the silicide film extending from the gate to Source/Drain regions instead of a silicide etch-back step. 
     The method of this invention includes the formation of a semiconductor device having a substrate and forming a gate dielectric layer over the substrate. A gate layer is formed over the gate dielectric layer, and then a cap layer is formed over that. After creating a lightly doped source/drain extension region in the substrate, spacers are formed on the side of the gate dielectric layer, gate layer, and cap layer, resulting in an intermediate structure. A deep source/drain region is then formed in the substrate. This is followed by an annealing step to activate dopants. The cap layer is then removed, and silicon film is deposited over the whole structure so far. A metal layer is then deposited over the silicon film. Using laser irradiation on the silicon film and the metal then creates a silicide. A pre-metal dielectric layer is then deposited and a chemical mechanical polishing is used to break the continuity of the silicide. 
     Semiconductor devices are well known in the art, and it is well known in the art that they can be either an N-MOS transistor or a P-MOS semiconductor. 
     The inventor has found the laser anneal process has advantages over conventional RTA and the advantages are: an extremely high heating and cooling rate; ability to form fine-grained suicides; and capability of heating only the top surface region. Another advantage, besides the laser process, is the SASM structure, which has the advantages of providing additional silicon for silicidation, thus forming thick silicide without junction consumption. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings forming a material part of this description there is shown: 
     FIG. 1 shows a cross sectional view of a first step in the method of the current invention. 
     FIGS. 2-10 show cross-sectional views of a number of steps in the method of the current invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now more particularly to FIG. 1, a basic structure  10  is a first step in a semiconductor device structure. Basic structure  10  has a substrate  12 , with a gate dielectric layer  14  on the substrate  12 . The gate dielectric layer  14  is preferably made of silicon oxynitride and has a thickness of 10 to 150 Angstroms but preferably 16 Angstroms. A gate layer  16  is formed on gate dielectric layer  14 . The gate layer  16  is preferably doped poly-silicon and has a thickness of 500 to 3000 Angstroms but preferably 1600 Angstroms. 
     Cap layer  18  is formed on the gate layer  16 . The cap layer  18  is preferably made of silicon nitride and has a thickness of 500 to 2000 Angstroms but preferably 1000 Angstroms. The gate and cap layers  16  and  18  are deposited and then patterned as is well known in the art. 
     In FIG. 2 ion implantation is done to form the lightly doped source/drain extension  20 . In FIG. 3 a spacer layer  22  is then deposited. The spacer layer  22  is preferably made of an oxide film and has a thickness of 300 to 1500 Angstroms but is preferable 800 Angstroms. 
     As shown in FIG. 4, an anisotropic etch is used to form spacers  24  from spacer layer  22 . The preferred anisotropic etch used to form the spacers  24  is an oxide dry etch. 
     Then FIG. 5 shows ion implantation to form deep source/drain regions  26 . This is followed by Rapid Thermal Annealing (RTA) to activate the dopants. Referring now to FIG. 6, a selective etching of the cap layer  18  is then done. 
     In FIG. 7, a blanket deposition of silicon film  30  is made. Preferably layer  30  is made of amorphous silicon but optionally the silicon can be poly silicon. Amorphous Silicon is deposited using low-pressure chemical vapor deposition (LPCVD) with silane (SiH4) as the reacting gas. Pyrolysis (thermal decomposition) of SiH4 causes the deposition of silicon. The temperature used is less than 580 degrees Centigrade. The deposited film is essentially amorphous. At higher temperatures 580 to 650 degrees Centigrade, polycrystalline silicon will be deposited instead. The silicon layer  30  has a thickness of 50 to 1000 Angstroms but is preferable 600 Angstroms. 
     The deposition of silicon layer  30  is followed by a metal deposition  32  over the silicon layer  30 . Metal layer  32  is preferably made of titanium, cobalt, or nickel and has a thickness of 50 to 500 Angstroms but preferably 400 Angstroms. Hence, an intermediate SASM structure is formed. The metal layer  32  is typically deposited using physical vapor deposition (PVD), which includes sputtering and evaporation. 
     As shown in FIG. 8, in a key step, preferably laser irradiation is used to heat up metal layer  32  and silicon layer  30  to form silicide layer  31 . Rapid Thermal annealing can also be used. The laser irradiation is preferably performed by pulsed laser irradiation of selected wavelengths and fluence. Fluence is the energy density of the irradiation. 
     Wavelength should be in the range of 157 nm to 308 nm. The preferred wavelength of laser irradiation is 248 nm. Fluence is in the range of 0.1 to 1.5 J/cm squared. Duration of annealing is proportional to the laser pulse duration, which is tens of nanoseconds. A pulsed laser can emit irradiation with a controllable number of pulses. 
     Since the melting temperature of amorphous silicon is lower than the melting temperatures of the metal and single crystal silicon, the amorphous silicon layer melts more easily. Stoichiometeric ratio between the metal and silicon layers  32  and  30  is such that the reaction between them and the source/drain regions  26  consumes a minimum amount of silicon from the source/drain regions  26 . It should be noted that some reactions with the source/drain regions  26  are necessary in order to form a desirable silicide with low contact resistance. Depending on the laser fluence, metal  32  and/or a minute portion of the source/drain regions  26  may also melt during laser irradiation. 
     Optionally, after laser irradiation, the silicon body is then subjected to a heat treatment to convert the silicided region into a highly crystalline silicide with a desired resistivity value. The heat treatment can either be a RTA step or subsequent multiple laser pulses at lower fluence. For RTA, temperature range is 250 to 900 degrees C.; duration ranges from 5 seconds to 1 hour. For heat treatment using subsequent multiple laser pulses, fluence should be in the range of 0.05 to 0.5 J/cm squared, and number of pulses applied range from 1 to 100. This SASM structure does not limit the annealing technique to laser irradiation. In fact, conventional RTA can also be used to perform silicidation. Silicide layer  31  can be titanium silicide, cobalt silicide, or nickel silicide. 
     FIG. 9 shows a cross-sectional view of semiconductor device after deposition of an Interlevel Dielectric Layer (ILD) layer  33 . ILD layer  33  is preferably made of oxide and has a thickness of 1000 to 5000 Angstroms, but preferable 3000 Angstroms. Finally FIG. 10 illustrates that a CMP is used to break the continuity of the silicide film extending from gate to the source/drain regions. Therefore, silicide layer  31  becomes source drain/silicide  34  and gate silicide  36 . Therefore a silicide etch back step is not necessary. 
     After this, another interlevel dielectric layer (ILD) is formed over the gate silicide  36  and the source/drain silicide  34 . Contact holes are formed in this ILD to expose the gate silicide  36  and the source/drain silicide  34 . Next, conventional techniques can be used to form additional conductive and insulating layers there over to connect the semiconductor to other devices. 
     Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form, and details may be made without departing from the spirit and scope of the invention.