Strain preserving ion implantation methods

The present invention relates to semiconductor manufacturing methods, and particularly to methods of preserving strain in silicon-containing semiconductor alloys through ion implantation processing steps.

Providing some degree of strain to the channel of a semiconductor device such an n-type field effect transistor (NFET) or a p-type field effect transistor (PFET) to improve device performance is known in the art. High performance semiconductor devices employ such strain to provide higher carrier mobility, lower transistor on-resistance, increased drive current (on-current), etc.

One method of providing strain to the channel of a semiconductor device is to embed a lattice-mismatched and epitaxially aligned semiconductor material adjacent to the channel of the field effect transistor. Exemplary latticed mismatched materials that may be embedded into a silicon substrate to provide a strain to a channel comprising silicon include a silicon-germanium alloy, a silicon-carbon alloy, a silicon-germanium-carbon alloy, etc. The placement of the embedded lattice-mismatched and epitaxially aligned semiconductor material in proximity to the channel induces a compressive strain or a tensile strain in the channel. Typically, a compressive strain is employed to enhance the charge carrier mobility of a PFET, and a tensile strain is employed to enhance the charge carrier mobility of an NFET. The greater the strain, the greater the enhancement of the charge carrier mobility and the enhancement of performance, as long as epitaxial alignment between the embedded semiconductor material and the semiconductor material of the substrate is maintained.

Some of the most destructive processing steps that often serve to reduce the stain generated by embedded semiconductor material portions are ion implantation steps that are employed to dope portions of the semiconductor substrate. Such ion implantation steps include deep source/drain ion implantation steps (or “source/drain ion implantation” steps), source/drain extension ion implantation steps (or “extension ion implantation” steps), and halo ion implantation steps. Such ion implantation steps introduce crystalline defects into the embedded semiconductor material portions, and thereby induce reduction of the magnitude of the strain applied to the channel of the semiconductor device. Such reduction in the magnitude of the strain reduces the degree of performance enhancement in the semiconductor devices.

The present invention provides methods of preserving strain in a semiconductor portion throughout ion implantation steps, wherein the strain in the semiconductor portion is induced by embedded semiconductor portions.

In the present invention, an embedded epitaxial semiconductor portion having a different composition than the matrix of the semiconductor substrate is formed with a lattice mismatch and epitaxial alignment with the matrix of the semiconductor substrate. The temperature of subsequent ion implantation steps is manipulated depending on the amorphizing or non-amorphizing nature of the ion implantation process. For a non-amorphizing ion implantation process, the ion implantation processing step is performed at an elevated temperature, i.e., a temperature greater than nominal room temperature range between 10 degrees Celsius and 30 degrees Celsius. For an amorphizing ion implantation process, the ion implantation processing step is performed at nominal room temperature range or a temperature lower than nominal room temperature range. By manipulating the temperature of ion implantation, the loss of strain in a strained semiconductor alloy material is minimized.

According to an aspect of the present invention, a method of forming a semiconductor structure is provided. The method includes: forming a strained semiconductor material portion directly on a semiconductor substrate, wherein the strained semiconductor material portion is epitaxially aligned to the semiconductor substrate and is lattice-mismatched relative to a semiconductor material of the semiconductor substrate; implanting dopant ions into the strained semiconductor material portion at a non-amorphizing dose at an elevated temperature greater than nominal room temperature range between 10 degrees Celsius and 30 degrees Celsius; and annealing the implanted strained semiconductor material portion at a temperature that removes structural damages induced by implantation of the dopant ions.

According to another aspect of the present invention, another method of forming a semiconductor structure is provided. The method includes: forming a strained semiconductor material portion directly on a semiconductor substrate, wherein the strained semiconductor material portion is epitaxially aligned to the semiconductor substrate and is lattice-mismatched relative to a semiconductor material of the semiconductor substrate; implanting dopant ions into the strained semiconductor material portion at an amorphizing dose at a temperature lower than nominal room temperature range between 10 degrees Celsius and 30 degrees Celsius; and annealing the implanted strained semiconductor material portion at a temperature that removes structural damages induced by implantation of the dopant ions.

