Abstract:
Photoresist, which contains hydrogen, is patterned over a semiconductor substrate then treated with either a molecular halogen or a liquid fluorinating agent in order to improve subsequent ion implantation. Hydrogen is replaced, to whatever extent is found desirable, with the halogen. Molecular fluorine (F 2 ) has been found to be particularly effective as the molecular halogen. Molecular fluorine (F 2 ) reacts very efficiently in replacing the hydrogen and further has the benefit of continuing to penetrate into the patterned photoresist so that the entire patterned photoresist layer can have the hydrogen atoms replaced with fluorine atoms if the molecular fluorine flow is continued long enough. The resulting treated photoresist is much more resistant to penetration by implanted ions so that the photoresist can be deposited to a lesser thickness. This is beneficial in shadowing problems such as can occur in halo implants and where the patterned photoresist has a high aspect ratio.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation-in-part under 37 C.F.R. 1.53(b) of the following pending application: 
    (1) U.S. Ser. No. 10/779,007 entitled “Method of Masking A Semiconductor Device Using Treated Photoresist” filed on Feb. 13, 2004 by Garza et al. and assigned to the assignee hereof.   
 
     
    
     FIELD OF THE INVENTION  
       [0003]     This invention relates generally to semiconductor devices, and more specifically, to methods of manufacturing semiconductors with photoresist masks.  
       BACKGROUND OF THE INVENTION  
       [0004]     As manufacturing of semiconductors has involved smaller and smaller dimensions, the photolithography has been moving to smaller and smaller wavelengths. The light provided at these reduced wavelengths has resulted in the need for different photoresists. This has been caused not just by the change in character of the light due to wavelength but also the reduced intensity of the light. With these required changes in the photoresist, the photoresists have also changed in their composition and thus affect semiconductor processing chemistries.  
         [0005]     As the semiconductor dimensions shrink, the conventional thickness of photoresist masks also needs to shrink. For example, when the dimension between adjoining semiconductor well regions that are separated by a narrow isolation shrinks, a conventional photoresist mask has a high aspect ratio which is difficult to pattern. Therefore, a thinner photoresist typically allows more depth of focus and process latitude. Also, the height of the photoresist causes unwanted shadowing of angled implants used at various points in semiconductor processing.  
         [0006]     Photoresist layers are often used as a masking layer to direct implantation in only certain areas. A known method to avoid the issues caused by thick photoresist is to use a thinner resist. However, thinner photoresists have the inherent disadvantage of a reduced stopping ability for any implantation process. When thin photoresists are used in conventional processes, a breakthrough may occur during an implant step and negatively impact the semiconductor devices in regions under the photoresist.  
         [0007]     In U.S. Pat. No. 6,815,359 Gabriel et al. propose a plasma process for treating a photoresist with fluorine wherein only exposed outer surfaces of the photoresist are modified. A plasma process is typically at an elevated process temperature, and the processing equipment and chemistry are complex. Plasma processes act by enhancing cross-linking of a polymer contained in the photoresist. This cross-linking is known to lead to stresses in the photoresist which can lead to modification or deformation of the intended pattern. A disadvantage of having a treated photoresist layer only at exposed surfaces is that various subsequent processing, such as etching and implanting, can readily penetrate the thin treated portion of the photoresist. Once penetrated, the remaining area of the photoresist is vulnerable and may fail to provide the desired masking protection.  
         [0008]     U.S. Pat. No. 6,544,894 is another example of a photoresist mask that is plasma treated with a fluorine-containing gas to enhance etching resistance. The process taught therein addresses the manufacturing of chromium masks which will subsequently be used in semiconductor processing. These masks are formed by patterning photoresist layers and etching the chromium. By introducing fluorine into the photoresist, the photoresist becomes less susceptible to degradation during the chromium etch step. The manner of introducing fluorine is similar to that described in U.S. Pat. No. 6,815,359 described above and thus suffers the same disadvantages. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention is illustrated by way of example and not limited to the accompanying figures, in which like references indicate similar elements.  
         [0010]      FIGS. 1 and 2  illustrate in cross-sectional form aspects of how photoresist thickness affects semiconductor processing;  
         [0011]      FIGS. 3-6  illustrate in cross-sectional form a method of manufacturing a semiconductor device using a treated photoresist mask in accordance with one form of the present invention;  
         [0012]      FIGS. 7-12  illustrate in cross-sectional form a method of manufacturing a semiconductor device using a treated photoresist mask in accordance with another form of the present invention; and  
         [0013]      FIG. 13  illustrates in flow chart form the method implemented in  FIGS. 3-12 . 
