JPH043420A - Contact hole burying method - Google Patents

Abstract

PURPOSE:To enable a contact hole to be buried completely in a polycrystalline silicon with a flat surface by opening a contact hole, initially performing high- concentration doping for allowing the polycrystalline silicon to be grown selectively, and then performing selective growth of the silicon continuously. CONSTITUTION:After forming a contact hole 23 on a source diffusion region 21 and a drain diffusion region 22, first Branson washing is performed, washing is performed within a diluted HF solution, and a natural oxide film on a silicon surface at a bottom of an opening of the contact hole 23 is eliminated. Then, after washing with water and drying, it is set into a reaction tube 11. After that, a P-doped high-concentration doped layer (a thin polycrystalline silicon layer) 24 is allowed to grow selectively. Then, a P-doped polycrystalline silicon 25 is allowed to grow selectively on the doped layer 24 and the contact hole 23 is buried completely. At this time, the surface becomes flat, thus forming a contact which is superb both structurally and electrically.

Description

[Detailed description of the invention]

[Industrial application field] The present invention relates to a contact hole burying method.

[Conventional technology]

As the size of devices decreases year by year, it becomes necessary to fill contact holes with high aspect ratios. As the aspect ratio increases, problems arise such as it becomes difficult to completely embed conventional aluminum contacts alone. A silicon selective growth technique is one of the contact burying methods for such microscopic elements. This is a method in which HCQ gas is added to hydrogen chloride gas such as S i H2 (j22), and growth is performed using hydrogen gas as a carrier gas. According to this method, growth is performed on a dielectric film such as an oxide film. Silicon does not grow, but silicon grows selectively only in the exposed silicon surface, that is, in the contact hole.In this way, by selectively growing silicon only in the contact hole, After selective growth, contact resistance can be lowered by implanting impurities using ion implantation, or impurity doping can be performed in the silicon crystal by flowing an impurity gas such as PH3 together with the source gas during growth. Alternatively, as an application of such selective epitaxial growth technology, by doping a large amount of impurities during growth, the crystal becomes polycrystalline and it grows selectively.
Filling of contact holes is also practiced. [Problem to be Solved by the Invention 1] For example, when a contact hole on a source or drain diffusion layer of a MOS h transistor is buried by ordinary selective growth of silicon, the buried film becomes a single crystal. In this case, facets occur at the interface between the sidewall and the membrane. Since the growth rate of this facet is slower than that of other parts, a flat film cannot be obtained. Therefore, contact failure may occur in the recessed portion. In order to avoid such problems, selective growth of polycrystals is required, but as mentioned above, polycrystals do not grow in normal selective growth of silicon. Therefore, attempts have been made to make the material polycrystalline by doping a large amount of impurities during growth. However, if doping is done in large quantities to the extent that it becomes polycrystalline, the surface will become rough.
A problem arises in that contact resistance increases. On the other hand, considering post-processing, it is required to fill the contact hole with polycrystalline material having a surface as flat as possible. An object of the present invention is to provide a contact hole burying method that solves the above problems. [Means for Solving the Problems] In order to achieve the above object, the contact hole filling method according to the present invention employs a CVD method using silicon chloride-based gas, hydrogen chloride gas, and doping gas, which are silicon raw materials. A thin, highly doped polycrystalline silicon layer is selectively deposited in the contact hole, and then polycrystalline silicon is selectively grown on the thin polycrystalline silicon film inside the contact hole to fill the contact hole. It is something. [Operation] The reasons why the surface of the film in which the contact hole is buried are not flat can be broadly classified into the following two types. First, when a contact hole is filled using a silicon selective epitaxial growth technique, a structure called a facet is generated at a portion where a sidewall and a film are in contact with each other. Since the growth rate of this facet portion is slow, the surface is not flat, but instead has a concave shape. For this reason, when an electrode is formed using aluminum on the silicon thus formed, there is a possibility that a contact failure may occur in the recessed portion. The occurrence of such facets is due to the fact that the buried crystal is a single crystal. Therefore, attempts are being made to selectively grow polycrystalline silicon in order to prevent facets. Since a single crystal grows in normal growth, in order to selectively grow polycrystalline silicon, a large amount of impurity such as P is doped during selective growth. However, if a large amount of doping is performed, the surface may become rough due to causes such as segregation of P. Further, when such a large amount of dopant is doped, a problem arises in that as the amount of doping increases, the contact resistance actually increases. For the reasons described above, it is generally difficult to use the technique of polycrystalizing a crystal by doping it at a high concentration to fill a contact hole. In contrast, the present invention does not fill all of the contact holes with highly doped polycrystalline silicon until it becomes polycrystalline, but instead performs doping at a high concentration at the beginning of filling the contact holes, and then the surface Do doping to an extent that does not cause roughness and can reduce contact resistance, or do not do doping during growth.
