In this paper, an improved modeling approach is described for simulating as-implanted boron impurity profiles for B + and BF2 ~ implants into single*crystal silicon. This method uses the sum of two Pearson distribution functions to account for the nonchanneling and channeling components of the implant distribution. The ratio of the two Pearson functions varies with dose, which accounts for the change in the degree of channeling with dose. This modeling approach has been compared with experimentally measured SIMS profiles for a wide range of energies and doses for shallow B § and BF2 § implants. The excellent agreement indicates that this method offers a large improvement in simulation capability for B § and BF2 § implants. In addition, this method should be applicable to accurately model other impurities which have channeling tendencies.In the development of submicron-integrated circuit technologies, much attention is currently focused on the achievement of reproducible and uniform (over the wafer) shallow, compact impurity profiles for both shallow junctions and the adjustment of various threshold voltages. Also, the entire impurity profile is of interest, in particular for the shallow source-drain junctions in CMOS. This is because of the need to simultaneously have low sheet resist~ ance, very high surface concentration for low contact resistance, a shallow junction, and profile control in order to minimize high electric fields which can cause hot carrier reliability problems. This has been a particularly difficult task for the case of boron due to the strong channeling tendency of this light atom in silicon. Indeed, the degree of channeling has been shown to depend considerably on both the tilt and rotation (or twist) angles during ion implantation, even for those ranges of angles for which channeling is generally considered to be minimal (1-3).Extensive use of process modeling is mandatory for timely, efficient technology development and in order to understand the process control issues in manufacturing. Thus it is necessary to be able to accurately predict impurity profiles beginning with the as-implanted distribution and continuing with the evolution (diffusion) of the profile in subsequent thermal treatments. In addition, the models used to describe the profile evolution in furnace and rapid thermal processing can only be valid over a wide range of conditions if they begin with the correct initial as-implanted impurity distribution. Otherwise, erroneous assumptions must be made in the model in order to relate its predicted diffused profile with the initial implanted profile. This is especially the case when rapid thermal annealing is used.Historically it has been difficult to accurately simulate as-implanted boron distributions for both B+ and BF2 + implants. This is mainly due to the ease with which boron is able to channel in the silicon lattice. Also, at the lower energies of interest for shallow profiles, channeling occurs more easily, further aggravating the simulation difficulty. The original LSS th...

Positive photoresist was characterized by Fourier transform infrared (FTIR) spectroscopy after high dose, high power ion implantation. The concentration of individual components in the resist such as the photosensitizer and organic C--H bonds were determined independently by examining the integrated absorbances at the corresponding infrared absorption peaks: 2040-2200 cm 1 for the sensitizer, and 2820-2995 cm 1 for the stretch of C--H bonds. Degradation of the sensitizer was found to be largely due to the elevated wafer temperature which is dependent on the heat generated by the ion implant and the cooling mechanism of the implanter. The thickness of the carbonized layer can be estimated by the loss of C--H bonds, which is in agreement with SEM results. A study of the implanted resist which was subjected to an oxygen plasma shows that the increased ashing resistance is due to the formation of the carbonized layer. The carbonized layer also reduces the degradation of the sensitizer in the implanted resist when exposed to an oxygen plasma.Over the years, photoresist has been used extensively as an ion implant mask in semiconductor device fabrication. For most practical applications, the ion dose ranges from 1.0Ell to 1.0El5 ions/cm 2. In this range the photoresist mask provides the advantages of process simplicity, effective masking, and ease of removal after implant. At higher dose levels, however, the optical density of the resist increases substantially and the films become more difficult to strip. Okuyama et al.(1) attributed the change to the "graphitization" of resist. In their report, they presented experimental data from the measurements of scratch resistance, optical density, and gas chromatography and showed similarities between high dose ion-implanted photoresist and disordered graphite. They concluded that physical ion bombardment during implant is responsible for the graphitization of the resist, which breaks chemical bonds within the resist. As a result, hydrogen, oxygen, and nitrogen atoms are lost from the base polymer chains and consequently the resist becomes richer in carbon.Later, Smith (2) proposed a model which related the thickness of the carbonized layer to ion dose and ion range within the photoresist. He suggested that there is a critical dose at which the original concentration of hydrogen within the carbonized layer is completely depleted. Below the critical dose, fractional carbonization exists and the thickness of the carbonized layer is determined by the ion range. Above the critical dose, the thickness of the carbonized layer can be estimated from the gas evolved from the resist and should slowly increase with dose. However, application of the model to estimate the thickness of the carbonized layer is limited, since the ion range within the resist will change toward that of amorphous carbon, as the carbonization proceeds.Another concern when using photoresist as an implant mask is the wafer temperature. Wafers can rise in temperature if the heat generated by the ion implant is not di...

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Abstruct-A novel germanium/boron implantation technique for improving the electrical field isolation for high-density CMOS circuits is demonstrated. Germanium implantation causes a reduction in dopant diffusion and segregation during field oxidation and is shown to increase the p-well field threshold voltage by as much as 40 percent with no significant degradation to junction or device performance. Selective germanium implantation with a blanket boron field implant can also improve the electrical field isolation behavior for CMOS circuits.

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