     
    
       [0014]     Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.  
       DETAILED DESCRIPTION  
       [0015]     Illustrated in  FIG. 1  is a known semiconductor device  10  having a substrate  12  having three distinct regions of differing conductivity. An NMOS region  14  is separated from a PMOS region  16  by an isolation region  20 . The PMOS region  16  is separated from an NMOS region  18  by an isolation region  22 . Overlying and in contact with the semiconductor device is a photoresist layer  24  which is uniformly in place over the semiconductor device  10 . A patterned chromium mask (not shown) overlies the semiconductor device  10  and allows light to expose only select regions of photoresist layer  24 . In particular, a region  25  of photoresist layer  24  is irradiated by light  28  having a wavelength of λ.  
         [0016]     The ability of the light  28  to uniformly react in the desired region  25  depends upon the wavelength of the light and the height of the photoresist layer  24 . Conventional photoresist layers are relatively thick in comparison with the distance between two isolated semiconductor features. The height of the photoresist layer may lead to inaccuracies in the patterning. In particular, due to the relative depth of the opening, the light will scatter in a manner that leads to less light reaching the surface to be exposed. Since the wavelength is fixed for a given semiconductor generation, the height of the photoresist layer  24  is the primary variable that can be adjusted. However, photoresist layer  24  may not be readily thinned to address this problem because at lower thicknesses the photoresist does not adequately function as a mask for subsequent implant steps.  
         [0017]     Illustrated in  FIG. 2  is a known semiconductor device  40  having a substrate  42  with three distinct regions of differing conductivity. An NMOS region  44  is separated from a PMOS region  46  by an isolation region  50 . The PMOS region  46  is separated from an NMOS region  48  by an isolation region  52 . Overlying each of these three regions is a feature, such as gate electrodes  54 ,  56  and  58 , respectively. Overlying gate electrode  54  and gate electrode  58  is a patterned photoresist layer  60  having an opening exposing the gate electrode  56 . An angled implant operation is being shown in which implant ions are directed onto semiconductor device  40  at a fixed angle from the left. As a result of the height of conventional photoresist layer  60 , a portion of the circuitry within the opening will not be exposed. In particular, a region  62  is not adequately exposed to the ion implant, if at all. This effect is known in the art as ‘shadowing’. It should be understood that when an angled ion implant from the opposing direction is implemented, a similar problem will be encountered for a region to the right side of gate electrode  56 . Therefore, the net effect is that the area from the gate electrode  56  to each of isolation regions  50  and  52  will be inadequately implanted. However, if the photoresist layer  60  is intentionally thinned to eliminate this noted problem, another problem is created. In particular, when photoresist layer  60  is thinned, the photoresist layer  60  does not adequately function as a mask for subsequent implant steps as noted above.  
         [0018]     Illustrated in  FIG. 3  is a cross-section of a semiconductor device  100 . A semiconductor substrate  101  has formed therein isolation regions  102 ,  104  and  106  to define intervening regions where devices will be formed. A thin dielectric layer  111  overlies semiconductor substrate  101  and functions to protect the semiconductor&#39;s surface between the isolation regions  102 ,  104  and  106 . A patterned photoresist layer  112  is put into place overlying a portion of the semiconductor substrate  101  between the isolation regions  102  and  104 . The photoresist layer  112  is formed in a conventional manner. For example, photoresist layer  112  may be uniformly spun onto semiconductor device  100  and then selectively irradiated with light and developed with a chemical. No further depth of discussion will be made regarding the patterning of the photoresist layer  112 . The photoresist layer  112  comprises carbon, oxygen, fluorine and hydrogen. Only hydrogen and carbon are illustrated in  FIG. 3  as the contributions of the other elements are not critical.  
         [0019]     Also illustrated in  FIG. 3  is an ambient  114  of molecular halogen. Molecular halogens which may be implemented are molecular bromine, molecular chlorine, molecular iodine and molecular fluorine. In the illustrated form the molecular halogen is implemented as molecular fluorine F 2  which is diluted with a carrier gas such as nitrogen. The percentage of the molecular fluorine in the carrier gas is small. In one form, the molecular fluorine is only one percent of the ambient gas, but it should be understood that other percentages may be used. The pressure of the carrier gas is within a range of 120 to 1500 Torr and the flow rate of the carrier gas in on the order of 1,000 standard cubic centimeters per minute. However, these parameters are exemplary and other pressures and flow rates may be used. This molecular fluorine penetrates deep into the photoresist layer  112 , dissociates, and displaces the hydrogen (i.e. chemical substitution) from the polymer. It should be noted that this displacement does not occur in a plasma at an elevated temperature, but rather is implemented without plasma and at temperatures varying as low as room temperature. In one form, the molecular fluorine is flowed at a temperature below around 50 degrees Celsius and above around 10 degrees Celsius. This is a chemical reaction which fundamentally changes the properties of the photoresist layer  112 . The depth to which this reaction is allowed to occur can be controlled by the fluorination time and is implementation specific but may include the entire thickness of the resist. As a result, the fluorine content of the photoresist layer  112  extends significantly beyond the exposed perimeters of photoresist layer  112 .  