After growth, contact holes are filled by ion implantation. If polycrystals are grown by doping at a high concentration in the initial stage of embedding in this way, the polycrystals will subsequently grow continuously regardless of the amount of doping or the presence or absence of doping. This can be seen from the fact that during normal growth, polycrystals grow on top of polycrystals. As a result, it becomes possible to completely fill the contact hole with polycrystal. [Example] Next, the present invention will be described in detail with reference to the drawings. In the present invention, after forming a contact hole, a thin film is doped with a high concentration to the extent that the silicon crystal becomes polycrystalline by a CVD method using silicon chloride gas, hydrogen chloride gas, and doping gas, which are raw materials for silicon. A silicon layer is selectively deposited in the contact hole, on which
This is a contact hole filling method characterized by filling a contact hole by selectively growing polycrystalline silicon. According to the present invention, a contact buried layer having a flat surface can be formed in a self-aligned manner. The flow rate ratio of the raw material gas, carrier gas, and OCR gas to selectively grow the highly doped layer and the silicon film thereon in the contact hole area varies depending on the types of raw material gas and carrier gas and the growth conditions. The optimum ratio that provides selectivity can be appropriately selected depending on the type of gas used and the growth conditions. The amount of doping into the heavily doped layer is appropriately selected depending on the type of dopant and the growth conditions, and the amount of doping to the heavily doped layer is selected as appropriate depending on the type of dopant and the growth conditions. or,
Impurity addition to the film to be grown thereafter is performed by ion implantation after forming the contact buried layer, or by flowing a doping gas in addition to the above-mentioned gases when depositing the film. Alternatively, use both methods together. Which method to use can be selected as appropriate. FIG. 1 is a schematic diagram showing an example of a semiconductor growth apparatus used in the method of the present invention. In the figure, the semiconductor growth apparatus according to the present invention includes a reaction tube 1
1 and a susceptor (S
iC-coated graphite) 12, a heating device 13 that heats the substrate 18 and the susceptor 12, cylinders 14a, 14b, 14c, 14d, a gas mixer 15, a flow rate control section 16, and a hydrogen gas purification device 17.
It is composed of. 100% 5i as raw material gas
H2CQ2 gas, +00% HC as etching gas
Hydrogen is used as the Q gas and carrier gas, and PH3 is used as the doping gas. The carrier gas was purified by a high purity purifier 17 and used. FIG. 2 is a diagram showing an example of the structure of a substrate used in the method of the present invention. In the figure, a p-channel MOS was fabricated using a conventional method. After forming the contact hole 23 on the source diffusion region 21 and drain diffusion region 22, the contact hole 23 portion is first filled with highly doped polycrystalline silicon until it becomes polycrystalline, and then the contact resistance is low and the surface is Selective growth of flat films was performed. As a pretreatment for the substrate, Branson cleaning was first performed. Next, the natural oxide film on the silicon surface at the bottom of the contact hole 23 is removed by cleaning in an HF solution diluted 50 times. Next, after washing with water and drying, it was set in the reaction tube 11. After that, hydrogen 51/min. 5iH2CQ230cc/min, H(j1120c
c/min, P) 130.5cc/win. Growth was performed under conditions of a growth temperature of 800° C., a growth pressure of 25 Torr, and a growth time of 20 seconds. As a result, a 2 nm thick P-doped heavily doped layer (thin polycrystalline silicon film)
I was able to grow 24 selectively. Next, 5iH2C (1
230cc/min, HCl220cc/min
Growth was performed under the following conditions: pH 30, lee/min, growth temperature 800° C., growth pressure 25 Torr, and growth time 15 minutes. As a result, P-doped polycrystalline silicon 25 selectively grew on the doped layer 24, and the contact hole 23 was completely filled. Moreover, its surface was also flat. As for the electrical characteristics of the contact, a roughly linear current vs. voltage characteristic was obtained, and a contact that was good both structurally and electrically was formed. This time, as raw material gas for silicon, in addition to S i H2 (J2) used this time,
5iHCQa. S i CO2 or the like may also be used. In this example, doping was performed by flowing a doping gas during growth, but similar effects can be obtained by using ion implantation technology. [Effects of the Invention] As described above in detail, according to the present invention, after opening the contact hole when filling the contact hole,
By first selectively growing polycrystalline silicon by doping it at a high concentration, and then continuing to selectively grow silicon, it is possible to completely fill the contact hole with polycrystalline silicon that has a flat surface. becomes. Also, when continuously selectively growing silicon, doping is performed by flowing a doping gas, or
By performing ion implantation after growth, contact resistance can be sufficiently reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a semiconductor device used in the method of the present invention, and FIG. 2 is a schematic diagram showing an example of a substrate structure used in the method of the present invention. 21...Source diffusion region 22...Drain diffusion region 23...Contact hole 24...High concentration doping layer 25...Polycrystalline silicon patent applicant NEC Corporation Bonnhe

Claims (1)

[Claims] (1) A thin polycrystalline silicon layer that is highly doped is selectively deposited in the contact hole by a CVD method using silicon chloride gas, hydrogen chloride gas, and doping gas, which are the raw materials for silicon, and then A contact hole filling method characterized by filling a contact hole by selectively growing polycrystalline silicon on a thin polycrystalline silicon film within the hole.