JPH02181924A - Method of polishing silicon - Google Patents

Abstract

PURPOSE:To control a polishing operation of silicon on a substrate by a method wherein the surface of silicon is polished by using a polishing liquid composed of an aqueous solution containing silica particles and a prescribed polishing operation is then executed by using a polishing liquid composed of an amine aqueous solution. CONSTITUTION:A silicon substrate 12 on which a selective epitaxial layer (SEG layer) has been grown is sucked to a pressurization head 13; while a lower surface plate 10 is being turned, e.g. at 50rpm, a polishing liquid A is dripped. The pressurization head 13 is turned and lowered; the surface of the silicon substrate 12 is pressed gradually to the surface of a polishing pad 11; the substrate is polished finally under a load of 100g/cm<2>. After the substrate has been polished for 2min in this state, the liquid A is stopped; a liquid B flows; the substrate is polished additionally for 15min. A spontaneous oxide film on the surface of the SEG layer 4 is removed by a polishing operation using the initial liquid A for 2min; after the 2min has elapsed, the liquid is switched to the liquid B; then, a concentration of silica particles in the polishing liquid on the pad is lowered gradually; lastly, the liquid is replaced by an amine aqueous solution; accordingly, a silicon oxide film 2 is not polished; the SEG layer 4 can be polished to be flat.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for polishing silicon (single crystal silicon-polysilicon) formed partially or entirely on the surface of a semiconductor substrate. .

[Conventional technology]

During the manufacturing process of semiconductor devices, silicon formed partially or completely on the surface of the semiconductor substrate is removed, and in the former case, the silicon is not formed, and in the latter case, the element part formed below the surface is removed. It often involves steps that require polishing without damaging the surface.

As a conventional polishing method of this type, there is a method of polishing silicon using only a polishing liquid consisting of an aqueous solution of amine. (For example, in Patent No. 58-004348 and below, the above polishing method is used as a selective epitaxial growth technique.
A manufacturing method for element isolation using epitaxial growth (5EG) will be explained as an example. FIG. 4 illustrates the formation of the SEG layer and the device isolation by polishing the SEG layer. As shown in FIG. A silicon oxide film 2 with a thickness of 1.51 Lm is formed by etching, and an opening 3 is formed in the area where the element is to be formed using photoresist technology and dry etching technology.
Dichlorosilane (Si820M?)・k as shown in
nf! a(HCI) ``Growth temperature 900℃, pressure 30Torr using Phos747 (PH3)/hydrogen as reaction gas
Next, while dropping a polishing liquid consisting of an aqueous amine solution onto the surface of a polishing pad, the surface of the silicon substrate was pressed against the pad with a pressure of 100 g/c2. The polishing pad is rotated to polish the protruding portion of the silicon 4. (For polishing methods, see, for example, the Institute of Electronics and Communication Engineers Technical Research Report Va1.8B N
o, 1313p, 37-42) [Problems to be Solved by the Invention] With the conventional polishing method described above, silicon polishing stops at the upper surface of the isolation oxide film, as shown by the dotted line in FIG. 4(C), Polishing of silicon with a flat profile 5 is possible. However, in some cases, a phenomenon may occur in which polishing does not proceed at all. It has been found that even wafers that cannot be polished can be polished by lightly etching them with a dilute HF solution.

Silicon polishing using an amine solution involves first reacting silicon and amine to form 5i(OH)62- on the silicon surface, and then wiping away this 5i(0)1)62- with a polishing pad. It is thought that it will proceed. By the way, there is always a natural oxide film on the silicon surface, so if this oxide film is very strong, it is thought that the reaction between the amine and silicon will be blocked, causing the phenomenon that polishing does not proceed as described above. It will be done. Therefore, when we tried polishing using a polishing liquid containing silica particles that can mechanically remove the silicon oxide film, the polishing proceeded stably, but as shown in Figure 4 (C). Problems arose in that the silicon oxide film 2 for isolation was thinned and a depression was formed on the surface of the SEG layer 4.

On the other hand, even when polishing silicon formed on the entire surface of a semiconductor substrate to a predetermined thickness, the polishing may not progress in some places and become uneven, but this is also thought to be due to the same cause. It will be done.