         [0020]     Illustrated in  FIG. 4  is the result of processing of semiconductor device  100  in  FIG. 3  wherein a resulting fluorinated photoresist layer  116  has been created. Depending upon processing equipment, various chemistries may be used to remove the molecular fluorine ambient of  FIG. 3  from semiconductor device  100 .  
         [0021]     Illustrated in  FIG. 5  is further processing of semiconductor device  100  wherein an ion implant  118  is implemented while using the fluorinated photoresist layer  112 . Various ion materials may be used such as boron, phosphorous, arsenic and others common in semiconductor processing. Because fluorinated photoresist layer  116  contains significant amounts of fluorine, its ability to block the implant is enhanced over typical photoresist and photoresist with only a fluorinated perimeter. As a result of the advantages provided by the process described herein, an initial thinner photoresist layer  112  may be used. As described above, the use of an initial thin photoresist layer as device geometries shrink avoids various problems.  
         [0022]     Illustrated in  FIG. 6  is further processing of semiconductor device  100  wherein the fluorinated photoresist layer  116  has been removed and an N-well region  120  created by ion implant  118  is illustrated. The N-well region  120  is a new conductivity region within semiconductor substrate  101 . It should be well understood that depending upon the conductivity of ion implant  118 , the N-well region  120  could be implemented as a P-well rather than an N-well. It should be understood that at this point in the processing, various additional semiconductor devices (not shown) may be formed in the N-well  120  to form a completed semiconductor.  
         [0023]     Illustrated in  FIG. 7  is processing of a semiconductor device  200  which represents another portion of the semiconductor device of  FIGS. 2-6 . In this portion of the semiconductor device  200 , gate electrode  122  and gate electrode  124  have been formed respectively overlying gate dielectric  126  and gate dielectric  128 . Protective oxides  130  cover the semiconductor substrate  101  in regions where a transistor source and drain regions will subsequently be formed. At the point illustrated in  FIG. 7 , a patterned photoresist layer  134  is formed and has been fluorinated as illustrated in  FIGS. 3 and 4 . Because a fluorinated photoresist layer exists, a thinner photoresist layer may be used which will prevent the shadowing effect described above.  
         [0024]     Illustrated in  FIG. 8  is further processing of semiconductor device  100  wherein an angled ion implant  140  is implemented. In the illustrated form, the ion implant  140  has an N-type doping concentration. Ion implant  140  is typical of what is commonly referred to as a ‘halo’ implant.  
         [0025]     Illustrated in  FIG. 9  are the resulting doping profiles  142  and  144  from the processing of  FIG. 8 . The doping profiles  142  and  144  are the same conductivity as the N-well region  120 . It should be noted that because of the reduced height of photoresist layer  134  due to the fluorination with molecular fluorine, the shadowing common with devices such as in  FIG. 2  does not occur. In particular, note that the height of photoresist layer  134  permits some implantation to occur to the left of gate electrode  124 .  
         [0026]     Illustrated in  FIG. 10  is further processing of semiconductor device  200 . Those areas immediately to the right of the reduced-height photoresist layer  134  which were not implanted in  FIG. 8  become implanted by a complementary angle implant referenced as ion implant (II)  146 . This use of complementary angle implants is conventional and therefore no depth of discussion will be devoted to this portion of the method taught herein.  
         [0027]     Illustrated in  FIG. 11  is further processing of semiconductor device  200  wherein the photoresist layer  134  has been removed and resulting halo regions  148  and  150  are illustrated. It should be well understood that depending upon the conductivity of ion implant  146 , the N-well region  120  could be implemented as a P-well. It should be understood that at this point in the processing, various additional semiconductor devices (not shown) may be formed in the N-well region  120  to form a completed semiconductor.  