According to yet another aspect of the present invention, yet another method of forming a semiconductor structure is provided. The method includes: forming a strained semiconductor material portion directly on a semiconductor substrate, wherein the strained semiconductor material portion is epitaxially aligned to the semiconductor substrate and is lattice-mismatched relative to a semiconductor material of the semiconductor substrate; implanting first dopant ions into the strained semiconductor material portion at a non-amorphizing dose at a first temperature greater than nominal room temperature range between 10 degrees Celsius and 30 degrees Celsius; implanting second dopant ions into the strained semiconductor material portion at an amorphizing dose at a second temperature lower than nominal room temperature range; and annealing the strained semiconductor material portion after implanting the first and second dopant ions at a temperature that removes structural damages induced by implantation of the dopant ions.

According to still another aspect of the present invention, still another method of forming a semiconductor structure is provided. The method includes: forming a gate dielectric and a gate electrode on a top surface of a single crystalline semiconductor layer having a doping of a first conductivity type and located in a semiconductor substrate; forming at least one strained semiconductor material portion directly on the single crystalline semiconductor layer, wherein the at least one strained semiconductor material portion is epitaxially aligned to the semiconductor substrate and is lattice-mismatched relative to a semiconductor material of the single crystalline semiconductor layer; performing a halo ion implantation at a first temperature higher than nominal room temperature range between 10 degrees Celsius and 30 degrees Celsius, wherein dopant ions of the first conductivity type are implanted into the at least one strained semiconductor material portion at a non-amorphizing dose; performing a source/drain ion implantation at a second temperature lower than nominal room temperature range, wherein dopants of a second conductivity type are implanted into the at least one strained semiconductor material portion at an amorphizing dose; and annealing the strained semiconductor material portion after performing the halo ion implantation and the source/drain ion implantation at a temperature that removes structural damages induced by implantation of the dopant ions.

FIG. 1 . is a graph showing composition dependence of residual strain for a non-amorphizing ion implantation process performed at different temperatures.

FIG. 2 is a graph showing composition dependence of residual strain for an amorphizing ion implantation process performed at different temperatures.

FIG. 3 is a graph showing the effect of a low temperature ion implantation on defect density.

FIG. 4 is a vertical cross-sectional view of an exemplary semiconductor structure having embedded strained semiconductor material portions and various implanted regions.

As stated above, the present invention relates to semiconductor manufacturing methods, and particularly to methods of preserving strain in silicon-containing semiconductor alloys through ion implantation processing steps, which are described herein with accompanying figures. The drawings are not necessarily drawn to scale.

According to the present invention, a strained semiconductor material portion is formed directly on a semiconductor substrate. In some cases, the strained semiconductor material portion may be formed embedded in the semiconductor substrate. The strained semiconductor material portion may be an unpatterned blanket layer, or may be a patterned and present in an area of the semiconductor substrate that is less than the entire area of the semiconductor substrate.

The semiconductor material of the semiconductor substrate, which is herein referred to as a first semiconductor material, is a single crystalline semiconductor material, and may be selected from, but is not limited to, silicon, germanium, silicon-germanium alloy, silicon carbon alloy, silicon-germanium-carbon alloy, gallium arsenide, indium arsenide, indium phosphide, III-V compound semiconductor materials, II-VI compound semiconductor materials, organic semiconductor materials, and other compound semiconductor materials. For example, the semiconductor material may comprise single crystalline silicon.

The strained semiconductor material portion comprises a second semiconductor material which has a different composition than the first semiconductor material. The second semiconductor material is another single crystalline semiconductor material, and may be selected from the same semiconductor materials that may be employed for the first semiconductor material provided that the second semiconductor material has a different composition than the first semiconductor material. The strained semiconductor material portion is epitaxially aligned to the semiconductor substrate, and is lattice-mismatched relative to the first semiconductor material of the semiconductor substrate. The lattice mismatch between the first semiconductor material and the second semiconductor material is the source of the strain exerted on the strained semiconductor material portion by the first semiconductor material in the semiconductor substrate.