In view of the above circumstances, an object of the present invention is to provide a polishing method that can controllably polish silicon on a semiconductor substrate.

[Means to solve the problem]

The method of the present invention includes a preliminary polishing step of polishing the silicon surface using a polishing liquid made of an aqueous solution containing silica particles, and a polishing step of performing a predetermined polishing using a polishing liquid made of an amine aqueous solution. .

Note that silicon includes polysilicon here.

[Effect]

During the pre-polishing step, even the strong oxide film on the silicon surface is easily removed by the silica particles contained in the aqueous solution.

Therefore, in this state, the polishing performed using the amine aqueous solution proceeds uniformly.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to one drawing. FIG. 1 shows a polishing apparatus in which two types of polishing liquids are supplied to carry out the present invention. 10 is a lower surface plate, 11 is a polishing pad, and 12 is a selective epitaxial layer (
1.3 is a pressure head, 14 is a bottle of polishing liquid A consisting of an aqueous solution of amine and silica particles, 15.16 is a pump and piping for feeding polishing liquid A,
17 is a bottle of polishing liquid B consisting of an aqueous solution of amine; 18.
Reference numeral 19 denotes a pump and piping for feeding the polishing liquid B.

The silicon substrate 12 on which 5EGN has been grown is pressed by a rad 13.
The polishing liquid A is dripped while rotating the lower surface plate 10 at a rate of 50 rpm. The pressure pad 13 is rotated and lowered to gradually press the surface of the silicon substrate 12 against the surface of the polishing pad 11 and finally polish it with a load of 100 g/cm 2 . After polishing in this state for 2 minutes, stop the liquid A and pour in the liquid B and polish for another 15 minutes.

The initial polishing with liquid A for 2 minutes removes the natural oxide film on the surface of the SEG layer 4, and after 2 minutes, by switching to liquid B, the concentration of silica particles in the polishing liquid on the pad gradually decreases. In the end, only the amine aqueous solution is substituted, so as shown in Figure 2, 1 g of silicon oxide! The flat polishing of the SEG layer 4 is performed without polishing the SEG layer 2.

Although the above embodiment is applied to selectively epitaxially grown silicon, similar effects can be obtained with polysilicon. Figure 3 is a silicon substrate! On top, the formed thickness 1
．． This figure shows the case where polysilicon is embedded in an opening in a silicon oxide film 2 having a thickness of 0 μm. As shown in FIG. 3(a), after growing a polysilicon oxide film 6 on the entire surface of silicon oxide I8!2 to a height of 0.8 gm, polishing was performed for 2 minutes with polishing solution A to remove the natural oxide film. After removing B
When you switch to liquid and polish for 10 minutes, silicon oxidizes! I
As explained above, the present invention first polishes the silicon surface using a polishing solution consisting of an aqueous solution containing silica particles. Since the native oxide film is removed and then polishing is performed using a polishing solution consisting of an aqueous amine solution, it is possible to stably polish silicon to a flat surface without scraping the isolation silicon oxide film.

In addition, even if silicon is formed on the entire surface of a semiconductor substrate, this method allows polishing to be uniform and even in thickness.
Since it becomes @, it does not damage the elements on the board.

As a means of removing the natural oxide film, HF solution treatment before polishing may be considered, but the removal of the natural oxide film and the polishing can be performed in the same device, which is highly effective in terms of process control.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a polishing apparatus for carrying out the method of the present invention, FIGS. 2 and 3 are cross-sectional views of an example applied to silicon Φ polysilicon polishing of a region surrounded by an isolation oxide film, and FIG. FIG. 4 is a cross-sectional view of the conventional method. 1... Silicon substrate, 2... Silicon oxide film,
3... Open hole, 4... S E GM. 5...Profile, 6...Polysilicon. SekillF Baekun and Figure 3 (dl Figure 2

Claims (1)

[Claims] In a method of polishing silicon formed on a semiconductor substrate surface, using a polishing liquid consisting of an aqueous solution containing silica particles,
A silicon polishing method comprising a preliminary polishing step of polishing a silicon surface, and a polishing step of performing a predetermined polishing using a polishing liquid made of an amine aqueous solution.