         [0028]     Illustrated in  FIG. 12  is further processing of semiconductor device  200  wherein completed N-channel and P-channel transistor devices are illustrated. Source and drain regions  152  and  154  are formed lateral to the gate electrode  124  and within the semiconductor substrate  101  to form a P-channel transistor. Adjacent the gate electrode  124  are gate liner  157  and sidewall spacer  156 . The gate liner  157  and sidewall spacer  156  are dielectric materials. A complementary N-channel transistor is formed on an opposing side of the isolation region  104 . In particular, halo regions  158  and  160  are formed similar to  FIGS. 7-10 . Source and drain regions  162  and  164  are formed lateral to the gate electrode  122  and within the semiconductor substrate  101 . The ion implantation required to form the halo regions, source and drain to the left of isolation region  104  occurs with a treated photoresist layer (not shown) overlying the N-channel transistor to the right of isolation region  104 , wherein such photoresist layer is treated in accordance with the same method used in  FIGS. 3 and 4  for fluorinated photoresist layer  116 . Gate electrode  122  overlies gate dielectric  126 . Gate liner  167  and sidewall spacer  168  are positioned adjacent to gate electrode  122 .  
         [0029]     Illustrated in  FIG. 13  is a flowchart of a method for making a semiconductor structure by treating a photoresist layer with molecular fluorine to be used as an implant mask. In particular, after a start step  170 , a photoresist layer is deposited overlying a semiconductor substrate and patterned in a step  172 . In a step  174  either molecular fluorine diluted in an inert gas or a liquid fluorinating agent is flowed over the photoresist layer to replace hydrogen atoms in the photoresist layer with fluorine atoms throughout either a substantial portion or throughout the entire photoresist layer. In a step  176  an ion implant, such as a halo implant, is performed using the treated photoresist layer as a mask to the ions. In a step  178  the formation of a semiconductor device is completed prior to ending the process at step  180 . Any type of semiconductor structure or semiconductor device may be formed in step  178 . It should be noted that the method described herein is used integral with a manufacturing process to form a semiconductor device as opposed to separately treating and creating a masking layer that is later placed over a semiconductor device as a mask function.  
         [0030]     At this point it should be appreciated that there has been provided a method for enhancing a photoresist layer with a molecular halogen for the purpose of enabling a thinner photoresist layer to be used without negative consequences. Although a discussion of molecular fluorine has been made, other elements which are halogens may be used. The penetration of molecular fluorine into the photoresist is dependent upon time, temperature and pressure. With a constant temperature and pressure, increased time exposure to the molecular fluorine gas allows deeper penetration into the photoresist. It is possible that molecular fluorine will penetrate to the lower portion of the photoresist. The fluorine profile in the photoresist may be either non-uniform or uniform in nature. To obtain a uniform fluorine profile, additional processing of the photoresist layer is needed. This additional processing includes either additional time, increased pressure, increased temperature or all of the above. It should be understood that rather than using molecular fluorine in a gas phase, a liquid fluorinating agent may be used instead to obtain a uniform fluorine profile. By using the disclosed method a very thin photoresist layer may be implemented. Exemplary thicknesses of photoresist that are fluorinated using the disclosed methods are one-half micron and less.  
         [0031]     In the foregoing specification, the invention has been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. For example, while the semiconductor devices described herein are in the context of metal oxide semiconductor (MOS) technology, it should be understood that various semiconductor processes may be used. Such processes include, but are not limited to, gallium arsenide and bipolar semiconductor processes. Various other structures may be used. For example, silicon on insulator (SOI) may be used and various transistor structures may be implemented. Such other transistor structures include elevated source/drain devices. Similarly, the semiconductor circuit function may vary widely from memory and data storage circuitry, digital signal processing (DSP), processor and microcontroller circuitry as well as special function logic circuitry.  
         [0032]     The treating of a photoresist film by using a molecular halogen or a liquid fluorinating agent is chemically different than previous suggested treatments of fluorine in a plasma. In addition to increased complexity and expense associated with a plasma, the exposure of photoresist to fluorine in a plasma is chemically limiting so that only exposed surfaces of the photoresist become fluorinated. When a plasma is used the reaction that produces fluorination results from chemical linking of elements. This reaction by its nature does not penetrate further than a small perimeter region. Therefore, the use of a plasma does not allow photoresist to be made smaller without the consequences associated with subsequent implanting of having shadowing as described herein and inadequate blocking of implanted ions. In contrast, the use of a molecular halogen or a liquid fluorinating agent functions chemically to replace hydrogen contained within the photoresist and penetrate an entire depth of a photoresist layer. While any depth percentage of fluorination of the photoresist may be implemented using the methods described herein, when very thin photoresist layers are used in state-of-the-art processes having extremely small dimensions it is more likely that all of the photoresist layer needs to be fluorinated for enhanced ion implant blocking.  