In a first embodiment of the present invention, dopant ions are implanted into the strained semiconductor material portion at a non-amorphizing dose at an elevated temperature than is greater than nominal room temperature range (10-30 degrees Celsius). The dopant ions are ions of electrical dopant atoms that dope the semiconductor material as a p-type material or an n-type material. For example, the dopant ions may be ions of B, BF 2 , Ga, In, P, As, and Sb. A non-amorphizing dose herein refers to a dose that preserves crystalline structure of the strained semiconductor material portion. A crystalline structure herein refers to a structure that is better characterized as having crystalline alignment among atoms than as having amorphous alignment among the atoms. A crystalline structure may include structural defects such as point defects and line defects. A non-amorphizing dose herein refers to a dose that renders the strained semiconductor material portion crystalline after ion implantation within nominal room temperature range despite the presence of crystalline defects.

The range of the non-amorphizing dose for a given material for the strained semiconductor material portion depends on the species of the implanted ions and the energy employed for the ion implantation. The atomic concentration of implanted ions after an ion implantation at a non-amorphizing dose may be from 1.0×10 13 /cm 3 to 1.0×10 20 /cm 3 , and typically from 1.0×10 15 /cm 3 to 1.0×10 19 /cm 3 , although lesser and greater atomic concentrations may also provide a non-amorphizing dose under some conditions.

The elevated temperature may be any temperature greater than nominal room temperature range between 10 degrees Celsius and 30 degrees Celsius and less than the melting temperature of the second semiconductor material. Nominal room temperature range herein refers to a temperature range in a habitable room and for normal ambient temperature range in a semiconductor fabrication facility. Specifically, nominal room temperature range herein refers to a temperature range within 10 degrees Celsius and 30 degrees Celsius. In practical terms, the elevated temperature may be between 30 degrees Celsius and 700 degrees Celsius. A preferred range of the elevated temperature may be between 100 degrees Celsius and 600 degrees Celsius. A more preferred range of the elevated temperature may be between 200 degrees Celsius and 500 degrees Celsius. By elevating the temperature of the semiconductor substrate, and thereby elevating the temperature of the stressed semiconductor material portion, a higher percentage of the stress in the stressed semiconductor material portion is preserved through the ion implantation step at the elevated temperature compared with an ion implantation process performed at nominal room temperature range.

Referring to FIG. 1 , a graph is shown in which the magnitude of a residual strain after an activation anneal is compared across various samples including a strained semiconductor material portion comprising a second semiconductor material and embedded in a semiconductor substrate comprising a first semiconductor material. The first semiconductor material is silicon, and the second semiconductor material is a silicon germanium alloy. The strained semiconductor material portion is a blanket film over a silicon substrate. The horizontal axis represents the atomic percentage of germanium, and the vertical axis represents the strain in percentage. Each point represents a different sample. All samples were subjected to an activation anneal, which is an anneal employed to remove structural damages in the strained semiconductor material portion and to activate dopants, if present, in the strained semiconductor material portion, at 1,080 degree Celsius for 1 second.

The data points represented by circles and connected by a first line 100 represent samples that are not implanted with any dopant ions. The data points represented by filled squares and connected by a second line 110 represent samples that are implanted at nominal room temperature range with arsenic ions at a non-amorphizing dose of 2.0×10 13 /cm 2 at 50 keV of implantation energy at 30 degree tilt angle from the surface normal of the strained semiconductor material portion. The data points represented by “X” marks and connected by a third line 120 represent samples that are implanted at 300 degrees Celsius with arsenic ions at a non-amorphizing dose of 2.0×10 13 /cm 2 at 50 keV of implantation energy at 30 degree tilt angle from the surface normal of the strained semiconductor material portion.

Comparison of the measured data for residual strain after the activation anneal shows that the samples represented by the “X” marks and connected by the third line 120 retain more residual strain relative to the sampled represented by the filled squares and connected by the second line 110 . By elevating the ion implantation temperature, the amount of residual strain is increased for the non-amorphizing ion implantation.

In a second embodiment of the present invention, dopant ions are implanted into the strained semiconductor material portion at an amorphizing dose at a cooled temperature than is lower than nominal room temperature (10-30 degrees Celsius). As in the first embodiment, the dopant ions may be ions of B, BF 2 , Ga, In, P, As, and Sb. An amorphizing dose herein refers to a dose that destroys crystalline structure of the strained semiconductor material portion and renders the strained semiconductor material portion substantially amorphous. A substantially amorphous structure herein refers to a structure that is better characterized as having random or amorphous alignment among atoms than as having crystalline alignment among the atoms. An amorphizing dose herein refers to a dose that renders the strained semiconductor material portion amorphous after ion implantation at nominal room temperature range.

The range of the amorphizing dose for a given material for the strained semiconductor material portion depends on the species of the implanted ions and the energy employed for the ion implantation. The atomic concentration of implanted ions after an ion implantation at an amorphizing dose may be from 1.0×10 19 /cm 3 to 1.0×10 22 /cm 3 , and typically from 1.0×10 20 /cm 3 to 1.0×10 21 /cm 3 , although lesser and greater atomic concentrations may also provide a non-amorphizing dose under some conditions.

The cooled temperature may be any temperature lower than nominal room temperature range and greater than 0 K. In practical terms, the cooled temperature may be between −267 degrees Celsius (the boiling temperature of Helium) and 10 degrees Celsius. A preferred range of the cooled temperature may be between −200 degrees Celsius and 0 degree Celsius. A more preferred range of the cooled temperature may be between −200 degrees Celsius and −50 degrees Celsius. By cooling the semiconductor substrate, and thereby cooling the stressed semiconductor material portion, a higher percentage of the stress in the stressed semiconductor material portion is preserved through the ion implantation step at an amorphizing dose compared with an ion implantation process performed at nominal room temperature range.

Referring to FIG. 2 , a graph is shown in which the magnitude of a residual strain after an activation anneal is compared across various samples including a strained semiconductor material portion comprising a second semiconductor material and embedded in a semiconductor substrate comprising a first semiconductor material. The first semiconductor material is silicon, and the second semiconductor material is a silicon germanium alloy. The strained semiconductor material portion is a blanket film over a silicon substrate. The horizontal axis represents the atomic percentage of germanium, and the vertical axis represents the strain in percentage. Each point represents a different sample. All samples were subjected to an activation anneal, which is an anneal employed to remove structural damages in the strained semiconductor material portion and to activate dopants, if present, in the strained semiconductor material portion, at 1,080 degree Celsius for 1 second.

The data points represented by circles and connected by a fourth line 200 represent samples that are not implanted with any dopant ions. The data points represented by filled squares and connected by a fifth line 210 represent samples that are implanted at nominal room temperature range with BF 2 ions at an amorphizing dose of 3.0×10 15 /cm 2 at 9 keV of implantation energy without tilt from the surface normal of the strained semiconductor material portion. The data points represented by “X” marks and connected by a sixth line 220 represent samples that are implanted at 300 degrees Celsius with BF 2 ions at an amorphizing dose of 3.0×10 15 /cm 2 at 9 keV of implantation energy without tilt from the surface normal of the strained semiconductor material portion. The ion implantation conditions selected for the data points for the fifth line 210 and the sixth line 220 correspond to the step of source/drain ion implantation in standard complementary metal-oxide-semiconductor (CMOS) processing.

Comparison of the measured data for residual strain after the activation anneal shows that the samples represented by the “X” marks and connected by the sixth line 220 retain more residual strain relative to the sampled represented by the filled squares and connected by the fifth line 210 . Ion implantation at an amorphizing dose at nominal room temperature range allows retention of more strain than ion implantation at the same amorphizing dose at 300 degrees Celsius. By extension, ion implantation at a temperature lower than nominal room temperature range provides more retention of residual strain than ion implantation at nominal room temperature range if other conditions of the ion implantation are the same.

Referring to FIG. 3 , a graph from U.S. Pat. No. 6,570,169 to Suguro shows the effect of lowering temperature during ion implantation on the defect density in a non-strained semiconductor material immediately after ion implantation and after an activation anneal. While a lower temperature increases the defect density immediately after ion implantation, the post-anneal defect density is lower for samples implanted at low temperature. While this data is indicative of the defect density, and is not suggestive of the effect on the stain, this data provides theoretical support for retention of more stress in samples implanted at a reduced temperature in the series of experiments that led to the present invention.

Similar tests employing ion implantation conditions for source/drain extension ion implantations show the same trend. Table 1 below shows the results of similar testing on a semiconductor structure in which the semiconductor substrate is a single crystalline silicon substrate and the strained semiconductor material portion is a 60 nm thick silicon germanium carbon alloy layer in which the germanium concentration is 30%. The ion implantation conditions correspond to a typical condition for a source/drain extension implantation.