         [0033]     In one form there is herein provided a method of making a device structure by providing a semiconductor substrate. A layer of photoresist is deposited over the substrate. The layer of photoresist is patterned to form a layer of patterned photoresist. A molecular halogen or a liquid fluorinating agent is flowed over the layer of patterned photoresist to form a layer of treated photoresist. An implant is performed using the layer of treated photoresist as a mask to the implant to form an implanted region in the substrate. Formation of the device structure is completed, wherein the device structure includes the implanted region. In one form the molecular halogen is molecular fluorine (F 2 ). In other forms the molecular halogen is one of bromine (Br 2 ), chlorine (Cl 2 ) or iodine (I 2 ). In another form molecular halogen is flowed by flowing nitrogen, wherein the molecular halogen has an atomic concentration of about 1 percent. In yet another form the molecular halogen is flowed at a temperature below 50 degrees Celsius and above 10 degrees Celsius. In another form the layer of photoresist comprises hydrogen and the flowing the molecular halogen or the liquid fluorinating agent results in replacing hydrogen atoms with halogen atoms. In another form the layer of patterned photoresist has a first thickness and flowing the molecular halogen or the liquid fluorinating agent results in replacing hydrogen atoms with halogen atoms to at least half of the first thickness. In another form hydrogen atoms are replaced with halogen atoms at substantially all depth levels of the patterned photoresist. In one form the implant is a halo implant. In another form the implant is a well implant. Each of the molecular halogen and the liquid fluorinating agent comprises fluorine. The layer of treated photoresist has a top surface. The layer of patterned photoresist comprises hydrogen. The step of flowing replaces hydrogen atoms with fluorine atoms and is for controlling a profile of the fluorine atoms from the top surface to control a profile of molecular weight of the patterned photoresist. In yet another form the molecular halogen is flowed at a pressure of at least 120 Torr.  
         [0034]     In another form there is provided a method of making a device structure by providing a semiconductor substrate and depositing a layer of photoresist over the substrate. The layer of photoresist comprises hydrogen and is patterned to form a layer of patterned photoresist having an exposed top surface, a bottom surface that is closest to the substrate, and a first thickness from the exposed top surface to the bottom surface. A molecular halogen or a liquid fluorinating agent is flowed over the layer of patterned photoresist to form a layer of treated photoresist by replacing substantially all of the hydrogen from at least the exposed top surface to half of the first thickness. An implant is performed using the layer of treated photoresist as a mask to the implant to form an implanted region in the substrate. In one form the molecular halogen comprises molecular fluorine (F 2 ). In another form the molecular halogen comprises one of the group consisting of chlorine, fluorine, bromine, and iodine. In yet another form the molecular halogen comprises about 1 percent fluorine: The molecular halogen is carried by nitrogen at a flow rate of about 1000 standard cubic centimeters per minute (SCCM). The flowing the molecular halogen is performed at a temperature between 10 and 50 degrees Celsius. In another form the implant comprises one of a group consisting of a well implant and a halo implant.  
         [0035]     In yet another form there is provided a method of making a device structure by providing a semiconductor substrate having a first region for forming N channel transistors and a second region for forming P channel transistors. A first layer of photoresist is deposited over the substrate wherein the layer of photoresist comprises hydrogen. The first layer of photoresist is patterned to form a first layer of patterned photoresist over the first region, wherein the first layer of patterned photoresist has an exposed top surface, a bottom surface that is closest to the substrate, and a first thickness from the exposed top surface to the bottom surface. A first molecular halogen is flowed over the first layer of patterned photoresist to replace substantially all of the hydrogen from the first layer of patterned photoresist from at least the exposed top surface to half of the first thickness. A well implant is performed using the first layer of treated photoresist as a mask to the implant to form the N-well. The first layer of treated photoresist is removed. A gate is formed over the N-well. A second layer of photoresist is deposited over the first region. The second layer of photoresist is patterned to form a second layer of patterned photoresist over the first region and exposing the second region. A second molecular halogen is flowed over the second layer of patterned photoresist. An angled implant is performed to form a halo region under the gate. Source/drain regions are formed in the second region substantially adjacent to the gate, wherein the device structure is a transistor. In another form the first molecular halogen and second molecular halogen comprise molecular fluorine (F 2 ). In yet another form the first molecular halogen and the second molecular halogen each comprise a same or a differing one of a group consisting of chlorine (Cl 2 ), fluorine (F 2 ), bromine (Br 2 ), and iodine (I 2 ).  
         [0036]     Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention.  
         [0037]     Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims. As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. The terms a or an, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.