Table 2 below shows the results a similar testing on a semiconductor structure in which the semiconductor substrate is a single crystalline silicon substrate and the strained semiconductor material portion is a 60 nm thick silicon germanium alloy in which the germanium concentration is 30%. The ion implantation conditions correspond to a typical condition for a source/drain extension implantation.

The data from Tables 1 and 2 show that the residual strain is greater in the strained semiconductor material portion of the sample implanted at nominal room temperature range than in the strained semiconductor material portion of the sample implanted at 400 degrees Celsius when other conditions are the same.

In a third embodiment of the present invention, the temperature of strained semiconductor material portions is manipulated depending on whether the dose of in each ion implantation step is amorphizing or non-amorphizing. Non-amorphizing ion implantation steps are performed at an elevated temperature, and amorphizing ion implantation steps are performed at a temperature lower than nominal room temperature range. As in previous embodiments, the dopant ions may be ions of B, BF 2 , Ga, In, P, As, and Sb.

Referring to FIG. 4 , a vertical cross-sectional view of an exemplary semiconductor structure including a field effect transistor is shown. The field effect transistor is formed on a semiconductor substrate 10 comprising the first semiconductor material described above. Shallow trench isolation structures 20 comprising a dielectric material such as silicon oxide are formed beneath the top surface of the semiconductor substrate 10 . After forming a gate dielectric 30 , a gate electrode 32 , and a dielectric gate spacer 34 , portions of the semiconductor substrate 10 are removed and filled with the second semiconductor material described above to form strained semiconductor material portions. Included among the strained semiconductor material portions are embedded source and drain regions 12 , which comprise the second semiconductor material having a lattice mismatch with the first semiconductor material of the semiconductor substrate. The embedded source and drain regions 12 are epitaxially aligned to the single crystalline lattice of the semiconductor substrate 10 .

Among the ion implantation steps employed to form the field effect transistor are a halo ion implantation step, a source and drain extension ion implantation step, and a deep source and drain ion implantation step that is also referred to as a source and drain ion implantation step. The halo ion implantation step implants dopants of the same conductivity type as the doping type of the semiconductor substrate, which is herein referred to as a first conductivity type. The halo ion implantation step is a non-amorphizing ion implantation step. The source and drain extension ion implantation step and the deep source and drain ion implantation step implants dopants of the opposite conductivity type to the doping type of the semiconductor substrate. The conductivity type of the ions implanted during the source and drain extension ion implantation step and the deep source and drain ion implantation step is herein referred to as a second conductivity type, which is the opposite of the first conductivity type. The source and drain extension ion implantation step and the deep source and drain ion implantation step are an amorphizing ion implantation steps.

The halo ion implantation step forms halo regions 40 in the exemplary semiconductor structure. The source and drain extension ion implantation step forms source and drain extension regions 50 in the exemplary semiconductor structure. The deep source and drain ion implantation step forms deep source and drain regions 60 in the exemplary semiconductor structure. Typically, the source and drain extension regions 50 and the deep source and drain regions 60 are collectively called source and drain regions.

The halo ion implantation step is performed at an elevated temperature in the same manner as in the first embodiment. The source and drain extension implantation step is performed at a temperature lower than nominal room temperature range in the same manner as in the second embodiment. The deep source and drain implantation step is performed at a temperature lower than nominal room temperature range in the same manner as in the second embodiment. Optimal temperature settings are employed to maximize the retention of strain in the strained semiconductor material portions, i.e., in the embedded source and drain regions 12 . This results in maximized strain in the embedded source and drain regions 12 after an activation anneal, which removes structural damages induced by the various ion implantation steps. By increasing the residual strain in the embedded source and drain regions 12 , the strain in the channel of the field effect transistor is also increased. The increased retention of strain in the channel of the transistor results in increase in the mobility of charge carriers in the channel of the field effect transistor, increased on-current of the field effect transistor, decreased on-resistance of the field effect transistor, and decreased threshold voltage of the field effect transistor, thereby enhancing overall performance of the field effect transistor.

While the invention has been described in terms of specific embodiments, it is evident in view of the foregoing description that numerous alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the invention is intended to encompass all such alternatives, modifications and variations which fall within the scope and spirit of the invention and the following claims.